Outdoor-calibration Method of the 3x3 Planar Array Antenna

Recently, superresolution techniques for Direction of arrival (DOA) estimation, such as MUSIC (MUltiple SIgnal Classification) algorithm [1], have become indispensable. By the assumption of an ideal array antenna, following problems are caused in an actual measurement. Array elements often have gain and phase errors, and mutual coupling effects cannot be also ignored in general, which degrade performance of the superresolution techniques for DOA estimation. Therefore, array calibration is necessary to estimate DOA with high accuracy. A variety to calibration techniques has been proposed, [2]-[4], and is divided into methods of using measured data of array antenna parameters and using reference signals from known sources. The former is a technique to use the mutual impedance derived from S parameter measured by a network analyzer [2]-[3], and the later is to calibrate antenna and receiver simultaneously. These techniques are carried out in an ideal environment such as an anechoic chamber without interference waves. When the array antenna is used in the outdoor experiment, estimation errors increase due to multi-path propagation. It is needed to calibrate the array antenna at outdoor environments, however, it is difficult because of the existence of some interference waves. In this paper, we propose the calibration technique using spreading sequence that is the reference signal for calibration. And we also propose a method of self-calibration using RF switches. We consider these techniques as an example with 3× 3 planar array antenna. However, these proposed methods are also applicable to the M×N planar array antenna.