(A) study on the improvement of angle-of-arrival finding system using switched multi-port network

Abstract

This dissertation presents the switched multi-port receiver and an estimation method of the angle-of-arrival (AoA) for high-speed, precise, and cost-effective AoA finding. The AoA finding system using an array antenna has high accuracy and has been used in various applications such as a phased array, sensor localization, and interference source identification. However, since it requires a lot of receiving channels, it has a high system complexity, high cost, and a slow processing speed. On the other hand, the multi-port technique can measure the amplitude and phase of input signals very accurately using few passive circuits and has been researched in many application fields such as network analyzer, wireless communication transceivers, beam direction finder, and radar systems in various frequency bands. However, the conventional multi-port circuit has a problem of ambiguity in finding AoA with a long baseline longer than half wavelength, and when used for an array antenna, the system complexity can be rather increased. First, a one-dimensional (1D) AoA finding system using a switched multi-port network is proposed. It includes 4-element array antennas with long baselines with different antenna spacings and a circuit measuring four different phase differences for an accurate AoA finding. The proposed switched multi-port network consists of two hybrid couplers, four power detectors, and two dual-pole-dual-throw (DPDT) switches. It selects two different antennas periodically, and can measure four different antenna spacings. As a result, a more simplified and more accurate AoA finding system can be achieved. In addition, an estimation algorithm to resolve the ambiguity and improve the accuracy is also presented. Through the simulation, the accuracy of 14% was improved over the existing system, and the root-mean-square error of ±2° occurred when the signal-noise ratio (SNR) of 15 dB was in the measurement. Next, it is extended to a two-dimensional (2D) AoA finding system for the ambient signal sources. A base-triangle consists of three antennas, and can measure a 2D AoA. The three-antenna 2-D AoA finding system includes a planar array antenna and another type of switched multi-port network for providing a base-triangle. The circuit can detect the phase difference between two different antenna spacings, and simplify the systems by integrating a switch. The accuracy is identical with the conventional 2D AoA finding system. For antenna spacing longer than half a wavelength, the accuracy is increased, but the 2-D AoA could be ambiguous at the low elevation angle especially. In order to improve this, the algorithm to remove ambiguity based on two base-triangles has been proposed. It can be achieved that a non-ambiguous base-triangle chooses the closest angle among possible angles to a non-ambiguous but less accurate angle detected by itself. This method can have a high accuracy without the ambiguity for the 2D AoA finding system. For verification, the proposed method is simulated, implemented, and measured. Through the simulation, the accuracy is improved by 28% than the conventional system. In conclusion, the proposed system is expected to be a candidate for a cost-effective and accurate AoA finding system for beamforming systems and Internet of Things (IoT) applications.