There must be an easier way to read off design values from an IEEE paper

August 25th, 2010

Illustrating the traditional graph tracing method.

Illustrating the traditional graph tracing method.


Don?t you find it interesting that one of the most important steps in designing most antennas requires a pencil, ruler and often a magnifying glass in order to obtain the correct values to use in design algorithms? Living in the year 2010 (and not in the years ?before television?) one would think that the method of reading-off graph data from a published IEEE paper should have developed to be at least digitized. But most people still use the same old pencil and ruler method and then have to approximate the value which for some reason always lies on the steepest gradient of the graph resulting in high margin for error.

One of our engineers wrote a very handy Matlab tool which allows you to import a graph as a jpeg image and records the coordinates when clicking on the trace with your mouse, interpolating the X ? Y data, so it saves you the effort of printing the graph and reading off the values by hand. If you think you can use this tool drop me an email and I?ll send it to you.

Such a tool would probably be a very handy feature in Antenna Magus?watch this space.

Author: Robert Kellerman

Comparison between a Cantenna and Coaxial cavity horn

August 18th, 2010

A few posts ago I showed some pictures and results of the Cantenna (also known as the Pin-fed Circular Waveguide Antenna) made from a Pringles potato chip container compared with a copper replica. Click here to read the post. We also compared the gain patterns of the copper cantenna (mentioned in the previous post) with a Coaxial cavity horn using the same wave guide dimensions as the Cantenna. Well actually Wilco (a 2nd year engineering student who did some vacation work for us) came up with a clever idea. He used the same copper Cantenna for the waveguide section and made the cavity section to slide over the cantenna forming the Coaxial cavity as shown in the next few images.

Copper cantenna and slideble cavity section which forms the coaxial cavity horn.

Copper cantenna and slideble cavity section which forms the coaxial cavity horn.


Coaxial cavity horn

Coaxial cavity horn


Measurements were done in an anechoic chamber

Measurements were done in an anechoic chamber

It was interesting to see the effect of the added cavity compared with the waveguide (Cantenna) by itself. Most of the back radiated power is directed toward the main beam which now has a much wider, almost flat shape which is ideal for being used as a reflector feed.

Comparison between the Cantenna and Coaxial cavity E-plane pattern measurements

Comparison between the Cantenna and Coaxial cavity E-plane pattern measurements

Author: Robert Kellerman

Taking a peek at your iPhone antenna ? the cost effective way

August 6th, 2010

As something of an antenna enthusiast, I was delighted to discover a source of reliable information about the antennas in many commercial devices ? including the iPhone. The Hong Kong Applied Science and Technology Research Institute (ASTRI) (www.astri.org) has taken apart many commercial phones, done measurements on them, and built 3D CAD models of them. Accurate impedance and pattern measurements are also done in anechoic chambers and published on their website for free. It is great to see a reliable, scientific, study of these devices, rather than anecdotal evidence from an enthusiast in their garage with 50% speculation, 50% measurement resolution error and 50% fact.

It is worth blocking time in your schedule to go to their website and look through some of the documentation. Follow this link to view their antenna R&D gallery.

Author: Sam Clarke

Introducing the new !Phone

July 21st, 2010

You?re probably aware of the iPhone4 antenna saga that?s been in the news the last couple of days. I find all the responses from different bloggers, news reporters and Apple quite amusing.? Something in particular that caught my attention is that most smartphone designers position the antennas at the bottom of the phone. My immediate response is, ?Why do they keep on putting the antenna at the bottom?? Why don?t they simply move it to the top of the phone where users? hands would least likely interfere with the signal??

I think Spencer Webb hit the nail on the head with his explanation in his blog entitled. Apple ?iPhone 4 Antennas…?. He explains why in spite of the fact that it?s the most impractical position, 99% of modern cell phones are manufactured with the antenna placed at the bottom, back of the phone. The FCC (Federal Communications Commission) puts strict limits on the amount of energy from a handheld device that may be absorbed by the body. The absorbed power is determined by measuring something called SAR (Specific Absorption Rate). All new phone models have to pass SAR tests which, surprisingly, are done in the vicinity if a human head model (or phantom) but without a model of a hand holding the device! Cell phone manufacturers are required to print the maximum SAR in the phones user manual and the test results have to be less than 1.6 or 2 watts/kg (in the US and Europe respectively). So in order push down measured SAR, the antennas are moved as far away from the head as possible – the bottom, back of the phone.

It seems to me like the issue that needs to be addressed isn?t the fact that Apple slipped up or how to improve mobile phone reception when the antenna is shielded off by a human hand.? Obviously SAR needs to be regulated but it seems like there?s a lot of hype generated by uninformed individuals who claim that RF radiation from mobile phones is a massive health risk. It seems that this is more of a marketing issue. The SAR value that is printed in a device?s user manual needs to be minimized to keep the public happy in spite of the fact that SAR in the hand is ignored during measurements. In practical situations more power needs to be radiated to compensate for signal loss due to the vicinity of the hand – increasing the actual SAR and reducing the phone?s battery life.

I wonder what would happen if the FCC includes a mandatory hand model in SAR tests – how many smartphones would pass these tests?? Or if they decide to double the allowable maximum SAR limit what would the response be??

Another solution for the iPhone 4 would have been to make the phone work when flipping it upside down (so the screen automatically rotates 180 ?) while on loud speaker or browsing the internet. This would in effect reposition the antenna in its most logical position ? at the top of the phone. Maybe they could then call it the ?!phone? : )

"Hold it like this."                                                   ????????????  by Cartoonist, Konrad Brand

"Hold it like this."                                                    by cartoonist, Konrad Brand

Author: Robert Kellerman

Version 2.2 released!

July 21st, 2010

To all our blog subscribers and those of you who might not be aware, we recently launched Antenna Magus 2.2.0. Version 2.2 includes 6 exciting new antennas and in addition to new FEKO and CST MICROWAVE STUDIO? antenna models that have been added to the database, improved memory management and performance really makes it worthwhile updating to Version 2.2. You can read more about?this release?in the latest Newsletter 2.2

Preview of newsletter 2.2

Preview of newsletter 2.2

Author: Robert Kellerman

Pringles Cantenna measured in an anechoic chamber

July 9th, 2010
Pringles Cantenna in anechoic chamber

Pringles Cantenna in anechoic chamber

We recently did some antenna pattern measurements and included the Pringles cantenna (which I blogged about a few weeks ago) amongst a couple of other great antennas. I doubt if this has ever been done before! The Pringles cantenna performed surprisingly well seeing that we did nothing to improve the conductivity of the can.

We also built a replica of the Pringle version out of copper as show in the image below. The graphs below compare measured S11 and gain patterns between these two antennas.

Pringles and copper cantennas

Pringles and copper cantennas

S11 simulation vs measurements

S11 simulation vs measurements

Pringles vs copper cantenna pattern comparisons

Pringles vs copper cantenna pattern comparisons

Author: Robert Kellerman

Modeling a wire zig-zag antenna

June 24th, 2010
Wire zig-zag antenna

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

Thin-wire model of a zig-zag corner

Detailed triangle mesh model of the 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

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.

Comparison between S11 for measured vs two types of simulation models

S11 comparison between the physical and two types of simulation models.

Author: Robert Kellerman

Test your antenna knowledge

June 17th, 2010
Antenna crossword puzzle

Antenna crossword puzzle

Someone in the office recently found a fun antenna cross word puzzle on http://www.antenna-theory.com/intro/antennacrossword.php and challenged all the antenna engineers to see who could solve it the fastest. I must say my memory was a bit rusty, but one of our engineers completed it in 11 minutes with only one mistake. Follow the link above and see if you can beat his time.

Author: Robert Kellerman

Building a Cantenna from a Pringles can

June 11th, 2010
Cantenna made from a Pringles potato chip can.

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

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

Inside of the Pringles cantenna showing the connector and pin

|S11| measured vs simulated results

|S11| measured vs simulated results

Cantenna sketch with physical dimentions.

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

,

lamictal price

The Marchand balun is not square

June 4th, 2010
Marchand balun image from original published article.

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

Real life Marchand balun

Author: Robert Kellerman