Broadband Dual-Polarized Filtering Antenna With Wideband and Deep Out-of-Band Suppression

A wideband dual-polarized cross-slot antenna (CSA) with wideband out-of-band suppression is first presented. Then, a new bandpass filter (BPF) with wideband harmonic suppression is cascaded with the CSA to achieve further out-of-band gain suppression. By adjusting the length of the cross-slot lines to operate in half a wavelength, a radiation zero can be generated at a low frequency. To improve the upper stopband selectivity in the high frequency, four V-shaped slots are etched under the feeding lines, and four controllable radiation nulls can be introduced. Without any filtering circuits, the dual-polarized CSA realizes a wide impedance bandwidth (IMBW) of 1.60–2.95 GHz (59.34%) and out-of-band gain lower than −11.4 dBi across 3.20–9.12 GHz (up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.01f_{0}$ </tex-math></inline-formula>). Then, a broadband BPF with five controllable transmission nulls is designed and cascaded with the filtering CSA to further improve the out-of-band suppression. Finally, cascading with the harmonic-suppressed BPF, the realized gain of the antenna is below −16.8 dBi across 3.05–10.92 GHz (up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.79f_{0}$ </tex-math></inline-formula>). For demonstration, two filtering antennas are implemented. Reasonable agreement between the measured and simulated results is observed.