Power Density Flashcards
(21 cards)
What is defined as the travel of electromagnetic waves through or along a medium?
Radio Frequency (RF) propagation
What is the dielectric constant of space?
1
A theoretical, lossless, omnidirectional antenna that radiates uniformly in all directions.
Antennas as an isotropic radiator
How is power density defined at any distance from an isotropic antenna?
Transmitter power (Pt) divided by the surface area of a sphere (4πR²) at that distance.
How does the surface area of a sphere change with the radius?
It increases by the square of the radius.
What is the relationship between power density and distance from an isotropic antenna?
Power density decreases by the square of the radius.
The ratio of power radiated in the desired direction compared to the power radiated from an isotropic antenna.
Gain (G) of an antenna
How is effective isotropic radiated power (EIRP) calculated?
EIRP = Pt Gt, where Pt is the transmitter power and Gt is the antenna gain.
A receiving antenna captures a portion of the EIRP determined by its ______
Effective capture area (Ae)
What happens to the received signal power as the distance doubles?
It decreases by 1/4 (6 dB) due to the R2 term in the denominator of equation
What must be done when antenna gain and power (or EIRP) are given in dB and dBm for calculations?
Convert back to ratios.
What is the formula to convert gain in dB to numeric gain?
Gt (dB) = 10^( Gt(in dB) / (10) )
What is the assumed aperture efficiency for the missile antenna in the absence of known gain?
0.7 (typical).
If the missile antenna gain is known to be 25 dB, what is the numeric gain?
316.
Fill in the blank: The power density at a distant point from a radar with an antenna gain of Gt is the power density from an isotropic antenna multiplied by the _______.
radar antenna gain.
True or False: The power density at a distance from an isotropic antenna increases with the square of the radius.
False.
RF propagation occurs between approximately _________.
100 MHz and 10 GHz
The power of a transmitter that is radiated from an isotropic antenna will have a ____________ in all directions
Uniform power density (power per unit area)
Radars use __________ to channel most of the radiated power in a particular direcion
Directional antennas
The received power available at the antenna terminals is the ______
Power density times the effective capture area (Ae) of the receiving antenna
The maximum input power actually received by the missile is either:
If effective antenna area is known
Pr = Pd*Ae
If missile antenna gain is known
Pr = PdGm(λ)^2 / 4*pi