A fast hopping frequency synthesiser

This paper gives a description of a fast hopping frequency synthesiser whose main features make it ideal for use in agile radar and spread spectrum communications systems. These include very fast switching speed coupled with close channel spacing, low phase noise and high spectral purity. Using conventional phase locked loop methods a limitation of channel spacing is imposed if optimum phase noise and fast switching speed are required. This has been overcome by incorporating a direct digital synthesiser, driven from a high frequency fundamental surface acoustic wave resonator oscillator (SAWRO) exhibiting very low noise. At present it can provide 50 MHz of bandwidth at S-band, but this could easily be increased by adding a direct analogue synthesiser into the feedback loop of the PLL, instead of the fixed 2 GHz source. Such a system would combine all three types of frequency synthesis. The digital sections can now be produced using Gigabit Logics´ new 32-bit phase accumulator producing a 3 chip solution with channel spacing down to 0.1 Hz and spurious below -54 dBc