Correlating radiometers are presented at D-band (100-120 GHz) and G-band (160-185 GHz). The D-band system is a heterodyne receiver focused around the 118.75 GHz oxygen line and the G-band system is a direct-detection pseudocorrelating receiver focused around the 183.31 GHz water-vapor line. These systems are integrated into multiple waveguide blocks to facilitate troubleshooting and to enable different RF filters to be applied to the low noise amplifier (LNA)-based front ends. Discussion of the data-processing is presented for both systems. The D-band system has a noise temperature of 410 K at 120 GHz. The correlated output of this system increased the Allan time from 100 ms to 7 s. The G-band system has an average noise temperature of 780 K, with an increase in Allan time from 1 ms to 10 s.

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This brief survey looks at some current challenges and advances in millimeter-wave and THz test equipment. In particular, spectral purity of mm-wave signal sources and downconverters is addressed, both at full power and in power-sweeping configurations. Higher-power VNA measurement capabilities are introduced. New advances in millimeter-wave noise measurements and wideband signal analysis are also described.

Dynamic nuclear polarization (DNP) improves the sensitivity of NMR spectroscopy by the transfer of electron polarization to nuclei via irradiation of electron-nuclear transitions with microwaves at the appropriate frequency. For fields > 5 T and using g ∼ 2 electrons as polarizing agents, this requires the availability of microwave sources operating at >140 GHz. Therefore, microwave sources for DNP have generally been continuous-wave (CW) gyrotrons, and more recently solid state, oscillators operating at a fixed frequency and power. This constraint has limited the DNP mechanisms which can be exploited, and stymied the development of new time domain mechanisms. We report here the incorporation of a microwave source enabling facile modulation of frequency, amplitude, and phase at 9 T (250 GHz microwave frequency), and we have used the source for magic-angle spinning (MAS) NMR experiments. The experiments include investigations of CW DNP mechanisms, the advantage of frequency-chirped irradiation, and a demonstration of an Overhauser enhancement of ∼25 with a recently reported water-soluble BDPA radical, highlighting the potential for affordable and compact microwave sources to achieve significant enhancement in aqueous samples, including biological macromolecules. With the development of suitable microwave amplifiers, it should permit exploration of multiple new avenues involving time domain experiments.

We recently used selective 2H labeling of BDPA to investigate the Overhauser Effect (OE) dynamic nuclear polarization (DNP) mechanism in insulating solids doped with 1,3-bis(diphenylene)-2-phenylallyl (BDPA), and established that the α and γ 1H spins on the fluorene rings are responsible for generating a zero quantum (ZQ) mediated positive bulk polarization. Here, we establish that the phenyl 1H spins relax via double-quantum (DQ) processes and therefore contribute negative enhancements which attenuate the OE-DNP. With measurements at different magnetic field strengths, we show that phenyl-d5-BDPA offers >50% improvement in OE-DNP enhancement compared to h21-BDPA attaining a maximum of ∼90 at 14.1 T and 5 kHz MAS, the highest observed OE-DNP enhancement to date under these conditions. The approach may be utilized to optimize other polarizing agents exhibiting an OE, an important DNP mechanism with a favorable field and spinning frequency dependence.

The development of broad-band power amplifier MMICs from 120 GHz and above is enabling a new generation of varactor sources. Power combining is an essential technique to maximize the amount of power available from these devices. Two, four and eight-way combining of four different amplifier MMICs is demonstrated, resulting in over 1 W of power at 140 GHz and 160 GHz, 400 mW at 195 GHz and 200mW at 230 GHz. A 260 GHz doubler driven by a 130 GHz 2-way combined amplifier is presented producing 100mW of power with less than 10 W DC power consumption.

This paper provides an overview of the IceCube project, including its payload and CubeSat development and performance in spaceflight. Like other CubeSat missions, IceCube has a goal to miniaturize remote-sensing sensors and to increase the reliability of small satellites. Using small, modular and standardized spacecraft along with miniaturized sensor units, we hope to advance Earth and planetary sciences by forming a space sensor constellation or sending scout-units from a mothership for targeted science investigations. IceCube is a pathfinder at NASA that infuses and integrates small spacecraft technologies to merge it with its larger mission goals. Effective governmentcommercial partnerships have played a key role in meeting the fast-track, lowcost requirements. Early lessons learned from IceCube will benefit the CubeSat community as well as the science investigations that plan to use nano/microsatellites.

Schottky diode technology has been used for the generation and detection of millimeter waves for decades. The advantages of this solid-state approach are compact size, frequency tunability, and relatively low cost. Recent drivers from the wideband communications, security imaging, spectroscopy, as well as test and measurement markets have pushed this technology further in recent years. This chapter highlights the most recent advances in Schottky diode based sources and detectors. This includes wideband tunable frequency sources up to 1 THz, such as a multiplier chain that provides -16 dBm typical output power over the full WM-250 750–1100 GHz band. Examples of narrowband high-power sources are also given, such as a 250 mW multiplier chain at 260 GHz, and a highly compact complete transmitter with 10 mW output power from 270–290 GHz for imaging applications. Several examples are also given of diode-based wideband receivers, for terrestrial and orbital applications, including broadband millimeter-wave downconverters operating up to 1.1 THz. Millimeter-wave heterodyne receivers for CubeSat atmospheric radiometery are also described, including a 880 GHz heterodyne receiver for ice cloud measurements and a 183 GHz 4-channel radiometer for tropical storm tracking.

Sideband separating receivers radically simplify analysis of spectral regions where many species exist, such as the 530-600 GHz band when studying planetary atmospheres. Sideband-separating mixers use quadrature combining of two mixers to down-convert both sidebands but require careful balancing of the two mixer paths. A simpler approach is possible if a fixed LO frequency can be used. This allows filtering of the image-band before a doublesideband mixer. In addition to reducing circuit complexity, this approach provides higher sideband rejection than typically achieved with sideband separating mixers. Fig 1 (top) shows the system diagram. The integrated receiver combines a 281GHz LO chain with a multiplication factor of 27 with two sub-harmonic mixers. IF filters follow each mixer. Both sidebands are downconverted by splitting the incoming signal and then filtering each path. The LO is located at 562GHz and down-converts 531-557GHz and 568-600GHz, providing an 11GHz band where the filters can cross-over. Secondary downconversion is used to place the species of interest into the spectrometer’s bandwidth. To set the noise temperature of the system, 520-600GHz LNAs will precede the splitter. This approach requires very precise location of the passband edges. Machining tolerances makes realization of the desired filters’ passbands unlikely, so a tunable waveguide filter approach is utilized. It has been found that waveguide filters can be effectively tuned by adjusting the gap in the E-plane split waveguide block [1]. By controlling the gap in the filter block with 5um thick shims, the filters can be aligned to within +/3 GHz, without significant change in the passband width or insertion loss. Fig. 1 (middle) shows the discrete version of this system, where the tunable filter and splitter have been separated from the integrated receiver to verify this tunable filter approach. The graph shows the conversion gain of each mixer path, which includes the loss of the splitter, filter and mixer, and the gain of an IF amplifier. To further reduce losses, a fully integrated version of the system that combines the receiver with the filter and splitter has been developed and results of this device will be presented at the conference.

The development of new, high-frequency solid-state diode sources capable of operating at 263 GHz, together with an optimized stator design for improved millimeter-wave coupling to the NMR sample, have enabled low-power DNP experiments at 263 GHz/400 MHz. With 250 mW output power, signal enhancements as high as 120 are achieved on standard samples - approximately 1/3 of the maximal enhancement available with high-power gyrotrons under similar conditions. Diode-based sources have a number of advantages over vacuum tube devices: they emit a pure mode, can be rapidly frequency-swept over a wide range of frequencies, have reproducible output power over this range, and have excellent output stability. By virtue of their small size, low thermal footprint, and lack of facility requirements, solid-state diodes are also considerably cheaper to operate and maintain than high-power vacuum tube devices. In light of these features, and anticipating further improvements in terms of available output power, solid-state diodes are likely to find widespread use in DNP and contribute to further advances in the field.

Cloud ice play important roles in Earth's climate and weather systems through their interactions with atmospheric radiation, dynamics, energy and precipitation processes. Submillimeter (submm) wave remote sensing at 200-1000 GHz is able to provide the sensitivity not covered by visible (VIS)/infrared (IR) and low-frequency microwave (MW) sensors (10-183 GHz), and measure cloud ice in the middle-to-upper troposphere. The IceCube 883-GHz cloud radiometer is the latest of NASA's efforts to advance the technology readiness level (TRL) of submm-wave receiver technology for future compact, low-cost implementation of Earth observing systems. Emerging CubeSat opportunities allow a fast-track development and spaceflight demonstration of IceCube on a 3-U CubeSat. Funded by NASA's In-Space Validation of Earth Science Technologies (InVEST) program and Science Mission Directorate (SMD), IceCube is the first CubeSat developed and flown by Goddard Space Flight Center (GSFC) in 2.5 years, using commercial off-the-shelf (COTS) components and subsystems. It was successfully released from International Space Station (ISS) in May 2017, acquired 15-month science data and produced the first global map of the 883-GHz cloud ice. It achieved all mission objectives and provided a pathway for future cost-effective cloud observations from CubeSat constellation.

The development and measurements of solid-state active multiplier sources for DNP-NMR experiments is described in this paper. The sources utilize power-combined Schottky diode frequency doublers as the final two stages. 250 mW output power was measured for two complete sources, one at 250 GHz and a second at 262 GHz. Using a 1.3 mm probe, DNP enhancements of 115-120 were measured.

The design of a single-sideband 675-693 GHz integrated polarimeter is presented here. The compact module, measuring 1.5 '' x 1.5 '' x 0.75 '' includes the OMT, RF LNAs, image-reject filters, mixers, IF LNAs, and LO active multiplier chain. Total power dissipation is expected to be approximately 6W. Receiver noise temperature is expected to be approximately 6000K SSB. The polarimeter has been machined and assembled with measurements to be presented at the conference.

Filters play an invaluable role in RF analysis and communications hardware, blocking unwanted signals, limiting bandwidth, attenuating harmonic components, etc. In waveguide construction for mm-wave frequencies, where the powers are generally low, the iris-coupled-resonator bandpass filte has proven to be very practical and amenable to easy machining. At Virginia Diodes, much of our technology has been constructed using standard "split-block" techniques, in which high-precision computer numerical control milling machines are used to mill out the features from solid blocks of metal. Typical machining tolerances are on the order of +/-5-10 mu m. Construction of such filter to similar to 200 GHz has been routine but pushing the operation into the Terahertz regime requires special considerations. Described here is a WM380 (WR1.5) filte for the 500-750 GHz waveguide band having a passband of 675-700 GHz. The filte is proof of concept for a 640 GHz heterodyne polarimeter, designed as a part of a Small Business Innovative Research (SBIR) Grant to develop technology for NASA's planned Aerosol, Cloud, and Ecosystems mission. From the very beginning, filte design and optimizations were carried out assuming the structure would be milled, hence necessitating that all internal features accommodate the finit radii of available machine tools. Construction of this filte required careful attention to machining tolerances to be able to push the milling machines to their absolute limits of +/-2.5 mu m or better. Measured results of a batch of f lters are shown and compared to simulations to illustrate just how well these filter can be made. Furthermore, the f lters can be tuned by simple mechanical means and data are presented to illustrate how easily the f lters can be adjusted. Additional modification to the filte topology to simplify machining, and allow other construction techniques to be utilized are also demonstrated. Ultimately it should be possible to push the split block technology to manufacture iris coupled resonator filter for use at frequencies of well over 1 THz.

We describe a set of compact millimeter-wave frequency converters for wideband digital signals. Frequency upconverters and downconverters have been developed for frequencies from WR-28 (26-40 GHz) to WR-2.2 (325-500 GHz). Bandpass filters with passband return loss > 20dB and stopband rejection > 50dB within 1 GHz from band edges were developed for use with these upconverters. Preliminary WR-12 link tests are shown.

We give a comparison of sensitivity and power estimates for heterodyne receivers operating at common atmospheric science bands using Schottky mixer or low-noise amplifier front ends. The receiver estimates rely on commercially available mixer systems and reported low noise amplifier data.

A compact 272-288 GHz transmitter with integrated VCO is presented. This source is suitable for use in compact radar, imaging, and spectroscopy systems as an alternative to a W-band Gunn oscillator cascaded with W-band power amplifier and frequency multiplier. The transmitter has a x36 multiplication factor and has external dimensions of 0.875" × 1.0" × 1.25". Measured output power is greater than +7 dBm over the 272-288 GHz frequency range with a peak power greater than +10 dBm. Overall power dissipation is less than 6 W.