You cannot do that directly but it's possible to realize indirectly.
First, you should measure the signal strength. It's not easy at RF frequencies but it's pretty easy to implement at IF stages if there is.
"Squelch" circuits are widely used in decades to suppress the noise during non communication time slot and it turns off the audio stage to prevent the operator from noisy sound. But this is done at IF stages then audio.
You can implement a similar system for your target. You measure the signal strength by RSSI signal ( some IF circuits have it ) then you limit/turn off the Gain of the LNA below of a certain limit. Some IF circuits are equipped with RSSI feature.
For instance this one works up to 500MHz
Order today, ships today. AD8307ARZ – Logarithmic Amplifier IC Receiver Signal Strength Indication (RSSI) 8-SOIC from Analog Devices Inc.. Pricing and Availability on millions of electronic components from Digi-Key Electronics.
There are possibly some cheaper ones. It's just an example.