A circularly-polarized planar array antenna using hexagonal aperture elements is proposed. A 22-element subarray as the basic unit is excited by a corporate-feed circuit located in the lower layer of the double-layered antenna. The hexagonal aperture is designed to achieve a good axial ratio in the boresight. A 1616-element array antenna with uniform element spacing smaller than the free-space wavelength was fabricated by diffusion bonding of laminated thin metal plates for the 60 GHz-band. The high gain of 33.4 dBic is measured with 91.6% antenna efficiency, including losses.

The authors propose a waveguide π-junction with an inductive post for the element of a multiple-way power divider in a single-layered slotted waveguide array. This π-junction splits part of the power into two branch waveguides through one coupling window, and can excite densely arrayed waveguides at equal phase and amplitude. The power dividing characteristics are analyzed by Galerkin's method of moments and are confirmed experimentally. Reflection from the π-junction is suppressed to the level below 30 dB over 5.4% bandwidth by attaching an inductive post.

This paper details the design of a plate that controls the beam direction in an aperture array excited by a waveguide 2-plane hybrid coupler. The beam direction can be controlled in the range of ±15-32deg. in the quasi H-plane, and ±26-54deg. in the quasi E-plane at the design frequency of 66.425GHz. Inductive irises are introduced into tapered waveguides in the plate and the reflection is suppressed by narrow apertures. A plate that has a larger tilt angle in the quasi E-plane and another plate with conventional rectangular waveguide ports as a reference are fabricated and measured. The measured values agree well with the simulation results.

A PCB-integratable metal cap slot antenna is developed for the 60-GHz band. The antenna is composed of two slots and a T-junction and is fed by a post-wall waveguide on a substrate. The dimensions of the designed antenna are 8.0×4.5×2.5mm3. The designed antenna is insensitive with a metal block behind the antenna. The designed antenna is fabricated by machining a brass block and evaluated by measurement. The measurement shows reflection less than -10.0dB, gain larger than 7.8dBi and beamwidth between 54°-65° over the 60-GHz band with endfire radiation. The antenna showed high gain together with short length of half wavelength in the radiation direction. This antenna also can be integrated with printed circuit board (PCB) and is suitable for mobile terminals such as smart phones and tablets.

The millimeter-wave band suffers strong attenuation due to rain. While calculating the link budget for a wireless system using this frequency band, the behavior of rain, attenuation due to rain, and the amount of degradation must be accurately understood. This paper presents an evaluation of the influence of rain and its attenuation on link performance in a Tokyo Institute of Technology (Tokyo Tech) millimeter-wave model mesh network. Conventional statistical analyses including cumulative rain rate distribution and specific rain attenuation constants are performed on data collected from 2009 onwards. The unique effects arising due to the highly localized behaviors of strong rainfalls have become clear and are characterized in terms of variograms rather than correlation coefficients. Spatial separation even in the small network here with links of less than 1 km provides effective diversity branches for better availability performance.

The authors proposed a switching beam slot array antenna with a 4-way Butler matrix. All are integrated in one substrate with post-wall waveguide techniques. The planar Butler matrix is realized by using short slot directional couplers (cross coupler). Experiments in 26GHz band confirmed the key operation of this antenna; almost identical four beams are switched to cover the total of horizontal 90-degree sector with equal angular spacing.

This paper presents the mode matching (MM)/finite element method (FEM) hybrid analysis for a short-slot 2-plane coupler, and an optimization process for a wideband design based on a genetic algorithm (GA). The method of the analysis combines a fast modal analysis of the MM which reduces the computation time, with the flexibility of an FEM which can be used with an arbitrary cross-section. In the analysis, the model is reduced into the one-eighth model by using the three-dimensional structural symmetry. The computed results agree well with those by the simulation and the computation time is reduced. The bandwidth is improved by the optimization based on the GA from 2.4% to 6.9% for the 2-plane hybrid coupler and from 5.4% to 7.5% for the 2-plane cross coupler. The measured results confirm the wideband design.

A new technique called the Dual Parasitic Beam (DPB) technique is proposed to suppress grating lobes in a rectangular waveguide broad wall transverse slot array. This technique involves an extra layer of parasitic strip dipoles that generate the DPB to suppress the grating lobes without opposing the main beam of the original slot linear array. A full wave EM analysis in Method of Moments (MoM) is conducted to compute the coupling excitation coefficients as well as the far field patterns of the slot and dipole currents. Analysis shows that a suitable dimension and arrangement of dipoles are needed to get a desired level of dipole excitations to meet the grating suppression condition. It is found that the grating lobes can be suppressed as much as 15 dB in the presence of the parasitic dipoles. Experiments are conducted to confirm the computed results.

A series of windows in the narrow wall of a fully-dielectric-filled rectangular waveguide to feed partially-dielectric-filled oversized-rectangular waveguide is presented. The overall structure is single-layer and 3-dimensional however; the waveguide which is uniform along the height is analyzed by the 2-dimensional method of moments and the oversized waveguide which is uniform in the longitudinal direction of the waveguide is analyzed by the 2-dimensional mode matching. It is found that utilizing simple mode conversions between the two orthogonally uniform structures is sufficient for obtaining the results similar to those of a 3-dimensional solver HFSS. The parameters for the windows designed for a uniform input division are presented. A simulation shows that a 12 window array provides a 3.5% bandwidth in terms of reflection below -20 dB. The uniform excitation of the quasi-TEM wave is confirmed in the 60 GHz band by measuring a uniform aperture field in amplitude and phase over the slotted oversized-waveguide.

Introducing diffusion bonding of laminated thin metal plates to the fabrication of slotted waveguide arrays enlightens the high potential and the feasibility of multi-layer antennas with high-performance. It is a promising process with low cost even for a double-layer antenna, because the number of etching patterns for thin metal plates is only five. In this paper, a double-layer antenna for broadband characteristics is designed in 39 GHz band as demonstration. A 20 20-element antenna is composed of 2 2 sub-arrays by installing a partially-corporate feed circuit in the bottom layer underneath radiating waveguides in the top layer. The five-element sub-arrays in both the feeding and radiating parts are designed first. A new structure for the last slot coupler with shortened termination is also proposed to avoid an extra slot-free region when assembling the neighbor sub-arrays. As the simulation results by HFSS, the maximum gain of 34.55 dBi with the antenna efficiency of 85.5% is estimated at 38.5 GHz. The test antenna is fabricated by the diffusion bonding of thin copper plates. As the measurement results, a very high aperture efficiency of 83.2% with the directivity of 34.5 dBi is realized at the center frequency of 38.75 GHz, where the antenna gain of 34.4 dBi with the high antenna efficiency of 81.4% is achieved. The bandwidth of 5.0% defined as 1 dB down from the maximum gain is achieved.

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.

A rectangular-to-radial waveguide transformer through a crossed slot is proposed as a feeder of a radial line slot antenna (RLSA) for use in a system of solar power satellite (SPS). The transformer is analyzed and designed by using the MoM with numerical eigenmode basis functions. The measured ripple of the amplitude is 3.0 dB in the φ-direction and a 7.0% frequency bandwidth for rotating mode with the ripple below 6 dB is obtained. This bandwidth is wider than that of conventional ring slot or cavity resonator with a coaxial feeder. The antenna measurements at 5.8 GHz show reasonable rotational symmetry both in the near-field distribution and the far field radiation patterns. The reflection is -27.7 dB at the design frequency and below -15 dB in the 7.0% bandwidth. The gain of the antenna with the diameter of 300 mm is 22.7 dBi and the efficiency is 56%.

The sidelobe level at tilts around 30-40 degrees in both the E and H planes due to a tapered excitation of units of 2×2 radiation slots is suppressed by introducing slit layers over a corporate-feed waveguide slot array antenna. The slit layers act as averaging the excitation of the adjacent radiating slots for sidelobe suppression in both planes. A 16×16-element array in the 70GHz band is fabricated. At the design frequency, the sidelobe levels at tilts around 30-40 degrees are suppressed from -25.4dB to -31.3dB in the E-plane and from -27.1dB to -38.9dB in the H-plane simultaneously as confirmed by measurements. They are suppressed over the desired range of 71.0-76.0GHz frequencies, compared to the conventional antenna.

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.

This study aims to propose a novel traveling-wave series-fed microstrip array antenna and its design. The proposed antenna has two features: additional slits placed on the output side of the antenna element are introduced as a new degree of freedom to control the radiation power from each element. Also, the unequal element spacing is applied to compensate passing phases of each antenna element; meander lines that would increase the insertion loss are not used. A 9-element linear array is designed and tested, and the simulated and measured results agree, thus validating the proposed design.

In this paper, a three-way divider is proposed for a partially-corporate feed in an alternating phase-fed single-layer slotted waveguide array. The divider is placed at the middle of the feed waveguide and reduces the long line effects; the frequency bandwidth is doubled. It is a kind of cross junction with one input port and three output ports; most of the power is equally divided into the right and left halves of the feed waveguide while the rest of power goes straight into the center radiating waveguide. Based upon the moment method design of the three-way divider, an inductive post is introduced for wide band power dividing control to the radiating waveguide. Reflection is below -20 dB over a wide bandwidth of 24.3-26.3 GHz, and the range of power dividing ratio ranges from 1/43 to 1/4. The amplitude and the phase from the two output ports to the feed waveguide are well balanced, and the differences are less than 0.1 dB and 5.0 degrees, respectively. The MoM analysis and the wide band design are verified experimentally in the 4 GHz band.

This paper presents the formulation for the evaluation of external coupling in the alternating-phase feed single-layer slotted waveguide array antenna with baffles by using the Spectrum of Two-Dimensional Solutions (S2DS) method. A one-dimensional slot array is extracted from the array by assuming the periodicity in transversal direction and introducing the perfect electric conductors in the external region. The uniform excitation over the finite array is synthesized iteratively to demonstrate the fast and accurate results by S2DS. A unit design model with the baffles is introduced to determine the initial parameters of the slot pair which accelerate the iteration. Experiment at 25.3 GHz demonstrates good uniformity of the aperture field distribution as well as the effects of the baffles. The directivity is 32.7 dB which corresponds to the aperture efficiency 90.5% and the reflection is below -15.0 dB over 1.3 GHz.

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.

A post-wall waveguide slot array with a three-way power divider on a single-layer substrate is designed to have a H-plane sectoral beam and an E-plane cosecant pattern with null-filling. Experiments in the 26 GHz band confirmed the sectoral beam with a -3 dB beam width of 117 deg and a ripple width of 2 dB in the sector.