Antenna scaling - confusion

[Roger Freeman]

Hello All

I'm loosely familiar with the notion of scaling e.g. an antenna at one particular wavelength can be scaled to a new frequency my multiplying all the dimensions by the ratio of new: old lambda. So for example a dipole ends up half as long at twice the frequency - and wire diameter would also half:

https://www.antennex.com/w4rnl/col0107/amod107.htm

But what about something like a helical - do I similarly just scale the helix length and helix diameter and number of turns on it (and the conductor diameter too)? Or is it the case that I scale the length of wire wrapped up into the helix and then wind that new length onto a new helical former (whose length and diameter is scaled), adjusting pitch to suit?

In the former case the length of wire would change by (scale factor)^2 which suggests the scaling should be based on conductor length.

Please can someone help me clear up my confusion? Thanks!

 

[Mark W. Ingalls]

Scale everything with 'length' dimensions. Do not scale dimensionless numbers or angles. You are seeking congruency...

 

[davenn]

Hello All

I'm loosely familiar with the notion of scaling e.g. an antenna at one particular wavelength can be scaled to a new frequency my multiplying all the dimensions by the ratio of new: old lambda. So for example a dipole ends up half as long at twice the frequency - and wire diameter would also half:

.................Thanks!

You wouldnt decrease the diameter of the wire unless due to construction space limitations, it was really necessary.
Wire (tubing etc) diameter has a huge effect on bandwidth of an antenna, so decreasing the diameter would also decrease the bandwidth,
something you may not really want, depending on your situation.

Dave

 

[Roger Freeman]

Mark - thanks for the feedback. I'll scale the helix former's length and diameter and also scale the conductor length therein

Dave - agreed; the conductor diameter will tend to dominate antenna Joule losses and would best be left as large as possible.

What I should perhaps have mentioned is that in my case,somewhat unusually, I am looking for maximum Q factor in the helix (I'm looking at it as a slow wave resonator in a bounded cavity i.e. as if it were part of a helical filter, rather than as a true radiating structure with power being developed in the far field.

Thanks both

 

[maurymw]

Antennas can be scaly from one regularity to another by showing their measurements with regards to wavelengths. Thus if we have an aerial style for one regularity, it is simple to turn the style to any other regularity basically by making the aerial the same dimension with regards to wave length.