A highly integrated frequency quadrupler MMIC that uses three-dimensional MMIC (3D-MMIC) technology is presented. It consists of four driver amplifiers, two doublers, and a 2-band elimination filter. These seven circuits are integrated in only a 2.36 mm2 area. The filter sufficiently suppresses spurious output components. The third and fifth harmonic components, which are the spurious components nearest to the desired component, are well suppressed. The desired/undesired ratio is about 40 dB. The driver amplifiers make the quadrupler output a constant power of the desired multiplied signal under low input power. The MMIC supplies +5 dBm of the fourth harmonic component in the input power range from -10 dBm to +5 dBm. The power dissipation of the MMIC is only 160 mW.

We previously proposed a unified wireless system called “Flexible Wireless System”. Comprising of flexible access points and a flexible signal processing unit, it collectively receives a wideband spectrum that includes multiple signals from various wireless systems. In cases of simultaneous multiple signal reception, however, reception performance degrades due to the interference among multiple signals. To address this problem, we propose a new signal separation and reconstruction method for spectrally overlapped signals. The method analyzes spectral information obtained by the short-time Fourier transform to extract amplitude and phase values at each center frequency of overlapped signals at a flexible signal processing unit. Using these values enables signals from received radio wave data to be separated and reconstructed for simultaneous multi-system reception. In this paper, the BER performance of the proposed method is evaluated using computer simulations. Also, the performance of the interference suppression is evaluated by analyzing the probability density distribution of the amplitude of the overlapped interference on a symbol of the received signal. Simulation results confirmed the effectiveness of the proposed method.

Novel multi-band mixers that can receive multiple band signals concurrently are proposed and evaluated. The mixers achieve independent gain control through novel relative power control method of the multiple local oscillator (LO) signals. Linear control is also achieved through multiple LO signal input with total LO power control. Theoretical analysis shows that odd-order nonlinearity components of the multiple LO signals support linear conversion gain control. Dual- and triple-band tests are conducted using typical three MOSFET mixers fabricated by a 0.25 µm SiGe BiCMOS process. Measurements confirm over 40 dB independent control of conversion gain, linear control achieved through LO input power control. The proposed mixers have high input linearity with a 5 dBm output third intercept point. A method is also proposed to reduce interference caused by mixing between multiple LO signals.

Newly developed multi-layer inductors on GaAs three-dimensional MMICs are presented. We analyzed single-, double-, triple-, and quadruple-layer stacked-type inductors in what may be the first report on inductors on a GaAs MMIC with three or more layers. The performance of single- and multi-layer inductors was measured and calculated by electromagnetic field simulation. The multi-layer inductors produce 2-11 times higher inductance than that of conventional inductors on 2D-MMICs although they are the same size. This means that the proposed multi-layer inductors have smaller areas with the same inductances than those of conventional inductors. We also conducted the first-ever investigation of how performance factors such as parasitic capacitance, Q-factor, and self-resonant frequency are degraded in multi-layer inductors vis-a-vis those of conventional inductors. A microwave amplifier using multi-layer inductors was demonstrated and found to reduce circuit size by 20%.

To satisfy the requirement of a unified platform which can flexibly deal with various wireless radio systems, we proposed and implemented a heterogeneous network system composed of distributed flexible access points and a protocol-free signal processing unit. Distributed flexible access points are remote RF devices which perform the reception of multiple types of radio wave data and transfer the received data to the protocol-free signal processing unit through wired access network. The protocol-free signal processing unit performs multiple types of signal analysis by software. To realize a highly flexible and efficient radio wave data reception and transfer, we employ the recently developed compressed sensing technology. Moreover, we propose a combined Nyquist and compressed sampling method for the decoding signals to be sampled at the Nyquist rate and for the sensing signals to be sampled at the compressed rate. For this purpose, the decoding signals and the sensing signals are converted into the intermediate band frequency (IF) and mixed. In the IF band, the decoding signals are set at lower center frequencies than those of the sensing signals. The down converted signals are sampled at the rate of four times of the whole bandwidth of the decoding signals plus two times of the whole bandwidth of the sensing signals. The purpose of above setting is to simultaneously conduct Nyquist rate and compressed rate sampling in a single ADC. Then, all of odd (or even) samples are preserved and some of even (or odd) samples are randomly discarded. This method reduces the data transfer burden in dealing with the sensing signals while guaranteeing the realization of Nyquist-rate decoding performance. Simulation and experiment results validate the efficiency of the proposed method.

We propose a novel feeding circuit for a 30 GHz planar multibeam antenna applied to high-speed wireless communication systems. The feeding circuit is a bi-layer 8-port Butler matrix constructed with phase adjusted slot-coupled hybrids and branch-line hybrids. The new circuit configuration eliminates troublesome vias and line crossings, so it can be manufactured by traditional photolithograph. The feeding circuit is designed by using the spectral domain moment method considering bonding film effects. A prototype of a multibeam antenna which has seven pencil-beams with 10 beamwidths is manufactured and tested; the beam scan angle error is less than 3 at 30 GHz.

This paper presents a spatial division (SD) transmission method based on two-ray fading that dispenses with the high signal processing cost of multiple-input and multiple-output (MIMO) detection and antennas with narrow beamwidth. We show the optimum array geometries as functions of the transmission distance for providing a concrete array design method. Moreover, we clarify achievable channel capacity considering reflection coefficients that depend on the polarization, incident angle, and dielectric constant. When the ground surface is conductive, for two- and three-element arrays, channel capacity is doubled and tripled, respectively, over that of free space propagation. We also clarify the application limit of this method for a dielectric ground by analyzing the channel capacity's dependency on the dielectric constant. With this method, increased channel capacity by SD transmission can be obtained merely by placing antennas of wireless transceiver sets that have only SISO (single-input and single-output) capability in a two-ray propagation environment. By using formulations presented in this paper for the first time and adding discussions on the adoption of polarization multiplexing, we clarify antenna geometries of SD transmission systems using polarization multiplexing for up to six streams.

In the near future, many sensors and terminals will be connected to the public network to provide various convenient IoT/M2M services. In order to connect many sensors to the network efficiently, wireless communication systems in the 920MHz band are seen as attractive solutions. We are focusing on the 920MHz band to research and develop high-capacity protocols that can accommodate many terminals, and low power consumption technologies for battery-driven terminals. In this paper, we describe the following three concrete wireless systems that use our proposals. (1) A physical distribution pallet management system that can handle thousands of pallet-embedded sensors and a wireless module with a battery lifetime of about ten years. (2) Water leakage monitoring system for underground pipes by using sensors and a wireless module in each valve box. (3) A wide-area and high-capacity radio relay system for smart metering services like the reading of gas meters. The radio relay system can accommodate various sensors and terminals and has large potential for providing various IoT/M2M services in conjunction with smart metering services.

This paper describes a broadband active terminal circuit and its application to a distributed amplifier. In this study, we first analyzed and compared three types of active terminal circuits using representative circuit configurations, namely, an active terminal circuit with a common-emitter BJT, an active terminal circuit with a Darlington BJT pair, and an active terminal circuit with cascode-connected BJTs. The simulation results showed that the active terminal circuit with cascode-connected BJTs kept the matching condition up to high frequency. After the simulation, we fabricated a distributed amplifier that used an active terminal circuit with cascode-connected BJTs. The RF amplifier achieved a flat gain of 9.7 1.0 dB over a range of 3-15 GHz.

We present a highly integrated quasi-millimeter-wave receiver MMIC that integrates 22 circuits in a 3 2.3 mm area using three-dimensional MMIC (3D-MMIC) technology. The MMIC achieves low noise (3 dB) and high gain (41 dB) at 26 GHz by using an on-chip image reject filter. It integrates a multiply-by-eight (X8) local oscillator (LO) chain with the IF frequency of the 2.4 GHz band and can use low-cost voltage-controlled oscillators (VCOs) and demodulators in a 2–3 GHz frequency band. Multilayer inductors contribute to the miniaturization especially in a 2–12 GHz frequency band. Furthermore, it achieves a high dynamic range by using two step attenuators with a new built-in inverter using an N-channel depression field-effect transistor (FET). The power consumption of the MMIC is only 450 mW.

We have developed a two-dimensional flat-panel imager (FPI) utilizing conventional amorphous silicon (a-Si) thin film transistor (TFT) technology for AM-LCDs, and we have made a prototype. We can experimentally manufacture the FPI basically by utilizing conventional production lines of AM-LCDs, because the imager is based on the TFT array for AM-LCDs. The TFT performs both switching and photo-detecting functions itself. Using the FPI, we can capture monochrome images in real time, and can also achieve full-color images by introducing time-sequential driving based on a color backlight system with RGB-LEDs. The reliability of the TFT under bias and irradiation stress caused by capturing images is maintained by introducing an original driving method and processing the captured image. By making use of advantages the FPI has over conventional imaging systems, we hope that the FPI will be a useful compact imaging device for documents, pictures, fingerprints, and the like.

This paper describes miniaturized broadband lumped-element in-phase power dividers. We first propose two types of miniaturized broadband lumped-element in-phase power dividers composed of two inductors, a resistor, and two capacitors. Next, we use a simulation to compare these dividers with conventional power dividers. The simulation results reveal that the proposed lumped-element in-phase power dividers can help miniaturize circuits (by decreasing inductances by about 30%, reducing the number of necessary capacitors by half, and decreasing necessary capacitances by about 30% as compared to conventional lumped-element dividers) and attain broadband frequency characteristics (by increasing normalized operating frequency bandwidths (f/f0) by about 80% as compared to conventional lumped-element dividers).

For quasi millimeter-wave and millimeter-wave high-speed wireless communications over wireless LANs and wireless ATMs, narrow beam antennas have been shown to provide high transmission quality by suppressing the troublesome multipath effect. However, the diameter of sector antennas needed to create the narrow beams rapidly increases with the sector number. In addition, the cylindrical shape of typical sector antennas does not suit portable terminals. This paper shows a methodology for designing planar sector antennas that overcomes these problems. The proposed antenna uses two kinds of beams and the antenna gains are equalized in all sectors. The antenna is developed as a 4-beam subarray fed by a planar Butler matrix circuit. The design method of the subarray and an evaluation of its characteristics in the 20 GHz band are discussed.

One of the procedures for increasing the number of multi-input and multi-output (MIMO) branches without increasing the computational cost for MIMO detection or multiplexing is to exploit parallel transmissions by using polarization multiplexing. In this paper the effectiveness of using polarization multiplexing is confirmed under the existence of polarization rotation, which is inevitably present in short-range multi-input and multi-output (SR-MIMO) channels with planar array antennas. It is confirmed that 8×8 SR-MIMO transmission system with polarization multiplexing has 60bit/s/Hz of channel capacity. This paper also shows a model for theoretical cross polarization discrimination (XPD) degradation, which is useful to calculate XPD degradations on diagonal paths.

Short-range Multiple-Input-Multiple-Output (SR-MIMO) transmission is an effective technique for achieving high-speed and short-range wireless communication. With this technique, however, the optimum aperture size of array antennas grows when the transmission distance is increased. Thus, antenna miniaturization is an important issue in SR-MIMO. In this paper, we clarify the effectiveness of using dual-polarized planar antennas as a means of miniaturizing SR-MIMO array antennas by measurements and analysis of MIMO transmission characteristics. We found that even in SR-MIMO transmission, the use of dual-polarized transmission enables higher channel capacity. Dual-polarized antennas can reduce by two thirds the array area that is needed to obtain the same channel capacity. For a transmission distance of two wavelengths, the use of a dual-polarized antenna improved the channel capacity by 26 bit/s/Hz while maintaining the same number of transmitters and receivers and the same antenna aperture size. Moreover, dual-polarized SR-MIMO has a further benefit when zero-forcing (ZF) reception without transmit beamforming is adopted, i.e., it effectively simplifies hardware configuration because it can reduce spatial correlation even in narrow element spacing. In this work, we confirmed that the application of dual-polarization to SR-MIMO is an effective way to both increase channel capacity and enhance transceiver simplification.

We analyze the mutual coupling between two microstrip antennas (MSAs) with the finite-difference time-domain (FDTD) method. It is suitable for substrates which have a complex configuration or include feed line structures. The mutual coupling between two MSAs on discontinuous orthogonal substrates is successfully calculated.

In the recently developed Flexible Wireless System (FWS), the same platform needs to deal with different wireless systems. This increases nonlinear distortion in its wideband power amplifier (PA) because the PA needs to concurrently amplify multi-band signals. By taking higher harmonics as well as inter- and cross-modulation distortion into consideration, we have developed a method to analytically evaluate the adjacent channel leakage power ratio (ACPR) and error vector magnitude (EVM) on the basis of the PA's nonlinear characteristics. We devise a novel method for modeling the PA amplifying dual-band signals. The method makes it possible to model it merely by performing a one-tone test, making use of the Volterra series expansion and the general Wiener model. We then use the Mehler formula to derive the closed-form expressions of the PA's output power spectral density (PSD), ACPR, and EVM. The derivations are based on the assumption that the transmitted signals are complex Gaussian distributed in orthogonal frequency division multiplexing (OFDM) transmission systems. We validate the method by comparing measurement and simulation results and confirm it can appropriately predict the ACPR and EVM performance of the nonlinear PA output with OFDM inputs. In short, the method enables correct modeling of a wideband PA that amplifies dual-band signals merely by conducting a one-tone test.

Software defined radio (SDR) is receiving much attention as the key technology to realize the next generation wireless communication system. This paper proposes the concept of system diversity on SDR and investigates the effectiveness of system diversity by using a concrete simulation model. System diversity allows the wireless communication system being used to be dynamically changed in addition to the signal processing algorithm or modulation/coding scheme being used. To clarify the validity of system diversity, we examine a system simulation model consisting of three wireless communication systems; algorithms are introduced to show how system diversity can be controlled using the QoS parameters of received signal level, data transmission rate, and channel capacity. The process by which system diversity switching is triggered is elucidated, and a practical example is introduced. Simulation results confirm that system diversity offers higher performance in terms of data throughput and system channel capacity than existing wireless communication systems. Finally, a comprehensive algorithm is described that protects existing single-mode traffic from being degraded by SDR switching.