Exercise Frequency Agility and Barrage Noise Jamming · MTD processing). These radars use ... This...

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Exercise 1-3

Frequency Agility and Barrage Noise Jamming

EXERCISE OBJECTIVE

To demonstrate frequency agility, a radar electronic protection is used against spotnoise jamming. To justify the use of barrage noise jamming against frequency-agileradars. To compare the jammer induced noise level produced in a radar receiver bya barrage noise jamming signal with that created by a spot noise jamming signal.

DISCUSSION

Introduction

A noise jamming signal is always directed toward the receiver system of a radar.This system is made to discriminate, to an extent, against all signals but the one ittransmits and is expected to receive from targets. A directional antenna limits thelocations of the possible sources of desired echo signals. The receiver is designedto accept only signals present within a certain frequency range known as the radarreceiver passband. As shown in Figure 1-19, the passband is centered on the radar’soperating frequency. Its width is adapted to the transmitted radar pulse width. Thenarrower the transmitted pulse width (which implies a better range resolution), thewider the receiver passband.

Figure 1-19. Spot noise jamming signal bandwidth and radar receiver passband represented in

the frequency domain.

In the case of the Lab-Volt radar receiver system (Radar Receiver and Dual-ChannelSampler), the passband width, also known as the radar receiver bandwidth, isapproximately 1.3 GHz. The small transmitted pulse width used by the radar is the


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reason that the receiver has a wide passband. The Radar Receiver and the Dual-Channel Sampler accept all signals with a frequency found within a 1.3-GHz bandcentered on the radar’s operating frequency.

As stated, spot noise jamming consists of a narrow bandwidth ( 30 MHz in the caseof the Radar Jamming Pod Trainer) RF signal transmitted by the jammer toward aradar antenna. For it to be effective against the radar, the jamming signal frequencymust be tuned to the radar’s operating frequency. The narrow bandwidth of a spotnoise jamming signal allows it to be contained entirely within the radar receiverpassband limits. This permits nearly all jamming signal power inserted through theradar antenna to pass unhindered into the radar receiver system. However, if theradar were to suddenly change its operating frequency such that the bandwidth ofthe jamming signal was no longer contained entirely within the radar receiverpassband limits, then only some or none of the jamming signal power would beinserted into the radar receiver system.

Frequency Agility

Certain radars are capable of changing their transmitted carrier frequency on apulse-to-pulse or burst-to-burst basis to eliminate the effects of narrowband jammingsignals (e.g., spot noise jamming signal). Illustrated in Figure 1-20, this capability isknown as frequency agility and when implemented takes the form of abrupt, randomfrequency changes over the entire frequency tuning range. When used as a radarelectronic protection against jamming, effective frequency agility forces potential spotnoise jammers to spread their jamming signal power over a wider bandwidth. Onewhich, for the jammer to no longer be susceptible to the radar’s frequency changes,must cover the entire radar frequency tuning range.

Frequency agility cannot be used by coherent pulse-Doppler radars (radars withMTD processing). These radars use Coherent pulse-Processing Intervals (CPIs). ACPI is a pre-detection period over which the radar’s operating frequency must staythe same so that returned radar pulses can be coherently integrated together togenerate basic target information. In effect, this type of radar must maintain aconstant frequency for at least a few consecutive pulses. If this type of radar wereto change its carrier frequency, a jammer conducting look-through jamming coulddetect and match the radar’s frequency change before the radar could switch itsfrequency again. Look-through jamming consists of periodically pausing jamming toevaluate jamming success and to ensure the correct jamming signal properties (suchas frequency, modulation, and bandwidth).

Conversely, coherent radars with analog MTI processing, such as the Lab-VoltTracking Radar, can use frequency agility as an effective countermeasure againstspot noise jamming. This type of radar does not use CPIs and so can continue targetdetection while changing its operating frequency. A spot noise jammer confrontedwith a frequency-agile radar cannot predict the radar’s next frequency change anddoes not have the time necessary to match the current frequency. In such cases, thejamming platform must resort to barrage noise jamming. That is, transmitting itsjamming signal over the entire radar frequency tuning range.


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Figure 1-20. Frequency agility as an EP against spot noise jamming.

Barrage Noise Jamming

Barrage noise jamming makes certain that jamming induced noise is created in theradar receiver for whatever the radar’s operating frequency. Thus, a frequency-agileradar can no longer eliminate the receiver jamming noise by changing its frequency.

When a radar is confronted with barrage noise jamming, the RF jamming signalpower accepted by the radar receiver is significantly less than if the radar wereconfronted with spot noise jamming. A platform conducting barrage noise jamminguniformly spreads its available jamming power over the entire frequency tuning rangeof the victim radar. Implying, as shown in Figure 1-21, that the bandwidth of abarrage noise jamming signal is much wider than the radar receiver passband limits.The receiver accepts only a fraction of the total power of a barrage noise jammingsignal.


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Figure 1-21. Jamming power received by a radar.

The RF signal power (PBARRAGE) accepted by a radar receiver from a barrage noisejammer can be represented by Equation (2). This equation is valid provided that thejamming is sufficiently noiselike, and that the jamming signal power is uniformlydistributed over the jamming signal bandwidth (i.e., a uniform spectral powerdensity).

(2)

PSPOT is the RF signal power accepted by the radar receiver from a spot noisejammer of equivalent radiated power. The wider the barrage noise jammer signalbandwidth (BBJ), the less jamming signal power is accepted into the radar receiver.Maximum barrage noise jamming efficiency is achieved by making the jammingsignal bandwidth (BBJ) only slightly wider than the radar receiver systembandwidth (BR).

The Radar Jamming Pod Trainer Noise Signal

Be it for narrowband or wideband noise jammers, the method taken to generate anoise jamming signal can be critical to the jammer’s success. It is important that thejamming induced noise in a radar receiver resembles thermal noise as closely aspossible. This implies that the noise amplitude has a Gaussian distribution with time,and that the noise spectral power density is uniform.

The Lab-Volt Radar Jamming Pod Trainer does not produce thermal noise. TheRadar Jamming Pod Trainer uses a Voltage Controlled Oscillator (VCO) to generatea frequency-swept Continuous Wave (CW) signal. A VCO is an electronic device thatgenerates a CW (sinusoidal) output signal whose frequency is proportional to thevoltage level of an input signal. The Radar Jamming Pod Trainer can be configuredto input an internal triangular signal, or a randomly generated signal to the VCO, asshown in Figure 1-22.


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Figure 1-22. Randomly controlled VCO input signal for generating an output signal spanning a

4-GHz frequency range.

By randomly varying the VCO input signal over a small voltage range, a narrowband“noise” jamming signal can be generated. This corresponds to the Radar JammingPod Trainer spot noise jamming signal. By similarly modulating the VCO input signalover a wide voltage range, a wideband “noise” jamming signal is generated. Thisproduces the Radar Jamming Pod Trainer barrage noise jamming signal.

Procedure Summary

The Tracking Radar is set up in the first part of the exercise.

During the second part, the efficiency of frequency agility as an electronic protectionagainst spot noise jamming is demonstrated.

In the third part of the exercise, the effect of barrage noise jamming and spot noisejamming on the radar video signal are compared.


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In the fourth part of the exercise, quantitative measures are made of the level ofnoise induced in the radar receiver system of the Tracking Radar, using spot noisejamming and barrage noise jamming. Four different bandwidths are used whenconducting barrage noise jamming. The levels of noise induced in the radar receiversystem using spot noise jamming and barrage noise jamming are compared, and aconclusion is drawn on the pertinence of using frequency agility when a radar isconfronted with noise jamming.

PROCEDURE

Setting Up the Tracking Radar

G 1. Before beginning this exercise, the main elements of the Tracking RadarTraining System (i.e., the antenna and its pedestal, the target table, theRTM and its power supply, the training modules, and the host computer)must be set up as shown in Appendix A.

On the Radar Transmitter, make sure that the RF POWER switch is set tothe STANDBY position.

On the Antenna Controller, make sure that the MANual ANTENNAROTATION MODE push button is depressed and the SPEED control is setto the 0 position.

Turn on all modules and make sure the POWER ON LED's are lit.

G 2. Turn on the host computer, start the LVRTS software, select TrackingRadar, and click OK. This begins a new session with all settings set to theirdefault values and with all faults deactivated. If the software is alreadyrunning, click Exit in the File menu and then restart the LVRTS software tobegin a new session.

G 3. Connect the modules as shown on the Tracking Radar tab of the LVRTSsoftware. For details of connections to the Reconfigurable Training Module,refer to the RTM Connections tab of the software.

Note: Make the connections to the Analog/Digital OutputInterface (plug-in module 9632) only if you wish to connect aconventional radar PPI display to the system or obtain anO-scope display on a conventional oscilloscope.

Note: The SYNC. TRIGGER INPUT of the Dual-Channel Samplerand the PULSE GENERATOR TRIGGER INPUT of the RadarTransmitter must be connected directly to OUTPUT B of theRadar Synchronizer without passing through BNC T-connectors.

Connect the hand control to a USB port of the host computer.


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G 4. Make the following settings:

On the Radar Transmitter

RF OSCILLATOR FREQUENCY . . . . . . . CAL.PULSE GENERATOR PULSE WIDTH . . . 1 ns

On the Radar Synchronizer / Antenna Controller

PRF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 HzPRF MODE . . . . . . . . . . . . . . . . . . . . . SINGLEANTENNA ROTATION MODE . . . PRF LOCK.DISPLAY MODE . . . . . . . . . . . . . . . POSITION

On the Dual-Channel Sampler

RANGE SPAN . . . . . . . . . . . . . . . . . . . . 3.6 m

In the LVRTS software

System Settings:Log./Lin. Mode . . . . . . . . . . . . . . . . . . . . Lin.Gain . . . . . . . . . . . . . . . . . . . . . . as required

Radar Display Settings:Range . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 m

G 5. Connect the cable of the target table to the connector located on the rearpanel of the Target Controller. Make sure that the surface of the target tableis free of any objects and then set its POWER switch to the I (on) position.

Place the target table so that its grid is located approximately 1.2 m from theRotating-Antenna Pedestal, as shown in Figure 1-23. Make sure that themetal rail of the target table is correctly aligned with the shaft of theRotating-Antenna Pedestal.


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Figure 1-23. Position of the Rotating-Antenna Pedestal and target table.

G 6. Calibrate the Tracking Radar Training System according to the instructionsin Appendix B.

Set the RF POWER switch on the Radar Transmitter to the STANDBYposition.

G 7. Make sure that the Tracking Radar is adjusted as follows:

Operating Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.0 GHzPulse-Repetition Frequency . . . . . . . . . . . . . . . . . . . . single, 288 HzPulse Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 nsObservation Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 m

Frequency Agility

G 8. Remove the semi-cylinder target, used for the Tracking Radar calibration,from the target table mast.

Turn off the target table. Move the metal rail to either end of the target table.The metal rail will not be used during the exercise.

Place the Radar Jamming Pod Trainer support (part number 9595-10),provided with the Connection Leads and Accessories, onto the target table.Position it so that it is in the center of the target table grid.


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G 9. Make sure that a 50- load is connected to the Radar Jamming Pod TrainerCOMPLEMENTARY RF OUTPUT.

Install the Radar Jamming Pod Trainer onto its support (in the horizontalposition) using the short support shaft (part number 33125).

Align the Radar Jamming Pod Trainer so that its horn antennas are facingthe Tracking Radar antenna and aligned with the shaft of the Rotating-Antenna Pedestal. The longitudinal axis of the Radar Jamming Pod Trainershould be aligned with the shaft of the Rotating-Antenna Pedestal.

Rotate the infrared receiver on the Radar Jamming Pod Trainer toward thedirection from which you will use the remote controller.

Install the Power Supply (Model 9609) of the Radar Jamming Pod Traineron the shelf located under the surface of the target table. Connect thePower Supply line cord to a wall outlet.

Connect the power cable of the Radar Jamming Pod Trainer to the multi-pinconnector located on top of the Power Supply.

Retract the Radar Jamming Pod Trainer's target positioning arm and placethe medium-size (15 x 15 cm) metal plate target at its tip (refer toFigure 1-24). Orient the metal plate target so that it squarely faces theTracking Radar antenna. The target should be perpendicular to thelongitudinal axis of the Radar Jamming Pod Trainer.

Figure 1-24. Installing a target on the target positioning arm of the Radar Jamming Pod Trainer.

G 10. On the Radar Transmitter, depress the RF POWER push button. The RFPOWER ON LED should start to flash on and off. This indicates that RFpower is being radiated by the Dual Feed Parabolic Antenna.

In LVRTS, turn off the AGC of the Radar Target Tracker.


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Turn on the Power Supply of the Radar Jamming Pod Trainer. Turn theRadar Jamming Pod Trainer on. Note that the Radar Jamming Pod Trainerstatus indicates that the Repeater is on.

G 11. Turn the repeater of the Radar Jamming Pod Trainer off by making thefollowing settings on the remote controller:

Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffAM/Blinking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffRepeater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffRGPO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffFalse Targets (FT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Off

Verify that the Radar Jamming Pod Trainer status, indicated on its rearpanel, shows that no jamming signal is being transmitted.

G 12. Make sure the radar antenna axis is aligned with the Radar Jamming PodTrainer. This can be done by observing the O-Scope Display of the TrackingRadar while adjusting the radar antenna orientation so that the amplitude ofthe Radar Jamming Pod Trainer's natural echo signal (radar echo signal ofthe metal plate installed on the target positioning arm) is the same for bothpositions of the antenna main beam.

Observing the O-Scope Display, set the Gain of the MTI Processor so thatthe amplitude of the Radar Jamming Pod Trainer's natural echo signal isapproximately 0.25 V.

Lock the Tracking Radar onto the Radar Jamming Pod Trainer's naturalecho signal.

In LVRTS, add persistence to the O-Scope Display by setting thecorresponding parameter to 6 traces.

G 13. Using the remote controller, make the following adjustments to the RadarJamming Pod Trainer:

Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OnFrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.0 GHzFrequency Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . 0.0 GHzFrequency Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . TriangleAttenuation 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . MaximumAttenuation 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 dB

AM/Blinking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffRepeater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffRGPO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffFalse Targets (FT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Off

This sets the Radar Jamming Pod Trainer VCO to an operating frequencyof 8.0 GHz, the same frequency as the Tracking Radar. The RadarJamming Pod Trainer is transmitting a spot noise jamming signal toward theradar antenna.


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G 14. Using the remote controller, decrease the Radar Jamming Pod TrainerNoise Attenuation until the video signal on the O-Scope Display is quitenoisy, but without causing the Tracking Radar to lose target track.

G 15. While observing the O-Scope Display, slowly increase the Tracking Radar’soperating frequency from 8.0 GHz to 9.0 GHz, and then from 9.0 GHz to10.0 GHz.

A significant decrease of the noise level in the radar video signal shouldoccur. Briefly explain why the video signal noise level decreases when theTracking Radar’s operating frequency is changed from 8.0 GHz to10.0 GHz.

Barrage Noise Jamming

G 16. Make sure that the Tracking Radar’s operating frequency is tuned to10.0 GHz.


Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OnFrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.0 GHzFrequency Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . 4.0 GHzFrequency Modulation . . . . . . . . . . . . . . . . . . . . . . . . . RandomAttenuation 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . No adjustmentAttenuation 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . No adjustment

AM/Blinking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffRepeater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffRGPO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffFalse Targets (FT) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Off

This places the Radar Jamming Pod Trainer into a wideband (from 8.0 GHzto 12.0 GHz) noise jamming signal transmission mode, known as barragenoise jamming. Note that the bandwidth (4.0 GHz) of the barrage noisejamming signal produced by the Radar Jamming Pod Trainer is much widerthan the radar receiver system passband limits.

G 18. While observing the O-Scope Display, slowly vary the Tracking Radar’soperating frequency over the entire frequency tuning range (8.0 GHz to10.0 GHz).


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The noise level in the radar video signal should remain virtually constantover the entire Tracking Radar's frequency tuning range. Briefly explain whythe noise level in the video signal does not vary over the Tracking Radar'sfrequency tuning range.

G 19. Tune the Tracking Radar’s operating frequency to 10.0 GHz.

Using the remote controller, slowly decrease the Radar Jamming PodTrainer Noise Attenuation 1 dB at a time until the Tracking Radar losestarget track. Note that barrage noise jamming has caused the TrackingRadar to lose target track, even though the Radar Jamming Pod Trainer hasspread its noise jamming power over a wide frequency band.

G 20. Using the remote controller, turn the Radar Jamming Pod Trainer Noise off.

In LVRTS, disable the persistence of the O-Scope Display by setting thecorresponding parameter to Off.

Induced Noise Level in the Radar Receiver System

G 21. Align the radar antenna axis with the Radar Jamming Pod Trainer. This canbe done by observing the O-Scope Display of the Tracking Radar whileadjusting the radar antenna orientation so that the amplitude of the RadarJamming Pod Trainer's natural echo signal is the same for both positions ofthe antenna main beam.


Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OnFrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.0 GHzFrequency Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . 0.0 GHzFrequency Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . RandomAttenuation 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . No adjustmentAttenuation 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . No adjustment


The Radar Jamming Pod Trainer is now transmitting spot noise jammingtoward the Tracking Radar.


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G 23. On the Radar Transmitter, disconnect the BNC-connector cable at theTRIGGER INPUT of the PULSE GENERATOR. By doing this, radar pulsetransmission is disabled but reception continues. Therefore, the RadarJamming Pod Trainer spot noise jamming signal is still received.

G 24. Make the following settings on the Oscilloscope:

Channel 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.2 V/DIVChannel 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffTime Base . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 ms/DIV

Set the Oscilloscope to Continuous Refresh. The noise induced in theI channel of the radar receiver system by the spot noise jamming signalshould be displayed on the Oscilloscope.

Slightly realign the radar antenna axis so that the trace on the O-ScopeDisplay does not appear as doubled due to the lobing action of the TrackingRadar. Figure 1-25 shows what you might observe on the O-Scope Displaybefore and after antenna realignment.

Figure 1-25. Noise on the O-Scope Display before and after antenna realignment.

G 25. In LVRTS, observe that the true RMS voltmeter at TP1 of the MTI Processorof the Tracking Radar indicates the RMS voltage of the noise induced in theI channel of the radar receiver system.


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G 26. Using the RMS voltmeter at TP1 of the MTI Processor of the TrackingRadar, measure the RMS voltage of the noise induced in the radar receiversystem by spot noise jamming. Record the value in the first row ofTable 1-1.

TYPE OF

RADAR NOISE JAMMING

RMS VOLTAGE OF THE

NOISE INDUCED IN THE

RADAR RECEIVER

SYSTEM (mV)

Spot Noise

Barrage Noise (1-GHz bandwidth)




Table 1-1. RMS voltage of the noise induced in the radar receiver system.


Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OnFrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.0 GHzFrequency Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . . 1.0 GHzFrequency Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . RandomAttenuation 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . No adjustmentAttenuation 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . No adjustment


The Radar Jamming Pod Trainer is now transmitting a barrage noisejamming signal having a 1-GHz bandwidth. The available jamming powerhas consequently been spread over a 1-GHz frequency band centered at10.0 GHz.

Using the RMS voltmeter at TP1 of the MTI Processor of the TrackingRadar, measure the RMS voltage of the noise induced in the radar receiversystem by barrage noise jamming. Record the value in the appropriate rowof Table 1-1.


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Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OnFrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.0 GHzFrequency Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . 2.0 GHzFrequency Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . RandomAttenuation 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . No adjustmentAttenuation 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . No adjustment


The Radar Jamming Pod Trainer is now transmitting a barrage noisejamming signal having a 2-GHz bandwidth centered at 10.0 GHz.










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G 31. From the results in Table 1-1, observe that the RMS voltage of the noiseinduced in the radar receiver system remains almost unchanged when theRadar Jamming Pod Trainer passes from spot noise jamming to barragenoise jamming with a 1-GHz bandwidth. Briefly explain why.

G 32. From the results in Table 1-1, observe that the RMS voltage of the noiseinduced in the radar receiver system starts to decrease when the bandwidthof the barrage noise jamming is greater than 1 GHz. Briefly explain why.

G 33. From the result in Table 1-1, what is the relationship between the bandwidthof the barrage noise jamming and the amount of noise induced in the radarreceiver system?


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What does this relationship imply for a radar operator confronted with noisejamming?

G 34. Turn off the Tracking Radar and the Radar Jamming Pod Trainer.Disconnect all cables and remove all accessories.

CONCLUSION

In this exercise, it was stated and you observed that a radar receiver system is madeto discriminate all signals with frequencies found outside its passband from signalswith frequencies found within its passband. Only signals present within the passbandfrequency range, which is centered on the radar’s operating frequency, are accepted.You used frequency agility to exploit this fact and to eliminate radar receiver noiseintroduced by spot noise jamming.

Frequency agility is used to force a potential spot noise jammer into a barrage noisejamming mode. Using the Radar Jamming Pod Trainer, you observed that forwhatever the Tracking Radar’s operating frequency, barrage noise jamming raisesthe noise level induced in the radar receiver system. However, the noise powerinduced in the radar receiver system by barrage noise jamming is less than thatinduced by spot noise jamming. This is because the available signal power of abarrage noise jammer is spread over a much wider frequency band than that of aspot noise jammer. During this exercise, you measured the level of noise insertedinto the radar receiver system with spot noise jamming as well as with barrage noisejamming (four different bandwidths were used for the barrage noise jamming).

You demonstrated that it is advantageous for a frequency-agile radar to force a spotnoise jammer into a barrage noise jamming mode because the available jammingpower of a barrage noise jammer is spread thinly over the radar receiver passband.To be as effective as a spot noise jammer, a barrage noise jammer must transmitextremely high levels of RF power. This may be difficult, or even impossible, incertain airborne applications.

REVIEW QUESTIONS

1. What is the difference between a spot noise jamming signal and a barrage noisejamming signal?


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2. Name two ways through which a radar receiver system is made to discriminateto an extent against all signals but the one it transmits and is meant to receive.

3. Define frequency agility.

4. Briefly explain why frequency agility is an effective countermeasure against spotnoise jamming.

5. Briefly explain why it is advantageous for a frequency-agile radar to force a spotnoise jammer into barrage noise jamming mode.

Exercise Frequency Agility and Barrage Noise Jamming · MTD processing). These radars use ... This...

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