*Question E4B11:
Which of the following can be measured with a vector network analyzer?*  

*Correct Answer is  D: All these choices are correct*  

### AI Response: (may contain errors)  

A vector network analyzer (VNA) is a powerful tool used in RF and microwave engineering to measure various parameters of electrical networks. 

1. **Why the correct answer is correct:**
   - A VNA can measure:
     - **Input impedance**: This is the impedance seen by the source at the input of a device.
     - **Output impedance**: This is the impedance seen by the load at the output of a device.
     - **Reflection coefficient**: This quantifies how much of an incident wave is reflected back due to impedance mismatches. It is defined as:
       $$\Gamma = \frac{Z_L - Z_0}{Z_L + Z_0}$$
       where:
       - $\Gamma$ = reflection coefficient
       - $Z_L$ = load impedance
       - $Z_0$ = characteristic impedance of the transmission line

   Since a VNA can measure all these parameters, the correct answer is **D: All these choices are correct**.

2. **Why the other choices are incorrect:**
   - Choices A and B are not incorrect on their own; they are specific instances of what a VNA can measure. However, they do not encompass the full capability of the VNA, which includes measuring the reflection coefficient as well. Therefore, selecting only A or B would be incomplete.

3. **Useful formulas or rules of thumb:**
   - The reflection coefficient ($\Gamma$) is crucial for understanding how well a load is matched to a transmission line. A reflection coefficient of 0 indicates perfect matching, while a coefficient of 1 indicates total reflection (no power is absorbed by the load).
   - The input and output impedances can be measured directly using the VNA by connecting it to the respective ports of the device under test (DUT) and analyzing the S-parameters, particularly $S_{11}$ for input and $S_{22}$ for output.

In summary, a VNA is capable of measuring input impedance, output impedance, and reflection coefficient, making option D the most comprehensive and correct choice.