Design of dual-frequency microstrip antennas using a shorting-pin loading

There are several designs of dual-frequency microstrip antennas, such as stacked microstrip antennas, slotted microstrip patch antennas, and dual-mode (operated at TM/sub 10/ and TM/sub 01/, modes) rectangular microstrip patch antennas. These dual-frequency designs, however, show only a moderate frequency ratio (up to about 2.0) between the two operating frequencies. We present several novel designs of single-feed microstrip antennas using a shorting-pin loading technique for providing dual-frequency operation with a relatively large frequency ratio of 2.0/spl sim/4.9. Experimental results for the characteristics of such dual-frequency microstrip antennas are presented and discussed.