Highly anisotropic LC material with low dielectric loss for the application of tunable notch filters

ABSTRACT

We present here a compact liquid crystal (LC) based tunable notch filter with a narrow 3 dB bandwidth and a high quality factor. The structure of the proposed filter consists of two embedded resonators in serial, with an impedance adaptor and linear taper at each port. The notch filter combines tunable dielectric material LC with inverted microstrip technology, and was designed, fabricated and characterized to deliver a continuously tuned rejection frequency range from 3.545 GHz to 3.731 GHz, together with a narrow 3 dB bandwidth of ∼ 0.8 GHz and a high quality factor of ∼ 4.6. Such a notch filter is both compact (41 mm × 13 mm) and light weight (18.08 grams, including SMA connectors). It is suitable for working in the S band to suppress WiMAX signals that may cause interference in UWB communication systems. The narrow stopband and high quality factor of the device can be further improved at the expense of a certain extent of tuning efficiency, by using a thicker LC layer, and this is verified in experiment. The measured results of the proposed devices confirm the feasibility of using the current LC technology to manufacture tunable notch filters with a narrow bandwidth and a high quality factor.

KEYWORDS:

• Tunable microwave devices
• tunable notch filters
• narrow stopband
• liquid crystal materials

Acknowledgements

The authors would like to thank the UK Engineering and Physical Sciences Research Council (EPSRC) for the support through the EPSRC Center for Innovative Manufacturing in Ultra Precision (EP/I033491/1). L.C. thanks Chinese Scholarship Council and Cambridge Commonwealth, European & International Trust, and the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20180364) for financial support.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Daping Chu http://orcid.org/0000-0001-9989-6238

Additional information

Funding

The authors would like to thank the UK Engineering and Physical Sciences Research Council (EPSRC) for the support through the EPSRC Center for Innovative Manufacturing in Ultra Precision (EP/I033491/1). L.C. thanks Chinese Scholarship Council and Cambridge Commonwealth, European & International Trust for financial support.