Investigations On Feed Networks For Scanning Slot Array

Conventional metal waveguide slot array antennas have been widely used in radar, wireless communication systems for their geometric simplicity, high efficiency, polarization purity, power capability. With the rapid development of the microwave technology, low-profile, miniaturization and high integration become the new requirements of high-frequency circuits. Substrate integrated waveguide(SIW), combining the advantages of both planar transmission-line and non-planar-waveguide structures, presents an excellent solution for the design and implementation of slot arrays. Thus, this dissertation focuses on the design methods of low side lobe power divider and beam-forming networks for SIW slot arrays at X-band.Firstly, this dissertation introduces the research backgrounds and significance of slot arrays and summaries current situation of SIW technique and planar multi-beam forming network. The design method of SIW and its equivalent waveguide model are studied from the commonly used structures as followes: SIW to microstrip transition, SIW to coaxial transition and unequal-width phase shifter.Secondly, this paper analyzed how the amplitude and phase error of feed network affect the sidelobe of array pattern. The simulation design of a compact 16-way power divider shows that phase error is a key factor to constrain low-sidelobe performance of array antennas with fewer elements. Owing to the narrow phase bandwidth, am improved arbitrary-way unequal power divider is proposed on the basis of the classical binary tree prototype, which can achieve low sidelobe at a wide bandwidth through simulation and measurement.Thirdly, a microstrip-SIW hybrid structure Rotman lens combining the benefits of the both transmission lines is proposed, which emploies SIW unequal-width phase shifter instead of microstrip delay lines for increasing isolation between the output ports and eliminating the adverse effects on amplitude and phase of outputs which brought by mutual coupling between microstrip delay line. In addition, compared with microstrip, SIW structure leads to a loss reduction and improves the efficiency of the lens.Finally, four schemes of low-sidelobe beamforming networks are summarized and the advantages and disadvantages of their application are listed. A new amplitude weighted network, consisting of double-layer SIW couplers, is proposed. The amplitude of all outports can be weighted to achieve low-sidelobe beam scanning when the original microstrip-SIW Rotman lens is loaded with the networks. The design is verified by simulation.