Antenna choices

cst · 02-03-2004

I see that there are many antenna designs which claim a similar level of gain.

For a 14 db gain, you can get an 18" yagi, an 8"x8" flat panel, a 10" diameter "pie pan" antenna, etc. etc.

I haven't seen a good discussion on when a particular type of directional antenna has an advantage over another type of the same gain - apart from space/mounting configurations.

I have seen "efficiency" figures quoted for different antennas, apart from their gain figures. How does this number figure into antenna effectiveness? Is "efficiency" also built into the gain numbers?

Any thoughts on this, or a link to an intelligent discussion that pulls all this together?

Thanks

Thorn · 02-03-2004

Quote:

Originally posted by cst
...
I haven't seen a good discussion on when a particular type of directional antenna has an advantage over another type of the same gain - apart from space/mounting configurations.
...

Because that's pretty much it.

Quote:

Originally posted by cst
... I have seen "efficiency" figures quoted for different antennas, apart from their gain figures. How does this number figure into antenna effectiveness? ...

I've dealt with different antennae over the years, but I don't recall seeing "efficiency" as a figure. Can you give a specific example? (And are you sure it's not advertising hype?)

Quote:

Originally posted by cst
... Is "efficiency" also built into the gain numbers?

If an antenna has a 3dBd gain over another, then it is twice as powerful, in the direction that the gain is made. It could be therefore be argued that it is twice as efficient in that direction. But your true RF geek would probably get naseated trying to put it that way, because it's reducing a rather complex subject to almost kindergarten level. For example: the signal will NOT go twice are far, which you might expect from hearing it's "twice as efficient."

If you really want ot learn about antennae, the bast place is probably the ARRL. (www.arrl.org)

cst · 02-03-2004

WRT "efficiency", I saw this in the catalogue for ARC Wireless panel antennas: http://www.antennas.com/pdf/2.45GhzAntennas.pdf

As gain goes up with these panel antennas, the "efficiency" goes down.

Maybe this is actually another way of expressing the typical VSWR ratio.

Thorn · 02-04-2004

Interesting.

The first instance in the copy is clearly marketing, but the second looks like they trying to tell you something, but I'm not sure what.

VSWR is certainly a possiblity, although that's usually specified as "VSWR >1:1.5" or some similar figure.

Many manufacturers of TX cable specify a "Velocity %" rating; the percentage of lightspeed that the cable will pass signal. That's about the only other thing I can think of that come close to what I'm seeing on that PDF. But I've never seen it on an antenna before.

02-03-2004	#1 (permalink)
cst Registered Member Join Date: Jan 2004 Posts: 28	Antenna choices I see that there are many antenna designs which claim a similar level of gain. For a 14 db gain, you can get an 18" yagi, an 8"x8" flat panel, a 10" diameter "pie pan" antenna, etc. etc. I haven't seen a good discussion on when a particular type of directional antenna has an advantage over another type of the same gain - apart from space/mounting configurations. I have seen "efficiency" figures quoted for different antennas, apart from their gain figures. How does this number figure into antenna effectiveness? Is "efficiency" also built into the gain numbers? Any thoughts on this, or a link to an intelligent discussion that pulls all this together? Thanks

02-04-2004	#4 (permalink)
Thorn Did you do the math? Join Date: Apr 2002 Location: Villa Straylight Posts: 10,361	Interesting. The first instance in the copy is clearly marketing, but the second looks like they trying to tell you something, but I'm not sure what. VSWR is certainly a possiblity, although that's usually specified as "VSWR >1:1.5" or some similar figure. Many manufacturers of TX cable specify a "Velocity %" rating; the percentage of lightspeed that the cable will pass signal. That's about the only other thing I can think of that come close to what I'm seeing on that PDF. But I've never seen it on an antenna before. __________________ Thorn "Read Altas Shrugged. Compare it to today. Repeat as necessary"

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02-03-2004	#3 (permalink)
cst Registered Member Join Date: Jan 2004 Posts: 28	WRT "efficiency", I saw this in the catalogue for ARC Wireless panel antennas: http://www.antennas.com/pdf/2.45GhzAntennas.pdf As gain goes up with these panel antennas, the "efficiency" goes down. Maybe this is actually another way of expressing the typical VSWR ratio.