Dual-frequency microstrip antennas

This paper presents the design of a dual-port microstrip patch antenna with dual-frequency operation. Two different feed mechanisms-aperture coupling and inset coplanar microstrip line-are used to excite the TM(10) and TM(01) modes, respectively on a single square patch. The frequency ratio of the proposed dual-frequency microstrip antenna can be varied by changing the inset length of the coplanar microstrip line while the peripheral dimensions of the patch are fixed. Several prototype antennas operating at frequency ratios ranging from 1.04 to 1.36 are constructed and tested. The experimental results show that the isolation level between the two input ports of the proposed dual-frequency antenna is primarily determined by its operating-frequency ratio. (c) 2005 Wiley Periodicals, Inc.