Topic: Microwave Engineering
A four port directional coupler has 4:1 power splitting ratio and has dissipation loss of 3dB. The coupler directivity is 40dB. What fraction of input power P1 will go to ports P2 and P3?
- A. $P2=0.4\times P1$, $P3=0.1\times P1$
- B. $P2=0.8\times P1$, $P3=0.2\times P1$
- C. $P2=0.6\times P1$, $P3=0.15\times P1$
- D. $P2=0.1\times P1$, $P3=0.4\times P1$
Answer: A. $P2=0.4\times P1$, $P3=0.1\times P1$
Explanation: A dissipation loss of 3 dB implies that half of the input power is dissipated as heat, leaving $0.5 P_1$ to be distributed between the output ports P2 and P3. With a 4:1 power splitting ratio (typically passing higher power to the through port P2), we have $P_2 = 4 P_3$. Thus, $P_2 + P_3 = 5 P_3 = 0.5 P_1 \implies P_3 = 0.1 P_1$ and $P_2 = 0.4 P_1$.