| The streamlined surface of the high-speed aircraft limits the installation space of the planar antenna,making it difficult to apply the large planar antenna array composed of the traditional planar antenna,which can be effectively solved by the conformal antenna.In addition,the bandwidth of common microstrip patch antennas is narrow,and it is difficult to meet actual demand,so the research of broadband conformal antennas is becoming increasingly important.The paper focuses on the design of the array element,antenna array,and common port antenna of the broadband microstrip conformal antenna.First,the theory of microstrip antennas is introduced,and then several design schemes for broadening the bandwidth of microstrip antennas used in this paper are listed: 1.The parasitic patch is added above the patch antenna,and the resonant frequency of the parasitic patch is superimposed with the bandwidth of the main radiating patch to expand the bandwidth;2.Wideband impedance matching is carried out using a wideband impedance converter;3.The slot is opened on the antenna patch to increase the resonant frequency of the antenna and suppress cross-polarization.Then the feeding network of Wilkinson power divider is introduced,and the fabrication method of base antenna based on Polydimethylsiloxane(PDMS)dielectric substrate is also introduced.Next,the array element structure of the broadband conformal antenna working in the S-band is designed,which is divided into a two-layer structure and a three-layer structure.The antennas are composed of the main radiation unit and parasitic patches.The broadband impedance matching is adjusted by a wideband impedance converter.The antenna structure is protected by covering a layer of the dielectric plate above the antenna,and the antenna area can be reduced and the antenna bandwidth can be expanded.In the design of the three-layer element,multiple slits are used to change the current distribution and suppress cross-polarized waves.The bandwidth of the three-layer antenna element structure is 2.7GHz-3.52 GHz,the relative bandwidth is26%,and the maximum radiation gain is 8.71 d Bi.Subsequently,based on the two antenna elements,a variety of antenna arrays with different numbers of array elements are designed,and conformal testing and darkroom testing were carried out on the 4×4 antenna array.When the antenna is conformal with a 500 mm radius cylinder,the gain of the antenna is greater than 17 d Bi in the band range of 2.65GHz-3.6GHz,and the voltage standing wave ratio(VSWR)is less than 2.5.Based on the test of the 4×4 array,a 4×8 common port antenna array is designed in this paper.The common port array is the foundation of the phased array,including the antenna array and feed network part of the phased array.After machining the common port array,the measured bandwidth of the antenna is 2.7GHz-3.5GHz,and the VSWR is less than 2.0.The simulated gain is 24.9d Bi,and the measured gain value can be obtained by adding 3d Bi to the test value of the 4×4antenna array,so it can be greater than 20 d Bi in the frequency band.This paper attempts to improve the conformal antenna by replacing the F4 BM microwave plate with PDMS material.PDMS is commonly found in flexible sensors,and its mechanical properties are similar to colloid,which can be closely attached to the skin.In this chapter,a three-layer PDMS cell structure is designed with a bandwidth of 2.78GHz-3.71 GHz and VSWR less than 2.0 in the bandwidth. |
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