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Exercise 3-2

Cross-Polarization Jamming

EXERCISE OBJECTIVE

To introduce the concept of antenna polarization. To demonstrate the effect of cross-polarization jamming on a tracking radar’s angular error signal.

DISCUSSION

All electromagnetic signals, be they in the radio, visible, or infrared frequencies of thespectrum, can be regarded as propagating waves consisting of an oscillating electricand magnetic field. The fields oscillate orthogonal to each other, and to their directionof propagation. All antennas can be characterized by their polarization. That is, thedirection in which the electric field of the transmitted signal is vibrating, and thedirection in which the electric field of a signal must be vibrating to be properlyreceived by the antenna. An antenna’s polarization can either be linear, circular, orelliptical, as shown in Figure 3-10. The name given to the polarization describes thepath traced out by the electric field vector in a plane perpendicular to the directionof propagation of the signal.

Antenna polarization agility can be used as a method of signal discrimination toprotect the radar from the effects of jamming. A cross-polarized signal, a signalwhose polarization is orthogonal to that of the antenna’s, is greatly attenuated uponreception. Therefore a radar, by controlling the polarization of its antenna, cansuppress the effects of the jamming signal. In theory, an infinite amount ofsuppression can be achieved if the radar is vertically polarized, and the jammerhorizontally polarized. Practically, however, antenna design limitations restrict theactual level of suppression to a finite value.


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Figure 3-10. Types of signal polarization.

That is to say, distortions in an antenna’s polarization make it able to receive cross-polarized signals of very strong levels. The polarization distortion is especiallyprominent in reflector-type antennas due to the curvature of the reflector. Becausethe antenna polarization distortion is a design weakness, the antenna’s cross-polarized response (called Condon lobes) is considerably different than its normallypolarized (co-polarized) response, as is illustrated in Figure 3-11 (a). An antenna’s


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polarization distortion is caused by several other phenomenon, such as the curvatureof the radome (if any), and diffraction of the received signal at the edges of theantenna.

As shown in Figure 3-11 (a), the specific level of polarization isolation that anantenna exhibits between a co-polarized signal, and a cross-polarized signal isproportional to the difference between the co-polarized and cross-polarized gains forthe signal.


The primary use of cross-polarization jamming is as self-protection against a trackingradar, it is not used as a support jammer technique. As stated in this Unit'sDiscussion of Fundamentals, cross-polarization jamming is a type of defect jamming.It is generally used against monopulse radars that have antennas exhibiting asignificant cross-polarized response. As shown in Figure 3-11 (b), cross-polarizationjamming exploits the fact that the antenna’s response to cross-polarized signals(Condon lobes) drastically changes the relationship between the actual angle-tracking error, and the angular error signal produced by the radar’s trackingservomechanism. Close examination of the co-polarized and cross-polarizeddifference patterns in Figure 3-11 (b) reveals that they are the inverse of each other(especially around the antenna beam axis). This can be used against monopulsetracking radars to invert the polarity of the angular error signal produced by thetracking mechanism.

By transmitting a cross-polarized repeated signal toward a radar antenna, a jammercan create a significant angular tracking offset, on the order of 5° between theantenna boresight and the target’s angular position. Once the repeated signal hascaptured the radar’s tracking gates, the polarity of the radar’s angular error signal isinverted for small angular tracking errors. The radar responds by rotating theantenna in the wrong direction until the angular error signal takes on a value of zeroagain, thus causing an angular tracking offset.


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Figure 3-11. Co-polarized and cross-polarized antenna responses and monopulse difference

patterns.


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For cross-polarization jamming to be effective, the jammer must provide a highjamming-to-signal (J/S) power ratio, it must be high enough to overcome the victimradar antenna’s low-response to cross-polarized signals. The orthogonality of thejamming signal to the radar’s must also be as perfect as possible. The slightestdeviation from true cross-polarization will allow a component of the jamming signalto be received by the radar antenna via its normal polarization. In general, a bit lessthan 5° from true cross-polarization is all that is required for the jammer signal tobecome a beacon for target tracking. However, to satisfy these stringent orthogo-nality requirements a cross-polarization jammer usually uses a configuration ofantennas that enable it to produce cross-polarized jamming independent of the angleof the radar and the jammer, as shown in Figure 3-12.

Figure 3-12. Cross-polarization jammer antenna configuration.

Most jammers employ either circularly polarized, or linearly (slant) polarized jammingantennas that inevitably have large cross-polarized components. Radars equippedwith an antenna that is susceptible to cross-polarized jamming signals can defeat thesignal’s effects by replacing the antenna with a phased-array (flat panel) antenna,that in general has a small cross-polarized response, or by using a polarizationscreen that prevents entry of cross-polarized signals. Many military radars have theability to change the polarization of their transmitted signal, and are thus able todefeat a cross-polarized jammer by using polarization agility.

Cross-Polarization Jamming Against a Sequential-Lobing Tracking Radar

Figure 3-13 illustrates the effect which cross-polarization jamming has on asequential-lobing tracking radar.


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Figure 3-13. Effect of cross-polarization jamming on a sequential-lobing tracking radar.


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The upper part of Figure 3-13 shows the normal-polarization response of the radarantenna for the two positions of the main beam. It also shows the cross-polarizationresponse of the radar antenna. As can be seen, the cross-polarization responsediffers greatly from the normal-polarization response. The main beam in the normal-polarization antenna response is split into two lobes in the cross-polarization antennaresponse. Furthermore, the amplitude of these lobes (Condon lobes) in the cross-polarization antenna response is much lower ( 24 dB in Figure 3-13) than that of themain beam in the normal-polarization antenna response.

These differences between the normal-polarization and cross-polarization responsesof the radar antenna drastically change the relationship between the actual angularerror and the angular error voltage that is produced by the tracking servomechanism,as shown in the lower part of Figure 3-13. The angular error voltage obtained witha cross-polarized signal is lower than that obtained with a co-polarized signal.Furthermore, the polarity of the angular error voltage is inverted for low angularerrors (up to ±5° in Figure 3-13). This is the key difference that allows cross-polarization jamming to produce angular deception in a tracking radar. When a lowangular error occurs, the angular tracking servomechanism rotates the antenna inthe wrong direction until the angular error voltage is zero again. This creates asignificant angular offset (+5° or 5° in Figure 3-13) between the antenna axisdirection and the target angular position.

Procedure Summary

During the first part of the exercise, you will set up and calibrate the Tracking Radar.You will also position the Target Positioning System with respect to the TrackingRadar.

In exercise part two, the Radar Jamming Pod Trainer is set up. A noise jammingsignal will be directed toward the Tracking Radar with the Radar Jamming PodTrainer in horizontal (0°), slanted (45°), and vertical (90°) positions. This will allowyou to determine the type of polarization used by the Tracking Radar and RadarJamming Pod Trainer antennas, as well as to demonstrate radar polarization agilityas a method to defeat noise jamming.

During the third part of the exercise, you will use a co-polarized noise jamming signalto measure and record the amplitude of the Tracking Radar’s angular error signal asa function of the actual position of the Radar Jamming Pod Trainer with respect tothe radar antenna axis. You will perform the same measurement with a cross-polarized noise jamming signal. You will then use the recorded data to plot curvesof the angular error signal amplitude versus the Radar Jamming Pod Trainerposition, that illustrate the radar's response to co-polarized and cross-polarizedjamming signals. This will allow you to make conclusions as to the reasons whycross-polarized jamming is efficient against tracking radars.

In the final part of the exercise, you will demonstrate the effect which cross-polarization jamming has on angular target tracking.


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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.

G 4. Make the following settings:

On the Radar Transmitter

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


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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 3-14. Make sure that themetal rail of the target table is correctly aligned with the shaft of theRotating-Antenna Pedestal.

Figure 3-14. Position of the Rotating-Antenna Pedestal and target table.


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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.

Make sure that the Tracking Radar is adjusted as follows:

Operating Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.0 GHzPulse-Repetition Frequency . . . . . . . . . . . . . . . . . . . . single, 288 HzPulse Width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 nsObservation Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 m

Signal Polarization

G 7. 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.

G 8. 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 long support shaft (part number 33125-01).

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.

G 9. 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.


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

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. Adjust the remote controller settingsto match the Radar Jamming Pod Trainer status (the Repeater is on, all elseis off).

G 10. 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 repeated echo signal is the same for bothpositions of the antenna main beam.

G 11. Observing the O-Scope Display, set the Gain of the MTI Processor so thatthe amplitude of the Radar Jamming Pod Trainer's repeated echo signal isapproximately 0.25 V.

G 12. Using the remote controller, make the following adjustments to the RadarJamming Pod Trainer:

Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OnFrequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.0 GHzFrequency Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . 0.0 GHzFrequency Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . TriangleAttenuation 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 dBAttenuation 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 dB

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

The Radar Jamming Pod Trainer is now transmitting a spot noise jammingsignal toward the radar antenna.

G 13. Adjust the Radar Jamming Pod Trainer Noise Attenuation so that theaverage amplitude of the noise spikes on the O-Scope Display isapproximately 0.25 V. Figure 3-15 is an example of what you shouldobserve on the O-Scope Display once the Attenuation is adjusted.

Note: Add persistence to the O-Scope Display while doing thisadjustment.


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Figure 3-15. Setting the average amplitude of the noise spikes on the O-Scope Display to

approximately 0.25 V.

G 14. Loosen the securing device found on the Radar Jamming Pod Trainerunderside and rotate the Radar Jamming Pod Trainer into a slanted positionof approximately 45°, while observing the noise on the O-Scope Display.Tighten the securing device.

How does this affect the jamming induced noise?

G 15. Loosen, once again, the securing device found on the Radar Jamming PodTrainer underside and rotate the Radar Jamming Pod Trainer to a verticalposition (90°), while observing the noise on the O-Scope Display. Tightenthe securing device.

How does this affect the jamming induced noise?


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Briefly explain what type of polarization is used by the Radar Jamming PodTrainer and Tracking Radar antennas, to account for the noise levelsobserved.

Comparison Between the Effect of Cross-Polarized and Co-polarized Jamming

G 16. Return the Radar Jamming Pod Trainer to the co-polarized jammingorientation. That is, loosen once again, the securing device found on theRadar Jamming Pod Trainer underside, and rotate the Radar Jamming PodTrainer to a horizontal position (0°). Tighten the securing device.

G 17. Align the Radar Jamming Pod Trainer horn antennas with the shaft of theRotating-Antenna Pedestal. The longitudinal axis of the Radar Jamming PodTrainer should be aligned with the shaft of the Rotating-Antenna Pedestal.

Align the radar antenna axis with the Radar Jamming Pod Trainer hornantennas.

G 18. On the Radar Transmitter, disconnect the BNC-connector cable from theTRIGGER INPUT of the PULSE GENERATOR. This disables pulsetransmission at the Tracking Radar, however reception is maintained. Thisis done so that the amplitude measurements of the radar’s angular errorsignal, taken later on, will be due to the jamming signal only. The effects ofradar clutter are thus eliminated from the measurements.

G 19. In LVRTS, disconnect Oscilloscope probes 1 and 2 from TP1 and TP2 of theMTI Processor. Connect Oscilloscope probe 1 to TP27 of the Radar TargetTracker.

Make the following settings on the Oscilloscope:

Channel 1 . . . . . . . . . . . . . . . . . . . . . . . . . 0.1 V/divChannel 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OffTime Base . . . . . . . . . . . . . . . . . . . . . . . . 20 ms/div

Set the Oscilloscope to Continuous Refresh.

The Oscilloscope is now set to display the angular error signal (TP27)produced by the Tracking Radar servomechanism (see Figure 3-16). Theamount by which the radar antenna turns to track a target is proportional tothe angular error signal voltage.


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Notice that the average value (AVG) of the voltage at TP27 (angular errorsignal voltage) is indicated in the Waveform Data section of theOscilloscope (see Figure 3-16). This value should fluctuate.

Figure 3-16. Angular error signal (TP27) produced by the Tracking Radar servomechanism.

G 20. Familiarize yourself with Table 3-1. This table will be used to record theamplitude of the Tracking Radar’s angular error signal maxima, and whenit has the value of zero. That is, you will record the average value of thevoltage at TP27 (angular error signal voltage), and the Radar Jamming PodTrainer’s X-axis position only when the voltage at TP27 is at a maximum orat a value of zero. In this manner, it will be possible to plot, in Figure 3-17,rough curves of the angular error signal voltage versus the position of theRadar Jamming Pod Trainer, that illustrate the Tracking Radar's responseto co-polarized and cross-polarized jamming signals.


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NOISE JAMMING

POLARIZATION

Radar Jamming Pod

Trainer

X-AXIS POSITION (cm)

AVERAGE VALUE OF

VOLTAGE AT TP27

(V)

Co-P

ola

rized

Cro

ss-P

ola

rized

Table 3-1. Average value of the voltage at TP27 (angular error signal voltage) as a function of the

Radar Jamming Pod Trainer's X-axis position and jamming signal polarization.

G 21. Begin the co-polarized noise jamming measurements.

While observing the signal at TP27 on the Oscilloscope, slightly slide theRadar Jamming Pod Trainer along the X-axis of the target table so that theaverage value of the voltage at TP27 is approximately 0.00 V. While slidingthe Radar Jamming Pod Trainer, attempt to maintain its target table Y-axisposition at 45.0 cm, and the pointing direction of its horn antennas.

When the signal at TP27 becomes approximately equal to zero, the transmithorn antenna of the Radar Jamming Pod Trainer should be aligned with theradar antenna axis.

Record the average value of the voltage at TP27 and the Radar JammingPod Trainer’s X-axis position in the first co-polarized row of Table 3-1.

G 22. Once again, slide the Radar Jamming Pod Trainer along the X-axis in thedirection of increasing values. Stop the displacement when the signal atTP27, being observed on the Oscilloscope, is maximum and has a positivepolarity.


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Record the average value of the voltage at TP27 and the Radar JammingPod Trainer’s X-axis position in the second co-polarized row of Table 3-1.

G 23. Continue sliding the Radar Jamming Pod Trainer along the X-axis in thedirection of increasing values. Stop the displacement when the signal atTP27, being observed on the Oscilloscope, has returned to a value ofapproximately 0.00 V.

Record the average value of the voltage at TP27 and the Radar JammingPod Trainer’s X-axis position in the third co-polarized row of Table 3-1.

G 24. Slide the Radar Jamming Pod Trainer along the X-axis, in the direction ofdecreasing values. Stop the displacement when the signal at TP27, beingobserved on the Oscilloscope, is maximum once again and has a negativepolarity (you will pass through a positive maximum and a zero beforereaching the negative maximum).

Record the average value of the voltage at TP27 and the Radar JammingPod Trainer’s X-axis position in the fourth co-polarized row of Table 3-1.

G 25. Continue sliding the Radar Jamming Pod Trainer along the X-axis, in thedirection of decreasing values. Stop the displacement when the voltage atTP27 has once again returned to a value of approximately 0.00 V.

Record the average value of the voltage at TP27 and the Radar JammingPod Trainer’s X-axis position in the fifth and final co-polarized row ofTable 3-1.

G 26. Adjust the Radar Jamming Pod Trainer orientation so as to transmit a cross-polarized noise jamming signal toward the Tracking Radar. That is, loosenthe securing device found on the Radar Jamming Pod Trainer undersideand rotate the Radar Jamming Pod Trainer to a vertical position (90°).Tighten the securing device.

G 27. Using the remote controller, decrease the Radar Jamming Pod Trainer’sNoise Attenuation to 0 dB. This adjustment will enable the cross-polarizednoise jamming signal to penetrate the radar receiver system.

Slowly slide the Radar Jamming Pod Trainer along the X-axis of the targetpositioning table so that it is aligned with the shaft of the Rotating-AntennaPedestal. While sliding the Radar Jamming Pod Trainer, attempt to maintainits target table Y-axis position at 45.0 cm, and the pointing direction of itshorn antennas. The voltage at TP27 should be approximately 0.00 V.

G 28. Begin the cross-polarized noise jamming measurements.

While the Tracking Radar's angular error response to a co-polarizedjamming signal only had one positive-polarity maximum, one negative-


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polarity maximum, and three zeroes (five measurements in all), the TrackingRadar's angular error response to a cross-polarized jamming signal has twopositive-polarity maxima, two negative-polarity maxima, and 5 zeroes (ninemeasurements in all).

To make the cross-polarized noise jamming measurements, use aprocedure similar to the one outlined in procedure steps 21 to 25 for theco-polarized noise jamming measurements. That is:

I. Slightly slide the Radar Jamming Pod Trainer along the X-axis of thetarget positioning table to find the central zero, record the average valueof the voltage at TP27, and the Radar Jamming Pod Trainer's X-axisposition.

II. Slowly slide the Radar Jamming Pod Trainer along the X-axis, in thedirection of increasing values until you locate a negative-polaritymaximum, a zero, a positive-polarity maximum, and another zero.Record your measurements.

Note: Change the sensitivity setting as required on theOscilloscope.

III. Slowly slide the Radar Jamming Pod Trainer along the X-axis, in thedirection of decreasing values to replace the Radar Jamming PodTrainer to the central zero position found in step I.

IV. Slowly slide the Radar Jamming Pod Trainer along the X-axis, in thedirection of decreasing values until you locate a positive-polaritymaximum, a zero, a negative-polarity maximum, and another zero.Record your measurements.

Note: If the Tracking Radar's angular error response to the cross-polarized noise jamming signal is not as expected, carefullyreadjust the Radar Jamming Pod Trainer orientation so that it isas near as possible to perfect orthogonality, then redo themeasurements.

G 29. Using the data recorded to Table 3-1, plot the Tracking Radar's angularerror response curves to the co-polarized and cross-polarized noisejamming signals in Figure 3-17. Label the curves as the "radar's angularerror response to co-polarized signals" and the "radar's angular errorresponse to cross-polarized signals".


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Figure 3-17. Amplitude of the radar angular error signal (TP27) as a function of the Radar Jamming

Pod Trainer's X-axis position for co-polarized and cross-polarized jamming signals.


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Note that the response curves which you plot in Figure 3-17 have significantdifferences between each other. Briefly describe the implications that thisdissimilarity has on angular tracking when the radar is confronted withcross-polarized jamming.

Cross-Polarization Jamming Demonstrated

G 30. Slowly slide the Radar Jamming Pod Trainer along the X-axis, in thedirection of increasing values to replace the Radar Jamming Pod Trainer tothe central zero position found previously. The radar antenna axis should bealigned with the Radar Jamming Pod Trainer and the voltage at TP27should be approximately 0.00 V.

G 31. Enable the Tracking Radar’s track-on-jamming mode by performing thefollowing manipulations:

I. Make certain that on the Radar Transmitter, the BNC-connector cableis disconnected from the TRIGGER INPUT of the PULSEGENERATOR. Thus radar pulse transmission is disabled, but receptionis maintained.

II. In LVRTS, set the Range Lock Disable to On. This disables automaticrange tracking.

III. Lock the Tracking Radar onto the cross-polarized noise jamming signalproduced by the Radar Jamming Pod Trainer while observing the radarantenna. The radar locks onto the noise jamming signal but the antennaaxis should be deflected away from the Radar Jamming Pod Trainer.This angular deception is due to the cross-polarized noise jammingsignal.

Note: If the radar antenna is still correctly aligned once theTracking Radar is locked onto the jamming signal, slightly movethe Radar Jamming Pod Trainer along the X-axis to create asmall angular error. This should cause the radar antenna to movein the opposite direction, thereby producing an angular offset ofa few degrees between the Radar Jamming Pod Trainer and theantenna axis direction.

G 32. Make sure the DISPLAY MODE on the Antenna Controller is set toPOSITION. This setting will permit you to quantitatively verify the extent ofany jamming induced angle tracking errors.


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What is the angular position of the radar antenna axis ( ANT.) as indicated onthe Antenna Controller?

ANT. = °

G 33. Unlock the Tracking Radar and align the antenna axis with the RadarJamming Pod Trainer.

What is the actual angular position of the Radar Jamming Pod Trainer ( POD)as indicated on the Antenna Controller?

POD = °

What is the value of the angular error ( MEASURED) induced by cross-polarization jamming?

MEASURED = POD - ANT = °

G 34. Note that in Figure 3-17, the cross-polarized angular error response haszeroes on each side of the central zero. Note that the slope of the curve atthe first zero on each side (side zero) of the central zero is of the correctsign for angular tracking. What is the average distance ( X) between eachside zero and the central zero?

X = cm

Knowing that the Radar Jamming Pod Trainer is at a range R ( 1.25 m)from the radar antenna, calculate the angular difference ( CALCULATED)corresponding to the average distance ( X) between the central zero andthe side zeroes in the Tracking Radar's angular error response to cross-polarized signals, as illustrated in Figure 3-18.

CALCULATED = = °


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Figure 3-18. Calculating the angular error induced by cross-polarization jamming.


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G 35. Compare MEASURED and CALCULATED. Briefly explain what this implies abouta radar’s angular tracking when confronted by a cross-polarization jammingsignal.

G 36. Turn off the Tracking Radar and the Radar Jamming Pod Trainer.Disconnect all cables and remove all accessories.

CONCLUSION

In this exercise, you demonstrated that radar polarization agility is an effectiveelectronic protection against jamming. However, you showed that if the radarantenna has a relatively high response to signals with a cross-polarized component,then it is vulnerable to cross-polarization jamming. Reflector-type antennas, such asthe parabolic antenna, are especially vulnerable to this type of jamming.

You showed that the angular error response of a radar to cross-polarized signals issignificantly different than its response to co-polarized signals. This was done bymeasuring the amplitude of the Tracking Radar’s angular error signal for differentpositions of the Radar Jamming Pod Trainer, transmitting either a co-polarized or across-polarized jamming signal. You demonstrated that when cross-polarizationjamming is effective against a tracking radar, it creates a significant angular trackingoffset.

REVIEW QUESTIONS

1. Briefly describe the concept of polarization.


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2. Briefly describe the electronic attack known as cross-polarization jamming.

3. What is radar polarization agility?

4. Does cross-polarization jamming target a specific radar design weakness or afundamental weakness in all radars? Briefly explain.

5. Could cross-polarization jamming be effectively conducted through the sidelobesof a radar antenna? Briefly explain.

exercise cross-polarization · pdf filecross-polarization jamming 3-29 for cross-polarization...

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