Lithographic spiral antennas at short wavelengths

We have extended the high efficiency of lithographic antennas to mid‐infrared wavelengths. Pattern measurements made at 9.5 μm wavelength on a 65°, self‐complementary, spiral antenna exhibit a ratio of response to orthogonal linear polarizations of 1.35 dB, a beamwidth of 85° (3 dB full width), a directivity of 8.2 dB, and surprisingly, a close resemblance to the theoretical pattern for a 65° spiral in free space. Direct detection measurements made with an ambient temperature blackbody source yield an antenna efficiency of 52±7%, when corrected for incomplete filling of the antenna beam by the source, at a mean effective wavelength of 19 μm.