Takao Kuki

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.

60-GHz Electronically Reconfigurable Large Reflectarray Using Single-Bit Phase Shifters

A large electronically reconfigurable reflectarray antenna that has 160 × 160 reflecting elements was designed, fabricated, and evaluated so that it could be applied to a millimeter-wave imaging system operating in the 60-GHz band. To make it feasible to construct such a large reflectarray, the reflecting element structure had to be simple and easily controlled; therefore, a reflecting element consisting of a microstrip patch and a single-bit digital phase shifter using a p-i-n diode was employed. A large reflectarray antenna was fabricated using the reflecting elements. The measured radiation patterns and antenna gain were in good agreement with those that were calculated. Furthermore, the near-field beam focusing capabilities, which was required to image near-field objects, were also verified through an experiment. Finally, the response time for beamforming was measured, which was far less than the system requirements.

60-GHz electrically reconfigurable reflectarray using p-i-n diode

A 60-GHz band electrically reconfigurable reflectarray has been investigated. Each reflecting element is printed on a dielectric substrate and has a rectangular microstrip patch and a stub loaded with a single p-i-n diode. The reflection phase is changed by 180° in accordance with the on/off state of the p-i-n diode; namely, the stub works as a single-bit phase shifter. A prototype consisting of 40 × 40 elements spaced at 0.7λ was fabricated, and the reflection coefficients of the elements and the radiation patterns while the beam steering was performed were measured. Good agreement was observed between the results of the simulations and experiments.

A Composite Right/Left-Handed Rectangular Waveguide with Tilted Corrugations for Millimeter-wave Frequency Scanning Antenna

A novel structure for a composite right/left-handed (CRLH) corrugated waveguide that operates in the millimeter-wave band is proposed. The CRLH waveguide is comprised of a rectangular waveguide which has tilted corrugations on its bottom broad wall. By operating both above and below the cutoff frequency of the dominant mode, the rectangular waveguide provides, respectively, an inherent series inductance and shunt capacitance, and an inherent shunt inductance, and the tilted corrugations provide a series inductance and capacitance, which can support CRLH propagation. A frequency scanning antenna using this CRLH waveguide was also studied numerically and experimentally. The results demonstrate that the antenna can provide backward-to-forward beam scanning, including the broadside direction. A scanning angle from -9.9 to + 2.2deg was achieved within a 1.8-GHz frequency range in the 60 GHz band.

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.

Thick polymer-stabilized liquid crystal films for microwave phase control

This article describes the use of thick polymer-stabilized liquid crystal films in a new design for microwave variable phase shifters. A fine μm-order sized polymer network was formed in a 100-μm-thick liquid crystal film, using a photopolymerization-induced phase-separation method to stabilize the molecular alignment of the liquid crystal. Measurement of the electro-optic properties of the liquid crystal film revealed that the relaxation response time of the liquid crystal alignment was drastically decreased by doping the polymer at a concentration of several wt %. A new variable phase shifter composed of a microstrip transmission line (length: 193 mm, width: 200 μm) was also fabricated by using the liquid crystal film as the dielectric material. This device exhibited a microwave phase shift of −80° at a frequency of 20 GHz, when a drive voltage of 70 Vrms was applied vertically to the liquid crystal film.

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.

Active MMW Imaging System using the Frequency-Encoding Technique

Millimeter wave imaging has important applications in detecting objects concealed by optically opaque media. In this paper, a prototype active millimeter wave imaging system that uses the frequency-encoding technique is outlined. The performance of the system when imaging a human mannequin at short range is demonstrated experimentally. Further results show the effect on the image when various opaque obstacles are positioned between the imager and the mannequin.

Frequency-encoding technique for active MMW imaging

A novel method of millimetre wave active imaging at video frame rate is proposed that does not require a sensor array, using the transmitter to encode the scene as a function of frequency. Image reconstruction is performed digitally, so a large potential reduction in system complexity may be realised. We show how resolution can be improved by coherent processing, and demonstrate the technique by a simple experiment. Finally the requirements for design of the transmitter aperture are considered.

Conductor loss reduction for liquid crystal millimeter-wave beam former

Means of reducing the conductor loss of a liquid crystal millimeter-wave beam former were studied. The conductor loss is caused by surface currents flowing on electrodes of the beam former for applying control voltages to the liquid crystal layers. By making the electrode thickness comparable to or thinner than the skin depth, the surface currents that flow on both sides of the electrode in opposite directions cancel each other; consequently, the conductor loss can be reduced. Simulation results proved that doing so can effectively reduce the conductor loss.