Study On Mutual Coupling Calibration Method For Adaptive Array Antenna

Array antenna has been widely used in many fields, such as radar, communications, navigation, electronic warfare, radio astronomy and so on. However, due to the demand for miniaturization and broadband on modern communication equipment, the mutual coupling between array elements cannot be ignored. The mutual coupling leads to resolution reduction, more direction finding error, higher interference nulling and more beam pointing deviations and some other adverse consequences. Therefore, aiming at improving the performance of the antenna array and achieving a broader application, the study on mutual coupling calibration methods is of great significance.With this background, the mutual coupling calibration methods for array antenna were studied in this dissertation. We have introduced the mechanism and analysis method of the mutual coupling. Additionally, the advantages and shortages of the available calibration methods were summed up in detail. On the basic of above analysis, the author proposed a new method for mutual coupling calibration. Moreover, a new mutual coupling calibration for wideband mutual coupling was proposed based on the aforementioned method. And the main work and contributions of the author are listed below:1. A new method for mutual coupling calibration has been proposed in the view of electromagnetic analysis based on the analysis of mutual coupling mechanism and available calibration methods. We call this method the element pattern reconstructed method. This method employed the difference between the isolated element pattern and the element pattern in the presence of mutual coupling effect to establish mutual coupling matrix equation. Through the analysis, the mutual coupling matrix can be obtained by the least squares method. Further, a simplify element pattern reconstruction method for the same element was derived.2. The mutual coupling method for omnidirectional and directional antenna array has been studied and the proposed method was employed to calibrate the mutual coupling. This method realized the mutual coupling calibration for various elements and array forms. The elements cover omnidirectional, directional and linear polarization and circularly polarized antenna, and the array forms cover uniform linear array, uniform circular array and conformal array and so on. The validity of the proposed method was verified by one-dimensional and two-dimensional DOA estimation.3. We proposed a new adaptive calibration method corresponding to the incident signals. Based on the element pattern reconstruction method, the mutual coupling calibration was employed in the direction of the incident signals, and more accurate calibration matrix can be got. By alternate iteration with MUSIC algorithm, the calibration matrix and wide angle direction of arrivals estimation can be achieved. The method was employed on calibrating the mutual coupling for a uniform linear array and L-shaped array and achieved accurate one-dimensional and two-dimensional direction of arrival estimations.4. A new wideband mutual coupling calibration method was proposed. The new method was developed by combining the element pattern reconstruction method and the interpolation method. For the curves of each entry in calibration matrix against the frequency, the interpolation method was an alternative method for the achievement of wideband mutual coupling calibration matrix. A uniform circular array with eight broadband dipoles was designed to verify this method by DOA estimation, and the validity of this method was verified by DOA estimation results.5. We studied the mutual coupling effects on MIMO system channel capacity. First, two miniaturized multi-frequency slot antennas were designed by the method of split ring loading and various slots on the ground. MIMO array was constructed by the presented two slot antennas as element. Then the mutual coupling matrix of the MIMO antenna array was obtained by the element pattern reconstruction method. For Rayleigh fading channel, the research about the mutual coupling effect on the performance of MIMO communication system was completed.6. We built experimental platform, and completed the validation of the method in the digital domain. There were three parts in the experimental system, which were the antenna array, RF modules and digital processing module and so on. The validation of the element pattern reconstruction method was verified by the DOA estimation experiments for omnidirectional monopole array and directional microstrip antenna array. Through the analysis and comparison of the DOA estimation results in different modes, the validity and usefulness of the element pattern reconstruction method were verified by the accuracy DOA estimation.