Yagi Array Spreadsheet

The linked Excel Spreadsheet allows you to evaluate the overall pattern when you have two to four directive antennas all connected together. The actual pattern data is derived from the output of a modeling program like NEC (in fact, I just cut and pasted the far field pattern data into the sheet). It assumes there's no mutual coupling, and that there aren't any funny interactions from feedpoint impedances.

It allows you to specify the "boresight" direction of each of the antennas.

It also allows you to specify an amplitude weighting and a phase shift for each antenna. You can "turn off" an antenna by setting the amplitude to zero.

Excel Spreadsheet (yagiarray.xls - 300 kB)

How to generate and load a new antenna pattern

Model your desired antenna in NEC, making sure you do a full azimuth cut at the desired elevation angle (that's phi and theta in NEC terms).

Load the NEC output file into a text editor such as notepad, then copy the entire radiation pattern section into the clipboard: highlight, edit>copy.

Paste the output file into the first column of the "Raw NEC data" sheet, starting at the appropriate point. Use the "Data>Convert text to columns" feature of Excel to break the data into columns. Note that NEC iterates theta first, then phi, so the ordering of the RP data isn't directly usable.

Highlight just the pattern data (not the header lines) and sort by theta (column A) and then phi (column B). (Data>Sort). This will group all azimuth cuts for a given elevation angle together.

Copy and paste the elevation data for just the desired theta (remembering that theta=0 is directly overhead, so you probably want theta=70 or theta=75) into the third sheet of the workbook. Now, adjust the offsets for azimuth so that the pattern is correctly oriented (some NEC models wind up with the main lobe at 180 azimuth). Check the definition of named range "yagipat2" to make sure it includes the three columns indicated, which must be "Azimuth, E field magnitude, and E field phase" in that order. In general, you want azimuths to range from -180 to +180, because that's what the VLOOKUP on the first page expects.

 

radio/antenna/yagiarray.htm - 16 March 2005 - Jim Lux
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