Антенны, СВЧ / OC / Broadband microstrip antennas

[82]Ray, K. P., and G. Kumar, ‘‘Compact Gap-Coupled Shorted 90° Sectoral Microstrip Antennas for Broadband and Dual Band Operations,’’ Microwave Optical Tech. Letters, Vol. 26, No. 3, 2000, pp. 143–145.

[83]Waterhouse R. B., ‘‘Broadband Stacked Shorted Patch,’’ Electronics Letters, Vol. 35, No. 2, 1999, pp. 98–99.

[84]Plessis, M. Du., and J. H. Cloete, ‘‘Tuning Stub for Microstrip Patch Antenna,’’

IEEE AP-S Int. Symp. Digest, June 1993, pp. 964–967.

[85]Ray, K. P., and G. Kumar, ‘‘Tunable and Dual-Band Circular Microstrip Antenna with Stubs,’’ IEEE Trans. Antennas Propagation, Vol. 48, July 2000, pp. 1036–1039.

[86]Bhartia, P., and I. J. Bahl, ‘‘A Frequency Agile Microstrip Antenna,’’ IEEE AP-S Int. Symp. Digest, May 1982, pp. 304–307.

[87]Maci, S., and G. B. Gentili, ‘‘Dual-Frequency Patch Antennas,’’ IEEE AP Magazine, Vol. 39, No. 6, 1997, pp. 13–19.

[88]Schaubert, H., et al., ‘‘Microstrip Antennas with Frequency Agility and Polarization Diversity,’’ IEEE Trans. Antennas Propagation, Vol. AP-29, January 1981, pp.118–123.

[89]Richards, W. F., S. E. Davidson, and S. A. Long, ‘‘Dual Band Reactively Loaded Microstrip Antenna,’’ IEEE Trans. Antennas Propagation, Vol. AP-33, May 1985, pp. 556–561.

[90]Long, S. A., and M. D. Walton, ‘‘A Dual-Frequency Stacked Circular-Disc Antenna,’’ IEEE Trans. Antennas Propagation, Vol. AP-27, March 1979, pp. 270–273.

[91]Syankal, M., and H. R. Hassani, ‘‘Characteristics of Stacked Rectangular and Triangular Patch Antennas for Dual Band Application,’’ Proc. IEE 8th International Conference on Antennas and Propagation, Edinburgh, Scotland, March 1993.

[92]Yazdi, M. L., M. Himdi, and J. P. Daniel, ‘‘Aperture-Coupled Microstrip Antenna

for Dual Frequency Operation,’’ Electronics Letters, Vol. 29, No. 17, 1993,

pp. 1506–1508.

[93]Sharma, P. C., and K. C. Gupta, ‘‘Analysis and Optimized Design of Single Feed Circularly Polarized Microstrip Antennas,’’ IEEE Trans. Antennas Propagation, Vol. 31, No. 6, 1983, pp. 949–955.

[94]Targonski, S. D., and D. M. Pozar, ‘‘Design of Wideband Circularly Polarized

Aperture-Coupled Microstrip Antennas,’’ IEEE Trans. Antennas Propagation, Vol. 41, No. 2, 1993, pp. 214–220.

[95]Pozar, D. M., and S. M. Duffy, ‘‘A Dual-Band Circularly Polarized Aperture-Coupled Stacked Microstrip Antenna for Global Positioning Satellite,’’ IEEE Trans. Antennas Propagation, Vol. 45, No. 11, 1997, pp. 1618–1625.

[96]Bhattacharya, A. K., and L. Shafai, ‘‘A Wider Band Microstrip Antenna for Circular Polarization,’’ IEEE Trans. Antennas Propagation, Vol. 36, No. 2, 1988, pp. 157–163.

[97]Kraft, U. R., ‘‘An Experimental Study on 2 × 2 Sequential Rotation Arrays with Circularly Polarized Microstrip Radiators,’’ IEEE Trans. Antennas Propagation, Vol. AP-45, No. 10, 1997, pp. 1459–1466.

[98]Iwasaki, H., T. Nakajima, and Y. Suzuki, ‘‘Gain Improvement of Circularly Polarized Array Antenna Using Linearly Polarized Elements,’’ IEEE Trans. Antennas Propagation, Vol. 43, No. 6, 1995, pp. 604–608.

[99]Ray, K. P., et al., ‘‘Broadband Planar Rectangular Monopole Antennas,’’ Microwave Optical Tech. Letters, Vol. 28, No. 1, 2001, pp. 55–59.

[100]Honda, S., et al., ‘‘A Disc Monopole Antenna with 1:8 Impedance BW and Omnidirectional Radiation Pattern,’’ Proc. ISAP, Sapporo, Japan, 1992, pp. 1145–1148.

[101]Hammoud, M., P. Poey, and F. Colombel, ‘‘Matching the Input Impedance of a Broadband Disc Monopole,’’ Electronics Letters, Vol. 29, February 1993, pp. 406–407.

[102]Agarwall, N. P., G. Kumar, and K. P. Ray, ‘‘Wideband Planar Monopole Antennas,’’

IEEE Trans. Antennas Propagation, Vol. 46, No. 2, 1998, pp. 294–295.

The fundamental TM10 mode implies that the field varies one l /2 cycle along the length, and there is no variation along the width of the patch. The variation of voltage V around the periphery and the current I along the length is shown in Figure 2.2(b). Along the width of the patch, the voltage is maximum and current is minimum due to the open end. It may be observed from Figure 2.2(a) that the vertical components of the electric field (E-field) at the two edges along the width are in opposite directions and hence cancel one another in the broadside direction, whereas the horizontal components are in same direction and hence combine in the broadside direction. Therefore, the edges along the width are termed as radiating edges. The fields due to the sinusoidal distribution along the length cancel in the broadside direction, and hence the edges along the length are known as nonradiating edges. The fringing fields along the width can be modeled as radiating slots as shown in Figure 2.2(c).

An RMSA operating at TM10 mode can be visualized as a transmission line, because the field is uniform along the width and varies sinusoidally along the length. The fringing fields along the edges and radiation from the slots are modeled by their equivalent capacitance and radiation resistance, respectively as shown in Figure 2.2(d).

To account for the fringing fields, instead of adding the capacitor at the edges, the dimensions around the periphery of the patch can be extended outwards. This can be explained in terms of the two parallel rectangular plates of dimensions L and W, which are separated by a dielectric substrate of thickness h . If the fringing fields along the periphery are ignored, then

However, due to the fringing capacitance (because of the fringing fields), the effective capacitance C e of the two parallel plates increases. One of the ways to account for the fringing capacitance is to extend the dimensions

The DL and DW are the extensions along the L and W, respectively. The expressions for calculating their values are given in Appendix B, which also accounts for the dispersion effect. Using these closed-form expressions, the variations of DL /h and ee with W /h for various values of er are given in Figure 2.3. For a given value of er , the values of DL /h and ee increase with an increase in W /h. These plots do not account for the dispersion effect at the higher frequencies. As the frequency increases, the electrical thickness of the substrate (i.e., h /l0 ) increases. The variations of DL /h and ee with f.h (or h /l0 ) for three values of er (2.3, 4.3, and 9.8) and a thickness of W /h (0.1, 1, and 10), obtained from expressions given in Appendix B, are plotted in Figure 2.4. The frequency is in gigahertz, and h is in millimeters. As the frequency increases, the fields are more confined to the substrate,

hence DL /h decreases and ee increases.

For RMSA, generally W >> h, so for quick analysis or design, the extension in length may be approximately calculated by the following simple formula:

where c = velocity of light in free space = 3 × 1010 cm/sec. This expression simplifies to

15

L e = (2.8) f 0 √ee

where L e is in cm and f 0 is in gigahertz. For a given length L , f 0 is calculated from