Multifunctional Bandpass Filter With Codesigned Tunable Attenuator and Reflectionless Phase Shifter Functionalities

A multifunctional bandpass filter (BPF) with two switchable modes of operation, namely: 1) a codesigned reflectionless BPF and variable phase shifter (BPF-VP) with 360 <tex-math notation="LaTeX">∘</tex-math> phase shift and 2) a codesigned BPF and variable attenuator (BPF-VA) is reported. The multifunctional BPF can also be intrinsically switched-off when operating in the BPF-VP mode. It is based on a combination of a filtering rat-race coupler (RFRC) with continuously tunable power and a switchable phase coupling element that controls the mode of operation. Notably, the proposed component combines four different functions, namely BPF, VP, VA, and RF switch into a single component, reducing the size of the RF front-end (RFFE). As a proof-of concept, a multilayer prototype was manufactured and tested. It exhibited: 1) a third-order BPF-VP at 700 MHz with a 360 <tex-math notation="LaTeX">∘</tex-math> continuously tunable phase and a reflectionless bandwidth of 375 MHz–1.093 GHz; 2) a switching off state with <tex-math notation="LaTeX">$>$</tex-math> 25 dB of isolation; and 3) a third-order BPF-VA mode at 700 MHz with tunable attenuation between 4 and 25 dB.