I try to understanding the workflow of directional antennas.

I want to implement a bluetooth communication with external, directional antenna. Lets suppose that I buy this:


My question is, if this antenna "looks" to the north (the white head looks to north and the back with cable looks to south) . If I transmitted signal from south to north, does the antenna recieve the transmitted signal ?

  • 1
    \$\begingroup\$ Buy one that has a proper data sheet. Posting a picture of an antenna does not mean it's radiating field pattern is immediately clear especially if it has a white circular cover over it. \$\endgroup\$ – Andy aka Jun 26 '17 at 11:39
  • \$\begingroup\$ do you mean something like this or more detailed(i cant find it) ? buerklin.com/medias/sys_master/download/download/hf7/h2f/… \$\endgroup\$ – Jordan Georgiadis Jun 26 '17 at 12:45
  • \$\begingroup\$ If your changing the power level by adding the antenna, your probably violating the spec and FCC laws. \$\endgroup\$ – Voltage Spike Jun 27 '17 at 1:03

Antennas follow a property called reciprocity. This means that if the majority of the directivity is in one direction during transmit, during receive the directivity will be the same and in the same direction.

So in the case of the PDF you posted for the LogiLink antenna, you can see the it is directive in one direction (for both transmit and receive). If you try to pick up a signal coming from the opposite direction, the signal will be highly attenuated. This means you may or may not receive the signal but you would certainly have a much better chance by pointing the antenna in the direction of the desired signal.

There are also omnidirectional antennas that exhibit gain. These may be more suitable for you if you need to receive signals approaching the antenna from various directions. An omnidirectional antenna exhibits gain by restricting the pattern in the vertical orientation.

  • \$\begingroup\$ please take a look at this image. prnt.sc/fobm3a .I mean that if antenna 1 transmitt, antenna 2 will recieve the signal ? Ι want directional to avoid the receiveing from side objects \$\endgroup\$ – Jordan Georgiadis Jun 26 '17 at 13:19
  • \$\begingroup\$ i dont want to receiving from various directions \$\endgroup\$ – Jordan Georgiadis Jun 26 '17 at 13:30
  • \$\begingroup\$ The antenna you have pictured is highly directional. Signals coming from the back side will be greatly attenuated. Generally speaking this is not effective. \$\endgroup\$ – Glenn W9IQ Jun 26 '17 at 13:40
  • \$\begingroup\$ Yes.this is what i want. I want to avoid the signals coming from the antenna 1. It can be happen ? Dont see the antenna only in the picture. Its for example. See the antenna at first link, or the pdf of the comments on the top \$\endgroup\$ – Jordan Georgiadis Jun 26 '17 at 14:14
  • \$\begingroup\$ It will greatly attenuate it but there is not sufficient information to determine if the receiver on antenna 2 will detect it. For this, you should examine the Friis formula. \$\endgroup\$ – Glenn W9IQ Jun 26 '17 at 14:18

Not the answer you're looking for? Browse other questions tagged or ask your own question.