Toshihiro Nomoto

Microwave variable delay line using dual-frequency switching-mode liquid crystal

A method was investigated to reduce the insertion loss and response time in the phase shift in a microwave variable delay line using liquid crystal (LC). In variable delay lines using conventional nematic LC, reducing the insertion loss conflicts with reducing the phase-shift response-time dependence on the thickness of the LC layer; thus, it is very difficult to simultaneously satisfy both requirements. Here, the use of dual-frequency switching-mode liquid crystal (DFSM LC) for the variable delay line is demonstrated as one approach to solving this problem. By using the characteristics of DFSM LC, in that the alignment of the LC can be controlled with a control voltage and its frequency, it becomes possible to control the LC alignment to be in an always electrically driven condition by applying a combination of control voltages of dc and several kilohertz. Experimental results of a microwave variable delay line using DFSM LC show that it is possible to reduce both the phase-shift response time and insertion loss.

A signal-to-noise enhancer using two MSSW filters and its application to noise reduction in DBS reception

This paper describes the design and development of a new type of MSW signal-to-noise enhancer which consists of a microwave circuit using two MSSW filters, one of which operates as a frequency selective power limiter. It also describes the first application of such an enhancer to DBS reception. Compared with a conventional enhancer, the threshold level and the limiting action level of this enhancer are 13 dB and 27 dB lower, respectively, and the slope from the former to the latter is much steeper. As a result, the enhancer makes it possible to achieve 20-dB lower-power operation (below +10 dBm) of periphery driving circuits. In DBS reception below the FM threshold, the enhancer improves the S/N of the video signal by 2 to 8 dB. >

Voltage-variable microwave delay line using ferroelectric liquid crystal with aligned submicron polymer fibers

This letter describes a variable microwave delay line that uses a thick ferroelectric liquid crystal film stabilized by aligned polymer fibers of submicron diameter. The delay line consists of a microstrip transmission line with a 50-μm-thick liquid crystal film as the dielectric material. The conical axis of the helical alignment of the ferroelectric liquid crystal molecules can be anchored in the microwave propagation direction by aligned polymer fibers dispersed in the liquid crystal film without conventional alignment layers coated on substrates. The phase shift of microwaves passed through the device could be varied by applying a voltage across the film to loosen the liquid crystal helical alignment.

Microwave variable delay line using a membrane impregnated with liquid crystal

A microwave variable delay line using a membrane impregnated with liquid crystal was newly fabricated. By employing this device configuration, the phase-shift response becomes fast independently of the liquid crystal thickness. Experimental results show that the phase-shift response time of 33 ms is obtained, which is two orders of magnitude faster than that of a conventional delay line. The new delay line also exhibits a 270-degree phase-shift and non-dispersive delay characteristics over a wide microwave-frequency range. Moreover, it is clarified that the phase-shift characteristics to a control voltage depend on the pore size of the membrane.