Arbitrary Prescribed Wideband Flat Group Delay Higher-Order Quasi-Reflectionless Bandpass Filter

This paper presents a design of quasi-reflectionless bandpass filter (BPF) with arbitrary prescribed wideband flat group delay (GD). The proposed circuit consists of λ/4 series short-circuited coupled lines and shunt coupled line terminated with transmission line and resistor. Analytical design equations are derived based on GD analysis. The proposed quasi-reflectionless BPF can be further extended to higher-order by cascading first-order quasi-reflectionless BPFs. For proof of concept, first and second-order quasi-reflectionless BPFs with GD of 1 ns and 2 ns are designed and fabricated at a center frequency of 3.5 GHz. The measurement results are well agreed with the simulations.