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Title: Liquid crystal measurements and devices at milimetre-wave frequencies
Author: Yazdanpanahi, Mani
ISNI:       0000 0004 2741 836X
Awarding Body: University of Essex
Current Institution: University of Essex
Date of Award: 2012
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The work presented here provides a comprehensive coverage in the development of an emerging breed of tuneable filters in the millimetre- wave range. It involves the application of nematic liquid crystal (LC) material as substrate to the device. The first focus of the research is accurate characterisation of LC in order to obtain its dielectric properties at millimetre-wave frequencies. Based on the findings, new tuneable filter designs are presented in this thesis. In this thesis, a planar patch resonator is developed to measure the dielectric constants of nematic LC at millimetre-wave frequencies. The resonator is excited using microstrip lines fed by 50D coplanar waveguides (CPWs) which allows for on-wafer measurements. The characterisation technique is achieved using a resonator operating at 40GHz. The switching of the LC molecules is performed using an external electric field by the direct application of a bias voltage. Ac- curate measurements for E~ and Ell are attained for a particular LC mixture, E7. A second resonator is established, operating in the 30 - 60GHz frequency band. Therefore, precise measurements of LC in the millimetre-wave range (up to 60 GHz) indicate a maximum tuning range of 3.58GHz. The first LC based filter presented in this thesis is the third order tuneable parallel-coup led-line bandpass filter. It has three poles with a centre frequency of 33GHz. The bandwidth of the filter is around 3.5GHz and is fixed over the tuning range. The tuneability range is 2GHz achieved for bias volt ages of OV and 10V. The biasing is directly applied to the individual resonators within the filter structure. A detailed investigation on coupled-line resonators based on LC is also provided. The insertion loss of the filter is about 4.5dB, attributed to the microstrip line to CPW transitions used for measurement of the filter by a probe-station. The second tuneable LC bandpass filter is realised using a microstrip line periodical structure and is presented for applications at millimeter- wave frequencies. The filter is designed to operate at a centre fre- quency of 49GHz and has about 20% fractional bandwidth (FBW) (9GHz). A tuneability range of 3.2GHz is achieved over bias volt ages OV to 10V as applied to the LC substrate. The insertion loss of the filter is about 4.7dB, which is comparable or better than the inser- tion losses of tuneable filters based on the semiconductor or MEMS technology, currently available. The dimensions of the filter can be scaled down in order to operate it at the 60GHz band covering vari- ous bandwidth standards for applications in different countries under voltage control.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available