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The door on your microwave has thousands of small holes through the metal shield yet you're safe on the other side of it too. The cone forms a tapered skeleton sleeve and the four radials are close enough to confine most of the lower 1/4 wave radiation on the center vertical inside the cone as a result.
In this case you have to avoid the idea of looking at the aluminum tube as a single element on the cone.

You must view all four radials as a single element that RF interprets as a virtually complete tapered cone without voids. It really appears as simple as coax with a good deal of CMC flowing on the outside braid. The differences are this braid is a tuned 1/4 wave cone that provides an ideal low impedance path to attract the CMC. The tapered shape allowed some impedance transformation to occur inside but it mostly allowed for a 90 degree delay feeding the top 1/2 wave. This is nice since it brings the top into phase with the CMC already on the outside of the coax or cone in the case of this design.

<blockquote data-quote="Shockwave" data-source="post: 494713" data-attributes="member: 10882">The door on your microwave has thousands of small holes through the metal shield yet you&#039;re safe on the other side of it too. The cone forms a tapered skeleton sleeve and the four radials are close enough to confine most of the lower 1/4 wave radiation on the center vertical inside the cone as a result. In this case you have to avoid the idea of looking at the aluminum tube as a single element on the cone.&nbsp;You must view all four radials as a single element that RF interprets as a virtually complete tapered cone without voids. It really appears as simple as coax with a good deal of CMC flowing on the outside braid. The differences are this braid is a tuned 1/4 wave cone that provides an ideal low impedance path to attract the CMC. The tapered shape allowed some impedance transformation to occur inside but it mostly allowed for a 90 degree delay feeding the top 1/2 wave. This is nice since it brings the top into phase with the CMC already on the outside of the coax or cone in the case of this design.</blockquote>

[QUOTE="Shockwave, post: 494713, member: 10882"] The door on your microwave has thousands of small holes through the metal shield yet you're safe on the other side of it too. The cone forms a tapered skeleton sleeve and the four radials are close enough to confine most of the lower 1/4 wave radiation on the center vertical inside the cone as a result. In this case you have to avoid the idea of looking at the aluminum tube as a single element on the cone. You must view all four radials as a single element that RF interprets as a virtually complete tapered cone without voids. It really appears as simple as coax with a good deal of CMC flowing on the outside braid. The differences are this braid is a tuned 1/4 wave cone that provides an ideal low impedance path to attract the CMC. The tapered shape allowed some impedance transformation to occur inside but it mostly allowed for a 90 degree delay feeding the top 1/2 wave. This is nice since it brings the top into phase with the CMC already on the outside of the coax or cone in the case of this design. [/QUOTE]

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