Wideband Reflectionless Antipodal Tapered Slot Filtenna With High Out-of-Band Absorption Ratio

An antipodal tapered slot antenna (ATSA) with wideband reflectionless filtering characteristic is proposed in this work. The ATSA incorporates a wideband absorptive bandpass filtering network, which consists of a parallel coupled line (CL), a stepped impedance open stub (SIOS), and a resistively terminated T-shaped bandstop filter. This network is designed using the frequency complementary diplexing concept, where in-band input energy is selected by the CL and SIOS and radiated by the ATSA; out-of-band energy is dissipated on the resistor through the bandstop filter. The SIOS also enhances out-of-band absorption and suppression by introducing additional gain nulls. A prototype was fabricated and measured, yielding a 3 dB gain bandwidth from 3.2 to 6.8 GHz and a wide impedance bandwidth from dc to 11.8 GHz with an out-of-band absorptive ratio greater than 80%. In addition, the realized gain exhibits a sharp bandpass radiation characteristic with measured out-of-band suppression higher than 25 dB in the lower stopband and 16 dB in the upper stopband.