Thursday, April 23, 2009

WA4PTZ Loop Analysis

Using the sketch Tim provided of his loop antenna, I entered the measurements into the 4nec2 program and got the far field patterns shown below. These are calculated with a 50-ohm generator at the feed point -- no feed line included. I expect that the field patterns would be similar with the feed line included.

160 m horizontal gain. Major lobes approximately north-south.

160 m vertical pattern. Mostly straight up, as expected.

75 m horizontal pattern. 4 lobes

75 m vertical pattern. 2 lobes; angle of radiation moving away from vertical.

40 m horizontal pattern. More lobes appearing.

40 m vertical pattern. Lobes continue to move toward lower angle.

20 m horizontal pattern. Lobes increasing rapidly and some nulls are deep.

Here's the 3D color coded version of the 20 m pattern.

20 m vertical pattern. Radiation angles continue to progress lower.

I have not looked at the patterns yet for higher bands. Below are SWR and impedance plots, without feed line included.

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