*Question E9E03:
What matching system uses a short length of transmission line connected in parallel with the feed line at or near the feed point?*  

*Correct Answer is  D: Stub match*  

### AI Response: (may contain errors)  

The correct answer to the question is **D: Stub match**. Here's why:

### Explanation of the Correct Answer:
- A **stub match** uses a short length of transmission line (the stub) connected in parallel with the feed line at or near the feed point. This configuration allows for impedance matching by introducing a reactive component that can cancel out the reactance of the load, thus improving the overall match to the transmission line.

### Why the Other Choices are Incorrect:
- **A: Gamma match**
  - A gamma match typically involves a single wire connected to the antenna at a point that is adjustable to achieve a match. It does not use a stub or a parallel transmission line.

- **B: Delta match**
  - A delta match is a type of matching network that uses a configuration of capacitors and inductors to achieve impedance matching. It does not involve a stub or parallel transmission line.

- **C: T-match**
  - A T-match uses a combination of capacitors and inductors arranged in a T-shape to match the impedance of the antenna. Like the delta match, it does not utilize a stub or parallel transmission line.

### Useful Formulas or Rules of Thumb:
- For stub matching, the length of the stub can be calculated based on the frequency and the desired reactance. The length of the stub ($L$) can be determined using the formula:

$$
L = \frac{c}{2f} \cdot \frac{1}{\sqrt{Z_0}}
$$

where:
- $c$ = speed of light (approximately $3 \times 10^8$ m/s)
- $f$ = frequency in Hz
- $Z_0$ = characteristic impedance of the transmission line

This formula helps in determining the appropriate length of the stub to achieve the desired impedance match. 

In summary, the stub match is the only option that specifically involves a short length of transmission line connected in parallel with the feed line, making it the correct answer.