Design of Wideband Microstrip Filters with Non-Equiripple Responses and Low Sensitivity

TL;DR

This paper introduces a new design method for wideband microstrip filters that achieve non-equiripple responses and low sensitivity, improving manufacturing tolerance and reducing the need for post-fabrication tuning.

Contribution

The paper proposes a novel synthesis approach for non-equiripple microstrip filters with redistributed zeros, enhancing robustness and accuracy over traditional Chebyshev designs.

Findings

Reduced sensitivity to manufacturing errors

Good agreement between measured and predicted results

Achieved wide fractional bandwidths without post-tuning

Abstract

This paper presents a novel design procedure for wideband microstrip bandpass filters with non-equiripple filtering frequency responses and low sensitivity. Different from the traditional Chebyshev transfer function filters, the return loss zeros of the proposed non-equiripple filters can be redistributed within the operating passband. For the industrial applications, the proposed filters have a reduced sensitivity to manufacturing errors and exhibit good tolerance control for both specified bandwidth and maximum in-band reflection loss. By deriving the transfer functions, a synthesis approach with a set of non-linear equations can be established according to the specifications such as the bandwidth and predetermined reflection lobes. Without performing any post optimization in the full-wave simulation, the non-equiripple synthesized results have less sensitivity and fractional bandwidth (delta) error in comparison with those obtained from traditional Chebyshev transfer functions with equiripple frequency responses. As design examples, a four-pole bandpass filter with delta=60% and a five-pole bandpass filter with delta=82.5% are designed and fabricated. Measured results show a good agreement with those obtained from the prediction, without any tuning or adjustments.