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Recommended reading: KonCEPT page 191-229 (chapter 7 + 8)

Start with transmission line (TL), the most difficult component.

characterized by: Characteristic impedance, Z_0, a geometry and material parameter. Length and the speed of light in the transmission line. Two metal conductors that guide the fields.

Used for high frequency signals. Lambda = 300/f [MHz], Lambda similar to length in size.

Waves propagate along transmission lines. Reflections along a TL are similar to light in a glass/water. Explain transmission/reflection coefficients.

Reflections cause standing waves and non-optimal power transfer/losses

VSWR = Voltage Standing Wave Ratio = Z1/Z2 OR Z2/Z1 so a x:1 relation is formed.

We want to “match” the antenna, transmission line and radio to minimize losses.

Balanced/unbalanced (differential/single-ended) TL are important and difficult. Explain this in detail.

balanced TL folded out → dipole antenna! Nice SWR achieved. L = lambda/2 = 300/(2*f) ~=(0,96*lambda/2)

Antenna = two port that converts energy from propagating in a transmission line to propagation in free-space. What is an antenna? An antenna is a device that converts EM waves between a bound medium and a free medium, for instance between a cable and free space.

Antenna types. There are many different types of antennas, since different antenna designs are optimised for solving different problems. There is no antenna that is perfect for every single operational situation. However, the opposite is true; there are indeed antennas that are quite bad at everything.

Different antenna types, roughly in order of most common → least common

• Dipole
• Monopole
• Small loop
• Yagi (Yagi-Uda)
• Patch
• Quad
• PCB/PIFA
• Waveguide slot
• Bowtie
• Spiral/Helical
• Vivaldi

Antennas may often be combined together for different effects. These group of antennas acting together as one, are denoted antenna arrays (gruppantenner). Some antenna arrays are more common than others, for example:

• Log-periodic dipole array (LDPA)

Very often, specific antennas are are combination of other antenna types. For example, the very common Yagi-Uda antenna, is a combination of three (or more) dipole antennas, and one magnetic loop antenna.

All antennas can be characterised using at least the following parameters:

• Input impedance, Z_in
• Standing wave ratio, SWR
• Operational frequency
• Resonance frequency, f_0
• Directivity, D
• Antenna gain, dBi, dBd
• Far-field distance = d_f > 2*D^2/lambda, given d_f » D, d_f » lambda
• Radiation efficiency, eta
• Radiation pattern, E & H patterns
• Polarisation and x-pol suppression

Of these parameters, only input impedance and operational frequency are arguably easy to analyse. This analysis is done with either a vector network analyser, or an antenna analyser. Let's do that at ETA.

Talk about antenna polarisation.

Common mode current on coax = bad!

HF/short wave

1) Ground wave (20-40 km typical)
2) Space wave (global range)
  * Reflections from the ionosphere's D, E, F regions. Sunlight ionize the ionosphere.
  * Reflections affect polarization chaotically.
  * D = 60-90 km height. 
    * "Dämpningsskiktet" attenuates signals
    * Only daytime
    * Attenuate <10MHz
  * E = 90-110 km
  * F = F1 + F2 = 150-350 km - reflection. 
    * Reflect <30-50MHz depending on sun activity
    * Created during daytime, slow to unionize

3.5-7 MHz

• Attenuated by D
• skyward wave/antenna can reflect back to local contacts (E/F)

14-30 MHz

• Not really affected by D
• skyward wave/antenna cannot reflect back to local contacts (E/F)
• Sporadic-E might enable local connections

DX → 10 degree max antenna gain is best

VHF/UHF/…

• Penetrates the atmosphere, EME possible
• Basically only local line-of-sight connections possible
• Troposphere propagation possible. Heat and humidity gradients guide waves. Ex. hearing Danish FM radio in Göteborg.
• northern lights reflections >25 MHz. Distorts signals, phone sounds creepy.
• Moon/meteor/satellite/airplane scatter
  • Reflect signals from big things

Microwaves

• Moon/meteor/satellite/airplane scatter
  • Reflect signals from big things
  • Also rain scatter

Fading example with cellphone if possible

Radio Antenna Fundamentals Part 1 1947

https://www.youtube.com/watch?v=JHSPRcRgmOw&ab_channel=GerryTrenwith