The fifth generation (5G) system using millimeter waves is considered for application to high traffic areas with a dense population of pedestrians. In such an environment, the effects of shadowing and scattering of radio waves by human bodies (HBs) on propagation channels cannot be ignored. In this paper, we clarify based on measurement the characteristics of waves scattered by the HB for typical non-line-of-sight scenarios in street canyon environments. In these scenarios, there are street intersections with pedestrians, and the angles that are formed by the transmission point, HB, and reception point are nearly equal to 90 degrees. We use a wide-band channel sounder for the 67-GHz band with a 1-GHz bandwidth and horn antennas in the measurements. The distance parameter between antennas and the HB is changed in the measurements. Moreover, the direction of the HB is changed from 0 to 360 degrees. The evaluation results show that the radar cross section (RCS) of the HB fluctuates randomly over the range of approximately 20dB. Moreover, the distribution of the RCS of the HB is a Gaussian distribution with a mean value of -9.4dBsm and the standard deviation of 4.2dBsm.

An alignment control system using beam-tilting 1-D arrays for a 120-GHz-band corporate-feed 2-D waveguide-slot array antenna is presented. The 2-D waveguide-slot array antenna transmits data, and the 1-D arrays are used to determine array alignment. We design two types of 1-D array antenna and fabricate a corporate-feed 2-D waveguide-slot array antenna surrounded by four beam-tilting 1-D arrays. We then construct an alignment control system and evaluate the performance of the control. We find that the angular accuracy of the antenna alignment control was within ±1deg.

A compact 120-GHz-band finline orthomode transducer (OMT) with high isolation between orthogonal ports (Iop) was designed and fabricated for bidirectional wireless data transmission with polarization multiplexing. To achieve high Iop, finline OMTs normally use a resistive card to decrease unwanted resonance, that occurs on the finline, but adding a resistive card complicates the fabrication process and raises the cost of fabrication. Our proposed finline OMT uses an improved finline design in which the resonance frequency is controlled in order to expel unwanted resonance from the operation bandwidth of the 120-GHz-band wireless link. The proposed finline design enables high Iop without using a resistive card, which simplifies the fabrication process and lowers the cost of fabrication. A square horn antenna, which is attached to the finline OMT, is also designed to suppress unwanted polarization rotation of reflected waves, which further improves Iop. The proposed finline OMT has a transmission loss of less than 1.2dB, return loss of more than 12dB, cross polarization discrimination of more than 30dB, and Iop of more than 50dB across the entire occupied bandwidth of the 120-GHz-band wireless link. These characteristics are sufficient not only for 10-Gbit/s bidirectional data transmission but also for 20-Gbit/s unidirectional 2-ch data transmission by polarization-multiplexing.

This paper presents 10-Gbit/s bidirectional and 20-Gbit/s unidirectional wireless data transmission systems using 120-GHz-band finline orthomode transducers (OMTs). A new finline OMT was fabricated with two improved designs, to adapt it to the data transmission characteristics of the 120-GHz-band wireless link. One improvement is higher isolation between orthogonal ports and the other is lower group delay variation. The measured isolation is more than 59dB at the carrier frequency of the 120-GHz-band wireless link, and the measured group delay variation is 43ps. Using the finline OMT, we developed 10-Gbit/s bidirectional and 20-Gbit/s unidirectional wireless equipment that can transmit two channels of 10-Gbit/s data using polarization multiplexing. With this wireless equipment, we succeeded in 10-Gbit/s bidirectional and 20-Gbit/s unidirectional wireless data transmission, which leads to successful seamless connection to 10 Gigabit Ethernet and 12-ch high definition television signal transmission.

Though millimeter wave applications have attracted much attention in recent years, they have not yet been put to practical use. The major reason for the failure may be a large transmission loss peculiar to the short wavelength. In order to overcome the inconvenience, it may be promising to introduce the technology of millimeter-wave NRD-guide circuits. In this technology, not only NRD-guide but also Gunn diodes and Schottky diodes play the important role in high bit-rate millimeter-wave applications. A variety of practical millimeter wave wireless systems have been proposed and fabricated. Performances and applications of them are discussed in detail as well.

Owing to simple structure, low cost and high performance, NRD-guide millimeter wave circuits have attracted much attention in recent years. In this paper, a variety of NRD-guide passive components are reviewed with emphasis on design techniques and performance estimation in the 60 GHz frequency band where the license-free advantage is available. The passive components to be discussed here include compact bends, wideband hybrid couplers, practical three-port junctions, versatile E-plane filters, and effective feeding structures for lens antennas. Some of them are employed to construct millimeter wave transceivers. Eye patterns observed at 1.5 Gbps confirm the potential ability of the fabricated NRD-guide transceivers for high bit-rate, wireless applications.

We measured the complex permittivities of whole blood and blood plasma in quasi millimeter and millimeter wave bands using a coaxial probe method. The validity of these measurements was confirmed by comparing with those of a different measurement method, i.e., a dielectric tube method. It is shown that the complex permittivities of the blood samples are similar to those of water in quasi millimeter and millimeter wave bands. Furthermore, the temperature dependences of the complex permittivities of the samples were measured.

A novel structure for a frequency-independent steerable composite right/left-handed (CRLH) leaky wave (LW) antenna in the millimeter-wave band is proposed. This has the advantages of wide beam scanning and low profile, and is a suitable structure for mass-production. The proposed antenna has features wherein a movable dielectric slab is placed above the CRLH LW antenna, and the radiation angle can be steered by changing the distance between the slab and the antenna using compact actuators. Moreover, slots are added to the antenna to control the aperture amplitude distribution of the array antenna in order to enhance aperture efficiency. A prototype CRLH LW antenna has been fabricated with these slots, and backward-to-forward beam scanning characteristics at 76 GHz have been demonstrated successfully by measurement. A wide scanning angle from 73 to 114 deg. has been achieved experimentally. The aperture efficiency is 25.3%.

A planar composite right/left-handed leaky wave antenna which operates at W-band is fabricated and its backward to forward beam scanning operation including broadside direction is confirmed experimentally. The scanning angle from 61 to 114 degrees with a frequency scanning range of 76 to 79 GHz is achieved.

The transient scattering characteristics of millimeter waves from a cylindrical object near a flat boundary were measured by the 50 GHz scatterometer to evaluate the multiple interactions of scattered waves with the objects and the boundary. Both perfectly conducting and dielectric cylinders are considered as a scattering object. The pulse intensities including waves scattered first from the object and then from the flat boundary or vice versa are shown to be significantly influenced by the distance from the object to the boundary, depending on the refractive index of the object. The observed higher order responses including the multiple scattering between the object and the boundary are also discussed. A preliminary comparison of the measured and calculated pulse responses for the perfectly conducting object is presented at slightly oblique incidence on a flat boundary.

A new automatic-threshold-control (ATC) system for the amplitude-shift-keying (ASK) transceivers without using automatic gain control (AGC) was developed. When signal-to-noise ratio (SNR) in a transmission system fluctuates, the new system optimizes the threshold by statistic processing. In this paper, the schematic block diagram, the theory of statistical processing, and the performance estimated by numerical simulations are shown. The simulations show that under ideal conditions, the system can control the threshold voltage in a broad SNR region (wider than 20 dB). Delay of response and trapping in real situation can occur, but, the problems can be avoided by waveform shaping. It is thus concluded that the new ATC system can be applied to ASK transceivers.

A resonant slit-type probe is proposed in this paper that can improve measurement sensitivity in millimeter-wave scanning near-field microscopy. The probe consists of a rectangular metal waveguide incorporating the following three sections; a straight section at the tip of the probe whose height is much smaller than the operating wavelength; a standard-height waveguide section; a quarter-wave transformer section to achieve impedance-matching between the other sections. The design procedure used for the probe is presented in detail and the performance of the fabricated resonant probe is evaluated experimentally. Experiments performed at U-band frequencies in which we reconstruct 2D images show that the sensitivity of the resonant probe is improved by more than four times compared with a conventional tapered slit-type probe. Some experimental results are compared with those obtained using the finite element method (Ansoft HFSS). Good agreement is demonstrated.

Development of non-invasive techniques to measure blood sugar level is strongly required. The application of millimeter waves has a great potentiality to realize the measuring technique. Nevertheless, the practical method of the technique is not yet reported. In this paper, a new technique is proposed to measure blood sugar level using millimeter waves. The technique proposed here is very rapid and safety way to obtain blood sugar level.

A new technique for optical generation of high-purity millimeter-wave (mm-wave) signals--namely, by synthesizing the outputs from cascadingly phase-locked multiple semiconductor lasers--was developed. Firstly, a high-spectral-purity mm-wave signal was optically generated by heterodyning the outputs from two phase-locked external-cavity semiconductor lasers. The beat signal was detected by a p-i-n photodiode whose output was directly coupled to a coax-waveguide converter followed by a W-band harmonic mixer. By constructing an optical phase-locked loop (OPLL), a high-spectral-purity mm-wave signal with an electrical power of 2.3 µW was successfully generated at 110 GHz with an rms phase fluctuation of 57 mrad. Secondly, the frequency of the mm-wave signal was extended by use of three cascadingly phase-locked semiconductor lasers. This technique uses a semiconductor optical amplifier (SOA) to generate four-wave-mixing (FWM) signals as well as to amplify the input signals. When the three lasers were appropriately tuned, two pairs of FWM signals were nearly degenerated. By phase-locking the offset frequency in one of the nearly degenerated pairs, the frequency separations among the three lasers were kept at a ratio of 1:2. Thus, we successfully generated high-purity millimeter-wave optical-beat signals at frequencies at 330.566 GHz with an rms phase fluctuation of 0.38 rad. A detailed analysis of the phase fluctuations was carried out on the basis of measured power spectral densities. The possibility of extending the mm-wave frequency up to 1 THz by using four cascadingly phase-locked lasers was also discussed.

This paper presents scattering characteristics of a TE electromagnetic plane wave by a photo-induced plasma strip grating in a semiconductor slab at millimeter wave frequencies. The characteristics are analyzed by using the moment method and estimated numerically over a frequency band from 30-50 GHz. It is shown that the resonance anomaly in the grating can be controlled by changing not only the periodic light illumination pattern but also the plasma density.

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.

A Superconductor-Insulator-Superconductor (SIS) mixer using two junctions connected in parallel through a stripline inductance has been studied. The essential point of the two-junctions device is that the capacitance of the junctions was tuned out by the inductance to obtain a broadband operation without mechanical tuning elements. It has been shown by theoretical analysis that the performance of this type of device is excellent and nearly quantum-limited performance of the mixer can be obtained. It has been demonstrated that the double sideband (DSB) noise temperature of a receiver employing this type of device was less than 40 K over the bandwidth of 90-120 GHz and that the lowest receiver noise temperature of 18 K, which is only 3.2 times as large as the quantum limited photon noise was obtained around 118 GHz. Junctions used in the two-junctions device have significantly larger area, i.e. larger capacitance, and smaller normal resistance than conventional ones. In order to obtain a good impedance match between the source and the junctions, an impedance transformer made of a superconductiong stripline was integrated with the junctions. This type of two-junctions device can easily be scaled to submillimeter frequency without using submicron-sized SIS junctions.

This paper presents an experimental study on the penetration characteristics of submillimeter waves in biological tissues and material. The measured values of the penetration depth in excised natural muscle, fat, and aqueous solution of protein, bovine serum albumin (BSA), over the wavelengths of 281 through 496µm are presented. Penetration depths at these wavelengths are 0.11-0.17mm in the natural pork muscle, and 0.69-0.98mm in the natural pork fat, and are the larger at the longer wavelengths. The values vary considerably from sample to sample. Since the measurement of the penetration depth in this study is shown sufficiently reproducible, the variation of the measured penetration depth is attributed to the variation of natural tissues such as that in water content. It is found that the penetration depth of submillimeter waves in aqueous solution of BSA depends almost linearly on the amount of protein content in the solution, and that the typical values of the penetration depth in the natural muscle roughly agree with that in the 35% aqueous solution of BSA in the submillimeter-wave region.