Need to determine/analyse link performance (e.g Bit Error Rate (BER)
or Packet Loss Rate) in terms of:
Antenna parameters (e.g. gain)
Received system noise levels (usually specified as noise temperature)
Other factors (e.g. propagation losses, interference, intermodulation)
Consider an isotropic antenna - radiates in all directions. Imagine antenna at
centre of hollow sphere.
Power flux density at radius d is:
PFD = PT / (4πd2) W/m2
'Inverse Square Law'
Antennas have gain to concentrate power in a wanted direction.
Gain is relative to Isotropic with units of dBi
Transmitter and receiver spaced distance d.
PFD in wanted direction is increased by a factor of GT
Then at receiver it looks as though there is an isotropic transmitter with
PTGT = Effective Isotropic Radiated Power (EIRP).
In dB: PT + GT = EIRP (dBW)
A transmit antenna has a gain of 50 dB and is fed with a power of 20
watts. What is its EIRP?
PT = 13 dBW, GT = 50 dB, so EIRP = 13 + 50 = 63 dBW
A transmit antenna has a gain of 27 dB and is fed with a power of
2 mW. What is its EIRP?
PT = -27 dBW, GT = 27 dB, so EIRP = 0 dBW.