electrics Flashcards
Types of wire antennas
Dipoles, loops and monopoles
Types of aperture antennas
parabolic dish
Types of array antennas
two or more antennas operating together
wire antenna features
lower frequencies (<1Ghz), easy to build, low gain
aperture antenna features
higher frequencies, high performance, high gain, point to point communication
array antenna features
better performance and flexibility than single antennas
isotropic radiation pattern
radiates equally in all directions (only theoretically possible)
directional radiation pattern
radiates/receives more power in some directions
omnidirectional radiation pattern
non-directional pattern in one plan and directional pattern at 90 degrees
radiation density equation
Si = P / 4pi*r^2
radiation intensity equation
U = P / 4pi
directivity equation
D = 4pi*U / P
gain equation
G = S4pir^2 / P(in) = DP(rad) / P(in) = 4pi / (delta)theta(delta)omega = 4pi*A / lambda^2
effective isotropic radiated power equation
P(iso) = P(in)*G
radiated power radius equation
R = 2D^2 / lambda
gain to dBi equation
dBi = 10log10(D(max))
maximum radiation density equation
Si(max) = PG(max) / 4pir^2
antenna effective area equation
Ae = P / Si = G*lambda^2 / 4pi
aperture efficiency equation
E(ap) = Ae / A
radar power density equation
P(D) = P(t) / 4pi*r^2
radar power rereadiated equation
P(D)sigma = P(t)G(t)sigma / 4pi*r^2
radar power density back at radar equation
P(RD) = P(t)G(t)sigma / (4pir^2)^2
radar received power equation
P(R) = P(t)G(t)G(r)*lambda^2 *sigma / (4pi)^3 * r^4
radar signal-noise ratio equation
P(R) / N = P(t)G(t)G(r)sigmalambda^2*Ls / (4pi)^3 *r^4 * N
pulsed radar features
transmits in pulsed radio frequency signals and receiver times how long it takes for the pulse to hit the target and return
pulsed radar range equation
R = c*tau(D) / 2 (tau = 2RC)
pulsed radar pulse width equation
tau <= 2*(delta)R / c
pulsed radar range resolution equation
(delta)R = c*tau / 2 = c / 2B (B = bandwidth)
pulse repetition frequency use
used when returning echo pulse time is greater than transmit pulse time to return from echo so ambiguity as to which is which (when t=2R / c > t = 1 / PRF)
doppler frequency equation
f(D) = 2Vcos(theta) / lambda
doppler rader Tx and Rx equation
Tx = cos(wot), Rx = Bcos(wdt)
doppler resolution equation
1 / integration time
surface clutter equation
sigma(0) = sigma(c) / A(c)
doppler ground area equation
A(G) = R(delta)phi(delta)R
wire antenna wavelength from length equation
L = wavelength / 2
wire antenna current equation
I = Vs / Zg+Za
radiation efficiency of antenna equation
eff = R(r) / R(r) + R(l)
radiated power from normalised intensities
P(rad) = integral(2pi->0) integral(pi->0) of s(0) * sin^2(theta) * R^2 d(theta).d(omega)
a larger beamwidth will
give faster scan coverage, fewer beam positions, poor angular resolution
number of beam positions equation
N(B) = 2pi / (delta)ohms = 2pi / (delta)theta*(delta)omega
dwell time equation
t / N(B)
effective area of antenna equation
A = (D/2)^2 * pi*efficiency
radar equation
R(max) = ( ( P(t)G^2 lambda^2 sigma) / ( (4pi)^3 P(min) ) )^1/4
radar power density incident on target, radar power density collected by target
P(inc) = P(t)G(t) / 4piR^2, P(col) = P(t)G(t)sigma / 4pi*r^2
signal to jam ratio, when does burn through occur?
SJR = P(r) / P(r jam), burn through when SJR=1
pulse repetition time equation
PRT = pulse-width / duty cycle
pulse repetition frequency equation
PRF = 1 / PRT = c / 2R(max)
average power equation
peak power * duty cycle
number of hits equation
n = (delta)thetaPRF / 6RPM
max range equation
c / 2*PRF
range resolution equation
c*tau / 2 (tau = pulse width/s)
duty cycle equation
pulse duration / pulse repetition interval
mean power
peak power * duty cycle
(delta)theta
lambda / width*efficiency
(delta)omega
lambda / height*efficiency
axial ratio equation
AR = a / b
doppler shift frequency equation
f(d) = 2Vcos(theta) / lambda
