Research On Ultra-Wideband Phased Array For Mid-Frequency Aperture Array Of Square Kilometer Array

The Square Kilometer Array will be an ultrasensitive radio telescope,built to further understand the most important phenomena in the universe,such as the birth and death of the universe itself.The construction work of the mid-frequency aperture array is planned to be deployed in Phase 2 of the Square Kilometer Array.The key scientific goal of the mid-frequency aperture array is to research the impacts of dark energy on the universe and measure pulsars as well as other radio transient events with a high speed.Thus,it is necessary to design a low-cost,high polarization isolation,ultra-wideband and wide angle scanning antenna array to meet the technical requirements of high sensitivity radio telescope.As the main part of a research project,this thesis mainly concerned the design principle,methods and engineering realization of ultra-wideband antenna array,for meeting the indicators of mid-frequency antenna array proposed by astronomers.The main contributions are outlined as follows:1.The ultra-wideband tightly coupled octagonal ring antenna array is studied.An ultra-wideband octagonal ring antenna element based on the resistive frequency selective surface is presented.The standing wave protrusion caused by the reverse phase superposition of the reflection plate at the corresponding frequency point can be effectively suppressed by inserting a square ring resistive frequency selective surface between antenna array and ground plane,which greatly improved impedance bandwidth and reduced the profile of antenna array.Simulation results indicate that based on the resistive frequency selective surface,a 5:1 impedance matching bandwidth is obtained within the ±45° scanning range.At the same time,the profile of the antenna has been also reduced by about 27%.2.The ultra-wideband tapered slot antenna array is studied.In order to further expand the bandwidth and reduce the cost of traditional tapered slot antenna array,a novel dual-polarization tapered slot antenna element with a cross-shaped structure is designed.By replacing square resonator of traditional tapered slot antenna with pentagon resonator,the operating bandwidth of the designed antenna has been extended without occupying the area of active circuit;What's more,without affecting the performance of antenna,the size of substrate has been reduced greatly by designing radiator and feeding balun separately,which leads to a significant reduction in costs and system noise;The antenna is processed into a cross-shaped structure,which provides good current continuity between elements and excellent polarization performance.The simulated results show that the proposed antenna,covering the 0.25-1.56GHz frequency range,demonstrated a stable cross polarization within the ±45°scan volume.Finally,a prototype of the dual-polarization 8×9 antenna array is fabricated to validate the feasibility and efficiency of the design method.In this thesis,through the depth study of the square kilometer array,we understand the design requirements and application scenarios of the mid-frequency array.Aiming at the shortcomings of the original antenna of the project,an improved method was proposed.The simulated and measured results show that the improved method proposed in this thesis has a high practical value for the design and construction of the mid-frequency aperture array.