Fundamentals of Electromagnetic Waves and Satellite Systems

Swing Circuits and Electromagnetic Waves

To produce damped oscillations, circuits must be complex: and . Electromagnetic waves are composed of an electric field and a magnetic field (also known as Hertzian waves).

Wavelength and Dipole Antennas

Wavelength is the distance a wave travels during one complete cycle, calculated as λ = c / f. A dipole is a half-wavelength antenna consisting of two symmetrical conductors. In a half-wave dipole, the length between its ends coincides with half the wavelength of the target frequency.

Radiation Resistance and Polarization

Radiation resistance is the resistance of the dipole at resonance, typically 75Ω. The polarization radiation diagram defines the direction of the electric field of the electromagnetic wave, which aligns with the dipole's position relative to the ground. Satellites can be polarized horizontally (H), vertically (V), elliptically, or circularly.

Frequency Bands and Channels

A band consists of all frequencies between two defined limits. A channel is a specific frequency band used for television broadcasting. VHF and UHF stations typically have a bandwidth of 7 or 8 MHz, respectively.

Reflection and Antenna Installation

The reflection coefficient (Γ) is defined as the ratio between the reflected voltage wave (Vr) and the incident voltage wave (Vi) at a point on a line. When installing a TV antenna, one must account for wind load. For heights under 20m, the calculation is based on 130 km/h; for altitudes above 20m, it is 150 km/h, using the dynamic pressure formula (Pd = γ · v²/2g), where γ = 1.2 kg/m³.

Signal Transmission and Cabling

The dimensions of a dipole depend on the reception frequency. A coaxial cable consists of two copper or aluminum conductors, and attenuation refers to the signal loss that occurs within a cable or transmission line.

Satellite Communications Systems

The geostationary orbit is located 35,806 km from Earth. Satellites utilize microwave frequencies for transmission.

Converters and Signal Quality

The mission of a converter is to transform a high-frequency signal into a lower-frequency signal. An indoor unit receives an RF signal at its output. The signal-to-noise ratio (C/N) measures signal quality; the C/N ratio expresses the quality of the input signal before demodulation. A digital signal is discontinuous in time, and the noise figure is often visible on TV screens as "snow."

Satellite Modules and Orbital Mechanics

Satellite modules include the antenna module, communications module (which amplifies and conditions the signal, known as a transponder), power module, service modules, and propulsion module.

• Frequency (Earth-Satellite): 12.7–14.5 GHz
• Frequency (Satellite-Earth): 10.7–12.75 GHz (1 GHz = 10⁹ Hz)
• Clarke Belt: The orbital path for geostationary satellites.
• Azimuth: The angle measured clockwise from North toward the satellite's direction.

Types of Wave Propagation

Existing wave types include: direct, surface, and ionospheric waves.