Microstrip filter design using FDTD and neural networks

Abstract

better than 15 dB over the same range. The simulated phase difference between the two outputs, 88.2°Ϯ 1.7°, changes from 86.6°to 89.9°within the same band. With the same software the comparison between the conventional coupler and the proposed one shows 63% area saving, 300-MHz bandwidth reduction of isolation and return loss, and 2°maximum decrease in phase difference between the two coupling arms over the same range. EXPERIMENTAL RESULTSThe coupler designed at 900 MHz in the previous section was fabricated on Duroid dielectric substrate with r ϭ 2.2 and h ϭ 0.78 mm. The simple etching microstrip process has been used. The measured performances are shown in Figure 12. The measured S 21 is 3.7 Ϯ 0.4 dB between 840 and 950 MHz (110 MHz). Over the same range, the measured S 31 is 3.1 Ϯ 0.3 dB. The measure of return loss and isolation are better than 14 dB over the same range. CONCLUSIONA new method of reducing the size of 3-dB quadrature hybrid couplers has been presented. Design equations and curves have been introduced. In order to demonstrate the advantages of the design approach two quadrature couplers at two different frequencies, 0.9 and 10 GHz, have been designed and simulated. The area saving of the fabricated hybrid, at 900 MHz, has more than 65% relative to the conventional type. The proposed method does not need lumped elements or via-hole grounding, which leads to a low-cost, simple fabrication process and excellent design accuracy. These hybrids are suitable for MICs and MMICs applications. ACKNOWLEDGMENTThe authors wish to thank Professor Esmat A. F. Abdallah, Electronics Research Institute, Egypt for her useful discussion. Dr. Samir F. Mahmoud thanks Kuwait University for providing him with a sabbatical to do this work. MICROSTRIP FILTER DESIGN USING FDTD AND NEURAL NETWORKS

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