Igor I. Tkachov

Millimeter-wave magnetooptics: New method for characterization of ferrites in the millimeter-wave range

This paper presents the application of the magneto-optical method for the first time in the millimeter wave range for the characterization of ferrites. The magneto-optical measurements were realized with a specially built millimeter wave spectrometer. Backward wave oscillators were used as a source of tunable coherent radiation. It is demonstrated that this new method is capable of generating accurate millimeter wave dielectric and magnetic data for any type of ferrite material.

A novel W-band spectrometer for dielectric measurements

A new spectrometer for the precision measurement of dielectric permittivity and loss tangent is presented. The new instrument is capable of providing the high resolution data for the first time over extended W-band (68-118 GHz) frequencies for specimens with a large range of absorption values, including highly absorbing specimens which otherwise would not be possible. A novel technique based on the unbalanced bridge is developed for the measurement of the phase of the wave passed through the specimen in free space (quasi-optical) with reference provided by a waveguide arm. Specially constructed precision waveguide and quasi-optical components allowed reliable broadband operation. A number of common dielectrics are measured and results are compared with previously reported data.

The millimeter wave magneto-optics: new method for characterization of ferrites in the millimeter wave range

This paper presents the application of the magneto-optical method for the first time in the millimeter wave range for the characterization of ferrites. The magneto-optical measurements were realized with a specially built millimeter wave spectrometer. Backward wave oscillators were used as a source of tunable coherent radiation. It is demonstrated that this new method is capable of generating accurate millimeter wave dielectric and magnetic data for any type of ferrite material.

New method for measurement of complex magnetic permeability in the millimeter-wave range, part II: hexaferrites

Magneto-optical methods were applied for the first time in millimeter wavelength range for characterization of anisotropic ferrites. The principles of the free-space magneto-optical method are presented and the new experimental procedures leading to the determination of millimeter-wave permeability and permittivity in anisotropic ferrite materials are described. The measurements were performed with a computer-controlled W-band (70-120 GHz) quasi-optical-waveguide bridge. A backward-wave oscillator was used as a source of tunable millimeter wave radiation. The oriented Sr-hexaferrite ceramic was selected for the verification of millimeter-wave magneto-optical method. The magneto optical measurements in transverse configuration revealed strong anomalous dispersion in the millimeter-wave refractive index spectrum for Sr hexaferrite, mainly due to the frequency variation of magnetic permeability. Computer simulations revealed a good agreement of measured parameters with known data for Sr hexaferrite. It was shown that the free-carrier absorption (/spl sigma//spl sim/0.05 /spl Omega//sup -1/ cm/sup -1/) and magnetic permeability contribute to the relatively high millimeter-wave losses in hexaferrite ceramics. The frequency dependence of Faraday rotation in the millimeter-wave range was measured, and the experimental results are discussed. The results presented in this paper demonstrate that this new magneto-optical method is capable of providing accurate dielectric and magnetic data in the millimeter-wavelength range.

Complex Dielectric Measurements of Materials at Q- Band, V- Band and W- Band Frequencies with High Power Sources

In this paper we present a systematic study of complex dielectric permittivity of various semiconductor and dielectric materials, including highly absorbing substances, in Q-, V- and W-band frequencies. The measurements have been done using broadband quasi-optical millimeter wave spectrometer with a backward-wave oscillator (BWO) as a non-destructive high power tunable source of coherent radiation. Values of real and imaginary parts of dielectric permittivity of materials are calculated from the transmittance spectra. Refractive index data, obtained using both unbalanced waveguide bridge technique and free space measurements have been compared with previously published results. Millimeter wave and terahertz imaging and spectroscopy with high power BWO tubes as sources of coherent radiation for security applications have been briefly discussed

Quasi-optical waveguide W-band spectrometer for precision dielectric measurement of absorbing materials

A quasi-optical waveguide bridge spectrometer is designed and constructed for the precision measurement of dielectric permittivity and loss tangent of medium and highly absorbing materials over an extended W-band frequency range. An electronically sweeping backward wave oscillator (BWO) is used as a source of tunable coherent radiation in the frequency range 70-118 GHz. The high output power of BWO (typically 50-100 mW at each frequency) and high sensitivity receiver system employing a liquid helium cooled InSb detector enable the accurate transmission measurement of highly absorbing materials. Data for very absorbing materials such as the low resistivity silicon and germanium are presented and compared.

Complex permittivity measurements of dielectrics and semiconductors at millimeter waves with high power sources

We present complex dielectric permittivity measurements of various semiconductor and dielectric materials, including highly absorbing substances, in Q-, V- and W-band frequencies. The measurements have been done using broadband quasioptical millimeter wave system with a backward-wave oscillator as a high power source of radiation. Frequency dependencies of real and imaginary parts of dielectric permittivity are calculated from the transmittance spectra. Complex dielectric permittivity data, obtained using both waveguide bridge technique and free space measurements have been compared with previously published results.

A waveguide bridge/quasi-optical W-band spectrometer for dielectric measurement of absorbing materials

A spectrometer system is designed and constructed for the precision measurement of dielectric permittivity and loss tangent of absorbing materials. The new instrument is capable of providing the high resolution data for the first time over an extended W-band (68-118 GHz) frequencies for specimens with large range of absorption values, including highly absorbing specimens which otherwise would not be possible. The technique is based on the unbalanced bridge which is developed for the measurement of the phase of the wave passed through the specimen in free space (quasi-optical) with reference provided by a waveguide arm. Precision waveguide and quasi-optical components allowed reliable broad band operation. A number of common dielectrics are measured and data for the real and imaginary parts of dielectric permittivity are presented.

A novel quasi-optical resonator for the surface near-millimeter waves

The theory and experimental investigations are presented for a new type of quasi-optical near-millimeter-wave prismatic resonator, which provides frequency selective transformation of the plane waves into the surface waves. Theoretical expressions are obtained for the Q-factor and finesse, which consider dielectric loss and the effect of prism finite aperture. The theoretical evaluations are verified by experimental measurements in the frequency range 300-500 GHz using a prismatic resonator made from the optical quality fused silica glass. The increase of intensity of surface waves by a factor of 10-25 is demonstrated for the prismatic resonator made from an extremely low-loss dielectric.

Millimeter- and submillimeter-wave transmission and dielectric properties of radome materials

Transmission, absorption coefficient, refractive index, real and imaginary parts of dielectric permittivity and loss tangent spectra of polytetrafluorethylene (teflon), Gore-Tex and another teflon based radome memebrane materials are presented as a continuous function of frequency over the range 60-2,400 GHz (5 mm-0.125 mm in wavelength). The new data are better resolved and cover a much wider frequency range. The transmission reduces significantly with increasing frequency for most radomes. The absorption coefficient or loss tangent values increase almost exponentially with increasing frequency for all these radome materials. The refractive index or the real part of permittivity values are alomst similar to teflon since these radomes are teflon based.