W-band Frequency Range Research Articles

Results of the Study of a New Generation Technological Gyrotron System With High Power and Efficiency

A series of work has been carried out to develop a new generation of technological gyrotrons on the first cyclotron harmonic with a radiation frequency of 28 GHz and a power beyond 20 kW. The generation efficiency reaches up to 55% at 6-kW power level without a system of recovery of residual electron energy. The efficiency of the entire setup is about 35% in the mode of maximum radiation power, which is achieved by using a magnetically shielded oil-cooled solenoid. The proper operation of the developed electron-optical system under conditions of a quasi-adiabatic magnetic field in the area of formation of a helical electron beam and a non-adiabatic one in the collector region is confirmed. The letter presents experimental data which is consistent with the results of numerical modeling. This allows us to further count on the implementation of generators up to the W-band frequency range using the magnetic system and high-voltage power sources.

Structured-Glass Waveguide Technology for High-Performance Millimetre-Wave Components and Systems

This work presents a novel waveguide medium based on laser-induced structured-glass for the design of high-end millimetre-wave components and systems. The material properties, fabrication process and functional attributes of the structured-glass technology are first described and then applied in order to demonstrate a fourth-order bandpass filter prototype operating within the W-band frequency range, centered around 88 GHz with a narrow fractional bandwidth of 2.3%. The basic filter design, dimensional considerations, and assembly process are discussed in order to outline the fabrication process. The prototype filter, along with its associated feed-line transitions and split-block interface are measured and characterized in the laboratory in order to validate the design approach. The measured response is shown to be exceptionally accurate; the insertion loss is found to be approximately 1.43 dB - 1.97 dB throughout the measured passband with a return loss of better than 22 dB and center-frequency offset of approximately 0.117%. A comparison to existing technologies is discussed in order to highlight the advantages of the proposed medium and to contrast the differences in both manufacture and achievable results for high-end components.

Demonstration of a W-Band Traveling-Wave Tube Power Amplifier With 10-GHz Bandwidth

We present the experimental demonstration of a traveling-wave tube (TWT) power amplifier operating in the W-band (75-110 GHz) frequency range. The device is based on a serpentine waveguide (SWG) amplification circuit, a slow wave circuit type capable of high power and broad instantaneous bandwidth in the upper millimeter-wave range. A 20 kV, 140-mA round solenoid-focused electron beam powers the device. At 20 kV, we measure 215 ± 2 W peak RF output power at 93 GHz with 20.1 ± 0.15 dB saturated gain, pulsed at 0.1% duty. We observe 10-GHz instantaneous amplification bandwidth at 100-W minimum output power, covering the range 88-98 GHz. Operating at 20.8 kV, the TWT produces 285 ± 3 W at 91 GHz with 22.4 ± 0.15 dB gain, and 7 GHz, 3-dB bandwidth. The peak electronic efficiency measured is approximately 10%.

High-Field (3.4 T) ENDOR Investigation of Asphaltenes in Native Oil and Vanadyl Complexes by Asphaltene Adsorption on Alumina Surface

Vanadyl porphyrin complexes in asphaltenes from heavy (Karmalinskoye) oil and in asphaltene films obtained as a result of adsorption on the surface of aluminum oxide were studied by electron paramagnetic resonance (EPR) and double electron-nuclear resonance (ENDOR) in the W-band frequency range (microwave frequency of 95 GHz, magnetic field of 3.4 T). Mims ENDOR spectra from 1H and 27Al nuclei are observed. ENDOR spectra are different for native oil and asphaltenes from one side and the adsorbed samples from the other side while no significant changes in X- (microwave frequency of 9 GHz) or W-band EPR spectra are found. The results allow supposing that vanadyl porphyrin complexes (at least in the studied asphaltene films) participate in the formation of asphaltene aggregates through the functional groups rather than π−π interactions. The data show the feasibility of the commercial pulsed ENDOR approaches for the investigation of crude oils and their constituents under external influence.

Improved broadband (75–110 GHz) radio frequency characteristics of MEMS shunt switches on quartz substrate

This paper presents improved W-band (75–110 GHz) radio frequency characteristics of micro-electromechanical switches in T and π-matched configurations. The switch structures consist of Au metallic bridge (s) suspended over the coplanar waveguide (CPW) signal line drawn on quartz substrate. Here, a high impedance transmission line is introduced on both the sides of the bridge structure to reduce the return loss. To further tune up the broadband RF response the bridge width (40–80 µm) as well the dielectric thickness (0.15–0.18 µm) are varied. At optimum condition (bridge width: 60 µm; dielectric thickness: 0.18 µm), the T-matched RFMEMS switch structure exhibits return loss better than − 20 dB; insertion loss ~ − 0.2 dB and isolation better than − 30 dB in full W-band frequency range. In π-match configuration, a short section of high impedance transmission line is being introduced between two switch structures for impedance matching. RF parameters of the π-matched shunt switch structure are studied as a function of width (10–40 µm) and length (30–180 µm) of the high impedance transmission line. At optimum condition (line width: 30 µm; length: 130 µm), the π-matched switch structure exhibits return loss: better than − 15 dB; insertion loss: better than − 0.5 dB; and isolation: better than − 45 dB over the entire W-band. From the equivalent circuit modeling, the equivalent inductance, capacitance and resistance values for the optimized switch structures are also reported.

Reduction of S-parameter errors using singular spectrum analysis.

A free space measurement method, which consists of two horn antennas, a network analyzer, two frequency extenders, and a sample holder, is used to measure transmission (S21) coefficients in 75-110 GHz (W-Band) frequency range. Singular spectrum analysis method is presented to eliminate the error and noise of raw S21 data after calibration and measurement processes. The proposed model can be applied easily to remove the repeated calibration process for each sample measurement. Hence, smooth, reliable, and accurate data are obtained to determine the dielectric properties of materials. In addition, the dielectric constant of materials (paper, polyvinylchloride-PVC, Ultralam® 3850HT, and glass) is calculated by thin sheet approximation and Newton-Raphson extracting techniques using a filtered S21 transmission parameter.

Heterogeneous integration of a miniaturized W-band radar module

For radar applications, the W-band frequency range (75 – 110 GHz) is a good candidate for high-resolution distance measurement and remote detection of small or hidden objects in distances of 10 cm to ≫ 20 m. As electromagnetic waves in this frequency range can easily penetrate rough atmosphere like fog, smoke or dust, W-band radars are perfectly suited for automotive, aviation, industrial and security applications. Additional benefit is that atmosphere has an absorption minimum at 94 GHz, so relative small output power is sufficient to achieve long range coverage. By combining and enhancing knowledge from the disciplines of heterogeneous integration technology and compound semiconductor-technology, the Fraunhofer Institutes IAF, IPA and IZM developed a miniaturized and low cost 94 GHz radar module. Result of this approach is a highly miniaturized radar module built using a modular approach. The radar components are mounted on a dedicated RF-NF-hybrid PCB while the signal processing is done on a separate board stacked below. This hybrid RF-module is combined with highly integrated digital processing PCB via micro connectors in a way that the radar system and an adapted conical HDPE-lens fit into an aluminum housing of 42×80×27 mm3 with a weight of only 160 grams for the whole module. The paper will describe the technological basis for such a frequency modulated continuous wave [FMCW] W-band radar module and describe in detail the technological features that enabled the assembly of such a miniaturized but high-performance system. The module yields an evaluated distance measurement accuracy of 5 ppm (5 μm deviation per meter target distance) while its low weight and small dimensions pave the way for a variety of new applications, including mobile operation.

High-Gain Millimeter-Wave AlGaN/GaN Transistors

In this paper, the fabrication and performance of common-source (CS) and common-gate transistors for operation at millimeter-wave frequencies are presented. The AlGaN/GaN devices have a gate length of 100 nm and yield a high maximum transconductance of above 550 mS/mm with a very low contact resistance of less than 0.12 Ω·mm. The baseline technology with its optimized epitaxial structures and their transition frequency of more than 80 GHz allows reproducible designs for monolithic microwave integrated circuits up to the W-band frequency range (75-110 GHz). In addition, GaN dual-gate (DG) devices were developed for substantial improvement of the bandwidth of the devices and of the gain per stage on circuit level. This paper discusses the advantages of the DG devices in power gain over the CS high electron mobility transistors for millimeter-wave applications.

A W-Band Multi-Layer Microwave Window for Pulsed Operation of Gyro-Devices

A broadband multi-layer microwave window operating in the W-band frequency range was numerically simulated, constructed and its microwave properties measured. The window acts to separate vacuum and atmosphere. It had to meet strict requirements for application in gyro-amplifiers of broadband, low reflection and high mechanical strength. The window was manufactured showing a ${- 20}~{\rm dB}$ reflection over 90–100 GHz (except in two small regions), which is in good agreement with the numerical simulation presented in this letter.

Investigation of a Wideband BiCMOS Fully On-Chip $W$-Band Bowtie Slot Antenna

Design and implementation of a W-band on-chip bowtie-shaped slot antenna fabricated in 180-nm BiCMOS process is presented, and its performance and limitations are discussed. This antenna has a measured impedance bandwidth (S11 <; -10 dB) across the W-band frequency range and a very wide gain bandwidth, making it a candidate for wideband applications. The measured gain for this antenna is 0-1 dBi at 94 GHz. This letter also analyzes the influence of the RF probe to the on-chip antenna performance.

Demonstration of Passive W-Band Millimeter Wave Imaging Using Optical Upconversion Detection Methodology with Applications

Millimeter wave (mmW) imaging has enjoyed a measure of success due to the unique properties of imaging in this spectral region, some of which are still being discovered. For example, a key advantage of mmW imaging is the ability to penetrate through various atmospheric obscurants, including fog, dust, sand, and smoke, due to its longer wavelengths as compared to visible or infrared imaging. Various methods of imaging with mmW energy exist, such as direct detection, downconversion, and upconversion, where this manuscript focuses on the latter. Until now, passive imaging using an optical upconversion method was limited to Q-band frequencies due to the lack of commercially available parts, namely a sufficiently high frequency optical modulator. To overcome this limitation, a custom-built modulator using in-house fabrication facilities was realized to allow imaging within the W-band frequency range (75–110 GHz). Therefore, in this manuscript we report new results of passive imaging in the W-band frequency range using a unique optical upconversion technique, where the higher frequency operation allows for greater detail in the imagery thus collected.

W‐band microstrip band‐pass filter using branch‐line coupler with open stubs

AbstractThis article presents the design and measurement of a microstrip band‐pass filter (BPF) using modified branch‐line coupler with asymmetric open‐circuit stubs in the W‐band frequency range. The fundamental topology consists of using the branch‐line coupler as a filtering section by loading the coupled ports with suitable lengths of open‐circuit stubs. Therefore, transmission responses with simultaneously good stopband and sharp cutoff slope are derived, while the passband bandwidth can be easily controlled by means of the design parameters of the filtering section. The proposed BPF structure has been designed and fabricated on GaAs substrate. The fabricated BPF shows a 3‐dB bandwidth from 81 to 107 GHz with insertion loss &lt;2 dB at center frequency, rejection of 51 dB, and return loss better than 18 dB. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1436–1439, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25185

Non-destructive microwave detection of layer thickness in degraded thermal barrier coatings using K- and W-band frequency range

Thermal barrier coatings have been widely used in gas turbine engines in order to protect the substrate metal alloy against high temperature and to enhance turbine efficiency. To monitor thermal barrier coating (TBC) integrity over its lifetime, the detection of top coat (TC) and thermally grown oxide (TGO) thicknesses was carried out using a microwave non-destructive technique. The results showed a good resolution of 1° change in phase for 15 μm TC thickness when a rectangular waveguide operating at relatively high frequency was applied. The phase of the reflection coefficient at the interface of TC and waveguide varies for different TGO and TC thicknesses. Therefore, measuring the phase of the reflection coefficient enables us to accurately calculate these thicknesses. Finally, a theoretical analysis was used to evaluate the reliability of the experimental results.

Reliable method for material characterisation using quasi-optical free-space measurement in W-band

An extension to the Nicolson–Ross–Weir (NRW) algorithm to retrieve complex permittivity and permeability from both reflection and transmission coefficients is presented. This new numerical retrieval approach solves the phase ambiguity problem associated with the NRW algorithm. A free-space quasi-optical two-port measurement setup is employed to obtain the scattering parameters of different samples in the W-band frequency range. The results of different samples with various thicknesses are presented. The advantages and limitations of the method are also discussed.

Complex permittivity and permeability measurements of ferrimagnets at Millimeter waves with high power sources

We present complex dielectric permittivity and magnetic permeability characteristics of strontium and nickel ferrite ceramics in Q-, V-, and W-band frequency range. The measurements have been done using broad-band quasi-optical millimeter wave spectrometer with backward-wave oscillator as a high power source of coherent radiation. Dielectric and magnetic parameters of the ferrite ceramic materials have been calculated by employing the best fit of the theoretical curves to the experimental transmittance spectra.

Zeolite–carbon composites prepared from industrial wastes: (II) evaluation of the adaptability as environmental materials

Novel zeolite–carbon composites were fabricated by a combined process of calcination and carbonization at 600–850 °C in the N 2 atmosphere followed by a hydrothermal treatment from industrial wastes of coal fly ash and sawdust mixtures in alkaline aqueous solutions. Adaptability of the resulting zeolite–carbon composites as high value-added environmental materials was evaluated. It was found that the composites consisted of micropores and mesopores with the ability to adsorb water vapor up to an amount of 20 mass% which was superior to some commercial zeolite building materials. The composites also demonstrated a capacity to absorb electromagnetic wave in the W-band frequency range (75–110 GHz) characterized as a reflection loss higher than 20 dB at the resonant frequencies. These results indicated that the zeolite–carbon composites were prominent candidates as environmental-friendly building materials for wall or flooring with adsorption abilities for water vapor as well as absorption and shielding effects of electromagnetic wave.

Characterization of semilumped CPW elements for Millimeter-wave filter design

In this paper, two accurate models for interdigital capacitors and shunt inductive stubs in coplanar-waveguide structures are presented and validated over the entire W-band frequency range. Using these models, a novel bandpass filter (BPF) and a miniaturized high-pass filter are designed and fabricated. By inserting interdigital capacitors in BPF resonators, an out-of-band transmission null is introduced, which improves rejection level up to 17 dB over standard designs of similar filters. A high-pass filter is also designed, using semilumped-element models in order to miniaturize the filter structure. It is shown that a fifth-order high-pass filter can be built with a maximum dimension of less than /spl lambda//sub g//3. Great agreement between simulated and measured responses of these filters is demonstrated.

Two-Stage Broadband High-Gain W-Band Amplifier Using 0.1-&amp;lt;tex&amp;gt;$mu$&amp;lt;/tex&amp;gt;m Metamorphic HEMT Technology

We report broadband high-gain W-band monolithic microwave integrated circuit amplifiers based on 0.1-/spl mu/m InGaAs-InAlAs-GaAs metamorphic high electron mobility transistor (MHEMT) technology. The amplifiers show excellent S/sub 21/ gains greater than 10 dB in a very broad W-band frequency range of 75-100 GHz, thereby exhibiting a S/sub 21/ gain of 10.1 dB, a S/sub 11/ of -5.1 dB and a S/sub 22/ of -5.2 dB at 100 GHz, respectively. The high gain of the amplifier is mainly attributed to the performance of the MHEMTs exhibiting a maximum transconductance of 691 mS/mm, a current gain cutoff frequency of 189 GHz, and a maximum oscillation frequency of 334 GHz.

A theoretical study of differing active region doping profiles for W-band (75–110 GHz) InP Gunn diodes

InP Gunn diodes are widely used as high power microwave sources in the W-band frequency range (75–110 GHz), but interesting questions remain as to the optimal active region doping profile for such devices. In this paper we carry out a detailed theoretical study, using Monte Carlo simulations, of three types of doping profiles: (i) uniform doping, (ii) graded doping (i.e. increasing linearly from cathode to anode) and (iii) notch doping (a lightly doped region adjacent to the cathode). By studying the effects of varying all the relevant parameters, such as doping levels, active region length, bias levels and temperature, under both DC and RF conditions, we argue that the notch doping approach is superior, offering high performance combined with a greater tolerance to doping fluctuations.

W -band CPW RF MEMs circuits on quartz substrates

This paper presents W-band coplanar waveguide RF microelectromechanical system (MEMS) capacitive shunt switches with very low insertion loss (-0.2 to -0.5 dB) and high-isolation (/spl les/ -30 dB) over the entire W-band frequency range. It is shown that full-wave electromagnetic modeling using Sonnet can predict the performance of RF MEMS switches up to 120 GHz. Also presented are W-band 0/spl deg//90/spl deg/ and 0/spl deg//180/spl deg/ switched-line phase shifters with very good insertion loss (1.75 dB/bit at 90 GHz) and a wide bandwidth of operation (75-100 GHz). These circuits are the first demonstration of RF MEMS digital-type phase shifters at W-band frequencies and they outperform their solid-state counterparts by a large margin.