Apparatus for transmitting a high-frequency signal, comprising: an electrically non-conductive carrier (4; 4'; 12) through which a passage (5; 50; 50') from a first surface (A1; 12-1) of the carrier (4; 4'; 12) to a second surface (A2; 12-2) of the carrier (4; 4'; 12) is formed; a first conductive layer which is formed on the first surface (A1; 12-1) of the carrier (4; 4'; 12) and has a first section (19; 19'-1) and a second section (19'-2) which are galvanically isolated from one another; a first closure element having a first reflector element (R1; 36) which is designed to reflect electromagnetic waves incident from the direction of the passage (5; 50; 50') in the direction of the passage (5; 50; 50'); a transmitting element (2; 32) which is located on the first surface (A1; 12-1) of the carrier (4; 4'; 12) between the carrier (4; 4'; 12) and the first reflector element (R1; 36) and to which the high-frequency signal can be applied via the first section (19; 19'-1) of the first conductive layer; and a receiving element (3; 42; 21'-3) which is located upon or on the second surface (A2; 12-2) of the carrier (4; 4'; 12) and which is galvanically isolated from the transmitting element (2; 32); wherein the first closure element comprises a further non-conductive carrier, and wherein the first closure element, on a side (34-i) of the further non-conductive carrier that faces the passage (5; 50; 50'), comprises a structured metal layer with a first section and a second section, wherein the first section of the structured metal layer comprises the transmitting element (2; 32) and is galvanically connected to the first section (19, 19'-1) of the first conductive layer via a first galvanic connection, and the second section of the structured metal layer is connected to the second section (19'-2) of the first conductive layer via a galvanic connection; and wherein the applied high-frequency signal can be transmitted through the passage (5; 50; 50') through the carrier (4; 4'; 12) as an electromagnetic wave to the receiving element (3; 42; 21'-3) by means of the transmitting element (2; 32). an electrically non-conductive carrier (4; 4'; 12) through which a passage (5; 50; 50') from a first surface (A1; 12-1) of the carrier (4; 4'; 12) to a second surface (A2; 12-2) of the carrier (4; 4'; 12) is formed; a first conductive layer which is formed on the first surface (A1; 12-1) of the carrier (4; 4'; 12) and has a first section (19; 19'-1) and a second section (19'-2) which are galvanically isolated from one another; a first closure element having a first reflector element (R1; 36) which is designed to reflect electromagnetic waves incident from the direction of the passage (5; 50; 50') in the direction of the passage (5; 50; 50'); a transmitting element (2; 32) which is located on the first surface (A1; 12-1) of the carrier (4; 4'; 12) between the carrier (4; 4'; 12) and the first reflector element (R1; 36) and to which the high-frequency signal can be applied via the first section (19; 19'-1) of the first conductive layer; and a receiving element (3; 42; 21'-3) which is located upon or on the second surface (A2; 12-2) of the carrier (4; 4'; 12) and which is galvanically isolated from the transmitting element (2; 32); wherein the first closure element comprises a further non-conductive carrier, and wherein the first closure element, on a side (34-i) of the further non-conductive carrier that faces the passage (5; 50; 50'), comprises a structured metal layer with a first section and a second section, wherein the first section of the structured metal layer comprises the transmitting element (2; 32) and is galvanically connected to the first section (19, 19'-1) of the first conductive layer via a first galvanic connection, and the second section of the structured metal layer is connected to the second section (19'-2) of the first conductive layer via a galvanic connection; and wherein the applied high-frequency signal can be transmitted through the passage (5; 50; 50') through the carrier (4; 4'; 12) as an electromagnetic wave to the receiving element (3; 42; 21'-3) by means of the transmitting element (2; 32).