Abstract
A low-profile differential-fed microstrip patch antenna (MPA) using TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> ) less than two times of the fundamental frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ). After that, the two adjacent TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> is progressively pushed up with a slight effect on that of TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> mode (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> ). Then, the patch width is enlarged with the parallel slots etched out on it to move f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> closely to f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> . Moreover, a narrow slot is etched at the center of the patch for good impedance matching. With these arrangements, f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> /f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> 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.
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