Design Of S-band Broadband Circularly Polarized Antenna

Circularly polarized antennas are widely used in communication systems such as satellites and radars because of their strong electromagnetic anti-interference ability.They can receive any polarized electromagnetic waves and reduce the loss of transmitting signals.With the development of radio technology,the design of the antennas gradually tends to be miniaturized,light-weight and easy to conform with carrier.Meanwhile,to reduce the influence of wind resistance during the high-speed movement of the carrier,the low-profile antenna is also a hot spot in current research.Broadening the bandwidth of antennas can allow the antenna to cover several narrow-band frequency bands at the same time,which can reduce the number and the volume of the antennas greatly while meeting the index requirements.According to the research requirements,three different types of single-feed broadband circularly polarized low-profile printed antennas are designed in this thesis.These antennas are used in S band.And the array and scanning design of the last antenna is also carried out to realize a wide-angle scanning.The first antenna is a broadband circularly polarized wide-slot antenna based on artificial magnetic conductor(AMC)structure.The radiation patch printed in the top surface of the substrate is a knife-shaped structure,and this structure can improve the impedance matching characteristics of the antenna greatly,and then broaden the antenna bandwidth.The circularly polarized characteristics is obtained by etching an asymmetric slot on the bottom surface of the substrate.However,the size of the slot is too large,which will cause back radiation.In order to make the wide-slot antenna radiate directionally and reduce the overall profile of the antenna,an AMC structure is placed under the wide-slot antenna.The AMC antenna has in-phase reflection characteristics for electromagnetic waves in specific frequency band.Using it instead of a metal reflector plate can shorten the distance between the antenna and the reflector and reduce the antenna profile.Finally,the antenna is fabricated and measured,and the measured 3d B axial ratio(AR)bandwidth is 31.4%(2.35GHz-3.26GHz),and the voltage standing wave ratio(VSWR)within the AR bandwidth is less than 2.The overall profile of the antenna is 0.13?₀(?₀is the wavelength corresponding to the center frequency).The second antenna is a low-profile broadband circularly polarized antenna based on a crossed dipole.Two dipoles are connected by a quarter-wavelength ring,and by feeding the single arm of one dipole,90°phase difference between the two dipoles can be formed because of the quarter wavelength.As a result,circular polarization(CP)can be produced.Compared with the double-feed antenna,the single-feed antenna can reduce the complexity of the subsequent feed network greatly,but the circular polarization bandwidth is narrower.In order to further broaden the CP bandwidth,metal cylinders are added to the four corners of the antenna,which can increase the current path to achieve the purpose of broadening the bandwidth,and the superposition of the pattern generated by the vertical metal cylinders and the pattern generated by the crossed dipole can broaden the beam bandwidth as well.Finally,the impedance bandwidth of the VSWR less than 2 of the low-profile broadband circularly polarized wide beam antenna is 70.8%(1.55GHz-3.25GHz),the impedance bandwidth of VSWR less than 1.5 is 44.9%(1.59GHz-2.51GHz),and the 3d B axial ratio bandwidth(ARBW)can reach 41%(1.61GHz-2.44GHz).The half-power beam width(HPBW)at the center frequency is greater than 110°,and the profile of this antenna is 0.09?₀.The third antenna is a double-layer substrated low-profile broadband circularly polarized antenna based on the metasurface.The antenna consists of two layers,and the lower layer is a traditional circularly polarized microstrip antenna with diagonal cuts on a rectangular radiation patch.The radiation patch is single-feed,and the CP bandwidth caused by the cuts is very narrow.Then,a metasurface structure is introduced above the radiation patch to broaden the CP bandwidth.A group of square patches with a tilted slot on each one are etched on the top surface of the upper layer periodically.The electromagnetic waves radiated from the lower layer will resonate with the metasurface,which can generate new resonance points and broaden the CP bandwidth.Then,according to the project requirements,two phased array antennas are designed based on the metasurface antenna.One is a 16-element square array,and a one-sixteen equal-power divider is designed for this square array.The other one is a 19-element hexagonal array,by comparing these two array antennas,the 19-element array is superior in the performance of wide-angle scanning,and the results basically meet the requirements.