volume | PIER Journals

2020-02-02

T-Shaped I/O Feed Based Differential Bandpass Filter with Symmetrical Transmission Zeros and High Common Mode Rejection Ratio

Rida Gadhafi,

Dr. Rida Gadhafi

Khalifa University, Masdar Institute

United Arab Emirates

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Dan Cracan,

Dr. Dan Cracan

Khalifa University, Masdar Institute

United Arab Emirates

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Ademola Akeem Mustapha,

Dr. Ademola Akeem Mustapha

Khalifa University, Masdar Institute

United Arab Emirates

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Mihai Sanduleanu

Dr. Mihai Sanduleanu

Khalifa University, Masdar Institute

United Arab Emirates

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Progress In Electromagnetics Research M, Vol. 89, 141-149, 2020

doi:10.2528/PIERM19111804

Abstract

A T-shaped feed based differential microstrip bandpass filter (BPF) with high common-mode (CM) rejection ratio is presented. The filter comprises two magnetically coupled conventional square open-loop resonators (SOLR), with capacitive coupled T-shaped input-output (I/O). The choice of the T-shaped I/O coupling feed enables a higher common-mode suppression of -57 dB at f₀^d that extends up to 4.1f₀^d with a value better than -30 dB. Frequency f₀^d is the cutoff frequency of the differential-mode (DM) passband. Moreover, this feed can symmetrically position two transmission zeros (TZs) at the upper and lower stopbands. This yields a highly selective and compact filter. Additionally, a T-shaped feed only excites the odd mode of the filter resulting in a wide stopband with high out of band rejection. The upper and stopband rejection of the filter is better than -50 dB. To demonstrate the design, DM and CM lumped models of the filter are proposed and studied. The filter operates at 1.263 GHz with a fractional bandwidth (FBW) of 3.9%. The design is validated experimentally by characterizing DM, CM, common-mode to differential-mode (CD), and differential-mode to common mode (DC). Moreover, the group delay (GD) response of the filter is measured, and a significantly flat response is observed with a maximum delay variation of only 0.88 ns in the 3 dB bandwidth.

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Rida Gadhafi, Dan Cracan, Ademola Akeem Mustapha, and Mihai Sanduleanu, "T-Shaped I/O Feed Based Differential Bandpass Filter with Symmetrical Transmission Zeros and High Common Mode Rejection Ratio," Progress In Electromagnetics Research M, Vol. 89, 141-149, 2020.
doi:10.2528/PIERM19111804

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