A spectrometer , comprising: an AC coupler for transmitting high-frequency components of a wideband signal; and an ion detector configured to communicate with an input end of the AC coupler ; wherein the AC coupler comprises: the input end for receiving the wideband signal; an output end for transmitting an output signal; a signal conductor in electrical communication between the input end and the output end, the signal conductor comprising a conductive element and a signal conductor capacitor configured to block direct current, DC, components of the wideband signal while transmitting high-frequency alternating current, AC, components of the wideband signal; and a shielding structure defining a signal return path between the input end and the output end, the shielding structure being configured for conducting at least the AC components of the wideband signal in the signal return path, wherein: the signal conductor has a signal conductor width; the shielding structure has a width substantially greater than the signal conductor width and is configured to confine electric fields and currents in the shielding structure substantially to a region proximate to the signal conductor; and the signal conductor and the shielding structure are arranged as a transmission line. an AC coupler for transmitting high-frequency components of a wideband signal; and an ion detector configured to communicate with an input end of the AC coupler ; wherein the AC coupler comprises: the input end for receiving the wideband signal; an output end for transmitting an output signal; a signal conductor in electrical communication between the input end and the output end, the signal conductor comprising a conductive element and a signal conductor capacitor configured to block direct current, DC, components of the wideband signal while transmitting high-frequency alternating current, AC, components of the wideband signal; and a shielding structure defining a signal return path between the input end and the output end, the shielding structure being configured for conducting at least the AC components of the wideband signal in the signal return path, wherein: the signal conductor has a signal conductor width; the shielding structure has a width substantially greater than the signal conductor width and is configured to confine electric fields and currents in the shielding structure substantially to a region proximate to the signal conductor; and the signal conductor and the shielding structure are arranged as a transmission line. the input end for receiving the wideband signal; an output end for transmitting an output signal; a signal conductor in electrical communication between the input end and the output end, the signal conductor comprising a conductive element and a signal conductor capacitor configured to block direct current, DC, components of the wideband signal while transmitting high-frequency alternating current, AC, components of the wideband signal; and a shielding structure defining a signal return path between the input end and the output end, the shielding structure being configured for conducting at least the AC components of the wideband signal in the signal return path, wherein: the signal conductor has a signal conductor width; the shielding structure has a width substantially greater than the signal conductor width and is configured to confine electric fields and currents in the shielding structure substantially to a region proximate to the signal conductor; and the signal conductor and the shielding structure are arranged as a transmission line. the signal conductor has a signal conductor width; the shielding structure has a width substantially greater than the signal conductor width and is configured to confine electric fields and currents in the shielding structure substantially to a region proximate to the signal conductor; and the signal conductor and the shielding structure are arranged as a transmission line. <EOS>