WR-10 Waveguide Research Articles

MEASUREMENT OF COMPLEX PERMITTIVITY OF LIQUIDS USING WAVEGUIDE TECHNIQUES - ABSTRACT

Complex permittivity of a number of liquids and binary mixtures has been studied by measurement using the waveguide techniques at the X and Ku band. Particular pieces of WR90 and WR62 waveguides were designed for the measurement of liquid materials. The custom designed TRL calibration kits are applied for calibration of the waveguide system. The measured results of complex permittivity of liquid dielectrics, such as methanol, propyl alcohol, ethyl alcohol, chlorobenzene, dioxane, cyclohexane and binary mixtures, are presented. Particular pieces of open-ended waveguides for the X and Ku bands were also designed for holding liquids and the measured data using the open-ended waveguide technique were compared with those measured using the waveguide technique. Some of the measured results are also compared with calculated data using the Debye equation and published data measured by the Fourier transform spectroscopy.

WR75 junction circulator using 90° and 180° ridge UEs

The gain–bandwidth product of a practical junction circulator is fixed by the quality factor of its junction and the topology of its matching circuit. One difficulty with the design of a large mean power circulator or a millimetre one is that its quality factor may not be compatible with the use of 30° and 90° UEs. A method of overcoming these difficulties is to employ a 180° UE at each so-called characteristic plane of the junction. The purpose of the paper is to describe one arrangement in a WR75 waveguide. The device has a return loss of 20 dB and an insertion loss of 0.17 dB over a 16% frequency band. The quality factor of its complex gyrator circuit is 4.0.

CPW to waveguide transition with tapered slotline probe

A new CPW to waveguide transition is developed based on the concept of tapered slot antenna and E-plane probe coupling. The transition consists of a tapered slotline probe and a slotline to CPW matching section. The current design has the advantages of broad bandwidth, compact size, low fabrication cost, and high reliability. The characteristics of a prototype transition are investigated by numerical simulation on Duroid substrate and WR-90 waveguide. The back-to-back combination is measured to verify the agreement with the simulated results and realization of this design.

High-power vacuum window in WR10

Results are presented in this paper for fabrication and test of a WR10 waveguide window for use in ultrahigh vacuum at 91.4 GHz. Low-power bench measurements are compared with analytic and simulation results. Operation at /spl ap/4-kW peak power, duty factor 10/sup -6/, and 10/sup -9/-scale vacuum is noted.

Electronic excitation temperature profiles in an air microwave plasma torch

A 0.9- to 1.5-kW 2.45-GHz atmospheric pressure air microwave plasma torch has been operated efficiently with less than 1% reflected power. The plasma is sustained in a 28-mm internal diameter fused quartz tube, which penetrates perpendicularly through the wide walls of a tapered and shorted WR-284 (72/spl times/17-mm cross section) waveguide. A study has been made of the effects of power and airflow on the electronic excitation temperature, T/sub exc/. Abel inversion of radial profile chord averaged Fe I emission lines in the 370-377-nm range have been used to obtain localized profile measurements of T/sub exc/ inside the waveguide excitation region. In general, temperature profiles peak on axis with no evidence of a skin effect in the large diameter (10-mm full width at half maximum emission intensity) plasmas. A maximum central T/sub exc/ of 6550 K/spl plusmn/350 K is observed at an airflow rate of 28 Ipm. When maintaining a constant flow rate of 14 Ipm, a 55% increase in microwave power from 0.9 to 1.4 kW causes a /spl sim/100% increase in plasma volume without any noticeable effect on the central T/sub exc/ value. At a constant microwave power of 1.4 kW, an increase in total flow rate from 11 to 28 Ipm decreases the volume of the plasma by /spl sim/25% and increases the central T/sub exc/ by /spl sim/13%. The axially peaked temperature profiles are consistent with an electron density of /spl sim/10/sup 13/ cm/sup -3/.

A Slotted Wavegume Applicator for Continuous Flow Grain Drying

A slotted waveguide antenna was designed and developed with series slots cut on the broad side that constituted a popular means of coupling microwaves with grain for drying. The radiating characteristics of the slotted zvaveguide antenruz mounted in a setup that simulated the coupling to a grain conveying tube were studied at a frequency of 2.45 GHz. The antenna consisted of a WR-340 waveguide made of copper. The effect of the slot inclination angle Ø, moisture content and the shape of the slots were investigated. The results indicated 55° as an optimum slot angle for slots having a width of 13 mm and a length 58 nun. Slots with a width of 6 mm did not exhibit any regular behavior and the Effect of Ø was not clearly identified.

Cryogenic indium-phosphide HEMT low-noise amplifiers at V-band

Indium-phosphide (InP) high electron-mobility transistors potentially have the lowest noise at frequencies below 100 GHz, especially when cryogenically cooled. We have designed monolithically integrated InP millimeter-wave low-noise amplifiers (LNAs) for the European Space Agency (ESA) science Planck mission. The Planck LNA's design goal for noise temperature is 35 K at the ambient temperature of 20 K. The operation bandwidth is over 20% at 70 GHz. The maximum allowable power consumption for a Planck LNA (gain 20 dB) is P/sub be/=5 mW at 20 K. The chosen foundry for these LNA's was DaimlerChrysler Research, Ulm, Germany. The DaimlerChrysler 0.18-/spl mu/m InP process was used. This process is well suited for V-band LNA design, giving sufficient gain with very low noise. Several one-, two-, and three-stage amplifiers were designed. The best of them exhibited a noise figure lower than 5.5 dB with a gain higher than 14 dB over the 50-68-GHz range at room temperature. The best single-stage amplifier demonstrated a noise figure of 4.5 dB and a gain higher than 5 dS from 50 to 60 GHz at room temperature. On-wafer measurements on these monolithic-microwave integrated circuits (MMIC's) have been done at MilliLab, Espoo, Finland. For the module fabrication, MMIC chips will be mounted in a WR-15 waveguide split-block housing.

Millimeter-wave sideband generation using varactor phase modulators

A sideband generator based on phase modulation is presented. The sideband generator consists of a Schottky varactor diode mounted in a WR-10 waveguide tuned resonant circuit. A microwave pump signal modulates the phase of the reflection coefficient the circuit presents to an incident millimeter-wave signal. This proof-of-principle circuit has shown a sideband conversion loss of 9 dB and bandwidth of nearly 10% at 80 GHz. These results represent significant improvements over the performance of sideband generators based on resistive mixing in corner-cube mounts.

Microwave plasma source for high current ion beam neutralization

A new microwave based plasma source for high current ion beam neutralization is presented. It consists of a tapered WR340 waveguide with a directly coupled 2.45 GHz magnetron and a quartz tube of 40 mm diameter inside the waveguide confined by two graphite electrodes. The upper electrode houses the gas feed, whereas the lower electrode serves as the plasma outlet. Both electrodes can be biased independently. Tuning is done via a magnetically controlled stab inserted into the waveguide. The plasma was characterized by use of the Langmuir probe. The electron concentration of 5×1011 cm−3 at 250 W was measured. Typical electron temperature is below 2.5 eV even for pressure as low as 2×10−3 Pa. The extractable electron current is dependent on microwave power and gas flow. A limitation is caused by the ion saturation current to the negatively biased electrodes. The voltage on the electrodes allows an easy control of electron current. Maximum electron current achieved so far is 400 mA for an argon flow of 5 sccm and microwave power of 300 W.

220-320 GHz Harmonic Mixer for a Full Band Sweep Vector Network Analyzer

This paper presents the design and characterization of a fixed tuned 220-320 GHz harmonic mixer employing commercial Schottky beam lead diodes in an antiparallel configuration. A diplexer provides distinct ports and matching for the subharmonic LO (26-40GHz) and the IF (20 MHz). The conversion loss was measured using a Gunn + tripler or quadrupler source calibrated with an absolute bolometer. We have built a 220-320 GHz full band sweep Vector Network Analyzer (VNA) using two WR3 waveguide couplers and three identical harmonic mixers (transmitter, reference, and receiver) pumped by two synthesizers (13-20GHz) followed by active doublers. The available dynamic range is 60 dBc/Hz over most of the band.

40-W CW broad-band spatial power combiner using dense finline arrays

This paper presents a broad-band spatial power-combining system based on tapered-slot antenna arrays integrated in a standard WR-90 waveguide environment. The system is designed using a modular tray architecture, providing full waveguide-band frequency coverage and an excellent thermal environment for a set of monolithic-microwave integrated-circuit (MMIC) amplifiers. The shape of the tapered-slot or finline structures was optimized to minimize return loss and provide a broad-band impedance transformation from the waveguide mode to the MMIC amplifiers. A prototype eight-element array using commercial GaAs MMIC power amplifiers yielded a maximum of 41 W output power (continuous wave) with a gain variation less than /spl plusmn/1.2 dB within the entire band of interest. The average combining efficiency over the operating band was estimated at 73%. The results suggest the efficacy of the design and a strong potential for higher powers by moving toward a greater number of MMIC's per tray and a larger number of trays. Should the 100 W system be realized in the near future, our combiner system will become a promising candidate to challenge the dominant position currently claimed by the traveling-wave tube amplifiers.

High-gain 150-215-GHz MMIC amplifier with integral waveguide transitions

The design and measured results of a six-stage InP monolithic microwave integrated circuit (MMIC) amplifier with 20/spl plusmn/6 dB gain from 150 to 215 GHz is reported. The MMIC has integral probes for direct coupling to 140-220 GHz WR5 waveguide without bond wires or external transitions. This is the first amplifier operating above 140 GHz with sufficient gain to be useful as a single-chip amplifier and demonstrates the practicality of MMIC-based systems in this frequency range for use in radiometry, compact radars, and communication systems.

Pulsed 35 Ghz Gyrotron with Overmoded Applicator for Sintering Experiments

AbstractThe microwave sintering of nanocrystalline alumina compacts is currently under investigation at NRL. This paper will discuss an overmoded microwave furnace based on a 35 GHz pulsed gyrotron which is currently being set up to extend ongoing microwave sintering experiments at 2.45 GHz to 35 GHz. The gyrotron operates at 70 kV and currents up to 10 A. It is driven by a hard tube, variable pulse length (1–15 μs) modulator at repetition rates up to 1 kHz. The gyrotron can produce peak powers up to 100 kW at an efficiency of 20%, and average powers up to 200 W. The gyrotron output is transported via pressurized Ka-Band waveguide to an overmoded resonator containing the workpiece. In initial experiments, the resonator will consist of a piece of WR-284 waveguide. The operation of the system in preliminary sintering experiments is described.

High-power microwave-induced TM/sub 01/ plasma ring

Open-shutter photography was used to capture the air breakdown pattern induced by a TM/sub 01/ mode radiated by a high-power backward wave oscillator. The resultant plasma ring was formed in air adjacent to a conical horn antenna fitted with a membrane to keep the experiment under vacuum. This image was digitized and further processed using Khoros 2.0 software to obtain the dimensions of the plasma ring. This information was used in an air breakdown analysis to estimate the radiated power, and agrees within 10% with the power measured using field mapping with an open-ended WR-90 waveguide.

Resonances in two-dimensional array oscillator circuits

We present experimental results on the emission from phase-locked two-dimensional arrays of Josephson junctions. We have coupled the emission from 10/spl times/10 arrays to a room-temperature mixer through a fin-line antenna and WR-12 waveguide. A single voltage-tunable peak was detected up to 230 GHz. A stripline resonance in antenna reduced the array's dynamic resistance and thereby the emission linewidth to as low as 10 kHz. We extract an effective noise temperature of 14 K from the linewidth data. When the array's emission was coupled to an on-chip detector junction through a dc blocking capacitor, we detected voltage-tunable emission from 75 GHz up to 300 GHz, and in some circuits emission above 400 GHz. Here, the coherent power spectrum depends on internal resonances.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Emission linewidth measurements of two-dimensional array Josephson oscillators

We have coupled emission from 10×10 arrays of Josephson junctions at 4 K to a room-temperature mixer through a fin-line antenna and a WR-12 waveguide. A single voltage-tunable peak was detected in the frequency range from 53 to 230 GHz. A stripline resonance in the antenna reduced the array’s dynamic resistance and thereby the emission linewidth to as low as 10 kHz. We extract an effective noise temperature of 14 K from the linewidth data.

Silicon micromachined waveguides for millimeter-wave and submillimeter-wave frequencies

The development of micromachining techniques to create silicon-based waveguide circuits, which can operate up to high submillimeter-wave frequencies, is reported. As a first step, a WR-10 waveguide has been fabricated from

Full-wave analysis of a lossy rectangular waveguide containing rough inner surfaces

The full-wave mode-matching method employing the similarity transformation is used to derive the eigenvalue equation for the periodic bumpy regions that model the surface roughness of a WR-10 (75-110-GHz) waveguide. For the case study reported, attenuation losses increased by approximately 60% (36%) at 75 GHz (110 GHz).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pulsed Microwave Processing of High-TC Superconducting Films

ABSTRACTWe have used 2.0-μsec microwave pulses at a frequency of 2.856 GHz to rapidly heat thin amorphous yttrium-barium-copper-oxide (YBCO) films deposited onto silicon substrates. The samples were irradiated inside a WR-284 waveguide by single-pass TE10 pulses in a traveling wave geometry. X-ray diffractometry studies show that an amorphous-to-crystalline phase transition occurs for incident pulse powers exceeding about 6 MW, in which case the amorphous YBCO layer is converted to Y2BaCuO5. Microscopy of the irradiated film reveals that the phase transition is brought about by melting of the YBCO precursor film and crystallization of the molten layer upon solidification. Time-resolved in situ experiments of the microwave reflectivity (R) and transmissivity (T) show that there is an abrupt change in R for microwave pulse powers exceeding the melt threshold, so that measurements of R and T can be used to monitor the onset of surface melting.

A rigorous and efficient method of moments solution for curved waveguide bends

An accurate and computationally efficient method of moments solution together with a mode-matching technique for the analysis of curved bends in a general parallel-plate waveguide is presented. In order to exemplify the techniques, the method is applied to study the transmission characteristics of single and cascaded curved E- and H-plane bends in a rectangular waveguide. It is shown that the effect of the orientation of cascaded bends on the transmission properties can be significant, and examples to demonstrate this effect are included. Results of the convergence with increasing number of expansion functions illustrate that only a few terms need to be considered for accurate evaluation of the transmission characteristics of structures with single and multiple bends. Comparison with measurements for single and cascaded curved H-plane bends in a WR-90 waveguide show good agreement with the predicted result. >