A Wideband Differential-Fed Dual-Polarized Microstrip Antenna Under Radiation of Dual Improved Odd-Order Resonant Modes

A low profile differential-fed dual-polarized microstrip patch antenna (MPA) with bandwidth enhancement is proposed under radiation of the first and second odd-order resonant modes. First, all of evenorder modes are fully suppressed by using a differentially feeding scheme instead of the single probe feed. Next, the radiation pattern of a square MPA is theoretically analyzed. It is demonstrated that the traditional monopole-like radiation of the second odd-order mode in the H-plane, i.e., TM21 mode, can be transformed into the broadside radiation by etching out a narrow slot at the center of the radiating patch. After that, an array of shorting pins is symmetrically embedded underneath the radiating patch so as to progressively push up the resonant frequency of the TM01 mode ( or TM10 mode), while almost maintaining that of TM21 mode ( or TM12 mode) to be unchanged. With these arrangements, a wide impedance bandwidth with stable radiation peak in the broadside direction is achieved for the MPA under this dual modes operation. Finally, the dual-polarized MPA is fabricated and measured. The measured results are found in good agreement with the simulated ones in terms of the reflection coefficient, radiation pattern, and realized gain, demonstrating that the MPA's impedance bandwidth (vertical bar S-dd11 vertical bar < -10 dB) is tremendously increased up to about 8% with a high differential port-to-port isolation of better than 22.6 dB. In particular, a low profile property of about 0.024 free-space wavelength and the stable radiation pattern are also achieved.