Multi-Band Bandpass and Bandstop RF Filtering Couplers With Dynamically-Controlled Bands

This paper reports on multi-band bandpass and bandstop RF filtering four-port couplers with programmable bands in terms of center frequency and number of passbands/stopbands. They are based on four multi-resonant bandpass/bandstop-type modules that are inter-coupled by means of 90°/270°-long transmission lines. Each multi-resonant module is shaped by K in-parallel-cascaded resonators through impedance inverters. The center frequency of each band is controlled by the resonant frequency of each resonator and its bandwidth by the interconnecting impedance inverter. The proposed multi-band coupler with co-integrated spectrally adaptive filtering capability can be designed for symmetrically and asymmetrically located bands, passbands/stopbands with equal or unequal bandwidths, output signals with 0° or 180° phase difference, and equal or unequal power-division ratios at its output ports. For practical-validation purposes, microstrip prototypes of reconfigurable dual-band bandpass and bandstop filtering couplers have been designed, manufactured, and measured. They exhibit two bands that can be independently tuned in frequency and additionally merged to create a wider band within the frequency range between 1.3 and 1.8 GHz.