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Graphics package for spiral antenna design.

Graphics package for spiral antenna design.

Graphics package for spiral antenna design.

Ddear Engineers,

I am trying to design a planar circular spiral antenna with a certain (pretty wide) beamwidth.This will mean I have to sacrifice gain –however, I don’t know from what direction the radio waves will come from so I need the wide beamwidth.

The maths for a spiral seems easy. –One would use a polar coordinate system and plot lines with points at a = k(theta) and  b=[k(theta) – x]……The spiral “trace” would then simply be the area in between these lines……(the width of the trace being “x”)

My problem is that I do not know of a graphics package which allows me to plot this spiral. –I would be grateful if anybody knew of a package that I could use to plot this mathematical function. –The package would also (hopefully) have the facility to allow me to “shade in” the area between my two lines so as to give me a spiral trace.  –I would then proceed to printing this spiral shape on to cooper clad dielectric and eventually etching away the copper that wasn’t needed for the spiral.

My next problem would be to find the relationship between beamwidth and the following spiral parameters:-

Width of spiral trace.
Gap length between adjacent spiral traces.
Number of curls.
Diameter of outer curl.
Thickness (depth) of spiral trace.

There must be some mathematical relationship between my spiral equations given above and the beamwidth….

Alternatively, does anybody know of any spiral antenna software which can allow me to do all this without going through all of the long prototype testing operations which I will inevitably need to go through?

RE: Graphics package for spiral antenna design.

Why a spiral? Did someone say go make a spiral?

I don't mean to be rude, but when I first start a job taking the easy route that gets you there is my first thought. I'd always opt for a simpler wide beam antenna like a monopole or patch or notch antenna. Spirals usually need a cavity, printed antenna, absorber, 180 degree hybrid. They are actually alot more complicated and have more parts than many other antennas.

Do you need Circular polarization?
do you need hemispherical coverage?
What % bandwidth is needed?
The above ground speed of a flying swallow is ?


RE: Graphics package for spiral antenna design.

I would think how to design the antenna is my first priority, not how to draw it.  Maybe in doing some research into how to design the antenna you may come up with a better method, one that doesn't even require drawing a spiral.

Dan - Owner

RE: Graphics package for spiral antenna design.

Thanks guys, -I am certain that a cavity-backed spiral is basically the only antenna choice available to me.
-I need circular polarisation because I dont know what    
 polarity the incoming radio waves will be.
-Also I do need hemispherical coverage.
-Incoming radio waves could be anywhere over a wide frequency range, so a spiral will give most chance of always picking something up. (in fact the range is 0.6 to 4.5GHz.)

The antenna also needs to be pretty robust, which is quite inherent in a cavity backed planar spiral. The planar dielectric will give good support for it.

I am pretty certain that a planar spiral is my only option.

I definetely need to draw the spiral as its image needs to be printed onto copper clad dielectric for etching purposes.

Once i find a way of drawing my mathematical spiral shapes then i can start producing them and seeing how they respond to pattern testing.  -Then i can find a relationship between the mathematical function for the spiral and its beamwidth & frequency properties. -Until i can find a way of drawing the spirals , i am completely stuck and cant produce/test/analyse anything.

RE: Graphics package for spiral antenna design.

"...mathematical relationship [or] ...function..."

Do you mean something like NEC (numerical electromagnetic code) or other similar programs? Likely the spiral and other curves would have to be approximated by a series of linear segments.


Others might have more specific advice as to the optimum software to use.

As far as preparing the model data based on your input parameters, a simple program should do it. Basic or MS-Excel or whatever you want. Something with a graphical output so you can see what you're doing. Some might recommend a CAD or drawing program, but a custom routine might be faster the 20th time you need to use it. I'd allow about 5-10 hours to write that from scratch. YMMV.

Also, double-check the www for on-line calculators. You never know... I didn't see any with a quick check, but it might be worth digging a bit deeper.

Starting point:

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