0
\$\begingroup\$

Is the gain of a directional antenna (for example Yagi-Uda) the only thing that we need, in order to describe each radiation pattern?

Isn't the gain a function of the azimuth and zenith angle that describes angular dependence of direction and received signal strength?

\$\endgroup\$
6
  • \$\begingroup\$ sometimes you want to know whether there are any nulls, and where they are. With Yagi, you certainly want to know the beamwidth. \$\endgroup\$
    – Neil_UK
    Nov 19, 2021 at 18:11
  • \$\begingroup\$ @Neil_UK what do you refer as null, the side lobs? The beam width we need that in order to check if we have high or low gain? \$\endgroup\$ Nov 19, 2021 at 19:26
  • 1
    \$\begingroup\$ Look up antenna nulls, I haven't the time or inclination to describe them now. Look up antenna beamwith, I haven't the time or inclination to describe how that's different from gain. \$\endgroup\$
    – Neil_UK
    Nov 19, 2021 at 19:30
  • \$\begingroup\$ You are correct. The gain of an antenna (at a particular direction) is a function of the azimuth and elevation angles of the received or transmitted signal, and the antenna's radiation pattern. \$\endgroup\$
    – SteveSh
    Nov 19, 2021 at 19:54
  • \$\begingroup\$ Another thing to keep in mind (though may be a bit off topic here) is that in array-type antennas (arrays of individual elements), gain is sacrificed in order to achieve some other desired performance, such as lower sidelobes. \$\endgroup\$
    – SteveSh
    Nov 19, 2021 at 22:08

2 Answers 2

2
\$\begingroup\$

It matters because your signals may vary over a 40 dB range which is not defined well by the antenna gain as there may be many side lobe nulls. It depends on the skew angle of detection you are using and the type of element, (bar, butterfly, etc) and how those lobes shift with frequency due to phase alignment of the elements.

  • For instance , blocking a strong transmitter off-axis while reaching a faint distant one to avoid IMD. Yet -3dB beamwidth and gain are related for 0 to -3dB but not very well below this. I do this to block the CN tower from North of Toronto to get Buffalo just slightly off-axis balancing for max weak SNR without knowing the imperfect patterns of my Yagi-Uda. This way I can get 30 FTA channels using a pre-amp.

enter image description here ref:

https://www.tvfool.com/ Find what gain you need.

ideal

enter image description here enter image description here

enter image description here

If elements are not perfectly in alignment, the side lobes may bulge out.

\$\endgroup\$
2
  • \$\begingroup\$ Also,.one more question are there closed formulas of the Yagi-Uda antenna gains, i.e. is the a formula for the $$G(\theta, ,\phi)$$? \$\endgroup\$ Nov 19, 2021 at 19:24
  • \$\begingroup\$ in a lossless antenna, the ratio of spherical surface to beam area is the antenna gain. This may be approximated with polarization to a 1D beamwidth angle. reflector may also affect gain from back side. \$\endgroup\$ Nov 19, 2021 at 19:43
1
\$\begingroup\$

The gain of an antenna is a measure of the overall radiation pattern of that antenna. That means that two antennas can have the same gain but an entirely different shaped radiation pattern. For example, an antenna with only one main lobe of width D degrees and low sidelobes can have a gain of X dB. Another antenna might have two main lobes of width D/2 degrees and low sidelobes. Because the gain represents an integration of the whole pattern, both of these antennas will (roughly) have the same gain.

\$\endgroup\$
3
  • \$\begingroup\$ But if we have two identical antennas, they will have the dame gain \$\endgroup\$ Nov 19, 2021 at 19:53
  • \$\begingroup\$ At the same azimuth and elevation angles, and at the same frequency - yes. \$\endgroup\$
    – SteveSh
    Nov 19, 2021 at 19:56
  • 1
    \$\begingroup\$ Why would anyone care about the integrated gain of an antenna? Aren't we really interested in the gain in a particular direction - to the signal source? \$\endgroup\$
    – SteveSh
    Nov 19, 2021 at 20:51

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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