Tunable Input-Quasi-Reflectionless Multiplexers

A class of frequency-tunable planar multiplexer with quasi-reflectionless behavior at its input port for modern RF wireless-communications transceivers is presented. To attain the input quasi-absorptive characteristic in a Kth-order N-channel realization, an additional Kth-order N-band multi-stopband channel terminated in a reference-impedance resistor is added. Each Kth-order stopband in this N-band bandstop channel exhibits a nearly-complementary frequency profile with regard to the one of a counterpart bandpass channel. Thus, the input-signal energy not transmitted by the bandpass channels in their stopband regions is dissipated in the resistor of the nearly-complementary multi-band bandstop branch. The theoretical operational principles and coupling-matrix-based design equations for the first-order input-quasi-reflectionless multiplexer stage are detailed. Furthermore, for experimental-validation purposes, a first-order microstrip duplexer prototype that can be tuned in the 0.85-1.15-GHz range is manufactured and characterized.