Ku-band Frequency Synthesizer Developed

Frequency synthesizer, as the heart of modern electronics system, is used in the fields of communication, radar, space electronics equipments. Its performance is very important to those systems. This paper is about a low phase noise and high spurious signals supperssion frequency synthesizer, which is used in a communication system.This paper introduced the theories and characteristics of all kinds of frequency synthesize technologies, then analyzed the creation reason and suppression method of the two important characteristics for frequency synthesizer, which are spurious signals and the phase noise,This paper according to the require of system, gave two scheme for the system's realization, one is using PLL(Phase Locked Loop), the other one is using frequency multipliers and frequency mixers to realize the frequency synthesizer. After demonstrated these two scheme from many aspects, this paper chose the second one. In this scheme, 100MHz signal output from the reference source, through powerdivider, frequency multiplicationg chain, mixers, became a 26 GHz singal point signal, then output from a fin-line transition and a wave-guide filter. During the course, a lot of low-noise amplifiers and band pass filters were used in the process of frequency multiplying and mixing. Low-noise ampliers choosing based on their gains and P1dB, that is enough to drive the multipliers and mixers or not. Filters were used after the process of multilying and mixing to reduce the spurious and harmonic signals. After analysing the harmonic signals's isolation ratios of the multipliers and mixers, the proper filters were chosen. These filters have good abilities, such as low insertion loss, good rectangle factor and suppressing the harmonic signals effectively. To be specific, in this system, dielectric filters were chosen for low-frequency sinnals; chamber filters were chosen for middle frequency signals; microstrip filters and wave-guide filter were chosen for high frequency signals.This paper also designed the system's power supply and EMC(Electromagnetic Compatibility). Then assembling and testing the whole system. The results of testing demonstrated that the Ku band frequency synthesizer has good performances, the output power is up to 15 dBm, spurious signals suppression is bigger than -55dBc and the phase noise at 1kHz offset from carrier is only about -89dBc/Hz.