Design of cascaded all pass network with monotonous group delay response for broadband radio frequency applications

Abstract

In this study, an iterative procedure is developed for designing radio frequency circuits with a specified group delay dispersion (GDD) characteristics over a broad bandwidth. Second order all pass networks (APNs) are cascaded systematically over multiple stages to achieve the same. The approach is flexible enough to design circuits for various group delay responses. This is demonstrated using two-stage APN with both positive and negative slopes of linear and non-linear group delay responses for a frequency band of 500 MHz-1 GHz. The proposed multi-stage design procedure is shown to help extend the bandwidth over which a uniform resolution of frequency discrimination is possible. Practical limitations in implementing this circuit are addressed while developing the prototype. The circuit is realised as a surface mount device-based implementation of modified two-stage APN. The realised circuit has a GDD of -6 ns/GHz and an insertion loss of 1.2 dB for 500 MHz-1 GHz band. The performance parameters such as GDD, insertion loss and device footprint of the proposed approach are significantly better than previously reported.