JED - January 2016 - (Page 27)

TECHNOLOGY SURVEY A SAMPLING OF RF SIGNAL GENERATORS By Ollie Holt rather than generators. AWGs are a better fit for testing COMINT systems, but they can still be used for test and verification of ELINT, ESM and RWR systems because they can easily mimic more complex radar signals. An AFG typically offers the following types of wave shapes: sine, square, triangle, pulsed and ramped. AFGs usually have internal or external methods of modulating output signals while keeping tight control of the frequency, phase and amplitude of the output signal. An AWG can provide these waveforms and more. The output signal from an AFG is either created from a stable RF oscillator tuned to the desired frequency with a phase-locked loop or by Direct Digital Synthesis (DDS). If a Direct Digital Synthesizer is used, it may have stored waveforms in memory that can be retrieved as required. The output from an AWG is typically created from a DDS or from a replay from memory. In the survey, we ask companies to identify the operational frequency range, which defines the lowest and highest frequency the generator can reproduce. For typical RWR, ESM, ELINT testing, this should cover at least 2-18 GHz. Lower and higher operational ranges may be desired for testing EW and communications systems, but this typically will add cost. The modulation types describe the different ways in which the waveform can be modified. For EW system testing, amplitude, time, frequency and phase modulations are desired. For communications system testing, additional control over the generated waveform may be necessary. Output power range and size describe the lowest to highest "power out," and the step sizes or resolution of each step define how much control the operator has in varying the output signal. Next, the applications will list the areas that the RF signal generator is best suited to test. The final columns describe the size and weight of the RF signal generator and also provide the supplier an opportunity to list any additional features. Next month's technology survey will cover FPGA boards. The Journal of Electronic Defense | January 2016 T his month's technology survey looks at RF Signal Generators that can be used for electronic warfare (EW) and signals intelligence (SIGINT) system development, integration and testing. EW engineers use signal generators to characterize EW system designs before taking them to test ranges to ensure that their design meets requirements. RF signal generators can simulate test signals that mimic a threat radar system or a communications system, or they can generate tones that are used to calibrate the RF system being developed. Sending an RF system to a test range is expensive in terms of dollars and prestige, so engineers need to ensure that the system performs as expected prior to range testing. An RF signal generator is exactly what the name implies - a device that can generate an RF time- and amplitude-variant signal to be used for test and verification of RF systems. An RF signal generator may produce a single tone (unmodulated RF signal) or an exact replica of a desired signal with specific modulation patterns. The generator can also add distortion to aid in system testing. The world of RF signal generators has evolved over the years as technology has matured. Signal generators have improved from simple, tunable, stable oscillators that could be modulated only in amplitude to today's complex waveform generators that can vary the output in amplitude, phase, time and frequency. As a result, signal generators are able to simulate the complex waveform patterns of RF signals that EW, radar and communications systems are designed to detect, demodulate, and identify. The main activity of an RF signal generator is its ability to control and modify certain characteristics of these waveforms: frequency, amplitude, phase, waveform shape, rise and fall times, etc. RF signal generators can be defined as one of two types: Arbitrary Function Generators (AFGs) or Arbitrary Waveform Generators (AWGs). The AFG is the leading workhorse in the EW test world. It typically offers fewer waveform variations than AWGs, has excellent stability, the ability to modify the output signal, and is usually lower in cost. An AWG provides the ability to generate more complex waveforms (they can generate any waveform you can imagine), but AWGs can be thought of as playback systems 27

Table of Contents for the Digital Edition of JED - January 2016

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
On the Brink: Laser Wars Not Just a Movie Fantasy
Light Saber – LaWS Prototype Brings Directed Energy Onto the Front-Line
Technology Survey: RF Signal Generators
Threat Monitor
EW 101
AOC News: Views from the AOC Symposium and Convention
AOC News
Index of Advertisers
JED Quick Look

JED - January 2016

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