The next generation of space-based submillimeter-wave remote cometary mapping instruments is being developed at NASA/JPL with two receiver bands at 210-240 and 500-580 GHz. This instrument requires an array of receivers to decrease image acquisition time of velocity-resolved maps of key cometary volatiles. Furthermore, a single shared focal plane is required to save power, mass, and space while maintaining overlapping and equal-beamwidth target illumination at both bands. Here, we describe the analysis, synthesis, fabrication, and measurement of a prototype dual-band, submillimeter-wave leaky-wave lens antenna intended for a 4x 4 focal-plane array (FPA) under a parabolic reflector that achieves these goals. The FPA elements are waveguide-fed leaky-wave lens antennas with a novel stratification including an integrated frequency-selective surface that enables 15% operational bandwidths around 225 and 540 GHz simultaneously. The propagating leaky-wave modes in this stratification are studied in detail and the stratification is then synthesized in manufacturable components. A submillimeter-wave lens antenna prototype was fabricated using high-precision silicon microfabrication techniques. Measurements of this prototype demonstrate a performance closely matching simulated results in both frequency bands.

In this article, we report on the development of a highperformance, tunable, solid-state, single-pole-single-throw (SPST) switch operating in G-band for radar applications. Future space-borne, high-power G-band radars may require an SPST switch for receiver protection. We explore a novel solid-state switching architecture based on planar GaAs Schottky diodes. The switch, optimized for operation from 158 to 175 GHz, achieves high isolation by absorbing, reflecting, and frequency multiplying the input power to the second harmonic. A first demonstrator is characterized with an ON-state insertion loss <0.86 dB and return loss >20 dB at 0 dBm input power. The OFF-state isolation exceeds 43 dB at 0 dBm input power and remains above 30 dB at +17 dBm input power. Depending on the required isolation, the switch is tunable with an instantaneous bandwidth ranging from 300 MHz (for 30 dB isolation) to 13 GHz (for 15 dB isolation). The switch is successfully demonstrated to operate at an ultra-fast 4 MHz switching rate with a switching speed of a few nanoseconds.

In this article, we introduce a groundbreaking 2-THz front end suitable for space use, operating at room temperature. Our objective is to measure high-altitude 3-D winds for precise Sun-earth energy coupling analysis. Employing Schottky-diode-based mixers and multipliers, we have developed a solid-state receiver with double-sideband sensitivity below 8000 K. This sensitivity enables the measurement of atomic oxygen in the approximate 100-200-km altitude range. Our approach encompasses design, fabrication, and sensitivity assessment of the receiver front end.

This article presents a novel waveguide-based terahertz (THz) variable attenuator, integrated with a piezo-electric motor, to achieve precise and fine step values of signal attenuation. A low-resistivity silicon slab, coated with a thin layer of Titanium metal, is inserted inside a waveguide that absorbs some of the electromagnetic waves traveling through the guide. Impedance matching is achieved by gradually perforating the silicon slab and thus, creating variable impedance needed for matching. The amount of signal absorbed by the slab is determined by the sheet resistance value of the metal coating and the position of the slab in the waveguide. A miniature nanometer-scale precision piezo electric motor is used for precise control of the signal attenuation. In this work, we present the attenuator design for a frequency band of 500-750 GHz where up to 40 dB of signal attenuation was achieved, using a 1.75 mm long silicon slab with a 25 nm Titanium metal coating. The presented variable attenuator design offers compactness, scalability, and easy integration with THz sources and receivers. Furthermore, the compact size and low power consumption open up possibilities for implementation on CubeSat/Smallsat/Drone-based platforms, further expanding its potential space applications.

This paper presents a Single-Pole Double-Throw MEMS waveguide switch operating at 500-750 GHz . The switch consist of a U-bend waveguide surrounded by an electromagnetic bandgap (EBG) surface. The EBG surface is used to isolate the electromagnetic wave without mechanical or electrical contact. The U-bend is placed on a rotating arm, that moves between two positions. The arms movement is controlled by a rotating MEMS motor that can rotate +/- 4.5(degrees) at 70 V . The switch is fabricated using silicon micromachining and is designed to be in-plane with the connecting waveguides. This allows it to be implemented into a silicon micromachined waveguide network. The waveguide switch has a measured insertion loss less than 2.5 dB and an isolation larger than 30dB between 550-750GHz . Since the electromagnetic wave can be routed with the EBG surface instead of needing electrical or mechanical contact, the MEMS waveguide switch can operate without the need for mechanical contact and avoids common MEMS switch issues such as stiction between the switch and its ports.

The design and performance of a subterahertz (sub-THz) single-pole double-throw waveguide switch is presented, operating from 250 to 310GHz. The piezo-motor actuated switch is suitable for high-fidelity calibration of THz spectroscopy and radiometry instruments, thanks to its low insertion loss, $< -0.6 \,\mathrm{dB}$ , low return loss, $< -20 \,\mathrm{dB}$ , and high isolation, $< -75 \,\mathrm{dB}$ . The high isolation and low leakage is achieved by using an array of rectangular metal pillars surrounding the waveguide apertures, which act as an electromagnetic band gap structure in the proximity of the switching element. The switching element is controlled with micrometric precision to direct the signal through a U-bend waveguide to either one of the two output waveguide apertures. The reliability and durability of the switch is tested by performing one million switch actions at its maximum switching rate of 1 Hz, resulting in a mean positioning error better than 2 $\mu \text{m}$ .

We report on the design, fabrication and preliminary characterization of the first fully solid-state room-temperature heterodyne receiver working around 2 THz. The receiver is based on a state-of-the-art subharmonically-pumped GaAs Schottky mixer and a state-of-the-art Schottky frequency multiplier chain at 1.0 THz that produces ~2mW of power. The receiver demonstrates a Double Side-band (DSB) noise temperature of less than 7000 K at room temperature. This result enables the construction of a space-borne heterodyne instrument to measure the wind velocities in the Earth’s thermosphere by observing the emission of the atomic oxygen at 2.06THz.

Space instruments that operate in the THz range can enable unique measurements for a better understanding of the chemical and physical processes taking place in our Universe. One such application of this technology is a compact 2.06 THz receiver that can measure the ionized oxygen line to determine wind velocity in Earth's upper atmosphere. Metal machined waveguide circuits have long been utilized to build and demonstrate functional receivers in the submillimeter-wave range. However, as the operational frequency is increased, extremely challenging requirements are placed on metal machining in terms of the required precision, surface roughness, and alignment tolerance. This work describes the design and implementation of the first-of-its-kind, vertically-integrated, 2-THz Schottky diode mixer using precise silicon micromachine technology. A traditional e-plane split waveguide package is re-designed to utilize the three-dimensional (3-D) capability of stacking silicon micromachined parts. The silicon microfabrication process has been optimized to produce smooth and precise features for packaging a 2 THz subharmonic GaAs Schottky diode mixer, providing surface roughness better than 1-micron rms with less than 5% variation on critical dimensions. The subharmonic mixer and a fully solid-state local oscillator (LO) chain is currently being implemented to validate silicon micromachining for THz packaging. The impact of micromachining variation on mixer performance is explored through simulations over a range of dimensions on the most sensitive regions of the Si module.

A variable attenuator is a critical component at microwave and terahertz frequencies to adjust the signal path loss-gain settings in the system. This facilitates designers and engineers to determine the optimum performance of their measurement systems and instruments. Attenuators, both fixed and tunable, are readily available at microwave frequencies however at submillimeter-wave and terahertz frequencies, design and fabrication are very challenging because such components need to be integrated with compact metal waveguide packaged subsystems and instruments. In this work, we demonstrate a novel waveguide based variable attenuator at WR1.5 band (500-750 GHz) using a metal coated silicon slab. A piezo electric motor is used to control the position of the slab on the path of the incoming electromagnetic signal to achieve variable attenuation. The amount of attenuation is determined by the volume of silicon slab inside the waveguide and the absorption coefficient of the metal coating.

Space instruments to perform measurements in the THz range can provide unique insight into the chemical and physical processes in space, motivating the need to develop key technology components to support this frequency domain. Development of a 2.06 THz receiver, used for the purposes of detecting the ionized oxygen (OI) line, is detailed here, including the process of its design, fabrication, and integration with an advanced local oscillator (LO) chain to support subharmonic mixing.

Considerable progress has recently been demonstrated for room temperature Schottky based receivers to 1200 GHz. However, pushing operating frequencies to above 2 THz is still considerably challenging due to parasitics associated with traditional planar Schottky diodes. Accurate determination of wind velocities in the thermospheric regime requires receivers at 2.06 and 4.75 THz corresponding to the ionized oxygen (OI) line. This work will provide details on how these receivers are being designed and built to enable measurement of the 3-D winds with high precision.

This article presents a low-loss silicon microelectrical mechanical system (MEMS) phase shifter operating in the 500-600 GHz band. The phase shifter consists of a 30-mu m thick perforated silicon slab that is moved in and out of a waveguide in the E-plane with a large deflection MEMS actuator. By implementing different hexagonal patterns in the silicon slab, a stepped permittivity is created to impedance match, and thus, reduce return loss. When the silicon slab is inserted into the waveguide, the phase velocity of the incoming wave is decreased, thus resulting in different phase shifts depending on the position of the slab inside the waveguide. The MEMS phase shifter is fully actuated at around 50 V and can move up to +/- 95 mu m, depending on the applied voltage. The insertion loss, when the maximum phase shift is achieved, is measured to be 1.8 dB, compared to a 1.6-dB insertion loss for a waveguide of equivalent length. The return loss is better than 18 dB for the desired band. The measured phase shift, with the slab fully inserted into the waveguide at 550 GHz was 145 degrees. The MEMS phase shifter enables a variety of applications including phased array antenna systems with scanning capability for mapping of planetary surfaces with an electronically steerable antenna.

We are developing Ka-band gallium nitride (GaN) monolithic microwave integrated circuits (MMICs) for a compact transceiver frontend. We present the design, fabrication and test results of a GaN power amplifier (PA), low noise amplifier (LNA), and single-pole-double-throw (SPDT) switch. These components are necessary for implementing a radar transceiver unit cell concept with digital calibration capabilities for future cloud radar arrays.

NASA's Planetary Science Decadal Survey has concluded that isotopic measurements of cometary water vapor are a means to unraveling the mysteries involving the origin of Earth's water and the evolution of our solar system. To support this, a recent Jet Propulsion Laboratory internal research program has developed quantum limited superconductor-insulator-superconductor (SIS) receivers in the important 500-600 GHz submillimeter frequency band. These instruments can be used to detect the deuterated water (HDO) ground state (1(10)-1(01)), (H2O)-O-16 ortho ground state (1(10) - 1(01)), and the oxygen isotopologues (H2O)-O-17 and (H2O)-O-18 with exquisite sensitivity. To achieve the presented results, we have investigated aluminum oxide (AlOx) and aluminum nitride (AlNx) barrier SIS tunnel junction mixers on the 6-mu msilicon-on-insulator substrate. The AlOx and AlNx junction mixer blocks utilize diagonal and smooth-profile conical horns, respectively. In both cases, a commercial 4-8-GHz intermediate frequency low-noise amplifier (LNA) has been integrated into the mixer block. The AlOx (low-current-density) barrier SIS junctions were fabricated with 2-mu m gold beam-lead technology, whereas in the case of the AlNx SIS tunnel junction, we use capacitive RF decoupling tabs. The latter approach simplifies fabrication, increases yield, eases the mounting process, and facilitates scaling to higher frequencies. For an actual flight mission, with operation <= 4.2 K, the allowed heat dissipation of the mixer-integrated LNA needs to be minimized. In this article, we also investigate the receiver sensitivity as a function of the LNA dc power consumption. We find that the dc power consumption of the LNA can be reduced to similar to 1.6 mW with minimal loss in sensitivity. It is anticipated that the continued InP HEMT development for quantum computer applications are likely to reduce the required LNA power dissipation even further.

A hybrid multiplier chain with a Si micromachined stack housing the 2.06-THz sub-harmonic Schottky-diode based mixer is developed for the purpose of THz sensing for NASA in space. Low-noise temperature measurements are performed using this hybrid local-oscillator (LO) chain.

By designing a Si three-dimensional stack, a reproducible process for iterative-use and accurate assembly at 2.06 THz is created. Low noise temperature is measured at 2.06 THz with a metal block at room temperature. The Si block system created via multi-step DRIE process is described. The mask layout and design considerations are discussed. Design for fine assembly, as well as process specifications of side wall smoothness and accurate etch depths of the μm-scale waveguides are essential to optimal sub-harmonic mixing performance. Variability tolerances are described, with future explorations covered.

In this paper, we report on a new 6-way MMIC power combiner amplifier utilizing cavity modes. The combiner is designed around a square cavity operating in the TM320 electromagnetic mode. Such a configuration produces a total of 6 lobes of maximum field intensity inside the cavity. By placing probes (attached to MMIC amplifier chips) in alignment with the points of maximum field strength, a highly compact power combiner can be achieved. We illustrate this concept using a set of 1 Watt W-band GaN MMIC chips, placed in layered copper sheets and oriented so the MMICs line up with the regions of maximum field strength. A 6-way power combiner was built and was able to deliver 5.5 Watts of output power and 13.4% PAE using a miniature package.

We have developed gallium nitride (GaN) monolithic microwave integrated circuit (MMIC) amplifiers that span different frequency ranges from Q-band (33–50 GHz) into G-band (140–220 GHz). We have designed, fabricated and tested a broadband amplifier with more than 11 dB of gain from 38 GHz to at least 110 GHz, and a broadband amplifier with gain across all of F-band (90–140 GHz) with peak gain of 18.9 dB and noise figure of 7.4 dB at 120 GHz. In G-band we have developed an amplifier with 8.7 dB small-signal gain at 149 GHz, and when two such amplifiers were placed in series, large signal power measurements gave 18.2 dBm of output RF power and 10 dB gain at 147 GHz. These results demonstrate 0.15 μm gate length GaN HEMTs are applicable for amplifiers through F-band and into G-band.

In this paper, we describe a miniature power-combiner for monolithic millimeter-wave integrated circuit (MMIC) chips using spatial power-combining with cavity modes. We have designed GaN MMIC power amplifier chips for 94 GHz, and illustrate the concept of the W-Band Spatial Power Combining Amplifier (WSPCA). Using 1 Watt, 94 GHz MMIC chips in a two-way cavity mode combiner, we were able to achieve 2 Watts of output power with 9 dB gain and 15 % PAE. This technique could be extended to high power MMICs and larger numbers of chips to achieve higher output power in a compact size. Current applications include earth science radar, and may be extended to other applications requiring wider bandwidth.

We report on a compact high-power 510-560 GHz GaAs Schottky diode based frequency tripler with enhanced power handling capabilities, showing a world-record measured peak power of 30 mW, at room-temperature, when pumped with 350-400 m W. This corresponds to a ten times better performance than previously reported sources in this frequency range. The increase in power handling capabilities is achieved by using an improved epitaxial structure together with an on -chip power combined topology that allows to combine several multiplying structures onto a single chip. The chip also exhibits a state-of-the-art conversion efficiency of 8-9% without any correction for the losses in fixtures/transitions used for the tests.