Design Of Low-noise And Thermostatic Cabinet For The Global Spectrum Receiver And Test Research

In order to meet the requirements for temperature constancy and electromagnetic compatibility of microwave devices such as built-in calibration noise source and lownoise amplifiers for the global spectrum measurement receiver of ’’Hongmeng Project’’,the design and testing of a constant room temperature and low-noise cabinet are carried out in this paper.By analyzing the field temperature environment of the global spectrum receiver and the working temperature requirements of the receiver’s functional devices,the overall scheme of the cabinet composed of a double-layer nested structure and analog PID temperature control technology is proposed.In the scheme,the microwave devices with constant temperature requirements of the receiver are placed in the inner chamber,and the TEC chilling sheets at the bottom of the inner chamber is heated or cooled based on analog PID control,thus reducing the volume of the constant temperature chamber of the cabinet,reducing system power consumption,and avoiding electromagnetic noise generated by itself.The main structure of the double-layer nested cabinet is ZL101 A aluminum alloy material,the thermal structure of the cabinet hybrid insulation and shielding external electromagnetic noise is designed by laying a double-layer polyurethane board at the bottom of the inner surface of the outer chamber,laying or wrapped rubber insulation cotton on the rest of the inner surface and the outer surface of the inner chamber,and installing TEC chilling sheets on the bottom plate of the inner chamber.Thermal simulation modeling of the cabinet structure was carried out,and thermal analysis of the receiver field extreme ambient temperature operating conditions was performed.The results show that the designed cabinet has the ability to maintain a constant temperature within the preset temperature range of the inner chamber under the external ambient temperature of-35°C to 60°C.The simulation modeling and analysis of the shielding effectiveness of the cabinet was carried out,and the results show that the minimum value of shielding effectiveness is 60.3dB and the maximum value is 82.2dB in the range of30MHz-200 MHz,which is higher than the 50 dB required by the receiver.The cabinet analog PID thermostatic control system mainly consists of temperature presetting module,temperature measurement module,comparison and amplification module,PID control module,limiting module,TEC drive module and TEC chilling sheets.The controller adjusts the direction and size of the current flowing through the semiconductor chilling sheets at the bottom of the inner chamber to heat or cool the inner chamber,so that the inner chamber can reach the required constant temperature.The transfer function of the cabinet thermostat controller was obtained using the step response test method,the thermostat controller parameters were rectified using the Cohen-Coon method.Simulink was used to carry out the simulation analysis of the thermostatic control system.The results show that the thermostatic control process can be stabilized quickly and has good dynamic regulation performance.After the analysis and design of the thermostatic cabinet,the prototype was built and commissioned.The cabinet prototype was tested for constant temperature in the laboratory and in the field under working conditions.The test results of indoor temperature environment continuous 24 hours show that the temperature of the measurement point of the inner chamber remains within the preset value +0.3℃,to meet the design requirements.Four temperature measurement experiments were conducted in the field working environment for 48 consecutive hours each with different constant temperature preset values.The results show that the temperature of the inner chamber measurement point is kept within ±0.5℃ of the preset value,in the experiment,when the ambient temperature changes greatly,the temperature of the inner chamber can respond quickly and maintain the constant temperature,which verified that the thermostatic analog PID controller has good steady-state and dynamic control performance.By comparing the measured temperature values with the corresponding working condition thermal simulation analysis temperature,the results show that the variance is 0.41%,which is a small dispersion and a good match,indicating that the thermal simulation model of this paper is accurate and reliable.The electromagnetic noise test of the prototype constant temperature analog controller is carried out,the test results show that when the constant temperature analog controller is energized,in the range of 30MHz-200 MHz,the average electromagnetic noise power is 0.003 dBm,and the maximum electromagnetic noise power is 0.6dBm,which is lower than the design requirement of1 dBm,indicating that the thermostatic analog PID temperature controller does not interfere with the normal operation of the global spectrum measurement receiver and has good electromagnetic compatibility.The low-noise constant room temperature cabinet of the global spectrum receiver designed in this paper has the characteristics of simple thermal structure,low power consumption,high temperature control accuracy,and good electromagnetic compatibility,etc.It generally meets the technical requirements of the ’’Hongmeng Project’’ cabinet,and will lay a solid technical foundation for the engineering design and development of the project receiver cabinet.