Investigation On Multibeam Antennas Based On Rotman Lens

Phased array antennas have been widely applied in traditional military fields such as multi-target tracking radar,electronic countermeasures,and electronic investigation.This kind of antenna usually employs T/R components to implement beam scanning in two dimensions or only one dimension.However,the complicated structure is often high-cost.In recent years,multi-beam array antennas have been rapidly applied and developed in communication base stations,satellite mobile communications,automotive anti-collision radars,millimeter-wave passive imaging,missile guidance,and space exploration.Compared to phased arrays,multi-beam forming network has the advantages of balancing performance,complexity,and cost.The Rotman lens is a multibeam forming network which has been widely used.It has many advantages such as ultra-wide operating frequency band,frequency invariant beam-pointing characteristic,simultaneous generation of several beams,simple design and easy integration.Since the Rotman lens was first proposed in 1963,it has been widely used in multibeam antenna systems such as radars,satellites,and wireless communications through several decades of development.Based on the existing applications of Rotman lens,this dissertation further extends the applications of functions and scenarios,which include applications of low-sidelobe multibeams,monopulse multibeams,cylindrically-conformal multibeams.In terms of the technical potentials of Rotman lens,it can be also designed for wide-angle scanning and dual-frequency dual-polarized antenna array.The feeding network and antenna arrays involved in this dissertation are fabricated by a printed circuit board(PCB)technology.The guided wave structures consist of microstrip transmission lines and substrate integrated waveguides(SIW),which have the merits of light weight,small size,high processing accuracy good consistency,high integration,and low cost.The rational combination of the two guided wave structures can overcome each other’s shortcomings and exploit their respective advantages,providing complementary performance for the feeding networks and antenna arrays.The main research contents are as follows:1.The traditional quasi-optical analysis method of Rotman lens is introduced in detail.Based on this method,a mixed structure of microstrip and SIW Rotman lens is designed.This type of lens can be easily integrated with the SIW antennas to validate its multibeam scanning performance.The design theory and method of SIW slot array antennas is introduced.As the main form of array antenna in this dissertation,an X-band antenna array by a Rotman lens of mixed structure is designed,processed and tested.Two integration solutions for the antenna and the lens are proposed: the single-plate structure and the doublelayer compact structure.2.A dual-layer SIW lossy network is proposed,which can weight amplitude and compensate phase.Base on the weighting network,a low-sidelobe multibeam forming network is designed to implement a compact dual-layer multi-beam slot array antenna.Simulated and measured results for the low-sidelobe multibeam antenna are analyzed.3.Combining a four-quadrant comparator with a multibeam network,a monopulse multibeam array antenna is proposed,which can improve the angle detection and tracking accuracy in the beam scanning direction.Measured results demonstrate the good performance of the monopulse multibeam array antenna.4.Based on the quasi-optical analysis method of a planar Rotman lens,the design equations of a cylindrical conformal Rotman lens are derived.The achievable bending degree of the Rotman lens and its effect on operating band are analyzed.An axially cylindrical conformal SIW slot array antenna fed by a conformal Rotman lens is fabricated,and the performance of the conformal antenna is shown by comparing simulated and measured data.5.Considering the potentials of the Rotman lens to generate wide-angle scanning beams,a simple and low-cost modified method to implement wide-angle scanning for SIW slot array antennas has been proposed.This research offers a trade-off strategy to improve the impedance matching in a wide range of scan angle.Using the transmissive characteristic of the metasurface to realize wide-angle impedance matching(WAIM)has been qualitatively analyzed and the WAIM in E-plane has been remarkably improved for an SIW slot array.6.A multibeam dual-band orthogonal linearly polarized antenna array has been presented.Two feeding techniques have been used on each side of the substrate to increase the isolation between transmitting and receiving band and improve the cross-polarization between the two polarization values.The array antenna fed by a Rotman lens can realize electronic scanning.If it is mounted on an azimuthally rotatable servo platform,it can realize mechanical scanning and further to automatically track communication satellites.