Synthesis of Reflection-Type Coupled Line All-Pass Circuit With Arbitrary Prescribed Wideband Flat Group Delay

In this letter, the analytical design method of a reflection-type coupled line all-pass circuit with arbitrary predefined wideband flat group delay (GD) is presented. The proposed circuit consists of 90° hybrid and coupled lines with a short-circuited load. The proposed structure is simple and does not require any iterative process to obtain optimum circuit parameters. Theoretical and experimental results are provided for validation of the proposed structure. The prototype circuits were fabricated at a center frequency of 2.5 GHz with 2 and 4 ns flat GD responses. The measurement results agreed well with the simulation and theoretical predicted results.