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Lumped-circuit design techniques applied to iris-coupled cavities. Waveguide/cavity filter imitates lumped series and parallel combinations of inductance and capacitance over narrow stopband centered at 7.190 GHz. Filter made of standard WR125 waveguide stock.
Stable, narrow far field produced. Array of lasers fabricated on single chip. Individual laser waveguides isolated from each other except in end portions, where diffraction coupling takes place. Radiation pattern far from laser array has single, sharp central lobe when all lasers operate in phase with each other. Shape of lobe does not vary appreciably with array current. Applications include recording, printing, and range finding.
Optical/electronic system senses rotation and emits pulses at angular increments. System provides linear scale factor across wide range of rotation rates with no lockup at null. Design needs analog-to-digital converters with elaborate signal-processing circuits. Light from laser diode split evenly into two beams propagating in opposite directions around rotation-sensing coil of optical-fiber waveguide. Beams acquire phase difference proportional to rotation rate as they pass through coil. After emerging from coil, beams recombine in beam splitter, and coherent sum led to photodiode.
It has become increasingly clear in recent years that the available models describing the acceleration of high speed streams in solar coronal holes are inadequate. Thermal models do not result in winds with the proper thermal speed and density. In addition models which assume acceleration by Alfven waves, though promising, are not self-consistent when applied low in coronal holes where the acceleration of the wind takes place. An Alfven wave in the corona with a period of a few hundred seconds will have a wavelength of the order of 10 cm. This is of the order of the diameter of a coronal hole in the low corona, and therefore it is expected that the MHD waves are guided in some sense by the coronal hole in which they propagate. This basic idea led to the development of a leaky waveguide theory to describe MHD wave propagation in coronal holes. Recent efforts were concentrated in two areas: the development of numerical codes to properly describe the hydrodynamics of the flow, and more realistic models of the coronal hole properties such as density gradients and spherical divergence of the flux tube. Some of the important aspects of the theory are discussed, including the effect of density inhomogeneities and smooth transverse density gradients. In addition it is hoped that some early results from the numerical models will be presented. The acceleration of cool winds is a problem of interest in cool supergiants also. Some work was done on the development of wind models for these stars as well.
An approach to the design of the planned NASA/JPL 34 m elevation-over-azimuth (Az-El) antenna structure at the Venus site (DSS-13) is presented. The antenna structural configuration accommodates a large (2.44 m) beam waveguide (BWG) tube centrally routed through the reflector-alidade structure, an elevation wheel design, and an optimal structural geometry. The design encompasses a cross-box elevation wheel-reflector base substructure that preserves homology while satisfying many constraints, such as structure weight, surface tolerance, stresses, natural frequency, and various functional constraints. The functional requirements are set to ensure that microwave performance at millimeter wavelengths is adequate. The cross-box configuration was modeled, optimized, and found to satisfy all DSN HEF baseline antenna specifications. In addition, the structure design was conceptualized and analyzed with an emphasis on preserving the structure envelope and keeping modifications relative to the HEF antennas to a minimum, thus enabling the transferability of the BWG technology for future retrofitting. Good performance results were obtained.
Using MMICs in phased-array applications above 20 GHz requires complex RF and control signal distribution systems. Conventional waveguide, coaxial cable, and microstrip methods are undesirable due to their high weight, high loss, limited mechanical flexibility and large volume. An attractive alternative to these transmission media, for RF and control signal distribution in MMIC phased-array antennas, is optical fiber. Presented are potential system architectures and their associated characteristics. The status of high frequency opto-electronic components needed to realize the potential system architectures is also discussed. It is concluded that an optical fiber network will reduce weight and complexity, and increase reliability and performance, but may require higher power.
Phased-array antennas are required for many future NASA missions. They will provide agile electronic beam forming for communications and tracking in the range of 1 to 100 GHz. Such phased arrays are expected to use several hundred GaAs monolithic integrated circuits (MMICs) as transmitting and receiving elements. However, the interconnections of these elements by conventional coaxial cables and waveguides add weight, reduce flexibility, and increase electrical interference. Alternative interconnections based on optical fibers, optical processing, and holography are under evaluation as possible solutions. In this paper, the current status of these techniques is described. Since high-frequency optical components such as photodetectors, lasers, and modulators are key elements in these interconnections, their performance and limitations are discussed.
In a shaft with a curved or straight primary segment and smaller off-shooting segments, at least one standing wave is generated in the primary segment. The shaft has either an open end or a closed end and approximates a cylindrical waveguide. A frequency of a standing wave that represents the fundamental mode characteristic of the primary segment can be measured. Alternatively, a frequency differential between two successive harmonic modes that are characteristic of the primary segment can be measured. In either event, the measured frequency or frequency differential is characteristic of the length and thus the volume of the shaft based on length times the bore area.
A ridge waveguide distributed feedback laser was developed in InGaAsP. These devices have demonstrated CW output powers over 7 mW with threshold currents as low as 60 mA at 25 C. Measurements of the frequency response of these devices show a 3 dB bandwidth of about 2 GHz, which may be limited by the mount. The best devices have a single mode spectra over the entire temperature range tested with a side mode suppression of about 20 dB in both CW and pulsed modes. The design of this device, including detailed modeling of the ridge guide structure, effective index calculations, and a discussion of the grating configuration are presented. Also, the fabrication of the devices is presented in some detail, especially the fabrication of and subsequent growth over the grating. In addition, a high frequency fiber pigtailed package was designed and tested, which is a suitable prototype for a commercial package.
The principle and design of an L-band omni-directional mobile communication antenna are discussed. The antenna is a circular wave guide aperture with hybrid circuits attached to higher order mode excitation. It produces polarized and symmetric two split beams in elevation. The circular waveguide is fed by eight probes with a 90 degree phase shift between their inputs. Radiation pattern characteristics are controlled by adjusting the aperture diameter and mode excitation. This antenna satisfies gain requirements as well as withstanding the harsh environment.
A cryogenic cooled, low-noise Field Effect Transistor (FET) amplifier assembly for use at 2.2 to 2.3 GHz was developed for the DSN to meet the requirements of a Very Long Baseline Interferometry (VLBI) upgrade. An amplifier assembly was developed at JPL that uses a commercial closed-cycle helium refrigerator (CCR) to cool a FET amplifier to an operating temperature of 15 K. A cooled probe waveguide-to-coaxial transition similar to that used in the research and development Ultra-Low-Noise S-band Traveling Wave Maser (TWM) is used to minimize input line losses. Typical performance includes an input flange equivalent noise contribution of 14.5 K, a gain slope of less than 0.05 dB/MHz across a bandwidth of 2.2 to 2.3 GHz, an input VSWR of 1.5:1 at 2.25 GHz, and an insertion gain of 45 + or - 1 dB across the bandwidth of 2.2 to 2.3 GHz. Three 2.3 GHz FET/CCR assemblies were delivered to the DSN in the spring of 1987.
A millimeter wave traveling wave tube was developed using a dispersive, high impedance forward interaction structure based on a ladder, with non-space harmonic interaction, for a tube with high gain per unit length and high efficiency. The TunneLadder interaction structure combines ladder properties modified to accommodate Pierce gun beam optics in a radially magnetized permanent magnet focusing structure. The development involved the fabrication of chemically milled, shaped ladders diffusion brazed to diamond cubes which are in turn active-diffusion brazed to each ridge of a doubly ridged waveguide. Cold test data are presented, representing the omega-beta and impedance characteristics of the modified ladder circuit. These results were used in small and large signal computer programs to predict TWT gain and efficiency. Actual data from tested tubes verify the predicted performance while providing broader bandwidth than expected.
A waveguide Mach-Zehnder electro-optic modulator and an interdigitated photoconductive detector designed to operate at 820 nm, fabricated on different GaAlAs/GaAs heterostructure materials, are being investigated for use in optical interconnects in phased array antenna systems. Measured optical attenuation effects in the modulator are discussed and the observed modulation performance up to 1 GHz is presented. Measurements of detector frequency response are described and results presented.
The output emission of a short CH3F metallic waveguide laser pumped by an injection-locked CO2 transversely excited atmosphere laser is studied experimentally. The output is found to be extremely unpredictable when lasing occurs in both the excited and ground vibrational states on two separate transitions (496 and 452 microns, respectively). The dynamics and sensitivity to initial conditions are explained in terms of two Lorenz lasers with pump coupled population inversions.
A complete dual-frequency cryogenic heterodyne receiver operating at 183 and 380 GHz is described. The cooled mixers are whisker-contacted GaAs Schottky diodes mounted in reduced-height fundamental-mode waveguide. The local oscillators are Gunn-oscillator-driven multipliers using GaAs varactor diodes as the harmonic generators. Quasi-optical techniques are used extensively for coupling the remote and local oscillator signals into the mixers. The overall system double side-band (DSB) noise temperature is 320 K for the 183-GHz receiver and 650 K for the 380 GHz receiver.
The purpose of this paper is to present the processes used to fabricate and load test the NASA Scatterometer Antenna Assemblies. The fabrication processes include layup, curing and machining of antenna components, and the bonding and assembly of the components into the final antenna configuration. The design of each antenna consists of an aluminum waveguide bonded to a sandwich structure of Nomex honeycomb core with graphite/epoxy skins. A titanium end fitting with fiberglass/epoxy transitions is bonded into one end of each antenna. Several antenna components are fabricated using a process where aluminum foil is co-cured to a composite surface. The antenna assemblies are radiographically inspected, thermally cycled, and load tested prior to shipment.
A feed network comprised of a combination of coplanar waveguide and slot transmission line is described for use in an array module of four microstrip elements. Examples of the module incorporating such networks are presented as well as experimentally obtained impedance and radiation characteristics.
Extended measurements and theory on the recently developed monolithic wavelength demultiplexer consisting of voltage-tunable superlattice p-i-n photodetectors in a waveguide configuration are discussed. It is shown that the device is able to demultiplex and detect two optical signals with a wavelength separation of 20 nm directly into different electrical channels at a data rate of 1 Gb/s and with a crosstalk attenuation varying between 20 and 28 dB, depending on the polarization. The minimum acceptable crosstalk attenuation at a data rate of 100 Mb/s is determined to be 10 dB. The feasibility of using the device as a polarization angle sensor for linearly polarized light is also demonstrated. A theory for the emission of photogenerated carriers out of the quantum wells is included, since this is potentially a speed limiting mechanism in these detectors. It is shown that a theory of thermally assisted tunneling by polar optical phonon interaction is able to predict emission times consistent with the observed temporal response.