Investigations On Microwave And Millimeter Wave Array Imaging Key Technologies

Microwave and millimeter wave imaging technologies utilize the microwave and millimeter wave receivers to receive and detect the differences of the background radiation distribution characteristics and then form an image. Microwave and millimeter wave imaging technologies have important values on many fields such as airport security, flight landing navigation, military surveillance, and medical diagnostics. Especially for concealed weapons inspection personnel security situation, microwave and millimeter wave imaging technology has a natural advantage. With the demands for the image quality and imaging speed are continuously increasing, the traditional single-channel imaging system with mechanical scanning technology is unable to meet the demands, and with the development of the semiconductor technology, microwave and millimeter wave devices have made significant progress, the imaging systems acquired a significant improvement on system size, imaging speed, spatial resolution and etc. Varieties of microwave and millimeter wave imaging systems are continuously researched and developed. However, due to the limitations of imaging schemes and the cost, size and performance of the devices, microwave and millimeter wave imaging technology currently still has a huge space for development.This dissertation focused on the microwave and millimeter wave imaging systems based on the phased array schemes and digital multi-beam schemes. Firstly, to study the phase shifting scheme for the imaging system and its effect to the system and imaging results, and then to study the digital multi-beam millimeter wave imaging technology. During these researches, several novel key technologies are proposed and investigated for the microwave and millimeter wave imaging systems, and then a Ku band passive microwave phased array imaging system and a E-band multi-beam imaging system are designed and implemented, and the relevant results of design and imaging are displayed and analyzed. It is organized as follows:Chapter 1 makes an introduction to the basic principles of the microwave and millimeter wave imaging, especially focusing on the principles of the phased array imaging and digital multi-beam imaging. Based on the basic principles of the object radiation, the principles of the real aperture microwave radiometers and the brightness temperature measurement are analyzed, and the system architectures of the phased array imaging system and digital multi-beam imaging system are indicated and analyzed.Chapter 2 studied and implemented a phase shifter scheme based on direct digital synthesis (DDS) designed for phased array microwave and millimeter wave imaging system, which can overcome the sparse phase shifting features of digital phase shifter scheme and the imaging beam can be scanned with very fine intervals, thus effectively improving the imaging resolution and quality, significantly reducing the workload the digital imaging processing.Chapter 3 proposed and implemented a planar circuits interconnection based on substrate integrated waveguide (SIW), which using SIW as the transmission line of a module port to realize an excellent transmission performance by introduction a double-layer metal structure for shielding and current diversion without any additional welding or connectors. This method is proposed and designed to solve the flexible interconnections issues between millimeter wave circuits and modules, which can significantly improve the performance of millimeter wave circuits and systems, improve the flexibility of the circuit design and migration, reduce the design and implementation costs.Chapter 4 proposed and implemented a novel wire bonding technology directly based on SIW. Compared to traditional microstrip wire bonding, the proposed SIW bonding technology can effectively reduce the sensitivity to bonding operations and circuit production accuracy, and then significantly improve the wire bonding performance. This method has been successfully applied in the E-band millimeter wave imaging system, effectively improve the success rate and performance of the wire bonding operation.Chapter 5 studied and implemented a passive Ku-band phased array microwave imaging system. The imaging system comprises an antenna array containing 256 antenna elements uniformly distributed in two dimensional surface, each antenna is followed by a complete RF receiver, compared to the traditional mechanical scanning radiometers, by using the equivalent LO phase shifter based on DDS, the imaging system greatly reduces the scan intervals, achieves a very fine beam scanning and effectively improves the imaging quality.Chapter 6 studied and implemented a multi-beam E-band millimeter wave imaging system. The imaging system comprises an antenna array containing 16 antenna elements uniformly distributed in two dimensional surface. Each antenna is followed by a complete RF receiver, and each RF receiver is followed by complete IF circuit and ADC circuit. In this system, by introducing the circuits interconnection technology based on SIW and the wire bonding technology based on SIW technology, the testing and migration complexity in the millimeter wave band are effectively simplified, the wire bonding performance of the millimeter wave chips are improved, the difficulty of the millimeter wave circuit design and test are reduced, and the millimeter wave performance and success rate of design are increased.Part of this work has been published in the journal of IEEE Microwave and Wireless Components Letters, vol.24, Issue 11,2014, some international conferences. Several patents have also been filed.