JED - July 2010 - (Page 47)

TECHNOLOGY SURVEY Radar Jammers By Ollie Holt T his month’s survey will focus on airborne radar jammers, in both podded and internal installations. In airborne applications, radar jammers are typically designed to be part of a self-protection suite (on a fighter for example) or they can be used in a support jamming role to protect a larger strike package. For our survey, we asked radar jammer manufacturers to provide information on the following parameters: installation (internal or podded), operational frequency range, installed sensitivity of the receiver within the jammer, effective radiated power (ERP)/gain of the jammer, modes, antenna type provided if part of the jammer system, jamming techniques supported and the weight, power and size. The first parameter – internal or pod is self-defining. The next parameter is the operational frequency range. Most of the support jammers cover frequencies as low as 500 MHz, and some go as low as 100 MHz (and a few even lower). The jammer’s transmit in these lower frequencies because that is the operational range of most early warning radars. In order to disrupt an enemy’s integrated air defense system, it is important to start by degrading or confusing the early warning and acquisition elements of the system. Most self-protection jammers usually start around 2 GHz and cover up to around 18 GHz, providing complete coverage of the frequency range from 7 to 12 GHz, where the majority of the tracking radars operate. The installed receiver sensitivity defines the ability of the radar jammer to detect the radar signal and provide the necessary jamming techniques. The lower the installed sensitivity value, the greater the detection range of the jamming system. This is important for self-protection jammers because of the need to begin jamming before the host aircraft is within the threat system’s missile launch range. Usually an installed sensitivity of between -45 dBm and -60 dBm is adequate to support self-protection needs. A low sensitivity has to be balanced with the jammer ERP to prevent interference between receive and transmit antennas. Different blanking techniques are used to optimize the sensitivity and ERP for maximum performance. Some support jammers, depending on the mode of operation, can be preprogrammed to transmit techniques without actually observing the radar signals. These techniques are usually a form of high power noise that degrades the radar system’s detection performance. For this type of support jammer, installed sensitivity is not that important. For more advanced support jamming concepts that require the detection of the radar signal, the lower the installed sensitivity performance, the greater the distance the jammer can stand-off and obtain the desired results. The next parameter is ERP/Gain. For this survey most of the responses are ERP. The ERP is the maximum output power of the jammer system. For support jammers using noise techniques, the larger the ERP, the more disruption it will cause. For self-protection jammers, the ERP required is a balance between the radar cross section of the host platform and the detection range of the threat radar system. The goal is to generate greater jamming power than signal power (the power of the radar signal as reflected from the target aircraft). This is referred to as the jamming-to-signal (J/S) ratio. Keeping the J/S ratio higher than 1 makes the jammer signal a more attractive signal to the radar system. Note: for coherent radar systems, additional signal constraints must be met for this rule to be true. The next parameter addresses jammer modes. In this case the survey was simply looking to determine if the jammer had the ability to provide a coherent response. Many of the current generation of radar systems integrate some form of coding in the radar signal for both signal processing improvements and jamming detection and protection. By generating a coherent response to the radar, the jammer can overcome these jamming protection schemes. The typical method of providing a coherent response is through the use of a digital RF memory (DFRM) that can capture a sample of the radar signal and then modify the captured RF signal with deception techniques and retransmit the signal at the correct time. The antenna parameter simply address whether or not the antenna is part of the jammer system and, if so, what type of antenna is used. The technique category provides information on the different types of techniques each jammer can provide. Most support jammers will provide different types of techniques, including wide and narrow band noise, sweep noise, barrage noise and blinking. The self-protection jammers will typically provide coherent and non-coherent range, velocity and angle techniques along with combinations of these techniques. The final set of parameters addresses the jamming system’s weight, size and power. If the jammer comprises more than one line replaceable unit (LRU), each LRU is listed individually. JED’s next survey, covering RF power sources for IED and communications jammers, will appear in the September edition. E-mail to request a survey questionnaire. The Journal of Electronic Defense | July 2010 47

Table of Contents for the Digital Edition of JED - July 2010

JED - July 2010
The View From Here
From the President
The Monitor
Washington Report
World Report
SIGINT for Special Mission Aircraft
Fighter Aircraft EW: Shifting from Defense to Attack
Technology Survey: Airborne Radar Jammers
EW 101
AOC News
Index of Advertisers
JED Sales Offices
JED Quick Look

JED - July 2010