Research On Feeding Network With Radiation Function For Microstrip Antenna Array And Its Application

The feeding network is an essential part of the antenna array,and its influence on the antenna array is crucial.Currently,the design of the microstrip feeding network is mainly focused on how to reduce its spurious radiation for reducing insertion loss and suppressing cross polarization.However,this paper breaks the traditional design concept.It is of great significance to study how to improve the radiation capability of the feeding network and design the polarization of the radiated electromagnetic wave as the same as that of the antenna array,so as to improve the performance of the microstrip antenna array.Specific innovation work completed includes:(1)A 1-to-4 power divider radiating the linearly-polarized wave is proposed.The power divider is composed of two 1-to-2 inverse-phase power dividers in parallel,each of which is mainly composed of a 270°sector patch.By optimizing the size of the sector patch,the output ports on the left and right.sides of the patch have equal-power and inverse-phase characteristics,and a part of the energy of the power divider is radiated by the sector patch with the circularly polarized wave to its normal direction.In.order to achieve a 1-to-4 power divider radiating the linearly polarized wave,two inverse-phase power dividers are symmetrically arranged and fed at the center point,so that the radiation waves of two inverse-phase power dividers having the same amplitude with left-handed and right-handed circularly polarized waves are superimposed into a linearly polarized wave.In addition,the proposed power divider is applied to the center-feeding 2×2 antenna array without the need of an additional 180° phase shifter.The input return loss of the proposed 1-to-4 power divider is greater than 15 dB,the insertion loss of each output port is 7.4±0.2dB,and the phase difference between the left and right output ports is 180±30 in the range of 9.215?9.640 GHz.When the output ports are connected with the matching loads,the gain is 9 dBi and the cross-polarization discrimination rate is greater than 40dB.The results show that the proposed 1-to-4 power divider realized the functions of linearly polarized radiation,equal-power dividing,and inverse-phase output.(2)A 1-to-4 power divider radiating the circularly polarized wave is proposed.The power divider consists of two 1-to-2 circularly polarized dividers,each of which contains the square patch defected with a pentagon.The two circularly polarized power dividers are arranged with center symmetry,and fed at quarter-wavelength off the center,so that the two circularly polarized power dividers are fed with opposite directions to radiate the same circularly polarized wave.The input return loss of the proposed 1-to-4 power divider is greater than 12dB,the insertion loss of each output port is 8.6±1.0 dB,and the phase difference between the upper and lower output ports is 180±12.50 in the range of 5.49?6.05 GHz.When the output ports are connected with the matching loads,the gain is 5 dBi and the 3-dB axial ratio bandwidth is 11.8%,which has good circularly polarized radiation characteristics.(3)An X-band marine radar microstrip antenna array is designed with the proposed 1-to-4 linearly polarized power divider as the feeding network.In order to make the structure of the antenna array compact,each output of the feeding network is cascaded with a series-fed sub-array.The polarization of the feeding network and the series-fed sub-array are both horizontal.Furthermore,the feeding lines in the series-fed sub-array are modified as the step-impedance microstrip lines to decrease the side-lobe level.To verify the method,a 28-element 9.41-GHz microstrip patch antenna array is designed and fabricated.Measured results show that the impedance bandwidth is 183 MHz with a peak gain of 21.3 dBi.The side-lobe level is-27.8 dB and-21.4dB in the horizontal and vertical planes,respectively.The cross-polarization discrimination rate is greater than 57 dB.The actual measurement shows that the linearly polarized feeding network improves the gain of the antenna array and effectively reduces cross polarization.(4)A wideband circularly polarized microstrip antenna array with the center frequency of 5.8 GHz is designed with the proposed 1-to-4 circularly polarized power divider.In order to integrate the antenna unit and the feeding network on the same plane,a novel single-feed side-coupled circularly polarized antenna unit is proposed..This antenna unit includes a U-shaped half-wavelength side-coupled microstrip line and a square patch defected with two triangles.The circular polarization performance of the antenna unit can be improved by adjusting the length of the branches at both ends of the U-shaped side-coupled microstrip line.By adjusting the size of the patch and its defected structure,the circular polarization working frequency band can be moved into the impedance matching frequency band,so as to obtain a microstrip antenna unit with 3-dB axial ratio bandwidth of 5.2%.Moreover,both of the microstrip antenna unit and the feeding network are designed with right-handed circular polarization to further widen the circularly polarized bandwidth and improve the gain.To verify the method,a 4-element 5.8-GHz circularly polarized microstrip antenna array is designed and fabricated.Measured results show that the gain of the antenna array is improved to 14.1dBi,the 3-dB axial ratio bandwidth is increased to 7.24%.The actual measurement shows that the circularly polarized feeding network enhances the gain and circularly polarized bandwidth.