Optimization of Multi-Ports Combline Filter Using Admittance Extraction Technique

This research study proposes a new geometric dimensioning and sizing adjustment strategy of a multi-ports combline filter based on rectangular waveguide cavities and Chebyshev approximation using High Frequency Structure Simulator (HFSS) for 1.85GHz microwave bandpass applications. The optimization technique is based on introducing additional internal ports to the filter design by admittance [Y] matrix extraction in a specific way that offers the advantage to directly access each resonator’s central frequency (fc), coupling matrix (CM) coefficients and external quality factor (Qs). Extracted values allow approximating the filter specified data via simple tuning procedures. A new structure of a 4^th pole Chebyshev bandpass filter is developed to resonate at 1.82GHz and present good electromagnetic response for the whole frequency band. The developed filter design can be easily adapted to other filter prototypes due to the accurate availability of the applied optimization method that allow designing other new high performance filter topologies.

I. Introduction

Filters are important components in different systems of wireless communication especially mobile, military, remote sensing and medical ones [1]-[2]. The main challenge is to master how to implement such miniaturized devices within the reception bloc system; in fact, many factors exhibit resonance phenomena when designing such a type of filters because of the electromagnetic interaction caused by microwave and millimeter-wave ranges [3]. Waveguide technology becomes one of the accurate technologies used for developing these filters providing many advantages including low profile and manufacturing cost, flexible central frequency and bandpass adjustment, and good electromagnetic performance [4]. Filters based on such a technology are mainly performed by interconnecting different boxed cavities generally loaded with partial-height metallic posts with a specific rectangular or cylindrical geometry [5]. In addition, designing procedures resort to a cross-coupling configuration when basing on introducing additional transmission zeros.