RC522 mini NFC, RFID (verified)

In my previous open-source RC522 design, I explained the RC522 circuit, component selection, and circuit verification. Therefore, I won't repeat the RC522 content here; those interested can check it out: https://oshwhub.com/oneline/rc522-ce-shi-ban-v4.
This iteration mainly addresses two issues:
1. A more streamlined circuit
; 2. A smaller PCB size. 
This time, I'll focus on how to design a smaller PCB. I even did four or five board builds for this. As always, I hope you avoid some pitfalls. I'll share the challenges I encountered here.
The main issue was layout.
Regarding high-frequency signals, we often talk about equal-length and equal-arithmetic-distance routing. For this module, the antenna section also follows this principle. The components starting from the surface-mount inductor must be symmetrically laid out! Symmetrically laid out! As for why, frankly, I can't really answer that. Perhaps it's because the board is smaller, and the circuits are too close together. TX is prone to electromagnetic interference, which disrupts the received data from RX, rendering the board unusable.
The reason I discovered this was because in my previous layouts, I only paid attention to the symmetry of the components after the inductor, but I still couldn't receive data. I redesigned a new board, and even though the wiring lengths between the inductor and the chip were asymmetrical, it didn't matter, and communication worked normally.
 
However, this alone isn't enough to draw a conclusion. The reason I knew it was interference was because I used an external coil. Once, during testing, I attached the antenna to the back of the board, and the test board couldn't detect any data! Therefore, future designers who want to integrate coils into the board should remember this: don't place them too close to the entire antenna circuit!