Doctoral Dissertation

The construction of a low-cost and reliable array antenna system is required to facilitate the practical use of the adaptive antenna in the mobile communication field. The array antenna system can be verified by DOA (Direction of Arrival) estimation. This dissertation describes the attempt to achieve a high-precision adaptive antenna and the examination of this device, which suppresses the number of array elements, in a real mobile communication environment. In chapter 2, we evaluate the array antenna system by DOA estimation, and on the basis of this evaluation, we clarify the problems related to the hardware and propagation environment of the array antenna system. It is necessary to model the array antenna system both statistically and quantitatively based on measurements. First, we formulate the array antenna and DOA estimation and explain the prototype array antenna systems. The prototype system has been improved after every evaluation. Next, an evaluation method using a rotating array antenna is proposed. Using a rotating array antenna and DOA estimation, this method can be used to evaluate the array antenna system in detail. Further, we analyze the error factor on the basis of an experiment in the anechoic chamber. In chapter 3, we undertake a detailed examination of the errors resulting from inaccuracies in array element positions, mutual coupling of elements, and plane-wave approximation in which the distance between transmitting and receiving antennas is small. Element position and mutual coupling influence each other and affect the antenna element pattern. First, we formulate the array antenna that takes into account the effects of the antenna element pattern and use the moment method to quantitatively and statistically, analyze the mutual coupling and DOA estimation error. The DOA estimation error is dependent on null steering of the adaptive antenna. Next, changing simulation is performed by varying the extent of 2 mutual coupling. It is impossible to realize an antenna without coupling; however, the coupling can be suppressed. This property will be useful in manufacturing the antenna array. In chapter 4, we propose a calibration method for suppressing the error factors. Steering vector compensation method is the most basic calibration method. Coupling calibration using a fixed calibration antenna can eliminate these problems and it can be calibrated during operation. The correlation matrix estimation method for the transmission array antenna is demonstrated experimentally in the anechoic chamber. Additionally, based on the discussion in chapter 3, the time of calibration of the pattern is reduced by employing the element interval tuning method and a low-coupling array antenna system. The array antenna element pattern is changed due to several error factors; however, optimum adjustment of the element interval, mutual coupling, and number of elements results in a high-precision array antenna system with reduced errors. In conclusion, inaccuracy of array element position and mutual coupling of elements influence each other and cause a DOA estimation error or adaptive null steering in the antenna element pattern. A high-precision array antenna system can be achieved through optimal adjustment of these factors.