In a transmitter chain with a power amplifier feeding an antenna, a commercial isolator is providing 18 dB isolation, will that much isolation will be enough for a 15 W power amplifier, so that it may not get damaged by any reflection due to mismatch?
The isolator is reducing the reflected power by 18 dB so for the worst case of an open circuit (no antenna), the reflected power is 18 dB less than ~42 dBm (15W) in absolute terms. This is a VSWR of ~1.3 as worst case that should be within the mismatch range of the PA. The PA specs may be checked though. And the Isolator must have capacity to absorb the heat loss, if this scenario is to be handled.
As Shiv Prasad Tripathy says, you should check the specification for the amplifier. It almost certainly gives a vswr or return loss that should not be exceeded. 18 dB is probably enough.
Not all isolators or loads will cope with dissipating 15 W.
for 15 watt amplifier with 18 dB isolator open circuit reflected power will be around less than 300mW. isolator should be able to dissipate this power . Transmitter will not get damaged by this much power at maximum mismatch. isolator will dissipate 14.7 forward and pA will have 300mw reflected power.
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