Contact-Less Near-Field Test of Active Integrated RF Phased Array Antennas

Future RF transceivers are expected to integrate the entire system, from baseband to antenna. Many emerging applications use beam forming, which necessitates RF phased arrays and multiple antennas integrated on the same die. This integration presents a challenge in testing the entire system including antennas. The electromagnetic signal output is combined in the air and no longer can be separated by physically connecting to the test equipment. Testing each element in isolation does not exercise the interaction between the elements and cannot characterize important parameters such as phase mismatch. Thus, systems with multiple integrated antennas need to be tested using wireless means. This paper presents a novel contact-less near-field test method for measuring the gain and phase mismatch of RF phased array antennas. The proposed method is based on using a known good die (KGD) receiver phased array antenna to capture the combined EM output of the transmitter antenna as the device under test (DUT). The mathematical model of mutual impedances and signal propagation is presented for a 16-element phased array to determine both gain and phase mismatches. The feasibility of the method is shown using hardware measurement. The accuracy of the method under process variations and imperfections in the test set-up, including noise and error in test set-up dimensions, is further investigated through electromagnetic (EM) simulations of a coplanar patch antenna array of sixteen elements.