JED - March 2011 - (Page 57)

EW 101 ES vs. SIGINT – Part 3 Receiver considerations By Dave Adamy his month, we will deal with receiver issues that can differentiate electronic warfare support (ES) and signals intelligence (SIGINT) system requirements. Like the issues discussed last month, these differences have to do with the anticipated intercept geometry, the different types of information taken from intercepted hostile signals, and time criticality of intercepts. There are a number of different types of receivers that can be used in either ES or SIGINT systems. Table 1 lists the most common types along with their characteristics that make them useful in ES or SIGINT applications. There was an “EW 101” series in the July 2006 to May 2007 JED issues which covers the various types of receivers and performance issues in detail. T IFM Superhet Digital signals are present in its band coverage (during the same 50 nsec.). Because of its relatively low sensitivity, it is primarily used in radar ES systems. The superhetrodyne (Superhet) receiver is very widely used in all communications applications. It is almost always found in any communications intelligence (COMINT) and communications ES systems, and is sometimes used in radar ES systems. The primary advantages of superhet receivers are: • Good sensitivity, • The ability to receive one signal in a dense signal environment • The ability to recover any type of modulation, • Measurement of the frequencies of received signals. The main disadvantage of the superhet receiver is that it receives only one frequency at a time and thus must be swept to Number of Signals 1 in range 1 in range 1 of many Multiple simultaneous Multiple simultaneous Multiple simultaneous Multiple simultaneous Features & Limitations AM only Frequency only Recovers modulation Recovers modulation Frequency only Frequency only Recovers modulation; Unique analysis capabilities The Journal of Electronic Defense | March 2011 Table 1: Receiver Types and Features Receiver Type Crystal Video Sens Low Low High High Low High High Dynamic Range High High High High Very Low High High Bandwidth Wide Wide Narrow Wide Wide Wide Flexible 57 Channelized Bragg Cell Compressive The crystal video receiver is primarily used in radar warning receivers (RWRs). It is ideal for this ES application because it covers a wide instantaneous frequency range – typically 4 GHz. This gives it the ability to receive any signal in a very short time. It typically has a wide enough bandwidth to receive very short pulses. However, it has the disadvantages of relatively poor sensitivity, an inability to determine the frequency of a received signal, and an inability to receive multiple simultaneous signals within its entire bandwidth. Although crystal video receivers have been used in reconnaissance systems under special circumstances, they are almost always Radar ES receivers. The instantaneous frequency measurement (IFM) receiver very quickly (typically 50 nsec) determines the frequency (and only the frequency) of any received signal over an octave of bandwidth. It has approximately the same sensitivity as the crystal video receiver. Its big disadvantage is that it has an invalid output any time multiple, approximately equal power search for threat signals. As explained below, there are tradeoffs of sensitivity and the time required to find a signal at an unknown frequency versus bandwidth. Channelized receivers allow the simultaneous recovery of multiple simultaneous signals. Their main disadvantage is the complexity (i.e., size, power and weight) if there are a significant number of channels. The electro-optical or Bragg cell receiver determines the frequency (and only the frequency) of multiple simultaneous signals in a dense environment. It has reasonable sensitivity, but it has the great disadvantage for both ES and SIGINT applications that it has extremely limited dynamic range. It is useful only in very limited applications. Compressive receivers provide the frequency (and only the frequency) of multiple simultaneous signals in a dense environment. They have good sensitivity, and are useful in both ES and SIGINT systems when used with superhet receivers set to identified signals of interest.

Table of Contents for the Digital Edition of JED - March 2011

JED - March 2011
The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
Washington Report
World Report
Airborne Maritime Patrol
What Electronic Warriors Should Know About Physics, Language and Concepts
Technology Survey: RWR/ESM Systems
EW 101
AOC News
AOC Membership Page
AOC Industry/Institute/University Member Guide
Index of Advertisers
JED Quick Look

JED - March 2011