Abstract
A low-profile microstrip antenna that has a broad impedance bandwidth by exciting three resonant modes is proposed. The proposed antenna mainly consists of a grid-slotted radiation patch, a metal ground, four vertical metal strips, and a vertical grounded balun feeding structure. The TM10, TM12, and antiphase TM22 modes are excited simultaneously. The vertical grounded balun feeding structure is used to avoid etching slot on the metal ground to get a high front-to-back ratio. The four vertical metal strips are introduced to enhance the impedance matching and reduce the sidelobe of the radiation pattern of the antiphase TM22 mode. With a profile of 0.07 λ 0 ( λ 0 is the center operating wavelength in the free space), the measured −15 dB impedance operating band is 3.31–4.31 GHz, and the relative bandwidth is 26.2%. The measured front-to-back ratio is larger than 16 dB, and the sidelobe level is lower than −10 dB. The proposed antenna has a stable broadside radiation performance in the operating band.
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