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Antenna_Selection_Guide.php   8452 Bytes    07-08-2015 18:25:21

Antenna Selection Guide

People often ask for GSM-Antenna, WiFi Antenna or XYZ Antenna. Unfortunately the answer is always : "There is no such thing" (and my search-engine shows no results), as all names describe a service. The antenna however does not care about your service nor modulation or power. Instead, antennas are classified regarding other properties like gain, bandwidth or radiation pattern. Our list suggests antenna types with respect to their relative position. The question here is always : Is the position fixed or is the sender / receiver moving around. An antenna does not care if used as receiver or transmitter. (First iteration ;-)

Scenario #1 : Sender fixed position, Receiver fixed position

This is the case when you watch television or radio at home (unless you live in a caravan :-)
In that case we suggest you use an antenna with a small aperture angle, pointing towards the Sender (Transmitter). Depending on the distance and frequency, you need more or less gain. More gain is necessary for large distances and for higher frequencies, as the radiowave is attenuated more. The following designs may be suiteable for that case :

Antenna TypeBandwidthConstructionCost
Yagi Uda Antenna small, ~ 10%easymedium
HB9CV Antenna small, ~ 4%easylow
LPDA broadbandeasymedium
Parabolic antenna smalladvancedhigh
Cantenna smalleasylow

Or anything else with a small aperture angle.

Scenario #2 : Sender fixed position, Receiver moving around

GSM Antenna @ ETH Hoenggerberg

This is the case when you listen radio in your car or when you make a call with your mobilephone. In that case we suggest you use an antenna with a large aperture angle, preferrably an omnidirectional design. This will make sure, that your signal strength is independant of your position (just getting smaller with increased distance). The following designs may be suiteable for that case :

Antenna TypeBandwidthConstructionCost
λ/4 Groundplane smalleasylow
Discone broadbandeasyhigh
J-Pole smalleasylow

Or anything else with an omnidirectional characteristic.

Antenna Gain versus Omnidirectivity

An isotropic radiator is a theoretical point source of electromagnetic or sound waves which radiates the same intensity of radiation in all directions. It has no preferred direction of radiation. It radiates uniformly in all directions over a sphere centred on the source. Isotropic radiators are used as reference radiators with which other sources are compared. Wikipedia Isotropic radiators have no gain.

The gain arises, when the pattern is no longer uniform in all directions. We may understand the gain as the ratio of radiation angle with respect to a sphere. The smaller the angle, the more power may be transmitted in one direction. The more "Gain" we have.

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t1 = 3876 d

t2 = 551 ms

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