This paper proposes a dual-polarized filtering antenna with extracted-pole unit (EPU) using LTCC substrate. The EPU realizes the high skirt characteristic of the bandpass filter with transmission zeros (TZs) located near the passband without cross coupling. The filtering antenna with EPU is designed and fabricated in 28GHz band for 5G Band-n257 (26.5-29.5GHz). The measured S11 is less than -10.6dB in Band-n257, and the isolation between two ports for dual polarization is greater than 20.0dB. The measured peak antenna gain is 4.0dBi at 28.8GHz and the gain is larger than 2.5dBi in Band-n257. The frequency characteristics of the measured antenna gain shows the high skirt characteristic out of band, which are in good agreement with electromagnetic (EM)-simulated results.

This paper presents the design of low sidelobe single-layer slotted waveguide arrays. The Taylor distribution with -25 dB sidelobe level is synthesized in two orthogonal directions in the aperture. The multiple-way power divider consisting of a cascade of novel π-junctions is introduced; each π-junction, two-way power divider, is so designed as to accept unequal power dividing by adopting an offset window. The smooth Taylor distribution is realized at the output of the multiple-way power divider, which was originally developed only for uniform distribution. A model antenna for Taylor distribution is tested at 76 GHz. The measured sidelobe level is below -24 dB in both E- and H-plane. The highest gain is 34.5 dBi with 50% efficiency which is only 15% lower than that for uniform aperture illumination.

Several configurations of millimeter wave Gaussian Beam Antennas (GBAs) are studied in this paper. A GBA is a quasi-planar radiating structure comprising a plano-convex half-wavelength Fabry-Perot (FP) resonator excited by a guided source or by a printed source. Both partially transparent mirrors of the resonator are formed with two-dimensional metal meshes. GBAs have very low side lobes, because of the gaussian distribution of the aperture electric field. They can be efficiently used in Wireless Local Area Networks in the 60 GHz band. After a brief presentation of intrinsic properties of FP cavities illuminated by a plane wave under normal incidence, performances of four passive GBAs are described and compared to theoretical results: the first two configurations concern cavities fed either by a waveguide (GBA#1), or by a pyramidal horn antenna (GBA#2); in the last two ones, the cavities are excited by a linearly polarized microstrip patch antenna (GBA#3), or by a coaxial-probe circularly polarized antenna array (GBA#4). These various examples enable to deduce and to compare typical radiation performances of GBAs, depending on (i) the feeding technique (planar or guided), on (ii) the geometry of the FP resonator (radius of curvature, grid parameters) and on (iii) the polarization (linear or circular). In particular, for a planar primary source, it is shown that the directivity and the efficiency of GBAs are respectively in the range [15.5 dB-23.5 dB] and [20%-50%], if power reflectivities of both mirrors are higher than 96.5% and lower than 99.5%, and if the radius of curvature of the cavity varies between 30λ0 and 1600λ0.

A novel millimeter-wave slotted waveguide array antenna is developed for automotive radar systems. An antenna structure suitable for mass-production is proposed in this paper. The waveguide is composed of two parts; an upper plate and a bottom plate. It is not necessary to contact each other closely because they are divided at the center of the broad wall of the waveguide where the electric current is small. In addition, grating lobes are suppressed by using a cylindrical cavity around each slot and by controlling the slot arrangement without using dielectric material in the waveguide. We have fabricated the proposed antenna by metal injection molding. The measured antenna efficiency results in 55%, which is quite high in comparison with any other conventional low cost millimeter-wave antenna. This efficiency is almost the same as that of the antenna fabricated by precision metal machining. In this paper, it is confirmed that the proposed antenna could be manufactured with low cost.

In order to highlight a rapid progress attained in the field of millimeter waves in Japan, this paper describes several key topics including transistors, integrated circuits, planar antennas, millimeter wave photonics, and others.