Low-Profile Filtering End-Fire Antenna Integrated With Compact Bandstop Filtering Element for High Selectivity

A high-selectivity low-profile filtering end-fire antenna is proposed using a bandstop filtering (BSF) element integrated into the feedline of the conventional quasi-Yagi antenna. Three transmission zeros (TZs) and six transmission poles (TPs) of the BSF element can be obtained through the odd–even mode equivalent circuit analysis and calculation. With the help of TP and TZ of the BSF element, an additional resonant mode within the operating band and additional radiation null at the upper band edge of the antenna can be obtained, respectively. Consequently, the impedance bandwidth and frequency selectivity of the proposed antenna can be improved compared with the conventional quasi-Yagi antenna. For demonstration, an antenna is fabricated whose measured results exhibit a stable end-fire gain response with two radiation nulls close to two sides of the operation band.