| By combining an antenna array with a passive beamforming network(BFN),the array antenna can achieve flexible beam control and meet functional requirements such as wide-angle beam coverage monitoring,flexible beam pointing communication and monopulse detection.This dissertation takes a multibeam antenna with a beam switching function as the research object and discusses the functional realization and compact design of passive BFNs,as well as the design method of high-performance antenna elements.The research content of this paper can be divided into the following parts:1.The beamforming method of a one-dimensional(1-D)beam switching antenna is studied.First,based on the principle of energy conservation,the numerical relationships among radiation energy,transmission phase and antenna size are established by accurately analyzing the energy distribution on a microstrip antenna element,and a new design method for a serial-fed microstrip array antenna is proposed.Then,by reasonably reducing the focal length of the lens,the lens design of a 120°phase shift is realized while ensuring the miniaturization of the lens.Further,a serial-fed microstrip array antenna based on a Rotman lens is designed,which can achieve ±45° area coverage through 13 high-gain beams with different orientations.Furthermore,a new method of sidelobe suppression on the scanning plane of Rotman lens is proposed,and the simple design of low sidelobe lens is realized by using the receiver port redistribution technology.Finally,a low sidelobe multibeam antenna is designed to verify the feasibility of the sidelobe suppression scheme and the good beam scanning capability of the antenna.2.The dual-beam small diversity angle technique of angle diversity reflector antenna is studied.To address the contradiction of a large aperture and a small defocus distance,a dual-beam dielectric rod feed antenna fed by waveguide OMT is designed.Based on this feed antenna,a multibeam parabolic antenna applied to an angular diversity scattering communication system is designed,which can achieve two high-gain beams pointing at different angles,and the beam angle is 0.75 times that of the HPBW.In order to meet the requirements of the vehiclea,a longitudinal size reduction scheme based on Cassegrain antenna is further proposed to achieve the same small-diversity angle performance under the compact size.3.The beamforming method of a 2-D beam switching array antenna is studied.(1)First of all.the operating mode and internal field distribution of a shorting microstrip antenna are studied.By symmetrically arranging shorting microstrip structures of different widths,dual-resonance wideband(34%)and wide-beam(154°)performance is achieved to meet the requirements of 2-D beam scanning.In addition,the a cross-polarized generation mechanism of the microstrip antenna is studied,and the H-plane polarization isolation of the antenna is effectively improved(>16 dB)by extending the width of the microstrip antenna and introducing shorting pins.Based on the above research,an all-metal shorting microstrip array antenna with coupled feeding is designed.Then,a novel 3-beam Butler matrix(BM)network topology is proposed to accommodate the array,which achieves compactness through the spatial and functional multiplexing of broadband components.The network can achieve the same amplitude signal output with three different linear phase differences within a relative bandwidth of 27.3%.Furthermore,according to the orthogonal beam control principle,six 3-beam BMs are divided into two groups and stacked together to manipulate the beam direction of two orthogonal directions.Based on this,a 2-D BFN is designed.Finally,by combining the 2-D BFN and the antenna array,the array antenna can achieve nine high-gain beam radiation levels with different directions in three-dimensional space.(2)By analyzing the resonant mode and surface current of SIW cavity,a simple and efficient four-element SIW back cavity antenna is designed,and the antenna is used as the array element to construct a 4×4 antenna array.Then.the formation mechanism and signal transmission matrix of the sum-difference beam are studied.Based on the layout and functional requirements of the antenna array,a compact cross-type monopulse feed network is designed.In a 13.75～14.75 GHz frequency band,the network can realize the signal output of three different sum and difference modes.Finally,a monopulse array antenna is designed,which can achieve 2-D monopulse performance through the combination of the monopulse feed network and the SIW cavity-backed antenna array.4.Based on the requirements of wide angle wide angle field beam coverage and high data transmission rate of multi-beam array antenna,the realization methods of broadband,wide beam and dual beam performances of antenna unit is studied.(1)Based on the resonant frequency redistribution of the microstrip antenna(MSA),the TM0.1/2 mode and TM0.3/2 mode resonant frequencies of the shorted patch antenna(SPA)are changed by the shorting pins and slot loading.Based on these operations,the SPA achieves a broadband performance(11%)due to mode fusion.Then,two SPAs are placed symmetrically.By analyzing the generation mechanism of the H-plane cross-polarization and E-plane wide beam radiation of the SPA,a broadband SPA with a wide beam and high polarization isolation performance is designed by means of differential feeding.Then,a broadband binary shorted patch patch array antenna with dual beam and high port isolation performance is designed by separately exciting the feed port and combined with compound decoupling measures.(2)The resonant characteristics of artificial magnetic conductor(AMC)and its effect on antenna miniaturization are analyzed by using equivalent circuit.In addition,a short circuit pin loading method is proposed to control the resonance frequency of AMC.Finally,the antenna achieves a 27.7%relative operating bandwidth at a compact size of 0.37 × 0.35λL2(λL is the wavelength corresponding to the lowest working frequency). |
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