Yoshihiko Kuwahara

Multiobjective optimization design of Yagi-Uda antenna

An optimization method, such as the steepest gradient methods, could not easily obtain globally optimum solutions for devising antenna design parameters that allow the antenna to simultaneously improve multiple performances such as gain, sidelobe level, and input impedance. The genetic algorithm (GA) is suitable for empirically solving optimization problems and is effective in designing an antenna. In particular, this method can solve the multiobjective optimization problem using various Pareto-optimal solutions in an extremely efficient manner. In this paper, the Pareto GA, by which various Pareto-optimal solutions for each objective function (performance) can be obtained in a single trial of a numerical simulation and which enables the selection of parameters in accordance with the design requirement, is applied to the multiobjective optimization design of the Yagi-Uda antenna. The effectiveness of the Pareto GA was demonstrated by comparing the performances obtained by the Pareto GA with those of the previously reported values, which were obtained by the conventional GA, and with the values of the design benchmark reference.

Design of Multibeam Dielectric Lens Antennas by Multiobjective Optimization

We propose an effective method for designing multibeam dielectric lens antennas. A genetic algorithm (GA) with multiobjective optimization is adopted to balance gain against sidelobe level. The lens shapes and the position of each feed are associated with chromosomes. The gain and sidelobe level are evaluated by a Pareto ranking method. The method yields the distribution of the objective function values and the corresponding antenna structures.

Trial model of adaptive antenna equipped with switched loads on parasitic elements

An adaptive antenna that forms an adaptive beam by adjusting current induced in the parasitic elements has been experimentally produced. The antenna consists of a radiating element placed at the center and six parasitic elements placed on the circumference of a circle with a radius of 0.5 /spl lambda/. These elements are monopoles on the reflector. A three-state switched load is connected with each parasitic element. The combination for which the correlation between the received signal and the reference signal maximizes is selected from all load setting combinations. The advantages of using three alternative loads instead of a variable reactance, that is, fast convergence and avoidance of falling into local cost function minimum are demonstrated by numerical experiments. The adaptive beam pattern and bit error rate (BER) of the binary phase shift keying (BPSK) signal were measured in an anechoic chamber, and the capability of the adaptive antenna to form adaptive beams was confirmed.

Novel ESPAR antenna

A novel ESPAR (electronically steerable passive array radiator) antenna has been proposed. The antenna aperture is a planar array composed of the microstrip patch antenna (MSPA). The MSPA is a stacked circular patch that generates a circular polarized wave over a wide frequency band. Variable reactance values set for maximizing the output SINR are globally searched by direct search. The validity of the proposed antenna is demonstrated by numerical simulation.

Transmitter with antenna array for MC-CDMA forward link

A novel transmitter for MC-CDMA has been proposed and excellent increase of user capacity has been confirmed by the numerical simulation. It became clear that 8 elements array for space diversity and 16 subcarriers for frequency diversity provide efficiency of 12 bit/s/Hz in case of Walsh-Hadamard sequence and MMSEC. We are to examine methods of estimating the response vector.

Conformal array antenna with the aspirator for the microwave mammography

Recently, the microwave imaging techniques attract attentions as a screening method of early breast cancer detection that takes place of an X-ray mammography. There are two categories of UWB radar [1] and microwave tomography [2]. A lot of basic experiments using the phantom have been reported [3]. For such experiments, antenna array and breast are soaked in the coupling liquid in order to maximize the amount of microwave energy coupled into the breast. In addition, we must know 3D surface of the breast to remove artifact reflected by skin using averaging technique in UWB radar or to solve ill-posed problem in microwave tomography [4].

Experiments of direction finder by RBF neural network with post processing

Evaluation tests of a direction finder, whose antenna aperture consists of 4 monopoles on the circumference of a 0.4/spl lambda/ diameter circle, has been carried out. An RBF neural network with a new post processing system is used for the DOA estimation algorithm. The estimation error by the RBF neural network has reduced to 1/10 compared with MUSIC.

VHF Adaptive Antenna Using a Rear Defogger

An array antenna for the VHF band, which has several ports on a defogger, is proposed. In addition, the concept of a reactively steered adaptive array is introduced to form an adaptive beam pattern. The resistivity of a heating wire does not degrade the receiving performance significantly. The cost of the adaptive array consisting of a single receiver is low, and this array does not impact the industrial design. Its performance is evaluated by numerical simulation and experiments over a bandwidth of FM radio.

A shared aperture VHF smart antenna using the rear defogger

In the land mobile propagation, there is no line of sight between transmitter and receiver. In addition, the delayed signal caused by huge buildings and heave may generate. In this situation, the transmission quality is significantly degraded. An adaptive antenna is an effective means to overcome such fading phenomena. However, an adaptive antenna is consisted of several antennas and receivers. Since a lot of antennas compromise the vehicular industrial design, it is preferable for industrial design not to use additional antenna elements. In Japan, various data communication service using VHF band for the analogue TV broadcast are planned. High speed digital data transmission will be used for the service. It will be necessary for the application to apply the diversity or the adaptive antennas.

Steering vector taking mutual coupling effects into consideration

The MUSIC spectrum in the range of a set angle is constructed by applying steering vector and eigenvectors, corresponding to the noise sub-space in a cost function after obtaining the eigenvalues from the covariance matrix of the signals received by each radiating element of array antenna when such parameters as number, DOA (direction of arrival), and relative power of incident wavefronts are estimated by means of MUSIC. Mutual coupling effects exert a serious influence upon the covariance matrix and steering vector and make degrade the capacity of the estimator. We present an analysis of the steering vector of a planar array antenna constituted by 9 dipole antennas with a back reflector taking mutual coupling effects into consideration.