Fractal antenna experiment

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    The aim of the project is test if fractal antennas can work acceptably on HF bands.

I started building two Minkowski loop type models on standard FR4 epoxy glass fibre board for 28.5MHz, ¼ wavelength.
Maximum size is limited to DIN A4. PCBs were designed on Protel DXP.
According with the scarce literature that I found related to practical building of fractal antennas, fractal loops geometry have the characteristic that its perimeter tends to increase to infinity but maintaining the volume fill, this enlargement in length reduce the volume occupied for the antenna then its size must be smaller and impedance will higher than a classic loop, therefore easier to match to 50 Ohms, in addition with three iterations in shape its behaviour became narrow band.


  Model I

Three iterations and 0.8 indentation, size is 175mm x 175mm, 25.4inch
PCB tracks are 1 mm.

  Model II

The second model was designed with more wide tracks than Model I to strengthen the overall antenna.
Three iterations 0.8 indentation and 1.8mm wide PCB tracks given a total size of 197mm x 197mm, 7.756inch.

  First test was measurement of the antennas “as is” without tuning elements.  
  Xs-RL plot    
  Xs-RL   Zs-RL  
All indicates that the antennas are highly reactive so a compensating capacitive reactance must be place in circuit.
  Xs-RL plot   ZS-RL plot  
  Xs-RL   Zs-RL  

  Next I want to try with dipoles. I am designing two ½ wave models, Archimedean spiral dipole and squared dipole, at the same frequency and DIN A4 maximum size. Soon we will see results.  

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