Research And Design Of UHF And S-band Circularly Polarized Antenna

The circular polarization（CP）antenna has the characteristics of anti-multipath fading and strong anti-ionospheric interference,and has wider application prospect than linear polarization antenna.At present,circularly polarized antennas are more and more widely used in these fields such as monopulse,satellite communication,radio frequency identification（RFID）and so on.Due to the different application scenarios above,the forms and electrical performances of these circularly polarized antennas are different.On some small platforms,antenna with miniaturization and low profile is required.On some platforms with multi-band integration and multi-function,antennas with a common aperture are desired.In the environment requiring high-precision target tracking,monopulse antenna is demanded.According to several application requirements,this paper introduces five types of antennas as follows:1.A miniaturized,low profile planar spiral antenna.The antenna uses the form of Archimedes spiral.Without increasing the aperture of antenna,by introducing the artificial magnetic conductor（AMC）as the reflector,the profile height of the antenna is reduced by19mm,only 0.11λ₀.The gain at low frequencies is improved by 0.5d B,and the axial ratio（AR）is also improved by 0.6d B.2.An S-band 8×8 low-sidelobe monopulse array antenna.The antenna array elements are arranged by sequential rotation,which effectively reduces the AR.Based on Taylor synthesis method,the unequal power division network is designed to realize the taper distribution of the excitation magnitude of the antenna element,so as to reduce the sidelobe level of the array antenna.In order to obtain the feed phase required by monopulse sum and difference beam,a broadband sum and difference network composed of broadband branch phase shifter and 3d B bridges is designed.The feeding network and antenna are tested,and the measured results are basically consistent with that of the simulated design.3.An S-band low-profile 2×2 array antenna based on AMC.It adoptes the form of double H-type slot coupling feed.Two groups of slots are introduced,which improves antenna gain at the center frequencies and reduces the cross-polarization of the antenna.Through the introduction of the AMC structure,the profile height of the antenna is reduced to 0.139λ₀,and the gain is improved at the same time.4.Two kinds of array antennas for radio frequency identification（RFID）.The first antenna uses the form of the series antennas with parallel feeding,the radiation array element and the feeding network are located on the same side of the substrate,easy to machined.According to the simulation results,the peak-to-peak value（PPV）of the electric field intensity is within 8d B along the direction perpendicular to the serial antenna at a distance of 150mm from the antenna normal direction.When the antenna input power increases by 3times,the PPV of the antenna field intensity is within 5d B.The second antenna uses a parallel feeding method,and the radiation array elements and the feeding network are distributed in different layers of the substrate.The PPV of the antenna field intensity is within6d B.Considering many factors such as cost and processing cycle,the first antenna was selected to be machined.The measured results are basically consistent with the simulated.5.A UHF-and S-band co-aperture antenna.The two antennas with a frequency band span of 5.6 octaves are combined on a common aperture surface.By introducing artificial magnetic conductor,the profile height of UHF-band antenna is reduced to the same height as the S-band antenna,and the decrease can reach 61.3%.At the same time,metal pillars and parasitic patches are introduced to improve the impedance bandwidth and axial ratio bandwidth of the antenna,so that the performances of both antennas are improved.