Submillimeter-wave measurements on liquid dielectrics

Recent advances in submillimeter-wave complex relative permittivity measurements on liquids are described. The developments include direct measurements of both real and imaginary parts of the complex relative permittivity both at spot frequencies using submillimeter-wave laser spectrometry and in the broad band using dispersive Fourier transform spectrometry.     

Correction to open-resonator permittivity and loss measurements

A correction to the length of a dielectric sample placed in an open resonator is derived using perturbation theory. The correction takes account of the additional volume of sample extending beyond the curved phase front normally assumed in the beam wave theory. Results are presented for a range of sample lengths of a high-density polyethylene, which illustrate the improvement obtained in both permittivity and loss measurements when this correction is used.     

High-sensitivity dielectric loss measurements by using superconducting microwave resonators in an oscillator loop

The method allows easy and highly accurate measurements of microwave resonator parameters. By using superconducting resonators, the loss tangent of polyethylene at 2.2 K and 6.5 GHz was found to be the lowest of any solid so far measured: tan ? = 3.7 × 10?7 ± 7%.     

Improvement in open-resonator permittivity measurement

The accuracy of permittivity measurement using an open resonator has been studied. The error in the determination of permittivity arising from the imperfection of beam-wave theory is estimated. It is further shown that, by an improved method of analysing the experimental results, the effect of the imperfection in the theory is reduced and a great improvement in accuracy can be obtained.     

The mm-wave dielectric measurements with an electric-field cross-correlation Fourier transform spectrometer

A method for measuring complex permittivity based on an electric-field cross-correlation Fourier transform spectrometer was proposed. Its principle can be extended over the whole microwave region. Two typical solid media, teflon and plexigrass, and a kind of sand were measured in 8mm-wave region by the method. The results show that this method has potentialities to perform accurate permittivity measurements.     

Novel open-resonator for a quasioptical gyrotron

A new kind of open-resonator for a quasioptical gyrotron—an axisymmetrical quasioptical cavity of oblique roiation at arbitrary angle (AQCORAA)—is proposed. Using scalar diffraction theory and an approximate method, the field distributions in the AQCORAA are derived, and the influence of rotating angle on the field distributions is analysed. The stored field energy in the cavity is also obtained.     

Submillimeter-wave InP Gunn devices

Recent advances in design and technology significantly improved the performance of low-noise InP Gunn devices in oscillators first at D-band (110-170 GHz) and then at W-band (75-110 GHz) frequencies. More importantly, they next resulted in orders of magnitude higher RF output power levels above D-band and operation in a second-harmonic mode up to at least 325 GHz. Examples of the state-of-the-art performance are continuous-wave RF power levels of more than 30 mW at 193 GHz, more than 3.5 mW at 300 GHz, and more than 2 mW at 315 GHz. The dc power requirements of these oscillators compare favorably with those of RF sources driving frequency multiplier chains to reach the same output RF power levels and frequencies. Two different types of doping profiles, a graded profile and one with a doping notch at the cathode, are prime candidates for operation at submillimeter-wave frequencies. Generation of significant RF power levels from InP Gunn devices with these optimized doping profiles is predicted up to at least 500 GHz and the performance predictions for the two different types of doping profiles are compared.     

Robust slot-fed dielectric resonator antenna using an intermediatesubstrate

A new slot-fed rectangular dielectric resonator antenna design is presented. An intermediate substrate is introduced between the slot and the resonator, resulting in a correct excitation of the fundamental mode and a particularly robust structure to adhesive thickness. Comparisons between finite difference time-domain simulations and measurements confirm the good properties of the proposed design     

Tissue dielectric measurement using an interstitial dipole antenna

The purpose of this study was to develop a technique to measure the dielectric properties of biological tissues with an interstitial dipole antenna based upon previous efforts for open-ended coaxial probes. The primary motivation for this technique is to facilitate treatment monitoring during microwave tumor ablation by utilizing the heating antenna without additional intervention or interruption of the treatment. The complex permittivity of a tissue volume surrounding the antenna was calculated from reflection coefficients measured after high-temperature microwave heating by using a rational function model of the antenna's input admittance. Three referencing liquids were needed for measurement calibration. The dielectric measurement technique was validated ex vivo in normal and ablated bovine livers. Relative permittivity and effective conductivity were lower in the ablation zone when compared to normal tissue, consistent with previous results. The dipole technique demonstrated a mean 10% difference of permittivity values when compared to open-ended coaxial cable measurements in the frequency range of 0.5-20 GHz. Variability in measured permittivities could be smoothed by fitting to a Cole-Cole dispersion model. Further development of this technique may facilitate real-time monitoring of microwave ablation treatments through the treatment applicator.     

A leaky-wave antenna using an artificial dielectric medium

A narrow-beam antenna using an artificial dielectric medium with effective permittivity less than unity has been investigated theoretically and experimentally. Complex propagation constant for a wave propagating along the structure is evaluated by solving the dispersion relation. The analysis indicates the presence of a leaky-wave mode. The radiation pattern is calculated by using Kirchhoff-Huygens integration method. Experimental results for an antenna of this type designed for operation atXband are reported and compared with theoretical calculations. Beam position varies from17degto47degwhen the frequency is changed from 8.6 to 11.5 GHz. Over this frequency range the half-power beamwidth varies from5.6degto4.8deg. An expression for the half-power beamwidth of a leakywave antenna of finite length has been derived and discussed in the Appendix.     

Improvement of accuracy in measurements of the surface resistanceof superconductors using dielectric resonators

Two techniques to minimize the influence of parasitic losses on surface resistance measurements of superconductors employing dielectric resonators have been described. The first method optimizes the sapphire resonator aspect ratio to minimize the parasitic losses for given superconductor sample dimensions and measurement frequency. The second utilizes a reference resonator with a perfect conductor plane to cancel out the influence of parasitic losses by measurements of the resonant frequencies and Q-factors of two resonators. The second technique is recommended when materials having noticeable dielectric losses are used to construct dielectric resonators     

Submillimeter-wave antennas on thin membranes

Submillimeter-wave antennas have been fabricated on 1-μm thick silicon-oxynitride membranes. This approach results in better patterns than previous lens-coupled antennas, and eliminates the dielectric loss associated with the substrate lens. Measurements on a wideband log-periodic antenna at 700 GHz, 370 GHz and 167 GHz show no sidelobes and 3-dB beamwidths between 40° and 60°. A linear imaging array has similar patterns at 700 GHz. Possible applications for membrane antennas include wideband superconducting tunnel-junction receivers for radio astronomy and imaging arrays for radiometry and plasma diagnostics.     

The synthesis of surface reactance using an artificial dielectric

A thin artificial dielectric layer consisting of a rectangular array of closely spaced, thin conductive cylinders (pins), was constructed above a perfectly conducting ground plane. The reactance of the surface was measured at 4.8 GHz for a variety of pin heights and dielectric embedding material by measuring the height-gain profile of a transverse magnetic (TM) surface wave launched across it. Design equations using the theories of artifical dielectrics and propagation in anisotropic media are given. These can be used to predict the surface reactance providing a correction factor accounting for fringing fields at the tops of the pins is included. Using an embedding dielectric tends to reduce this fringing effect.     

Submillimeter-wave detection with superconducting tunnel diodes

The review presents a theoretical framework for understanding submillimeter detection using an optical photodiode theory. Both gain and noise in the superconductor-insulator-superconductor (SIS) mixer are described in terms of mixing on a photodiode. The role of impedance matching in the proper design of an SIS mixer is described. A variety of methods for achieving good impedance match at submillimeter frequencies are presented. The state of the submillimeter SIS mixer art as practiced in a variety of laboratories is described and summarized     

Millimeter-wave measurements of the complex dielectric constant of an advanced thick film UV photoresist

The first measurement of the relative permittivity (ε_r) and loss tangent (tan δ) of EPON™ SU-8 advanced thick film ultraviolet photoresist is reported at frequencies between 75–110 GHz (W-band). The problems associated with such a measurement are discussed, an error analysis given, and values of ε_r=1.725±0.08 and tanδ =0.02±0.001 are determined.     

Accuracy issues in surface resistance measurements of hightemperature superconductors using dielectric resonators (corrected)

Reproducible and accurate measurements of the surface resistance of high temperature superconductors are essential for the development and commercialization of the next generation of high performance cryoelectronic systems. Dielectric resonators are the best, most accurate technique for this measurement and have been suggested for the international standard technique. This paper discusses trade-offs amongst the various types of dielectric resonators including choices of the dielectric rod, the metallic enclosure, the electrical measurements of Q-factor, resonant frequency and coupling coefficients, and other issues to ensure reproducible and accurate measurements     

Submillimeter-wave properties of thermospheric rocket plumes

The problem of detecting rocket plumes at thermospheric altitudes with satellite-borne submillimeter-wave radiometers is examined theoretically. To estimate the sizes of plume signatures contrasted against a 250-K earth background or in self-emission against the cold sky, a computer program has been developed to predict plume brightness temperatures and optical depths of rotational lines of plume molecular constituents (e.g., H₂O) as a function of distance from the nozzle. The methods employed in the computations are described in general terms, and examples are presented to indicate that detectable H₂O signatures extending to several thousand nozzle diameters should exist at plume altitudes above 250 km.     

Submillimeter-wave emission assignments for 1,1-difluoroethylene

Many of the known submillimeter wave emissions of 1,1-difluoroethylene are assigned by using new data from infrared diode laser heterodyne spectroscopy. Six new submillimeter lines are also reported and assigned.