Novel X-Band Phase Shifter Using Reconfigurable Bandstop Filter

In this article, a new type of X-band phase shifter based on bandstop filter with reconfigurable transmission zeros is proposed. The phase shifter consists of 14 pairs of varactor-loaded shunt stubs. 360 degrees phase range can be achieved by simultaneously varying the capacitance values. First, we compared two different designs: simple periodic stub loading and rigorously-synthesized bandstop filter. It is shown that simple periodic loading can provide wider bandwidth, larger phase range, and smaller insertion loss. Then, we explore different characteristic impedances of the stub. The higher characteristic impedance improves phase range and insertion loss without affecting bandwidth. Finally, the length of the phase shifter is reduced by half by loading two stubs at the same junction. The proposed design is verified using ADS simulations. The proposed phase shifter can achieve an insertion loss of 1.9-2.8 dB, a frequency bandwidth of 0.65 GHz, a phase range of 393 degrees, considering the loss from varactors, substrate, and metal.