Unambiguous 2-D Angle-of-Arrival Estimation Receiver Based on a 16-Port Interferometer

Multiport interferometer (MPI) techniques are getting more and more attention, especially for passive receiver (Rx) beyond 24 GHz. However, MPIs with more than six ports are rarely been studied. And the existing MPI techniques only can achieve 2-D angle-of-arrival (AOA) estimation in a narrow range of angle, which means they have an ambiguous problem. In this article, an unambiguous 2-D AOA estimation Rx based on a 16-port interferometer is proposed and demonstrated. It has three main components: eight antennas, a 16-port interferometer, and a signal processor. The 16-port interferometer with eight input ports and eight output ports is the key part and the main point of this article. The eight input signals are superposed on eight output port signals in the interferometer. First, a 16-port interferometer and the corresponding AOA estimation algorithm are proposed. The algorithm transposes the phase differences between the antenna elements into the power relationship of the output signals. Then, the Rx error models are established to obtain the systematic errors. After that, a method for reducing angle ambiguity is introduced. The method allows for the distance between the antenna elements to be larger than $\lambda $ /2, and the angle detection range is theoretically–90° to 90°. An Rx operating at 31 GHz was fabricated. The measurements demonstrate that the system operates as expected, with AOAs ranging from–40° to 40° and a mean squared error (MSE) of approximately 1°.