| In recent years,with the rapid development of mobile broadband,the demand for network capacity is increasing.As one of the main backhaul methods of the bearer network,the microwave network has a large capacity business demand.The E-band microwave has wider tunable channel spacing,large transmission capacity and higher high-frequency gain,which is suitable for large bandwidth service bearer network.In this paper,a new design method of antenna structure combining monopulse tracking and communication is proposed,which can be applied to E-band communication and self-tracking system.The main research contents of this paper are as follows.1.The design of E-band monopulse antenna usually realizes the tracking and positioning function of E-band and the information transmission function of E-band in the same antenna.In practical applications,the communication bandwidth of the E-band is large,and the bandwidth of the monopulse feed network is small.When used together,the loss of communication becomes larger through the monopulse feed network,and the positioning accuracy of the monopulse antenna in the wide bandwidth range will be unstable.Therefore,a dual-band antenna structure combining E-band horn antenna and Ka-band patch monopulse antenna is proposed,which ensures communication transmission efficiency and tracking accuracy.Based on this scheme,a radiation structure combining an E-band horn and a Ka-band patch antenna is first designed.The measured results show that in the overall antenna structure,the E-band horn has reflection coefficient less than-17dB and an average gain of 1OdBi in the frequency range of 71 GHz to 86GHz.The simulation results show that the Ka-band patch antenna has reflection coefficient less than-10dB in the frequency range of 34.3 GHz to 35.7GHz.The sum beam average gain is 15dBi,the difference beam average gain is 11 dBi,and the null depth is less than-45dB.A single-pulse feed network is designed.The structure consists of rat-race couplers,T-type power dividers,vertical interconnection structures and feed conversion joints.In this paper,a sumdifference network composed of three rat-race couplers and a T-type power divider is proposed.Compared with the four rat-race couplers,the structure is simple,the insertion loss is small,and the amplitude error is small.According to the antenna structure of multi-layer substrate with large and complex feed network,the propagation principle and solution of high-order mode surface wave of 2x2 patch array are analyzed.A new substrate structure design is proposed to effectively suppress the surface wave propagation of the antenna.The simulation results show that the reflection coefficient of the feed network is less than-19.5dB,the isolation is greater than 35dB,the phase error is less than 0.3 degrees,and the amplitude error is less than 0.3dB.The results confirm the feasibility of the structure and can be applied to the E-band monopulse antenna structure.2.According to the requirements of E-band transmission tracking and the antenna radiation part and feed network part designed in this paper,in order to achieve the purpose of monopulse tracking communication,three monopulse antennas are designed in order to meet different performance and processing requirements.Finally,a scheme of stripline bottom feed antenna is selected for processing and testing.The first antenna is a monopulse antenna composed of a side-fed patch antenna and a microstrip line feed network on the back substrate of the antenna.The simulation results show that the reflection coefficient of the sum-difference port is less than-1OdB in the bandwidth of 34.1GHz to 35.9GHz,the isolation is greater than 28dB,the average maximum gain is 12dBi,and the null depth is-29dB.However,the back lobe of the sum-difference beam has obvious radiation with a gain of 7dBi due to the radiation interference of the microstrip line in the millimeter wave.The second antenna is the patch antenna unit with coaxial bottom feed as the radiation unit and the strip line as the antenna structure of the feed network.The reflection coefficient is less than-10 dB and the isolation is higher than 35dB in the operating bandwidth of 34.6GHz to 35.4GHz.The average maximum gain is 10 dBi,and the null depth is-38dB.Compared with the first structure,the maximum sidelobe level is 2-3dBi lower,and there is no obvious bulge in the backward radiation lobe.The angle accuracy of the null point depth is higher,the angle error is smaller,and the null point depth is deeper.However,the structure design is complex and the processing is difficult.Therefore,the antenna structure with simple structure,small processing error and tracking performance is designed.The third antenna is the side fed patch antenna unit as the radiation unit and the strip line as the antenna structure of the feed network.When the average operating frequency is 35GHz,the loss tangent of Rogers RO4350b material is set to 0.01.The measured results show that the reflection coefficient is less than-9.5dB and the port isolation is greater than 27dB in the 34.7GHz-35.3GHz band.The sum beam gain is 6dBi,the azimuth and elevation difference beam gains are 5dBi.The maximum sidelobe level of the sum beam is-3dBi.The fixed screw of the conversion joint will interfere with the antenna radiation.The null depth of the antenna with screw fixed structure is-28.5dB and-29dB respectively.The null depth of the antenna fixed without screws is-33.5 dB and-35dB,respectively. |
