Practice Problems

Problem 1

You and your wingman are flying over hostile territory in your advanced F-169 Next Generation Stealth Fighters. An SA-20 SAM site knows you are in the area and is actively searching the skies. The SAM site’s fire control RADAR has the following characteristics: \(80\ \text{kW}\) transmit power, operating frequency of \(5\ \text{GHz}\), and a transmit/receive antenna gain of \(5000\). The RADAR has a PRF of \(10\ \text{kHz}\) and a pulse width of \(75\ \text{ns}\). The RADAR receiver requires a minimum received power of \(1\ \text{pW}\) to detect and process the signal. The F-169s have an RCS of \(0.5\ \text{m}^2\) and are equipped with a RADAR jamming system. This system has an antenna gain of \(7\) but requires \(10\ \mu\text{W}\) of received power to accurately identify the emitter location. The fighters are \(48\ \text{km}\) from the SAM site and flying at a speed of \(223.85\ \text{m/s}\). The F-169s are \(10\ \text{m}\) apart.

a. Can the RADAR detect the F-169s? (assume no LOS issues)

b. At what range (in km) can the fighter’s RADAR jamming system detect the RADAR? (assume no LOS issues)

c. Will the RADAR be able to distinguish both F-169s?

d. What is the maximum distance that the RADAR can determine the F-169s range with certainty?

Problem 2

A convoy in Iraq employs a jammer system to prevent the remote detonation of improvised explosive devices (IEDs). As the convoy approaches an IED, according to the Friis equation, is the jammer becoming more or less effective?

Problem 3

In order for an attack to be successful, the planners determine a SAM site must be destroyed. What kind of electronic warfare is this?

(a) SEAD

(b) DEAD

(c) Jamming

(d) Chaff

Problem 4

Both RADAR jamming and communications jamming become more effective as the jamming platform moves toward the site being jammed.

(a) True

(b) False

Problem 5

Which of these techniques is not used to counter jamming?

(a) Chirp signals

(b) Chaff and flares

(c) Direct-sequence spread spectrum

(d) Frequency hopping

Problem 6

Chaff creates a false RADAR target that is brighter than the actual target.

(a) True

(b) False

Problem 7

A UAS under your control is jamming communications for a command and control site. The communications signal is transmitted from a distance of \(50\ \text{km}\) at a frequency of \(1.8\ \text{GHz}\) with a transmit power of \(1.4\ \text{kW}\). The transmit and receive antennas both have a gain of \(3.0\). The jammer on your UAS has an antenna gain of \(20\) with a transmit power of \(2.4\ \text{kW}\). Your UAS is \(35\ \text{km}\) from the command and control site. If the communications system requires a signal-to-noise ratio of \(0.1\) to process and receive communications, is your jamming effective?

Problem 8

A targeting RADAR has a pulse width of \(50\ \text{ns}\). If you wish to mask the number of aircraft in your formation, how close must your aircraft fly?

Problem 9

A search RADAR transmits at \(800\ \text{MHz}\). What length of chaff do you need to be effective against this RADAR?

Problem 10

If attacked by a fighter with Doppler RADAR, why might you want to turn to put the fighter on your \(3\) or \(9\) o’clock position?

Problem 11

Given the following information about an enemy SAM site and the capabilities of your jammer, at what distance does your jamming pod become ineffective?

Enemy RADAR	Your jamming equipment
\(P_T = 1\ \text{kW}\)	\(P_{jam} = 20\ \text{W}\)
\(G_T = 3000\)	\(G_{jam} = 3.5\)
\(f = 7\ \text{GHz}\)	\(f = 7\ \text{GHz}\)
\(SNR_{\min} = 0.02\)	\(\sigma = 25\ \text{m}^2\)