Capacitive Tuning of High Selective T-Shaped Band-Stop Filter: Theory and Experiment

Sahu, Amit K.; Panda, Dhruba C.; Parida, Rajeev K.

doi:10.1590/2179-10742024v23i1276403

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Journal of Microwaves, Optoelectronics and Electromagnetic Applications

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Article • J. Microw. Optoelectron. Electromagn. Appl. 23 (01) • 2024 • https://doi.org/10.1590/2179-10742024v23i1276403 copy

Capacitive Tuning of High Selective T-Shaped Band-Stop Filter: Theory and Experiment

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Article

This paper develops an easy design analysis for a simple high selective T-shaped band-stop filter (BSF) loaded with a capacitance. It applies the developed design theory to obtain an appropriate capacitance value for tuning the cut-off frequency. This paper clearly explains the design mechanism for such a simple tunable BSF using ABCD matrices. Simulated filters loaded with capacitances (up to 1.1 pF) show a change in rejection frequencies from 2 GHz (un-tuned) down to 1.047 GHz with 50dB rejection and around 36% -3dB fractional bandwidth. It also shows the effect on pass frequencies which change from 1 GHz down to 111 MHz, while the separation between pass and stop frequency remains around 1 GHz. Measurements on fabricated prototypes match the simulation and theory for tunable frequencies closely. It also compares the performance of the filter with previously reported similar structures.

Index Terms
Band-stop filter; capacitive loading; T-shaped transmission line; tunable.

References	Tuning Mechanism	Rejection (dB)	Frequency Tuning Range (GHz)	Fractional Bandwidth % @ -3dB	Stop-Band Return Loss (dB)	Roll-off Factor ζ
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This Work	Varactor	>50	1.047-2.00 (63%)	36 ± 6	0.14	190

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