Masataka Ohtsuka

On-Board Calibration Methods for Mechanical Distortions of Satellite Phased Array Antennas

In satellite phased-array antennas, mechanical distortions, which may be due to vibrations caused when launching the satellite into the orbit or thermal variations in the orbit, result in significant degradation of electrical performance. In this paper, two on-board calibration methods are proposed for such mechanical distortions: One compensates for the element phase differences resulting from mechanical distortions, and the other is used to set the best-fit phase distribution obtained from the measured phases. The latter method is effective even at a low signal-to-noise ratio (SNR). The proposed methods have been validated by experiments, through which the theoretically predicted calibration accuracy of the methods has been successfully reproduced.

A dual-polarized planar array antenna for Ku-band satellite communications

The authors propose a low sidelobe dual-polarized planar array antenna for Ku-band satellite communications. In conventional dual-polarized planar array antennas using strip lines and microstrip patch antennas, it is difficult to obtain low sidelobe characteristics because the aperture distribution is deformed from the desired one by electrical coupling between feed lines and element antennas. In the proposed antenna, rectangular coaxial lines have been adopted as feed lines in order to reduce coupling between feed lines. We have developed a dual-polarized element antenna shielded by a cavity, in order to reduce coupling between element antennas and feed lines. Also, we have developed an element antenna arrangement forming the desired aperture distribution by adjusting the number of antenna elements in each row. These developed techniques can achieve sidelobe levels of less than -23 dB which would be lower than those of the conventional dual-polarized planar array antennas.

A linear array antenna using bifilar helical elements for mobile satellite communications

In mobile satellite communication systems such as the AMSC/TMI system [Lunsford et al., 1992], circularly polarized omni-directional antennas are attractive for vehicle antennas because any satellite tracking mechanism in the azimuth direction is not necessary for these antennas [Ohmori, 1991]. As one type of omni-directional antenna, a bifilar helical antenna has been proposed [Nakano et al., 1991]. This antenna is convenient owing to its thin diameter. However, this antenna. has a disadvantage that the beam direction in an elevation plane moves according to frequency change. In the present paper, the authors propose a linear array antenna using two bifilar helical antenna elements placed along the helix axis. The capability of reduction of beam direction movement is discussed for this array antenna.<<ETX>>

Basic study on wideband microstrip patch antenna incorporating matching-stubs onto patch conductor

This study demonstrates a new bandwidth improvement technique using a structure of impedance-matching function which is composed of two series-stubs located on the patch conductor.The effectiveness of the matching stubs on the bandwidth improvement has been confirmed experimentally. The proposed method is especially effective against a thin microstrip patch antenna that it is hard to apply L-probe method.

Optimization of cross polarization characteristics for dual-polarized patch antennas

Base station dual-polarized patch antennas for cellular mobile radio require us to decrease cross-polarization for the planes tilted from the horizontal plane. We report the cross polarization characteristics in the tilted planes, and derive analytically that there exists the optimum substrate permittivity to achieve low cross-polarization. Moreover, we validate these characteristics both by FDTD simulations and by experiments.

One-element diversity antenna with reactance-switching circuit for mobile phones

We have proposed a novel type of diversity antenna construction for compact mobile telephones. The proposed diversity antenna basically consists of one excitation element, the conducting-plate, and the reactance-switching circuit connecting between the end of the element and the conducting-plate, and need not install two excitation elements. We have demonstrated numerically and experimentally that the current phase distribution and radiation pattern can be controlled by appropriately switching the reactance value of the reactance-switching circuit. Our next works are to establish an optimum design theory and to investigate the performance in talking and browsing situations.

A helical antenna with a self-complementary shape

The authors propose a bifilar helical antenna with a self-complementary shape. Bifilar helical antennas having an omnidirectional radiation pattern often have been composed of thin wires . In these conventional shapes, it is difficult to design an antenna satisfying both desired characteristics of the radiation and the reflection because the design parameters, such as antenna diameter, simultaneously influence these characteristics. The proposed antenna has an input impedance of which the conductance is almost constant by applying a self-complementary shape to the antenna structure. This technique allows selection of the optimal antenna diameter for the radiation characteristic independent of its impedance matching.

Statistical analysis for null shift by random phase errors in thinned monopulse phased array antennas

The authors present a statistical analysis for the null shift due to random phase errors in a thinned monopulse phased array antenna. The resultant equations are simple and can be applied to a phased array antenna whose aperture amplitude is tapered by thinning. The usefulness of this analysis is verified by a comparison of the deviation of the null shift obtained by the equations presented with that obtained by numerical simulations using random numbers.<<ETX>>