диафрагмированные волноводные фильтры / e0f36221-c251-4001-b2a3-6b36caac86bc

Mode Matching Analysis and Design of Waveguide E-Plane Filters and Diplexers

Gregory Shimonov, Khona Garb and Raphael Kastner

Department of Electrical Engineering-Physical Electronics, Tel Aviv University, Tel Aviv 69978, Israel kast@eng.tau.ac.il

ABSTRACT: Implementations of wireless techniques call for low return and insertion losses and high slope selectivity of mm wave devices. Not many structures potentially satisfy all of the above criteria. In this work, diplexers with E-plane filters combined with an H-plane Y-junction splitter are investigated. The Y-junction configuration of the splitter is chosen based on its favorable S-parameter behavior. Filter analysis is facilitated using the mode matching technique (MMT). Based on this analysis, a band pass filter for the K band was built and tested. In order to integrate the filters with the Y-junction, the filters are positioned appropriately along the junction arms. The integrated filter-junction structure was then analyzed by an MMT code for the entire structure. An integrated diplexer model was built and tested, confirming the predicted performance based on the MMT.

INTRODUCTION

In this work, we address a diplexer comprising a splitter "J" in the form of a lossless reciprocal symmetrical three port junction connected via ports 1 and 2 to high and low band (transmit and receive) filters, as shown schematically in

Fig. 1. The power splitter junction is to be matched to the filters using the transitions lines LHigh Band and LLow Band .

Port 3

Fig. 1 Diplexer block diagram

Mode Matching Technique (MMT) codes are developed for the analysis of both junction and filters, and the results are validated using the HFSS® software. Working filters were designed and fabricated as initial examples for the design procedure. Further, an integrated MMT code fuses together the codes for the junction and filters for the efficient analysis of the entire structure. In comparison, mutli-purpose commercial software requires a much higher memory allocation. Having designed the diplexer using this code, a working model of the integrated structure has been fabricated and tested, with the test results confirming the MMT-based predictions.

Diplexer designs described in [1] – [3] are tailored to given power splitter junction configurations and use optimization techniques. Alternatively, we apply an S-parameter analysis as in [4] and require the splitter to obey certain S-parameter conditions that represent the following requirements: (1) Perfect transmission between ports 3 and 2 over the low band, (2) Perfect transmission between ports 3 and 1 over the high band. A splitter with the property

2) satisfies this condition and thus becomes our choice. MMT analysis results, based on the general formulation in [5] are shown for the reflection and transmission coefficients in Figs. 2a and 2b, respectively.

SYNTHESIS OF E-PLANE FILTERS

A ninth order (n=9) Chebyshev filter that is modeled as cascaded K-inverters [6] is shown in Fig. 3. The septum structure in the waveguide filter can be represented by a cascaded structure of posts and resonators gaps. Analysis was carried out using the MMT [7]. Based on this analysis, the filter was fabricated and tested, see Fig. 4.

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