line section 70 second tuning means 68 is a parallel resonant lc circuit arranged for double tuning the impedance of second monopole 22 and the length of line 70 is chosen so that signals reaching monopole 22 have the desired relative phase as compared to signals at monopoles 20 and 24 in operation of the fig6 array antenna the two quarter wave transformers 56 and 58 force the currents ia and ic in the third and first monopoles 24 and 20 to be dependent substantially wholly on the voltage at the common voltage point 42 thus ia and ic are forced to be in the ratio ic ic zoc zoa where the latter are the respective transmission line impedances of the transformers 58 and 56 the half wave line 60 introduces a reversal in the polarity of ic at element 20 relative to ia at element 24 the ratio of ib to the ia and ic currents is not forced and cannot be forced because of the 90 u00b0 phase difference needed to obtain the desired signal component relationship of ia j ib 2 and i j as shown in fig5 however if ia ic then the second monopole 22 will effectively be at a null point midway between the equal and opposite signals at elements 20 and 24 and no net signal from those monopoles will be coupled to element 22 in this case there is no need for ib to element 22 to be forced as a specific example computations of impedance were made using a commercial computer program for three monopoles arranged as in fig5 with currents as in fig5 the computations were made.