metal housing structure 34 matching groundplane regions may also be formed on the opposed surface of the substrate opposite regions 80 82 the circuit pattern includes a conductor strip 62 having a width selected to provide a characteristic transmission line impedance zt at the substrate edge the strip forms a first i o port 70 the circuit pattern also includes conductor strips 64 and 66 each having an effective electrical length of one quarter wavelength at a frequency within the operating band e g at the center frequency of the operating band the width of strip 64 is selected to provide a characteristic transmission line impedance z 1 the width of strip 66 is selected to provide a characteristic transmission line impedance z 2 the strips 62 64 and 66 thus provide respective quarter wave transformer sections in an exemplary embodiment the conductor strip 66 has a tapered configuration at node b to reduce parasitic shunt capacitance and improve the match ends of the strips 62 64 and 66 are connected at node a a resistor r 1 is connected at the opposite end of the strip 64 at node b resistor r 1 is electrically connected at node b between the strip 64 and the strip 66 a resistor r 2 is electrically connected between the end of strip 66 and the groundplane 80 these resistors r 1 r 2 may be printed onto the circuit board 40 or mounted as discrete chips using for example.