Research Of The Receiver Front-end Of S-band Non-lineae Junction Detector

As an essential part of radar and communication system, receiver plays critical roles for the whole system performance and application. S band(2-4GHz) is popular in wireless communication and radar cause of its relative high frequency. S band non-linear junction detector, which is used to search for the devices that contains non-linear junction, can receive strong harmonic echo signals and miniaturize the requirements at the same time. It also helps to detect tiny objects more accurately. This thesis is supposed to design a low noise, low spurious, high gain, high sensitivity and low power consumption portable receiver front-end.This thesis firstly simply introduces the development and current situation of S band non-linear detector and illustrates the significance of our research. A double-conversion low IF architecture is employed to achieve a high sensitivity and stability performance. Electromagnetic software ADS is used to simulate and optimize the receiver circuit.This thesis focuses on the key modules and components of the receiver. A suspended stripline filter with an insertion loss less than 1d B is achieved through CST simulation and optimization. The basic design criterion of amplifier and mixer is illustrated in detail. Detector module that outputs low level voltage when the target is discovered is realized through cascading a logarithmic detector and a voltage comparer. The power module which provides voltage for the amplifiers is implemented with a output voltage ripple PPV ?10mV based on a switching power supply.Finally, the receiver front-end is realized through Altium Designer and Auto CAD. Test results show that the receiver achieves a high gain ?40dB, a low noise < 5dB a large dynamic range ?70dB, a superior harmonic and spurious suppression ?60dB and a high sensitivity at-100 dBm with a compact size 120mm?50mm?12mm.The performances of the designed receiver perfectly satisfy the requirements of design index.To guarantee the superior performance of the receiver, we need to choose reasonable mixers and filters to ensure an excellent harmonic and spurious suppression. Meanwhile, we also should pay attention to the layout of the circuit and cavity to win a high gain and excellent electromagnetic capacitance.