Research And Design Of Wideband Receiver RF Front-End

Wideband receivers are broadly used in military and civil communications.Modern receivers not only have high linearity,sensitivity and large dynamic range,but also require wider bandwidth for RF front-end circuits.The Wideband RF front-end circuit is studied,and the RF front-end pre-selection filter and local oscillator source are designed in this thesis.In the case of limited oversize,the receiver has higher requirements on the suppression of spurious and image frequency,so the front-end pre-selection filter is important.Wideband receiver is used for 500MHz~3000MHz signal reception,and the final output is 70 MHz IF signal.A three-frequency conversion scheme is adopted to meet the requirements of image rejection and other interference suppression.The receiver system is mainly composed of three parts,namely a RF amplifying and mixing link module,a local oscillator source module and a main control communication module.The IF of receiver is fixed at 5500 MHz and the second IF at 1615 MHz.The main work of this thesis includes:1.By studying the structure of the receiver,superheterodyne structures according to the corresponding system requirements are adopted.The RF link is mainly composed of pre-selected filter bank,low noise amplifier,programmable attenuator,frequency conversion module(mixer,local oscillator source)and IF filter.The gain and noise figure of the RF link are determined by ADS.The parameters such as third-order intermodulation and spur suppression are simulated and demonstrated,and the transmitter link is also designed.The circuit structure is similar to that of the receiver.2.The frequency selection of the wideband receiver consists of three segments of electrically tunable filters.The three pre-selected filters cover 500 MHz to 900 MHz,900MHz to 1500 MHz,and 1500 MHz to 3000 MHz,respectively.The comb line tunable filter is used to select particular frequency.The first range is adjustable from 500 MHz to 920 MHz,the corresponding 3dB bandwidth is 65MHz~110MHz,and the insertion loss is better than 3dB.The second range is adjustable from 878 MHz to 1580 MHz,the corresponding 3dB bandwidth is 70MHz~140MHz,and the insertion loss is better than 6dB.The third range is adjustable from 1450 MHz to 3000 MHz,and the corresponding 3dB bandwidth is 120MHz~240MHz,and the insertion loss is better than 10 dB.3.Based on the fundamental principle of phase-locked loop,a local oscillator source covering 6000MHz~8500MHz frequency is designed using LMX2592 chip.The test results show that the phase noise is better than-90 dBc/Hz at 10 KHz off center frequency.The 3885 MHz and 1545 MHz fixed frequency source is designed using ADF4350 chip and divided into two channels by the power splitter,which are used as the second and third local oscillators of the receiver and the transmitter respectively.The test results show that the phase noise is better than-90 dBc/Hz at 100 KHz off center frequency.4.The receiver link and the local oscillator source are controlled by the PIC microcontroller,and the reference clock of the local oscillator source is properly allocated,and the local oscillator auxiliary module(power division,amplification and filtering circuit)of the receiver and the transmitter are designed.Design and selection of the required components such as mixers,amplifiers,attenuators,filters,etc.are accomplished.5.The receiver and transmitter schematic and PCB layout are drawn using Altium designer 15.The cavity design is completed using Solidworks 2014.Finally,the layouts were fabricated and relevant tests were completed.