Omnidirectional radiation patterns based on gain

[DylanMadigan]

Is there a chart or a good way to calculate the radiation patterns of omnidirectional antennas based on their gain? For example, I want a high gain wifi antenna on my roof, but I don't want it to be so high gain that noone on ground gets wifi lol. I also want to figure out what is the highest gain antennas i should get for the UHF radios in the trucks. I tried looking around, but all I could really find is "higher gain is a narrower radiation patter" but I wish to understand exactly how wide those patterns are.

Anyone know of any places I can find this out?

 

[nd5y]

You can use antenna modelling software to calculate the gain and radiation pattern of any antenna but you have to know the exact dimentions of all the parts of the antenna and the values of any matching network, coils and capacitors in it. This is a very steep learning curve and requires a lot of antenna knowledge.

 

[zz0468]

The manufacturer should provide a pattern on the antenna's data sheet. If not, use a different antenna that does.

 

[zz0468]

The manufacturer should provide a pattern on the antenna's data sheet. If not, use a different antenna that does.

Also, be aware that the figures used in the antenna pattern plots are not brick walls of coverage, they're reference levels.

 

[RadioGuy7268]

Normally, a manufacturer will post 2 types of plots. For an omnidirectional antenna that's typically mounted straight up on a vertical mast, the Horizontal pattern (not surprisingly) resembles a full circle. I find that in the higher frequency bands, the Horizontal pattern is also called the Azimuth, because if you are using a directional or yagi antenna, the Azimuth pattern would tell you the direction where most of your antenna pattern is focused.

The more telling pattern (in regards to your question) will be the vertical pattern or elevation plot. This would be the "side view" of the antenna pattern, and would show the main beam, as well as any lobes or downtilt that is built into the antenna. From the way you asked your question, I think you already realize that the horizontal pattern will become more compressed as the antenna gain is increased. We often use the analogy that a Unity gain (zero gain) antenna resembles a real fat bagel, while a high gain antenna pattern becomes flattened down like a pancake. You've still go the same amount of dough, just the shape has changed. It's important to realize that the total energy being transmitted has not changed, you have only changed the pattern. Getting a "gain" in one area means that energy is no longer present somewhere else.

As others have said, any decent manufacturer will have charts and plot patterns for any antenna they're making, and you can compare them to see the differences.

If you haven't seen it before - this guy Nigel has a pretty good Blog that's focused on WiFi - but he's not US Based, so some of his observations don't have a US perspective as far as what's legal or common.

WifiNigel: Antenna Radiation Patterns in the Real World

 

[mmckenna]

Also, it's a representation of the coverage.
It doesn't mean there is zero signal outside the radiation pattern.

Even if you are using a high gain antenna that is sending most of it's signal out towards the horizon, there are lobes and some signal directly under the antenna.
Where it becomes an issue is very high installations (as in hundreds or thousands of feet, or if the antenna is mounted on something like a steel reinforced concrete building where you need some penetration down into the basement.

Mechanical and electrical down tilt can be your friend in these applications.

 

[Ubbe]

GHz frequencies will bounce around a lot and reflect on any solid objects so if you have a high gain antenna on the chimney it will most propably bounce back thru the windows to create indoor coverage.

/Ubbe

 

[W5lz]

Besides the shap/size of antenna the surroundings of the antenna will have an affect on the radiation pattern. Everything affects the pattern to some extent, some more than others. So there's no definite pattern for your antenna unless you take all the stuff around it into effect too. Most published radiation patterns are only approximations, at best, and some times just plain fantasy. They can give you a general idea of where signals go/come from though...