A waveguide structure (10) that provides a transition from a polymeric waveguide (26) to a coaxial connection (48). The coaxial connection (48) includes an outer conductor (50) electrically connected to a top ground plate (36) of the waveguide (26) and an inner conductor (52) that extends into the polymeric material within the waveguide (26). The inner conductor (52) is electrically connected to a capacitive plate (56), and the capacitive plate (56) is electrically connected to an elongated conductive probe (58). The conductive probe (58) is electrically connected to a conductive post (60), which is electrically connected to a bottom ground plate (38) opposite to the top ground plate (36). The conductive probe (58) extends in a direction transverse to the propagation direction of electromagnetic waves, and acts to pick up the energy in the electromagnetic radiation. The capacitive plate (56) provides a shunt capacitance that resonates out the inductance caused by the conductive probe (58) and the inner conductor (52). The conductive probe (58) is positioned relative to a backshort surface (44) of the waveguide (26) a distance that is less than a quarter wavelength of the electromagnetic radiation of interest. The position and the dimensional characteristics of the probe (58), the capacitive plate (56), the inner conductor (52) and the conductive post (60) are optimized such that the electromagnetic radiation of interest is impedance matched to the coaxial connection (48) to minimize losses.
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