Slotted Waveguide Antennae for 802.11b Applications

After much research on waveguide antennae, we determined that it should not cost as much as a commercial waveguide to get one machined. All we needed were the designs. I spent about 3 weeks doing research and drawing up designs in AutoCAD. After eight revisions, I was finally happy with the design. I sent it off to several engineering companies for quotations on getting the first prototype machined up.

After several outrageous quotes (excess of $1000), I was finally put in contact with a company who said they would machine it up for $250 including materials. After one more design revision, I took the designs over to the company, and waited for them to machine the first prototype. A couple of weeks later, I went and collected the machined parts. He had done a good job.

I took the machined parts home and proceeded to inspect them. The machinist had done a really professional job. All that was left to do was to clean the swarf out of it, and assemble it. After about 30mins of internal cleaning, the inside of the waveguide had a mirror finish. The end plates already had a mirror finish from the machining process, and did not require cleaning.

To assemble the waveguide, I inserted the two end-plates in each end, and fastened them with their screws. Next, I made the feeding element on a Dick Smith brand "N-Type" connector, and attached it. The waveguide was ready for preliminary testing. I had my BR500 set up with a vertical colinear omnidirectional antenna in the room next door, so I attached a pigtail to the waveguide and plugged it into a Compaq WL110 and proceeded to fire up netstumbler.

I was disappointed to see that the signal had not changed, and initially I thought that my waveguide wasn't working. Then I rememberd that the waveguide is horizontally polarised, and vertical colinear antenna is vertically polarised. Silly me. So i went into the next room and turned the colinear antenna on its side. When I went back to the waveguide antenna, I could not belive that the signal had jumped up about 20dB! I disconnected the waveguide, gave ChrisK (HH operator) a call, and went for a drive up to the HH.

We sealed up the waveguide with silicone (see picture), and proceeded to climb onto the roof and attach it to the mast (see picture). Some spacers were made up out of some old water pipe, placed over the U bolts, and then the nuts were tightened with a "box spanner" (see picture). Duct tape was placed over the slots to stop dust & dirt ingress (see picture). The waveguide was then plugged into the HH access point (see picture), and the installation was complete (see extremely sexy picture). The rest of the HH Waveguide install pics may be found here.

The antenna was taken down again a few days later to be painted and waterproofed, and is now back up, and fully operational as you read this.

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Since the waveguide antenna worked so well, I decided to start taking orders. I recieved enough orders to get a bulk batch machined.

Recently, I was loaned an extremely cool VSWR meter (Anritsu S331B) to test the waveguides with, and I recieved the first waveguide from the new bulk batch. After tuning the waveguide's tuning screw, and tuning the feed, the following VSWR reading was obtained. Click here to view the graph. At all points the VSWR is lower than 1.30:1. That is really good. Please see the table below for an explanation of the markers.

Marker Name	VSWR	Frequency	Channel	Significance
M1	1.03:1	2412.0 MHz	1	Start of 802.11b Spectrum
M2	1.27:1	2484.1 MHz	14	End of 802.11b Spectrum
M3	1.21:1	2445.0 MHz	-	Taken as common "mid" spectrum
M4	1.02:1	2408.9 MHz	-	Lowest VSWR at this point

For those that don't know what VSWR is,

voltage standing wave ratio (VSWR): In a transmission line, the ratio of maximum to minimum voltage in a standing wave pattern. Note: The VSWR is a measure of impedance mismatch between the transmission line and its load. The higher the VSWR, the greater the mismatch. The minimum VSWR, i.e., that which corresponds to a perfect impedance match, is 1:1.

I will be tuning each waveguide antenna I sell with this machine, and providing a printout of the VSWR.

Update (1-4-2002): I have recieved my 360s, although the VSWR plot looks different, they still have a VSWR of less than 1.3:1 across the 802.11b spectrum. I will upload a plot soon. Also, I have found that the minimum VSWR on the 180s and 360s changes slightly on each antenna produced. This is due to machining tolerances.

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Geoff Watts (from innaloo.net) and I recently went up to Reabold Hill for some antenna testing. The GPS said that we were 25.5km from HH. As soon as we plugged the waveguide in, it picked up the HH, and the signal did not change much as we rotated it around its entire azimuth. Waveguide to waveguide with a distance of 25.5km.

Another member of the network connected to the HH in Duncraig (29.9km away) with trees in the way. See the HH guestbook for a log of all sucessful connections. You must be logged into the HH to add an entry.

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Specifications:

Please note that antennae are supplied painted and sealed, and ready to bolt onto a mast. U-Bolts not included.

	180º Version	360º Version
Frequency Range	2400MHz - 2500MHz	2400MHz - 2500MHz
VSWR	Less than 1.3:1 across spectrum.	Less than 1.3:1 across spectrum.
Gain	Approx. 14dBi	Approx. 11dBi
Polarisation	Horizontal	Horizontal
Azimuth	180 degrees	360 degrees
Antenna Connector	Female N-Type Connector	Female N-Type Connector
Finish	White Epoxy Enamel	White Epoxy Enamel
Dimensions W*D*H	100mm*50mm*1000mm	100mm*50mm*1000mm
Weight	Approx 2.5 kilogram	Approx 2.5 kilogram
Price	Please e-mail	Please e-mail

Prices subject to change without notice.

Please note that prices will rise when I finish testing these antennas. If you want to purchase one or more of my antennae, please contact me at mike at forrestfieldwireless dot net.

 

Links to my waveguides being used in wireless projects:

My Menora-Net

WaFreeNet Node 4 - "The Hills Hub"

Forrestfield Wireless Network

WaFreeNet Node 235 - "CTNet"

WaFreeNet Node 48 - "mc"

Innaloo.net Mast

Morley Air Net Mast

Zank's Access Point

 

Related Links:

www.wafreenet.org - The official WaFreeNet site

View the WaFreeNet node database