A circuit module including a transition for coupling a microwave signal into a hollow waveguide, the circuit module comprising: a conductive ground plane slab having an edge; a dielectric substrate coupled to the conductive ground plane slab, the dielectric substrate including an extended portion extending beyond the edge of the ground plane slab and configured to be inserted through an open end of the hollow waveguide and into a hollow passage of the hollow waveguide; wherein the transition comprises: a transmission line formed on the dielectric substrate; and a half-notch antenna formed on the extended portion of the dielectric substrate and coupled to the transmission line; and wherein the half-notch antenna comprises: a first tapered conductor formed on a first surface of the dielectric substrate and gradually changing in width from wider to narrower along a direction of propagation of the microwave signal; a second tapered conductor formed on a second surface of the dielectric substrate and gradually changing in width from wider to narrower along the direction of propagation of the microwave signal, the second surface of the dielectric substrate on a substantially opposite side from the first surface; and at least one conductive via connecting the first tapered conductor and the second tapered conductor. a conductive ground plane slab having an edge; a dielectric substrate coupled to the conductive ground plane slab, the dielectric substrate including an extended portion extending beyond the edge of the ground plane slab and configured to be inserted through an open end of the hollow waveguide and into a hollow passage of the hollow waveguide; wherein the transition comprises: a transmission line formed on the dielectric substrate; and a half-notch antenna formed on the extended portion of the dielectric substrate and coupled to the transmission line; and a transmission line formed on the dielectric substrate; and a half-notch antenna formed on the extended portion of the dielectric substrate and coupled to the transmission line; and wherein the half-notch antenna comprises: a first tapered conductor formed on a first surface of the dielectric substrate and gradually changing in width from wider to narrower along a direction of propagation of the microwave signal; a second tapered conductor formed on a second surface of the dielectric substrate and gradually changing in width from wider to narrower along the direction of propagation of the microwave signal, the second surface of the dielectric substrate on a substantially opposite side from the first surface; and at least one conductive via connecting the first tapered conductor and the second tapered conductor. a first tapered conductor formed on a first surface of the dielectric substrate and gradually changing in width from wider to narrower along a direction of propagation of the microwave signal; a second tapered conductor formed on a second surface of the dielectric substrate and gradually changing in width from wider to narrower along the direction of propagation of the microwave signal, the second surface of the dielectric substrate on a substantially opposite side from the first surface; and at least one conductive via connecting the first tapered conductor and the second tapered conductor.