Multimode Directional Coupler

communications
Multimode Directional Coupler (LEW-TOPS-91)
Makes additional frequencies available for satellite communication
Overview
Researchers at NASA's Glenn Research Center have patented a novel multimode directional coupler (MDC). This rugged and easily constructed waveguide is used to extract second- or higher-order harmonics, which are generally unused but contain sufficient power to be amplified and transmitted to a receiving station on Earth. Glenn's innovators developed the MDC as a means to extract signal harmonics from a satellite transmitter, with minimum perturbation to a fundamental frequency. The ability of the MDC to allow the fundamental frequency to propagate with negligible power losses makes it a substantial upgrade over the conventional diplexer. Glenn's MDC offers an innovative way to increase the number of terrestrial stations that can receive signals from a single satellite, potentially increasing the return on the investment involved in launching and maintaining satellites.

The Technology
Glenn's researchers originally created the MDC to improve the beacon sources for atmospheric propagation studies. These studies are typically conducted to test atmospheric conditions to determine the signal strength needed for satellite communications. A low-power transmitter (e.g., a beacon source) is attached to the satellite, and transmits a continuous waveform (CW) signal to a receiving station on Earth. However, when a separate frequency is desired, building a new beacon source for the transmitter on the satellite - especially one that will operate at higher frequencies - presents numerous challenges. For one, a single-frequency beacon source requires a temperature-stabilized oscillator for frequency generation separate from that provided by the spacecraft receiver. To solve such problems, Glenn's innovators fabricated the MDC from two sections of waveguide: a primary waveguide for the fundamental frequency (Ku-band), and a secondary waveguide for the harmonics (Ka-band). These sections are joined together so that precision-machined slots in the second waveguide selectively couple the harmonics, for amplification and transmission. The harmonics can then be used as an additional beacon source with very small power losses to the fundamental signal. Once the separation takes place, the second or higher harmonic can be amplified and transmitted to a station on Earth. The efficiency and performance of the MDC can be optimized through appropriate computer modeling software and currently available high-precision fabrication techniques. Without the complexity and expense involved in building separate traveling wave tube amplifiers to generate additional frequencies, Glenn's MDC enables satellites to produce multiple signals that can be received by multiple stations - a significant leap forward in satellite productivity.
Satellite Starry Sky Glenn's MDC offers a novel way to increase the number of terrestrial stations that can receive signals from a single satellite
Benefits
  • Versatile: Allows configuration to support second-order and higher harmonics
  • Efficient: Extracts harmonics with negligible perturbation to the fundamental frequency
  • Cost-effective: Permits transmitters to communicate with more than one receiving station at a time
  • Easy to construct and maintain: Relies on rugged traditional waveguide and is simple to fabricate

Applications
  • Satellite beacon
  • Satellite communication
  • Atmospheric testing
  • Terrestrial transmission strength modifier
Technology Details

communications
LEW-TOPS-91
LEW-19045-1 LEW-19045-2
Similar Results
Tech Planet Earth Satellite
Microwave Power Combiner
MMICs are a type of integrated circuit that operates at microwave frequencies to amplify electronic signals. The system has at least two power amplifiers; input ports to receive power from the amplifiers; at least one power combiner, which receives power from each input port and combines them to produce maximized power; an output port that sends this maximized power to its destination; and an isolated port, either grounded or match-terminated, that receives no or negligible power from the combiner. The output port can be connected to a load, and can employ more than one combiner, so that the power from another combiner and an input port can be combined, for example, in a 3-way unequal power combiner. Glenn's Ka-band demonstration power combiner has an output return loss better than 20 dB, and a high degree of isolation between the output port and the isolated port, as well as between the two input ports. When the ratio of output power for two MMICs is two-to-one, the combined efficiency is better than 90%. However, the design is not limited to a two-to-one ratio; it can be customized to any arbitrary power output ratio. This means that a low-power gallium arsenide MMIC can be combined with a high-power gallium nitride MMIC, giving designers much more flexibility. The output impedance of the MMIC power amplifier is matched directly to the waveguide impedance, without first transitioning into a transmission line. This technique eliminates the losses associated with a transition and enhances the overall efficiency. Furthermore, the MMIC power combiner is dual purpose- run in reverse it serves as a power divider. To reduce the cost and weight the combiner can be manufactured using 3-D printing and metal-plated plastic. By combining MMIC amplifiers more efficiently, Glenn's technology greatly enhances communications from near-Earth and deep space-to-Earth.
Radar Jets
Solid-State Microwave Power Module
Typically, microwave power modules (MPMs) are useful only for radar and navigation purposes because they lack the linearity and efficiency required for communications. In standard configurations, conventional MPMs require both a solid-state amplifier at the front end and a microwave vacuum electronics amplifier at the back end. By contrast, Glenn's design features a wideband multi-stage distributed amplifier system. The low-power stage is a high-efficiency gallium arsenide (GaAs) pseudomorphic high-electron-mobility transistor (pHEMT)-based monolithic microwave integrated circuit (MMIC) distributed amplifier. The medium-power stage is configured to pick up and amplify the low-power signal. This stage can be either another high-efficiency GaAs pHEMT or a gallium nitride (GaN) HEMT-based MMIC distributed amplifier, depending on the need. The high-power stage, configured to pick up the signal from the second amplifier, is a high-efficiency GaN HEMT-based MMIC distributed amplifier, which supplants the traveling-wave tube amplifier found in most microwave power modules. In Glenn's novel MPM, the radar functions as a scatterometer, radiometer, and synthetic aperture imager. The high-speed communications system down-links science data acquired by Earth-observing instruments. The navigation system functions like a transponder for autonomous rendezvous and docking, and estimates the range information. Glenn's MPM gives systems the versatility to use a single power module to drive not only radar and navigation but also communications systems.
Ground Station
Signal Combiner for Wideband Communication
Through low-loss signal combination, Glenn is leading the way to optimize radio transmission remotely during self-checking routines. Glenn's signal combiner offers a simple method to minimize signal loss significantly when combining two signals. Using conventional combiners in bit-error-rate testing results in a loss of 3 to 4 dB per band, and with a directional coupler the secondary signal experiences losses of 10 dB or more. Moreover, during signal measurements, the additional components must be placed and later removed to prevent any impact to the measurement, making for a cumbersome process. Glenn's solution is to combine the primary and secondary signals in the frequency domain through the use of a frequency division diplexer/multiplexer in combination with a wideband ADC. The multiplexer selects one or more bands in the frequency domain, and the ADC performs a non-linear conversion to digital domain by folding out-of-band signals in with the primary signal. NASA makes use of subsampling a given band within the ADC bandwidth to fold it into another band of interest, effectively frequency-shifting them to a common frequency bandwidth. Glenn's breakthrough method has two significant advantages over the conventional use of a power combiner or directional coupler in bit-error-rate testing: 1) it combines signal and noise (secondary signal) with very low loss, and 2) it enables the selection of the desired signal-to-noise ratio with no need for the later cumbersome removal of components. This streamlined process allows for invaluable in-situ or installed measurement. Glenn's novel technology has great potential for satellite, telecommunications, and wireless industries, especially with respect to equipment testing, measurement, calibration, and check-out.
Airport Control Tower
The Teletenna - A Hybrid Telescope Antenna System
Initially developed for missions to Mars, Teletenna integrates RF and optical communication technologies to transmit data from deep space to Earth at extremely high speeds. The system combines a co-boresighted telescope and a Ka-band RF antenna to minimize system mass and enhance performance. Designed with an optimal focal length-to-diameter ratio, the apparatus features a classical Cassegrain geometry, including a sub-reflector in front of the RF feed which acts as a mirror for the optical signal while being transparent to the RF signal. The apparatus also mechanically and thermally isolates the RF reflector system from the optics to offer maximum stability. Teletenna was created to overcome two significant challenges to DSOC: 1) laser inefficiency due to poor alignment during spacecraft disturbances and 2) performance degradation due to lack of rigidity in vibrational environments (such as space). The first challenge is addressed by the telescope portion of this technology, which facilitates the acquisition and maintenance of the link with ease - even in less than ideal conditions. The second challenge is addressed by rigidly fixing the RF reflector to the spacecraft body and attaching the optical section to a vibration isolation platform. The result is a device that can point to within 0.5 degrees of the sun (traditional optical systems are limited to 3 degrees), allowing for approximately 20 extra days of contact time between Earth and Mars. By combining RF and optical communications, this breakthrough innovation has the power to transform communications as we know it. Glenn welcomes co-development opportunities.
Front Image
Tunable Multi-Tone, Multi-Band, High-Frequency Synthesizer
Glenn's revolutionary new multi-tone, high-frequency synthesizer can enable a major upgrade in the design of high data rate, wide-band satellite communications links, in addition to the study of atmospheric effects. Conventional single-frequency beacon transmitters have a major limitation: they must assume that atmospheric attenuation and group delay effects are constant at all frequencies across the band of interest. Glenn's synthesizer overcomes this limitation by enabling measurements to be made at multiple frequencies across the entire multi-GHz wide frequency, providing much more accurate and actionable readings. This novel synthesizer consists of a solid-state frequency comb or harmonic generator that uses step-recovery semiconductor diodes to generate a broad range of evenly spaced harmonic frequencies, which are coherent and tunable over a wide frequency range. These harmonics are then filtered by a tunable bandpass filter and amplified to the necessary power level by a tunable millimeter-wave power amplifier. Next, the amplified signals are transmitted as beacon signals from a satellite to a ground receiving station. By measuring the relative signal strength and phase at ground sites the atmospheric induced effects can be determined, enabling scientists to gather essential climate data on hurricanes and climate change. In addition, the synthesizer can serve as a wideband source in place of a satellite transponder, making it easier to downlink high volumes of collected data to the scientific community. Glenn's synthesizer enables a beacon transmitter that, from the economical CubeSat platform, offers simultaneous, fast, and more accurate wideband transmission from space through the Earth's atmosphere than has ever been possible before.
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