Waveguide type directional antenna

[abcd567]

Calculators for Directional Waveguide type antenna:

Cantenna Calculator

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http://www.turnpoint.net/wireless/cantennahowto.html
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http://www.wikarekare.org/Antenna/WaveguideCan.html

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[abcd567]

@xlr99 said

GDogg,

In addition to abcd’s recomendations (all very good ones I might add) you may want to look at this:
Lincomatic's Homebrew WiFi Antennas
He mentions something I’ve not seen in any of the other waveguide antenna construction articles.

Contrary to popular belief on the Internet, a can length of 3/4 the waveguide wavelength is not optimal. The ARRL Antenna book recommends 2-3 waveguide wavelengths instead. I’ve found that adding more cans indeed increases the gain. A 4-can one is the longest I tried; I didn’t write down the gain testing results, but it was considerably better than the 1-can antenna.

The additional cans will give you a narrower radiation pattern (than you would get with a single can) which may or may not be what you want. You get more gain with a longer waveguide, at the expense of beamwidth.

For additional gain, have a look at his “Bazooka Cantenna” article near the bottom of the page.
The addition of the “horn” gives the antenna about 5-6dB more gain vice the bare waveguide.

[abcd567]

@GDoggRaspberry said:

abcd567 & xlr99 - Thanks for the information. I grabbed a Progresso soup can out of my pantry and it’s about 85 mm diameter by 110 mm high. Using the calculator links and assuming that the TE11 & TM01 frequencies define the bandwidth, my vegetable soup is not looking like a good antenna for ADSB at 1090 MHz. I need a can of around 200 mm diameter and 99 mm length for the 3/4 wavelength, and more likely 263.8 mm to go with xlr99’s observation regarding 2 wavelengths. Fortunately, an 8" duct might be just about right so it looks like I’ve got a trip to the hardware store in the near future.

[abcd567]

@xlr99 said:

YVW,S!

8 inch duct will give you a lower cutoff of 865 MHz and an upper of 1130 MHz. Should work like a champ.

[abcd567]

@GDoggRaspberry

Fortunately, an 8" duct might be just about right so it looks like I’ve got a trip to the hardware store in the near future.

Great.
Keep us informed of your progress and outcome.

[abcd567]

@xlr99

YVW,S!

8 inch duct will give you a lower cutoff of 865 MHz and an upper of 1130 MHz. Should work like a champ.

A lower cutoff of 990 Mhz is more desireable to get rid of both the GSM-800 and EGSM-950 Mobile/Cell signals - A directional antenna + a cavity filter - buy one get one free

[abcd567]

@xlr99 said:

@abcd567

A lower cutoff of 990 Mhz is more desireable to get rid of both the GSM-800 and EGSM-950 Mobile/Cell signals

Which is definitely a good thing.

The problem there is that he would need a somewhat smaller cylinder and that might not be readily available. (a waveguide diameter of 6.96 inches (177 mm) would give him a lower cutoff of 992 MHz.
So if he can find suitable metallic tubing with a diameter of 7 inches, he should be good to go)

But, if he builds it multiple waveguide-lengths long, as he indicated he might do, that will make the antenna
beamwidth narrower which will eliminate any signals his antenna isn’t aimed at. If the signals are not in the antenna pattern main lobe, but are very strong, they will be attenuated considerably.

If the interfering signal is in-line with the desired signal, then an inline filter might be required. The rolloff
of the antenna will help knock down the interference, but the skirts of the antenna response curve aren’t as steep as those of a cavity filter, hence the possible need for a filter at the antenna feedpoint.

The downside to a longer waveguide and thus narrower beamwidth, is aiming the antenna. The narrower
the beamwidth is, the more precise one must be when aiming the antenna at the signal source.

[SoNic67]

Maybe a 7-1/8" diameter will work?

Tablecraft HU4 7 1/8" Round Brushed Stainless Steel Utensil Holder

[xlr99]

It will work, but the lower cutoff frequency would be 976 Mhz,
a bit lower than 990 Mhz as suggested by abcd567.

At 1.09 GHz, it doesn’t take much to make a difference in resonant frequency.
Two or three millimeters is enough to change it significantly. The effect is directly
proportional to frequency, i.e. the higher the frequency, the greater the change in
resonant frequency with respect to the same change in length.

The price is certainly right. Otherwise, a good call.

[abcd567]

@xlr99

It will work, but the lower cutoff frequency would be 976 Mhz, a bit lower than the 990 Mhz suggested by abcd567

Yes but still better than 865 Mhz of 8 inch dia cylinder. Entire GSM-850 and EGSM-900 will befiltered even with 976 MHz cut-off

E-GSM-900

Uplink from Mobile/Cell Phone to Base Station = 880 – 915 Mhz (This is weak, as Phones are not powerful transmitters)

Downlink from Base Station to Mobile/Cell Phone = 925 – 960 Mhz (This is the one which is very strong as it is transmitted by the powerful Base Station on Cell Phone Mast or Building roofs)
.

.

[xlr99]

@abcd567

Yes but still better than 865 Mhz of 8 inch dia cylinder. Entire GSM-850 and EGSM-900 will befiltered even with 976 MHz cut-off

Quite true. Depending on the rolloff, the effect may not be much different between the two.
i.e. they may end up performing about the same.

One thing it has going for it though is the fact it’s made from Stainless Steel. That means
attaching Zinc coated (galvanized) hardware won’t result in corrosion like it would with a
Copper or Aluminum waveguide.

It’s also long enough from top to bottom that it satisifes the 2-3 waveguide-lengths dimension.

[abcd567]

An interesting read for different types of WiFi DIY Directional Antennas.
(40 pages, slow site, takes a while to download. Takes time to display due to embeded sketches. First page is blank)

https://roelof.info/projects/(2014)Pretty_Fly_For_A_Wifi/Pretty_Fly_For_A_Wi-Fi_booklet.pdf

[xlr99]

I came across that site a couple of months ago. Lots of good info.
Especially interesting was the Bottlenet antenna. More info on that one at:

How to make a bottleNet Antenna :) ? - Weefi Wifi

[GDoggRaspberry]

Well it was either play with this or work on preparing for a presentation next week, so the decision was pretty easy. I considered the route of the utensil holder since I have one on my counter, but I decided that it would probably lead to Relationship Problems. So off to Home Depot I went. I’ll have to get some pictures but I’m using 8" X 12" duct mounted on a tripod. The antenna is 32.9 mm from the closed end and 68.8 mm tall. I take blood thinners so the real measure of success for me working with duct work is amount of blood loss. So far no cuts but this stuff is sharp.

Initial results are good but puzzling. With no changes to the previous spider configuration, just swapping the antenna and pointing in the general direction of the airport, I’m definitely seeing more low altitude general aviation than I normally pick up. The puzzling part is the performance I’m seeing in all directions. I’m getting really good range at a 90 deg angle to the direction of the antenna and even getting pretty good performance in the opposite direction. Does anyone have a beam pattern calculator for these dimensions?

Edit: I’ve got it inside of my house and I believe that my wall boarding has a foil layer, which could account for some of the reflections.

[abcd567]

Good progress.
Let us see how it performs when installed outdoor.

Waiting for photos.

[wiedehopf]

@GDoggRaspberry

Edit: I’ve got it inside of my house and I believe that my wall boarding has a foil layer, which could account for some of the reflections.

Could you provide a picture of your build? It’s easier to interpret the results then.

[GDoggRaspberry]

Here’s what it looks like. The duct is designed with swivels to change direction, but it was the closest I could find to the dimensions that I needed.

[GDoggRaspberry]

Optimize_gain results with FA Blue Pro Stick and FA Filter:

===Totals===
Gain, Messages, Positions, Aircraft
-10 33425 2829 201
49.6 70907 5874 245
48.0 36411 2990 201
44.5 35094 2850 207
42.1 34453 2850 206
40.2 32740 2747 198
38.6 31289 2756 194
36.4 30468 2596 184
33.8 30299 2584 178
29.7 25416 2194 155
28.0 23279 1887 145
25.4 17564 1423 124
22.9 15189 1208 109
49.6 70907 5874 245

[GDoggRaspberry]

Better picture of the monopole inside. I did not have any solid copper was thin enough to stick in the barrel connector so had to make due with some hookup wire.

[GDoggRaspberry]

Clearly FA filter hurts me more than it helps me. Just a few minutes difference between the test runs while I removed the filter.

test 5 of 5 - with FA filter, pointed South
gain= -10 messages= 5589 positions= 470 planes= 67
gain= 49.6 messages= 6418 positions= 550 planes= 61
gain= 48.0 messages= 6378 positions= 505 planes= 62
gain= 44.5 messages= 6778 positions= 528 planes= 66
gain= 42.1 messages= 6758 positions= 536 planes= 63
gain= 40.2 messages= 7093 positions= 557 planes= 65
gain= 38.6 messages= 6936 positions= 532 planes= 62
gain= 36.4 messages= 6507 positions= 479 planes= 52
gain= 33.8 messages= 6976 positions= 488 planes= 53
gain= 29.7 messages= 6016 positions= 393 planes= 48
gain= 28.0 messages= 6067 positions= 371 planes= 47
gain= 25.4 messages= 4874 positions= 299 planes= 41
gain= 22.9 messages= 3834 positions= 241 planes= 37
gain= 49.6 messages= 8226 positions= 621 planes= 66

test 1 of 5 - No FA Filter, pointed South
gain= -10 messages= 8760 positions= 709 planes= 81
gain= 49.6 messages= 9028 positions= 708 planes= 81
gain= 48.0 messages= 8836 positions= 716 planes= 78
gain= 44.5 messages= 6535 positions= 524 planes= 78
gain= 42.1 messages= 8318 positions= 656 planes= 82
gain= 40.2 messages= 8124 positions= 602 planes= 77
gain= 38.6 messages= 7619 positions= 578 planes= 75
gain= 36.4 messages= 6700 positions= 478 planes= 73
gain= 33.8 messages= 6601 positions= 438 planes= 66
gain= 29.7 messages= 5218 positions= 321 planes= 51
gain= 28.0 messages= 5028 positions= 308 planes= 48
gain= 25.4 messages= 3490 positions= 207 planes= 30
gain= 22.9 messages= 3407 positions= 176 planes= 24
gain= 49.6 messages= 8025 positions= 517 planes= 83