Recent optical heterodyne measurements with distributed-Bragg-reflector diode-laser pumps demonstrate that low-temperature-grown ͑LTG͒ GaAs photomixers will be useful in a compact all-solid-state terahertz source. Electrical 3 dB bandwidths as large as 650 GHz are measured in mixers with low electrode capacitance. These bandwidths appear to be independent of pump-laser wavelength over the range 780-850 nm. Shorter wavelength pumping results in a significant reduction of the bandwidth. The best LTG-GaAs photomixers are used to generate coherent continuous-wave output radiation at frequencies up to 5 THz.

An electromagnetic stop band spanning about one octave is observed in a periodic structure consisting of a face-centered-cubic Bravais lattice of metal spheres supported by a low-loss dielectric. The low-frequency edge of the stop band is consistent with the Mie condition for the metallic spheres, and the center frequency of the stop band is a function of the lattice constant and the support dielectric material. For example, a sample having a cubic lattice constant of 1.65 cm, 3/8 in. diam chrome spheres at each atomic core, and Teflon support dielectric displayed a lower band edge of approximately 5.2 GHz, an upper band edge of about 12.8 GHz, and a maximum rejection at the center of the band of roughly 20 dB.

A strip dipole on a (111)-oriented face centered cubic photonic crystal is found to have a copolarized directivity and radiative gain of 9.1 and 7.2±1.4, respectively, along the zenith and at a frequency in the first stop band of 18.0 GHz. Under the same conditions, the maximum copolarized directivity and radiative gain were 10.0 and 8.1±1.6, respectively, in the H-plane 5° down from the zenith. The zenithal results correspond to a 5.5-times greater radiation intensity than displayed by the same dipole in free space. From power balance measurements, only 10% of this enhancement is attributed to superior power transfer between the generator and antenna. The remainder is associated with constructive interference between the primary antenna radiation and radiation reflected from the crystal.