Advanced Utilization of Microwave Resonant ... - Semantic Scholar
IEICE TRANS. ELECTRON., VOL.E89–C, NO.12 DECEMBER 2006
1798
INVITED PAPER
Special Section on Emerging Microwave Techniques
Advanced Utilization of Microwave Resonant Fields and Its Applications to Push-Push Oscillators and Reconfigurable Antennas Masayoshi AIKAWA†a) , Fellow, Eisuke NISHIYAMA†b) , and Takayuki TANAKA†c) , Members
SUMMARY This paper presents an advanced and extensive utilization approach of microwave resonant fields, and the applications to push-push oscillators and reconfigurable planar antennas. The excellent coherency, synchronous harmonics and the degenerative orthogonal modes of electromagnetic field built up on microwave resonators are noticeable features in this approach. Another crucial point is the resonant field controllability that is especially essential feature for reconfigurable antennas in this paper. All the features can be realized by embedding semiconductor devices and/or IC’s on a microwave resonator. Push-push oscillators and reconfigurable planar antennas are described as good examples of this approach. The push-push oscillators can generate very higher frequency signals due to the selective use of the 4th harmonic up to the 8th harmonic resonant fields, suppressing undesired harmonic signals. As a result, very high frequency band oscillators up to millimeter-wave bands with good suppression of undesired harmonic signals can be easily realized at very low cost by use of commercially available active devices for low frequency bands. The reconfigurable planar antennas are also demonstrated, where the boundary condition of the resonant field on planar antennas can be purposefully controlled to realize reconfigurable antenna performances by the semiconductor devices embedded on the patch as well. The orthogonal linear polarization controllable patch, the dual-band switching patch and the continuously frequency controllable patch have been demonstrated as the successful applications of this approach. key words: microwave, resonator, reconfigurable, oscillator, antenna
1.
Introduction
Recent rapid progress of ubiquitous society has demanded much more advanced progress in microwave and millimeterwave technologies. The main requirements are the better performance at low cost, more reconfigurable RF technologies especially in millimeter-wave bands. Since the crucial parts of the wireless equipments are the RF oscillators and the advanced antennas, this paper focuses on these technologies which are based on the concept what the authors called “Microwave Integration Technology” [1]–[3]. This approach is very promising to meet above-mentioned issues in microwave and millimeter-wave bands. In this approach, the circuit components such as semiconductor devices and various kinds of IC’s are integrated with the microwave circuits in broad-sense including various transmission lines, Manuscript received March 4, 2006. Manuscript revised August 28, 2006. † The authors are with the Department of Electric and Electronic Engineering, Faculty of Science and Engineering, Saga University, Saga-shi, 840-8502 Japan. a) E-mail: [email protected] b) E-mail: [email protected] c) E-mail: [email protected] DOI: 10.1093/ietele/e89–c.12.1798
microwave resonators and antennas etc., to build up the purposeful electromagnetic field on them, aiming the practical application goals. Authors have published a few technical papers on basic studies based on this approach. Recently, similar approach results have been reported mainly in reconfigurable antennas [4]–[8]. This approach has been clas1 2 modes, resonant sified into three types, that is, guided 3 fields, according to the properties of fields and radiation the electromagnetic fields [3]. The electromagnetic field plays the leading part. Needless to say, almost all the microwave technologies including antennas utilize the coherency of electromagnetic fields and RF signals more or less. The excellent coherency in time and space of the electromagnetic field built up on the microwave circuit is most noticeable and effective feature in this approach, because it can be utilized effectively as much as possible to achieve the advanced RF performance and characteristics. This paper focuses on advanced utilization of mi2 in order to make the most crowave resonant fields (type ) of the coherency and the other features extensively, including its practical applications to push-push oscillators and reconfigurable planar antennas, where a planar antenna is considered to be a kind of microwave resonators. To put it more concretely, the highly coherent field, synchronous harmonic field and the degenerative orthogonal modes on microwave resonators are remarkable features in this approach. In addition, the field controllability is another crucial point to develop the novel and reconfigurable antennas as well. In this paper, this technical approach is called “AURF” for short, which stands for Advanced Utilization of Resonant Fields. The push-push principle is widely accepted as a very effective approach to realize low phase noise and high frequency oscillators [9]–[12]. The push-push oscillators proposed before by authors have very simple configurations, that is, they consist of a half wavelength line resonator or a wavelength ring resonator, negative resistances and the output port [13]. They need no in-phase power combiner circuit that is necessary in conventional circuits, and consequently, the 4th harmonic push-push oscillators with excellent performances was firstly realized [14]. In this paper, more advanced push-push oscillators are proposed, making use the synchronous harmonic field on both a line resonator and a ring resonator. They can provide an enhanced harmonic signal selectively due to both the synchronous harmonics and the degenerative orthogonal modes, suppressing the unde-
c 2006 The Institute of Electronics, Information and Communication Engineers Copyright
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sired harmonics successfully. The reconfigurable antenna is also a very good application subject of the AURF [15]. Various kinds of wireless systems have required varieties of active antennas, and then the reconfigurable antennas can provide their versatility in various kinds of wireless systems. This paper describes the reconfigurable planar antennas based on the AURF, where circuit components such as switching devices or varactor diodes are embedded on planar antenna or feeder circuit to control their resonant fields. The first application subject, push-push oscillators can generate the 4th order up to the 8th order harmonic signals effectively, which means that very high frequency oscillators can be easily achieved at low cost. The second application subject, reconfigurable planar antennas can achieve attractive functions such as multi-band frequency switching, orthogonal polarization switching and continuous frequency controllability, etc. In the following Sect. 2, the technical concept of the AURF on microwave resonators is summarized briefly, which is followed by two practical applications, the higher harmonic push-push oscillators and the reconfigurable planar antennas described in Sects. 3 and 4, respectively.
antennas etc. The essential resonant field including radiation field is purposefully built up on the resonators, aiming the final application goals. Figure 1 shows the technical concept of the AURF on microwave resonators including planar antennas, since planar antennas such as a patch antenna can be considered to be a kind of two-dimensional resonators. In order to build up and control the resonant field, microwave circuits and the related elements such as diodes, transistors and IC’s are embedded in a body. The built up field on the resonator can be used for developing higher performance microwave circuits and reconfigurable antennas, etc. As shown in Fig. 1, the electromagnetic field plays leading part in this approach. The microwave line resonators have practically noticeable advantages of very good coherency, synchronous harmonics and degenerative modes of the resonant field if necessary, and relatively easy use due to the compact size and easy fabrication. In addition, the other advantage of this approach is the field controllability to realize adaptable or reconfigurable behaviors. In this figure, a microwave resonator is, as it were, a platform for the resonant field to be essential to achieve higher order harmonic push-push oscillators and reconfigurable antennas. 3.
2.
Advanced Utilization Technology of Microwave Resonant Fields
In the microwave and millimeter-wave technical field, various kinds of resonators are used commonly and very widely, and the considerable progress has been made especially in the engineering branch of microwave filters and the related practical resonators such as dielectric resonators and various kinds of line resonators [16] for mobile and wireless communication systems. In the advanced utilization technology of microwave and millimeter-wave resonant fields (AURF), the highly coherent feature of electromagnetic fields built up on microwave resonators is extensively used to the utmost limit to develop novel microwave circuits and reconfigurable antennas in microwave and millimeter-wave bands. The microwave resonators in broad-sense means microwave transmission line resonators, dielectric resonators and various kinds of microwave resonators including resonant types of antennas such as many kinds of planar antenna and linear
Higher Order Harmonic Push-Push Oscillators
Push-push oscillators have very attractive advantages as much higher frequency generators, especially in millimeterand sub-millimeter-wave bands, because they can oscillate at harmonic frequency, where comparatively low frequency semiconductor devises and resonator can be adopted. Consequently, inexpensive millimeter-wave oscillators can be realized easily. Besides, their phase noise properties are comparatively better mainly due to the mutual coupling behavior among semiconductor devices. Conventional push-push oscillators consist of two identical oscillator units, a common resonator and an in-phase power combiner. The two oscillator units oscillate out of phase at the fundamental frequency ( f0 ), then in-phase combined output signals are even order harmonics 2n f0 (n = 1, 2, 3, 4 ) due to the push-push principle. Authors have proposed a novel push-push circuit shown in Fig. 2 [13]. The two negative resistances (N.R.) are embedded on a λg /2 line resonator at the both ends. In this oscillator, a λg /2 line resonator plays two roles, that is, a common resonator for two
Fig. 1 Advanced utilization of microwave resonant fields on device embedded resonators and its application in this paper.
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Fig. 2
Basic push-push oscillator using λg /2 line resonator.
Fig. 4 Higher harmonic push-push oscillator using N.R. device embedded active resonator.
(a) The 2nd harmonic enhanced push-push oscillator. Fig. 3
Resonant harmonic voltage on λg /2 line resonator.
N.R. and the in-phase output circuit. It should be noticeable that circuit configuration of this push-push oscillator is quite different from that of the conventional push-push oscillators. In conventional oscillators, a common resonator, two oscillator units and an in-phase power combiner are necessary as discrete elements to compose a push-push oscillator. On the other hand, in the push-push oscillator shown in Fig. 2, N.R. embedded line resonator oscillates at the fundamental frequency f0 , including the harmonic oscillations due to the nonlinearity of the N.R. In this circuit configuration, only the even order harmonic signals can be effectively available at the center of the active resonator indicated by O in Fig. 3, because the resonant harmonic field is as shown in this figure. Needless to say, all the odd harmonics including the fundamental frequency signal are not available, because the point O is null for all the harmonics. Therefore, the fundamental frequency signal and the odd harmonics can be perfectly suppressed in principle. Moreover, taking the resonant harmonics field shown in Fig. 3 into consideration, it can be recognized that there are some suitable points on which the negative resistances can be embedded. For example, points B and B are well suited to enhance the 2nd harmonic resonance selectively. In this case, it is worth noting that both B and B are null points of the 4th harmonic. It means that there is a capability to depress the 4th harmonic resonance on the resonator in principle. The 4th harmonic is an undesired signal and adjacent to the desired 2nd harmonic. In the same way, regarding the output circuit, there are proper points on the resonator in addition to the point O. For example, the 4th harmonic signal can be effectively available from points C and C , suppressing the 2nd harmonic signal, because C and C are both null points for the 2nd harmonic on the resonator. Generalizing these interesting facts as mentioned
(b) The 4th harmonic enhanced push-push oscillator. Fig. 5
Desired harmonic enhanced push-push oscillators.
above, the basic concept of higher harmonic push-push oscillators based on the AURF is expressed as shown in Fig. 4. If the negative resistances are exactly embedded at the proper points on the resonator, the required harmonic can be selectively enhanced, depressing the undesired harmonics. Besides, the output circuit is capable of harmonicselective power combining, due to both the good coherency and the synchronous harmonics of the resonant field. Figures 5(a) and (b) show the 2nd harmonic and the 4th harmonic push-push oscillators, respectively. As for the 2nd harmonic oscillator, two negative resistances are embedded at the points B and B , λg /16 away from the open end of the resonator. Since these two points are null for the 4th harmonic signal, the undesired 4th harmonic resonant field can be suppressed in principle. On the other hand, negative resistances for the 4th harmonic push-push oscillator are embedded at the points C and C , λg /8 away from the open end of a half wavelength line resonator, where these points are null for the 2nd and the 6th harmonic resonant fields. Consequently, undesired 2nd and 6th harmonic resonant fields can be suppressed in principle due to the synchronous harmonics and the coherent electromagnetic field on the resonator. The harmonic-selective power combining is also based on the effective use of the resonant field including the synchronous harmonics on a half wavelength line resonator. Tables 1 and 2 summarize resonant harmonic fields and the output from the point O for the 2nd and the 4th harmonic push-push oscillators shown in Fig. 5, respectively. For ex-
AIKAWA et al.: ADVANCED UTILIZATION OF MICROWAVE RESONANT FIELDS
1801 Table 1 Resonant harmonic field of the 2nd harmonic enhanced pushpush oscillator and the output.
(a) The 2nd harmonic enhanced push-push oscillator (a) in Fig. 5. Table 2 Resonant harmonic field of the 4th harmonic enhanced pushpush oscillator and the output.
(b) The 4th harmonic enhanced push-push oscillator (b) in Fig. 5. Fig. 6
ample, as for the 4th harmonic push-push oscillator, the 4th harmonic can be enhanced, because the 2nd and the 6th harmonics are depressed as indicated in Table 2. Figures 6(a) and (b) show the simulated results of the power spectrum available for the push-push oscillators (a) and (b) shown in Fig. 5 respectively. These results show the remarkable enhancement of the required harmonic, as well as the good suppression of undesired harmonics on the resonator. Figure 7 shows the 4th harmonic push-push oscillators using a ring resonator [14]. They can be easily derived from the resonant field on a ring resonator as well. It is well known that a wavelength ring resonator has two degenerative orthogonal modes at the fundamental frequency ( f0 ). In Fig. 7(a), a resonant mode is exited by the N.R.I and N.R.III, and the orthogonal resonant mode is exited by N.R.II and N.R.IV. They can exist independently at the fundamental frequency of f0 on a ring resonator. However, in the case of nonlinear circuit system, they are mutually coupled due to the mutual synchronization of the harmonic signals. In the case of the push-push oscillators shown in Fig. 7, four negative resistances are mutually synchronized through a half wavelength lines at the 2nd harmonic frequency (2 f0 ), where they are out of phase in any adjoining N.R. pair, which means that at the fundamental frequency f0 , the phase difference of any adjoining N.R. pair is π/2 autonomously. Consequently, the phase relation of the four N.R. at the frequency of f0 and 2 f0 are as shown in Fig. 7(a). In much the same way as the push-push oscillator using a line resonator, the 4th harmonic signal can be available in both circuit configurations, Type-I and Type-II in Fig. 7. Figure 8 is a fabricated Ka-band 4th harmonic push-push oscillator Type-I in Fig. 7, where a microstrip ring resonator is used. The mea-
Output power of push-push oscillators shown in Fig. 5.
(a) Type-I.
(b) Type-II. Fig. 7
The 4th harmonic push-push oscillator using ring resonator.
sured output power spectrum is also shown in Fig. 8 This oscillator adopted X-band HEMT (FHX35LP, Fujitsu) for the negative resistance units, and the output power is +1.7 dBm at the 4th harmonic frequency of 36 GHz. The phase noise is −104.0 dBc/Hz at 1 MHz offset [17].
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(a) Ka-band push-push oscillator.
Figure 9 shows the 8th harmonic push-push oscillators, which can be derived from the resonant harmonic field on a ring resonator in the same way. The 8th harmonic can be selectively enhanced, depressing the other undesired harmonics in principle. As mentioned above, higher order harmonic push-push oscillator can be realized very easily because of the extensive use of the resonant coherent field based on the AURF, in which the coherent field, the synchronous harmonic field and the degenerative orthogonal modes on a resonator are practically noteworthy properties. As the result, much higher harmonic frequency signal can be selectively generated, as well as good suppression of undesired harmonics effectively. 4.
(b) Output power spectrum. (4 f0 =36 GHz) Fig. 8 The 4th harmonic push-push oscillator using ring resonator shown in Fig. 7(a).
(a) Type-I.
(b) Type-II. Fig. 9
The 8th harmonic push-push oscillator using ring resonator.
Reconfigurable Planar Antenna
Reconfigurable antennas have attracted much attention recently, because of their versatility in various wireless systems, mainly due to their frequency controllability and polarization diversities. Reconfigurable planar antennas are attractive candidates in wireless systems due to their various functionalities as well as lightness, low profile and easy fabrication properties. Additionally, they can be good technical subjects of the AURF shown in Fig. 1, in which planar antennas are considered to be a kind of microwave resonators. Figure 10 shows the technical concept for reconfigurable planar antennas including the related applications, where the resonant electromagnetic field on planar antennas plays the important role as well. In this approach, semiconductor devices such as diodes, transistors or MMIC chips are embedded on the antenna conductor to control the boundary condition of the resonant field on the planar antennas. They are also embedded on the antenna feeder circuits, if necessary. In the same manner as the configuration here, an integrated planar antenna-mixer for the reception of orthogonally polarized microwave signals was formerly proposed [18], in which the quad-connected diodes ware embedded on a slot-ring antenna. This is a kind of multi-functional antenna of both the RF reception and the double-balanced down converter. Due to a couple of promising features of the AURF denoted in Fig. 10, practical applications such as reconfigurable antenna, beam steering, rectenna and RF signal processing etc. can be realized extensively. Figure 11 shows typical reconfigurable patch antennas based on the AURF approach. Figure 11(a) is a dual-band patch antenna [19], in which anti-series connected diodes are embedded in the patch. It has two frequency bands, f1 and f2 , which depends on the on/off state of the diodes switched by the bias voltage polarity, as shown in Fig. 11(a), where the surface current path is switched by the on and off condition of the diodes. Figure 12 shows both the calculated and the experimental results of the dual-band patch antenna in 3 GHz band. The FDTD method is used to simulate the antenna, where the on-state diode is replaced by conductor line. The simulated results agree well with the experimental values.
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Fig. 10
Device embedded planar antenna and the applications.
(a) Dual-band patch.
(a) Resistance.
(b) Frequency controllable patch.
(c) Polarization controllable patch. Fig. 11
Reconfigurable patch antenna.
(b) Reactance. Fig. 12 The frequency characteristics of impedance of dual-band patch antenna.
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crowave and millimeter-wave bands. 5.
(a) Polarization angle φ.
(b) Current distribution. ( f =3.5 GHz) Fig. 13 The polarization angle and the surface current distribution of polarization controllable patch antenna.
Figure 11(b) is a frequency controllable patch antenna, where anti-series connected varactor diodes are embedded in the patch [20]. The operating frequency can be controlled continuously by the capacitance value of these diodes. It is practically very attractive to expand the operating band, because a patch antenna has essentially very narrow band performance. Figure 11(c) is a polarization controllable patch antenna, that has a cross slot in which cross-connected switching diodes are embedded [15], [21]. The linear polarization can be orthogonally controlled to change the surface current path, as shown in this figure. Figure 13 shows both the calculated and the experimental results of the polarization controllable patch in 3 GHz band, as well as the surface current distribution on the patch. The FDTD method is also used to simulate the antenna, where the on-state diode is replaced by conductor line as well. The orthogonal polarization controllability is successfully confirmed both experimentally and theoretically. The above mentioned reconfigurable planar antennas are very easily realized and fabricated, where the boundary condition of the resonant field is controlled by embedded semiconductor devices or IC’s on the antenna conductors. Moreover, this approach can be expanded to develop the beam steering array antennas [22] and RF signal processing antenna modules with functionalities of RF oscillation, modulation, direct conversion and rectenna etc. in mi-
Conclusion
This paper presents the extensive utilization approach of microwave and millimeter-wave resonant fields, and the applications to the push-push oscillators and the reconfigurable planar antennas. The most noticeable point of this approach is to utilize the highly coherent field, synchronous harmonics and degenerative orthogonal modes of electromagnetic resonant field built up on microwave resonators in broadsense as much as possible. Another significant point is the resonant field controllability, which can be realized by semiconductor devices or IC’s embedded on microwave resonators including planar antennas. Two kinds of the applications, that is, the push-push oscillators and the reconfigurable planar antennas are described as effective and suitable subjects of this approach. Both applications make the most use of the highly coherent fields on microwave resonators. Push-push oscillators proposed here can generate much higher frequency signals due to the selective use of the 4th harmonic up to the 8th harmonic resonant fields, suppressing undesired harmonic signals. As a result, very high frequency band oscillators up to millimeter-wave and submillimeter-wave bands with good suppression of undesired harmonic signals can be realized at very low cost by use of commercially available active devices for low frequency bands. Reconfigurable planar antennas are also demonstrated as the other good applications of this approach. The boundary condition of the resonant field on planar antennas can be purposefully controlled to realize reconfigurable antennas with semiconductor devices embedded on the patch conductor. The linear polarization controllable patch, a dual-band switching patch and a continuously frequency controllable patch have been demonstrated as the successful applications of this approach. Many expert comments and suggestions will be highly appreciated. References [1] M. Aikawa, “Technical approach for advanced microwave circuits and antennas—An approach on microwave integration,” IEICE Technical Report, MW2003-202, Nov. 2003. [2] M. Aikawa, “Prospect of microwave engineering: Evolution for adaptive microwave circuits,” J. IEICE, vol.83, no.8, pp.595–599, Aug. 2000. [3] M. Aikawa, E. Nishiyama, and T. Tanaka, “Evaluational integration approach for microwave planar circuits,” IEICE Trans. Electron. (Japanese Edition), vol.J89-C, no.5, pp.183–190, May 2006. [4] J.H. Lim and T.Y. Yun, “Reconfigurable antenna of frequency and polarization diversity for PCS and DMB,” Proc. ISAP2005, pp.347– 350, Seoul, 2005. [5] K. Chung, Y. Nam, T. Yun, and J. Choi, “Reconfigurable microstrip antenna with frequency and polarization diversities,” Proc. ISAP2005, pp.981–984, Seoul, 2005. [6] A.Y. Simba, M. Yamamoto, T. Nojima, and K. Itoh, “Circularly polarized proximity-fed microstrip antenna with switchable polariza-
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tion ability,” Proc. ISAP2005, pp.985–988, Seoul, 2005. [7] F. Yang and Y.R. Samii, “Patch antennas with switchable slots (PASS) in wireless communications: Concepts, designs, and applications,” IEEE Antennas Propag. Mag., vol.47, no.2, pp.13–29, April 2005. [8] H. Aissat, L. Cirio, M. Grzeskowiak, J.-M. Laheure, and O. Picon, “Reconfigurable circularly polarized antenna for short-range communication systems,” IEEE Trans. Microw. Theory Tech., vol.54, no.6, pp.2856–2863, June 2006. [9] R. Winner and H. Scafer, et al., “A fully integrated 70 GHz SiGe low phase noise push-push oscillator,” IEEE Proc. IMS2005, pp.1523– 1526, 2005. [10] M. Schott, F. Lenk, C. Meliani, and W. Heinrich, “Low phase noise X-band push-push oscillator with frequency divider,” IEEE Proc. IMS2005, pp.1527–1530, 2005. [11] J. Choi and A. Mortazawi, “Design of push-push oscillators for reducing 1/f noise upconversion,” IEEE Proc. IMS2005, pp.1531– 1534, 2005. [12] U.L. Rohde, A.K. Poddar, J. Schoepf, R. Rebel, and P. Patel, “Low noise low cost ultra wideband N-push VCO,” IEEE Proc. IMS2005, pp.1171–1174, 2005. [13] H. Xiao, T. Tanaka, and M. Aikawa, “Push-push oscillator with simplified circuit structure,” IEE Electron. Lett., vol.38, no.24, pp.1545– 1547, Nov. 2002. [14] H. Xiao, T. Tanaka, and M. Aikawa, “A Ka-band quadruple-push oscillator,” IEEE MTT-S, IMS-2003, pp.889–892, 2003. [15] E. Nishiyama, K. Takenaka, and M. Aikawa, “Polarization controlled microstrip antenna,” IEICE Trans. Commun. (Japanese Edition), vol.J85-B, no.9, pp.1519–1525, Sept. 2002. [16] M. Makimoto and S. Yamashita, Microwave Resonators and Filters for Wireless Communication, Springer Series in Advanced Microelectronics, Springer, 2001. [17] H. Xiao, T. Tanaka, and M. Aikawa, “Basic behavior of quadruplepush oscillator using ring resonator,” IEICE Trans. Electron., vol.E88-C, no.7, pp.1502–1508, July 2005. [18] T. Itoh and K. Stephan, “Quasi-optical polarization duplexed balanced mixer,” US Patent, US-4,509,209, April 1985. [19] K. Sakamoto, E. Nishiyama, and M. Aikawa, “Active microstrip planar antenna for frequency switching,” IEICE Trans. Commun. (Japanese Edition), vol.J87-B, no.11, pp.1918–1925, Nov. 2004. [20] K. Sakamoto, E. Nishiyama, and M. Aikawa, “Active antenna with continuously varying frequency performance,” J. ITE, vol.58, no.7, pp.952–956, July 2004. [21] S. Sasaki, E. Nishiyama, and M. Aikawa, “Polarization controllable circular slot antenna,” Proc. ISAP 2005, pp.1193–1196, 2005. [22] E. Nishiyama, R. Hisadomi, and M. Aikawa, “Directivity controllable microstrip antenna with switching diodes,” Proc. KJMW2005, pp.87–90, Busan, 2005.
Masayoshi Aikawa graduated from the Department of Electronic Engineering, Kyushu University, in 1969, completed the M.S. program in 1971, and joined Nippon Telegraph and Telephone (now NTT). Since then, he has been engaged in the development of microwave and millimeter wave integrated circuits, MMIC, and various communication devices. In 1997, he has been a professor at Saga University. He holds a Dr. Eng. degree, and is a member of IEEE.
Eisuke Nishiyama graduated from the Department of Electronics, Saga University, in 1987, completed the M.S. program in 1989, and become a member of the technical staff there. He has been a research associate since 1997. His research interest is planar antennas. He holds a Dr. Eng. degree, and is a member of IEEE.
Takayuki Tanaka received the B.E. and M.E. degrees in Electronics Engineering from Saga University, Saga, Japan in 1986 and 1988, respectively. He received the Dr. Eng. degree from Kyushu University, Fukuoka, Japan in 2002. He was a Research Associate from 1988 to 2004 and is currently a Lecturer in the department of Electrical and Electronic Engineering at Saga University. His current research interests are microwave are millimeter wave circuits. He is a member of IEEE.
1798
INVITED PAPER
Special Section on Emerging Microwave Techniques
Advanced Utilization of Microwave Resonant Fields and Its Applications to Push-Push Oscillators and Reconfigurable Antennas Masayoshi AIKAWA†a) , Fellow, Eisuke NISHIYAMA†b) , and Takayuki TANAKA†c) , Members
SUMMARY This paper presents an advanced and extensive utilization approach of microwave resonant fields, and the applications to push-push oscillators and reconfigurable planar antennas. The excellent coherency, synchronous harmonics and the degenerative orthogonal modes of electromagnetic field built up on microwave resonators are noticeable features in this approach. Another crucial point is the resonant field controllability that is especially essential feature for reconfigurable antennas in this paper. All the features can be realized by embedding semiconductor devices and/or IC’s on a microwave resonator. Push-push oscillators and reconfigurable planar antennas are described as good examples of this approach. The push-push oscillators can generate very higher frequency signals due to the selective use of the 4th harmonic up to the 8th harmonic resonant fields, suppressing undesired harmonic signals. As a result, very high frequency band oscillators up to millimeter-wave bands with good suppression of undesired harmonic signals can be easily realized at very low cost by use of commercially available active devices for low frequency bands. The reconfigurable planar antennas are also demonstrated, where the boundary condition of the resonant field on planar antennas can be purposefully controlled to realize reconfigurable antenna performances by the semiconductor devices embedded on the patch as well. The orthogonal linear polarization controllable patch, the dual-band switching patch and the continuously frequency controllable patch have been demonstrated as the successful applications of this approach. key words: microwave, resonator, reconfigurable, oscillator, antenna
1.
Introduction
Recent rapid progress of ubiquitous society has demanded much more advanced progress in microwave and millimeterwave technologies. The main requirements are the better performance at low cost, more reconfigurable RF technologies especially in millimeter-wave bands. Since the crucial parts of the wireless equipments are the RF oscillators and the advanced antennas, this paper focuses on these technologies which are based on the concept what the authors called “Microwave Integration Technology” [1]–[3]. This approach is very promising to meet above-mentioned issues in microwave and millimeter-wave bands. In this approach, the circuit components such as semiconductor devices and various kinds of IC’s are integrated with the microwave circuits in broad-sense including various transmission lines, Manuscript received March 4, 2006. Manuscript revised August 28, 2006. † The authors are with the Department of Electric and Electronic Engineering, Faculty of Science and Engineering, Saga University, Saga-shi, 840-8502 Japan. a) E-mail: [email protected] b) E-mail: [email protected] c) E-mail: [email protected] DOI: 10.1093/ietele/e89–c.12.1798
microwave resonators and antennas etc., to build up the purposeful electromagnetic field on them, aiming the practical application goals. Authors have published a few technical papers on basic studies based on this approach. Recently, similar approach results have been reported mainly in reconfigurable antennas [4]–[8]. This approach has been clas1 2 modes, resonant sified into three types, that is, guided 3 fields, according to the properties of fields and radiation the electromagnetic fields [3]. The electromagnetic field plays the leading part. Needless to say, almost all the microwave technologies including antennas utilize the coherency of electromagnetic fields and RF signals more or less. The excellent coherency in time and space of the electromagnetic field built up on the microwave circuit is most noticeable and effective feature in this approach, because it can be utilized effectively as much as possible to achieve the advanced RF performance and characteristics. This paper focuses on advanced utilization of mi2 in order to make the most crowave resonant fields (type ) of the coherency and the other features extensively, including its practical applications to push-push oscillators and reconfigurable planar antennas, where a planar antenna is considered to be a kind of microwave resonators. To put it more concretely, the highly coherent field, synchronous harmonic field and the degenerative orthogonal modes on microwave resonators are remarkable features in this approach. In addition, the field controllability is another crucial point to develop the novel and reconfigurable antennas as well. In this paper, this technical approach is called “AURF” for short, which stands for Advanced Utilization of Resonant Fields. The push-push principle is widely accepted as a very effective approach to realize low phase noise and high frequency oscillators [9]–[12]. The push-push oscillators proposed before by authors have very simple configurations, that is, they consist of a half wavelength line resonator or a wavelength ring resonator, negative resistances and the output port [13]. They need no in-phase power combiner circuit that is necessary in conventional circuits, and consequently, the 4th harmonic push-push oscillators with excellent performances was firstly realized [14]. In this paper, more advanced push-push oscillators are proposed, making use the synchronous harmonic field on both a line resonator and a ring resonator. They can provide an enhanced harmonic signal selectively due to both the synchronous harmonics and the degenerative orthogonal modes, suppressing the unde-
c 2006 The Institute of Electronics, Information and Communication Engineers Copyright
AIKAWA et al.: ADVANCED UTILIZATION OF MICROWAVE RESONANT FIELDS
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sired harmonics successfully. The reconfigurable antenna is also a very good application subject of the AURF [15]. Various kinds of wireless systems have required varieties of active antennas, and then the reconfigurable antennas can provide their versatility in various kinds of wireless systems. This paper describes the reconfigurable planar antennas based on the AURF, where circuit components such as switching devices or varactor diodes are embedded on planar antenna or feeder circuit to control their resonant fields. The first application subject, push-push oscillators can generate the 4th order up to the 8th order harmonic signals effectively, which means that very high frequency oscillators can be easily achieved at low cost. The second application subject, reconfigurable planar antennas can achieve attractive functions such as multi-band frequency switching, orthogonal polarization switching and continuous frequency controllability, etc. In the following Sect. 2, the technical concept of the AURF on microwave resonators is summarized briefly, which is followed by two practical applications, the higher harmonic push-push oscillators and the reconfigurable planar antennas described in Sects. 3 and 4, respectively.
antennas etc. The essential resonant field including radiation field is purposefully built up on the resonators, aiming the final application goals. Figure 1 shows the technical concept of the AURF on microwave resonators including planar antennas, since planar antennas such as a patch antenna can be considered to be a kind of two-dimensional resonators. In order to build up and control the resonant field, microwave circuits and the related elements such as diodes, transistors and IC’s are embedded in a body. The built up field on the resonator can be used for developing higher performance microwave circuits and reconfigurable antennas, etc. As shown in Fig. 1, the electromagnetic field plays leading part in this approach. The microwave line resonators have practically noticeable advantages of very good coherency, synchronous harmonics and degenerative modes of the resonant field if necessary, and relatively easy use due to the compact size and easy fabrication. In addition, the other advantage of this approach is the field controllability to realize adaptable or reconfigurable behaviors. In this figure, a microwave resonator is, as it were, a platform for the resonant field to be essential to achieve higher order harmonic push-push oscillators and reconfigurable antennas. 3.
2.
Advanced Utilization Technology of Microwave Resonant Fields
In the microwave and millimeter-wave technical field, various kinds of resonators are used commonly and very widely, and the considerable progress has been made especially in the engineering branch of microwave filters and the related practical resonators such as dielectric resonators and various kinds of line resonators [16] for mobile and wireless communication systems. In the advanced utilization technology of microwave and millimeter-wave resonant fields (AURF), the highly coherent feature of electromagnetic fields built up on microwave resonators is extensively used to the utmost limit to develop novel microwave circuits and reconfigurable antennas in microwave and millimeter-wave bands. The microwave resonators in broad-sense means microwave transmission line resonators, dielectric resonators and various kinds of microwave resonators including resonant types of antennas such as many kinds of planar antenna and linear
Higher Order Harmonic Push-Push Oscillators
Push-push oscillators have very attractive advantages as much higher frequency generators, especially in millimeterand sub-millimeter-wave bands, because they can oscillate at harmonic frequency, where comparatively low frequency semiconductor devises and resonator can be adopted. Consequently, inexpensive millimeter-wave oscillators can be realized easily. Besides, their phase noise properties are comparatively better mainly due to the mutual coupling behavior among semiconductor devices. Conventional push-push oscillators consist of two identical oscillator units, a common resonator and an in-phase power combiner. The two oscillator units oscillate out of phase at the fundamental frequency ( f0 ), then in-phase combined output signals are even order harmonics 2n f0 (n = 1, 2, 3, 4 ) due to the push-push principle. Authors have proposed a novel push-push circuit shown in Fig. 2 [13]. The two negative resistances (N.R.) are embedded on a λg /2 line resonator at the both ends. In this oscillator, a λg /2 line resonator plays two roles, that is, a common resonator for two
Fig. 1 Advanced utilization of microwave resonant fields on device embedded resonators and its application in this paper.
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Fig. 2
Basic push-push oscillator using λg /2 line resonator.
Fig. 4 Higher harmonic push-push oscillator using N.R. device embedded active resonator.
(a) The 2nd harmonic enhanced push-push oscillator. Fig. 3
Resonant harmonic voltage on λg /2 line resonator.
N.R. and the in-phase output circuit. It should be noticeable that circuit configuration of this push-push oscillator is quite different from that of the conventional push-push oscillators. In conventional oscillators, a common resonator, two oscillator units and an in-phase power combiner are necessary as discrete elements to compose a push-push oscillator. On the other hand, in the push-push oscillator shown in Fig. 2, N.R. embedded line resonator oscillates at the fundamental frequency f0 , including the harmonic oscillations due to the nonlinearity of the N.R. In this circuit configuration, only the even order harmonic signals can be effectively available at the center of the active resonator indicated by O in Fig. 3, because the resonant harmonic field is as shown in this figure. Needless to say, all the odd harmonics including the fundamental frequency signal are not available, because the point O is null for all the harmonics. Therefore, the fundamental frequency signal and the odd harmonics can be perfectly suppressed in principle. Moreover, taking the resonant harmonics field shown in Fig. 3 into consideration, it can be recognized that there are some suitable points on which the negative resistances can be embedded. For example, points B and B are well suited to enhance the 2nd harmonic resonance selectively. In this case, it is worth noting that both B and B are null points of the 4th harmonic. It means that there is a capability to depress the 4th harmonic resonance on the resonator in principle. The 4th harmonic is an undesired signal and adjacent to the desired 2nd harmonic. In the same way, regarding the output circuit, there are proper points on the resonator in addition to the point O. For example, the 4th harmonic signal can be effectively available from points C and C , suppressing the 2nd harmonic signal, because C and C are both null points for the 2nd harmonic on the resonator. Generalizing these interesting facts as mentioned
(b) The 4th harmonic enhanced push-push oscillator. Fig. 5
Desired harmonic enhanced push-push oscillators.
above, the basic concept of higher harmonic push-push oscillators based on the AURF is expressed as shown in Fig. 4. If the negative resistances are exactly embedded at the proper points on the resonator, the required harmonic can be selectively enhanced, depressing the undesired harmonics. Besides, the output circuit is capable of harmonicselective power combining, due to both the good coherency and the synchronous harmonics of the resonant field. Figures 5(a) and (b) show the 2nd harmonic and the 4th harmonic push-push oscillators, respectively. As for the 2nd harmonic oscillator, two negative resistances are embedded at the points B and B , λg /16 away from the open end of the resonator. Since these two points are null for the 4th harmonic signal, the undesired 4th harmonic resonant field can be suppressed in principle. On the other hand, negative resistances for the 4th harmonic push-push oscillator are embedded at the points C and C , λg /8 away from the open end of a half wavelength line resonator, where these points are null for the 2nd and the 6th harmonic resonant fields. Consequently, undesired 2nd and 6th harmonic resonant fields can be suppressed in principle due to the synchronous harmonics and the coherent electromagnetic field on the resonator. The harmonic-selective power combining is also based on the effective use of the resonant field including the synchronous harmonics on a half wavelength line resonator. Tables 1 and 2 summarize resonant harmonic fields and the output from the point O for the 2nd and the 4th harmonic push-push oscillators shown in Fig. 5, respectively. For ex-
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(a) The 2nd harmonic enhanced push-push oscillator (a) in Fig. 5. Table 2 Resonant harmonic field of the 4th harmonic enhanced pushpush oscillator and the output.
(b) The 4th harmonic enhanced push-push oscillator (b) in Fig. 5. Fig. 6
ample, as for the 4th harmonic push-push oscillator, the 4th harmonic can be enhanced, because the 2nd and the 6th harmonics are depressed as indicated in Table 2. Figures 6(a) and (b) show the simulated results of the power spectrum available for the push-push oscillators (a) and (b) shown in Fig. 5 respectively. These results show the remarkable enhancement of the required harmonic, as well as the good suppression of undesired harmonics on the resonator. Figure 7 shows the 4th harmonic push-push oscillators using a ring resonator [14]. They can be easily derived from the resonant field on a ring resonator as well. It is well known that a wavelength ring resonator has two degenerative orthogonal modes at the fundamental frequency ( f0 ). In Fig. 7(a), a resonant mode is exited by the N.R.I and N.R.III, and the orthogonal resonant mode is exited by N.R.II and N.R.IV. They can exist independently at the fundamental frequency of f0 on a ring resonator. However, in the case of nonlinear circuit system, they are mutually coupled due to the mutual synchronization of the harmonic signals. In the case of the push-push oscillators shown in Fig. 7, four negative resistances are mutually synchronized through a half wavelength lines at the 2nd harmonic frequency (2 f0 ), where they are out of phase in any adjoining N.R. pair, which means that at the fundamental frequency f0 , the phase difference of any adjoining N.R. pair is π/2 autonomously. Consequently, the phase relation of the four N.R. at the frequency of f0 and 2 f0 are as shown in Fig. 7(a). In much the same way as the push-push oscillator using a line resonator, the 4th harmonic signal can be available in both circuit configurations, Type-I and Type-II in Fig. 7. Figure 8 is a fabricated Ka-band 4th harmonic push-push oscillator Type-I in Fig. 7, where a microstrip ring resonator is used. The mea-
Output power of push-push oscillators shown in Fig. 5.
(a) Type-I.
(b) Type-II. Fig. 7
The 4th harmonic push-push oscillator using ring resonator.
sured output power spectrum is also shown in Fig. 8 This oscillator adopted X-band HEMT (FHX35LP, Fujitsu) for the negative resistance units, and the output power is +1.7 dBm at the 4th harmonic frequency of 36 GHz. The phase noise is −104.0 dBc/Hz at 1 MHz offset [17].
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(a) Ka-band push-push oscillator.
Figure 9 shows the 8th harmonic push-push oscillators, which can be derived from the resonant harmonic field on a ring resonator in the same way. The 8th harmonic can be selectively enhanced, depressing the other undesired harmonics in principle. As mentioned above, higher order harmonic push-push oscillator can be realized very easily because of the extensive use of the resonant coherent field based on the AURF, in which the coherent field, the synchronous harmonic field and the degenerative orthogonal modes on a resonator are practically noteworthy properties. As the result, much higher harmonic frequency signal can be selectively generated, as well as good suppression of undesired harmonics effectively. 4.
(b) Output power spectrum. (4 f0 =36 GHz) Fig. 8 The 4th harmonic push-push oscillator using ring resonator shown in Fig. 7(a).
(a) Type-I.
(b) Type-II. Fig. 9
The 8th harmonic push-push oscillator using ring resonator.
Reconfigurable Planar Antenna
Reconfigurable antennas have attracted much attention recently, because of their versatility in various wireless systems, mainly due to their frequency controllability and polarization diversities. Reconfigurable planar antennas are attractive candidates in wireless systems due to their various functionalities as well as lightness, low profile and easy fabrication properties. Additionally, they can be good technical subjects of the AURF shown in Fig. 1, in which planar antennas are considered to be a kind of microwave resonators. Figure 10 shows the technical concept for reconfigurable planar antennas including the related applications, where the resonant electromagnetic field on planar antennas plays the important role as well. In this approach, semiconductor devices such as diodes, transistors or MMIC chips are embedded on the antenna conductor to control the boundary condition of the resonant field on the planar antennas. They are also embedded on the antenna feeder circuits, if necessary. In the same manner as the configuration here, an integrated planar antenna-mixer for the reception of orthogonally polarized microwave signals was formerly proposed [18], in which the quad-connected diodes ware embedded on a slot-ring antenna. This is a kind of multi-functional antenna of both the RF reception and the double-balanced down converter. Due to a couple of promising features of the AURF denoted in Fig. 10, practical applications such as reconfigurable antenna, beam steering, rectenna and RF signal processing etc. can be realized extensively. Figure 11 shows typical reconfigurable patch antennas based on the AURF approach. Figure 11(a) is a dual-band patch antenna [19], in which anti-series connected diodes are embedded in the patch. It has two frequency bands, f1 and f2 , which depends on the on/off state of the diodes switched by the bias voltage polarity, as shown in Fig. 11(a), where the surface current path is switched by the on and off condition of the diodes. Figure 12 shows both the calculated and the experimental results of the dual-band patch antenna in 3 GHz band. The FDTD method is used to simulate the antenna, where the on-state diode is replaced by conductor line. The simulated results agree well with the experimental values.
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Fig. 10
Device embedded planar antenna and the applications.
(a) Dual-band patch.
(a) Resistance.
(b) Frequency controllable patch.
(c) Polarization controllable patch. Fig. 11
Reconfigurable patch antenna.
(b) Reactance. Fig. 12 The frequency characteristics of impedance of dual-band patch antenna.
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crowave and millimeter-wave bands. 5.
(a) Polarization angle φ.
(b) Current distribution. ( f =3.5 GHz) Fig. 13 The polarization angle and the surface current distribution of polarization controllable patch antenna.
Figure 11(b) is a frequency controllable patch antenna, where anti-series connected varactor diodes are embedded in the patch [20]. The operating frequency can be controlled continuously by the capacitance value of these diodes. It is practically very attractive to expand the operating band, because a patch antenna has essentially very narrow band performance. Figure 11(c) is a polarization controllable patch antenna, that has a cross slot in which cross-connected switching diodes are embedded [15], [21]. The linear polarization can be orthogonally controlled to change the surface current path, as shown in this figure. Figure 13 shows both the calculated and the experimental results of the polarization controllable patch in 3 GHz band, as well as the surface current distribution on the patch. The FDTD method is also used to simulate the antenna, where the on-state diode is replaced by conductor line as well. The orthogonal polarization controllability is successfully confirmed both experimentally and theoretically. The above mentioned reconfigurable planar antennas are very easily realized and fabricated, where the boundary condition of the resonant field is controlled by embedded semiconductor devices or IC’s on the antenna conductors. Moreover, this approach can be expanded to develop the beam steering array antennas [22] and RF signal processing antenna modules with functionalities of RF oscillation, modulation, direct conversion and rectenna etc. in mi-
Conclusion
This paper presents the extensive utilization approach of microwave and millimeter-wave resonant fields, and the applications to the push-push oscillators and the reconfigurable planar antennas. The most noticeable point of this approach is to utilize the highly coherent field, synchronous harmonics and degenerative orthogonal modes of electromagnetic resonant field built up on microwave resonators in broadsense as much as possible. Another significant point is the resonant field controllability, which can be realized by semiconductor devices or IC’s embedded on microwave resonators including planar antennas. Two kinds of the applications, that is, the push-push oscillators and the reconfigurable planar antennas are described as effective and suitable subjects of this approach. Both applications make the most use of the highly coherent fields on microwave resonators. Push-push oscillators proposed here can generate much higher frequency signals due to the selective use of the 4th harmonic up to the 8th harmonic resonant fields, suppressing undesired harmonic signals. As a result, very high frequency band oscillators up to millimeter-wave and submillimeter-wave bands with good suppression of undesired harmonic signals can be realized at very low cost by use of commercially available active devices for low frequency bands. Reconfigurable planar antennas are also demonstrated as the other good applications of this approach. The boundary condition of the resonant field on planar antennas can be purposefully controlled to realize reconfigurable antennas with semiconductor devices embedded on the patch conductor. The linear polarization controllable patch, a dual-band switching patch and a continuously frequency controllable patch have been demonstrated as the successful applications of this approach. Many expert comments and suggestions will be highly appreciated. References [1] M. Aikawa, “Technical approach for advanced microwave circuits and antennas—An approach on microwave integration,” IEICE Technical Report, MW2003-202, Nov. 2003. [2] M. Aikawa, “Prospect of microwave engineering: Evolution for adaptive microwave circuits,” J. IEICE, vol.83, no.8, pp.595–599, Aug. 2000. [3] M. Aikawa, E. Nishiyama, and T. Tanaka, “Evaluational integration approach for microwave planar circuits,” IEICE Trans. Electron. (Japanese Edition), vol.J89-C, no.5, pp.183–190, May 2006. [4] J.H. Lim and T.Y. Yun, “Reconfigurable antenna of frequency and polarization diversity for PCS and DMB,” Proc. ISAP2005, pp.347– 350, Seoul, 2005. [5] K. Chung, Y. Nam, T. Yun, and J. Choi, “Reconfigurable microstrip antenna with frequency and polarization diversities,” Proc. ISAP2005, pp.981–984, Seoul, 2005. [6] A.Y. Simba, M. Yamamoto, T. Nojima, and K. Itoh, “Circularly polarized proximity-fed microstrip antenna with switchable polariza-
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tion ability,” Proc. ISAP2005, pp.985–988, Seoul, 2005. [7] F. Yang and Y.R. Samii, “Patch antennas with switchable slots (PASS) in wireless communications: Concepts, designs, and applications,” IEEE Antennas Propag. Mag., vol.47, no.2, pp.13–29, April 2005. [8] H. Aissat, L. Cirio, M. Grzeskowiak, J.-M. Laheure, and O. Picon, “Reconfigurable circularly polarized antenna for short-range communication systems,” IEEE Trans. Microw. Theory Tech., vol.54, no.6, pp.2856–2863, June 2006. [9] R. Winner and H. Scafer, et al., “A fully integrated 70 GHz SiGe low phase noise push-push oscillator,” IEEE Proc. IMS2005, pp.1523– 1526, 2005. [10] M. Schott, F. Lenk, C. Meliani, and W. Heinrich, “Low phase noise X-band push-push oscillator with frequency divider,” IEEE Proc. IMS2005, pp.1527–1530, 2005. [11] J. Choi and A. Mortazawi, “Design of push-push oscillators for reducing 1/f noise upconversion,” IEEE Proc. IMS2005, pp.1531– 1534, 2005. [12] U.L. Rohde, A.K. Poddar, J. Schoepf, R. Rebel, and P. Patel, “Low noise low cost ultra wideband N-push VCO,” IEEE Proc. IMS2005, pp.1171–1174, 2005. [13] H. Xiao, T. Tanaka, and M. Aikawa, “Push-push oscillator with simplified circuit structure,” IEE Electron. Lett., vol.38, no.24, pp.1545– 1547, Nov. 2002. [14] H. Xiao, T. Tanaka, and M. Aikawa, “A Ka-band quadruple-push oscillator,” IEEE MTT-S, IMS-2003, pp.889–892, 2003. [15] E. Nishiyama, K. Takenaka, and M. Aikawa, “Polarization controlled microstrip antenna,” IEICE Trans. Commun. (Japanese Edition), vol.J85-B, no.9, pp.1519–1525, Sept. 2002. [16] M. Makimoto and S. Yamashita, Microwave Resonators and Filters for Wireless Communication, Springer Series in Advanced Microelectronics, Springer, 2001. [17] H. Xiao, T. Tanaka, and M. Aikawa, “Basic behavior of quadruplepush oscillator using ring resonator,” IEICE Trans. Electron., vol.E88-C, no.7, pp.1502–1508, July 2005. [18] T. Itoh and K. Stephan, “Quasi-optical polarization duplexed balanced mixer,” US Patent, US-4,509,209, April 1985. [19] K. Sakamoto, E. Nishiyama, and M. Aikawa, “Active microstrip planar antenna for frequency switching,” IEICE Trans. Commun. (Japanese Edition), vol.J87-B, no.11, pp.1918–1925, Nov. 2004. [20] K. Sakamoto, E. Nishiyama, and M. Aikawa, “Active antenna with continuously varying frequency performance,” J. ITE, vol.58, no.7, pp.952–956, July 2004. [21] S. Sasaki, E. Nishiyama, and M. Aikawa, “Polarization controllable circular slot antenna,” Proc. ISAP 2005, pp.1193–1196, 2005. [22] E. Nishiyama, R. Hisadomi, and M. Aikawa, “Directivity controllable microstrip antenna with switching diodes,” Proc. KJMW2005, pp.87–90, Busan, 2005.
Masayoshi Aikawa graduated from the Department of Electronic Engineering, Kyushu University, in 1969, completed the M.S. program in 1971, and joined Nippon Telegraph and Telephone (now NTT). Since then, he has been engaged in the development of microwave and millimeter wave integrated circuits, MMIC, and various communication devices. In 1997, he has been a professor at Saga University. He holds a Dr. Eng. degree, and is a member of IEEE.
Eisuke Nishiyama graduated from the Department of Electronics, Saga University, in 1987, completed the M.S. program in 1989, and become a member of the technical staff there. He has been a research associate since 1997. His research interest is planar antennas. He holds a Dr. Eng. degree, and is a member of IEEE.
Takayuki Tanaka received the B.E. and M.E. degrees in Electronics Engineering from Saga University, Saga, Japan in 1986 and 1988, respectively. He received the Dr. Eng. degree from Kyushu University, Fukuoka, Japan in 2002. He was a Research Associate from 1988 to 2004 and is currently a Lecturer in the department of Electrical and Electronic Engineering at Saga University. His current research interests are microwave are millimeter wave circuits. He is a member of IEEE.
