Design of high frequency equipment / Ahmad Asari Sulaiman and Meor Mohd Azreen Meor Hamzah

This report is an explanation to the work that have been carried out to design monolithic microwave integrated circuit (MMIC) low pass filters using circuit and electromagnetic simulators. The filters were designed to be constructed on GaAs semiconductor wafer. The principal objectives were to reduce both circuit size and spurious content. Two types of designs are proposed here. The first is a Butterworth filter made of the m-derived type which is realized using a single gold layer on the semiconductor substrate. The metal and substrate layers used in the design were optimized using the aid of the electromagnetic simulator to improve the steepness at the transition region. The filter demonstrated a maximally flat passband with a cut-off frequency of 10 GHz and passband and stopband insertion losses of 0.2 dB and greater than 20 dB respectively. The overall size of the circuit was 1.296 x 1.6 mm2, smaller than filters constructed from transmission lines designed by other workers before. The filters used standard materials compatible with MMIC technology. The second filter uses a novel metal/polyimide/metal multilayer structure consisting of buried coplanar waveguide and polyimide overlay. Two via holes were used to connect the coplanar waveguide to a transmission line at the top. The structure and the materials used are compatible with MMIC processing. Owing to the unique multilayer architecture, the filter operates well without spurious in the passband and stopband. The combination of several different materials in the structure also reduces the size. The proposed filter has a cut-off frequency of 3 GHz and an area of 1.0 x 0.7 mm2 while the stopband insertion and return losses were 20 dB and 25 dB respectively. Optimum performance was obtained when the metal and polyimide thicknesses were 5 ^m each. The filters have been simulated using electromagnetic simulator. Due to the fact that electromagnetic signals tend to radiate into space at microwave frequencies, more accurate designs were made possible using electromagnetic simulators in this work. A theoretical model to explain the new structure and design methodology are also discussed in detail in this report.