Antennas for experimentation

[joeqsmith]

Shown are my latest experimental slip joints for easy tuning.   Also shown are the new high tech materials used for spacers.

[tautech]

Looking good Joe. 

I used 1/8" brazing rod so to be able to fit 2 screw cable joiner inners for the feed points whereas I could've used 1/4" solid copper rod but needed to manufacture adjustable feed points which really wouldn't be a problem on the lathe but as the J Pole was quite small so the the 1/8" brazing rod was quite adequate.

[joeqsmith]

Maybe some hobby brass tubing and make everything adjustable.   Come up with something you like, solder it up.   This one can be tuned over a fairly wide range but may not radiate very well.   

[joeqsmith]

Second Slim Jim. 

[joeqsmith]

The Vivaldi is a bit more directional.   

These last two antennas were taken with a 5deg resolution, or 36 elevation and 72 azimuth.  Taking 2592 data points by hand would be a nightmare.   Added one more zoomed in a bit on the backside.

[joeqsmith]

Taking the same Vivaldi and moving to a half meter away from the reference antenna does have an effect on the pattern.  Considering that I am testing these in my home lab it's actually closer than I would have expected.   Shown from two different viewing angles along with a low res 2D plot of the same setup.    Where the SlimJimII was tested a bit over 900MHz,  this Vivaldi is being tested at 2.4GHz.   

The low cost VNAs don't have very good noise specs and moving it further away could be a problem.  My Signal Hound would do a better job making these measurements but it's fun playing with this $120 unit.    The LiteVNA's firmware limits measurements to 9.3GHz.  I have included data comparing it's noise floor against my old Agilent PNA, both using a 1k IF and again with the PNA set to 100Hz.   Also shown is the SA with nothing but a 10dB attenuator attached to it, using the realtime mode with a 2.4GHz center.  Note it still picks up interference from my router.   

Article using a drone to map the radiation pattern.   
https://signalhound.com/news/antenna-measurement-and-characterization-with-uavs/

[joeqsmith]

May not look as pretty,  but an effective demo showing the radiation pattern of a dipole.   



Walter Lewin Electromagnetic Waves, Solutions to Maxwell's Equations, Polarization

[joeqsmith]

Attempting to use the LiteVNA to sweep an X-band horn.       It's a tradeoff.  The performance of the Lite is pretty poor but still, $120.

[Thedrunkenflea]

Very interesting stuff - i might have found my next project or two! 

[joeqsmith]

Looking forward to seeing what you come up with.