energy & radar elements

Question 1

electromagnetic wave applications

Answer 1

communications, radar, missile guidance, GPS

Question 2

WAVE

Answer 2

a disturbance which travels thru a medium, transverse (EM energy, water) and longitudinal (sound, spring compressions)

Question 3

amplitude

Answer 3

max displacement of any point on the wave from the wave’s axis

Question 4

wavelength

Answer 4

distance covered by a wave during one complete cycle (meters)

Question 5

period

Answer 5

time for one complete cycle of a wave (seconds)

Question 6

frequency

Answer 6

the number of cycles per second (hertz)

Question 7

Velocity

Answer 7

EM waves travel at the speed of light in a perfect vacuum

Question 8

constructive interference

Answer 8

wave strength increases

Question 9

destructive interference

Answer 9

wave strength decreases

Question 10

radar beam forming

Answer 10

illuminates a specific location with a more intense radar beam

Question 11

phased arrays

Answer 11

create and move radar beams by adjusting transmitter phases. NOT physical antenna rotation

Question 12

relection

Answer 12

incident and ___ waves travel in directions that make equal angle perpendicular to the _____ surface

Question 13

refraction

Answer 13

waves are bent while passing thru different mediums. due to change in wave speed

Question 14

diffraction

Answer 14

waves traveling in a straight path bend around a boundary or obstruction

Question 15

pulse transmission

Answer 15

RADAR transmits a series of pulses separated by non-transmission intervals during which the radar “listens” for a return

Question 16

continuous wave

Answer 16

constantly emitting radar, relative motion of either the radar or the target is required to indicate target position, frequency shift

Question 17

range determination

Answer 17

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

Question 18

pulse width (PW)

Answer 18

length of duration of a given pulse

Question 19

pulse repetition time (PRT)

Answer 19

time from beginning of one pule to beginning of next

Question 20

pulse repetition frequency (PRF)

Answer 20

frequency at which consecutive pulses are transmitted PRT = 1/PRF

Question 21

LONGER PULSE

Answer 21

longer detection ranges

Question 22

shorter pulse

Answer 22

better range resolution & short range detection

Question 23

long pulse adv vs disadv

Answer 23

Advantage: transmits farther, can detect further contacts. Disadvantage: overlooks close contacts, pulse returns while transmitting, receiver cannot process return

Question 24

long pulse close contact

Answer 24

echo is received during transmit time, NOT detected

Question 25

short pulse adv vs disadv

Answer 25

ADV: clearer return, processes return quicker, detect close contact. DISADV: doesn't transmit as far

Question 26

range resolution

Answer 26

ability to differentiate between two closely spaced contacts

Question 27

radar cross section

Answer 27

measures the reflective properties of a contact, function of size, shape, material and angle

Question 28

doppler shift

Answer 28

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

Question 29

transmitter antenna

Answer 29

sends out continuous EM wave, provides reference signal to receiving antenna

Question 30

receiver antenna

Answer 30

picks up returned signals, compares it to the reference signal

Question 31

phased array/ SPY-1D

Answer 31

search, track, beam steering, weapon guidance

Question 32

phased array operation

Answer 32

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

Question 33

beam steering

Answer 33

radiate the antenna elements out of phase with one another

Question 34

mechanical scanning

Answer 34

requires large amounts of power, processing multiple high-speed targets. antenna inertia, slower reaction times due to stable beam positioning

Question 35

electronic scanning

Answer 35

increased data rates, faster reaction time, less mechanical failures, multi-mode operation, automatic multi-target tracking, missile guidance

Question 36

electronic scanning USAGE

Answer 36

TICONDEROGA's CG's, ARLEIGH BURKE DDG's, AN/SPS -48 Air search, FORD CVN's