Reflectionless Filtering 90° Coupler Using Stacked Cross Coupled-Line and Loaded Cross-Stub

Abstract

In this letter, a wideband reflectionless filtering 90° coupler with a wide stopband is proposed, which consists of two parallel connected channels. The main channel is implemented by the stacked cross coupled-lines, which can not only introduce a filtering 90° coupler with a compact size but also achieve a wide-stopband response. Meanwhile, the stepped-impedance microstrip line, loaded cross-stub, and resistor are used to construct the absorptive bandstop filter in the auxiliary channel, which absorbs the reflected signal from the filtering coupler to obtain the wideband reflectionless operation. To verify the aforementioned mechanism, a wideband reflectionless filtering 90° coupler operating at 1.47–2.53 GHz is implemented and fabricated. The measured results demonstrate that the proposed coupler has the merits of low passband insertion loss, low amplitude and phase imbalances, wide stopband, and wide reflectionless range.