An AC coupler for transmitting high-frequency components of a wideband signal includes a signal conductor and a shielding structure arranged as a transmission line. The signal conductor includes a conductive element and a capacitor configured to block direct current (DC) components of the wideband signal while transmitting high-frequency alternating current (AC) components of the wideband signal. The shielding structure is configured for conducting at least the AC components of the wideband signal while confining electric fields and currents in the shielding structure substantially to a region proximate to the signal conductor. The shielding structure has a width substantially greater than a width of the signal conductor. The difference between the shielding structure width and the signal conductor width may be substantially greater than an offset distance between the signal conductor and the shielding structure.