Sequencing radar jamming--method and tehnical solution.

Grzan, Marijan ; Covo, Petar ; Belak, Branko 等

Abstract: Sequencing jamming of all radar types has been increasingly used. The purpose of sequencing jamming is to jam specified radars in specified time with a specified type of radar clutters so to get optimal results. The aim is that the radar operator or the system automatics cannot or do not provide accurate elements for further processing or analysis.

Key words: Sequencing jamming, radar jamming, mode of jamming

1. INTRODUCTION

The task of a radar device is to provide coordinates of an object in air, on ground or on sea surface at as far range as possible, or to provide as accurate data as possible on the land surface or objects on it.

Consequently, the development of radar countermeasures has taken place at the same time as the improvement of radar technology. Therefore an ultimate purpose of the development of radar and protection against electronic countermeasures is the development of such radar devices and systems that will make the other side to take its radar countermeasures with highly sophisticated equipment. Modern radar devices or a radar system require the application of numerous various devices for the protection against radar countermeasures.

2. TYPES AND KINDS OF CLUTTER

Radar countermeasures may be, according to the effects they achieve, classified into a number of groups, which in turn can be intentionally or unintentionally combined.

Radar countermeasures is basically divided into:

* Intentional countermeasures aiming at the neutralization of a certain radar device or system.

* Unintentional countermeasures resulted from the close operation of radars or radios, or caused by location, local objects or meteorological conditions.

According to the effects achieved, intentional radar countermeasures can be divided as follows (Grzan. M. 1992.):

* Countermeasures with masking effects--by an active or a passive mode certain parts of a radar display are covered so to cover--mask real targets.

* Countermeasures with confusing effects--causing an effect on a radar display that is quite similar to the symptoms causing a device failure. The aim is to make an impression of device failure with the radar operator.

* Countermeasures with imitating effects--generation of false reflexes close to real ones, with the same electrical characteristics to direct attention and measures towards false reflexes.

* Change of target coordinates--generation of false reflexes with a successive change of coordinates towards the other side

* Change of radar reflex surface of a target--by certain coatings or passive reflectors radar reflex surface of a target or environment can be increased or decreased.

3. ACTIVE RADAR JAMMING

An organized radar jamming affects in fact all the performances of a radar, as well as accuracy and reliability of data display. Based on its origin, organized jamming can be (Grzan M. 1992.):

* Active jamming, achieved by various transmitters--radar jammers, with various signal modulation and patterns

* Passive jamming, achieved by increasing or decreasing of reflection of radar transmitting signal from artificial or natural objects on land, sea surface or in air. Passive jamming is in fact a protective measure.

Jamming in narrow-band frequency--narrow-band jamming requires good knowledge of jammed device frequency. In principle, these are low-priced and simple devices. The disadvantage is that their efficiency deteriorates if a radar possesses more channels or changes frequency.

Jamming in wideband frequency--wideband jamming emits energy within a wideband frequency thus jamming the operation of all the devices occurring within that frequency range and jammer range.

Sweep jamming within a frequency range is a compromise between wideband and narrow-band jamming. With this jamming the transmitter frequency changes within a frequency range at slower or higher velocity.

Jamming by response is made by radar signal reception, its amplification on target and reemission in such a pattern and in such a time that target reflexes, that do not exist in the space under surveillance, appear on the jammed radar, or the coordinates with the existing target have been shifted so to remain within the reliability required.

4. TYPES OF JAMMING SIGNAL

Main radar jamming modes are (Schlesinger R, 1999):

* Jamming by continuous unmodulated signal. This is the simplest mode of jamming. The jamming signal with a sufficient size at the place of reception causes the radar saturation thus making the target signals invisible. The saturation causes noise on the display. If jamming is carried out at close range and with a sufficiently high signal, then image and noise completely disappear from the radar display. The symptoms are the same as in case of a device failure.

* Continuous amplitude-modulated signal. This signal appears on the radar display in the form of intensive modulated bright fans the density and width of which depend on the modulated signal frequency. In case of a synchronous clutter, the fans on the display are motionless. Otherwise, they circle round the display and after some time the display achieves maximum illumination and does not react to targets.

* Continuous frequency-modulated signal. It causes various visual effects on the display depending on the type of signal with which frequency modulation of a jammer carrier wave is executed.

* Jamming pulse signal. It is carried out by a series of modulated and unmodulated pulses in the radar frequency, which can be synchronous or non-synchronous with the radar pulse frequency. On the jammed radar display there appears a series of bright spots that are motionless in case of a synchronous clutter, or travel round the display in case of a non-synchronous one.

* Jamming by response. It is classified within the group of synchronous pulse jamming but with each emitted radar pulse, one or more jamming pulses are emitted. The effects of this measure are manifested in the coordinate or feature changes to distract attention.

5. MODES OF JAMMING, TYPES OF RADARS ON WHICH THEY ARE APPLIED AND ELEMENTS ON WHICH THEY ARE MANIFESTED

6. CONCLUSION

Understanding that there exists a clutter in any form is very important and should enable a radar operator to find solutions for the radar operation under those conditions as well. It is evident that accurate range determination, angle coordinates and surface resolution depend considerably on the radar condition and its capability to perform its function even under clutters. Consequently, the radar operator himself must be enabled to identify the interference and take necessary measures to lessen it accordingly.

7. REFERENCES

Schslezinger R. (1999). Principles of Electronic Warfare..., Peninsula Publishing USA, ISBN 0-932146-01-05, Los Altos

Grzan M. (1992). Sequencing Radar Jamming..., Master's Thesis ETF Zagreb, UDK 621.396.96:623.624, Zagreb

Table 1. Sequencing jamming modes (Grzan. M. 1992.)

Modes of jamming Radar type Elements affected

RGWO Impulse-incoherent Time range gate
 radar pull-off

SWEPT AUDIO Sight radar with Error in angle
 conical scanning tracking
 system

SPOT NOISE JAMMING All radar types Failure to detect a
 except frequency target (high noise
 agile ones density within
 receiver bandwidth)

VGWO Pulse or CW radars Disable detection of
 for rapid tracking phase bits in an
 and scanning impulse

REPETATIVE REPEATER To jam radars using False target
 pseudorandom scanning generation
 techniques of any
 kind

REPETATIVE PULSE To jam radars using Radar video
NOISE pseudorandom scanning integrator efficiency
 techniques of any decreasing
 kind

IN-BITE PHASE JAMMING Phase-coded impulse Disable detection of
 compressed radars phase bits in a pulse

INVERSE GAIN Jamming of radars Disable target
 with special beam positioning
 sweeping techniques

FALSE TARGET Pulse or False target
GENERATION phase-modulated generation
 radars

PULSE COUNT Radars with an AGC Disable switching
 unit from scanning mode
 into tracking mode

PHASE DETECTOR Generation of phase
 noise at phase
 detector output

PSEUDORANDOM Pulse radars, radars Disable target
SEQUENCING JAMMING with conical tracking, i.e. target
 scanning, radars coordinates
 using single-tone identification
 signal

INJECTION SCAN Radars using Disable obtaining of
FREQUENCY ECM pseudorandom control sweeping frequency
 of digital modulation

DUAL-FREQUENCY Monopulse radars Error in angle
JAMMING tracking

IF JAMMING Monopulse radars Operating frequency
 or LO frequency
 error

SCAN FREQUENCY Pulse, Doppler radars Generation of
JAMMING or radars with velocity gate error
 conical beam sweeping (false Doppler
 targets)

BILEVEL CONICAL SCAN Radars with conical Affects conical
JAMMING beam sweeping scanning algorithm

BIPHASE JAMMING Jamming of radars Generation of targets
 tracking targets by with false velocity
 velocity

DELTA JAMMING Monopulse radars Angle tracking

IMAGE JAMMING Radars using for Antenna pull-off
 tracking phase from target direction
 difference caused by
 target shift

ANGLE GATE ECM Jamming of radars for Angle error
 tracking by
 elevation, azimuth,
 and radars scanning
 in reception only

ANGLE GATE WALKOFF Jamming of radars Angle error
 gaining information
 on angle by
 continuous scanning
 of a sawtooth beam

BLANKIG MAIN LOBE Radars scanning Jamming through
 periodically side beams

AGC JAMMING Radars with conical Angle error
 scanning or certain
 monopulse radars
 using AGC

COVER PULSE JAMMING Radars with pulse Range gate pull-off
 compression

COVER PULSE FALSE Phase-coded pulse Suppression of
DOPPLER radars Doppler signal below
 detection threshold

CONICAL SCAN NOISE Radars scanning Error in angle
 conically at tracking
 reception

BARAGE NOISE A number of radar Masking of expected
 types radar reception
 signal