Compact Circularly Polarized Mono-pulse Antenna Array With Frequency Agility

Monopulse antennas have been widely used in precision measurement and radar tracking.With the emergence of new technologies and new designs,the structure and function of monopulse antennas are diversified.This paper investigates the monopulse antenna and develops the design.The main tasks are as follows:Firstly,the basic parameters of the microstrip antenna are briefly described,and the antenna's circular polarization characteristics and methods to achieve circular polarization are briefly summarized.The basic principle,structure and important parameters of the monopulse antenna are analyzed in this paper.Realize the function of monopulse antenna,and introduce the loop bridge and 3dB directional coupler in the vital feeding network,which lays the foundation for the design of monopulse antenna.Secondly,a circularly polarized patch antenna unit with frequency agility is designed.By properly switching between the different states of these PIN diodes,four discrete operating frequency bands can be achieved.Circularly polarization can be achieved by the perturbation segment.On the base of the antenna unit,the compact 4-cell array patch antenna with low-profile?i.e.,about 0.013?₀?has been designed for circular polarization mono-pulse applications.Because of the high isolation between the ports of the Rat-Race coupler,it is used as a feed network for the antenna;by exciting the sum and difference ports of the ring bridge,a sum and difference beam applied to mono-pulse antenna can be generated.Because of a suitable replacement of the sum and difference ports,the antenna radiation patterns were symmetrical.The simulated peak gains of the four discrete operating frequencies for 4.4GHz,4.7GHz,5.3GHz and 5.6GHz are 11.7dBi,12.0dBi,12.1dBi,and 12.3dBi,respectively.Both the null-depth at four different frequencies are less than-15dBi.The simulation results show that the3dB axial ratio at four different center frequencies are 0.89dB,1.87dB,0.91dB and 2.15dB,respectively.The results show that the antenna meets the design requirements.Finally,on the base of the above work,a 4×4 element monopulse antenna array is simulated and designed,which overcomes the shortcomings of the 4-element antenna array.Using a new designed three-branch directional coupler and 90°phase shifter are combined to form a new type sum-difference network.Each port of the sum-difference network has a good VSWR performance in the operating frequency band,which is less than 1.6.The simulation results show that the gain of the antenna at the four discrete operating frequencies increased by approximately 3.5dBi,4.0dBi,4.5dBi,and 5.0dBi,respectively.The zero-value depth of the four frequency is less than-22dBi,and the axial ratios at the four center frequencies are less than 3dB.The results show that the antenna meets the design requirements.