Submillimeter-wave Systems Research Articles

Enabling Applications of Electromagnetic Waves at 0.3-1.0 THz Using Silicon Electronic Integrated Circuits.

Over the past 15 years, the output power of silicon submillimeter-wave electronics has increased by a factor greater than 1000 reaching -3.9 dBm at 440 GHz for a single unit in CMOS and -10.7 dBm at 1.01 THz for a 42-element array in SiGe BiCMOS. The smallest power of a 1 kHz bandwidth signal at 420 GHz that can be detected has improved by 100 million times. These and the expected improvements from the ongoing activities should be sufficient to support high resolution imaging with a range of up to several hundred meters, gas sensing up to ∼1 THz, and communication over ∼1000 m. The silicon IC technologies enable integration of complex systems into a small form factor and reduction of manufacturing cost. When broad deployment of submillimeter wave systems for everyday life applications becomes necessary, the silicon IC infrastructure will be the most capable to support the high-volume manufacturing need.

Real-Time Discrete Fractional Fourier Transform Using Metamaterial Coupled Lines Network

Discrete fractional Fourier transforms (DFrFTs) are universal mathematical tools in signal processing, communications, and microwave sensing. Despite the excessive applications of DFrFT, the implementation of corresponding fractional orders in the baseband signal often leads to bulky, power-hungry, and high-latency systems. In this article, we present a passive metamaterial coupled lines network (MCLN) that performs the analog DFrFT in real-time at microwave frequencies. The proposed MCLN consists of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$M$</tex-math> </inline-formula> parallel microstrip transmission lines (TLs) in which adjacent TLs are loaded with interdigital capacitors to enhance the coupling level. We show that with the proper design of the coupling coefficients between adjacent channels, the MCLN can perform an M-point DFrFT of an arbitrary fractional order that can be designed through the length of the network. In the context of real-time signal processing for the realization of DFrFT, we design, model, simulate, and implement a 16 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 16 MCLN and experimentally demonstrate the performance of the proposed structure. The proposed innovative approach is versatile and is capable to be used in various applications where DFrFT is an essential tool. The proposed design scheme based on MCLN is scalable across the frequency spectrum and can be applied to the millimeter and submillimeter wave systems.

CMOS Platform for Everyday Applications Using Submillimeter Electromagnetic Waves

CMOS (Complementary Metal Oxide Silicon) integrated circuits (ICs) technology is emerging as a means for realization of capable and affordable systems that operate at frequencies near 300GHz and higher. This is lowering a key barrier for utilizing the sub-millimeter electromagnetic waves in everyday applications. Despite the fact that the unity maximum available gain frequency, fmax of NMOS transistors (with connections to the tope metal layer) has peaked at 320 GHz, signal generation up to 1.33 THz, coherent detection up to 1.2 THz and incoherent detection up to 10 THz have been demonstrated using CMOS integrated circuits. Furthermore, highly integrated rotational spectroscopy transceivers operating at frequencies up to near 300 GHz, 300-GHz and 400-GHz concurrent transceiver pixels and arrays for high resolution radar imaging, and 300-GHz and 390-GHz transmitters, and 300-GHz receivers for high data-rate communication have been demonstrated in CMOS. The performances of these CMOS circuits are sufficient or close to being sufficient to support electronic smelling using rotational spectroscopy that can detect and quantify concentrations of a wide variety of gases; imaging that can enable operation in a wide range of visually impaired conditions; and high-bandwidth communication. Lastly, techniques for affordable packaging and testing sub-millimeter wave systems are suggested based on experimental demonstrations.

H-Band Quartz-Silicon Leaky-Wave Lens With Air-Bridge Interconnect to GaAs Front-End

Thanks to the large bandwidth availability, millimeter and submillimeter wave systems are getting more attractive to be used in a wide range of applications, such as high-resolution radar or high-speed communications. In this contribution, a new lens antenna in-package solution is presented for the H-band (220–320 GHz), including a wideband quartz-cavity leaky-wave feed combined with an air-bridge chip interconnect technology, based on spray coating and laser lithography. This interconnection acts as a wideband, low-loss transition between the GaAs front-end and the quartz antenna, avoiding the use of expensive waveguide split-blocks. An antenna prototype including the interconnect has been manufactured and characterized, validating the full-wave simulated results for the integrated H-band leaky-wave with aperture efficiency higher than 74% over 34% bandwidth, and radiation efficiency higher than 70% over 37% of bandwidth.

Wideband Circularly Polarized Horn Antenna Exploiting Open Slotted End Structure

In this letter, a compact circularly polarized horn antenna is presented. By cutting a slot along the 45° direction at the end of the circular waveguide, the proposed antenna achieves the wideband circularly polarized radiation. A prototype working at W-band is fabricated. Both the impedance bandwidth (S(1, 1) <−10 dB) and the circular polarization bandwidth (AR < 3 dB) of the processed antenna are measured as 37.8% (75–110 GHz). The proposed antenna exhibits a simple structure, and it is easy to design, so it can be extensively applied in millimeter-wave (mm-wave) and submillimeter-wave systems.

Design and Performance of a High- $Q$ Narrow Bandwidth Bandpass Filter in Empty Substrate Integrated Coaxial Line at $K_{u}$ -Band

This letter presents the design and performance of a planar narrow bandwidth bandpass filter with high quality factor. The structure is composed of an empty substrate integrated coaxial line with the center conductor suspended in air. The component dimensions have been calculated by means of classical microwave filter design theory. The filter has been manufactured using standard printed circuit board fabrication processes. A measured insertion loss of 1.59 dB, 2.93% fractional bandwidth, and a $Q$ -factor of 1505 have been obtained at 15 GHz. A $Q$ -factor comparison with other substrate and empty substrate integrated technologies shows the advantages of the solution considered in this letter. The proposed filter proves to be suitable for the implementation of integrated microwave or millimeter-wave subsystems with severe restrictions, i.e., low in-band losses, very narrow bandpass responses, low frequency dispersion, high out-of-band rejection, and low manufacturing cost.

THz Diode Technology: Status, Prospects, and Applications

Found in many terahertz (THz) and submillimeter-wave systems, GaAs Schottky diodes continue to be one of the most useful THz devices. As a low-parasitic device that operates well into the THz range, Schottky diodes provide useful detection and power generation for a number of practical applications. Mixers and multipliers, working as high as ~3 THz, have already been demonstrated. This paper reviews the current status of diode technology, detailing some of the different ways for fabricating THz chips. An overview regarding the current state of technology and performance for THz frequency multipliers and mixers is presented, along with applications enabled by these diodes.

Micromachined Interfaces for Metrology and Packaging Applications in the Submillimeter-Wave Band

The continued emergence of new terahertz devices has created a need for improved approaches to packaging, integration, and measurement tools for diagnostics and characterization in this portion of the spectrum. Rectangular waveguide has for many years been the primary transmission medium for terahertz and submillimeter-wave systems operating from 300 GHz to 1 THz, with the UG-387 flange the most common interface for mating waveguide components over this frequency range. Alignment of UG-387 flanges is accomplished with pins and alignment holes that are placed around the flange perimeter and, under the standard MIL SPECS tolerances, misalignments of up to 6 mils (150 microns) are possible as a result of practical milling tolerances. With the emergence of vector network analyzers operating beyond 1 THz, such misalignment of waveguide mating flanges is not negligible and is recognized as a fundamental issue limiting calibration and measurement precision at frequencies greater than 300 GHz. In response to this issue, a number of new waveguide flange concepts have been investigated to reduce flange misalignment and the P1785 IEEE Standard was recently issued to recommend designs for waveguide interfaces at frequencies above 110 GHz. Among the new flange concepts being proposed is a modified UG-387 that utilizes tighter machining tolerances and the ring-centered flange where alignment is accomplished using a precision coupling ring that fits over raised bosses that are centered on each waveguide. This paper discusses the new interface concepts that are being developed to address waveguide flange misalignment as well as emerging micromachined interconnects, calibration standards and heterogeneous integration methods that are being applied to implement low-loss and high-performance circuit architectures for the terahertz frequency range. Among the technologies that will be described are (1) design and characterization methods for the new ring-centered waveguide standard, (2) micromachined waveguide components and calibration standards for the terahertz band, (3) silicon-based micromachined probe structures for direct-contact interfacing and metrology, and (4) epitaxial transfer of III-V semiconductor material onto high-resistivity silicon to realize a low-loss platform for integration of terahertz components. Details of the processing methods used to realize these components as well as measurement techniques for assessing their performance will be described.

Compact Wideband Corrugated Feedhorns With Ultra-Low Sidelobes for Very High Performance Antennas and Quasi-Optical Systems

The corrugated or scalar feedhorn has found many applications in millimeter wave and sub-millimeter wave systems due to its high beam symmetry, relatively low sidelobe levels and strong coupling to the fundamental mode Gaussian beam. However, for applications such as millimeter wave cosmology, space-based experiments, or even high performance imaging, there is a generic requirement to reduce the size of horns whilst maintaining very high levels of performance. In this paper we describe a general analytic methodology for the design of compact dual-profiled corrugated horns with extremely low sidelobe levels. We demonstrate that it is possible to achieve -50 dB sidelobe levels, over wide bandwidths with short horns, which we believe represents state-of-the-art performance. We also demonstrate experimentally a simple scalar design that operates over wide bandwidths and can achieve sidelobes of better than -40 dB, whilst maintaining a frequency independent phase center. This design methodology has been validated experimentally by the successful manufacture and characterization of feedhorns at 94 GHz and 340 GHz for both radar and quasi-optical instrumentation applications.

Amplifier based broadband pixel for sub-millimeter wave imaging

Broadband sub-millimeter wave technology has received significant attention for potential applications in security, medical, and military imaging. Despite theoretical advantages of reduced size, weight, and power compared to current millimeter wave systems, sub-millimeter wave systems have been hampered by a fundamental lack of amplification with sufficient gain and noise figure properties. We report a broadband pixel operating from 300 to 340 GHz, biased off a single 2 V power supply. Over this frequency range, the amplifiers provide > 40 dB gain and 1.0 THz. The first sub-millimeter wave-based images using active amplification are demonstrated as part of the Joint Improvised Explosive Device Defeat Organization Longe Range Personnel Imager Program. This development and demonstration may bring to life future sub-millimeter-wave and THz applications such as solutions to brownout problems, ultra-high bandwidth satellite communication cross-links, and future planetary exploration missions.

A Low VSWR 2SB Schottky Receiver

A novel high performance waveguide integrated sideband separating (2SB) Schottky receiver operating in the 320-360 GHz band is presented. The unique receiver design is based on a core of two subharmonic Schottky diode mixers with embedded LNA's with a minimum noise figure of 1.8 dB, fed by LO and RF quadrature hybrids. At room temperature, a typical receiver SSB noise temperature of 3000 K is measured over most of the band reaching a minimum of 2700 K, with only 4 mW of LO power. The sideband ratio (SBR) is typically below 15 dB over the whole band and the measured LO input return loss is typically below 15 dB broadband. High performance sideband separating Schottky receivers can now for the first time be considered for submillimeter wave systems enabling new types of instrument concepts.

Design and Characterization of a $W$-Band Micromachined Cavity Filter Including a Novel Integrated Transition From CPW Feeding Lines

This paper demonstrates a novel coplanar waveguide (CPW) to rectangular waveguide (RWG) transition and its application as an integration enabling structure for filters at W-band for the first time to the best of the authors' knowledge. In the proposed wideband transition, the CPW and RWG are integrated on one side of the substrate, while the coupling probe is patterned directly on the substrate instead of being made separately. The transition is fabricated using silicon micromachining and thick-film surface micromachining techniques with high precision, which is suitable for millimeter-wave subsystems and are easily extendable to terahertz applications compared to the existing approaches. In the proposed filter design, the metallized probes are used to couple signals from the CPW to waveguide resonant cavities, therefore, the need for waveguide input/output ports is eliminated. This significantly reduces the size of the filter by approximately 30%. The transition and filter components are optimized using Ansoft's high frequency structure simulator 10 (HFSS 10). The measured response of the filter has the center frequency at 96.6 GHz, 2.9% bandwidth, and a 4.14-dB insertion loss in the passband.

Advances in millimeter-wave subsystems in Japan

The authors describe the development trends and results of millimeter-wave systems in Japan in such fields as communication, radar, and measurement systems. The applications included are the W-40G waveguide transmission communication system, an automobile traffic control system using the 60-GHz band, a collision avoidance radar system for an automobile, a plasma electron density measuring system, and satellite communication. The authors describe the development of devices such as high-power FET amplifiers, traveling wave tube amplifiers (TWTAs), IMPATT amplifiers, low-noise amplifiers, and monolithic microwave integrated circuit (MMIC) devices used in constructing the millimeter-wave systems. >

A Review of the Panel Discussion on Advances in Millimeter-Wave Subsystems

The millimeter-wave subsystems panel, was formed to provide an overall picture of the status of millimeter-wave subsystems as seen by a group of panelists from six of the major international companies. The principal features were to be the application of current technologies to systems requiring large quantities of millimeter-wave subsystems. Members of the panel were selected to represent a cross section of technologies and applications as well as to provide an overview of the current technologies throughout the industry. It was recognized early that a diversified group of experts would bring about a varied number of technologies for construction. Emphasis was placed on current and in-place construction techniques, and how these techniques are used to produce practical multifunction subsystems. Almost as an afterthought, panelists were asked to discuss techniques that are applicable to low-volume as well as high-volume production. This last minute change of format seemed appropriate since the current state of the art for many of the techniques is in the prototype stages, that is, still not in the high-volume stage. During the panel discussion, this factor was brought out even more.

Small-signal theory of a large-orbit electron-cyclotron harmonic maser

The small-signal theory of a harmonic gyrotron is presented for the case of axis-encircling electron orbits. The beam current required for oscillation is found to be highly dependent on the electron energy. Gyrotron cavities operating on this principle at very high harmonic numbers (n≂10) and high frequency in weak magnetic fields are well matched to low-current, moderate-energy, rf-accelerated electron beams (≂50 mA, ≂250 keV), resulting in compact submillimeter wave systems.