A Filtering Antenna with Low Reflection Characteristics at Band-Edges

In this letter, an absorptive filter antenna is designed for application in the n78 frequency band. The antenna consists of two parts, a reflective filter antenna (RFA) with four filter zeros, and a band-stop filter (BSF) with a stop band containing the n78 band, where a 50-ohm absorptive load is connected to the output of the BSF. The initial design of the patch antenna itself has a low-frequency zero, a low-frequency and a high-frequency zero are created for the antenna by extending the length of the microstrip line of the feed network, and a straight section of open-circuit microstrip line is used to bring a new highfrequency filtering zero to the antenna. Finally, a metal shorting pin is used to connect the inputs of the RFA and the BSF together into a parallel form to realize an antenna that operates with a bandwidth of 14% <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(3.3 \text{GHz} \sim 3.8 \text{GHz})$</tex> within the frequency band <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3.08 \text{GHz} \sim 3.98 \text{GHz}$</tex>, with a maximum in-band gain of 8.2 dB, and with an overall antenna size of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.7 \lambda_0 \times \lambda_0 \times 0.12 \lambda_0 ( &gt;\lambda_{0}$</tex> is the center of the antenna's wavelength at the frequency), an out-of-band rejection level of more than 19.3 dB, and an AFA with high rolloff rate and out-of-band frequency signal absorption performance.