Hardware tells you why the shielding cover affects harmonics

A friend asked, how to solve the problem of the shielding cover affecting harmonics? The following Xiaoshuo analyzes the reasons based on experience: There are three possible reasons: 1. The impedance of the matching component is affected by the shielding cover. If the shielding cover is too close to the matching component, the parasitic effect changes its inductance or capacitance and the impedance changes. Of course, the conducted harmonics become larger, especially the early 0402 components. But now 0201 components rarely do this. 2. The RF signal leaks to the Vcc of the PA. When you cover the shield, the PA will radiate or couple the RF signal to the shield. The upper part means that there will be residual TX signals above the shielding case. If the shielding case is well grounded, these residual TX signals will flow through to GND. If the shielding case is well grounded, some of these residual TX signals will flow to GND and some will be reflected again. If the TX signal hits the Vcc of the PA, of course the TX performance will be degraded. 3. The parasitic effect between the shield and the PA too close changes the PA characteristic verification method: The first one is rare now, so the second one is not mentioned. If you use this method, you can verify the following figure: Because you said that the conduction spurs will be better when the shield is not added, so if you use this method without the shield, the conduction stray becomes the same as when the shield is added. The murderer may be due to this reason. It is worth noting that the DC Block should add DC power to prevent Vcc from being recharged to the PA or CMW500. The third method is to put a tape on the top of the PA without the shielding cover, and then put a piece of metal. You said that the conduction spurs would be better without a shielding cover. Therefore, if you use this method without a shielding cover, if the conduction spurs become as bad as when the shielding cover is added, the killer may be from This reason Solution: The first kind is rare now, so I won’t mention the second kind because the killer comes from the RF signal injected into Vcc, so you put a floor capacitor on the Vcc side to let the RF signal injected into Vcc flow to GND. Your main frequency is DCS. In terms of 0201 capacitor, you just put 18 pF. The third type can only change the structure. Do you want to increase the distance between the shielding cover and the PA, otherwise it is directly open the skylight above the PA. The above is Xiaoshuo’s 15 years of experience analysis I hope it will be helpful to you if the shielding cover has some influence on harmonics.