The electric field contribution of the differential feeding
system shows a 180° phase difference in each branch
therefore the antennas are excited with 180° phase shift and
it is caused that the radiation pattern of each antenna are
added destructively. This problem is solved with an
additional Ȝ/2 differential line. Fig. 6 shows the radiation
pattern of two antenna elements with and without Ȝ/2 line.
The required characteristic impedance is found as: