A tapered airline directional coupler comprising: a housing having a length with an input end and an output end disposed at opposite ends of the length, the housing having a slot formed therein extending between the input end and the output end, wherein a cross-sectional area of the slot varies along the length of the housing; a main conductor disposed within the slot and extending between the input end and the output end of the housing, the main conductor being in electrical communication with an input port connector mounted on the housing at the input end thereof and with an output port connector mounted on the housing at the output end thereof, the main conductor having a cross-sectional area that varies along the length of the housing; and a coupled conductor disposed within the slot and spaced apart from the main conductor, the coupled conductor being in electrical communication with and extending between a forward coupling port connector mounted on the housing adjacent to the input end thereof and a reverse coupling port connector mounted on the housing adjacent to the output end thereof, the coupled conductor having a cross-sectional area that varies along the length of the housing; characterized by the slot having (i) a lower section, which has a generally round cross-section of substantially constant diameter, which receives the main conductor, and (ii) an upper section, which has a generally rectangular cross-section with a width which tapers from a larger width adjacent to the input end of the housing to a smaller width adjacent to the output end of the housing, which receives the coupled conductor; the main conductor having a generally circular cross-section and a diameter that varies depending upon where the cross-section is taken along the length of the housing; and the coupled conductor having a generally rectangular cross-section and a thickness which is substantially constant along the length of the housing and a height which tapers from a larger height adjacent to the input end of the housing to a smaller height adjacent to the output end of the housing. a housing having a length with an input end and an output end disposed at opposite ends of the length, the housing having a slot formed therein extending between the input end and the output end, wherein a cross-sectional area of the slot varies along the length of the housing; a main conductor disposed within the slot and extending between the input end and the output end of the housing, the main conductor being in electrical communication with an input port connector mounted on the housing at the input end thereof and with an output port connector mounted on the housing at the output end thereof, the main conductor having a cross-sectional area that varies along the length of the housing; and a coupled conductor disposed within the slot and spaced apart from the main conductor, the coupled conductor being in electrical communication with and extending between a forward coupling port connector mounted on the housing adjacent to the input end thereof and a reverse coupling port connector mounted on the housing adjacent to the output end thereof, the coupled conductor having a cross-sectional area that varies along the length of the housing; characterized by the slot having (i) a lower section, which has a generally round cross-section of substantially constant diameter, which receives the main conductor, and (ii) an upper section, which has a generally rectangular cross-section with a width which tapers from a larger width adjacent to the input end of the housing to a smaller width adjacent to the output end of the housing, which receives the coupled conductor; (i) a lower section, which has a generally round cross-section of substantially constant diameter, which receives the main conductor, and (ii) an upper section, which has a generally rectangular cross-section with a width which tapers from a larger width adjacent to the input end of the housing to a smaller width adjacent to the output end of the housing, which receives the coupled conductor; the main conductor having a generally circular cross-section and a diameter that varies depending upon where the cross-section is taken along the length of the housing; and the coupled conductor having a generally rectangular cross-section and a thickness which is substantially constant along the length of the housing and a height which tapers from a larger height adjacent to the input end of the housing to a smaller height adjacent to the output end of the housing.