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 TM
₁₀
and TM
₁₂
modes 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 TM
₁₀
mode 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 TM
₁₀
mode (f
₁₀
) less than two times of the fundamental frequency (f
₀
). After that, the two adjacent TM
₁₀
and TM
₁₂
modes 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, f
₁₀
is progressively pushed up with a slight effect on that of TM
₁₂
mode (f
₁₂
). Then, the patch width is enlarged with the parallel slots etched out on it to move f
₁₂
closely to f
₁₀
. Moreover, a narrow slot is etched at the center of the patch for good impedance matching. With these arrangements, f
₁₀
/f
₀
can 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.