Lithographic antennas for submillimeter and infrared frequencies

The paper presents a semi-tutorial review of lithographic feed antennas, with an emphasis on issues that become important at extremely high frequencies. One of the most fundamental facts about antennas deposited on a dielectric substrate is that they couple primarily into the dielectric half-space rather than into the air. The stronger coupling into the dielectric implies that some special form of substrate geometry is required in order to achieve high coupling efficiencies. A number of substrate lens geometries are investigated, as well as thin membranes and micromachined horns. The basic geometric configurations of commonly used lithographic antennas, including elementary dipoles and slots, broadband double-dipole and double-slots, and the very broadband bowtie, equiangular spiral, and log-periodic antennas are examined. Some basic facts are reviewed about the antenna pattern and frequency-dependent impedance of these devices. Some issues, particularly the finite surface impedance of thin metallic films, which are specific to very high frequencies are considered. Experiments performed at MST to explore the capabilities and limitations of antenna-coupling at frequencies as high as 30 THz (10 μm wavelength) are also described