Design And Research Of The RF Rront-end In A Radio Telescope

Radio telescope is the equipment of the receiving celestial radio waves, which is mainly consmposed of a directional antenna and a high-sensitivity receiver. RF front-end is the key to the receiver and has critical implications for the performance of the whole system. It realizes the functions such as low noise amplifier application, filtering and mixing, completes the conversion between the IF signal and the RF signal, and ensures effective communication system flexibility and versatility. In this paper, based on the structure of the superheterodyne receiver, a RF front-end circuit has been designed and realized with auto gain control.Based on the super-heterodyne structure, a RF front-end circuit has been designed by analyzing several common topological structures and their function of receiver’s RF front-end. On combination of the modules of RF front-end circuit:low-nosie amplifier, local oscillator, digitally controlled attenuator, detector, ARM control module, the simulation of overall system has been done to verify the feasibility of the scheme.The modules are connected together with necessary filters and matching circuit, and the test results have been achieved through debugging and improving the whole receiver system:the signal frequency of local oscillator is935MHz, the phase noise is-84.76dBc/Hz@1KHz、-91.3dBc/Hz@10KHz、-100.1dBc/Hz@20KHz; the center frequency of the input signal is750MHz with bandwidth100MHz, the power range is-90dBm～-50dBm, through the RF Front-end the center frequency becomes185MHz, the output power is around OdBm (the fluctuation is less than2dB). When the input signal power is-100dBm, the system the output power is between-7.42dBm and-9.38dBm which caused by background noise within100MHz bandwidth. The experimental results show that the whole RF Front-end gain can be achieved100dB within100MHz bandwidth, the dynamic range is50dB, noise figure is2.45dB, the fluctuation band is2dB, and output ldB compression point is30.34dB.