In the next three articles, I will focus on the subject of antennas:
1. Criteria for choosing the right antenna
2. An example of a roof antenna
3. Antennas in the automotive industry
I'll try to explain the subject in as understandable as possible, considering my personal experiences and adding some practical tips.
What does an antenna do?
An antenna is a special technical arrangement of electrical conductors to receive and/or emit electromagnetic waves (EM waves).
Which criteria are considered when choosing the right antenna?
1) Frequency
2) Polarization
3) Area of application
1) Frequency
The frequency of the antenna describes how many times an EM wave oscillates within one second. Frequency is always expressed in Hertz (Hz) (named after physicist Heinrich Hertz, the discoverer of electromagnetic waves).
1 Hz means that the time it takes for an EM wave to travel from one wave trough to another is 1 second. Thus, this wave oscillates once a second.
For comparison:
1) When you look at a blue balloon, the light (EM wave) hitting the retina has a frequency of about 650 THz = 650,000,000,000,000 Hz.
2) A modern computer processor operates at a frequency of about 4.2 GHz = 4,200,000,000 Hz.
3) The 1Live radio station in the Ruhrgebiet (in Germany) broadcasts at 106.7 MHz = 106,700,000 Hz.
Frequencies in the radio frequency range are globally allocated and assigned to specific services. In Germany, this is regulated by the Federal Network Agency.
2) Polarization
Polarization is the way EM waves move geometrically through free space. They can be radiated in various ways (vertical, horizontal, or even circular). Depending on the type of antenna, it may be more sensitive to certain polarization types than others. For example, NOAA weather satellites emit a right-hand circularly polarized signal, best received with a quadrifilar helix antenna.
A brief aside: Polarization can be best illustrated with the polarizing filter of a single-lens reflex camera. Polarizing filters are used to remove unwanted reflections from a scene and intensify the contrast of a picture. Light rays are also electromagnetic waves, but in the visible range for the human eye. Without a polarizing filter, light enters the lens at various angles. By using and rotating the polarizing filter, different effects can be achieved by filtering light waves and allowing them to pass through only in predefined areas.
3) Area of application
Examples: Radio reception (DAB + FM), GPS, mobile communication, and networks, etc.
Depending upon the application and environment, an antenna must be appropriately dimensioned. An antenna for GPS reception is shorter than one for FM radio reception. This is because EM waves have a fixed wavelength depending on the frequency (details in the next chapter).
In addition, a transmitting antenna must be perfectly tuned to the planned frequency. Otherwise, the transmitter can be damaged by an unfavorable standing wave ratio (SWR) because the transmission power is dissipated within the transmitter itself (heat development). Reception antennas must also be optimized for the intended working range to achieve the best possible signal-to-noise ratio (= reception quality).
In the next part, we will construct a theoretical roof antenna for radio reception.