A microstripline transmission line arrangement carries a signal having a fundamental frequency. The arrangement includes a first microstripline transmission line, a second microstripline transmission line, and a coaxial electrically conductive conduit interconnecting the first transmission line and the second transmission line. The conduit includes a signal conductor and an electrically grounded shield substantially surrounding the signal conductor. The conductor and the shield are positioned relative to each other to thereby comprise a means for lowpass filtering the signal. A cutoff frequency of the lowpass filtering is less than a third harmonic of the fundamental frequency.