The conducted stray of cell phone jammer amplifier with shield is 5-6dB worse than that without shield
There are three possible reasons:
1. The matching components are affected by the Shielding Cover so that the impedance is biased.
If the Shielding Cover is too close to the matching component, its parasitic effect will change its inductance or capacitance value.
So that the impedance changes, of course the conduction harmonics become larger.
Especially early 0402 components were more likely to do this, but now 0201 components rarely do this.
2. The RF signal leaks to the Vcc of the PA.
The PA will radiate or couple the RF signal above the shield when you put the shield on.
That is to say, there will be residual TX signal above the shield.
If the shield is well grounded then these residual TX signals will flow through to GND.
If the shield is well grounded then these residual TX signals.
Part of it flows to GND and part of it will be reflected again.
If the reflected signal hits the Vcc of the PA, then of course the TX performance will be degraded.
3. The parasitic effect between the shield and the PA too close changes the PA characteristics.