Research To The Characteristics Of Microstrip Passive Devices Using Numatic Liquid Crystal

In the wireless communication field, the devices that can obtain continuous frequency tuned are getting more and more attention. The three approaches of frequency tuned is: mechanical drives, Integrated electronic device, and tunable materials, which can obtain continuous frequency tuned. Compared with the other tunable materials, liquid crystal has the advantages of low loss, continuous frequency tunable, low bias voltage and low dielectric constant. The effective dielectric ratio of LC in the electric field performs a distribution state, which is neglected in the present literatures of LC microwave devices while be discussed in this thesis. The frequency tunable characteristics and fabrication of LC microstrip device is also studied in the thesis. The concrete contents are as follows:1)The influences of the distribution feature of the effective dielectric ratio of LC to the mode and transmission characteristics is studied by import the distribution of effective dielectric ratio of LC into the microstrip model. Simulation results indicates that the distribution feature of the effective dielectric ratio of LC reduces the reflection of the transmission line as well as the resonate frequency.2)A open circuit half wavelength transmission line resonator based on the tunable dielectric ratio of LC is designed. The resonator is designed by the simulation software of CST and resonates at the Ka wave band, 33.46 GHz in specific. The insert loss and return loss of the resonator at the inherent resonant frequency is respectively-1.56 d B,-23.5d B. The width of the frequency band which return loss below-20 d B is 370 MHz. For the effective dielectric ratio of LC turn to 3.2 from original 2.8 when been exerted a certain bias voltage. Simulation results indicates that by a various range of 0.4 in the effective dielectric ratio of LC cause the resonate frequency declines about 1.87 GHz.3)The fabrication method of LC microstrip device through experiments is implement by researching two programmes: lithography with glass substrate that is coated with a thin metal layer and printed circuit board. The fabrication of the LC microwave device is completed with the access of printed circuit board after a compare of the two programmes. The experiment test suggests that the actual device has a resonant frequency of 34.5GHz,insert loss of-6.6d B,and return loss of-15.3d B. The experiment resonant frequency differs about 1GHz from simulation result.