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.

A 12×16-element corporate-feed slot array is presented. The corporate-feed circuit for the 12×16-elemtent array consists of cross-junctions and asymmetric T-junctions, whereas the conventional one is limited to arrays of 2m×2n slots by its use of symmetric T-junctions. Simulations of the 12×16-element array show a 7.6% bandwidth for reflection less than -14dB. A 31.7-dBi gain with an antenna efficiency of 82.6% is obtained at the design frequency of 61.5GHz. The 12×16-element array is fabricated by diffusion bonding of laminated thin metal plates. Measurements indicate 31.1-dBi gain with 71.9% antenna efficiency at 61.5GHz.

A 16×16-element corporate-feed waveguide slot array antenna in the 60-GHz band is designed to achieve broadband reflection and high antenna efficiency. The sub-arrays consisting of 2×2-elements are designed to improve the reflection bandwidth by implementing lower Q and triple resonance. The designed antenna is fabricated by diffusion bonding of thin copper plates. A wide reflection bandwidth with VSWR less than 2.0 is obtained over 21.5%, 13.2GHz (54.7-67.8GHz). The measured gain is 32.6dBi and the corresponding antenna efficiency is 76.5%. The broad bandwidth of more than 31.5-dBi gain is realized over 19.2%, 11.9GHz (56.1-68.0GHz). The gain in bandwidth covers the whole of the license-free 60-GHz band (57-66GHz).

As a promising lamination-loss-free fabrication technique, diffusion bonding of etched thin metal plates is used to realize double-layer waveguide slot antennas. Alternating-phase feed is adopted in this paper to reduce the number of laminated plates to simplify fabrication as well as to reduce cost. A 20 × 20-element double-layer waveguide slot antenna with a bottom partially-corporate feed circuit is designed for 39GHz band operation as an example. The adjacent radiating waveguides as well as the 2 × 2 sub-arrays fed in an alternating-phase manner eliminate the need for complete electrical contact in the top layer. However, the feed circuit in the bottom layer has to be completely diffusion-bonded. These two layers are simply assembled by screws. An antenna laminated by only diffusion bonding is also fabricated and evaluated for comparison. The comparison proved that the simply fabricated antenna is comparable in performance to the fully diffusion-bonded one.

A point-to-point fixed wireless access (FWA) system with a maximum throughput of 1Gbps has been developed in the 39GHz band. A double-layer plate-laminated waveguide slot array antenna is successfully realized with specific considerations of practical application. The antenna is designed so as to hold the VSWR under 1.5. The antenna input as well as feeding network is configured to reduce the antenna profile as well as the antenna weight. In addition, integrating the antenna into a wireless terminal is taken into account. A shielding wall, whose effectiveness is experimentally demonstrated, is set in the middle of the wireless terminal to achieve the spatial isolation of more than 65dB between two antennas on the H-plane. 30 test antennas are fabricated by diffusion bonding of thin metal plates, to investigate the tolerance and mass-productivity of this process. An aluminum antenna, which has the advantages of light weight and anti-aging, is also fabricated and evaluated with an eye to the future.

A novel design technique for two-dimensional (2-D) waveguide slot arrays is proposed in this paper that combines a full-wave method of moments (MoM) analysis and an equivalent circuit with the explicit restraint of input matching. The admittance and slot spacing are determined first in an equivalent circuit to realize the desired distribution of power dissipation and phase, with the explicit restraint of input matching. Secondly by applying a full-wave MoM analysis to the finite 2-D array, slot parameters are iteratively determined to realize the active admittance designed above where slot mutual coupling and wall thickness are fully taken into account. The admittance, treated as the key parameter in the equivalent circuit corresponds to the power dissipation of the slots but not to the slot voltage, which is directly synthesized from the radiation pattern. The initial value of the power dissipation is assumed to be proportional to the square of the amplitude of the desired slot voltage. This assumption leads to a feedback procedure, because the resultant slot voltage distribution generally differs from the desired ones due to the effect of non-uniformity in the characteristic impedance on slot apertures. This slot voltage error is used to renew the initial distribution of power dissipation in the equivalent circuit. Generally, only one feedback cycle is needed. Two 2427-element arrays with uniform and Taylor distributions were designed and fabricated at 25.3 GHz. The measured overall reflections for both antennas were suppressed below -18 dB over the 24.3-26.3 GHz frequency range. High aperture efficiencies of 86.8% and 55.1% were realized for the antennas with uniform and Taylor distributions, the latter of which has very low sidelobes below -33 dB in both the E- and H-planes.