Fundamental Studies on Integrated Antennas

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We have investigated (1) excitation of integrated antennas and their radiation properties, (2) highーresolution timeーdomain measurements and (3) multipath suppression in mobile communications.The principal results are as follows :1. The integrated antennas have multiーlayed structure of radiation elements and feeders including active circuits. The radiation elements are excited through a small aperture by electroーmagnetic coupling. We have formulated analysis of the antennas using a spectral domain moment method. We carried out numerical calculations and fundamental experiments for several models, and showed their input and radiation properties. Also, we showed behavior of a parallelーplate wave guide mode and conditions of suppression of it.2. Timeーdomain measurements are useful and attractive for electromagnetic devices. However, a conventional method using an FFT (Fast Fourier Transform) requires broad bandwidth frequency data to obtain high resolution in a time domain. Namely, the FFT is not adequate for narrow bandwidth devices such as antennas. We have proposed the time-domain measurements using a MUSIC Algorithm. Furthermore, we investigated fundamental properties and applications of the algorithm. It was shown that the frequency bandwidth required by the MUSIC Algorithm to resolve distinct time-domain responses is much narrower than that by the FFT.3. Frequency-selective fading due to a multipath signal is one of the most serious hindrance in high-speed digital mobile communications. We have proposed to suppress the multipath signal using an adaptive antenna. We carried out computer simulations and showed that the adaptive antenna is useful in high-speed digital communications. Also, we proposed a method to generate a reference signal in the adaptive antenna and an advanced processing technique using a diversity scheme.