EW Fundamentals Flashcards
Define RADAR
RAdio Detection And Ranging
Target discriminators
Range
Velocity
Angle
Define Range discrimination
target range equals measured time, multiplied by the speed of light (“c”), divided by 2
Define velocity discrimination
Velocity discrimination is a specific capability of CW and pulse Doppler radar systems. The transmitters of CW radars send out continuous RF at a specific frequency (Figure 1-7). The reflected signal frequency is changed, or shifted, by a specific amount by a moving target. This frequency shift, called the Doppler effect, allows the measurement of the velocity of that target relative to the radar. The receiver measures this frequency difference which equates to a specific radial velocity. Pulse Doppler radars can measure the Doppler effect while still obtaining the range.
Define angle discrimination
The ability of a radar system to accurately determine angle is a function of the horizontal beamwidth of the antenna. If the radar sweep is referenced to true North, the angle of a radar return can be measured relative to true North
What are the three components of a pulsed radar system
pulse radar system consists of a transmitter, antenna, receiver, and a master timer
Define early warning radar
Radar systems specifically designed to provide attack warning are called early warning (EW) radars (Figure 1-9). These radars are characterized by high power output, large antennas, and low frequencies. These same characteristics limit the accuracy of the target parameters available from early warning radars. The long-range detection of aircraft and the earliest possible attack warning capabilities of early warning radars provide the first line of defense for the air defense system.
Define Ground Control Intercept Radar
GCI radars are designed to provide sufficiently accurate target aircraft range, azimuth, and altitude information to vector Al assets to intercept and destroy attacking aircraft
Define Acquisition radar
Acquisition radar systems generally have shorter range capability than early warning radars and operate at higher frequencies. These radar systems provide accurate target range and azimuth data to TTRs to facilitate target engagement.
Define Target Tracking Radar
provide continuous and accurate target parameters to a fire control computer. The fire control computer uses this data to guide missiles or aim antiaircraft artillery (AAA) to destroy attacking aircraft. TTRs employ various tracking techniques to continuously update target parameters. TTRs generally employ high frequencies, narrow beamwidths, and computer signal processing to enhance the accuracy of target parameters provided to the fire control computer
Define Airborne Intercept Radar
Al radar systems are TTRs employed by fighter aircraft to engage and destroy airborne targets. These radar systems are characterized by high frequency, sophisticated computer processing, and accurate target tracking capability. They are designed to allow the Al asset to employ air-to-air missiles and guns/cannons. TTRs and Al radars constitute the highest radar threat associated with an air defense system.
Define Frequency
The frequency of the transmitted signal is the number of times per second the RF energy completes one cycle.
What unit of measurement do you use with frequencies
The basic unit of measurement is the hertz (Hz). One hertz equals one cycle per second. Most radars have an RF in the millions of hertz, or megahertz (MHz).
Define wavelength
Wavelength is a measure of the physical distance between peaks of a sine wave propagated in space
What is the relationship between RF and wavelength?
The relationship between wavelength and frequency is inverse: the higher the frequency, the shorter the wavelength.
Define polarization
Polarization is determined by the radar antenna and refers to the orientation of the RF wave as it travels through space.
What determines polarization
The polarization of the wave is defined in terms of the orientation to the electrostatic field.
Define circular polarization
circular polarization, the direction of the electrostatic field varies with time and traces a circular locus about a fixed plane perpendicular to the direction of propagation.
Define cross polarization
If an antenna is designed to receive a particular polarization, it will have difficulty receiving a signal with an opposite polarization
Define the Doppler Effect
The “Doppler effect” takes advantage of the fact that the frequency of RF waves will be changed or shifted when reflected from a target moving relative to the radar. The shifted frequency of the returning RF wave depends on the movement of the aircraft in relation to the radar.
Frequency range of HF/VHF
0-.250 Ghz
