*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)  

A stub match is a matching system that uses a short length of transmission line, known as a "stub," connected in parallel with the feed line at or near the feed point. This stub is typically either open or short-circuited at one end and is used to cancel out reactive components of the load impedance, thereby achieving impedance matching.

### Explanation:

1. **Correct Answer: Stub match**
   - A stub match involves placing a short section of transmission line (the stub) in parallel with the main feed line. The stub is adjusted in length and position to provide the necessary reactance to cancel out the unwanted reactance of the antenna system, thus achieving impedance matching. This method is effective for matching a wide range of impedances and is commonly used in RF applications.

2. **Why the other choices are incorrect:**
   - **Gamma match:** 
     - A gamma match is a method of matching a balanced antenna to an unbalanced feed line. It uses a series capacitor and a shorting bar along the antenna element, not a parallel stub.
   - **Delta match:** 
     - A delta match is used with balanced antennas and involves a triangular or delta-shaped section of the feed line. It does not use a parallel stub.
   - **T-match:** 
     - A T-match is similar to a gamma match but is used with balanced antennas. It involves a T-shaped configuration of the feed line and antenna elements, not a parallel stub.

### Useful Concept:

- **Stub Tuning:**
  - The length of the stub is typically a quarter-wavelength ($\lambda/4$) or some multiple thereof, depending on whether it is open or short-circuited. The stub's length and position are adjusted to provide the necessary inductive or capacitive reactance to achieve a match.

Understanding these concepts will help you identify the correct matching system based on the description provided in the question.