Tunable Multi-Tone, Multi-Band, High-Frequency Synthesizer

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.

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.

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.

The novel mixer offers wideband and sub-harmonic conversion capabilities for enhanced signal processing across a broad frequency range. The mixer operates at 470-600 GHz and includes a LO waveguide to allow 265-300 GHz input signal and a radio frequency (RF) waveguide for the 470-600 GHz operation. The LO and RF signal multiply and down-convert the RF signal to an IF signal to a much lower frequencies for further digitization. The mixer is designed on a gold and quartz substrate for a lower dielectric constant. The filter design uses a triangular patch resonator-based low-pass filter to reduce the size of the mixer as well as isolates the LO signal and the wide IF signal. Additionally, an IF filter, RF filter, Schottky diode, LO, and RF probes are integrated into a single chip to further reduce the dimensions of the mixer. The invention also leverages an antiparallel diode orientation, where the LO frequency is half of the RF input. This LO signal is amplified and multiplied up to 265-300 GHz to provide an input power of 3-5 mW to pump the antiparallel mixer. The technology offers significant advantages in remote sensing and high-speed communications, enabling simultaneous detection of multiple molecular species and enhancing the efficiency of submillimeter-wave heterodyne spectrometers. The wideband functionality achieves high data rates required in emerging 6G networks and offers exceptional sensitivity, with prototype tests showing a conversion loss below 12 dB and noise temperatures under 4000 K at 470 GHz. The integration of components such as filters and diodes into a single chip reduces system size and complexity, contrasting with traditional multi-chip setups. The design is scalable across frequencies from 1 GHz-1 THz with minimal modifications, with the system's form factor inversely scaling with frequency. These features make the technology versatile for applications in environmental monitoring, planetary exploration, radar systems, and advanced communication systems.

This NASA invention is a highly compact and sensitive 530-600 GHz, 1x8 receiver array employing a multi-pixel approach to enhance simultaneous detection capabilities. The receiver has a conversion loss of 1 THz and the center frequency can be tuned by adjusting design parameters. While NASA originally developed this receiver to enable miniaturized, low power consumption, high sensitivity heterodyne-based submillimeter wave spectrometers for small satellite-based planetary atmospheric sensing, potential applications of the novel receiver are broad. The multi-pixel, wideband receiver can be used in spectrometer and radar systems for applications including astronomy, plasma fusion, military, and emerging communication technologies such as 5G and 6G. The invention is available for patent licensing.