Magneettikehät

Magneettikehät, also known as magnetic loops or loop antennas, are a type of radio antenna characterized by their physical structure being a loop of conductive material. This loop can be of various shapes, most commonly circular, square, or triangular, and is typically a fraction of a wavelength in circumference. Unlike dipole antennas that are resonant at a half-wavelength, magnetic loops are often electrically short, meaning their circumference is significantly less than a full wavelength.

The primary operating principle of a magnetic loop antenna is its ability to generate and respond to the magnetic component of an electromagnetic wave, rather than the electric component which is dominant in dipole antennas. This is achieved by passing a significant current around the loop. A key feature of many magnetic loop designs is the presence of a high-quality tuning capacitor. This capacitor is crucial for resonating the loop at the desired operating frequency and is often the component that must handle high voltages and currents.

Magnetic loops are known for their relatively narrow bandwidth, meaning they are most efficient over a limited range of frequencies. However, they offer some advantages, including their compact size for a given operating frequency, making them suitable for portable or space-constrained applications. They can also exhibit a null in their radiation pattern, which can be useful for rejecting interference from specific directions. Despite their limitations, magnetic loops are a popular choice for amateur radio operators and in certain specialized communication systems due to their unique characteristics.