Finite element analysis of high power striplines for beamformers

The application of the FEM to calculate the characteristic impedance and the cut-off frequency values for the lowest order TE mode in stripline transmission lines has been described. The results obtained have been used to identify possible problems in the design of the stripline beamformers discussed by Davies (1988). The change in impedance which occurs because of the irregularly positioned dielectric supports has been evaluated. The use of a notch in the strip conductor positioned at the dielectric support is shown to reduce this impedance mismatch. The cut-off frequency of the lowest order TE modes has also been examined in both single and coupled striplines. The decrease in the cut-off frequency for identical coupled lines must be taken into account in the design of the output arms of the power splitter. Further work is currently being done to extend the analysis of higher modes to non-identical coupled lines which occur when the power splitter is no longer equi-amplitude