Broadband Microstrip fed Dielectric Resonator ...
IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS
1
Broadband Microstrip fed Dielectric Resonator Antenna for X-Band Applications Yacouba Coulibaly, Tayeb A. Denidni, and Halim Boutayeb
Abstract— A new microstrip fed low profile broadband dielectric resonator antenna is proposed. The antenna is composed of a dielectric resonator, a microstrip fed stepped patch and an intermediate substrate. The stepped patch and the intermediate substrate allow to widen the matching bandwidth. Using a finite integration method (CST Microwave), a parametric investigation was performed for the optimization. To validate our analysis, a prototype of the optimized antenna was fabricated and measured. The predicted results are computed with measured data and good agreement is reported. With the proposed antenna, a fractional bandwidth of 50% around the center frequency 10 GHz is achieved, and relatively stable radiation patterns are obtained in the matching band. Index Terms— Dielectric Resonator, patch antennas, hybrid structure, broadband.
I. I NTRODUCTION
D
IELECTRIC Resonators (DRs) are important components for several communication systems operating at microwave and millimeter wave-bands [1]. These applications include filters, shielded oscillators and antennas. The first Dielectric Resonator Antenna (DRA) was proposed in 1983 [2]. Over the last few decades, increasing attention has been paid to the investigation of DRAs due to their attractive features. DRAs have several advantages, such as low losses, high radiation efficiency, high integration, reduced size, low cost and low weight. They also allow to obtain different radiation characteristics by exciting different radiation modes. For a single-mode excitation, the bandwidth of a DRA is generally below 10% which is not enough for ultra wide-band applications and spread spectrum systems. Recently, different techniques have been proposed to enhance the bandwidth [310]. In respect to this issue, DRAs with different shapes, such as conical [3], tetrahedron and triangular [4] shapes, have been analyzed. Another method for widening the bandwidth consists on stacking two or more elements of different sizes with different dielectric constants to improve the coupling between the feed line and the antenna [5]. In addition, coplanar parasitic DRAs can also be used to increase the bandwidth [6]. However, these different techniques are generally difficult to fabricate and the parasitic DRAs can increase the antenna size. An approach based on the use of multiple resonances have been also proposed [7-9]. This method consists on using different radiating structures having different resonant modes and to combine them in order to obtain a wide-band hybrid Manuscript received November 2007. This work was supported in part by the National Science Engineering Research Council of Canada (NSERC). The authors are with Institut National de Recherche Scientifique (INRS)EMT, Montr´eal, Canada. Email : {couli}{denidni}{boutayeb}@emt.inrs.ca.
structure. For examples, a combination of a DRA and a slot has been proposed in [7], whereas a combination of a patch antenna and a DRA has been proposed in [8]. In [10], a low profile DRA fed by a stepped microstrip line has been designed, and a bandwidth of 17% has been achieved. In [11], an ultra wide-band antenna fed by a coaxial probe has been designed by inserting a dielectric segment between the ground plane and the radiating dielectric resonator. In this letter, a new broadband Dielectric Resonator Antenna, with a fractional bandwidth of 50%, is proposed. It is composed of three parts: a dielectric resonator (DR), an intermediate substrate and a microstrip fed stepped patch. The stepped patch and the intermediate substrate allow the increasing of the matching bandwidth. A parametric analysis was carried out by using a finite integration method (CST Microwave). Numerical results for the near field inside the antenna and the return losses are also presented in Section II. To validate our analysis, a prototype of the antenna was fabricated and measured, and the experimental results are presented in Section III. Finally, concluding remarks are given in Section IV. II. A NTENNA D ESIGN Figure 1 shows the topology of the proposed hybrid antenna. It consists of a Dielectric Resonator (DR), an intermediate substrate and a microstrip fed patch. The parameters of the DR are the height 2c, the width b, the length a, and the relative permittivity εdra . The intermediate substrate is of thickness h2 , has the permittivity ε2 , and the width Wi . The feeding circuit is composed of a microstrip line of width W connected to a stepped patch, constituted of three strips, as illustrated in Fig. 1.(b). The width and length of patch strips are Ws and Ls , for the first strip, Ws1 and Ls1 , for the second, and Ws and Ls , for the last one. The distance from the edge of the DRA to the edge of the patch is d. A parametric analysis of the proposed hybrid antenna was carried out by using the commercial software CST Microwave, which is based on the finite integration method. The initials dimensions of the DRA, which fix the excited mode, can be found by using the modified waveguide model [12]. Using this model, the frequency of the fundamental mode y of the DRA T E111 , which is a hybrid mode, is around 11 GHz. For the DRA, the followings parameters are considered: εdra = 10.2, b = a = 10.4 mm, and 2c = 2.54 mm. The values of the other parameters of the antenna are h1 =1.27 mm, W = 1.2mm, L = 27mm, Ls = 2mm, Ws = 5mm, Ls1 = 1mm, Ws1 = 7.5mm, and Wi = 30mm. Different values of the parameters h2 , d and ε2 were tested.
IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS
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Figure 2 presents the simulated return loss of the antenna for different values of h2 . When h2 is null, the DRA is located on the patch, and there is no intermediate substrate. In this case, the simulated results show that the DRA resonates around 10.8 GHz. By adding the intermediate substrate, the effective permittivity of the substrate-DRA structure decreases. This conducts to the reduction of the Q-factor of the equivalent resonator and then to the improvement of the impedance bandwidth. According to Fig. 2, the optimum thickness is h2 = 0.8 mm.
Now we analyze the effect of the distance between the edge of the DRA and the edge of the patch, called d. Figure 3 presents the simulated return loss for different values of d, showing that the choice of d affects the bandwidth of the antenna. This distance is critical to have an efficient coupling.
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Fig. 3. Simulated return loss for different values of d (h = 0.8 and ε2 =2.2).
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Simulated return loss for different values of ε2 .
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Fig. 2. Simulated return loss for different values of h2 (d = 2.15 and ε2 =2.2).
Finally, the influence of the permittivity of the intermediate substrate ε2 is investigated. Several simulations were carried out to find the optimal permittivity ε2 which gives the larger bandwidth. These results are shown in Fig. 4. From these curves, the matching bandwidth decreases when the permittivity increases. In order to understand further the antenna mechanism, the near fields are examined numerically. Figures 5 shows the top view of the electrical field and the side view of the magnetic view at the three resonant frequencies. From these figures, at the two lower frequencies, the near field is mainly concentred in the dielectric resonator, which confirms that the radiation at
IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS
3
these frequencies are due to the DR. At the upper frequency we can notice that the magnetic field spreads from the feed patch. We can conclude that at the upper edge of the matching bandwidth, the radiation is due to the metallic patch.
without the dielectric resonator. These results confirm that the resonance at higher frequencies are due to the patch. The wideband characteristics of the optimized antenna is thus achieved by merging the resonant frequencies of the patch and the DR. III. E XPERIMENTAL RESULTS
Top view
(a)
Top view
(b)
Top view
(c)
A prototype of the optimized antenna was fabricated and tested. Figure 7 shows the photograph of the fabricated antenna. The DRA is made of a 2.54 mm thick RT/Duroid 6010 substrate with the permittivity εdra = 10.2. The microstrip line and the patch are printed on a h1 =1.27 mm thick substrate. The intermediate dielectric is a RT/Duroid 3060 substrate of permittivity ε2 = 2.2 and thickness h2 = 0.8 mm. The values of the other parameters of the antenna are the followings: a = b = 10.4mm, W = 1.2mm, L = 26.5mm, Ls = 2mm, W s = 5mm, Ls1 = 1mm, W s1 = 7.5mm, and W i = 30mm.
Side view
Side view
Side view
Fig. 7.
Top view
Side view
(d)
Fig. 5. Distribution of the field inside the antenna. Top view of the modulus of electrical field and the side view of the modulus of the magnetic field at (a) 8.3 GHz (b) 9.3 GHz (c) 10.3 GHz and (d) 12 GHz.
Photograph of the fabricated broadband antenna.
The measured and simulated S parameters are shown in Fig. 8. From these curves, it can be observed that there is a good agreement between the measured and simulated results. Only a small shift between the measured and simulated center frequencies is observed. This is due to measurement set up. From the measured results, a bandwidth of 50% (for S11 < −10 dB) around 10.16 GHz is achieved.
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Fig. 6.
Simulated return loss with and without the dielectric resonator.
Figure 6 shows the return loss of the antenna with and
Fig. 8.
Simulated and measured return losses of the optimized antenna.
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Figure 9 presents the measured co- and cross-polarized patterns, in the E- and H-planes, at 7.5 GHz, 9.5 GHz and 11.5 GHz. These results show that the patterns are stable across the matching band. One can note that there is a small asymmetry in the H-plane patterns, which is due to the radiation of the microstrip line and the patch. The small ripples in the back radiations are caused by the diffractions at the edge of the ground plane. 0
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Fig. 9. Measured radiations patterns in E-and H-planes (in dB) at (a) 7.5 GHz (b) 9.5 GHz and (c) 11.5 GHz
IV. C ONCLUSION A new low profile broadband dielectric resonator antenna has been proposed. A large bandwidth has been obtained by adding an intermediate substrate and using a stepped patch. A parametric investigation was carried out and a prototype was fabricated. Simulations and experimental results show that the proposed antenna can offer a bandwidth of 50% around the center frequency 10.16 GHz, with return losses less than −10 dB and the same radiation characteristics all over the band. With these features, this antenna can be suitable for broadband wireless communication systems operating at X-Band.
R EFERENCES [1] K.M. Luk and K. W. Leung, Dielectric Resonator Antennas, Research Studies Press Ltd Press, Baldock, Herfordshire, UK, 2002 . [2] S. A. Long, M. W. Mcallister, and L. C. Shen, “The resonant cylindrical dielectric cavity antenna”, IEEE Trans. Antennas and Propagat., vol. 31, pp. 406-412, 1983. [3] A.A. Kishk , Y.Yin , W.Glisson , “Conical Dielectric Resonator Antennas For Wideband Applications”, IEEE Trans. Antennas and Propagat., vol. 50, pp 469-474, April 2002. [4] A.A. Kishk, “Tetrahedron and Triangular Dielectric Resonator with wideband Performance”, in Proc. IEEE AP-S Int. Symp. Dig., vol.4, pp 462-465, June 2002. [5] A.A Kishk, B.Ahn and D. Kajfez, “Broadband Stacked Dielectric Resonator”, Electron. Lett., vol. 25, pp 1232-1233, Aug 1999. [6] Z.Fan , Y.M.M Antar., A. Ittipiboon, and A. Petosa, “Parastic Coplanar Three-element Dielectric Resonator Antenna Subarray”, Electron. Lett., vol. 32, pp 789-790, April 1996. [7] A. Buerkle, K. Sarabandi and H. Mosallaei, “Compact slot and dielectric resonator antenna with dual-resonance, broadband characteristics”, IEEE Trans. Antennas and Propagat., vol. 53, pp 1020-1027, March 2005. [8] Q. Rao , T.A. Denidni, and A.R. Sebak, “A new dual-frequency hybrid resonator antenna”, IEEE Antennas and Wir. Prop. Lett., vol. 4, no.9, pp 308-311 April 2005. [9] Q. Rao, T.A. Denidni, A.R. Sebak and R. H. Johnston,“A dual band compact hybrid resonator antenna”, in Proc. IEEE AP-S Int. Symp. Dig., vol. 2A, pp 156-159, July 2005. [10] M. Saed, and R. Yadla, “Microstrip-fed low profile and compact dielectric resonator antennas”, Progress In Electromagnetic Research, vol.56, pp 151-162, Jan. 2006. [11] Y. Ge, K. P. Esselle, and T. S. Bird, “A wideband probe-fed stacked dielectric resonator antenna”, Microwave Opt. Technol. Lett., vol. 48, pp. 1630-1632, August 2006 [12] R.K Mongia and A. Ittipiboon, “Theoretical and experimental investigations on rectangular dielectric resonator antennas”, IEEE Trans. Antennas Propag., vol. 45, pp 1348-1356, September 1997.
1
Broadband Microstrip fed Dielectric Resonator Antenna for X-Band Applications Yacouba Coulibaly, Tayeb A. Denidni, and Halim Boutayeb
Abstract— A new microstrip fed low profile broadband dielectric resonator antenna is proposed. The antenna is composed of a dielectric resonator, a microstrip fed stepped patch and an intermediate substrate. The stepped patch and the intermediate substrate allow to widen the matching bandwidth. Using a finite integration method (CST Microwave), a parametric investigation was performed for the optimization. To validate our analysis, a prototype of the optimized antenna was fabricated and measured. The predicted results are computed with measured data and good agreement is reported. With the proposed antenna, a fractional bandwidth of 50% around the center frequency 10 GHz is achieved, and relatively stable radiation patterns are obtained in the matching band. Index Terms— Dielectric Resonator, patch antennas, hybrid structure, broadband.
I. I NTRODUCTION
D
IELECTRIC Resonators (DRs) are important components for several communication systems operating at microwave and millimeter wave-bands [1]. These applications include filters, shielded oscillators and antennas. The first Dielectric Resonator Antenna (DRA) was proposed in 1983 [2]. Over the last few decades, increasing attention has been paid to the investigation of DRAs due to their attractive features. DRAs have several advantages, such as low losses, high radiation efficiency, high integration, reduced size, low cost and low weight. They also allow to obtain different radiation characteristics by exciting different radiation modes. For a single-mode excitation, the bandwidth of a DRA is generally below 10% which is not enough for ultra wide-band applications and spread spectrum systems. Recently, different techniques have been proposed to enhance the bandwidth [310]. In respect to this issue, DRAs with different shapes, such as conical [3], tetrahedron and triangular [4] shapes, have been analyzed. Another method for widening the bandwidth consists on stacking two or more elements of different sizes with different dielectric constants to improve the coupling between the feed line and the antenna [5]. In addition, coplanar parasitic DRAs can also be used to increase the bandwidth [6]. However, these different techniques are generally difficult to fabricate and the parasitic DRAs can increase the antenna size. An approach based on the use of multiple resonances have been also proposed [7-9]. This method consists on using different radiating structures having different resonant modes and to combine them in order to obtain a wide-band hybrid Manuscript received November 2007. This work was supported in part by the National Science Engineering Research Council of Canada (NSERC). The authors are with Institut National de Recherche Scientifique (INRS)EMT, Montr´eal, Canada. Email : {couli}{denidni}{boutayeb}@emt.inrs.ca.
structure. For examples, a combination of a DRA and a slot has been proposed in [7], whereas a combination of a patch antenna and a DRA has been proposed in [8]. In [10], a low profile DRA fed by a stepped microstrip line has been designed, and a bandwidth of 17% has been achieved. In [11], an ultra wide-band antenna fed by a coaxial probe has been designed by inserting a dielectric segment between the ground plane and the radiating dielectric resonator. In this letter, a new broadband Dielectric Resonator Antenna, with a fractional bandwidth of 50%, is proposed. It is composed of three parts: a dielectric resonator (DR), an intermediate substrate and a microstrip fed stepped patch. The stepped patch and the intermediate substrate allow the increasing of the matching bandwidth. A parametric analysis was carried out by using a finite integration method (CST Microwave). Numerical results for the near field inside the antenna and the return losses are also presented in Section II. To validate our analysis, a prototype of the antenna was fabricated and measured, and the experimental results are presented in Section III. Finally, concluding remarks are given in Section IV. II. A NTENNA D ESIGN Figure 1 shows the topology of the proposed hybrid antenna. It consists of a Dielectric Resonator (DR), an intermediate substrate and a microstrip fed patch. The parameters of the DR are the height 2c, the width b, the length a, and the relative permittivity εdra . The intermediate substrate is of thickness h2 , has the permittivity ε2 , and the width Wi . The feeding circuit is composed of a microstrip line of width W connected to a stepped patch, constituted of three strips, as illustrated in Fig. 1.(b). The width and length of patch strips are Ws and Ls , for the first strip, Ws1 and Ls1 , for the second, and Ws and Ls , for the last one. The distance from the edge of the DRA to the edge of the patch is d. A parametric analysis of the proposed hybrid antenna was carried out by using the commercial software CST Microwave, which is based on the finite integration method. The initials dimensions of the DRA, which fix the excited mode, can be found by using the modified waveguide model [12]. Using this model, the frequency of the fundamental mode y of the DRA T E111 , which is a hybrid mode, is around 11 GHz. For the DRA, the followings parameters are considered: εdra = 10.2, b = a = 10.4 mm, and 2c = 2.54 mm. The values of the other parameters of the antenna are h1 =1.27 mm, W = 1.2mm, L = 27mm, Ls = 2mm, Ws = 5mm, Ls1 = 1mm, Ws1 = 7.5mm, and Wi = 30mm. Different values of the parameters h2 , d and ε2 were tested.
IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS
2
Figure 2 presents the simulated return loss of the antenna for different values of h2 . When h2 is null, the DRA is located on the patch, and there is no intermediate substrate. In this case, the simulated results show that the DRA resonates around 10.8 GHz. By adding the intermediate substrate, the effective permittivity of the substrate-DRA structure decreases. This conducts to the reduction of the Q-factor of the equivalent resonator and then to the improvement of the impedance bandwidth. According to Fig. 2, the optimum thickness is h2 = 0.8 mm.
Now we analyze the effect of the distance between the edge of the DRA and the edge of the patch, called d. Figure 3 presents the simulated return loss for different values of d, showing that the choice of d affects the bandwidth of the antenna. This distance is critical to have an efficient coupling.
0
S11 (dB)
-10
-20
d= 0.15 mm = 1.15 mm d= 2.15 mm d= 3.15 mm d
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-40 6
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Fig. 3. Simulated return loss for different values of d (h = 0.8 and ε2 =2.2).
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Geometry of the proposed antenna.
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Fig. 4.
Simulated return loss for different values of ε2 .
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Fig. 2. Simulated return loss for different values of h2 (d = 2.15 and ε2 =2.2).
Finally, the influence of the permittivity of the intermediate substrate ε2 is investigated. Several simulations were carried out to find the optimal permittivity ε2 which gives the larger bandwidth. These results are shown in Fig. 4. From these curves, the matching bandwidth decreases when the permittivity increases. In order to understand further the antenna mechanism, the near fields are examined numerically. Figures 5 shows the top view of the electrical field and the side view of the magnetic view at the three resonant frequencies. From these figures, at the two lower frequencies, the near field is mainly concentred in the dielectric resonator, which confirms that the radiation at
IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS
3
these frequencies are due to the DR. At the upper frequency we can notice that the magnetic field spreads from the feed patch. We can conclude that at the upper edge of the matching bandwidth, the radiation is due to the metallic patch.
without the dielectric resonator. These results confirm that the resonance at higher frequencies are due to the patch. The wideband characteristics of the optimized antenna is thus achieved by merging the resonant frequencies of the patch and the DR. III. E XPERIMENTAL RESULTS
Top view
(a)
Top view
(b)
Top view
(c)
A prototype of the optimized antenna was fabricated and tested. Figure 7 shows the photograph of the fabricated antenna. The DRA is made of a 2.54 mm thick RT/Duroid 6010 substrate with the permittivity εdra = 10.2. The microstrip line and the patch are printed on a h1 =1.27 mm thick substrate. The intermediate dielectric is a RT/Duroid 3060 substrate of permittivity ε2 = 2.2 and thickness h2 = 0.8 mm. The values of the other parameters of the antenna are the followings: a = b = 10.4mm, W = 1.2mm, L = 26.5mm, Ls = 2mm, W s = 5mm, Ls1 = 1mm, W s1 = 7.5mm, and W i = 30mm.
Side view
Side view
Side view
Fig. 7.
Top view
Side view
(d)
Fig. 5. Distribution of the field inside the antenna. Top view of the modulus of electrical field and the side view of the modulus of the magnetic field at (a) 8.3 GHz (b) 9.3 GHz (c) 10.3 GHz and (d) 12 GHz.
Photograph of the fabricated broadband antenna.
The measured and simulated S parameters are shown in Fig. 8. From these curves, it can be observed that there is a good agreement between the measured and simulated results. Only a small shift between the measured and simulated center frequencies is observed. This is due to measurement set up. From the measured results, a bandwidth of 50% (for S11 < −10 dB) around 10.16 GHz is achieved.
0
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Fig. 6.
Simulated return loss with and without the dielectric resonator.
Figure 6 shows the return loss of the antenna with and
Fig. 8.
Simulated and measured return losses of the optimized antenna.
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4
Figure 9 presents the measured co- and cross-polarized patterns, in the E- and H-planes, at 7.5 GHz, 9.5 GHz and 11.5 GHz. These results show that the patterns are stable across the matching band. One can note that there is a small asymmetry in the H-plane patterns, which is due to the radiation of the microstrip line and the patch. The small ripples in the back radiations are caused by the diffractions at the edge of the ground plane. 0
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Fig. 9. Measured radiations patterns in E-and H-planes (in dB) at (a) 7.5 GHz (b) 9.5 GHz and (c) 11.5 GHz
IV. C ONCLUSION A new low profile broadband dielectric resonator antenna has been proposed. A large bandwidth has been obtained by adding an intermediate substrate and using a stepped patch. A parametric investigation was carried out and a prototype was fabricated. Simulations and experimental results show that the proposed antenna can offer a bandwidth of 50% around the center frequency 10.16 GHz, with return losses less than −10 dB and the same radiation characteristics all over the band. With these features, this antenna can be suitable for broadband wireless communication systems operating at X-Band.
R EFERENCES [1] K.M. Luk and K. W. Leung, Dielectric Resonator Antennas, Research Studies Press Ltd Press, Baldock, Herfordshire, UK, 2002 . [2] S. A. Long, M. W. Mcallister, and L. C. Shen, “The resonant cylindrical dielectric cavity antenna”, IEEE Trans. Antennas and Propagat., vol. 31, pp. 406-412, 1983. [3] A.A. Kishk , Y.Yin , W.Glisson , “Conical Dielectric Resonator Antennas For Wideband Applications”, IEEE Trans. Antennas and Propagat., vol. 50, pp 469-474, April 2002. [4] A.A. Kishk, “Tetrahedron and Triangular Dielectric Resonator with wideband Performance”, in Proc. IEEE AP-S Int. Symp. Dig., vol.4, pp 462-465, June 2002. [5] A.A Kishk, B.Ahn and D. Kajfez, “Broadband Stacked Dielectric Resonator”, Electron. Lett., vol. 25, pp 1232-1233, Aug 1999. [6] Z.Fan , Y.M.M Antar., A. Ittipiboon, and A. Petosa, “Parastic Coplanar Three-element Dielectric Resonator Antenna Subarray”, Electron. Lett., vol. 32, pp 789-790, April 1996. [7] A. Buerkle, K. Sarabandi and H. Mosallaei, “Compact slot and dielectric resonator antenna with dual-resonance, broadband characteristics”, IEEE Trans. Antennas and Propagat., vol. 53, pp 1020-1027, March 2005. [8] Q. Rao , T.A. Denidni, and A.R. Sebak, “A new dual-frequency hybrid resonator antenna”, IEEE Antennas and Wir. Prop. Lett., vol. 4, no.9, pp 308-311 April 2005. [9] Q. Rao, T.A. Denidni, A.R. Sebak and R. H. Johnston,“A dual band compact hybrid resonator antenna”, in Proc. IEEE AP-S Int. Symp. Dig., vol. 2A, pp 156-159, July 2005. [10] M. Saed, and R. Yadla, “Microstrip-fed low profile and compact dielectric resonator antennas”, Progress In Electromagnetic Research, vol.56, pp 151-162, Jan. 2006. [11] Y. Ge, K. P. Esselle, and T. S. Bird, “A wideband probe-fed stacked dielectric resonator antenna”, Microwave Opt. Technol. Lett., vol. 48, pp. 1630-1632, August 2006 [12] R.K Mongia and A. Ittipiboon, “Theoretical and experimental investigations on rectangular dielectric resonator antennas”, IEEE Trans. Antennas Propag., vol. 45, pp 1348-1356, September 1997.
