A Low-Profile Differential-Fed Patch Antenna With Bandwidth Enhancement and Sidelobe Reduction Under Operation of TM₁₀ and TM₁₂ Modes

A low-profile differential-fed microstrip patch antenna (MPA) using TM10and TM12modes is proposed in this communication toward simultaneously achieving the impedance-bandwidth enhancement and sidelobe reduction. Based on the transmission-line model, the radiation patterns of TM10mode of the MPA loaded with shorting pins and slots are at first deeply investigated. The results demonstrate that the E-plane sidelobe could be gradually reduced by lowering the resonant frequency of TM10mode (f10) less than two times of the fundamental frequency (f0). After that, the two adjacent TM10and TM12modes of the MPA are relocated to resonate in proximity to each other for bandwidth improvement and sidelobe reduction. By inserting the shorting pins underneath the radiating patch, f10is progressively pushed up with a slight effect on that of TM12mode (f12). Then, the patch width is enlarged with the parallel slots etched out on it to move f12closely to f10. Moreover, a narrow slot is etched at the center of the patch for good impedance matching. With these arrangements, f10/f0can be decreased dramatically to about 1.27. Finally, the antenna prototype is fabricated and measured. Experimental results show that the impedance bandwidth of the MPA is tremendously extended to about 10%, while keeping a low profile of 0.039 free-space wavelength. In particular, the sidelobe level of the antenna is dramatically reduced to about -12 dB.