Millimeter-wave Region Research Articles

Hydrogen Network Fluctuations and the Microwave Dielectric Properties of Liquid Water

A short tutorial is given on interactions of water with electromagnetic fields, particularly in the microwave frequency range. Properties of the water molecule are sketched and attributes of the percolating tetrahedral hydrogen bond network of liquid water are presented. Characteristics in the polarization noise of liquid water are discussed and are related to the dielectric spectrum of water. The principal dielectric relaxation in the microwave region is represented by a Debye-type spectrum, the parameter values of which are given as a function of temperature in tabular form. At 19°C, as an example, the complex dielectric water spectrum is shown in an extended frequency range, also covering the near millimetre and submillimetre wave region up to 2 THz. A wait-and-switch model of dielectric relaxation, as suggested by computer simulation studies, is briefly outlined, in order to illustrate the mechanisms behind the hydrogen network fluctuations.

Effective permittivity and attenuation coefficient of microstrip transmission line determined by 1-port and 2-port measuring methods

Both 1-port and 2-port measuring methods have been demonstrated and compared to determine the real part of the frequency-dependent effective relative permittivity, re(f), of microstrip lines fabricated on an alumina substrate. Signal flow diagram analysis has been used to derive equations from which re(f) was calculated at discrete frequencies for the substrate with a known dielectric constant, r = 9.5. Both methods gave similar results for re(f) from 45 MHz to 50 GHz. In addition, the measured frequency dependence of re(f) was in agreement with the Kirschning-Jansen dispersion model within better than 2%. From the measured S-parameter data it was also possible to determine approximately the attenuation coefficient of the microstrips. Measured values obtained by the 2-port method were about 1.5-2 times the calculated values whereas the 1-port method suffered from radiation loss at the open end of the microstrips in the millimetre wave region. Both 1-port and 2-port methods can be used, for example, for quality checking purposes to verify how well the r value of the substrate material employed is within the specified range in a broad frequency band. However, the 1-port method can be more easily used to determine r of the substrate material at low microwave frequencies because it is faster than the 2-port method, the test structure is simpler and the calibration routine is easier to perform.

The generation of Bessel beams at millimetre-wave frequencies by use of an axicon

An axicon is used to generate a Bessel beam at 90 GHz in the millimetre-wave region of the spectrum. The Bessel beam has a central intensity maximum of approximately 4 mm in diameter that is maintained over a propagation distance greater than 60 mm .

Rotational spectrum, ring-puckering vibration and ab initio calculations on 1,1-difluorocyclobutane

The rotational spectra of the ground and first five ring-puckering excited states of 1,1-difluorocyclobutane have been investigated in the centimeter- (8–40 GHz) and millimeter-wave regions (96–106 and 144–159 GHz). Analysis of the spectra for the pairs of coupled vibrational states vp=0/1 and vp=2/3 has been carried out using two-state Hamiltonians, yielding accurate rotational and centrifugal distortion constants, vibration-rotation coupling parameters, and the energy spacings ΔE01 and ΔE23. The spectrum for the vp=4 to vp=6 ring-puckering states was satisfactorily accounted for in terms of effective semi-rigid Hamiltonians for each vibrational state. A double minimum ring-puckering potential function with a barrier to ring inversion of 231(4) cm−1 has been obtained from the analysis of the vibrational dependence of the rotational constants and inversion splittings ΔE01 and ΔE23. The calculated variation of the quartic centrifugal distortion constants with the ring-puckering quantum number reproduces satisfactorily the experimental trends, confirming the validity of the derived potential function. Ab initio calculations with HF, MP2, and B3LYP density functional hybrid methods have been carried out for this molecule using different basis sets. The experimental and ab initio potential functions, coupling terms, and ring-puckering dynamical parameters are compared. Finally, an ab initio near-equilibrium structure is presented.

Mid- and Near-Infrared Spectra, Millimeterwave Spectra, and Global Analysis of 16O12C80Se

We have recorded a total of 12 FTIR spectra of monoisotopic OC80Se in different spectral regions with a resolution (1/maximum optical path difference) between 2.7 and 13.2 × 10−3 cm−1. These spectra spanned the range from 350 to 7800 cm−1, many bands being studied with different p × L products in order to also detect weak hot bands. Altogether 18 band systems comprising 81 different bands, mostly of Σ type, were observed and analyzed by means of polynomial expansions in J(J + 1). New rotational transitions of vibrationally excited states as high as 2200 cm−1 with J" 17–25 in the 140–210 GHz and J" 53–58 in the 430–470 GHz millimeterwave regions were measured with the assistance of predictions by the global fit. This fit was performed using a weighted least-squares procedure and employing the whole body of data, and about 100 molecular parameters were determined that describe the energy level of 16O12C80Se with statistical accuracy. Improved highly accurate ground state parameters up to sextic centrifugal distortion terms were obtained by a merge of ground state combination differences and pure rotational data. The v1, v2, v3 polyad interacts anharmonically with the v1 − 1, v2 + p, v3 + q polyads with p + 2q = 4. Moreover, some local crossings with Coriolis interactions between (v1, v2, v3) and (v1 − 1, v2 + 3, v3 + 1) levels were observed and treated perturbationally.

The structure of carbodiimide, HNCNH

An experimentally determined r s -type structure of HNCNH is reported: r NH = 1.0074 Å, r CN = 1.2242 Å, ∠HNC = 118.63°, ∠NCN = 170.63°, ∠HN ··· NH = 88.99°. The number of digits quoted allow for errors with two significant figures. In order to obtain these values we recorded rotational—torsional spectra of HN13CNH, H15NC15NH and DNCND, by using isotopically enriched cyanamide. A chemical equilibrium exists between carbodiimide, HNCNH, and the more stable isomer cyanamide, H2NCN, which strongly favours cyanamide (approximately 1:115 at 110 °C). The expensive C- and N-substituted isotopomers could only be investigated in the millimetre wave region, while for DNCND the far infrared spectrum between 10–350 cm−1 was also recorded. Rotational constants of the three isotopomers, as well as of the parent species, were determined by fitting the assigned spectral transitions to the Watson Hamiltonian in S reduction. Using fitting programs written by Schwendeman and Rudolph, r o, rs and rρ m structures of HNCNH were derived. The experimentally determined structural parameters are compared with an ab initio re structure.

Locking performance analysis of MESFET subharmonically injection-locked oscillator

Subharmonically injection locking to an oscillator is an approach to obtain a stable source operated in microwave of millimeter-wave regions. In this paper, we present the formulation and results on the locking performance of metal-semiconductor field-effect transistor (MESFET) subharmonically injection-locked oscillator (SILO). Nonlinear-state equations of SILO are derived based on the use of a power series expression for MESFET nonlinear elements. The locking performance includes SILO output power, conversion gain, locking bandwidth, and the critical injection-locking signal level. The derived formulation is useful in the design of a MESFET SILO. Simulation results are shown to be in good agreement with those of experimental test measurement.

Miniaturized millimeter-wave masterslice 3-D MMIC amplifier and mixer

Masterslice three-dimensional MMIC (3-D MMIC) technology has (even in the millimeter-wave region) the advantages of high integration levels, simple design procedures, short turnaround time, and low fabrication cost. This paper clarifies the advantages of the thin-film microstrip line by drawing comparisons to the characteristics of other transmission lines. The simple design procedures of the masterslice 3-D MMIC are elucidated by referring to fabricated MMICs. A V-band amplifier and an image rejection mixer fabricated by using the same master array are demonstrated. The V-band amplifier offers an 8-dB gain and a 5.3-dB noise figure in the area of just 0.27 mm/sup 2/. The image rejection mixer achieves a conversion gain of /spl sim/10 db and an image rejection ratio of 20 db. The performance of the millimeter-wave 3-D MMIC's is competitive with those of the conventional planar-formed MMIC's.

Lamb-dip millimeter-wave spectrum, structure and dipole moment of HCCCCF

The ground state rotational spectrum of HCCCCF has been observed in the millimeter-wave region using the Lamb-dip technique and very accurate values of the spectroscopic constants have been obtained. Moreover, the observation of the ground state rotational spectra of the four 13C monosubstituted isotopomers and of the deuterated species of fluorodiacetylene have enabled the determination of the r0 and rs molecular structures. The electric dipole moment of HCCCCF has been determined by observing the Stark spectrum of the J=3�2 rotational transition. The equilibrium geometry and the dipole moment have been evaluated using different abinitio methods and comparison between experimental and theoretical results has been made.

Utilization of coherent transition radiation from a linear accelerator as a source of millimeter-wave spectroscopy

A spectroscopic system for the millimeter-wave region has been constructed on the coherent radiation beamline at the KURRI-LINAC of the research reactor institute, Kyoto University. Coherent transition radiation has been used as the light source. The observed spectrum of radiation was distributed throughout the entire millimeter-wave region and the intensity was four orders of magnitude larger than that of the conventional light source which has the continuous spectrum, i.e., a mercury-arc lamp. The interference between wave packets emitted from successive bunches was observed. It showed that the spectrum of coherent transition radiation was constituted of the higher harmonics of the L-band radio frequency (1.3 GHz) and that the high resolution spectrum was not a continuous spectrum. The diameter of the light beam at the position of a sample was about 9 mm (full width half maximum) and it increased as the wavelength became long because of the diffraction effect for the finite sizes of the optical components. Using the spectroscopic system, the pure rotational spectrum of N2O gas was observed in the millimeter-wave region.

Millimeter-wave spectroscopy of chromium monochloride (CrCl)

The rotational spectrum of chromium monochloride in the 6Σ+ ground electronic state has been observed with a source-modulated microwave spectrometer in the millimeter-wave region. The CrCl radical was produced in a free space absorption cell by a dc glow discharge in a mixture of AlCl3 vapor and He using stainless steel electrodes. Chromium atom was supplied from the electrodes by the sputtering reaction. Observed spectral lines were analyzed by a least-squares fit and the molecular constants including the rotational and centrifugal distortion constants and the spin-spin and spin-rotation interaction constants were determined. The experimental rotational constants B0 for 52Cr35Cl and 52Cr37Cl are 5 009.345 69(69) and 4 847.851 00(32) MHz, respectively, where the uncertainties attached to the last digit correspond to one standard deviation.

Performance of Cu‐ and Ag‐based microstrips up to millimetre wave frequencies

Attenuation characteristics of microstrip transmission lines on alumina substrates up to 50GHz are discussed. The lines under test came from three different manufacturers, each of whom used different processes to realise the transmission lines. Two of the manufacturers used silver (Ag) paste, whereas the process of one of the manufacturers was copper (Cu) based. Each manufacturer used identical alumina substrates and identical test pattern files so that the measured attenuation properties reflected manufacturer’s capability to fabricate microstrips and the quality of the metal system used. Measurements showed that the attenuation of copper microstrips was slightly lower than that of the silver microstrips, but the difference was small. Measured attenuation (S21) of about 50Ω microstrips was approximately 0.5db/cm at 30GHz and 0.8dB/cm at 50GHz, respectively. The loss coefficient, αt, of about 0.035dB/mm at 40GHz was obtained for the Cu microstrips. Such an attenuation is reasonable for many practical applications in the microwave and millimetre wave regions.

Pressure broadening of HNO 3 by N 2 and O 2: an intercomparison of results in the millimeter wave region

It is well known that systematic effects make the evaluation of absolute uncertainties in pressure broadening parameters difficult. In many cases, especially in the retrieval of remote sensing information, it is important that these uncertainties be well understood. In response, the pressure broadening of HNO 3 by N 2 and O 2 has been studied in the millimeter-wave region by two different methods in two different laboratories. The focus of this work has been on the strong lines near 206 GHz which are used by the Microwave Limb Sounder for measurement of HNO 3 in the Earth's atmosphere.

Lamb–Dip Millimeter-Wave and High-Resolution Far Infrared Spectra of HCCF

The ground state rotational spectrum of fluoroacetylene was measured in the millimeter-wave and FIR regions up to 1280 GHz andJ= 65. Very accurate values of the rotational and centrifugal distortion constants were determined and in particular a more reliable value ofH0= 2.0 10−4Hz has been obtained compared to that previously determined of −0.30 Hz. HCCF was prepared in a dc glow discharge in presence of 1,3,5-trifluorobenzene.

Observations of cirrus clouds with airborne MIR, CLS, and MAS during SUCCESS

Observations of cirrus clouds were made with a host of instruments on board the NASA ER‐2 aircraft on April 16, 1996. These instruments provide radiometric measurements covering the visible, infrared, and millimeter‐wave regions of the electromagnetic wave spectrum, as well as profiles of lidar backscatter at 1.064 µm. The cirrus clouds are classified into two groups: the modest cirrus clouds with lidar backscatter from the surface and the intense cirrus clouds without lidar surface returns. For the modest clouds, the magnitudes of brightness depressions are typically less than 5 K and are comparable at 150 GHz and 220 GHz. The depressions for the water vapor channels (e.g. 183.3±7 GHz) are smaller. We interpret the microwave brightness depressions for the modest cirrus cases as due to reduced skin temperature from the cloud shadow, rather than ice scattering. For the intense cirrus cases, the magnitude of brightness depression at 220 GHz reach 35 K and are far greater than those at 150 GHz. After correcting for the skin temperature effect, a regression between the observed brightness depressions at 150 and 220 GHz frequencies results in a slope of 2.75. Comparison with radiative transfer modeling for solid spherical ice particles, indicates a median equivalent mass diameter of about 350 µm, and ice water path ranging up to 300 g/m². The results illustrate the potential utility of millimeter and sub‐millimeter wave radiometry for characterizing microphysical properties of thick cirrus.

Millimeter-wave Ti:LiNbO/sub 3/ optical modulators

The design, fabrication, and characteristics of ridged Ti:LiNbO/sub 3/ optical modulators that work in the millimeter-wave region are presented. A new concept of design under velocity matching is demonstrated for the proposed modulator. It has been shown by calculation that impedance matching is achieved and conductor loss is greatly reduced under velocity matching with wider gaps and a thicker coplanar waveguide electrode in conjunction with a ridge structure. Two types of Mach-Zehnder optical intensity modulators for the wavelength of 1.5 /spl mu/m are developed. A fully packaged module for 40 Gb/s transmission with a half-wave voltage of 3.5 V and a broadband modulator responsible up to 100 GHz with a half-wave voltage of 5.1 V.

High-speed monolithic millimeter-wave switch array

A quasi-optical planar grid switch array comprised of hundreds of Schottky varactor diodes embedded within an overmoded waveguide is capable of generating switching times of 100-500 ps in the millimeter-wave region with Watt-level power-handling capabilities. A proof-of-principle high-speed V band switch array has been constructed with excellent agreement between theory and experiment. Less than 1.6-dB insertion loss and >16-dB on/off contrast ratio are measured at 61.5 GHz. The switch rise/fall time is 7 GHz (contrast ratio >15 dB) has also been measured.

Coherent Smith-Purcell radiation in the millimeter-wave region from a short-bunch beam of relativistic electrons

Coherent Smith-Purcell radiation, generated by the passage of short-bunched electrons of 150 and 40 MeV above a lamellar-type grating, has been observed in the millimeter-wave region. The intensity of the coherent radiation is proportional to the square of the beam current, and is enhanced by a factor of $\ensuremath{\sim}{10}^{8}$ in comparison with theoretical intensity of ordinary Smith-Purcell radiation. The enhancement factor is of the same order of magnitude as the number of electrons in a bunch. The intensity decreases with the increase of the beam height, or the distance of the beam from the grating, and the dependence on the beam height is expressed approximately by the modified Bessel function of the zeroth order. Owing to a relativistic effect the radiation is emitted in a narrow direction along the plane normal to the grating. The intensity of the radiation varies in a periodic way when the groove depth of the grating was changed. The observed properties of radiation are explained well by a three-dimensional theory of Smith-Purcell radiation, in which the coherence effect due to bunched electrons is taken into account.

Inter- and in-plane electromagnetic response of YBCO thin films in the millimeter-wave region and its dependence on weak magnetic field

The temperature dependence of the inter- and in-plane complex conductivities of YBCO thin films in the millimeter-wave region (75 ∼ 170 GHz) has been measured by using a Mach-Zehnder type interferometric spectrometer. Furthermore, the weak magnetic field dependence of the relative change of the London penetration depth is also studied. The results of these measurements are consistent with the recent theoretical predictions assuming d-wave pairing.

Millimeter-Wave Spectrum of the NO Dimer

The pure rotational spectrum of the NO dimer, (14N16O)2, has been studied in the 225–400 GHz millimeter-wave region by means of direct absorption in a supersonic jet expansion. Previously, only 4 rotational transitions of (NO)2had been measured in the microwave region. To these, we have added 66 new millimeter-wave transitions with values ofJranging from 4 to 16 and ofKafrom 2 to 7. Most transitions were observed as single lines, but a few showed partially resolved hyperfine structure. The analysis of these data, in combination with the previous microwave transitions and an extensive set of infrared (ν1band) measurements, has resulted in a greatly improved set of parameters for the ground state of the NO dimer, including the first sextic distortion parameters.