Monopolantennen

Monopolantennen, also known as monopole antennas, are a class of radio antennas. They consist of a straight rod-shaped conductor, or a set of conductors, that is typically perpendicular to a conducting surface called a ground plane. This ground plane is essential for the proper operation of the monopole antenna; it acts as a mirror, effectively creating a second, virtual monopole below the ground plane. This mirrored image, along with the physical monopole, forms a dipole-like structure that radiates electromagnetic waves.

The most common form of a monopole antenna is the quarter-wave monopole, where the length of the conductor is approximately one-quarter of the wavelength of the radio frequency it is designed to transmit or receive. The impedance of a quarter-wave monopole over a perfect ground plane is theoretically 36.5 ohms. In practice, the ground plane is often imperfect, leading to variations in impedance and radiation patterns.

Monopole antennas are widely used due to their simplicity, ease of construction, and relatively small size, especially at lower frequencies. They are commonly found in applications such as car radios, handheld transceivers, and as elements in larger antenna arrays. The ground plane can be a physical metallic surface, a network of radial wires, or even the chassis of a vehicle. The performance of a monopole antenna is significantly influenced by the size and conductivity of its ground plane.