Many tones into an LNA?

[rfengg]

Could anyone advice if driving a wideband LNA with 2 tones of equal amplitude of -10dBm from a RF mixer , say at 10Ghz and 15Ghz,  will reduce the output of the LNA compared to  driving the LNA with a single tone say 10Ghz at -10dBm?
I am facing this issue that when I drive a LNA with one tone @ 10Ghz and  -10dBm,  I get the expected output, but when 2 tones 10Ghz and 15Ghz are present at the LNA input  , the output of the LNA is reduced at both tones.

[mawyatt]

Likely LNA saturation, -10dBm is a large input level for an LNA.

Best,

[TimFox]

Note that on a power basis, two tones at -10 dBm each add up to a total power of -7 dBm, but the peak envelope power of each tone singly is -7 dBm and the peak envelope power of both together is -1 dBm.
For independent waveforms, the (mean) powers add directly, but the peak amplitudes (voltage) add directly to give the peak power.
The peak power (voltage) is what saturates the amplifier.

[ejeffrey]

Your amplifier should have it's 1 dB compression point in its data sheet, which up to the beating concern raised by TimFox should basically tell you what you need to know.

[Chat GPT]

The presence of two tones at different frequencies can result in intermodulation distortion (IMD) products, which can fall within the frequency range of interest and interfere with the LNA's operation. This effect is more pronounced in wideband LNAs, which are designed to amplify a wide range of frequencies.

When two tones of equal amplitude are present at the LNA input, they can mix in the LNA itself or in any other non-linear component in the signal chain, creating IMD products at frequencies that are the sum or difference of the original frequencies. In your case, the difference frequency would fall within the frequency range of the LNA, causing interference.

To mitigate this effect, you can use a bandpass filter at the input of the LNA to remove any unwanted signals outside the frequency range of interest. You can also adjust the amplitude and frequency of the tones to avoid creating IMD products within the frequency range of the LNA.

Another solution would be to use a mixer or frequency converter to downconvert the signals to a lower frequency before amplification, which would reduce the impact of IMD products.

In terms of testing, it is important to ensure that the measurement setup is properly calibrated and that any unwanted signals or noise sources are properly controlled or shielded