Step 1: Convert height into km.
Height of antenna:
\[
h = 70\,m = 0.07\,km
\]
Step 2: Use line-of-sight distance formula.
For small height compared to Earth radius:
\[
d = \sqrt{2Rh}
\]
where \(R = 6400\,km\).
Step 3: Substitute values.
\[
d = \sqrt{2 \times 6400 \times 0.07}
\]
Step 4: Simplify inside root.
\[
d = \sqrt{896}
\approx 29.93\,km
\]
Step 5: Calculate covered area.
Coverage area is circular:
\[
A = \pi d^2 = \pi \times 896
\]
Step 6: Final simplification.
\[
A = 896\pi \approx 2816\,km^2
\]
Final Answer:
\[
\boxed{2816\,km^2}
\]