Nonreciprocal filtering power dividers

Abstract

We propose the concept of nonreciprocal filtering power dividers, which are compact devices able to merge the functionalities of power dividers and combiners, the selectivity of bandpass filters, and magnetless nonreciprocity from time-modulation. A prototype of this type of devices operating at microwaves has been implemented in microstrip technology. The device is composed of a Wilkinson power divider integrated with two identical microstrip filters based on quarter-wavelength coupled lines. The resonators of the filters are terminated with varactors that are time-modulated using low-frequency harmonic signals from a Coplanar Waveguide (CPW) feeding network printed on the ground plane of the microstrip structure. The resulting compact device behaves as a nonreciprocal power divider, nonreciprocal power combiner, or a common filtering power divider depending on the modulation parameters. In addition, it exhibits electrical frequency reconfigurability (over 15%), high rejection out of the passband, and enhanced isolation among the ports. A manufactured prototype shows relative fractional bandwidth of 3.1% measured at a return loss level of 11 dB, and insertion losses of 5.9 dB, together with a nonreciprocal response with over 21 dB of directivity at the center frequency.