Low Phase Noise Ka-band Rf Transceiver Front-end Developed

One of the most important part of T/R front end is Frequency Synthesizer ,and it is also the key part of communication,radar and many other electronic system ,and people regard it as the"heart"of electronic system. With the development of modern electronic technology, frequency synthesizers are required to have wider band, higher resolution, short frequency switching time and lower spurious level .In nowadays, the technology of Direct Digital Frequency Synthesis (DDFS) has been widely used, but its output frequency is limited, then in the microwave waveband, frequency Synthesize technology is needed.Different modes of Frequency Synthesizer are all designed bases on the calculate of width of band, resolution, frequency switching time and spurious level. This dissertation presents four manners of designing Frequency Synthesizer in common use firstly ,Including Direct Frequency Synthesis , Indirect Frequency Synthesis (Phase locked Loop Frequency Synthesizer,PLL ), Direct Digital Frequency Synthesis and the and the DDS+PLL synthesis . We analyze the main advantages and disadvantages of these architectures, which mainly focus on the phase noise and spurs.For this project requires different waveband outputs ,in order to simplify the system ,we analyzed the reason of engendering spur and how to restrain it of the main elements used in frequency synthesizer, such as PLL, mixer, frequency multiplier and frequency divider, etc .we also create the phase noise model of series system .To enhancing the performance of insulating of different function module ,we must take EMI/EMC shielding into account ,and designing the electrocircuit and its antrum .The frequency synthesizer in this dissertation is used on the T/R front end of coherent radar in 8mm band .The outputs of this synthesizer include S/C waveband local oscillator , S/C waveband transmitting signal , mm-wave local oscillator , and mm-wave transmitting signal .This designing fully used the different capability of DDS ,PLL ,FPGA .So this system dose not only make the generating of required signal more easier , but also has good performance of spectrum purity and converting time . The mm-wave LFM (linear frequency modulation) signal is generated through three up-converters and the IF signal of receiver is got by two down-converters. The converters'local oscillator is implemented by the frequency multiplier and PLL.According to test result, in S/C band, the local oscillator's bandwidth is 500MHz and frequency resolution is 10MHz, the spur level of receiver's local oscillator and transmitter is both less than -65dBc, the phase noise level is all less than -85dBc/Hz@1KHz.,the maximum frequency converting time is less than 15us .And all of these parameters fulfill the project's requirement.