An End-Fed Half-Wave (EFHW) antenna is a type of wire antenna commonly used in amateur (ham) radio. As its name suggests, it is typically a half-wavelength long at the frequency of operation and is fed at one end rather than in the center, which is more common for half-wave dipole antennas.

Here are some key characteristics and features of an EFHW antenna:

1. Length: The antenna’s length is approximately half the wavelength of the frequency it is designed to operate on. For instance, for a 40-meter band, the EFHW antenna would be around 20 meters long.
2. Feeding Point: Unlike the center-fed dipole, the EFHW antenna is fed at one end. This end-feeding can be advantageous in terms of installation flexibility and simplicity, especially in limited-space environments.
3. High Impedance at Feed Point: The end of a half-wave antenna has a high impedance, often several thousand ohms. This high impedance requires a matching network or transformer (usually a 49:1 or 64:1 impedance transformer) to match the antenna to the typical 50-ohm impedance of the transmitter and feedline.
4. Radiation Pattern: The radiation pattern of an EFHW antenna is similar to that of a half-wave dipole, with maximum radiation broadside to the wire. However, the end-fed design can sometimes result in more complex patterns due to the potential for currents on the feedline.
5. Multi-Band Operation: With appropriate matching and design, EFHW antennas can operate on multiple bands. This is because the end-fed design’s impedance transformation properties allow it to be used on harmonics of the fundamental frequency.
6. Installation Flexibility: The EFHW antenna can be installed in various configurations such as horizontal, vertical, inverted-L, or sloper, making it versatile for different locations and space constraints.
7. Ease of Deployment: Due to its end-fed nature, the EFHW antenna can be easier to deploy, especially in portable or temporary setups, where a single support (such as a tree or a pole) might be used.

Overall, the EFHW antenna is valued for its simplicity, versatility, and ease of deployment, making it a popular choice among amateur radio enthusiasts, especially for portable operations and situations where space is limited.