Sawen_Blog

The document discusses antenna characteristics and loading techniques. 1. **Optimal Radiation Length**: - For an ideal vertical monopole antenna, the best radiation efficiency occurs at a length of \( L = \frac{\lambda}{4} \) (one-quarter of the wavelength). - Other types include half-wave dipole antennas (\( L = \frac{\lambda}{2} \)) and full-wave antennas (\( L = \lambda \)). - A grounded vertical antenna has maximum voltage at the top and maximum current at the base when its length is \( \frac{\lambda}{4} \). 2. **Antenna Loading**: - Loading extends the effective electrical length of shorter antennas, adjusting their resonance conditions. - **Inductive Loading**: Used for antennas shorter than \( \frac{\lambda}{4} \) to compensate for capacitive reactance by adding inductance, typically near the bottom or middle. - **Capacitive Loading**: Increases the equivalent length by adding capacitance at the top, enhancing voltage and radiation efficiency while reducing ground reactance. | Aspect | Inductive Loading | Capacitive Loading | |----------------------|---------------------------|----------------------------| | Purpose | Compensate capacitive reactance | Enhance voltage, increase efficiency | | Location | Series at bottom/middle | Parallel at top/loading "capacitive hat" | | Function | Achieve resonance | Electrically extend length | | Common Applications | Shortwave whip antennas | Mobile and vehicle antennas | **Loading Position Impact**: - Bottom loading has minimal current impact but requires larger inductance, resulting in lower efficiency. - Middle loading offers better efficiency but is structurally complex. - Top loading provides the best radiation efficiency but is also complex and has higher wind resistance.