Design of Wideband Differential-Fed Filtering Antenna With End-Fire Radiation Characteristics

This brief presents a wideband differential-fed filtering antenna with end-fire radiation characteristics. The proposed differential-fed end-fire filtering antenna consists of a
$\lambda $
/4 stepped impedance slot, a dual-mode resonator, a pair of rectangular slots, a microstrip line, and a folded microstrip line. The
$\lambda $
/4 stepped impedance slot resonates at its first two odd modes and exhibits end-fire radiation under differential ports excitation. Then, the dual-mode resonator is utilized to simultaneously broaden the impedance bandwidth and improve the out-of-band frequency selectivity of the gain curve. In order to improve the front-to-back ratio of the antenna, the rectangular slots with one open end are etched at the edges of the metallic ground. Finally, the multiple coupling paths are realized from the dual-mode resonator to the
$\lambda $
/4 stepped impedance slot by adding the microstrip line and the folded microstrip line to generate two radiation nulls at the passband edges, and thus the frequency selectivity can be further enhanced. For the purpose of verification, a prototype of the proposed antenna is designed, fabricated and measured. The measured results are in good agreement with the simulated results, exhibiting an impedance bandwidth of 49.1% from 3.2 to 5.28 GHz, a flat in-band gain response with a maximum realized gain of 6.7 dBi, a front-to-back ratio over 11.5 dB within the entire operating passband. Besides, the suppression levels are higher than 18 dB and 29 dB for low and high frequency, respectively.