[Show abstract][Hide abstract] ABSTRACT: The multiport parasitic array radiator (MuPAR) antenna is a compact low-profile beam-steering antenna, which is composed of two excited inverted-F elements and two parasitic elements with variable reactors. Although the MuPAR antenna seems to have a good potentiality to achieve full azimuthal beam/null steering performance, the detailed controllability of the beam and null has not been clarified yet. This is because the two different types of variables, which are excitation coefficients and reactance values, make the gain optimization problem complex and difficult. Thus, in this paper, we have first developed a generalized model of the inverted-F MuPAR antenna. For the accurate modeling, structural features of inverted-F antennas are taken into account, and also the closed-form gain definition for the MuPAR antenna is derived. The formulation enables us to efficiently obtain both excitation coefficients and reactance values with optimization techniques. Applying the model to both a gradient-based optimization and a particle swarm optimization successfully, the beam/null forming performances of the four-element MuPAR antenna is made clear. Through experiments including numerical calculations and measurements at 2.45 GHz, the validity of our model and precise formulation is confirmed.
IEEE Transactions on Antennas and Propagation 03/2012; 60(3):1352-1361. DOI:10.1109/TAP.2011.2180338 · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The wireless harness is a new emerging short-range communication to replace wire harness implemented in devices with wireless communications between internal components. In such an in-device wireless harness, the communication distance is up to a couple of meters at most. Through the challenge to apply this wireless communication technology to information and communication technology (ICT) equipment, we found that the radio channel inside the ICT equipment deeply depends on its internal structure more than we expected. In order to understand the radio propagation characteristics inside such equipment, we propose a new modeling technique with using a frequency- dependent path loss exponent expressing the near- and far-field propagation, which enables us to successfully extract attenuation factors for the frequency and the propagation distance from the measured data. The results shows the path loss characteristics can be divided into three regions; line-of-sight (LOS), non-line-of-sight (NLOS), and a transition range. The transition range, which appears between the LOS and the NLOS, is caused by a blocking due to the densely-packaged internal components. These findings and equations can be criteria to design a wireless harness communication link.
IEEE Transactions on Antennas and Propagation 01/2012; 59(12-59):4757 - 4765. DOI:10.1109/TAP.2011.2165494 · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A very compact monopole antenna with an evolutionarily generated subwavelength planar element is proposed for the antenna miniaturization without using any lumped capacitors and inductors. The monopole antenna is composed of a coaxial-fed short line etched on one side of dielectric substrate and a subwavelength element on the other side, enabling an easy fabrication using a printed circuit technology. To design the arbitrarily shaped subwavelength element, an efficient genetic algorithm (GA) design technique is employed. As a design example, a monopole antenna with 1/23-wavelength height and 1/17-wavelength width at 430 MHz is demonstrated. The predicted results of the radiation pattern and the reflection characteristic are compared to measured data, and good agreement between the two results is achieved.
[Show abstract][Hide abstract] ABSTRACT: We propose a proof-of-concept of a switchable multi-frequency MMIC (monolithic microwave integrated circuit) oscillator device, operating in the 60GHz millimeter wave band, which is implemented in GaAs p-HEMT transistor technology. Oscillators that can switch between two frequencies have been designed, fabricated and evaluated. The oscillator uses a cross-coupled FET topology, combined with a bent asymmetric coplanar stripline for the resonator, and a switched-capacitor for the frequency switching components. The oscillator generates two oscillations at ƒ/2 and ƒ where ƒ is the target frequency of around 60GHz. The switchable oscillator has been demonstrated for the range of frequency from 44GHz to 68.9GHz. Moreover, the designed oscillator exhibits a wide-band negative resistance property that allows fabricating switchable oscillators covering the 50 to 75GHz V-band. An evaluated switchable oscillator delivers -17.09dBm and -13.72dBm output power at 62.45GHz and 64.78GHz, for a supplied power of 40.6mW and 39.1mW, respectively.
[Show abstract][Hide abstract] ABSTRACT: A new wideband waveguide slot array is proposed for covering a wide elevation-angle range with a planar sector antenna of a multigigabit wireless LAN in the 60-GHz band. The requirement of millimeter-wave sector antennas is to realize both wide bandwidth of 11.2% and wide elevation-angle coverage with a required gain of over 10 dBi. To satisfy both the required gain and bandwidth, the important structural features of the proposed antenna are that multiple slot elements are successively arranged at an interval of the length less than one quarter guide wavelengths and that the slot length increases from the shorted waveguide end to the feed end. The operational principle of the slot array is based on multisection quarter-wavelength reflection cancellation, so the slot array can achieve the required bandwidth. Furthermore, this antenna produces a unidirectional radiation pattern by using the radiators and the reflectors, resulting in the required gain over a wide elevation-angle range. In the design, the structural parameters of the slot array are selected to meet the requirements for 60-GHz-band sector antenna. The developed substrate-integrated-waveguide (SIW) slot array achieves both the 10 dB return-loss bandwidth of 15% and the specified gain in 88-96% of the one-sector coverage range of 59-66 GHz. The effectiveness of the proposed slot array for a sector antenna is verified by the good agreement between the simulated and measured results.
IEEE Transactions on Antennas and Propagation 04/2010; 58(3-58):993 - 998. DOI:10.1109/TAP.2009.2039329 · 2.18 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We propose a proof-of-concept of a switchable multi-frequency MMIC (monolithic microwave integrated circuit) oscillator device, operating in the 60GHz millimeter wave band, which is implemented in GaAs p-HEMT transistor technology. Oscillators that can switch between two frequencies have been designed, fabricated and evaluated. The oscillator uses a cross-coupled FET topology, combined with a bent asymmetric coplanar stripline for the resonator, and a switched-capacitor for the frequency switching components. The oscillator generates two oscillations at f/2 and f where f is the target frequency of around 60GHz. The switchable oscillator has been demonstrated for the range of frequency from 44GHz to 68.9GHz. Moreover, the designed oscillator exhibits a wide-band negative resistance property that allows fabricating switchable oscillators covering the 50 to 75GHz V-band. An evaluated switchable oscillator delivers -17.09dBm and -13.72dBm output power at 62.45GHz and 64.78GHz, for a supplied power of 40.6mW and 39.1mW, respectively.
[Show abstract][Hide abstract] ABSTRACT: This paper proposes a new switched-beam eight-sector antenna for multi-gigabit wireless LAN in the 60-GHz band. Our antenna system introduces access-point (AP) and user-terminal (UT) antennas having the same sec theta pattern in the elevation plane so that the received signal power at the receiver is kept constant, independent of the position of the UT. For this system, an eight-sector antenna, a single-pole eight-throw (SP8T) switch, and a beam control unit are integrated as the switched-beam eight-sector antenna. The specifications of the antenna are wide bandwidth (>=3GHz), high-gain (>=13dBi at theta=66°), and wide coverage area in both azimuth (0°
[Show abstract][Hide abstract] ABSTRACT: This paper presents a prototype group modem for a hyper-multipoint data gathering satellite communication system. It can handle arbitrarily and dynamically assigned FDMA signals by employing a novel FFT-type block demultiplexer/multiplexer. We clarify its configuration and operational principle. Experiments show that the developed modem offers excellent performance.
[Show abstract][Hide abstract] ABSTRACT: A single carrier transmission system is proposed. It is a dynamic spectrum access system designed for ISM bands where various radio systems are operating. The proposed system divides the spectrum of the single carrier modulation into a few Â¿subspectraÂ¿ and allocates them for fragmented vacant spectra, which are called Â¿white spaceÂ¿ in the band. Not FFT/IFFT operations for each signal block with cyclic prefix, but band-limiting filters, of cosine roll-off characteristics for example, are adopted for the spectrum dividing in order to reduce ACPR (or ACLP, adjacent channel leakage power ratio). Simulation results show that PAPR (peak-to-average power ratio) of the transmitted signal can be reduced by limiting the number of the spectrum division within a few pieces. The proposed system utilizes the remaining vacant spectra thoroughly so that it copes with the increasing demand of spectrum use expected in ISM bands toward the ubiquitous network world in the near future.
Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on; 10/2009
[Show abstract][Hide abstract] ABSTRACT: To improve the area throughput of OFDM-based IEEE 802.11 wireless LAN systems in an OBSS environment, this paper proposes a new overlay transmission protocol which does not require any signal/frame exchange prior to DATA frame transmission. The proposed protocol introduces a new field which containing a portion of the BSSID to which the destination node belongs in order to indicate who must listen this frame without decoding the succeeding MAC frame. This protocol can reduce the deferring time for new frame transmission and increase the transmission chances of each node with a small overhead, whereas it causes interference toward existing communications. To suppress such interference, we employ a pre-FFT type MMSE adaptive array antenna (AAA) to suppress sporadic interference at the receiver's side. The average area throughput of a system based on IEEE 802.11g ERP-OFDM in an OBSS environment is evaluated through PHY/MAC cross-layer computer simulations assuming an AWGN channel. Simulation results shows that the area throughput improvement of about 60% can be achieved at an offered load of 24Mbytes/s by employing our proposed protocol and AAA.
Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on; 10/2009
[Show abstract][Hide abstract] ABSTRACT: This paper describes a new inclinometer that compensates for ultralow-frequency acceleration disturbances. This inclinometer consists of a low-cost accelerometer, pendulum, and rotary encoder. The key feature of this inclinometer is the estimation method used to calculate the pendulum's inertial angle. We propose two algorithms to estimate the pendulum's angle. Algorithm I uses time-averaged accelerations and some assumptions. Algorithm II applies the pendulum's equation of motion. The results of simulations and experiments confirm that both algorithms can achieve highly accurate level/angle estimations under acceleration disturbance conditions. We apply this inclinometer to an autotracking antenna system for vessels. Time simulations verify its effectiveness.
IEEE Transactions on Instrumentation and Measurement 09/2009; 58(8-58):2525 - 2534. DOI:10.1109/TIM.2009.2014622 · 1.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper introduces our proposed pre-FFT type MMSE-AAA for an OFDM packet transmission system to suppress sporadic interference. The AAA scheme controls an antenna weight to minimize the mean square error between its output signals of two periods with identical transmitted waveform and iterates the weight updating process in an OFDM symbol to rapidly converge the weight. The average PER performance of the proposed AAA with the presence of a sporadic inter-system/intra-system interference signal is evaluated through computer simulations that assume an exponentially decaying 12-path LOS fading channel and IEEE 802.11a data frame transmission. Simulation results show that the proposed AAA can effectively suppress sporadic inter-system interference that is irrelevant to its arrival timing. Sporadic intra-system interference can also be suppressed by the proposed AAA more efficiently than inter-system interference as long as the interference arrives between 13% and 90% of the OFDM symbol duration after the beginning of an OFDM symbol of the desired signal.
[Show abstract][Hide abstract] ABSTRACT: We have developed a new 60-GHz band millimeter wave multi-gigabit wireless local area network (WLAN) system that achieves a throughput of more than 1 Gbps. The developed system consists of high-gain eight-sector antenna, physical layer (PHY) for orthogonal frequency multiple access (OFDM) modulation/demodulation, and media access control (MAC) for time and space resource control on point to multi-point (P-MP) communication. The performance of the developed system was evaluated in a room environment. As a result, we confirmed that developed system achieves a high throughput, which exceeds considerably that of current microwave-band WLAN systems based on IEEE802.11.
[Show abstract][Hide abstract] ABSTRACT: This paper reports on practical study of a switchable dual-frequency oscillator for 60-GHz binary FSK modulation, using a 0.15 mum commercial GaAs p-HEMT technology. The oscillator obtained an output power of 1.8 dBm at 61.43 GHz with a phase noise of -65dBc/Hz at 100 kHz offset and -87dBc/Hz at 1MHz offset to the carrier at the free-run state. A 500 Mbit/s FSK modulation was confirmed with the developed oscillator. This type of oscillator is feasible for of multi-gigabit data rate FSK modulation.
[Show abstract][Hide abstract] ABSTRACT: We have applied the bandwidth-enhancement technique to a transition between coaxial line and post-wall waveguide with a short-ended straight post. The straight post connected to the coaxial line works for not only impedance matching for input coaxial port but also impedance inverter between two cavities. The dual resonance behavior of the transition was confirmed by numerical studies. Using our bandwidth-enhancement technique, a transition with straight short-ended post was successfully designed for the waveguide slot-array antenna at 60 GHz. It can be concluded from our designed transition that the effectiveness of our bandwidth enhancement technique is verified.
[Show abstract][Hide abstract] ABSTRACT: This paper addressed cable network configurations to improve surface accuracies for large mesh antennas. In this study, we focused on manufacturing error, assembling error, and sensitivity to displacements of support points. To facilitate accuracy management by the lengths of cables, high stiffness cables were used in surface cable network. Then, low stiffness cables were used in other cables. The effect of the lengths of errors was estimated by analysis and experiments for a test model. Micro-gravity test was also executed to estimate the accuracy of shape adjustment on ground. The sensitivity is calculated under some variations of cable stiffness. From the results, it is clarified that the proposed configuration can reduce the surface distortion and keep high surface accuracy.