Electronic warfare (EW), electronic countermeasures (ECM), secure communications, and electronic intelligence systems have the daunting challenge of detecting, characterizing, and countering threats with a diverse combination of characteristics over a wide frequency range. To accomplish this, they must be able to generate signals with precisely defined attributes at the frequency of the threat and do so at high speed.
Spinnaker Microwave has created the compact model SMS-ACX RF converter/ exciter module to perform these functions that is small, lightweight, and widely configurable. It is a cost-effective alternative to expensive arbitrary waveform generators (AWGs) in any system in which a signal with precise and well-controlled characteristics such as phase and amplitude must be rapidly placed at a specific frequency. Typical applications include frequency-agile threat emitters in an EW training platform, automatic-test-equipment (ATE) systems, and synthetic-aperture-radar (SAR) systems that produce wideband swept linear frequency modulation (FM) or chirped linear FM or hopping signals that have tightly controlled phase an frequency characteristics.
Threats of years past were far fewer in number and at a narrower range of frequencies than they are today, thanks to the proliferation of both analog and digital waveforms. They can range from simple frequency-or phase-modulated signals to fast frequency-hopping types with myriad combinations of phase and amplitude. Once the signal is detected, the countering system must be able to replicate it and its waveform while strictly maintaining signal characteristics over wide bandwidths.
This challenge is accentuated at higher frequencies. For example, if a high-sample rate AWG is used to produce a signal at 10 GHz, the sample rate must be 40 GSamples/s. Since faster clocks typically have only 8-b resolution, dynamic range and spurious suppression are constrained. In contrast, the SMS-ACX (Fig. 1) can take a 1-GHz AWG signal (that has many more bits of resolution) and upconvert it to 10 GHz, effectively providing more bits than a fundamental sampled system. This eliminates the need for expensive highsample- rate AWGs, which are available only as laboratory instruments or as custom-built subsystems, and whose size, weight, power consumption and cost preclude them from being used in most embedded applications such as EW threat simulators.
The SMS-ACX benefits from the proprietary techniques employed in the company's line of fast-tuning synthesizers. It is housed in an aluminum enclosure measuring only 4.65 x 4.70 x 1.68 in., weighs less than 2.3 lb., and consumes less than 20 W from its 5 and +15 VDC supplies. Standard switching speed from any frequency within its 10-MHz-to-14-GHz range is 50 s and optionally 10 s. Detailed specifications are shown in the table.
The SMS-ACX can generate or accept intermediate-frequency (IF) signals with arbitrary phase, frequency, and amplitude characteristics with bandwidths from DC to 1 GHz, and produce an output at any frequency from 10 MHz to 14 GHz and optionally to 40 GHz. The modulating signal can be generated using the module's internal direct digital synthesizer (DDS) or externally by an IF signal from a DDS or from an arbitrary waveform generator.
A block diagram of the SMS-ACX (Fig. 2) shows the module's three conversion stages that upconvert the design from an IF (that can be generated either internally or externally) to K-band. The number of conversion stages can be modified to meet customer IF requirements. The signal is then downconverted to cover the desired frequency range. Spinnaker takes this approach so that the modulation characteristics of the IF can be spread over a very wide bandwidth without the need to upconvert multiple channels. The result is reduced design complexity, smaller size, and lower manufacturing cost. This method of "band expansion" allows more effective filtering of spurious signals created in the mixing process when compared to direct quadrature modulation of the output alone, which will always have LO and upper-and lower-sideband components that are difficult to filter.
This type of scheme is inherently limited in spurious performance by the presence of spurious signals produced through the mixing process. However, the company's experience in frequency planning, mixer selection, and filtering allow spurious leakage and compression problems that occur during the mixing process to be mitigated in order to preserve signal integrity. In addition, the module upconverts the lower-frequency input signal via four phase-locked loop (PLL) synthesizers, which allow original waveform characteristics to be accurately maintained from the IF through final output frequencies. Conventional techniques in which the PLL is modulated limit the ability to generate arbitrary waveforms.
The SMS-ACX is housed in an aluminum enclosure, and its configuration and specifications can be customized in many ways to meet specific customer requirements. In addition to it physical configuration, various output frequency ranges and bandwidths, reduced phase noise, faster switching speed, conversion gain, and control scheme options are available, as is hermetic packaging and screening to military standards for shock, vibration, and environmental conditions.
In addition to the converter/exciter, the firm also offers extensive lines of single-loop and multiband frequency synthesizers. The single-loop phaselocked fixed-frequency oscillators can be specified at frequencies from 100 MHz to 26.5 GHz in a package measuring just 1.9 x 1.9 x 0.45 in. They feature better than 50 microseconds switching speed and are available with screening to established military standards. They are rated for output levels to +10 dBm with typical harmonic levels of -15 dBc (and options to -40 dBc) and typical spurious levels of -60 dBc (and optionally to -70 dBc). The phase noise at a fixed output is typically -100 dBc/Hz offset 10 kHz from the carrier. The synthesizers are supplied with SMA female connectors.
In addition, the firm supplies multiband frequency synthesizers in a package measuring just 3.0 x 3.0 x 0.7 in. with female SMA connectors. Models are available from 2 to 20 GHz with bandwidths as wide as 18 GHz and better than 50 microseconds tuning speed. The synthesizer designs make use of compact monolithic- microwave-integrated-circuit (MMIC) components for small size, light weight, and reliability. They also incorporate a 16-step programmable loop filter bank for fast settling time and consistent phase noise across wide bandwidths. The synthesizers can be specified with tuning steps from 2.5 to 10 MHz abd with +17 dBm typical output power in standard models (with options to +17 dBm). The output power falls within an amplitude window of 4 dB. Harmonic levels are typically -15 dBc in standard models (with optional performance to -30 dBc available) while spurious levels are typically -60 dBc in standard models (with optional performance to -70 dBc).
The multiband frequency synthesizers are designed for reference frequencies from 10 to 200 MHz at reference power levels of -3 to + 3 dBm. The single-sideband (SSB) phase noise is typically -80 dNc/Hz offset 1 kHz from the carrier, -80 dBc/Hz offset 10 kHz from the carrier, -75 dBc/Hz offset 100 kHz from the carrier, and -110 dBc/Hz offset 1 MHz from the carrier. The frequency synthesizers are programmed by means of a 25-pin Micro-D connector. They operate on 600 mA and +5 VDC and 200 mA and +15 VDC. Spinnaker Microwave, Inc., 3281 Kifer Rd., Santa Clara, CA 95051; (408) 732-9828, Internet: www.spinnakermicrowave.com.