Topic: Antennas and Wave Propagation
A gain-standard horn is known to have a gain G = 10. It is being used to measure the gain of a large directional antenna by the comparison method. When the antenna being measured is connected to the receiver it is found to be necessary to insert an attenuator adjust to attenuate by 23 dB in order to have the same receiver output that was observed with the horn connected. What is the gain of the large antenna?
- A. 13 db
- B. 23 db
- C. 33 dB
- D. 230 dB
Answer: C. 33 dB
Explanation: Let the gain of the unknown antenna be $G_1$ (in dB) and receiver loss be $L$. The gain of the horn antenna is $G = 10$ dB. The output of the receiver when the horn is used equals the output when the unknown gain antenna is used plus the loss of the attenuator. Therefore, $L + G = L + G_1 - 23$. Substituting $G = 10$, we get $10 = G_1 - 23$, which yields $G_1 = 33$ dB.