IntroductionUniversiti Teknologi Malaysia (UTM) is one of the 26 public universities in Malaysia. It started as a technical school over a century ago. The research on microwave filters in UTM only started in 1999. The Malaysian government has allocated several types of research funds for researchers in the academic, industrial and research institutions. The research on microwave filters in UTM began by developing a computer aided educational filter environment that is suitable for undergraduate laboratory experiments. Mathematical problems were solved using MathCAD mathematical software [1] and the filter configurations were simulated using several simulation software packages. Many final year undergraduates had the opportunities to work on different filter configurations. Some of them worked on simple modifications of designs available in the literature and investigated their frequency response performances. Several master's degree students were also involved, with higher level research investigations. The research on microwave filters progressed with that of antenna designs that are made of normal metals, superconductors and new materials. A doctoral student is currently completing a thesis that focus on parallel-coupled filters.This paper describes four microwave filter configurations that have been recently developed over the past five years. These are a direct coupled cavity waveguide filter [2], an internallycoupled hairpin-line filter [3], a meander-gap hairpin line filter [4] and a three-element parallel-coupled filter [5].
Direct-Coupled Cavity Waveguide, C_DWB, FilterAn interactive mathematical package that is able to present the performance of the designed direct-coupled cavity waveguide filters of optimum and varying filter orders was developed. A design was aimed for 3.902 GHz VSAT operation. The filter is a robust structure and able to handle high power well. The VSAT communication system is a transportable unit. The antenna consists of a gyrostabilized and motorized C-Band antenna system with radome. The developed mathematical design file consists of formulae related to the derivation of the internal vertical inductive posts physical dimensions such as in [6]. The computations include determining the optimum number of the filter order and the displaying of frequency responses. Good agreement achieved between theory and simulations showed that the simulation software used has verified the theory. The introduction part of the math file is given in Fig. 1. For a 7 order filter, the math and simulated performances are shown in Fig. 2.
Internally-Coupled Hairpin-Line, ICHL, FilterAn internally-coupled hairpin-line bandpass filter based on resonator elements was designed [7]. Investigations on the optimum resonator were first carried out. The final configuration of a 3-element filter is shown in Fig. 3. Parametric investigations were performed using em simulations. The parameters that affect the filter performances were identified. It was found that the design dimensions can be optimized for desired spec...
