Quasi Elliptic Bandpass Filter with Defected Ground Structure for Improved Performance
Prof. Dr Mazlina Esa, N. N. N. Abd Malik, M. K. H. Ismail

Filters are widely used in the telecommunication industry in recent years. They selectively sort signals and pass through a desired range of signals while suppressing or removing others. This project presents the design of a quasi-elliptic bandpass filter (QE) that operates at 2.4 GHz employing Defected Ground Structure (DGS) slot. The objective of this project is to enhance the performance of a bandpass filter in terms of better return loss and increased bandwidth by employing DGS element in the ground plane. The chosen filter topology is based on a square open loop resonator. DGS elements of rectangular geometries have been chosen for the project. Two sets of QE filters have been designed and investigated. The first set is without DGS, while the second set is with variations of rectangular DGS slot elements. The filters are named QE and QE_R filter sets. The effects of introducing DGS slots into the filter ground plane have been successfully investigated. It is observed that the QE_R filter exhibits excellent low return loss at 2.4 GHz, and increased operating bandwidth, compared to the QE filter. The optimum configuration is chosen to be the QE_2R filter. It is observed that the QE_2R filter exhibits excellent simulated low return loss of -28.07 dB at 2.4 GHz, and the bandwidth of the filter reached to 98.39 MHz which is 19.39 MHz wider than QE filter. Its stopband responses are quite similar, ie approximately -30 dB, within the observed lower and higher bands.

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