Research On The Beam Of New Type Frequency Diverse Array In Range And Angle Domains

To satisfy the increasing diversified demand,antenna,as the forefront of electronic equipment,has gone through the development from mechanical scanning antenna to electronic scanning antenna,resulting in the rapid improvement in the beam scanning velocity and beam steering accuracy.For the past few years,a new type array antenna,namely the frequency diverse array which possessing the more flexible beam control ability,gradually caused the attention of researchers from domestic and overseas.By introducing the difference of transmitting frequency among elements,the concept of frequency diverse array ascends the antenna theory to a brand new stage of development,greatly enriching and successfully opening a fresh design thought of array antenna.Therefore,it is of significant importance in theory and application to research on the correlated techniques and new application fields of frequency diverse array.Under the support of national natural science fund project,i.e.“research on the theory and key techniques of frequency diverse array antenna(61571356)”,the characteristics of the beampattern of frequency diverse array in spatial range and angle domains are analyzed in depth,the controlling approaches for beam steering and the corresponding beampattern synthesis methods are investigated systematically.The main contributions of this dissertation are summarized as follows:1.Focused on the complex spatial electromagnetic properties of frequency diverse planar array,the spatial distribution of its electronic field in range and angle domains is systematically analyzed.Two theoretical models respectively for horizon frequency diverse planar array(which only applies frequency offset in horizon dimension)and horizon-elevation two dimensions frequency diverse planar array(which applies frequency offset both in horizon and elevation dimension)are established,and the approaches to control the beam steering corresponding to these two array antennas are derived at the same time.The whole beam coverage can be achieve by jointly utilizing the frequency offset and phase offset in horizon dimension,and those in elevation dimension.2.Focused on the difficulty in controlling the mainbeam direction and the complexity of signal processing induced by the time-dependent characteristics of beampattern of frequency diverse array,a quasi-static beamforming method is proposed with the frequency diverse array excited by impulse waves.In this way,an approximate time-invariant beampattern is generated which is similar to the static beampattern of conventional phased array.The theoretical model of pulsed frequency diverse array is firstly established,based on which the constraint to form quasi-static beampattern is derived.In the sequel,a quasi-static method to control the mainbeam direction is obtained.3.Focused on the utilization of the new controllable degrees-of-freedom(DOFs)induced by frequency diverse array,the flat-top beampattern synthesis in range and angle domains is conducted based on the second-order cone programming approach.The mainbeam is properly broadened both in range and angle domains after the synthesis.Based on the observation that the electromagnetic distribution of frequency diverse array is correlated with the frequency offset,the array is partitioned into two symmetrical subarrays and each subarray adopts a distinguishable frequency offset.In this way,one mainbeam is generated in the whole observation region.In the sequel,the flat-top beampattern synthesis problem is constructed as a second-order cone programming problem to maintain the response of the array in the mainbeam region.The transmit energy efficiency is improved after optimizing the amplitude and phase part of the transmit weight vector.4.The initial trial proposed structure in 3 has the inherent disadvantages of high peak sidelobe level and limited flexibility in beampattern synthesis.To further focus the transmit energy in the desired local region in range and angle domains,the author next explores and analyzes the characteristics of the resultant spatial electronic field distribution of the frequency diverse array which is divided into multiple non-overlapped subarrays.To analyze the electronic field superposition of these subarrays in detail,the whole observation region is divided into three non-overlapped regions.The resultant electronic field intensity of the array is elaborately analyzed and discussed in each sub-region.The relationship between the peak sidelobe level of the array and the number of the subarray / the element number in each subarray is derived and analyzed in detail.Based on this multiple subarray structure,the range-angle-decoupled beampattern synthesis is investigated.In specific,the relevant optimization models based on the two criterions,i.e.,the minimum mean square error criterion and the minimax criterion are respectively constructed,each of which can be fast and efficiently solved via convex optimization method.Three synthesis implementations are carried out,i.e.,the low-sidelobe beampattern synthesis,flat-top beampattern synthesis in range domain and multiple beams synthesis in range and angle domains.