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proposed antenna can maintain good symmetrical characteristic. The symmetrical radiation pattern is highly desired because the maximum direction would not shift at different frequencies. The 3-dB beamwidths at both planes are around 66 at 1.51 GHz. The co-polarizations are at least 17 dB larger than the cross-polarizations in the bore sight direction at the dual frequencies. Besides, the F/B ratios range from 19.8 dB to 21.8 dB. Larger F/B ratios indicate the backward radiations are very small, which are preferred by the unidirectional antenna. V. CONCLUSIONA novel unidirectional dual-band CP patch antenna has been presented. The dual-band CP operations are achieved by loading a pair of L-shaped stubs outside the truncated patch. Since the meandering probe feed technique is adopted, the proposed antenna inherits the wide impedance bandwidth characteristic. The measured 3-dB CP bandwidths are 3% and 4%, while the measured impedance bandwidths are 8% for the lower band and 19% for the upper band. Its peak gains are 9 dBic and 8.2 dBic for the dual bands with a low profile of 0:086. In addition, the antenna enjoys the favorable characteristics of symmetrical radiation patterns and large front-to-back ratios.

An aperture-coupled ring-antenna is presented in this communication. The antenna is fed by a microstrip line through a unique aperture configuration. The aperture contains a square slot ring with four short branch slots protruding toward the center of the ring. It is studied that axial-ratio and return-loss bandwidths of 8.7% centered at 2.53 GHz can be achieved. Within 2.42 GHz-2.64 GHz, the gains are all greater than 7 dBic.