Highly-Selective Tunable Bandpass Filter With Two-Path Mixed Coupling

This letter proposes a two-path mixed coupling tunable bandpass filter with constant bandwidth. This compact configuration can achieve little bandwidth variation in a large tuning range. Presented with the equivalent circuit of the coupling structure, the analytical formulas of the two-path mixed co...

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Bibliographic Details
Published in:IEEE microwave and wireless components letters 2014-07, Vol.24 (7), p.451-453
Main Authors: CHUAN GE, ZHU, Xiao-Wei
Format: Article
Language:English
Subjects:
Adjustable
Applied sciences
Bandpass filters
Bandwidth
Circuit properties
Circuits
Constants
Couplings
Electric, optical and optoelectronic circuits
Electronic circuits
Electronics
Exact sciences and technology
Filtering theory
Frequency filters
High selectivity
Inverters
Joining
multiple transmission zeros
Noise levels
Oscillators, resonators, synthetizers
Resonant frequency
Resonators
RLC circuits
tunable filter
Tuning
two-path mixed coupling
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Description
Summary:This letter proposes a two-path mixed coupling tunable bandpass filter with constant bandwidth. This compact configuration can achieve little bandwidth variation in a large tuning range. Presented with the equivalent circuit of the coupling structure, the analytical formulas of the two-path mixed coupling structure are derived to determine the initial dimensions of the resonator quickly. Furthermore, to enhance the selectivity and the out-of-band rejection, additional resonance circuit is introduced in the I/O structure to generate multiple adjustable transmission zeros. For verification, a tunable filter covering the frequency band of 0.78-1.35 GHz is implemented and measured. The filter has a 3 dB bandwidth variation of only 5.8% in the tuning range of 54.2%, an insertion loss of 1.68-2.9 dB and measured BW 10 dB /BW 3 dB 1.74 throughout. The experimental results are in good agreement with theory and simulations.
ISSN:1531-1309
2771-957X
1558-1764
2771-9588
DOI:10.1109/LMWC.2014.2316218