Research On Low Profile Circular-polarized Antenna Array Based On Microstrip Line Structure

Compared with linearly polarized antenna,circularly polarized antenna has the advantages of overcoming the attitude change of receiving and transmitting antenna,combating multi-path interferences and reduce Faraday rotation effect,so it is widely used in satellite communi-cation,positioning and navigation,radio frequency identification and other fields.High gain and miniaturization have always been the key technologies in wireless communication sys-tems,and they are also the research hotspots.For circularly polarized antenna arrays,the complex feed network has long design cycle,high cost and large system loss.How to reduce the size of feed network and simplify the array structure is the goal that antenna engineers are constantly pursuing.Simple array structure not only has low loss and low cost,but also simplifies the design process.In this paper,two kinds of low-profile circularly polarized antenna arrays with microstrip line as feed network are proposed:The first type of the proposed antenna periodically loads quarter-wavelength short-circuit arms on both sides of the microstrip line to suppress the fringe electric field on one side of the microstrip line,thus enabling the microstrip line to generate effective radiation.With this structure as the coupling feed network of the antenna,the radiating element of the an-tenna and the feed network can be integrated on a dielectric board,which reduces the profile height,and reduces the transmission loss without designing a complex feed network.Based on this structure,two different polarized antennas are designed,and one of them is processed and measured.It can be seen from the test results that the antenna achieves 3dB axial ratio bandwidth(19.65GHz-20.35GHz)of 700MHz near its working frequency point,the mea-sured gain of the central frequency point is 15.2dB,the front aperture of the whole antenna is 1.34?₀×8.6?₀,the structure is compact,and the height is only 0.1?₀.This kind of antenna has the advantages of low processing cost and less design difficulty.The second type antenna is an improvement on the first type antenna.The feeding network of the first type antenna has certain radiation,which has a certain influence on its radiation characteristics.Therefore,when designing the second type antenna,the feeding network is changed to two parallel coupled microstrip lines excited by differential modes,and the antenna elements are fed by proximity coupling.In order to compensate the influence of the feeding network on the radiation parameters of the antenna,the radiating element of the second type of antenna no longer uses the traditional chamfered patch,but uses an L-shaped patch with adjustable size.By modifying the size of the element,the radiation produced by the feeding network is compensated,thus reducing the influence of the feeding network on the radiation characteristics of the antenna.Then,two kinds of power dividers are designed,one is designed by waveguide coaxial converter to provide stable differential excitations,and the other is based on substrate integrated waveguide structure to provide equal amplitude and in-phase excitations for two parallel coupled transmission lines.The test results show that the far-field pattern of the antenna is symmetrical,the radiation gain at the center frequency point is 11.25dB,and the 3dB AR bandwidth is 400MHz(19.7GHz-20.1GHz).This kind of antenna not only has better radiation performance,but also has stronger array expansion potential.The radiating element and feeding network of the antenna are integrated on a dielectric board,which is compact in structure and simple in design,and is suitable for the application scenarios of circularly polarized antennas with low profile.