Tunable Multi-Tone, Multi-Band, High-Frequency Synthesizer
communications
Tunable Multi-Tone, Multi-Band, High-Frequency Synthesizer (LEW-TOPS-95)
Pioneering synthesizer enables game-changing new capabilities in satellite communications
Overview
Innovators at NASA's Glenn Research Center have developed a multi-tone, multi-band, high frequency synthesizer that enables unprecedented satellite communications and atmospheric studies. Because of the increased congestion at currently used frequency bands, it would be game-changing to open other millimeter-wave frequency bands for satellite communications with stations on Earth. When used as part of a CubeSat beacon transmitter, the synthesizer would enable rigorous characterization of atmospheric effects (e.g., rainfall, climate change, hurricane monitoring, cloud cover, and gaseous adsorption). Although the synthesizer can be used on other platforms, the use of the CubeSat allows these studies to be conducted without the huge expense of a larger satellite. The synthesizer can also be used for space-borne active remote sensors such as scatterometers.
The Technology
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.
Benefits
- Flexible: Generates and transmits signals that are tunable over wide frequency ranges, including Q-band (37-42 GHz), V/W-band (71-76 GHz), and K-band (18-26GHz)
- Reliable: Provides more accurate wideband characterization through multi-tone frequency generator, with noise less than -70dBc
- Efficient: Has smaller antenna size and lower mass, which yield fuel savings
- Compact: Has small size and weight, enabling integration into the CubeSat platform
- Simple: Uses harmonic generation of high-frequency beacon signals rather than direct generation, which requires much more complex circuitry
- Accurate: Excellent frequency stability because the input drive signal is locked to a stable crystal oscillator
Applications
- Communications satellites
- CubeSats
- Climate studies (e.g., analysis of hurricanes, climate change)
- Space-to-ground communications
- Active remote sensors (e.g., scatterometers)
Similar Results
High-Speed, Low-Cost Telemetry Access from Space
NASA's SDR uses Field-Programmable Gate Array (FPGA) technology to enable flexible performance on orbit. A first-generation FM-modulated transceiver is capable of operating at up to 1 Mbps downlink and 50 kbps uplink, full duplex. An FPGA performs Reed-Solomon (255,223) encoding, decoding, and bit synchronization, providing Consultative Committee for Space Data Systems (CCSDS) and Near Earth Network (NEN) telemetry protocol compatibility. The transceiver accepts data from the onboard flight computer via a source synchronous RS422 interface.
NASA's second-generation full duplex SDR, known as PULSAR (programmable ultra-lightweight system-adaptable radio, Figures 1 and 2 below) incorporates command receiver and telemetry transmitters, as well as updated processing and power capabilities. An S-band command receiver offers a max uplink data rate of 300 Kbps and built-in QPSK demodulation. X- and S-Band telemetry transmitters offer a max downlink data rate of 150 Mbps and flexible forward-error correction (FEC) using Reed-Solomon encoding (LDPC rate 7/8 and 1/2 convolution in development), and it uses QPSK modulation. The use of FEC adds an order of magnitude increase in telemetry throughput due to an improved coding gain. An onboard FPGA uses high-speed logic for uplink/downlink and encoding/decoding processes. Balloon flight testing has been conducted and is ongoing for PULSAR.
Data Transfer for Multiple Sensor Networks
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.
Optical Tunable-Based Transmitter for Multiple High-Frequency Bands
NASA Glenn's researchers have developed a means of transporting multiple radio frequency carriers through a common optical beam. In contrast to RF infrastructure systems alone, this type of hybrid RF/optical system can provide a very high data-capacity signal communication and significantly reduce power, volume, and complexity. Based on an optical wavelength division multiplexing (WDM) technique, in which optical wavelengths are generated by a tunable diode laser (TDL), the system enables multiple microwave bands to be combined and transmitted all in one unit. The WDM technique uses a different optical wavelength to carry each separate and independent high-frequency microwave band (e.g., L, C, X, Ku, Ka, Q, or higher bands). Since each RF carrier operates at a different optical wavelength, the tunable diode laser can, with the use of an electronic tunable laser controller unit, adjust the spacing wavelength and thereby minimize any crosstalk effect.
Glenn's novel design features a tunable laser, configured to generate multiple optical wavelengths, along with an optical transmitter. The optical transmitter modulates each of the optical wavelengths with a corresponding RF band and then encodes each of the modulated optical wavelengths onto a single laser beam. In this way, the system can transmit multiple radio frequency bands using a single laser beam. Glenn's groundbreaking concept can greatly improve the system flexibility and scalability - not to mention the cost of - both ground and space communications.
Direction of Arrival Estimation Signal of Opportunity Receiver
The Direction of Arrival Estimation Signal of Opportunity Receiver is a transceiver technology for small satellite and CubeSat platforms that enables maximization of antenna gain in a specific direction to receive desired signals and suppress signals from other directions. The receive is a four-channel transceiver system to be operating in a LEO orbit for receiving direct as well as reflected signal (signals reflected from the ground) of a communication satellite. An adaptive array processing is implemented to steer the receiver beam towards the GEO satellites as well as steer the antenna beam towards the ground. When the beam is steered towards the ground the receiver provides attenuation for the direct signal incident from the GEO satellite, thus isolating the reflected signal from the strong direct signal.
Usually a simple pair of cross dipoles are used for receiving signals transmitted by communication satellites. One pair is used to receive direct signals and another pair is used receive reflected signals. These dipoles are ideally supposed to receive only the reflected signals from the ground. However, because of close proximity and strong coupling to each other through their mutual coupling and because of their broad beam patterns, these dipole antennas receive signals reflected from other targets, as well as the direct transmitted signal. Since the strength of direct signals will be above the strength of reflected signals, reflected signals typically are completely masked by the strong direct signals. The Direction of Arrival Estimation Signal of Opportunity Receiver maximizes antenna gain in a desired direction to maximize desired signal and suppress unwanted signals.
Lightweight, Self-Deployable Helical Antenna
NASA's newly developed antenna is lightweight (at or below 2 grams), low volume (at or below 1.2 cm3), and low stowage thickness (approx. 0.7 mm), all while delivering high performance (at or above 10 dBi gain). The antenna includes a novel design-material combination in a helical coil conformation. The design allows the antenna to compress for stowage (e.g., satellite launch), then self-deploy at the desired time in orbit.
NASA's lightweight, self-deployable helical antenna can be integrated into a thin-film solar array (or other large deployable structures). Integrating antenna elements into deployable structures such as power generation arrays allows spacecraft designers to maximize the inherently limited resources (e.g., mass, volume, surface area) available in a small spacecraft. When used as a standalone (i.e., single antenna) setup, the the invention offers moderate advantages in terms of stowage thickness, volume, and mass. However, in applications that require antenna arrays, these advantages become multiplicative, resulting in the system offering the same or higher data rate performance while possessing a significantly reduced form factor.
Prototypes of NASA's self-deployable, helical antenna have been fabricated in S-band, X-band, and Ka-band, all of which exhibited high performance. The antenna may find application in SmallSat communications (in deep space and LEO), as well as cases where low mass and stowage volume are valued and high antenna gain is required.
