A Miniaturization Approach for Microstrip Parallel Coupled Lines Filters

Abstract

In this paper, a miniaturization approach for microstrip coupled line filters is proposed. The approach is based on designing the filter with smaller size that works at a high frequency range, and then loading the lines of the filter with identical capacitors to shift down the response and meet the desired response. Due to the challenging nature of loading capacitors with small values to a microstrip filter, this paper proposes the use of radial stubs to provide the same loading effects without altering the fabrication process and with minimum change to the filter performance. To validate the proposed method, a GHz miniaturized bandpass filter is designed and fabricated by loading the coupled lines of a GHz filter with radial stubs of carefully chosen parameters. This process shows a more than  size reduction from a similar filter designed using unloaded parallel coupled lines. The proposed approach can achieve higher rates of miniaturization by optimizing the radial stub parameters and improving the microstrip fabrication process. 

Keywords:Microstrip Parallel; Coupled Lines Filters; bandpass; signal