Absorptive Filtering Antennas With Predictable Flat Gain and Wideband Impedance Matching

As the complexity of advanced communication systems increases, filtering antennas (FAs) have been extensively used to avoid interaction between antennas. However, there are still issues regarding its out-of-band reflection at the port, which may cause internal interference or affect system stability. To solve these problems, an absorptive FA (AFA) with both frequency selectivity and wideband matching is presented in this article. The antenna is designed by coupling an absorptive resonator to a common resonant antenna. On the basis of a microstrip-fed slot antenna, the proposed prototype is obtained by employing the short-circuited quarter-wavelength line as the microwave resonator and the quarter-wavelength sectional line as the admittance inverter. The performances are exhaustively analyzed with the equivalent circuit. Finally, a practical design with the microstrip line (MSL) structure is implemented for experimental verification. The circuit calculation, electromagnetic simulation, and measurement lead to consistent results, showing a flat gain within 1.88–2.13 GHz and a wide matching band over 1.22–2.92 GHz. The results reveal that the proposed antenna has attained a superior matching bandwidth compared to other absorptive antennas. Moreover, it is verified that one can readily determine and tailor all the geometrical parameters, by virtue of such a simple equivalent circuit, to acquire the desired performances.