A 2-Stage Cascaded Reflection-Type Group Delay Controller with Large Group Delay Range using Coupled-Line Transformer

This paper presents a wideband reflection-type group delay controller (RTGDC) that achieves a large group delay range and tunable center-frequency operation using a dual-varactor reflective load. Two identical RTGDC units are cascaded to obtain a wideband and flat group delay response. Each reflective load consists of an open-ended coupled line (OECL) and a series LC resonator. A varactor, connected between the coupled-line gap, controls the coupling coefficient of OECL, which determines the achievable group delay range. And another varactor tunes the resonance frequency of the series LC resonator. The proposed RTGDC achieves a 4.5-ns group delay range with less than 130-ps group delay variation. The center frequency is tunable from 3.3 to 3.9 GHz with at least a 120-MHz bandwidth. The measured return loss exceeds 15 dB, and the insertion loss is 3.2–12 dB.