Tailoring Arbitrary Filter Group Delay

Lim, Jia Jie (2018) Tailoring Arbitrary Filter Group Delay. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

An ideal filter would have zero insertion loss in the passband, infinite attenuation in the stopband and flat group delay. However, such filter does not exist in practice. Conventional filters design are normally based on insertion loss methods to achieve desirable amplitude passband characteristics, however, no provision for the group delay characteristics, thus may jeopardize the signal fidelity. In order to preserve signal fidelity, these conventional filters are normally coupled with an all pass filter in a communication system. Nonetheless, the inclusion of an all pass filter will increase the system design complexity and cost. Thus, an investigation of filter synthesis based on transfer function to tailor arbitrary group delay and approximate ideal amplitude responses have been proposed in this project. Polynomial approximation techniques based on Maclaurin series expansion and least square method have been employed to compute the polynomial coefficients for an arbitrary prescribed group delay. The computed polynomial coefficients enable low pass prototype elements to be synthesized, which is essential for any filter circuits transformation such as low pass, high pass, band-pass and band-stop. In this work, a fourth order microwave band-pass filter based on micro-strip line implementation has been designed to verify the developed synthesis method. The simulated results both from full-wave and circuit simulation are in good agreement