Novel Compact Magnetless Isolators With Quasi-Ellipic BPF Response

This brief presents a design method for magnetless isolators with quasi-elliptic bandpass filter (BPF) response using a new combination of the nonreciprocal element and the directional coupler. Different from previous works, the nonreciprocal element is connected between the through and coupling ports of the directional coupler. By controlling the phase and magnitude of the nonreciprocal element and the coupling coefficient of the coupler, two transmission zeros can be obtained without additional resonators because of two-way signal cancellation in the forward direction. The theoretical analysis of the proposed isolator unit with transmission zeros is presented and two isolators were designed and fabricated with quasi-elliptic BPF response and compact size at around 2GHz. The proposed isolator A achieves a minimum insertion loss (IL) of 1.9 dB and a 20-dB reverse isolation bandwidth of 120 MHz. The isolator B achieves a minimum IL of 4.1 dB and a 40-dB reverse isolation bandwidth of 150 MHz.