MOWWA Fractal Antennas

PCB Fractal Loop Antenna

Minkowski loop type

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Model II
	The aim of the project is test if fractal loop antennas can work acceptably on HF bands. My model is a Minkowski loop model starting with a square shape. Test Report
	The second model was designed with more wide tracks than model I to strengthen the overall antenna. Calculations were done for 28.5MHz, ¼ wavelength, three iterations 0.8 indentation and 1.8mm wide PCB tracks given a total size of 197mm x 197mm, 7.756inch, on glass fiber board FR4.The PCB was designed with Protel DXP.
	The specifications for the copper clad board are: Base material: FR4 epoxy all woven glass laminate to BS4584. Tickness: 1.6mm. ;1/16 inch. Copper cladding/square ft: 1oz ;35 microns. Dielectric constant @1MHz: 5.0 Dissipation factor@1MHz: 0.020
	The measurement gave 1.44uH of inductance and Q of 70@28MHz. Z and Rs-Xs are show below, no resonances were observed.

Impedance		Rs,Xs
	Measurament Spreadsheet		Measurament Spreadsheet

Next I am trying to find some "Greek Alphabet Letter-Match" system to adapt the High Z of the antenna to 50Ω without capacitors.
I have start to experimenting with toroidal RF transformers.

Model I

Test Report

Calculations were done for 28.5MHz, ¼ wavelength, three iterations and 0.8 indentation given a total size of 175mm x 175mm, 25.4inch with 1mm wide pcb tracks on glass fiber board FR4 .The PCB was dessigned with Protel DXP.

According with the scarce literature that I found related to built 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 behavior became narrow band.

First test was measurements of the antenna as is without tuning components, impedance and RS-Xs, equivalent series resistance and reactance, with my Vector Network Analyzer and inductance and Q factor with L/C Meter IIB and HP 4342A Inductance/Q meter.

The measurement gave 1.78uH of inductance and Q of 50. Z and Rs-Xs are show in pictures 1 and 2, no resonances were observed.


Picture 1 (click to enlarge)	Picture 2 (click to enlarge)

All indicates that the antenna is high reactive and so a compensating capacitive reactance must be place in circuit, capacitor C2 only.

Fractal Loop schematic.

(click to enlarge)

On picture 3 we can see that the resonant frequency is now 43.250MHz and the return loss is -39dB equivalent to a SWR of 1.02.

Picture 3

(click to enlarge)

Because it is resonating out of the band of interest thanks to the stray capacitance, a second capacitor was introduced in circuit, C1 schematic picture.

The result is show in picture 5, -50dB Return loss at 28.4MHz equivalent to a SWR less that 1.05, picture 4.

Picture 4

(click to enlarge)

I don't have experience working with loop antennas but its behavior in the shack show few interference with surrounding objects, that probably means that the magnetic field predominates.

Although first tests are promising, for field test purposes I am designing the next antenna, model 2, with more wide PCB tracks but keeping the same size.

PCB Fractal Loop Antenna

Minkowski loop type

Model II

Test Report

Impedance

Rs,Xs

Model I

Test Report

Calculations were done for 28.5MHz, ¼ wavelength, three iterations and 0.8 indentation given a total size of 175mm x 175mm, 25.4inch with 1mm wide pcb tracks on glass fiber board FR4 .The PCB was dessigned with Protel DXP.

First test was measurements of the antenna as is without tuning components, impedance and RS-Xs, equivalent series resistance and reactance, with my Vector Network Analyzer and inductance and Q factor with L/C Meter IIB and HP 4342A Inductance/Q meter.

The measurement gave 1.78uH of inductance and Q of 50. Z and Rs-Xs are show in pictures 1 and 2, no resonances were observed.

Picture 1

Picture 2

All indicates that the antenna is high reactive and so a compensating capacitive reactance must be place in circuit, capacitor C2 only.

Fractal Loop schematic.

On picture 3 we can see that the resonant frequency is now 43.250MHz and the return loss is -39dB equivalent to a SWR of 1.02.

Picture 3

Because it is resonating out of the band of interest thanks to the stray capacitance, a second capacitor was introduced in circuit, C1 schematic picture.

The result is show in picture 5, -50dB Return loss at 28.4MHz equivalent to a SWR less that 1.05, picture 4.

Picture 4

I don't have experience working with loop antennas but its behavior in the shack show few interference with surrounding objects, that probably means that the magnetic field predominates.

Although first tests are promising, for field test purposes I am designing the next antenna, model 2, with more wide PCB tracks but keeping the same size.

Any comments will be welcome.