- Effective Radiated Power - ERP
One important use for decibels is computing the effective radiated power (ERP) of
a radar. ERP is of primary interest for communications, passive electronic surveillance (ESM) and
electronic countermeasures (ECM). To determine how far away a signal can be observed,
or to determine how much power is required for a countermeasure, the first step is
to assess radar transmitter power. The power level that a radar detector sees is
then dependent on the gain of the radar antenna in the direction of the detector.
The ERP is simply the transmitter power times the antenna gain, and this can
be done in units of Watts, milliwatts, or dBW or dBm.
| ERP = PT·GT |
| ERP (dBW) = PT (dBW) + GT (dBi) |
- A radar has a peak transmitter power of 15000 Watts, a transmit loss
(from transmitter output to antenna input) of 1.5 dB, and a mainlobe antenna gain of
31 dBi. What is the mainlobe ERP of this radar in Watts, milliwatts, dBW, and dBm?
- The average sidelobes of this antenna are -30 dB. What is the power out
the sidelobes of the antenna?
- A radar has an ERP of 93 dBW. If the antenna has a gain of 40 dBi, what is the
peak transmit power? Ignore losses between the transmitter and the antenna.
- Another radar has an ERP of 95 dBm. The transmitter power is 1,400 W, and the
transmitter losses are 2 dB. What is the antenna gain required?