Research And Design On The Down-conversion Channel In C Band

In recent years, wireless communication technique and its applications get greatdevelopment, especially for the Personal Mobile Communication, SatelliteCommunication and Broadband Wireless Access. The rapid development of wirelesscommunication brings a lot of challenges to RF front end of a wireless transmissionsystem. And so, the down-conversion wireless communication link which plays animportant role in the RF receiver has become a research hotspot.The development of wireless communication system is introduced firstly, andfocus on learning about the hot research at present and the developing trend in futureon the down-conversion system of receivers. After knowing the main performanceparameters and the common system architectures of receivers, on this basis, considerwith specific requirements in this research, superheterodyne structure with twiceconversions were chosen at last. Taking into account various combined frequencyinterference and the difficulty of making intermediate-frequency (IF) filter，947.5MHz was selected as the higher intermediate frequency, and the lower intermediatefrequency was140MHz, and this frequency distribution was verified by Genesys. Forthe distribution of gain, a low noise amplifier located at the RF modular was needed,since the RF modular has a great influence on the noise figure of our system. Theamplifiers located at IF modular were designed in the means of gain compensations toensure the output power.So far we have allocated all system’s indicators to every modular. Then, thesuitable devices were chosen according to the indicators of every modular, and variousperformance parameters of the chosen devices were discussed in detail to assure thesystem we designed meet the requirement of original design targets. And last, with thehelp of RF simulation software ADS, a behavior model was set up at ADS, the systemmodel was simulated by the way of link budget simulation, selective simulation andthe harmonic balance simulation. The results show that the design satisfies originaldesign targets perfectly, the designed down-conversion system has good cut-offcharacteristic out of band and flatness in band. And the harmonic balance simulationindicates that our designed down-conversion system possesses exceptional interferencerejection, and its OP1dB is11dBm, and the phase noise distribution is:-66.99dBc/Hz@100HZ；-81.96dBc/Hz@1KHZ；-91.66dBc/Hz@10KHZ；-96.01dBc/Hz@100KHZ. After the verification by ADS, a hardware circuit is made and debugged subsequently. The link test declares that the approach designed by takingadvantages of EDA tools such as ADS, Genesys and HFSS becomes ahigh-performance and high-reliability down-conversion system in C band which meetsthe design requirements. Considering the system may be applied under extremeambient temperature, so the designed system has been under the high and lowtemperature test, and the results show that the ambient temperature mainly affects thepower characteristic of the system output, with the increase of temperature, the outputpower is lower. But over the full temperature range (-40℃~+80℃), the output powervaries less than1.5dB with every10℃.