This set of Microwave Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Generator And Load Mismatches”.

1. When a load is matched to a transmission line, the condition that is satisfied when matched is:
a) ZL=Z0
b) ZL=2Z00
c) ZL=Zin
d) ZL=2Zin

Explanation: In order to deliver the maximum power from source to load, the transmission line has to be matched to the load. Hence for the transmission line to be matched to the load, the condition to be satisfied is ZL=Z0.

2. When a load ZL is matched to a line, the value of standing wave ratio is:
a) 1
b) 0
c) infinity
d) insufficient data to calculate SWR

Explanation: When the load is matched to the transmission line, they are said to be matched. Hence standing waves exist on the transmission line. Hence SWR is 1.

3. The value of reflection co efficient when a transmission line is matched to the load is:
a) 1
b) 0
c) 0.707
d) cannot be determined

Explanation: When the transmission line and the load are matched, no reflections occur in the transmission line and hence no voltage wave is reflected back. Hence, the reflection co-efficient for a matched line is 0.

4. The value of transmission co efficient when a transmission line is matched to a load is:
a) 1
b) 0
c) 0.5
d) 0.707

Explanation: Transmission co-efficient is defined as the ratio of the incident power to transmitted power at the load end. When the transmission line is matched, the incident power is completely transmitted. Hence, transmission co-efficient is 1.

5. The expression for power delivered to a load , when a line is matched and supplied with a source of Vg with generator impedance Rg +jXg is:
a) 0.5*Vg2/Rg
b) 0.5*Vg2Rg/4(Rg2+ Xg2)
c) Rg/4(Rg2+ Xg2)
d) generator impedance does not cause any losses

Explanation: Due to the generator impedance, there will be some power dissipated and hence the total source power is not transmitted. Hence that power dissipated due to generator impedance is also removed from the total power delivered.

6. If a transmission line is exited from a source of 4V at 1.2GHz frequency with a generator impedance of 4+j3 with a characteristic impedance of the transmission line 50Ω,then the power delivered to the load is:
a) 0.1 watt
b) 0.9 watt
c) 0.8 watt
d) 1watt

Explanation: The expression for total power delivered given the generator impedance is 0.5*Vg2Rg/4(Rg2+ Xg2). Substituting the given values in the above equation, the total power delivered is 0.8 watt.

7. If the generator impedance of a source connected to a transmission line is 50+j100Ω, then for conjugate matching to occur, the input impedance must be:
a) 50-j100 Ω
b) 50+100 Ω
c) 50 Ω
d) one of the mentioned

Explanation: The condition for conjugate matching is Zin=*Zg, where Zin is the input impedance of the transmission line and Zg is the generator impedance. For conjugate matching, taking the conjugate of the given impedance, the input impedance must be 50-100j Ω.

8. After conjugate impedance matching the input impedance used for matching after normalization was 1+j with the characteristic impedance of the transmission line being 100Ω, then the generator impedance must have been:
a) 100+100j
b) 1+j
c) 100-100j
d) 1-j

Explanation: After conjugate matching the input impedance of a transmission line after normalization is 1+j. hence the generator impedance will be the conjugate, that is 1-j. multiplying with the characteristic impedance, we get 100-100j.

9. For a matched transmission line with a generator impedance of 50Ω and the source being 4V,1GHZ,then the maximum power delivered to the line is:
a) 0.4 watt
b) 0.04 watt
c) 0.5 watt
d) no power is delivered

Explanation: The maximum power delivered to the load given the generator impedance is 0.5*Vg2Rg/4(Rg2+ Xg2). Substituting in the above equation the given values, power delivered is 0.04 watt.

10. If the power delivered to a load is 0.04w, then the normalized generator impedance if the source use is 4V at 2GHz and the generator impedance is real and characteristic impedance of the transmission line is 50Ω is:
a) 1 Ω
b) 1+j Ω
c) 1-j Ω
d) 50 Ω