1. **Problem Statement:** We need to find the length $L_f$ of the feed line in the patch antenna design. 2. **Given Data:** From the table, we have dimensions including $W_f = 1$ mm (width of feed line), but $L_f$ (length of feed line) is not directly given. 3. **Understanding the Design:** The feed line is a small vertical rectangle at the bottom middle of the patch. Typically, the feed line length $L_f$ is related to the patch dimensions and the slot/gap dimensions near it. 4. **Using the given parameters:** We have $L_C = 0.8$ mm (length near the gap), and the patch length $L_P = 4.9$ mm. 5. **Assumption:** Usually, the feed line length $L_f$ is equal to or slightly less than $L_C$ to ensure proper feeding. 6. **Conclusion:** Since $L_f$ is not explicitly given, and $L_C$ is the closest related length near the feed line, we take $L_f = L_C = 0.8$ mm. **Final answer:** $$L_f = 0.8\ \text{mm}$$