A Wideband Triple-Mode Differentially Fed Microstrip Patch Antenna

A wideband differentially fed microstrip patch antenna (MPA) with triple-resonant modes is presented in this letter. The proposed triple-mode MPA is realized by combining two dual-mode MPAs (MPA-I and MPA-II) with different resonant frequency ratios. First, the TM 0,1 mode and TM 0,1/2 mode of dual-mode MPA-I can be concurrently excited by adding a pair of coupling shorted patches beside the strip MPA. The ratio of f 0,1/2 /f 0,1 can be easily adjusted by moving the shorting pins between the strip MPA and shorted patches. Second, by properly designing the dimensions of a conventional MPA, the TM 0,1 and TM 2,1 modes of dual-mode MPA-II are simultaneously excited. To further reduce the ratio of f 2,1 /f 0,1 , four slots are elaborately etched on the conventional MPA. Finally, by combining the two dual-mode MPAs, a triple-mode MPA with the frequency ratio of f 0,1/2 :f 2,1 :f 0,1 = 1.2:1.1:1 is realized. To verify the design concept, a prototype of triple-mode MPA was fabricated and measured. Experimental results show that the proposed microstrip antenna achieves a wide bandwidth of 26.5%, a low cross polarization of -23 dB, and high harmonic suppression.