Y. Pastol

Broad-band microwave measurements with transient radiation from optoelectronically pulsed antennas

A broadband microwave measurement technique based on picosecond transient radiation from optoelectronically pulsed antennas is described. It is performed with exponentially tapered coplanar stripline antennas which are integrated with the photoconductive devices used for ultrafast pulse generation and sampling. The signal analysis required for deriving the desired physical properties from the measured time-domain waveforms is discussed. This is a coherent technique that independently determines both the real and the imaginary parts of the dielectric constants of materials, from 10 to 130 GHz, in a single experiment. Some representative results are presented. >

Coherent broadband microwave spectroscopy using picosecond optoelectronic antennas

We describe coherent microwave transient spectroscopy experiments using picosecond optoelectronic integrated antennas. The effectiveness of the experimental setup for the measurement of the loss and dispersion properties of materials in the 10–125 GHz range is characterized using microwave filters of predictable behavior. We also present measurements of the absorption coefficient and refractive index of fused silica over this frequency band.

Dielectric properties of uniaxial crystals measured with optoelectronically generated microwave transient radiation

Absorption and dispersion properties of sapphire and crystal quartz between 15 and 130 GHz were measured using the freely propagating transient radiation from optoelectronically pulsed integrated antennas. The polarization sensitivity of the experimental apparatus was characterized and used to obtain the absorption coefficients and refractive indices in the above frequency range for both ordinary and extraordinary beam propagation. We also studied the frequency‐dependent transmission (amplitude and phase) of these two materials as a function of the angle between the electric field and the optic axis.

Optoelectronically-pulsed antennas: characterization and applications

A brief tutorial on the picosecond photoconductive effect is given. The use of picosecond optoelectronics for the characterization of broadband antennas is described. In particular, the transient radiation properties of equiangular-spiral and exponentially tapered coplanar-strip antennas are discussed. The transient radiation behavior and the polarization and radiation patterns of these antennas are easily determined with this measurement technique, without the need for anechoic chambers. Applications of picosecond-duration transient electromagnetic radiation to filter measurements, materials measurements, and scattering studies are discussed.<<ETX>>

Anisotropic conductivity in stretch‐oriented polymers measured with coherent microwave transient spectroscopy

Stretch‐oriented and doped polyacetylene and polyaniline are characterized using the coherent microwave transient spectroscopy technique. Conductivities parallel and perpendicular to the direction of elongation are determined. The measured orientation dependence of the sample transmissions are observed to follow the predictions of theory.

Transient radiation properties of an integrated equiangular spiral antenna

Self-complementary two-arm equiangular spiral antennas were fabricated on silicon-on-sapphire substrates. Picosecond photoconductive pulse generation and sampling were used to investigate their transient radiation properties. Results are presented on transient response, bandwidth, polarization, and radiation pattern. The equiangular spiral antenna is found to be highly efficient, and its transient response exhibits a frequency sweep which is a direct consequence of the antenna structure. In this mode of excitation, the antenna remains circularly polarized, and the pattern for radiation through the substrate is quite broad.<<ETX>>

Measurement of frequency-selective surfaces with optoelectronically generated microwave transients

The complex transmission functions (amplitude and phase) of frequency selective surfaces were measured using optoelectrically generated broadband microwave transients. The amplitude and phase of the transmission function of an array of cross dipoles with a=462 mu m, b=214 mu m, and g=1770 mu m are shown. The corresponding results of a sample with a=927 mu m, b=422 mu m, and g=3551 mu m are shown. The amplitude spectra clearly indicate that the samples are indeed band-stop filters, and the corresponding phase spectra follow the predictions of the Kramers-Kronig relations. The results of the measurement are in good agreement with the predictions of full-wave electromagnetic simulation.<<ETX>>

Microwave Properties of Anisotropic Materials Characterized with Picosecond Transient Radiation

The anisotropic microwave dielectric properties of uniaxial crystals and stretch-oriented conducting polymers are characterized using the coherent microwave transient spectroscopy technique.