P. C. Claspy

Superconducting microstrip antennas: an experimental comparison of two feeding methods

The recent discovery of high-temperature superconductors (HTSs) has generated a substantial amount of interest in microstrip antenna applications. However, the high permittivity of substrates compatible with HTS causes difficulty in feeding such antennas because of the high patch edge impedance. Two methods for feeding HTS microstrip antennas at K- and Ka-band are examined. Superconducting microstrip antennas that are directly coupled and gas-coupled to a microstrip transmission line have been designed and fabricated on lanthanum aluminate substrates using Y-Ba-Cu-O superconducting thin films. Measurements from these antennas, including input impedance, bandwidth, efficiency, and patterns, are presented and compared with published models. The measured results demonstrate that usable antennas can be constructed using either of these architectures, although the antennas suffer from narrow bandwidths. In each case, the HTS antenna shows a substantial improvement over an identical antenna made with normal metals. >

Optoacoustic detection of NO(2) using a pulsed dye laser.

Using a pulsed dye laser and a nonresonant optoacoustic detector, the absorption spectrum of NO(2) has been measured in the spectral region of 480-625 nm at various cell pressures and at various concentrations in air. The results of the measurements as a function of NO(2) concentration in air demonstrate the detection capability of the system. An extrapolated sensitivity of 4 ppb NO(2)/W of laser power has been achieved.

Laser optoacoustic detection of explosive vapors

The direct detection of nitroglycerine, ethylene glycol dinitrate, and dinitrotoluene by optoacoustic spectroscopy techniques at 6 microm, 9 microm, and 11 microm is reported. The effect of interference by normal atmospheric pollutants is investigated, and it is found that of those wavelengths used in this investigation the 9-microm and 11-/microm spectral regions, using a CO(2) laser as radiation source, are the most promising for use in explosive detection.

Estimates of atmospheric attenuation sensitivity with respect to absolute humidity at 337 GHz

A 640-m field transmissometer was operated for a three-day period during late July 1986. Using an optically pumped, near-millimeter wave laser as the source, clear-air relative attenuation measurements were collected at an operating frequency of 337 GHz. The ambient and dew point temperatures were recorded concurrent with the relative attenuation measurements. An expression was synthesized to provide absolute humidity measurements from the recorded temperatures. By assuming static attenuation due to atmospheric constituents other than water vapor, the sensitivity of attenuation to absolute humidity at 337 GHz was estimated at a number of temperatures. Comparison of these estimates to a previous investigation at the same frequency indicates general agreement. >

Electronic heterodyne recording and processing of optical holograms using phase modulated reference waves

The use of a phase-modulated reference wave for the electronic heterodyne recording and processing of a hologram is described. Heterodyne recording is used to eliminate the self-interference terms of a hologram and to create a Leith-Upatnieks hologram with coaxial object and reference waves. Phase modulation is also shown to be the foundation of a multiple-view hologram system. When combined with hologram scale transformations, heterodyne recording is the key to general optical processing. Spatial filtering is treated as an example.

CO 2 Laser Signature Problem

A CO(2) laser may oscillate at any one of many possible lines. As the cavity length of such a laser is varied over a distance of lambda/2, a large number of lines oscillate one at a time in succession. The listing of the identities of the sequences of lines constitutes a signature of the laser and is a matter of practical importance in the operation of these lasers in remote controlled applications without the use of mode-selecting elements in the cavity of the laser. We report here a rather remarkable result, namely, that the lines P(20) and P(16) of the 10.4-microm band compete so effectively relative to all the other modes that they can be relied on to oscillate over quite a wide gain curve and for a wide range of operating conditions.

Atmospheric Propagation Studies At Near-Millimeter Wavelengths

An experiment to study the effect of a meterologically well-characterized atmosphere on near-millimeter wave propagation has been designed and is being implemented. The primary emphasis of this experiment is on measurement of atmospheric mutual coherence function (MCF) simultaneously with measurement of temperature/humidity structure parameters C2T C2Q, and CTQ. Quasi-optical techniques, which make use of the Fourier transforming properties of focussing reflective optics, will be applied to measure real and imaginary parts of the MCF, while fast temperature and humidity sensors will provide derived structure parameters. This paper will discuss experimental concepts and range instrumentation.

Comparison of GaAs and CdTe crystals for high-frequency intracavity coupling modulation of CO 2 lasers

High-frequency intracavity coupling modulation of the CO 2 laser has recently attracted considerable interest as an efficient means of achieving wide-bandwidth modulation with low modulator drive power. In the present investigation, intracavity coupling modulation was achieved at 1 GHz. Both GaAs and CdTe crystals were investigated and an optical beat method was used to explore the operational characteristics of such systems without having to go to the expense and trouble of high-speed detectors. The modulation efficiencies at the 1-GHz modulation rate were 0.5 and 1 percent for GaAs and CdTe electrooptic modulators, respectively. Modulator crystal characteristics such as electrical resistivity, radiation absorption, crystal uniformity, etc., which are of critical importance for intracavity modulation, were also measured for both crystals.

Design of an optically controlled Ka-band GaAs MMIC phased-array antenna

Phased array antennas long were investigated to support the agile, multibeam radiating apertures with rapid reconfigurability needs of radar and communications. With the development of the Monolithic Microwave Integrated Circuit (MMIC), phased array antennas having the stated characteristics are becoming realizable. However, at K-band frequencies (20 to 40 GHz) and higher, the problem of controlling the MMICs using conventional techniques either severely limits the array size or becomes insurmountable due to the close spacing of the radiating elements necessary to achieve the desired antenna performance. Investigations were made that indicate using fiber optics as a transmission line for control information for the MMICs provides a potential solution. By adding an optical interface circuit to pre-existing MMIC designs, it is possible to take advantage of the small size, lightweight, mechanical flexibility and RFI/EMI resistant characteristics of fiber optics to distribute MMIC control signals. The architecture, circuit development, testing and integration of optically controlled K-band MMIC phased array antennas are described.

Instrumentation for near-millimeter wave propagation studies

Instrumentation for studying the propagation of near-millimeter waves has been designed and is currently being implemented at a 1 mile long test site in Sandusky, Ohio. An optically pumped near-millimeter (NMM) wave laser, used as a source of radiation for frequencies near 300 GHz, is located at one end of this site. The laser beam spot size arriving at the other end of the propagation path is controlled by a two-lens optical system placed at the lasers output. The receiver system consists of a parabolic reflector, a focal plane scanning system, and a fast-response liquid-helium-cooled InSb detector, all of which is controlled by a 68000-based microcomputer. Measurement of the characteristics of the received beam is based upon a quasi-optical method. The temperature/humidity atmospheric structure parameters and hydrometeor characteristics along the path are obtained simultaneously with the propagation measurements. These two measurements are then correlated to provide a meteorologically well-verified propagation model for near-millimeter wavelengths.