Single-Layer Wideband and Dual-Band Endfire Filtering Antennas With High Front-to-Back Ratio

In this letter, the single-layer wideband and dual-band endfire filtering antennas with high front-to-back ratio (FTBR) are developed. The wideband design mainly consists of five parts: the double-sided parallel-strip line (DSPSL) feeding structure, two sets of driven elements, the parasitic strips, the directors, and the U-shaped ground. Herein, the adoption of two sets of driven elements realizes a natural lower radiation null, while the incorporation of parasitic strips facilitates an upper radiation null. The dual-band design is achieved by simply loading the additional longer parasitic strips onto the wideband design, which creates a middle radiation null between the two bands. Including the elaborated ground and the directors effectively enhances the FTBR of both designs. For verification, prototypes were manufactured and measured, and the measured results are in good agreement with the simulated ones. The overlapped bandwidth (|<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub>| ≤ −10 dB and FTBR ≥ 15 dB) of the wideband design reaches 54.3%, and that of the dual-band design is 33.6% and 15.5%, respectively. Moreover, both designs exhibit good frequency selectivity with multiple radiation nulls.