Design of Nonreciprocal Multifunctional Reflectionless Bandpass Filters by Using Circulators

In this brief, the method of using nonreciprocal circulator networks to construct multifunctional components is proposed. A nonreciprocal single-ended bandpass filter based on two circulators is proposed. Because the circulator has a characteristic of nonreciprocal structure, the filter has different responses in the forward and reverse signal paths. And a nonreciprocal balanced bandpass filter is also introduced. This brief shows that signal transmission states in circulator networks are different when they terminate in different loads. Therefore, when different ports are used as input ports, the nonreciprocal balanced bandpass filter can be viewed as a filter or a power divider. A nonreciprocal single-ended bandpass filter working at 3.44 GHz and 3.21 GHz and a nonreciprocal balanced bandpass filter with 3-dB bandwidth from 2.80 GHz to 3.66 GHz and $\vert{S} _{\mathrm{ ccBA}}~\vert$ below −16.74 dB are realized. When the nonreciprocal balanced bandpass filter is used as a power divider, its minimum insertion loss is 1.07 dB and the amplitude difference is only 0.15 dB at the center frequency.