We design and fabricate a double-layer hollow-waveguide slot array antenna with wide bandwidth and high antenna efficiency for the 120 GHz band. The antenna is fabricated by diffusion bonding of laminated thin metal plates for high precision and perfect electrical contact. The 1616-element antenna shows more than 70% antenna efficiency over a 13 GHz bandwidth. Furthermore, it realizes error-free data transmission in 2.5 m distance at up to 10 Gbit/s. To our knowledge, this is the first report of the design and fabrication of a high-efficiency wideband planar antenna for the 120 GHz band.

The authors have proposed a 1 m2 single-layer slotted waveguide array consisting of conducting baffles and quartz glass strips positioned in front of the slot aperture, which is referred to as a vacuum window, for microwave plasma excitation. The effect of the complicated outer vacuum window hinders the realization of uniform distribution. In this paper, a unit-cell of the alternating-phase fed single-layer slotted waveguide array with the vacuum window is analyzed by generalized scattering matrix method (GSM)-method of moments (MoM) hybridization analysis, and the array is designed to realize uniform aperture electromagnetic field distribution, where the plasma and the chamber is neglected. The GSM-MoM analysis gives reliable numerical results while the MoM has numerical errors due to singularities of Green's function for a long cavity. Uniform aperture EM field distribution outside of the vacuum window is observed in near field measurements using a 1/5 scale model antenna, and the validity of the analysis and design is verified.

The characteristics of circular polarization from a slot with a parasitic dipole are investigated analytically. It is derived that its phase is linearly dependent upon the angle of the dipole and is independent of that of slot. This interesting behavior is also confirmed by experiments.

Post-wall waveguide slot arrays are potential candidates for millimeter-wave systems. The modeling of the post-walls by the equivalent solid-walls in terms of guided wavelength is indispensable for intensive optimization of slot design for reducing computational load. In the single mode waveguide slot arrays, the modeling errors of the post-wall waveguide by the solid-wall waveguide are serious especially for the transversely located slots. The S-parameter prediction errors become larger as we increase the height of the waveguide to utilize the low-loss advantage of the waveguide. The authors propose a novel post-wall waveguide structure, named as a connected post-wall (C-PW), to enhance the equivalence. The C-PW waveguide keeps enhanced equivalence to the solid-walls even for a larger substrate height. The predictions are confirmed by simulations and measurements. An 8-element linear array of reflection-cancelling slot pairs is designed by using the equivalent solid-wall model to demonstrate the feasibility of the simple design in the C-PW.

This paper presents an antenna for the UHF-TV reception consisting of skeleton slot array installed on a reflector. We propose a dipole model of the skeleton-slot elements to calculate its radiation pattern. The prototype antenna has 13 dBi antenna gain, 30% frequency band width and a function of beam tilting, which are sufficient characteristics for the UHF-TV reception.

Light weight RLSAs with a honeycomb-type parallel plate are promising candidates for satellite antennas. However, the design of slot lengths and positions in honeycomb RLSAs consisting of a core, skin and adhesive layers involves time-consuming EM analysis. In this paper, an equivalent double layer model is devised for fast slot coupling analysis by the Method of moments (MoM) together with a simplified array design procedure. A fabricated antenna with a diameter of 900mm demonstrates the high directivity of 48.3dBi and a gain of 44.6dBi at 32GHz, with the reflection below -15dB. This antenna weighs only 1.16kg.

A radial line slot antenna (RLSA) is a high efficiency and high gain planar antenna. The efficiency of RLSA becomes lower as the aperture size reduces due to rotational asymmetry of the illumination. A concentric array RLSA (CA-RLSA) was proposed to overcome this difficulty. It adopted three new techniques; (1) not spirally but concentrically arrayed slots, (2) a rotating mode feed circuit, (3) matching slot pairs eliminating termination loss. This paper proposes the basic slot design for (1) and (2) of CA-RLSA. Excellent characteristics of very small CA-RLSAs based upon this design are confirmed by measurements.

Honeycomb structures are widely used in aerospace industry because of the lightweight and durable properties they provide. Here we propose to use a honeycomb core as the wave guiding structure in Radial Line Slot Antennas (RLSAs). This paper quantifies the propagation characteristics, especially the loss due to the honeycomb. At 32GHz, by choosing the proper cell size, both good isotropy and reasonably low effective dielectric constants are realized with the honeycomb as a spacer in a radial line waveguide. To estimate the material loss factor, several methods are compared and a factor of about 0.014∼0.018dB/mm is predicted and measured. A fabricated 90cm diameter honeycomb RLSA suffers about a 3.5∼5dB loss, which coincides with the estimates using the predicted loss factor.

This paper describes the characteristics of a one dimensional narrow-wall slotted waveguide array with a single-layer linear-to-circular polarization converter consisting of a dipole array. An external boundary value problem of one slot and three dipoles, which approximates the mutual coupling between the dipole array and an edge slot extending over three faces of a rectangular waveguide, is formulated and analyzed by the method of moments; design of polarization conversion is conducted for this model as a unit element. If every unit element has perfect circular polarization, grating lobes appear in the array pattern due to the alternating slot angle: these are suppressed in this paper by changing the dipole angle and degrading the axial ratio of the unit element. The validity of the design is confirmed by the measurements. The dipole array has negligible effects upon slot impedance; the polarization conversion for existing narrow-wall slotted arrays is realized by add-on dipole array.

This paper presents a measurement method for determining effective conductivity of copper-clad dielectric laminate substrates in the millimeter-wave region. The conductivity is indirectly evaluated from measured resonant frequencies and unloaded Q values of a number of Whispering Gallery modes excited in a circular disk sample, which consists of a copper-clad dielectric substrate with a large diameter of 20-30 wavelengths. We can, therefore, obtain easily the frequency dependence of the effective conductivity of the sample under test in a wide range of frequency at once. Almost identical conductivity is predicted for two kinds of WG resonators (the copper-clad type and the sandwich type) with different field distribution; it is self-consistent and provides the important foundation for the method if not for the alternative method at this moment. We measure three kinds of copper foils in 55-65 GHz band, where the conductivity of electrodeposited copper foil is smaller than that of rolled copper foil and shiny-both-sides copper foil. The measured conductivity for the electrodeposited copper foil decreases with an increase in the frequency. The transmission losses measured for microstrip lines which are fabricated from these substrates are accurately predicted with the conductivity evaluated by this method.

Two-dimensional diffracted fields from semiinfinite conducting plane with a circular cylinder of various types at its apex are studied for the purpose of suppressing the backward radiations from the reflector antennas. The basic policy for the suppression of the diffracted fields was already obtained by the authors. It concludes that the electrically and magnetically conducting cylinders are most effective in suppressing the diffraction for the E and H wave incidence, respectively. From the practical point of view, the main difficulty in this policy is how to realize the magnetically conducting cylinder which suppresses the H wave diffraction. In this paper, a corrugated cylinder is adopted for the purpose of the suppression of the H wave diffraction. The characteristics of this cylinder are analyzed by the mode-matching techniques and it is indicated that the corrugated cylinder fairly suppresses the diffracted fields, not only for the H wave but also for the E wave incidence, to almost the optimal level. Additionally, the wideband frequency characteristics are introduced. All these theoretical results are confirmed by the equivalent two-dimensional experiments. At the end of this paper, the applicability of the corrugated cylinder to the suppression of the three-dimensional diffracted fields is suggested experimentally.