Broadband Filtering Antenna With Asymmetric Feeding Structure

A compact highly selective broadband filter antenna with an asymmetric feed structure is proposed. The radiating patch of the antenna unit consists of a central elliptical patch and a pair of semi-annular patches, and the antenna forms multiple coupling paths from the feed ports to the radiating patches to generate a radiation null (6.28 GHz), which achieves the roll-off rate of 193 dB/GHz. The innovation of this design is that asymmetric L-shaped branches of about half a wavelength are added on both sides of the microstrip feedline of the antenna to expand the operating bandwidth and generate a low-frequency radiation null (4.66 GHz), which achieves the roll-off rates of 164 dB/GHz. The simulated results show that impedance bandwidth is 23.8% (4.77–6.06 GHz) with the peak gain of 5.86 dBi, which size is 0.5λ₀ × 0.5λ₀× 0.09λ₀. Then, a 2 × 2 filtered antenna array is designed for experimental validation. The test results indicate that the impedance bandwidth of the antenna array is 21.5% (4.45–5.52 GHz), the in-band gain is greater than 10 dBi and flat, and the out-of-band rejection level is greater than 20 dB. Attributed to the characteristics of easy and inexpensive manufacturing, the designed antenna has well application prospects in modern wireless communication systems.