Dual-Polarized Low-Profile Filtering Patch Antenna Without Extra Circuit

This paper proposes a novel dual-polarized filtering patch antenna without an extra circuit. The proposed antenna shows a quasi-elliptic filtering response with four radiation nulls. One radiation null is achieved with a stacked patch, and three more radiation nulls are introduced by the split ring resonators (SRRs) placed inside the antenna aperture. The SRR can achieve one radiation null, and the shorted SRR (SSRR) can achieve two radiation nulls for its odd and even modes. This filtering antenna is fabricated on two stacked substrates with three metallic layers, which is suitable for integration. As demonstrations, two antennas are designed to meet the applications for the 5G band (4.8-5 GHz) for S11 <; -10 dB with the total profile of 0.06 λL, where λL is the free-space wavelength at the lowest operating frequency. The antenna implemented on FR4 substrate achieves an average gain of 5 dBi, while the antenna fabricated on two substrates, Rogers-4350 and FR4, can improve the realized gain to over 6 dBi. The measured isolation is better than 20 dB within the operating band. The out-of-band gain suppression level is more than 15 dB within the 3.4-3.6 GHz and more than 20 dB for WLAN band.