Power Density Flashcards

(21 cards)

1
Q

What is defined as the travel of electromagnetic waves through or along a medium?

A

Radio Frequency (RF) propagation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the dielectric constant of space?

A

1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

A theoretical, lossless, omnidirectional antenna that radiates uniformly in all directions.

A

Antennas as an isotropic radiator

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How is power density defined at any distance from an isotropic antenna?

A

Transmitter power (Pt) divided by the surface area of a sphere (4πR²) at that distance.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How does the surface area of a sphere change with the radius?

A

It increases by the square of the radius.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the relationship between power density and distance from an isotropic antenna?

A

Power density decreases by the square of the radius.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

The ratio of power radiated in the desired direction compared to the power radiated from an isotropic antenna.

A

Gain (G) of an antenna

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How is effective isotropic radiated power (EIRP) calculated?

A

EIRP = Pt Gt, where Pt is the transmitter power and Gt is the antenna gain.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

A receiving antenna captures a portion of the EIRP determined by its ______

A

Effective capture area (Ae)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What happens to the received signal power as the distance doubles?

A

It decreases by 1/4 (6 dB) due to the R2 term in the denominator of equation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What must be done when antenna gain and power (or EIRP) are given in dB and dBm for calculations?

A

Convert back to ratios.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the formula to convert gain in dB to numeric gain?

A

Gt (dB) = 10^( Gt(in dB) / (10) )

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the assumed aperture efficiency for the missile antenna in the absence of known gain?

A

0.7 (typical).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

If the missile antenna gain is known to be 25 dB, what is the numeric gain?

A

316.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

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 _______.

A

radar antenna gain.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

True or False: The power density at a distance from an isotropic antenna increases with the square of the radius.

17
Q

RF propagation occurs between approximately _________.

A

100 MHz and 10 GHz

18
Q

The power of a transmitter that is radiated from an isotropic antenna will have a ____________ in all directions

A

Uniform power density (power per unit area)

19
Q

Radars use __________ to channel most of the radiated power in a particular direcion

A

Directional antennas

20
Q

The received power available at the antenna terminals is the ______

A

Power density times the effective capture area (Ae) of the receiving antenna

21
Q

The maximum input power actually received by the missile is either:

A

If effective antenna area is known
Pr = Pd*Ae

If missile antenna gain is known
Pr = PdGm(λ)^2 / 4*pi