Electromagnetic fields and transmission characteristics of a filter composed of transmission lines

When two transmission lines (TLs) such as microstrip lines are set in the neighborhood, coupling or crosstalk fields may be generated between them. To investigate fields caused by passive circuits, coupled printed-circuit traces are focused upon. The fields can be obtained by estimating vector potentials of currents in the line and the terminal sections, where the terminals are fabricated like a configuration as "via". The filter performance characteristics and the fields at frequencies of pass and stop bands of the filters are measured and calculated; the results show that the currents at the line terminals cause serious effects, and the fields exist even at frequencies of the stop band.