AdvancedTopic 90 of 101Signals, Control & Comms
Antennas and propagation
Radiation patterns, gain and path loss describe wireless links.
In depth
Antennas convert guided waves to radiated waves; parameters: gain, directivity, pattern, polarisation, bandwidth, impedance. Free-space path loss FSPL=20log(4πd/λ). Propagation: line-of-sight, reflection, diffraction, scattering; ground waves, sky waves and tropospheric effects at different bands.
Key points
- dBi gain
- Radiation resistance
- Fresnel zone
ExampleA 2.4 GHz link of 100 m has about 80 dB free-space loss.
What is Antennas and propagation?
Radiation patterns, gain and path loss describe wireless links.
Why is it important to understand antennas and propagation?
Antennas and propagation determine how far a radio link reaches and how it is shaped, so they set the design of every wireless system.
What is antenna gain?
The ratio of power in a direction to the power from an isotropic radiator, which concentrates energy where it is needed.
What is path loss?
The reduction in signal power over distance, which increases with frequency and distance and depends on the environment.
How is Antennas and propagation used in practice?
Typical applications include choosing a directional antenna for a long rural link, estimating the path loss for a radio link between two towers and designing a monopole antenna for a sensor node.
What should I learn before Antennas and propagation?
Study "Spread spectrum" first (topic 89 of 101 in Signals, Control & Comms). It covers the groundwork this topic builds on.
What are the key points of Antennas and propagation?
dBi gain. Radiation resistance. Fresnel zone.
Can you give an example of Antennas and propagation?
A 2.4 GHz link of 100 m has about 80 dB free-space loss.
What comes after Antennas and propagation?
The next topic is "Link budget", which builds directly on this one.
How difficult is Antennas and propagation?
It is classed as Advanced in Signals, Control & Comms (topic 90 of 101). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Signals, Control & Comms.