Topic: Antennas and Wave Propagation
In a telecommunication trans-receive system, the transmitting antenna with antenna aperture of 1m is fed with 1W of power at 10 GHz. The receive antenna with antenna aperture of 0.5m located at 1km away receives x mW of power. If the transmitting frequency changes to 20 GHz, what will happen to receive power?
- A. Increase by 3 dB
- B. Increase by 6 dB
- C. Decrease by 3 dB
- D. Decrease by 6 dB
Answer: B. Increase by 6 dB
Explanation: The received power $P_r$ is proportional to the transmitting antenna gain $G_t$. For a parabolic dish, $G_t$ is proportional to the square of the frequency ($f²$). Thus, $P_r \propto f²$. When the frequency doubles from 10 GHz to 20 GHz, the received power increases by a factor of 4. In decibels, this is an increase of $10 \log_{10}(4) = 6\text{ dB}$.