Regarding the doubts in the debugging of cross-coupled passive cavity filter, thank you for your guidance and high score.

When adjusting the screws, first understand the sensitivity and function of each screw, such as moving the passband and smoothing the waveform. The correlation between return loss and passband stopband can be detected slowly. Adjust the center frequency first, then smooth the waveform, and finally fine-tune the insertion loss. Note the correlation between S2 1 and S 1 1.

It takes a lot of time to get familiar with it at the beginning of debugging, and it will become faster gradually. The larger the cavity, the higher the Q value (less insertion loss). The problem I often encounter now is that the insertion loss can't reach the index (generally less than 1dB), so I need high-precision processing technology and good materials from big factories, silver-plated cavities and screws.