A Wideband Frequency Synthesizer For Fast Hopping Based On DDS

Frequency hopping technology has the capabilities of anti-interference and anti -interception. And it can increase the bandwidth efficiency as well. So it becomes more and more important in electronic counter systems. The core of a frequency hopping system is the frequency synthesizer. This paper makes a design on a frequency synthesizer for a wideband and high-speed frequency hopping transmitter-receiver, combined with the background of National Defense Technology Pre-research Project and practical engineering.It is necessary for the frequency synthesizer we design for the transmitter-receiver to have the following features: fast frequency-hopping rate, wide frequency-hopping band, low outputting spur and low phase noise, small size and lightweight. So, after analyzing and summarizing the technique for frequency-hopping synthesis and the advantage & disadvantage of several realization schemes of it, the fractional-divider synthesizer/PLL with the DDS in the feedback path of a closed loop is chosen in the paper.The scheme offers the benefits combining the DDS and PLL. The application of such a synthesizer used in the wideband and high-speed frequency hopping transmitter-receive not only solves the questions about between the frequency resolution and the rate of frequency change in the integer-N PLL, the phase jitter of the fractional-divider PLL, but also achieves high frequency and low power. We choose the chip AD9956 as the DDS.The range of the output frequency is from 225 Megahertz to 512 Megahertz, the space frequency is 200 Kilohertz, the time of frequency-agile is less than 50μs and the rate of frequency-agile is up to l000hops /s, and the phase noise is less than -75dBc/lKHz .So, the frequency synthesizer is just sufficient to the need of the wideband and high-speed frequency hopping transmitter-receiver because of its broad band frequency, the short time of frequency-agile and the little phase noise.The frequency synthesizer is used in the specimen of the wideband andhigh-speed frequency hopping transmitter-receivers, and it keeps ahead in the same class of the domestic equipments.