energy & radar elements Flashcards
electromagnetic wave applications
communications, radar, missile guidance, GPS
WAVE
a disturbance which travels thru a medium, transverse (EM energy, water) and longitudinal (sound, spring compressions)
amplitude
max displacement of any point on the wave from the wave’s axis
wavelength
distance covered by a wave during one complete cycle (meters)
period
time for one complete cycle of a wave (seconds)
frequency
the number of cycles per second (hertz)
Velocity
EM waves travel at the speed of light in a perfect vacuum
constructive interference
wave strength increases
destructive interference
wave strength decreases
radar beam forming
illuminates a specific location with a more intense radar beam
phased arrays
create and move radar beams by adjusting transmitter phases. NOT physical antenna rotation
relection
incident and ___ waves travel in directions that make equal angle perpendicular to the _____ surface
refraction
waves are bent while passing thru different mediums. due to change in wave speed
diffraction
waves traveling in a straight path bend around a boundary or obstruction
pulse transmission
RADAR transmits a series of pulses separated by non-transmission intervals during which the radar “listens” for a return
continuous wave
constantly emitting radar, relative motion of either the radar or the target is required to indicate target position, frequency shift
range determination
pulse transmission measures distance with time. EM waves travel at a constant velocity of about 3x10^8 m/s. Range determined by the 2 way energy transmission. Radar measures total time for reflected pulse to return from target and calculates distance. Direction determined from bearing of radar return
pulse width (PW)
length of duration of a given pulse
pulse repetition time (PRT)
time from beginning of one pule to beginning of next
pulse repetition frequency (PRF)
frequency at which consecutive pulses are transmitted PRT = 1/PRF
LONGER PULSE
longer detection ranges
shorter pulse
better range resolution & short range detection
long pulse adv vs disadv
Advantage: transmits farther, can detect further contacts. Disadvantage: overlooks close contacts, pulse returns while transmitting, receiver cannot process return
long pulse close contact
echo is received during transmit time, NOT detected
short pulse adv vs disadv
ADV: clearer return, processes return quicker, detect close contact. DISADV: doesn’t transmit as far
range resolution
ability to differentiate between two closely spaced contacts
radar cross section
measures the reflective properties of a contact, function of size, shape, material and angle
doppler shift
Difference between reference signal and received signal due to target’s motion. A target moving away will reflect a lower frequency return. A target closing in will reflect a higher frequency return
transmitter antenna
sends out continuous EM wave, provides reference signal to receiving antenna
receiver antenna
picks up returned signals, compares it to the reference signal
phased array/ SPY-1D
search, track, beam steering, weapon guidance
phased array operation
EM energy received from two or more closely spaced radiating elements is maximized when energy from each radiating element arrives at the point in phase. employs constructive and destructive interference. Path lengths from the elements from point P equalize as P approaches infinity
beam steering
radiate the antenna elements out of phase with one another
mechanical scanning
requires large amounts of power, processing multiple high-speed targets. antenna inertia, slower reaction times due to stable beam positioning
electronic scanning
increased data rates, faster reaction time, less mechanical failures, multi-mode operation, automatic multi-target tracking, missile guidance
electronic scanning USAGE
TICONDEROGA’s CG’s, ARLEIGH BURKE DDG’s, AN/SPS -48 Air search, FORD CVN’s
