Abstract: A gyrator circuit usable in a resonant filter circuit comprises a first and a second transconductance amplifier circuit, A and B, respectively, having opposite conductances, which amplifiers are arranged in parallel between a first terminal a and a second terminal b and comprise a first capacitance C.sub.1 arranged between said first terminal a and an earth terminal m, which gyrator circuit simulates an inductance L.sub.g arranged between said second terminal b and said earth terminal m and comprises means for controlling the quality factor Q of said inductance, characterized in that the first transconductance amplifier circuit A comprises two series-connected inverting amplifier stages P.sub.1 and P.sub.2, in that the second transconductance amplifier circuit B comprises an inverting amplifier stage P.sub.3, and in that the means for controlling the quality factor Q comprise a first means P.sub.5 for influencing the output conductance q.sub.2 of the gyrator and a second means P.sub.

Abstract: An impedance-matching microstrip network for matching a predetermined impedance to a lower impedance over a wide frequency band having a tapered line section for transposing the predetermined impedance to a higher impedance. At least one quarter wave line section is coupled to the narrow end of the tapered line section for transposing the higher impedance to the lower impedance.