Interesting compact log-periodic antenna

This is an interesting patent for a compact log periodic antenna. The longer elements get a wire box on the end to shorten them…

Foreshortened dipole antenna with triangular radiating elements and tapered coaxial feedline

US 4907011 A


A foreshortened log-periodic antenna which includes variously configured dipole elements and a tapered feedline is disclosed. The dipole elements are arranged in four regions. A first region, located nearest to a feed end of the antenna, includes solid triangular dipoles having constant base-to-height ratios. A second region, adjacent to the first region, includes solid triangular dipoles having decreasing base-to-height ratios. A third region, located adjacent to the second region, includes a single linear dipole. A fourth region, located adjacent to the third region and nearest to a low frequency end of the antenna, includes foreshortened dipoles. The feedline may be implemented either in coaxial or microstrip form so that a lower characteristic impedance is pressed at the feed end of the antenna than at the low frequency end of the antenna. Specifically, for a coaxial feedline having individual conductors separated by a distance “d” at the feed end of the antenna, the individual conductors taper relative to each other so that they are separated by a distance of 2d-5d at the low frequency end of the antenna.

Looks like by using fat dipoles at each end, the whole thing can be smaller.

Compact log periodic antenna

Compact log periodic antenna

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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One Response to Interesting compact log-periodic antenna

  1. Larry Ledwick says:

    Similar to a top loaded CB antenna, or a top hat vertical you can compress the physical length of an antenna element by putting a coil (or T section) in it so it acts as a longer physical element in a smaller space. Depending on the shape of that modified section, you add either capacitance (T top hat on 80 or 160 meters vertical) or inductance in the case of the loading coil. That additional capacitance / inductance combined with the physical length can be used to tweak the resonant length of the antenna to the frequency of interest.

    It would also perhaps broaden the band width of the antenna a bit as well.

    As noted with some to the other fractal designs there are near infinite possible combinations that can work, and the RF will find some way/place on the antenna array that it is happy to radiate or receive from.

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