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In the first half of this paper, an efficient method to calculate transmission and reflection characteristics of wire-grids consisting of periodic arrays of cylindrical conductors for arbitrary directions of incidence is presented by extending exact theory of wire-grids proposed by Yasumoto et al. In the latter half of this paper, an approximate calculation method for wire-grids with slight random irregularity in their spacings between wires is proposed by treating the irregularity as a small perturbation to the theory for regular grids. A comparison with preliminary measurements for actual wire-grids in millimeter- and submillimeter-wave regions demonstrated that this method is effectively applicable to wire-grids whose irregularity is not too much. Index Terms--Electromagnetic reflection, electromagnetic scattering by periodic structures, submillimeter wave devices, submillimeter wave measurements, wire grids. more...

This paper presents a new configuration of quasi-optical polarization-rotating dual-beam interferometer, which uses a pair of frequency-selective polarizers (FSPs) consisting of a wire-grid placed in front of a flat mirror, and has a function similar to the conventional Martin-Puplett interferometer (MPI). Advantages of this new configuration over the conventional MPI are lower residual reflection at the input and output ports and suitability to fixed-tuned applications. An experiment has shown it to have an MPI-like frequency characteristic as calculated. Careful machining was successful in achieving accuracy needed for a specified filter characteristic. This FSP-based quasi-optical device is to be used as a sideband separator in a space-borne submillimeter receiver for atmospheric research. Index Terms--Martin-Puplett interferometers (MPIs), polarization-rotating dual-beam interferometers, quasi-optical filters, sideband separators. more...

The complex refractive index of concrete is measured at 57.5 GHz by the combined use of free-space reflection and transmission methods. The measured refractive index of the concrete 14 months after concreting was 2.55 - j0.084. This index, in particular the imaginary part, is sensitive to the curing time after concreting and the water content. The transmission coefficient of a concrete plate, mainly determined from the imaginary part of the complex refractive index, is less than -20 dB/cm when the concrete is fresh and moist and reaches -9 dB/cm after aging for fourteen months. In contrast, the reflection coefficient of a concrete plate is less dependent on water content. more...

A switchable multi-sector antenna for indoor wireless local-area network (LAN) systems in the 60-GHz band has been proposed. The antenna has a pyramidal configuration. Each isosceles-triangular surface of the pyramid has been inclined 30[degrees] from the vertical axis in order to cover an appropriate elevation angle range. This antenna excites a right-handed circularly polarized wave to suppress unwanted multipath delayed waves. The low-loss curved microstrip-line feeding has been introduced at the junction between antenna feed lines and monolithic microwave integrated circuit (MMIC) amplifiers at the bottoms of the pyramid. Using this antenna, the terminal receiver for indoor wireless LAN systems in the 60-GHz band has been developed. Index Terms - Curved micro, trip lines, millimeter-wave LAN's, multi-sector antenna, patch antennas. more...