A frequency ramp generator for an HF skywave radar implemented with direct digital synthesis techniques

Presents the design and development of a frequency ramp (also known as a sweep or chirp) generator. The implementation of the design uses gallium arsenide logic for high speed operation and is capable of generating both CW and FMCW signals, both with known phase characteristics, in the HF region for use in an OTHR. The basic performance of the waveform generator is: frequency range nominally 3-30 MHz but capable of generating signals up to 45 MHz with slightly reduced performance; frequency ramp rates from 0 Hz/μsec (CW) to greater than ±38 kHz/μsec in 18 μHz/μsec increments; FMCW ramp repetition intervals from 1 μsec to greater than 16 seconds in 1 μsec increments, and a frequency switching time of 10 nsec