Car antennas are often shorter than the wavelength they are trying to receive or transmit because of a phenomenon known as the "quarter-wavelength matching." This concept is based on the principle that when an antenna has a length that is approximately one-quarter (1/4) of the wavelength it is designed for, it can efficiently transmit or receive electromagnetic waves.
When an antenna is shorter than the wavelength, it doesn't resonate well with the incoming signal. The efficiency of the antenna, known as impedance matching, is reduced, leading to weaker reception or transmission. However, by using an antenna that is a fraction of the full wavelength, such as one-quarter (1/4), the impedance mismatch can be improved, resulting in better performance.
This quarter-wavelength matching technique takes advantage of the fact that an electromagnetic wave reflects off the end of an antenna and creates a virtual image of the antenna. When the physical length of the antenna is one-quarter (1/4) of the wavelength, the reflected wave interferes constructively with the incoming wave, reinforcing the signal and maximizing the antenna's efficiency.
Additionally, car antennas often employ additional tuning and impedance matching techniques, such as loading coils or capacitors, to further optimize their performance. These techniques help compensate for the shorter length of the antenna and enhance its ability to transmit and receive signals efficiently within the desired frequency range.
By designing car antennas to be shorter than the wavelength, engineers can achieve a practical and effective antenna size that performs well for the intended frequency range while maintaining the desired impedance matching properties.