The 4-way feed Gerald describes is an effective way to distribute power to
an array where all 4 antennas are to be fed in phase. The system is
described accurately, but I want to add a note.
It may be tempting to not adhere to Gerald's requirement that the initial
lines from each antenna be the same length on their way to the power
splitter. After all, it is 50 ohms all the way.
However, the object is to feed each antenna the same magnitude of current
at the same phase angle as all the other antennas. On a perfectly matched
line, the current magnitude remains the same, but the phase angle is
continuously changing. The voltage phase angle is also changing by the
same amount, which is what yields the impedance magnitude with a phase
angle of zero.
However, only equal line lengths will ensure that each antenna receives
its current at the same phase angle as the others. It does not really
matter what that phase angle is as long as it is the same for all the
antennas in the array.
Of course, be sure to check each antenna's feedpoint Z before connecting
the power distribution system.
-73-
LB, W4RNL
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