Low Spurious Frequency Agile Millimeter-wave Frequency Synthesizer Developed

It is well known that the quality of the front-end design of the system directly influences the quality of the transmit signal, the receiver of noise figure, the index of sensitivity and the signal-to-noise ratio and so on, and the performance of the front-end inevitable involves the realization and the performance of synthesizer. With the development of information and technology, the demand of the index of frequency source for modern electronic system is becoming higher and higher, which at the same time needs the performances of high frequency, wideband, frequency agility, small step's frequency, low phase noise and low spurious. At present, most of the frequency source accomplishes its performance of frequency agility through phase locked loop, but it dose not solve the problems between frequency resolution and frequency agility, this is to say, the frequency conversion time is limited by phase demodulation frequency and loop bandwidth, and generally it can reach the microsecond level, which seriously restricts the performance of Frequency Synthesizer.In the front-end of the system of the receiver and transmitter of millimeter wave band, the production of frequency source of the local oscillator is a key problem all the time and directly determines the performance of the whole system, at the same time, for the system of full-coherent parameter, in order to improve its performance, it is generally required to have good performance of frequency stability and spectral purity of frequency source of the local oscillator. In addition, the system of Frequency Synthesizer needs to reach the miniaturization.Therefore, on the basis of analysis and comparing of the current basic frequency synthesis technology and used scheme of frequency hopping, then this paper proposes a kind of designed scheme consisted of DDS, doubling frequency and mixing frequency which apply to the hypervelocity frequency hopping, and adopt this design to accomplish the front-end design work of a set of 8 millimeter-wave transceiver of full-coherent radar. In this design method, it comprehensively takes the features and the requirements of design of local oscillator of frequency conversion and the circuits of the front-end of radio frequency into consideration and makes reasonable planning for the frequency analyzing. Finally the pulse compression signal on millimeter wave band is realized through frequency conversion elevated by three times of the Linear Frequency-Modulated output by the DDS. According to concrete realization, the structure of frequency conversion elevated by three times not only reduces the difficulty of the realization of local oscillator and reaches the relatively good performance in the aspect of spectrum purity and the time of frequency conversion. In theory, the frequency synthesizer for the time of the frequency conversion on millimeter wave band can reach the nanosecond level and better solves the technical difficulties which make sure that under the situation of highly frequency switching it meets the need of high spectrum purity.The testing displays that, in the system of millimeter wave band, the phase noise level is all less than -91dBc/Hz@1KHz, the steps of output frequency is 1MHz and its bandwidth is 160MHz, the spur level of transmitter signal is less than -60dBc, and the oscillator signal spur level is less than -65dBc, the maximum frequency converting time is less than 1μs. At last, the frequency synthesizer meets the need of frond-end.