Direct-digital synthesis (DDS) is capable of impressive frequency and amplitude switching speeds and, depending upon the bit resolution of the DDS architecture, extremely fine frequency and phase control. DDS technology is the basis for the WaveCor line of high-performance microwave signal sources from ITT Microwave Systems (Lowell, MA), notably the firm's latest addition, the WaveCor synthesized local oscillator (SLO) model 20.0 frequency synthesizer. It tunes from 50 MHz to 20.48 GHz with 1-kHz resolution while maintaining low phase noise and spurious levels. The compact WaveCor SLO 20.0 synthesizer is suitable for a wide range of military applications in electronic warfare (EW), radar, signalintelligence (SIGINT), and automatictest- equipment (ATE) systems.

The DDS-based WaveCor SLO is housed in a small and unassuming package (see figure) measuring just 6.00 x 6.00 x 2.75 in. and weighing 5 lbs. or less. Because of its extremely wide bandwidth, this single fast-switching source can take the place of several narrower-band frequency synthesizers based on alternative technologies, such as YIG oscillators or voltage-controlled oscillators (VCOs).

One of the traditional limitations to DDS technology has been controlling spurious frequency products. But it is here that WaveCor SLO 20.0 frequency synthesizer excels, with typical spurious performance of -70 dBc from 50 MHz to 5 GHz, -64 dBc from 5 to 10 GHz, and -57 dBc from 10.00 to 20.48 GHz. Add to that spurious performance the outstanding phase noise of -126 dBc/Hz measured at an offset of 10 kHz from a 10-GHz carrier signal, and the WaveCor SLO 20.0 is a signal source that is as capable of serving critical EW and radar systems as well as demanding test and measurement applications.

On the other hand, one of the stronger features of DDS technology has been its capabilities in switching speed and in the programmability of output signals to meet the changing needs of frequency-agile radars and software-defined-radio (SDR) communications systems. The WaveCor SLO 20.0 frequency synthesizer incorporates a 30-b binary-coded-decimal (BCD) digital control interface for frequency control, and can switch frequencies in less than 10 s, for any two frequency points within the full bandwidth. The DDS-based frequency synthesizer provides tuning resolution of 1 kHz, but can just as easily hold a fixed output frequency for fixed- LO requirements. The WaveCor SLO 20.0 frequency synthesizer delivers +14 dBm output power with +/-1 dB amplitude flatness across the full 50-MHz-to- 20.48-GHz frequency range. The DDS-based synthesizer is designed to work with an input signal from external 10-MHz reference at a level of 0 dBm.

The rugged mechanical design of the WaveCor SLO 20.0 frequency synthesizer translates into reliable operation, with the DDS-based source rated for minimum mean time before failure (MTBF) of 75,000 hours. The synthesizer has an operating temperature range of -20 to +70C and draws 1 A typical current from a +28-VDC supply. ITT Corp., Microwave Systems, Advanced Engineering & Sciences, 59 Technology Dr., Lowell, MA 01851; (978) 441-0200, FAX: (978) 453-6299, Internet: www.ittmicrowave.com.