I was reading the datasheet of an antenna and I came across the parameter "Max. Power (total)", measured in Watts. What does this stand for? Can it be measured to check that the datasheet is right?
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1\$\begingroup\$ RF current flows through an antenna. The antenna has a resistance and therefore \$\small I^2R\$ will generate heat. \$\endgroup\$– ChuDec 8, 2018 at 1:19
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3 Answers
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When connected to a transmitter, this (or any) antenna is designed to handle transmitter power levels up to this specified limit without degrading performance or posing a safety hazard. There is no easy way for you to test this manufacturer's rating without destroying the antenna or risking harm.
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2\$\begingroup\$ Thanks for your answer. So, there is "no easy way"... but is there a "difficult one"? \$\endgroup\$– TenderoDec 7, 2018 at 13:36
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8\$\begingroup\$ The "difficult" one might be the destructive (or near-destructive) test that's already been suggested. Put some power in, increase it while measuring the VSWR (or return loss) and look for VSWR changes, melting, smoke or worse. ;-) \$\endgroup\$ Dec 7, 2018 at 13:54
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It actually stands for the maximum power that you can push through this antenna.
This typically has three reasons:
- When designing the antenna, there's some point at which the electrical field is maximal. You have to be sure that the electrical field still doesn't lead to dielectric breakdown (or excessive nonlinearities)
- Safety: Power -> voltage -> safe to operate in the specified environment (electrocution risk); also: power -> power density -> safe to operate (hurting people in the main beam); this is usually more of a system than an antenna aspect.
- Heat: No real-world antenna is 100% efficient. The remainder of energy is converted to heat, which increases antenna temperature, which might change or damage the antenna.
So, to evaluate these, you'd need to have a pretty detailed simulation of the antenna; typically, you'd want to actually test maximum power, not only simulate it, which will inevitably risk damaging the antenna you have.
answered Dec 7, 2018 at 13:52
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It's just the maximum transmit power the antenna is designed to handle. If the transmitter ends up pumping more power than the stated maximum into the antenna, the losses in the antenna will overcome its heat dissipation capability and things will start to overheat/melt.
Note that it's specified at a particular ambient temperature, because running the antenna in a hotter environment will compromise its cooling, so it won't be able to take as much power.
Why do you suspect the datasheet is not right? Do you think it's underestimating the capabilities of the antenna? Or that it's overestimating it and the antenna will melt way sooner than at the rated power? Either way, the only way to check experimentally is to take a transmitter, make it feed the rated power into the antenna, and see whether things melt. Note that you will probably destroy an (expensive!) transmitter this way if the antenna fails.
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1\$\begingroup\$ Well, actually, it's a safe bet that the data sheet does underestimate the capabilities of the antenna. After all, the manufacturer is essentially guaranteeing the performance below the limit. Exactly how much margin the manufacturer is allowing is a very different question. \$\endgroup\$ Dec 7, 2018 at 17:15
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1\$\begingroup\$ @WhatRoughBeast Of course there'll always be some safety factor in it. But from a user perspective, it's rarely wise to exceed the specs and rely on these margins all the time. Manufacturers are not very likely to be overly generous with safety factors, as that costs money. \$\endgroup\$– TooTeaDec 7, 2018 at 20:02