Kevin M. Lambert

Demonstration of a X-band multilayer Yagi-like microstrip patch antenna with high directivity and large bandwidth

The feasibility of obtaining large bandwidth and high directivity from a multilayer Yagi-like microstrip patch antenna at 10 GHz is investigated. A measured 10-dB bandwidth of ~20% and directivity of ~11 dBi is demonstrated through the implementation of a vertically-stacked structure with three parasitic directors, above the driven patch, and a single reflector underneath the driven patch. Simulated and measured results are compared and show fairly close agreement. This antenna offers the advantages of large bandwidth, high directivity and symmetrical broadside patterns, and could be applicable to satellite as well as terrestrial communications

Design of an 8–40 GHz antenna for the wideband instrument for snow measurements (WISM)

Measurement of land surface snow remains a significant challenge in the remote sensing arena. Developing the tools needed to remotely measure Snow Water Equivalent (SWE) is an important priority. The Wideband Instrument for Snow Measurements (WISM) is being developed to address this need. WISM is an airborne instrument comprised of a dual-frequency (X- and Ku-band) Synthetic Aperture Radar (SAR) and dual-frequency (K- and Ka-band) radiometer. A unique feature of this instrument is that all measurement bands share a common antenna aperture consisting of an array-feed reflector that covers the entire bandwidth. This paper covers the design and fabrication of the wideband array feed, which is based on tightly coupled dipole arrays. Implementation using a relatively new multi-layer microfabrication process results in a small, 6×6-element, dual-linear polarized array with beamformer that operates from 8 to 40 GHz.

Antenna characterization for the Wideband Instrument for Snow Measurements (WISM)

Experimental characterization of the antenna for the Wideband Instrument for Snow Measurement (WISM) under development for the NASA Earth Science Technology Office (ESTO) Instrument Incubator Program (IIP), is discussed. A current sheet antenna, consisting of a small, 6×6 element, dual-linear polarized array with integrated beamformer, feeds an offset parabolic reflector, enabling WISM operation over an 8 to 40 GHz frequency band. An overview of the test program implemented for both the feed and the reflector antenna is given along with select results for specific frequencies utilized by the radar and radiometric sensors of the WISM.

Test and Analysis of an Inflatable Parabolic Dish Antenna

NASA is developing ultra-lightweight structures technology for large communication antennas for application to space missions. With these goals in mind, SRS Technologies has been funded by NASA Glenn Research Center (GRC) to undertake the development of a subscale ultra-thin membrane inflatable antenna for deep-space applications. One of the research goals is to develop approaches for prediction of the radio frequency and structural characteristics of inflatable and rigidizable membrane antenna structures. GRC has teamed with NASA Langley Research Center (LaRC) to evaluate inflatable and rigidizable antenna concepts for potential space missions. GRC has completed tests to evaluate RF performance, while LaRC completed structural tests and analysis to evaluate the static shape and structural dynamic responses of a laboratory model of a 0.3 meter antenna. This paper presents the details of the tests and analysis completed to evaluate the radio frequency and structural characteristics of the antenna.

Prototype antenna elements for the next-generation TDRS enhanced multiple-access array

This paper summarizes a study performed to produce prototype antenna elements for the next-generation enhanced Tracking and Data Relay Satellite Continuation (TDRS-C) multiple-access (MA) S-band phased-array antenna. Compared to the multiple-access antenna on the current class of TORS, the enhanced multiple-access antenna requires elements that achieve greater on-axis gain, simultaneous circular polarization capability, and increased beamwidth. To demonstrate that array elements could be realized meeting these requirements, designs that were successful in simulation were fabricated and tested. These included a helical antenna; a novel short backfire antenna, excited with a circular waveguide (cup waveguide) with integrated polarizer and orthomode transducer (OMT); and a corrugated-horn antenna with integrated polarizer and OMVT. The paper describes the design process for the novel elements, and compares measured and simulated results. It also compares the elements in terms of performance, size, and mass.

Experimental demonstration of the effects of an electric thruster plasma plume on microwave propagation

Electric thrusters are being considered for a wide variety of space missions because of the significant propellant savings that result from the use of high performance, electric propulsion technologies. The impact of electric thruster plasma plumes on microwave propagation is a key integration concern for planners of the next generation of spacecraft. Arcjets were the first electric thrusters to be considered for operational missions. The effect of arcjet plumes on propagation was studied by Ling, et al. (see IEEE Transactions on Antennas and Propagation, vol.39, no.9, p.1412-1420, 1991). Arcjets produce a lightly ionized plume and Lings analysis predicted that the plume would have a negligible effect on communication. Arcjets are now operational on the AT&T Telstar 401 satellite, and the analysis has been validated by in-space operations. However, plumes from the higher performance thrusters being developed exhibit higher ionization levels, plasma temperatures and particle velocities than arcjets. Therefore a need has risen to determine the effects of these plumes. To address this need, the authors have designed and performed an experiment to assess the attenuation and phase shift caused by these types of plasmas. The challenge with this experiment was that it was a microwave propagation experiment that had to be performed inside a metal vacuum chamber. Thus the experiment had to be designed to minimize multiple reflections within the chamber. This paper describes the experiment and presents some of the results that were obtained.

A microstrip patch-fed short backfire antenna for the tracking and data relay satellite system-continuation (TDRSS-C) multiple access (MA) array

A novel microstrip patch-fed short backfire antenna has been presented here for the first time as a candidate antenna element for the next generation TDRSS-C MA array. This design meets nearly all the specifications required for the enhanced MA array antenna element and promises to provide a lightweight low cost alternative over other designs presently being considered (i.e., corrugated horn, helix, waveguide-fed SBA). Simulations performed using IE3D and MWS agree with measured data, thus far, and indicate an 11% 15-dB bandwidth and a maximum directivity of 15.2 dBi. Future work involves further optimization of the radiation characteristics and the construction of the complete short backfire antenna structure to verify simulated results

Experimental Demonstration of Microwave Signal/Electric Thruster Plasma Interaction Effects

An experiment was designed and conducted in the Electric Propulsion Laboratory of NASA Lewis Research Center to assess the impact of ion thruster exhaust plasma plume on electromagnetic signal propagation. A microwave transmission experiment was set up inside the propulsion test bed using a pair of broadband horn antennas and a 30 cm 2.3 kW ion thruster. Frequency of signal propagation covered from 6.5 to 18 GHz range. The stainless steel test bed when enclosed can be depressurized to simulate a near vacuum environment. A pulsed CW system with gating hardware was utilized to eliminate multiple chamber reflections from the test signal. Microwave signal was transmitted and received between the two hours when the thruster was operating at a given power level in such a way that the signal propagation path crossed directly through the plume volume. Signal attenuation and phase shift due to the plume was measured for the entire frequency band. Results for this worst case configuration simulation indicate that the effects of the ion thruster plume on microwave signals is a negligible attenuation (within 0.15 dB) and a small phase shift (within 8 deg.). This paper describes the detailed experiment and presents some of the results.

Comparative study of antenna elements for TDRSS enhanced multiple access system

The tracking and data relay satellite system (TDRSS) is a constellation of geosynchronous satellites, which are the primary source of space-to-ground voice, data and telemetry for the space shuttle. The satellites also provide communications with the International Space Station and scientific spacecraft in low-Earth orbit such as the Hubble Space Telescope. Integral to the design of the TDRSS class of satellites is an architecture consisting of a multiple access (MA), S-band, phased array antenna. This MA system receives and relays data simultaneously from five lower data-rate users and transmits commands to a single user. This paper describes a study (design, fabrication, and testing) of several modified antenna elements for the enhanced MA phased array. Several antenna elements were investigated including a helix antenna, a novel short backfire antenna excited with a circular waveguide, and a corrugated horn antenna. The results for each element in terms of performance; fabrication, assembly and tuning complexity; size and mass are compared