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At least 397 records · Page 22

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NASA NTRS1986

Design considerations for the beam-waveguide retrofit of a ground antenna station

Retrofitting an antenna that was originally designed without a beam waveguide introduces special difficulties because it is desirable to minimize alteration of the original mechanical truss work and to image the actual feed without distortion at the focal point of the dual-shaped reflector. To obtain an acceptable image, certain Geometrical Optics (GO) design criteria are followed as closely as possible. The problems associated with applying these design criteria to a 34-meter dual-shaped DSN (Deep Space Network) antenna are discussed. The use of various diffraction analysis techniques in the design process is also discussed. GTD and FFT algorithms are particularly necessary at the higher frequencies, while Physical Optics and Spherical Wave Expansions proved necessary at the lower frequencies.

Veruttipong, T.↗

NASA NTRS1986

A new model for broadband waveguide to microstrip transition design

A new model is presented which permits the prediction of the resonant frequencies created by antipodal finline waveguide to microstrip transitions. The transition is modeled as a tapered transmission line in series with an infinite set of coupled resonant circuits. The resonant circuits are modeled as simple microwave resonant cavities of which the resonant frequencies are easily determined. The model is developed and the resonant frequencies determined for several different transitions. Experimental results are given to confirm the models.

Ponchak, George E.↗

NASA NTRS1987

Directional couplers for detecting the TE sub 11 and TE sub 12 circular waveguide modes

The theoretical and experimental results for a pair of mode-selective directional couplers designed to detect the TE sub 11 and TE sub 12 modes in a multimode circular wavelength are described. A brief description of the design of the couplers is presented, followed by a comparison of their measured and calculated parameters. The couplers were used to measure the characteristics of a circular waveguide mode converter. The results of these measurements are described.

Hoppe, D.↗

NASA NTRS1987

Structural design options for the new 34 meter beam waveguide antenna

In addition to the successful network of 34 m High Efficiency antennas recently built by JPL, the Deep Space Network (DSN) is embarking on the construction of a 34 m high performance, research and development antenna with beam waveguide optics at the Venus site. The construction of this antenna presents many engineering challenges in the area of structural, mechanical, RF, and pointing system design. A set of functional and structural design requirements is outlined to guide analysts in the final configuration selection. Five design concepts are presented covering both the conventional center-fed beam optics as well as the nonconventional, by-pass beam configuration. The merits of each concept are discussed with an emphasis on obtaining a homologous design. The preliminary results of structural optimization efforts, currently in progress, are promising, indicating the feasibility of meeting, as a minimum, all X-band (8.4 GHz) requirements, with a goal towards meeting Ka-band (32 GHz) quality performance, at the present budget constraints.

Katow, S.↗

NASA NTRS1986

Design method for four-reflector type beam waveguide systems

Discussed is a method for the design of four reflector type beam waveguide feed systems, comprised of a conical horn and 4 focused reflectors, which are used widely as the primary reflector systems for communications satellite Earth station antennas. The design parameters for these systems are clarified, the relations between each parameter are brought out based on the beam mode development, and the independent design parameters are specified. The characteristics of these systems, namely spillover loss, crosspolarization components, and frequency characteristics, and their relation to the design parameters, are also shown. It is also indicated that design parameters which decide the dimensions of the conical horn or the shape of the focused reflectors can be unerringly established once the design standard for the system has been selected as either: (1) minimizing the crosspolarization component by keeping the spillover loss to within acceptable limits, or (2) minimizing the spillover loss by maintaining the crossover components below an acceptable level and the independent design parameters, such as the respective sizes of the focused reflectors and the distances between the focussed reflectors, etc., have been established according to mechanical restrictions. A sample design is also shown. In addition to being able to clarify the effects of each of the design parameters on the system and improving insight into these systems, the efficiency of these systems will also be increased with this design method.

Betsudan, S.↗

NASA NTRS1986

High-speed dual-wavelength demultiplexing and detection in a monolithic superlattice p-i-n waveguide detector array

High-speed (1 Gbit/x) dual-wavelength demultiplexing and detection in a monolithic linear array of superlattice p-i-n photodetectors in a waveguide configuration is demonstrated. A crosstalk attenuation of 28 dB was achieved between two digital transmission channels with an interchannel wavelength spacing of 30 nm. The device performance is a result of an enhanced electroabsorption due to the quantum-confined Stark effect in the superlattice p-i-n diodes.

Larsson, A.↗

NASA NTRS1987

Radar cross section of an open-ended circular waveguide Calculation of second-order diffraction terms

The radar cross section of an open-ended, semi-infinite circular waveguide is calculated by the geometrical theory of diffraction and the equivalent-current (EC) method. Both single- and double-diffraction terms are included. It is found that the double-diffraction term is stronger than the single-diffraction term for the horizontal polarization at wide-angle incidence. Its inclusion is necessary in order to check with experimental data and the asymptotic expansion of the exact Wiener-Hopf solution. The EC method is used for the single diffraction. On the other hand the double-diffraction term is obtained by using the EC method for axial incidence and geometrical theory of diffraction for wide-angle incidence. These two solutions are matched with a proper matching function. This technique is computationally more efficient than the matching technique of integration over the equivalent currents.

Lee, C. S.↗

NASA NTRS1987

Effect of numerical aperture on signal level in cylindrical waveguide evanescent fluorosensors

The effect of numerical aperture on signal level from fluorescent substances or solutions in the evanescent zone of a cylindrical waveguide is analyzed. The analysis applies to the case in which the fluorescence is excited by the evanescent wave of a fiber and the fluorescence signal is that which tunnels back into the same fiber. The analysis is for two cases: bulk fluorescence and fluorescence of a thin film layer. Experimental results are also presented.

Glass, Thomas R.↗

NASA NTRS1988

Circular-Waveguide Power Combiner/Divider

Power combiner/divider devised in which output from several solid-state modules combined directly into TE01 mode of circular waveguide. Results in low-loss, wide band device: because axisymmetry of TE01 mode, no essential limit on N. Latter feature is advantage in design of wide band, high-power, solid-state amplifiers operating at millimeter wavelengths.

Dunn, Vernon↗

NASA NTRS1988

Modeling of Some Coplanar Waveguide Discontinuities

Presented are lumped equivalent circuit models for several coplanar waveguide discontinuities such as an open circuit, a series gap, and a symmetric step, and their element values as a function of the discontinuity physical dimensions. The model element values are de-embedded from measured S-parameters. The frequency dependence of the effective dielectric constant was measured and compared to computed values.

Simons, Rainee N.↗

NASA NTRS1988

Fiber waveguide sensors for intelligent materials

This report, an addendum to the six month report submitted to NASA Langley Research Center in December 1987, covers research performed by the Fiber and Electro-Optics Research Center (FEORC) at Virginia Tech for the NASA Langley Research Center, Grant NAG1-780, for the period from December 1987 to June 1988. This final report discusses the research performed in the following four areas as described in the proposal: Fabrication of Sensor Fibers Optimized for Embedding in Advanced Composites; Fabrication of Sensor Fiber with In-Line Splices and Evaluation via OTR methods; Modal Domain Optical Fiber Sensor Analysis; and Acoustic Fiber Waveguide Implementation.

Flax, A. R.↗

NASA NTRS1988

Optical waveguides in oxygen-implanted buried-oxide silicon-on-insulator structures

An analysis is made of the waveguiding properties of the oxygen-implanted, buried-oxide, silicon-on-insulator structures currently being developed for use in microelectronics. It is found that in spite of the fact that the buried-oxide layer is only a few tenths of a micrometer thick, the single-crystal overlayer can support TEo guided-wave propagation, at subbandgap wavelengths, with losses due to substrate radiation leakage at or below the benchmark level of 1 dB/cm.

Kurdi, B. N.↗

NASA NTRS1988

A new model for broadband waveguide-to-microstrip transition design

Ponchak, George E.↗

NASA NTRS1988

Modal attenuation in multilayered coated waveguides

Propagation and attenuation constants of low-order normal modes in a circular waveguide lined with lossy coating layers are calculated using a generalized dispersion equation. It is found that the use of multilayered coating can significantly enhance modal attenuations over a broader frequency range compared to that for a single-layer coated structure. For a cylinder with radius a = 2 lambda, the attenuation constants for the dominant modes are shown to increase by 20 dB per a by adding a lossless padding layer to a lossy magnetic coating. Application of this result in radar cross-section (RCS) reduction is discussed.

Chou, Ri-Chee↗

NASA NTRS1989

Computing Resonances Of Waveguide-To-Microstrip Transitions

Simplified mathematical model used to predict resonant frequencies of antipodal-finline waveguide-to-microstrip transitions. Makes it possible to place undesired resonances outside desired frequency band during design process; eliminates much of iteration in design process and thereby reduces both time and cost of design.

Ponchak, George E.↗

NASA NTRS1989

Design of a 60 GHz beam waveguide antenna positioner

A development model antenna positioner mechanism with an integral 60 GHz radio frequency beam waveguide is discussed. The system features a 2-ft diameter carbon-fiber reinforced epoxy antenna reflector and support structure, and a 2-degree-of-freedom elevation over azimuth mechanism providing hemispherical field of view. Emphasis is placed on the constraints imposed on the mechanism by the radio frequency subsystems and how they impacted the mechanical configuration.

Emerick, Kenneth S.↗

NASA NTRS1989

CWG: A FORTRAN program for mutual coupling in a planar array of circular waveguide-fed apertures

A FORTRAN program which calculates the mutual coupling between circular apertures in a conductive plane is documented. The program is quite general in that the apertures do not have to be the same sizes, nor do they have to be polarized in the same direction. In addition, several waveguide modes (TE and/or TM) may be specified in the apertures and the mutual coupling between all combinations of apertures and modes will be calculated. The program also allows multiple layers of homogeneous dielectrics to be placed over the aperture array. Outside the layered region, one can specify either a homogeneous half-space, or a perfect reflecting surface.

Bailey, M. C.↗

NASA NTRS1989

A new analysis of beam-waveguide antennas considering the presence of the enclosure

Beam-waveguide (BWG) antennas provide multiple frequency band operations and other operational benefits for large ground-station antennas. Present design practices use diffraction analyses that ignore the presence of the BWG enclosure and may be inaccurate at lower frequency bands for ground-station antennas operating over multiple frequency bands. Introduced here is a new analysis approach that considers the presence of the BWG enclosure. Results based on the new analysis have revealed new understandings of the performance degradation mechanisms in a BWG antenna and have provided direction for potential design improvements.

Cha, A. G.↗