Design and Analysis of an X-band Phased Array Patch Antenna

Abstract

An 8x8 array antenna has been designed for a frequency band of 8-8.5 GHz. The design has been made as a part of a project to develop a digital, active MIMO radar at the Norwegian Defence Research Establishment (FFI). The array consists of 64 resonant aperture stacked patch (ASP) antennas. An element spacing of 16.5 mm ensures that no grating lobes occur over the entire scan range. A scan range of -55° to 55° and -45° to 45° have been achieved in the E-plane and H- plane respectively. This scan range was achieved using wide band antenna elements. Methods to improve the scan range and the reflection coefficient such as electromagnetic bandgap (EBG) material, defected ground structures (DGS), and adaptive matching circuits was investigated. All three alternatives were discarded due to either added complexity to the design or problems incorporating the methods into the design. The array has achieved a half power beam width of 14° when scanned in broadside direction. The efficiency of the array is 0.96 which is an important result considering that 50 W is to be applied to each element.The antenna element used in the array was based on a design developed during the specialization project. Measurements on this antenna element were conducted and large deviations between measured and simulated input impedance were discovered. These deviations were found to be caused by mechanical properties of the antenna element. The antenna element was improved and better compliance between measured and simulated results has been achieved.