DR OMUX for Satellite Communications: A Complete Step-by-Step Design Procedure for the C-Band Dielectric Resonator Output Multiplexer

Abstract

Although the behavior of dielectric materials has been known since 1939 when R.D. Richtmyer showed that unmetalized dielectrics can operate as microwave resonators [1], it was only in the 1970s when real breakthroughs occurred in ceramic technology, and low loss and temperature stable ceramics were developed. In 1975 the first practical dielectric resonator (DR) loaded microwave filter was reported at the IEEE MTT-S International Microwave Symposium [2]. Significant advancements in ceramic technology and the progress in satellite and mobile communications in the 1990s revived interest in DR applications for a wide variety of microwave components. A number of new materials such as zirconium-tin titanate, ZST ((Zr ? Sn)TiO4), barium zinc tantalate, BZT (Ba(Zn,Ta)O3), and barium magnesium tantalate, BMT (Ba(Mg,Ta)O3), with high-dielectric constant, high-quality factor and low-temperature coefficient were developed [3]. These new materials, along with the application of rigorous full-wave modeling and analysis methods, fueled the development of new DR filter configurations such as single and dual mode filters with elliptic transfer function. Today, DR filters and output multiplexers (OMUXs) are widely used in satellite communications because of their superior characteristics, such as smaller size, better temperature stability, and higher unloaded Q compared to conventional cavity-based OMUXs. A number of papers have been published on DR filters and OMUXs [4]?[6], [8], [9], but no comprehensive paper on the design of a DR-based OMUX has been reported. The large interchannel interaction (due to contiguity of channel filter frequencies, performance of one channel filter is effected by the presence of other channel filters), wide spurious free frequency band, and stringent in-band and out-of-band (OOB) specifications (such as large near band and far band rejections, small passband group delay and flatness), along with the requirement of high Q, low frequency drift with temperature, and high power handling capability, make the design of DR OMUXs extremely challenging. This article presents a practical approach to the design of C-band high power OMUXs based on single mode DR filters for space application (Figures 1 and 2), making extensive use of present day simulation capabilities. All the major steps involved in the design of a DR OMUX such as the concept of a singly terminated filter, conversion of doubly terminated filters to singly terminated filters using a series L-C circuit, modeling of the DR OMUX in a circuit simulator incorporating full wave effects, and the OMUX optimization sequence are explained in detail. A successful design of the DR filter is crucial to the eventual design of the DR OMUX.