A Closer Look at the HF Skeleton Slot Antenna

[AN-SOF Antenna Simulator Group]

Here, we present another article that has been revised, thanks to the queries we have received. In this case, it focuses on a skeleton slot antenna for HF.

A Closer Look at the HF Skeleton Slot Antenna >

[Simon Shaw]

So how does one calculate what height and width combination to use?

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[AN-SOF Antenna Simulator Group]

Hello! 

In principle, it is essential to maintain the 3:4.5 proportions of each loop. I am currently working on a script that will enable us to run numerous calculations with various loop proportions and determine which one yields the highest antenna gain. Stay tuned!

[Simon Shaw]

Great!

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[Keith Rawlings]

There is a description of the skelton slot  by Sykes G2HCG in the January 1955 issue of Shortwave Magazine that may give some background.

A copy of which can be found here 
https://worldradiohistory.com/UK/Short-Wave-UK/50s/SWM-1955-01.pdf

Keith

G4MIU

[AN-SOF Antenna Simulator Group]

Thank you, Keith, for your contribution. The figure below presents preliminary results obtained after running a script that modifies the aspect ratio of the skeleton slot while maintaining the perimeter of each loop at one wavelength. The upper graph displays the input impedance, while the lower graph illustrates the gain as a function of the aspect ratio (from left to right, the skeleton starts out wide and gets thinner). Note that I use the aspect ratio of each loop, so to obtain Sykes's definition, you should multiply this value by 2.

The reactance curve (Xin in red) remains quite flat, indicating that maintaining the perimeter of each loop at one wavelength (in this case, 15 meters) effectively creates a self-resonant antenna. It appears that for feeding it with a 50 Ohm coaxial cable, an optimal loop aspect ratio is 1.75, which corresponds to a 3.5:1 ratio for the complete skeleton, greater than the 3:1 ratio achieved by Sykes.

The graph of the input resistance (Rin = radiation resistance since I haven't incorporated losses) demonstrates a decrease as the skeleton becomes slimmer. This observation is consistent with the behavior of loop antennas. As the enclosed area of the loop decreases, the radiation resistance also decreases because it is dependent on the loop area. I will soon present this data in a more organized format within an article to better convey the findings.

Warm regards,

Tony