Coupling between two slot antennas on an infinite ground plane and radiation patterns on a finite ground plane are calculated. We introduce a parasitic wire between slot antennas to reduce coupling. Two typical cases with a monopole or a half-loop are considered in this paper. Numerical results show that the reduction of 13.9 dB is obtained by adjusting a monopole height to about a quarter wavelength of the operating frequency. Also a properly adjusted parasitic half-loop reduces the coupling coefficient by 24 dB. Radiation patterns of the antennas on a 365 mm 465 mm ground plane at 1.5 GHz are calculated where the diffracted fields are taken into account. It is found that the parasitic elements little affect the antenna patterns around the +z-axis that is perpendicular to the ground plane although the reduction of coupling between slot antennas is obtained.

We have shown that a photonic sensor can be used as an electric-field probe for planar near-field measurements of X-band antennas. Because an antenna on the photonic sensor is small (about 0.1 λ) compared to the wavelength, the photonic sensor can directly measure the amplitude and the phase of the electric field close (about 0.3 λ) to the apertures of antennas without disturbing the electric field to be measured. Therefore we can obtain the antenna pattern by transforming the measured electric field without probe compensation. To verify the merits of the photonic sensor, we have evaluated the antenna patterns of a standard gain horn antenna and a microstrip array antenna at 9.41 GHz. Comparing the results obtained using the photonic sensor with those obtained using the conventional open-ended waveguide probe and other methods, we have shown that the antenna patterns agree with each other within 1 dB over wide ranges of directivity.

The microwave scattering from periodical waves on water surface is analyzed with a model of sinusoidal water-wave and experiments. By X-band experiments in a periodical water-wave tank, it is shown that the intensity of the first order scattering varies in the manners of a sinc function of the water wave-number and of Bessel functions of the wave height.

The authors implemented a directionally-constrained adaptive array system in an audio-frequency range. This system has a good prospect of applications since it does not require a rigorous a priori knowledge of the desired signal. Its algorithm contains matrix calculation, for which some technique has to be devised in implementation. For this, data are sampled and A-D converted so that the necessary processing for feedback control may be done by a microcomputer in digital form. The signal path remains in analog form, which will allow us to extend the system to higher frequency range. The performance of the system is demonstrated through the experiments. Effects of hardware errors are found: (1) Nulling behavior against the interference is not affected at all by virtue of the feedback control. (2) A little deviation from the constrained response to the desired signal is perceived. The behavior against a wideband interference is investigated analytically and experimentally. It was found that the final SIR becomes lower with wider frequency bandwidth.