JED - August 2011 - (Page 37)

TECHNOLOGY SURVEY SIGINT AND DIRECTION FINDING ANTENNAS By Ollie Holt A ntenna directional characteristics and the different properties of an RF signal can be used to determine signal direction of arrival (DOA) or angle of arrival (AOA). These characteristics are: antenna pattern characteristics and signal, amplitude, phase, time and Doppler artifacts. Let’s look at the simplest and oldest form of DF first, which utilizes the directional characteristics of an antenna. Using a simple spinning or pointable antenna that correlates the received signal amplitude with antenna pointing angle, a DF solution can be determined. The reported DOA for the signal would be the pointing angle, where the highest amplitude level was received. This technique requires a relatively narrow beamwidth antenna and a mechanical or human pointing system. The accuracy of the DF measurement depends on the ability to continually know the pointing angle of the antenna to a fine angular resolution and the precision of the amplitude measurement. If these parameters can be held to a high tolerance, the DF accuracy can be very good. This approach works for ground-based applications, but it can be a structural design problem for an airborne platform. An alternative to a mechanical scanned antenna would be an electronically steered antenna array. This consists of an array of at least two or more antenna elements. More elements allow the creation of narrower beamwidths and therefore finer AOA resolution. Using phase and amplitude control of each antenna element allows the generation of a SUM and DELTA pattern. The DELTA pattern forms a null in the center of the SUM beam. By scanning the SUM and DELTA beam through the signal recording, the position of maximum signal amplitude (SUM) and minimum signal amplitude (DELTA) results in a bearing solution. DF performance is a function of the beamwidth (number of elements) and can easily achieve accuracy of 1 degree or better with 16 or more elements. A simpler technique that reduces installation issues on airborne platforms is amplitude DF. Amplitude DF uses antennas that have fixed, overlapping fields of view. The simplest installation is four antennas located perpendicular to each other – usually one located in each quadrant. For a good amplitude system, well characterized antennas are required. The antennas should provide around 180 degrees of coverage overlapping into the adjacent quadrants. The received signal amplitude is measured by two overlapping antennas; the measured amplitudes are normalized and converted into an amplitude ratio. The amplitude ratio is then compared to the antenna characterization data to find a match. The amplitude ratio match then correlates to an AOA solution. Typical amplitude AOA installations can achieve 3 to 10 degrees AOA accuracy. The DF accuracy is very dependent on how well the antennas can be characterized in the installation and amplitude measurement accuracy. Time Difference of Arrival or TDOA uses a similar antenna arrangement as amplitude DF, but the installation and measurement requirements are more critical. For the installation, all the time delays between the antenna element and the measurement device must be known. For installations with minimal antenna separation the measurement resolution requirements need to be in the nanosecond range or less. For a time difference, remember that in 10 nano- seconds the signal would travel about 3 meters, so for antenna installations with element spacing less than 3 meters and allowing for some measurement error, we are looking at some challenging time measurements. Performance of typical TDOA systems is in the 1-degree range for a system capable of measuring time difference accurately to around 1 nanosecond. This technique is better suited to a large platform or multiple platforms that are time synchronized in order to achieve maximum antenna separation. Wider antenna separation reduces the requirement for fine time resolution. Phase difference of arrival or phase interferometry is the measurement of the signal’s electrical phase difference at two or more antenna elements looking in the same field of view. For unambiguous results, at least two of the elements should be spaced less than a half-wavelength apart. The more elements used, the more accurate the results. Typical performance for three or more elements can be 1 degree AOA or better. The only drawback to this technique is the requirement to control phase errors induced between the antenna and the phase measurement device. Doppler DF measures the frequency difference of arrival between two or more antenna elements. Doppler DF requires that either, or both, the signal source and the measurement antennas are moving. Doppler DF also requires very fine frequency measurements in order to achieve single-digit AOA accuracies. This month’s survey covers 80 SIGINT/DF antenna products from 19 companies. JED’s next technology survey, slated for the October issue, will focus on flightline test equipment for EW applications. The Journal of Electronic Defense | August 2011 37

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

The View From Here
Conference Calendar
From the President
The Monitor
Washington Report
World Report
Defining a Career Path in EW
Technology Survey:SIGINT/DF Antennas
Book Review
EW 101
AOC Member Page
Index of Advertisers
JED Quick Look

JED - August 2011

https://www.nxtbook.com/naylor/JEDM/JEDM0318
https://www.nxtbook.com/naylor/JEDM/JEDM0218
https://www.nxtbook.com/naylor/JEDM/JEDM0118
https://www.nxtbook.com/naylor/JEDM/JEDM1217
https://www.nxtbook.com/naylor/JEDM/JEDM1117
https://www.nxtbook.com/naylor/JEDM/JEDM1017
https://www.nxtbook.com/naylor/JEDM/JEDM0917
https://www.nxtbook.com/naylor/JEDM/JEDM0817
https://www.nxtbook.com/naylor/JEDM/JEDM0717
https://www.nxtbook.com/naylor/JEDM/JEDM0617
https://www.nxtbook.com/naylor/JEDM/JEDM0517
https://www.nxtbook.com/naylor/JEDM/JEDM0417
https://www.nxtbook.com/naylor/JEDM/JEDM0317
https://www.nxtbook.com/naylor/JEDM/JEDM0217
https://www.nxtbook.com/naylor/JEDM/JEDM0117
https://www.nxtbook.com/naylor/JEDM/JEDM1216
https://www.nxtbook.com/naylor/JEDM/JEDM1116
https://www.nxtbook.com/naylor/JEDM/JEDM1016
https://www.nxtbook.com/naylor/JEDM/JEDM0916
https://www.nxtbook.com/naylor/JEDM/JEDM0816
https://www.nxtbook.com/naylor/JEDM/JEDM0716
https://www.nxtbook.com/naylor/JEDM/JEDM0616
https://www.nxtbook.com/naylor/JEDM/JEDM0516
https://www.nxtbook.com/naylor/JEDM/JEDM0416
https://www.nxtbook.com/naylor/JEDM/JEDM0316
https://www.nxtbook.com/naylor/JEDM/JEDM0216
https://www.nxtbook.com/naylor/JEDM/JEDM0116
https://www.nxtbook.com/naylor/JEDM/JEDM1215
https://www.nxtbook.com/naylor/JEDM/JEDM1115
https://www.nxtbook.com/naylor/JEDM/JEDM1015
https://www.nxtbook.com/naylor/JEDM/JEDM0915
https://www.nxtbook.com/naylor/JEDM/JEDM0815
https://www.nxtbook.com/naylor/JEDM/JEDM0715
https://www.nxtbook.com/naylor/JEDM/JEDM0615
https://www.nxtbook.com/naylor/JEDM/JEDM0515
https://www.nxtbook.com/naylor/JEDM/JEDM0415
https://www.nxtbook.com/naylor/JEDM/JEDM0315
https://www.nxtbook.com/naylor/JEDM/JEDM0215
https://www.nxtbook.com/naylor/JEDM/JEDM0115
https://www.nxtbook.com/naylor/JEDM/JEDM1214
https://www.nxtbook.com/naylor/JEDM/JEDM1114
https://www.nxtbook.com/naylor/JEDM/JEDM1014
https://www.nxtbook.com/naylor/JEDM/JEDM0914
https://www.nxtbook.com/naylor/JEDM/JEDM0814
https://www.nxtbook.com/naylor/JEDM/JEDM0714
https://www.nxtbook.com/naylor/JEDM/JEDM0614
https://www.nxtbook.com/naylor/JEDM/JEDM0514
https://www.nxtbook.com/naylor/JEDM/JEDM0414
https://www.nxtbook.com/naylor/JEDM/JEDM0314
https://www.nxtbook.com/naylor/JEDM/JEDM0214
https://www.nxtbook.com/naylor/JEDM/JEDM0114
https://www.nxtbook.com/naylor/JEDM/JEDM1213
https://www.nxtbook.com/naylor/JEDM/JEDM1113
https://www.nxtbook.com/naylor/JEDM/JEDM1013
https://www.nxtbook.com/naylor/JEDM/JEDM0913
https://www.nxtbook.com/naylor/JEDM/JEDM0813
https://www.nxtbook.com/naylor/JEDM/JEDM0713
https://www.nxtbook.com/naylor/JEDM/JEDM0613
https://www.nxtbook.com/naylor/JEDM/JEDM0513
https://www.nxtbook.com/naylor/JEDM/JEDM0413
https://www.nxtbook.com/naylor/JEDM/JEDM0313
https://www.nxtbook.com/nxtbooks/naylor/JEDM0213
https://www.nxtbook.com/nxtbooks/naylor/JEDM0113
https://www.nxtbook.com/nxtbooks/naylor/JEDM1212
https://www.nxtbook.com/nxtbooks/naylor/JEDM1112
https://www.nxtbook.com/nxtbooks/naylor/JEDM1012
https://www.nxtbook.com/nxtbooks/naylor/JEDM0912
https://www.nxtbook.com/nxtbooks/naylor/JEDM0812
https://www.nxtbook.com/nxtbooks/naylor/JEDM0712
https://www.nxtbook.com/nxtbooks/naylor/JEDM0612
https://www.nxtbook.com/nxtbooks/naylor/JEDM0512
https://www.nxtbook.com/nxtbooks/naylor/JEDM0412
https://www.nxtbook.com/nxtbooks/naylor/JEDM0312
https://www.nxtbook.com/nxtbooks/naylor/JEDM0212
https://www.nxtbook.com/nxtbooks/naylor/JEDM0112
https://www.nxtbook.com/nxtbooks/naylor/JEDM1211
https://www.nxtbook.com/nxtbooks/naylor/JEDM1111
https://www.nxtbook.com/nxtbooks/naylor/JEDM1011
https://www.nxtbook.com/nxtbooks/naylor/JEDM0911
https://www.nxtbook.com/nxtbooks/naylor/JEDM0811
https://www.nxtbook.com/nxtbooks/naylor/JEDM0711
https://www.nxtbook.com/nxtbooks/naylor/JEDM0611
https://www.nxtbook.com/nxtbooks/naylor/JEDM0511
https://www.nxtbook.com/nxtbooks/naylor/JEDM0411
https://www.nxtbook.com/nxtbooks/naylor/JEDM0311
https://www.nxtbook.com/nxtbooks/naylor/JEDM0211
https://www.nxtbook.com/nxtbooks/naylor/JEDM0111
https://www.nxtbook.com/nxtbooks/naylor/JEDM1210
https://www.nxtbook.com/nxtbooks/naylor/JEDM1110
https://www.nxtbook.com/nxtbooks/naylor/JEDM1010
https://www.nxtbook.com/nxtbooks/naylor/JEDM0910
https://www.nxtbook.com/nxtbooks/naylor/JEDM0810
https://www.nxtbook.com/nxtbooks/naylor/JEDM0710
https://www.nxtbook.com/nxtbooks/naylor/JEDM0610
https://www.nxtbook.com/nxtbooks/naylor/JEDM0510
https://www.nxtbook.com/nxtbooks/naylor/JEDM0410
https://www.nxtbook.com/nxtbooks/naylor/JEDM0310
https://www.nxtbook.com/nxtbooks/naylor/JEDM0210
https://www.nxtbook.com/nxtbooks/naylor/JEDM0110
https://www.nxtbook.com/nxtbooks/naylor/JEDM1209
https://www.nxtbook.com/nxtbooks/naylor/JEDM1109
https://www.nxtbook.com/nxtbooks/naylor/JEDM1009
https://www.nxtbook.com/nxtbooks/naylor/JEDM0909
https://www.nxtbook.com/nxtbooks/naylor/JEDM0809
https://www.nxtbook.com/nxtbooks/naylor/JEDM0709
https://www.nxtbook.com/nxtbooks/naylor/JEDM0609
https://www.nxtbook.com/nxtbooks/naylor/JEDM0509
https://www.nxtbook.com/nxtbooks/naylor/JEDM0409
https://www.nxtbook.com/nxtbooks/naylor/JEDM0309
https://www.nxtbook.com/nxtbooks/naylor/JEDM0209
https://www.nxtbook.com/nxtbooks/naylor/JEDM0109
https://www.nxtbook.com/nxtbooks/naylor/JEDM0908
https://www.nxtbookmedia.com