Wire zig-zag antenna

It is not always apparent when modeling wire structures whether a thin-wire model approximation will still give reliable answers. We recently included the Wire zig zag antenna in Antenna Magus and had some trouble validating designs of this antenna with many cells. There are various methods to model and physically construct a wire zigzag and we found that the corners of a >10 cell zigzag have a noticeable effect on the performance.

Thin-wire model of a zig-zag corner

Detailed triangle mesh model of the zig-zag corner

The thin-wire model is obviously the quickest and easiest way to model the antenna but the simulation results differed from the more detailed triangular mesh model. To see which of the two simulation models could be trusted we built and measured a 12 cell zigzag (shown in the first image above) from copper brazing rods and filed each wire at the correct angle to ensure neat flush corners as shown in the zoomed photo below.

Zoomed view of the zig zag corners

The following image shows a comparison between the measured data and two simulation models which proved that a high gain wire zigzag has to be modeled with more detail.

|S11| Comparison between measured and simulated results

Author: Robert Kellerman

Cantenna made from a Pringles potato chip can.

A couple of months ago I blogged about how hard it is to find reliable measured data for a Cantenna (also known as the Pin-fed circular waveguide antenna) which we wanted to use to verify our Antenna Magus design. You can read the blog here. We decided to make and measure one ourselves.

After designing a Cantenna at 2.45 GHz, Wilco (a 2nd year engineering student from the university, doing vacation work for us) went to the local grocery store to see if he could find a can with the right dimensions. All the cans with the right diameter at 2.45 GHz were too short so he bought a can of large Pringles chips. After we ate the chips he adjusted the design to fit the inner diameter of the Pringles can and cut it to the right length. The new design worked at 2.85 GHz. The inside of the can is lined with a thin aluminium sheet with a thin wax coating which saved a lot of effort – not having to stick conducting material on the inside ourselves.

He soldered the sma connector onto a small copper plate (shown in the next image) and attached it to the waveguide with two small screws after sanding off the wax coating on the inside to assure good contact with the aluminum.

Sma connector soldered onto a small copper sheet

The following image shows the inside of the antenna with the connector and pin. We measured s11 and compared it with the simulation (see graph below) which had pretty good correlation. Most industrial cantennas have a thin dielectric coating on the outside of the waveguide to prevent unwanted surface currents. We didn’t measure the dielectric properties of the Pringles can but it seems like a very cheap, practical antenna with 8 dBi gain and 20% bandwidth at 2.85 GHz.

Inside of the Pringles cantenna showing the connector and pin

|S11| measured vs simulated results

Cantenna sketch with physical dimentions.

For those who might want to try to make this antenna, I added the above sketch showing the required physical parameters that will work using a Pringles can operating at 2.85 GHz center frequency.

Author: Robert Kellerman

Marchand balun image from original published article.

I recently had the privilege of seeing the inside of a real vintage Marchand Balun. One of the Professors at Stellenbosch University lent one to us that he built in the 70s so we could see how it looks (from the outside). Even seeing just the outside was quite informative as all Marchant balun sketches found in papers and text books makes it seem like these baluns are square (as shown in the image above, taken from the original paper “N. Marchand, “Transmission-line conversion transformers,” Electronics, vol. 17, December 1944, pp. 142-145. (Reprinted in J.L.B. Walker et al.”) but they’re not. They’re rectangular like the one shown in the image below.

Like with most engineers, curiosity often overrides the desire for preservation. So while I was busy writing this blog entry, a couple of the engineers in the office unsoldered, cut off the semi rigid and opened up the cavity to have a look inside. These baluns are actually quite impressive as they have very wide operation bands from 2:1 up to 10:1.

Real life Marchand balun

Author: Robert Kellerman