Cascaded Reflection-Type Group Delay Controller With a Wideband Flat Group Delay

This letter presents a wideband group delay controller (GDC) based on cascaded reflection-type phase shifters (RTPSs). Frequency tunable resonators are used as the reflective loads of each phase shifter so that the phase shifter has a variable group delay resulting in a reflection-type GDC (RTGDC). Two RTGDCs with different types of reflective loads are cascaded to compensate for their group delay variation over frequency. The first and the second stage of the cascaded RTGDC are respectively in charge of the delay in low and high-frequency bands and the cascaded delay is flat over a wide bandwidth. The proposed cascaded RTGDC operates at 3.7 GHz over 200-MHz bandwidth. The measured group delay varies from 0.67 to 2.18 ns, which is a 1.51-ns group delay variation under 9.1% normalized group delay variation over the bandwidth. The return loss is over 18 dB and the insertion loss is 2.1 \pm 1.3 dB at 3.7 GHz.