Omnidirectional Multi-beam Antenna For Short-range Low-slow-small Target Detection

In order to monitor low-altitude flying targets,some Western countries have already begun research on radar technology in the last century.At that time,birds were the targets of radar detection,so these radars were also called "bird detection radars".Nowadays,"bird detection radar" has once again attracted attention.At present,this type of radar is large and expensive.It is only used in airports and some important places.In order to meet the civilian needs of UAV detection,this paper designs a radar antenna for short-range low-slow-small target detection.The design method are given below.First,based on the existing literature,this article preliminary understands the basic structure of various radar antennas,and determines to use biconical horn antenna as a prototype for antenna design.Second,this paper studies the field distribution in the coaxial and waveguide transmission lines,and connects the biconical horn antenna to the ring-shaped metal waveguide with metal partitions.Due to the metal partition,the ring-shaped metal waveguide is evenly divided into several arc-shaped waveguides,and its internal field distribution is similar to that in a rectangular waveguide.After the coaxial probe feeding each section of the arc-shaped waveguide,the electric field reaches the biconical horn antenna through the waveguide to radiate,so that multiple ports share one biconical horn antenna.Then,this article nests the transceiver ports in the form of concentric circles.The number of ports on the inside of the transmit antenna is less than the number of ports on the outside of the receive antenna,thus ensuring that the arc-shaped waveguides of each port are similar in size.At the same time,the metal near the central axis is hollowed out,leaving a through hole for the coaxial line to pass through.A bi-cone antenna is designed to be connected to the coaxial line near the exit of the through hole.It will cooperate with the receiving antenna nested in the outer ring to achieve elevation angle measurement.Then,the antenna is simulated by CST simulation software,and the antenna structure is optimized according to the actual situation.In order to reduce the difficulty of antenna processing,the biconical horn of the exponential structure is changed to a linear structure.Because the flying target has a certain height,the asymmetric biconical horn structure is adopted in this paper to make the antenna patterns have a certain elevation angle.Finally,this paper completes the design of the coaxially fed 6-transmission 12-receive biconical horn antenna,and the key performance parameters of the antenna are obtained by simulation.The antenna operates at 10.5GHz and the bandwidth is greater than 1GHz.The half-power beam width of each port in the vertical direction is greater than 30 degrees and the main radiation direction is around ?=40°.In the horizontal direction,the half-power beam width of each port is greater than 65°,which meets the requirements of omnidirectional coverage.In addition,this paper also studies the antenna structure when working at 35GHz and using waveguide feeding.In this paper,through the hollowing out of the metal cone,an independent waveguide horn structure is designed to replace the common biconical horn antenna,and the straight waveguide structure is used to reduce the difficulty of processing the hollowing out.Finally,after optimization and simulation,the performance parameters of the antenna are obtained.The reflection coefficient of each port of the antenna is less than-12.5dB in the frequency range of 30-40GHz,and less than-16dB at the center frequency of 35GHz.In the vertical direction,the half-power beams of each port of the antenna cover 19 degrees to 69 degrees.In the horizontal direction,the half-power beam widths of 6 transmitting antennas and 12 receiving antennas are greater than 80 degrees,which realizes the 360-degree omnidirectional coverage requirements of the transmitting antennas,and also ensures that electromagnetic waves in any direction can be received by more than 3 receiving antennas.In the last chapter of this paper,the working method of the antenna is studied.This paper compares the amplitude and the phase of the received waves in different directions,summarizes the relationship between them and the angle of the target,explores the working principle of the amplitude comparison method and the phase comparison method,and verifies the feasibility of the antenna design method.