Isamu Chiba

A combination of two adaptive algorithms SMI and CMA

A combination of two major adaptive algorithms, the SMI (sample matrix inversion) method and the CMA (constant modulus algorithm), is presented. The idea is to use the SMI method to determine the initial weights for the CMA operation. Although the merit of the CMA, being a blind algorithm, is not fully taken advantage of, the good aspects of both the SMI and CMA can be introduced. By this approach, two major problems of the CMA can be solved, the ill convergence with false solution when the interfering signal is stronger than the desired signal and its slow convergence time. Simulation results are shown to confirm the theory.

Inclined GEO satellite communication system with deployable phased array antennas

We propose a new satellite communication system using inclined GEO satellites which mount deployable phased array antennas. An example is shown of the inclined GEO locus. In this system, the satellite illuminates multiple beams to a certain area from a high elevation angle, so that the degradation due to shadowing effect can be reduced. When large aperture phased array antennas are used for satellite antennas, high communication capacity can be attained using small size portable terminals as earth stations. The system configuration of this system is shown. A large aperture phased array antenna is used for the satellite antenna, so as to achieve low power portable terminal.

Power inversion adaptive array antenna for high power interference suppression in DS-CDMA system

We propose an adaptive array antenna for high power interference suppression in DS-CDMA (direct sequence code division multiple access) system. In the proposed adaptive array, the interference cancellation is performed by a two-element array antenna using an auxiliary antenna before despreading. It is not necessary to derive the weights for each channel thus it can decrease the consumption power of the system. We describe the results of numerical calculation using a fundamental model.

Null points adjusting method providing low sidelobe patterns in conformal array antennas

A novel pattern synthesis method (null points adjusting method) for providing a low sidelobe pattern in a conformal array antenna is presented. This method is based on the principle that the level of sidelobe between null points can be determined by controlling their positions. The usefulness of this method is verified by synthesizing a low sidelobe pattern of a hemispherical array antenna. Using the proposed method, even if in a large-scale or complexly shaped conformal array antenna which cannot be characterized by a single curve, the optimum excitation amplitude and phase of elements can be easily determined.<<ETX>>

Study on circularly polarized cavity antenna fed by L-shaped probes

A circularly polarized cavity antenna that is fed by L-shaped probes is proposed in this paper. This antenna has a simple configuration and good connectivity with a feed circuit. Wideband impedance matching is achieved by using the vertical arm of the L-shaped probe located near the side of the cavity as an impedance transformer, thus eliminating the need for other impedance matching circuits. The effectiveness of the proposed antenna has been confirmed experimentally.

Beam pointing error analysis for phased array antennas with true time delay modules

The beam pointing error theory for the phased array antennas (PAA) with true-time-delay (TTD) module is proposed in closed form and is confirmed to be valid. The proposed theory easily gives the optimum subarray size, which is a unit of a TTD module, and maximum delay length of the TTD module in order to attain the desired beam pointing accuracy.

Beam direction of the difference pattern in a monopulse phased array antenna

The beam direction of a monopulse phased array antenna can be changed rapidly by controlling the phase shifters, which is useful in detecting the direction of arrival of radio waves. In monopulse tracking, the null point of the difference pattern is used as the reference for direction determination. However, errors of phase setting, including the quantization error of the phase shifters, give rise to the problem of null shift, that is, the null point shifts from the set direction. This study examines the relation between the phase setting error and the null shift from the statistical point of view and expresses the relation between the two in a simple formula. In the general evaluation function, the position of the element antenna and the excitation amplitude are used as the parameters. Then, an expression is derived by approximating the amplitude distribution over the antenna aperture as a quadratic function, with the result that the evaluation function can be derived without defining the element position. The effectiveness of these expressions is verified by numerical calculation examples. In addition, the minimum change of the beam direction, which determines the angular measurement accuracy of the monopulse phased array antenna, depends on the phase setting accuracy of the digital phase shifters and on the accuracy of the operation unit that calculates the phase to be set in the phase shifters. The accuracies (expressed as numbers of bits) required by the phase shifters and the operation unit so that they can produce the minimum change of the beam direction are investigated, and a simple formula is obtained. In order to verify the results of these investigations, experimental results and numerical calculations are presented.

Reduction of near field interference by beam controlling in a transmit phased array antenna

A method of reducing the electromagnetic interference over a broad frequency range by controlling the excitation phase of the element antennas for beam shaping in a phase array used in such systems as wireless LAN is discussed. In this method, an optimum excitation phase of each element antenna is determined by means of the output power minimization algorithm [1] with a directional constraint based on the amplitude and phase data of each element antenna in the far and near fields in the array configuration. The method presented here not only reduces the interference in the near field but also can maintain the radiation level in the desired direction in the far field. In regard to the reduction of interference in the near field by controlling the phase of the transmitting phased array, a method based on the output power minimization with a directional constraint is discussed. Also, in an experiment with an eight-element patch array antenna, the confirmed reduction of the interference is 13.2 dB with a bandwidth of 500 MHz at the frequency of 9.55 GHz and 31.7 dB at the center frequency only. Further, a method is presented for eliminating the effect of quantization error when a digital phase shifter is used for phase control, and its effectiveness is confirmed.

Progress of phased array systems in Japan

This paper reviews the research and development on the phased array antennas (PAAs) for several applications in Japan. First, the author shows the historical overview of the PAA for radar, satellite and mobile communication uses. Then, the author introduces a millimeter-wave PAA, an optical beam forming, and an ultra wideband antenna element as modern applications of PAA systems.

Pattern synthesis of an array antenna in a radome

The authors describe the results of a highly accurate pattern synthesis realized by analytic correction of the active element pattern, after determining the effects of scattered waves caused by the metal frames of a radome, using the geometrical theory of diffraction (GTD). Measured results on the null depth improvement ratio at different observation points are shown. These results indicate that a radiation pattern with the required accuracy has been obtained by taking into account the effects of scattered waves using the GTD.<<ETX>>