Signal Combiner for Wideband Communication

High-temperature sensors have been used in silicon carbide electronic oscillator circuits. The frequency of the oscillator changes as a function of changes in the sensor's parameters, such as pressure. This change is analogous to changes in the pitch of a person's voice. The output of this oscillator, and many others may be superimposed onto a single medium. This medium may be the power lines supplying current to the sensors, a third wire dedicated to data transmission, the airwaves through radio transmission, or an optical or other medium. However, with nothing to distinguish the identities of each source, this system is useless. Using frequency dividers and linear feedback shift registers, comprised of flip flops and combinatorial logic gates connected to each oscillator, unique bit stream codes may be generated. These unique codes are used to amplitude modulate the output of the sensor (both amplitude shift keying and on-off keying are applicable). By using a dividend of the oscillator frequency to generate the code, a constant a priori number of oscillator cycles will define each bit. At the receiver, a detected frequency will have associated with it a stored code pattern. Thus, a detected frequency will have a unique modulation pattern or "voice," disassociating it from noise and from other transmitting sensors. These codes may be pseudorandom binary sequences (PRBS), ASCII characters, gold codes, etc. The detected code length and frequency are measured, offering intelligent data transfer. This is an early-stage technology requiring additional development. Glenn welcomes co-development opportunities.

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.

Electronic waveforms exist that exceed the capabilities of state-of-the-art data acquisition hardware that is commonly available. The electronic waveforms that need to be measured simultaneously contain wide bandwidth, high frequency content, a DC reference, high dynamic range, and a high crest factor. The NASA Glenn high-speed data acquisition system creates a voltage compression effect with a custom transfer function that is adapted to the voltage range, frequency bandwidth, and electrical impedance of both the test article and data acquisition device. The compression transfer function is later reversed (or decompressed) with a software algorithm to restore the original signal's voltage from the acquired data. The data is thus improved via better signal-to-noise ratio, better low-amplitude accuracy, better resolution, and preservation of high-frequency spectral content. The circuit can be realized with either passive components or both active and passive components. Either realization is specialized for the test article and data acquisition hardware. This is an early-stage technology requiring additional development. Glenn welcomes co-development opportunities.

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.

Components of the HYDRA system include an RFID reader (aka an RFID transceiver or interrogator), RF cables, antennas, and one or more Intelligent Multiplexer Modules (IMMs). The IMM is the core building block of the HYDRA system. In one of its basic embodiments, the IMM comprises an RF directional coupler, RF switch, RFID chip, micro-controller, and power generation and management hardware. In this basic implementation, a single RF port from the RFID reader is attached to the IMM and transfers power thereto. Internally within the IMM, the RF directional coupler diverts a small amount of RF power to rectification and power management circuitry for conversion to DC power that drives the RFID chip, microcontroller, and RF switch. The RFID chip enables communication with the RFID reader and allows the reader to administer changes to the microcontroller‘s embedded software. The microcontroller controls the RF switch, which passes power along to one or more output channels. Connections to the output channels can include antennas, additional IMMs, or other sensors. The HYDRA system may include numerous alternate embodiments to enhance and customize the basic functionality. In one embodiment, the microcontroller is replaced with a simple timer. In another embodiment, the switch has multiple output ports to connect to a distributed chain of HYDRA system or local antennas. Also, the entirety of RF power exiting a HYDRA module can be rectified and used to power a local sensor node, which could be implemented via WiFi or Bluetooth Low Energy (BLE). Features of the HYDRA system include the ability to cover both open regions and enclosures, the ability to switch RF power to an unused load for assisting in the resolution of tag antenna ambiguities, and the ability to accept plug-and-play add-ons such that the reader’s software can use the system without requiring any embedded modifications. The HYDRA system is technology readiness level (TRL) 7 (system prototype demonstrated in an operational environment) and is now available for patent licensing. Please note that NASA does not manufacture products itself for commercial sale.