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Agilent E8257D 20GHz Signal generator ?, N9030A 50GHz spectrum analyzer , power sweep in 0.5Db steps from 0 to 30dBm CW

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尝辞迟丑补谤…

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What test gear did you use for the power sweep and what were the test points? I have a couple here I’d like to compare.

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Years ago I had this discussion with a PhD student ,? his argument was that the limiter doesn’t matter unless it is triggered so I set up a experiment doing a power sweep of the limiter and capturing the output spectrum for each point ,? he was quite surprised

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Lothar,

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Correct. The same thing happens with Zeners below 6.2V and TVS Diodes (way too much Capacitance for RF Applications).

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Look at the Breakover point of the RF Limiter (or TVS), it is a curve. Its Impedance changes below the breakover voltage as current flows through it and approaches the knee. If it is not specified, it can be obtained via a Curve Tracer or manually generated I-V Curves that you can produce with a simple Power Supply UUT and Resistance Standard or Resistance Decade.

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Many Signal Integrity issues develop when they are not used properly and the curve is well understood.

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Ross

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What many people seem to forget is the fact that the non linear behavior of a limiter kicks in way before the limiter is actually “triggered” ?although the distortions are not as bad

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Tom,

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That is also why MIL-STD-461 CE102 requires a 20dB Pad on the signal path from the LISN to the Receiver. They do not recommend a Limiter due to non-linearities that Lothar points out.

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Limiters can really hurt the Noise Figure of a receiver input at well.

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Ross

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Limiters are very commonly recommended for Conducted Immunity testing in EMC labs where the Spec An input comes from the Line Impedance Stabilization Network (LISN) because the turn on/off transients can be quite high. The levels expected to be measured typically should be much less than the distortion level of the limiter. The recommended limiter in this case actually has an intentional 10 dB insertion loss.

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A few words about limiters ,

Generally limiters are used in systems to protect receivers usually in RADAR or EW applications ,? in test systems the use of limiters s usually frowned upon ( with very few exceptions)? and for good reason !

First of there is a cost penalty that is not insignificant , the cost for a connectorized limiter usually starts at about $600 and can go up into the $2K range .

Limiters also degrade VSWR and add additional system loss .

But the by far biggest problem is that limiters are non linear devices and as such excellent harmonics generators , harmonics will start to occur before the limiter hits the hard threshold and worsens as the power increases so if you put one in front a spectrum analyzer you have to be cautious not to end up with tst results that are worse than they actually are

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