Improvement of technique to convert Chebyshev, Butterworth and composite low pass filter into microstrip circuit

Abstract

The aim of this thesis is to improve the technique of converting Chebyshev, Butterworth and Composite Low Pass Filter into microstrip line circuit operating at Ultra-High Frequency (UHF) band (2.5 GHz) for wireless communication system. An improved technique for transforming lumped circuit into microstrip line circuit for all high-order Chebyshev, Butterworth and Composite low pass filter is introduced. The high-order Butterworth and Chebyshev low pass filters are designed with a band pass ripple of 0.01 dB of order, n=3, 4, 5, 6, 7, 8 and 9, and implemented on FR4. The circuits are simulated and developed using Advanced Design System (ADS) without applying any optimization in order to maintain the actual response characteristic. The filters are then converted into microstrip lines using fringing compensation technique. A fringing compensation factor has been considered due to fringing in microstrip inductor and microstrip capacitor. The analytical results of lumped circuit are compared to the proposed microstrip line circuit transformed of lumped circuit. The ADS simulation results show that the response of the microstrip circuit for all types of low pass filter with fringing compensation factor have excellent agreement with its lumped circuit. Overall, the simulation results have accomplished excellent agreement with measurement results of all 3 types of microstrip low pass filters. It shows that the proposed technique achieved good agreement with the lumped circuit design. In other words, this technique is able to transform the design of high order Butterworth, Chebyshev, and Composite low pass filters into microstrip line circuit. The return loss (S11) which represents a matching response has achieved values greater than 20 dB. The results show that the insertion loss is less than 1 dB, whereby about 80% of the transmitted signal is received by the load. The achieved frequency response performance at the stopband (S21 at 2fc) is more than 40 dB. The output performance is improved as the number of order increases, and more unwanted frequency can be eliminated.