The Doppler velocity enhanced 79 GHz band millimeter wave (MMW) radar imaging approach is presented here, assuming a human body imaging or recognition application. There are numerous situations in which the spatial resolution is insufficient, due to aperture angle limitations, especially for vehicle mounted MMW radar systems. As the 79 GHz band MMW radar has a definitive advantage for higher Doppler velocity resolution even with a short coherent processing interval (CPI), this study introduces the Doppler velocity decomposed imaging scheme, focusing on micro-Doppler variations of the walking human model. The real experimental data show that our proposed approach provides further improvement for accurate and high resolution radar imaging.

In this paper, we delve into wireless communications in the 300 GHz band, focusing in particular on the continuous bandwidth of 44 GHz from 252 GHz to 296 GHz, positioning it as a pivotal element in the trajectory toward 6G communications. While terahertz communications have traditionally been praised for the high speeds they can achieve using their wide bandwidth, focusing the beam has also shown the potential to achieve high energy efficiency and support numerous simultaneous connectivity. To this end, new performance metrics, EIRPλ and EINFλ, are introduced as important benchmarks for transmitter and receiver performance, and their consistency is discussed. We then show that, assuming conventional bandwidth and communication capacity, the communication distance is independent of carrier frequency. Located between radio waves and light in the electromagnetic spectrum, terahertz waves promise to usher in a new era of wireless communications characterized not only by high-speed communication, but also by convenience and efficiency. Improvements in antenna gain, beam focusing, and precise beam steering are essential to its realization. As these technologies advance, the paradigm of wireless communications is expected to be transformed. The synergistic effects of antenna gain enhancement, beam focusing, and steering will not only push high-speed communications to unprecedented levels, but also lay the foundation for a wireless communications landscape defined by unparalleled convenience and efficiency. This paper will discuss a future in which terahertz communications will reshape the contours of wireless communications as the realization of such technological breakthroughs draws near.

We have developed an all-optical fiber link antenna measurement system for a millimeter wave 5th generation mobile communication frequency band around 28 GHz. Our developed system consists of an optical fiber link an electrical signal transmission system, an antenna-coupled-electrode electric-field (EO) sensor system for 28GHz-band as an electrical signal receiving system, and a 6-axis vertically articulated robot with an arm length of 1m. Our developed optical fiber link electrical signal transmission system can transmit the electrical signal of more than 40GHz with more than -30dBm output level. Our developed EO sensor can receive the electrical signal from 27GHz to 30GHz. In addition, we have estimated a far field antenna factor of the EO sensor system for the 28GHz-band using an amplitude center modified antenna factor estimation equation. The estimated far field antenna factor of the sensor system is 83.2dB/m at 28GHz.

In order to enhance the fifth generation (5G) mobile communication system further toward 5G Evolution, high bit-rate transmission using high SHF bands (28GHz or EHF bands) should be more stable even in high-mobility environments such as high speed trains. Of particular importance, dynamic changes in the beam direction and the larger Doppler frequency shift can degrade transmission performances in such high frequency bands. Thus, we conduct the world's first 28 GHz-band 5G experimental trial on an actual Shinkansen running at a speed of 283km/h in Japan. This paper introduces the 28GHz-band experimental system used in the 5G experimental trial using the Shinkansen, and then it presents the experimental configuration in which three base stations (BSs) are deployed along the Tokaido Shinkansen railway and a mobile station is located in the train. In addition, transmission performances measured in this ultra high-mobility environment, show that a peak throughput of exceeding 1.0Gbps and successful consecutive BS connection among the three BSs.

This paper studies the performance of the quantitative RF power variation in Radio-over-Fiber beam forming system utilizing a phased array-antenna integrating photo-diodes in downlink network for next generation millimeter wave band radio access. Firstly, we described details of fabrication of an integrated photonic array-antenna (IPA), where a 60GHz patch antenna 4×2 array and high-speed photo-diodes were integrated into a substrate. We evaluated RF transmission efficiency as an IPA system for Radio-over-Fiber (RoF)-based mobile front hall architecture with remote antenna beam forming capability. We clarified the characteristics of discrete and integrated devices such as an intensity modulator (IM), an optical fiber and the IPA and calculated RF power radiated from the IPA taking account of the measured data of the devices. Based on the experimental results on RF tone signal transmission by utilizing the IPA, attainable transmission distance of wireless communication by improvement and optimization of the used devices was discussed. We deduced that the antenna could output sufficient power when we consider that the cell size of the future mobile communication systems would be around 100 meters or smaller.

This paper presents a new form of gap waveguide technology - the half-height-pin gap waveguide. The gap waveguide technology is a new transmission line technology introduced recently, which makes use of the stopband of wave propagation created by a pair of parallel plates, one PEC (perfect electric conductor) and one PMC (perfect magnetic conductor), with an air gap in between less than a quarter of the wavelength at operation frequency. Applying this PEC/PMC gap plate structure to ridged waveguides, rectangular hollow waveguides and microstrip lines, we can have the ridged gap waveguides, groove gap waveguides and inverted gap waveguide microstrip lines, respectively, without requiring a conductive or galvanic contact between the upper PEC and the lower PMC plates. This contactless property of the gap waveguide technology relaxes significantly the manufacturing requirements for devices and antennas at millimeter wave frequencies. PMC material does not exist in nature, and an artificial PMC boundary can be made by such as periodic pin array with the pin length about a quarter wavelength. However, the quarter-wavelength pins, referred to as the full-height pins, are often too long for manufacturing. In order to overcome this difficulty, a new half-height-pin gap waveguide is introduced. The working principles and Q factors for the half-height-pin gap waveguides are described, analyzed and verified with measurements in this paper. It is concluded that half-height-pin gap waveguides have similar Q factors and operation bandwidth to the full-height-pin gap waveguides. As an example of the applications, a high gain planar array antenna at V band by using the half-height-pin gap waveguide has been designed and is presented in the paper with a good reflection coefficient and high aperture efficiency.

This paper presents a novel 60 GHz-band photonic-integrated array-antenna and module for radio-over-fiber (RoF)-based beam forming. An integrated photonic array-antennas (IPA), where eight photodiodes and 4×2 arrayed patch-antenna are integrated in a single board, is actually fabricated, and 3.5-Gbit/s QPSK digital signal transmission with beam forming of the IPA is experimentally demonstrated. In addition, a novel 60-GHz compact antenna module is proposed and fabricated for increasing the number of antenna elements and flexibility creating various beam patterns. The feasibility of beam forming operation for the proposed antenna module is confirmed by a 60-GHz RoF transmission experiment. The capability of detecting the mobile terminal direction, which is one of the indispensable functions for actual environment, is also studied. The obtained results in this paper will be useful for designing future radio access networks based on RoF transmission technology.

This paper proposes the use of two transmit and two receive antennas spaced at roughly the width of a human body to improve communication quality in the presence of shadowing by a human body in the 60GHz band. In the proposed method, the transmit power is divided between the two transmit antennas, and the receive antenna that provides the maximum receive level is then chosen. Although the receive level is reduced by 3dB, the maximum attenuation caused by human body shadowing is totally suppressed. The relationship between the antenna element spacing and the theoretical spacing based on the 1st. Fresnel zone theory is clarified. Experiments confirm that antenna spacing several centimeters wider than that given by the 1st. Fresnel zone theory is enough to attain a significant performance improvement.

In order to realize millimeter-wave (MMW) 3-D system-in-package (SiP) front-end modules, we propose a 60-GHz band copper ball vertical interconnection structure, which interconnects between vertically stacked substrates. The structure enables ICs to be placed between the vertically stacked substrates. Since the diameter of the copper balls must exceed the thickness of the ICs, the distance between the substrates in the modules is larger than that of the flip-chip interconnection widely used in the MMW-band. Therefore, the conventional flip-chip interconnection does not scale for the interconnection between the substrates in MMW 3-D SiP front-end modules. The layout of grounded copper balls and the patterns of inner ground layers in the upper/lower substrates are designed using 3-D electromagnetic field simulation. The designed structure allows less than 1 dB transmission loss up to 71.1 GHz, compared with a through transmission line. The result is verified with fabrication and measurement and confirms the feasibility of MMW 3-D SiP front-end modules.

To clarify the mechanism of the generation of electromagnetic (EM) noise, current and radiation noise up to the GHz band generated by slowly breaking silver-compound contacts were investigated experimentally. The current and radiation noise at the GHz band were observed. It was demonstrated that the frequency spectrums of the current and radiation noise correspond to the frequency responses of the circuit admittance and radiation efficiency of the experimental setup, respectively. It was revealed that even if current noise at the GHz band is very small, it can cause a large EM radiation noise because of the high radiation efficiency. From the time-frequency domain characteristics of current noise, it was clarified that the peaks of current noise at 10 MHz band arise immediately after the initiation of the arc discharge and the transition from metallic phase to gaseous phase. On the other hand, the peak current noise above 100 MHz arises immediately after the initiation of the arc discharge.

In this study, a multiple U-shaped slot microstrip patch antenna for application to the 5 GHz band is designed and fabricated. To obtain sufficient bandwidth in the operating band, foam is inserted between the substrate and ground plane, the type of form is styrofoam, the coaxial probe source is used, and the position of the probe shift is adjusted from the center to the left. The measured result (5.02-5.955 GHz) of the fabricated antenna satisfies the conditions of VSWR < 2.0 in 5 GHz band (5.15-5.35 GHz, 5.47-5.725 GHz, 5.725-5.825 GHz), gain of 3.88-9.28 dBi, and broad radiation pattern.

In this paper, a meander-type microstrip patch antenna for application in 5 GHz-band is designed and fabricated. To obtain enough bandwidth in VSWR<2, the foam is inserted between substrate and ground plane, the coaxial probe source is used. The measured result of fabricated antenna is obtained 1 GHz (17.5%) of bandwidth in VSWR<2, the gain of 7.3-9.5 dBi and unidirectional pattern.

Rectangular/circular-to-radial waveguide tra-nsformers through a ring slot have been proposed for the feeder of radial line slot antennas (RLSAs) in millimeter wave application. Rotating electric modes are excited by a set of ring slot and perturbation dog bone slot. Basic operation is observed in 12 GHz band. Concentric array radial line slot antennas fed by these transformers are fabricated and the antenna gain of 26.9 dBi with the efficiency more than 60% is measured. The applicability for millimeter wave is verified for 38 GHz band RLSA fed by the rectangular waveguide. The measured gain of the antenna is 22.5 dBi with the efficiency of 53% with the diameter of 46mm and 26.4 dBi with 61% with the diameter of 66mm.

A 3 to 5-GHz Si-bipolar quadrature modulator and demodulator are described. Both feature a wideband frequency-doubling 90-degree phase shifter that has a mechanism for self-correction of phase errors caused by an original 90-degree phase-shift network at the half frequency of the carrier. Therefore, the phase shifter produces accurate quadrature carrier signals with doubled frequency. The quadrature modulator and demodulator in 30-GHz Si bipolar technology dissipate 80 mA at a 3-V supply. Image rejection of the modulator is more than 40 dB between 3.2 to 5.2 GHz. The phase and amplitude errors of the demodulator are less than 1.5 degrees and less than 0.15 dB, respectively, between 3.5 to 5.2 GHz. Therefore, both are suitable for either direct conversion or image-rejection transceivers for 5-GHz applications.

A 2.4 GHz band direct sequence (DS) spread spectrum (SS) radio frequency modem with a wide bandwidth of 26 MHz in half-duplex system has been newly developed using the small size (832 mm) and highly-efficient (-57 dBm) elastic type of surface acoustic wave (SAW) convolver. The size of SS modem is 905011 mm and the weight is 75 g. The power consumption of SS modem is 1.5 W and data rate is 206 kbps with 63 chips of PN code. Electrical characteristics measurements were made to evaluate the SS modem performance.