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MDR nulling antennas: Ensuring secure tactical military communications TRW FACT SHEET Posted: January 10, 2002 The medium data rate (MDR) payload of Milstar 2 satellites -- delivering data to field terminals at T1 rates of 1.544 megabits per second, or more than 50 times the speed of a 28.8 kilobit-per-second computer modem‹will make possible secure, real-time transmission of voice, image, and data among tactical users. TRW-developed adaptive nulling antennas on each MDR payload protect Milstar MDR communications against electronic jamming by enemy forces. Each "nuller" is a fully autonomous antenna system that continuously maximizes user signals while minimizing jammer signals.
Extending the Range and Ensuring the Protection of Military Tactical Communications
Yet, the very feature that makes satellites so desirable for military communications‹line-of-sight access over a large area‹makes satellite uplinks vulnerable to enemy jamming. Jammers may be 100 or even 1000 times more powerful than the ground terminals of friendly forces.
The null effectively "screens out" jammers, and all this happens automatically with no interruption to communications. Nulling is required at MDR data rates to ensure the integrity of the communications data. (Milstar's low-data-rate (LDR) payload, with much lower data rates, relies entirely on frequency-hopping, spread-spectrum techniques, and error-correction to protect messages).
The MDR Antenna Suite Close-in jamming (where jammer and friendly terminals are both located within a single antenna beam) is a serious threat to the Army, which tends to operate near the front, close to enemy jammers. The Navy often operates from bases and carriers some distance from the front, where the jammers are often out of beam. Two nulling antennas onboard each MDR payload are capable of negating the effects of both in-beam and out-of-beam jammers. In addition, the MDR payload carries six smaller antennas that produce spot beams without nulling. These are called Distributed User Coverage Antennas (DUCAs). Generally speaking, the nulling antennas are best matched to theater-type requirements, while DUCAs better match those of dispersed global users such as the Navy.
Adaptive Nulling: How The Nulling Antenna Works In the absence of jammers, user signals received by the nulling antenna fall within an expected distribution of frequencies. When a jammer terminal begins operating within the satellite's spot beam coverage area, its radiated power does not follow the satellite's frequency-hopping pattern. As a result, anomalies appear in the nuller's power distribution curve, revealing the presence of jamming signals. The antenna takes immediate steps to eliminate these unwanted signals. It calculates appropriate signal-weighting factors for the power received at each antenna feed to determine the position of the jammer and produces a null in that direction. The MDR nulling antenna consists of four major components:
TRW also developed the algorithm for the nulling antenna processor. The TRW-patented algorithm determines the weight updates from the correlator error signals. The algorithm's performance, along with the speed of the processor, is essential to the nulling antenna's ability to counter jammers.
Nulling: Key to MDR Performance The MDR nulling antennas do far more than simply receive RF signals. Each antenna is a complete feedback control system designed to continuously maximize desired signals while processing out jamming signals. With nulling antennas in operation, the Milstar MDR payload can push data rates to 1.544 megabits per second. Or, by switching to lower data rates, it can receive signals from small, low-power ground terminals. Or it can operate at some intermediate combination of data rate and terminal power -- all without sacrificing antijam performance.
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Flight data file Vehicle: Titan 4B (B-38) Payload: Milstar 5 Launch date: Jan. 15, 2002 Launch window: 2148-0148 GMT (4:48-8:48 p.m. EST) Launch site: SLC-40, Cape Canaveral, Florida Pre-launch briefing Launch timeline - Chart with the key events to occur during the launch. Titan 4B - Description of America's most powerful unmanned rocket. Milstar satellite - A look at the Military Strategic and Tactical Relay satellite program. Communications - Overview of Boeing's Medium Data Rate and crosslink payloads on Milstar. DPS - TRW's digital processing subsystem on Milstar is key to payload. Titan 4 history - Chart with listing of previous Titan 4 flights. On to Mars A wide variety of papers presented at the first four years of the Mars Society's annual conference are collected together in this volume.Apollo 11 special patch Special collectors' patch marking the 35th anniversary of the historic Apollo 11 moon landing is now available.U.S. - U.K. - E.U. - Worldwide Inside Apollo mission control
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