Anomalous Low-Loss Transmission in a Gas-Confined Dielectric Waveguide for Millimeter and Submillimeter Wavelengths

A novel low-loss (gas-confined) dielectric waveguide for millimeter and submillimeter wavelengths was previously reported by the author. The waveguide consists of a thin dielectric tube separating an internal high-dielectric-constant gas from an external low-dielectric-constant gas. The attenuation constant of this form of waveguide usually increases with increasing tube thickness. The thick tube is indispensable for a mechanically stable waveguide. In this paper, anomalous low-loss transmission characteristics in a gas-confined dielectric waveguide with a thick tube are described. Some condtions are theoretically found where the attenuation constant of the waveguide with a thick tube is extremely low, due to tight field confinement within the internal gas. A qualitative explanation of the operation mechanism is also given.     

Precise Dielectric Measurements of Low-Loss Materials at Millimeter and Submillimeter Wavelengths

Transmission dispersive Fourier transform, spectrometry (DFTS) has been used for the measurements of both real and imaginary parts of the complex relative permittivity of low-loss materials at millimeter and submillimeter wavelengths. The materials investigated include cis and trans decalin and polypropylene.     

Measurement of Dielectric Properties for Low-Loss Materials at Millimeter Wavelengths

We describe here a system for accurate measurement of the dielectric properties of very low-loss materials in the 130 to 170 GHz frequency range. This system utilizes an open resonator with a quality factor ∼ 1 × 10⁶. Resonance curves for this resonator are acquired with a commercial spectrum analyzer equipped with an external millimeter-wave harmonic mixer. The excitation source is a backward-wave oscillator locked to the spectrum analyzer local oscillator via a digital phase-locked loop. This system permits rapid and accurate measurement of resonance curve line widths, permitting determination of loss tangents down to the 10^-6 range. Results are reported for silicon carbide (SiC), CVD diamond, sapphire, and quartz.     

A Novel Quasi-Optical Frequency Multiplier Design for Millimeter and Submillimeter Wavelengths

This paper describes a novel design for millimeter and sub-millimeter wavelength varactor frequency triplers and quadruplers. The varactor diode is coupled to the pump source via waveguide and stripline impedance matching and filtering structures. Output power at the various harmonics of the pump frequency is fed to quasi-optical filtering and tuning elements. The low-loss quasi-optical structures enable near-optimum control of the impedances seen by the varactor diode at the idler and output frequencies, resulting in efficient high-order harmonic conversion. A minimum efficiency of 4 percent with 30-mW input power has been obtained for a tripler operating between 200 and 280 GHz, with a peak efficiency of 8 percent between 250 and 280 GHz. Another tripler, designed for the 260-350-GHz band, gave a minimum conversion efficiency of 3 percent with 30-mW input power, with a peak efficiency of 5 percent at 340 GHz.     

Resonators for Millimeter and Submillimeter Wavelengths

Further considerations on the mm-wave Fabry-Perot interferometer are presented. Computed Q values for parallel metal plate resonators indicate that at spacings around 2.5 cm, values ranging from 60,000 at 3 mm, to 300,000 at 0.1 mm wavelengths are possible. The plates must, however, be quite flat. These results are important for many investigations, and in particular for mm and sub-mm wave maser research. For the aperture per wavelength ratios possible here, diffraction effects should be small. Consideration is given to using curved reflectors or focused radiation in applications where the fields must be concentrated. For this purpose, re-entrant conical spherical resonators are treated in detail, as regards operation in the TEM mode at high orders of interference. Expressions for the Q and shunt impedance are given, and high values are possible at mm and sub-mm wavelengths. Quasi-optical methods of coupling into and out of such a resonator are proposed, and the higher modes possible in such a resonator are considered. Results indicate that it could have application to the mm-wave generation problem, and that it represents a good resonant cavity for solid state research at mm and sub-mm wavelengths, and for maser applications in particular.     

Power-Handling Capabilities of Circular Dielectric Waveguide at Millimeter Wavelengths

The power-handling capabilities of a circular dielectric waveguide propagating the single HE/sub 11/ mode are discussed. Simple calculations illustrate the limits imposed by dielectric heating and dielectric breakdown. Examples are presented for polystyrene and polytetrafluoroethylene (PTFE) guides at 70 GHz. The results suggest that maximum power levels for circular dielectric waveguide in the millimeter-wave specturm will be of the orders of 10 to 100 W and that dielectric heating is the limiting phenomenon.     

Attenuation Characteristics of Circular Dielectric Waveguide at Millimeter Wavelengths

Experiments were done to determine the practicality of using circular dielectric waveguide for a low-loss transmission line at millimeter wavelengths. The lowest order mode on a circular dielectric guide will propagate regardless of how small the guide diameter is. Thus it is possible to make the attenuation factor of a circular dielectric guide arbitrarily small by reducing its diameter. Loss measurements for several different diameters of polystyrene and Teflon rods were made at 72.70 GHz. The measurements were made by directly probing long sections of dielectric guide and plotting the average power as a function of length on an X-Y plotter. Dielectric constants were measured from the standing wave patterns of polystyrene Teflon, and fused quartz rods at 71.0 GHz. Teflon rods exhibited attenuation factors from 0.8 dB/m to 2.2 dB/m depending on the diameter. This is an improvement over silver waveguide at this frequency. Polystyrene rods were found to have attenuation factors ranging from 3.9 dB/m to 12.5 dB/m, again depending on the diameter of the rod. The measured dielectric constants are consistent with previously published data. The various attenuation factors are related to the intrinsic loss tangent of the dielectric using the theory of the HE/sub 11/ mode. Values of tan delta derived from measurements of different rods are consistent indicating that the experimental results are valid. The problem of radiation from dielectric rods is discussed. The experimental results are not conclusive but it appears likely that radiation loss is negligible.     

A Proposal of Low-Loss Leaky Waveguide for Submillimeter Waves Transmission

A low-loss dielectric leaky waveguide which carries most of the power in air is proposed for long-distance transmission of submillimeter waves, and its guiding mechanism is fully analyzed by using a two-dimensional slab-waveguide model. It is shown that transmission losses of the guide can become several decibels per kilometer and are not significantly affected by dielectric losses of material used for practical guide parameters.     

Rain Attenuation at Millimeter and Submillimeter Wavelengths

The rain attenuation was calculated by using the Marshall-Palmer, Best, Joss-Thomas-Waldvogel and Weibull distributions for raindrop-size. The results were compared with the recent measurements from 8 to 312.5 GHz at the rain rate R = 50mm/hr. Especially, the Weibull distribution has a good agreement with the measurements at 312.5 GHz (0.96 mm) in the submillimeter wavelength. Specific attenuation values from 1 to 1000 GHz were calculated for a rain temperature of ?10°C, 0°C and 20°C by using the Weibull distribution.     

A Directional Filter Diplexer Using Optical Techniques for Millimeter to Submillimeter Wavelengths

An optical diplexer for injection of a local oscillator into a mixer, useful in the submillimeter and short millimeter range, is described. It has very low insertion loss for both the signal and local oscillator (L.O.) and high rejection of L.O. noise. Measured performance of a unit tested at 337 GHz indicates ~.2 dB loss for both inputs and 20 dB noise rejection.     

Hollow-Cylinder Waveguide Isolators for Use at Millimeter Wavelengths

The device considered in this study is a semiconductor waveguide isolator consisting of a hollow column of a semiconductor mounted coaxially in a circular waveguide in a longitudinal dc magnetic field. An elementary and physical analysis based on the excitation of plane waves in the guide and a more rigorous mode-matching analysis (MMA) are presented. These theoretical predictions are compared with experimental results for an InSb isolator at 94 GHz and 7.5 K.     

Randomly Imperfect Waveguides for Millimeter and Submillimeter Wavelengths for Long-Distance Transmission Applications

Randomly imperfect waveguides are considered for use in long-distance transmission at millimeter and submillimeter wave-lengths. The steady-state attenuation constant, modal power distribution, and pulse spreading are calculated from Marcuse's coupled power equations. The result shows that a random waveguide can transmit 3.6 Gbit/s per square root of kilometer with a loss of 1.7 dB/km at 500 GHz. Mode conversions due to circular bends are considered next. It is shown that the systematic mode conversion due to bends is not of prime importance if the random coupling coefficient is much larger than the systematic one. This may be the most important feature of random metal waveguides for long-distance transmission applications.     

The Groove Guide, a Low-Loss Waveguide for Millimeter Waves

A new waveguide for the low-loss transmission of millimeter waves is presented. The guide consists of two parallel conducting walls with grooves in the central region of the guide cross section. The grooves run along the guide in the direction of the wave propagation. It is shown that the waveguide, if excited in the TE-wave mode, has properties similar to those of the H guide, which contains a dielectric slab between the conducting walls in the center. The new guide is characterized by an exponential transverse decrease of the field distributions in direction from the center and by low attenuation. Theoretical considerations dealing with the field distribution and the data of the guide are presented.     

Modified H Guide for Millimeter and Submillimeter Wavelengths (Short Papers)

A theoretical and experimental investigation is being made of a modified form of H guide as a possible guided wave structure for millimeter and submilliieter wavelengths. The effects of channels in the conducting planes to support a dielectric film has been studied by scaled-up models at 3-cm wavelength. Low losses, even at the shorter wavelengths, are predicted. The channels may be used to filter unwanted higher order modes, and the use of high-permittivity dielectric is suggested to further reduce the guide attenuation.     

Novel Applications of Millimeter and Submillimeter Wave Gyro-Devices

The possible applications of high-power millimeter (mm) and submillimeter waves from gyro-devices span a wide range of technologies. The plasma physics community has already taken advantage of recent advances in applying high-power micro- and mm-waves generated by gyrotron oscillators in the areas of RF-plasma production, heating, noninductive current drive, plasma stabilization and active plasma diagnostics for magnetic confinement thermonuclear fusion research, such as lower hybrid current drive (8 GHz), electron cyclotron resonance heating (ECRH) (28–170 GHz), electron cyclotron current drive (ECCD), collective Thomson scattering and heat-wave propagation experiments. Other important applications of gyrotrons are electron cyclotron resonance (ECR) discharges for generation of multi-charged ions and soft X-rays, as well as industrial materials processing and plasma chemistry. Submillimeter wave gyrotrons are employed in high-frequency broadband electron paramagnetic resonance (EPR) spectroscopy. Future applications which await the development of novel high-power gyro-amplifiers include high resolution radar ranging and imaging in atmospheric and planetary science as well as deep-space and specialized satellite communications and RF drivers for next-generation high-gradient linear accelerators (supercolliders). The present paper reviews the state-of-the-art and future prospects of these recent applications of gyro-devices.     

The Screening Potential Theory of Excess Conduction Loss at Millimeter and Submillimeter Wavelengths

On using the screening potential theory, the room-temperature excess conduction Ioss in copper waveguide is explained and calcuIated. The low-frequency and long-wavelength conductivity with spatial dispersion has been shown to give 30-percent more conduction loss in copper at submillimeter-wave frequency. Good agreement between experimental and theoretical results is obtained.     

Open Resonator System for Automatic and Precise Dielectric Measurement at Millimeter Wavelengths

As low loss dielectric materials, ZnS, MgF₂, MgAl₂O₄ and quartz ceramic have a very important application at millimeter frequencies. However, there is little information about their dielectric properties in the millimeter wavelength band. To obtain their dielectric properties, an automatic open resonator measurement system at Ka-band is designed and constructed. The importance on the precision determination of cavity length over a broad band and the checking of a measurement system are emphasized and their solutions are put forward in this paper for the first time so far as we know. The solutions of above problems ensure the credibility and high accuracy of our measurement system. The certified measurement system after a series of checking is used to measure the above materials. Lots of measurement results show that the standard deviation of measurement error is less than 0.154% in permittivity and 20.42% in loss tangent. Meanwhile, some experimental summaries on the open resonator technique are provided. Software that controls the measurement system is developed and it improves the testing efficiency greatly.     

Some Characteristics of Dielectric Image Lines at Millimeter Wavelengths

The attenuation characteristics of several dielectric image lines have been calculated for the frequency range extending from 24 to 100 kmc and have been checked experimentally at 35 and 70 kmc. To obtain low attenuation at these high frequencies, dielectric materials with little loss and small size of cross section are required, while low values of the dielectric constant are also desirable. The effects of the size and shape of the dielectric cross section and of low dielectric constant are treated separately. To find proper materials with low dielectric constants several new foam plastics were investigated. Three types were found suitable for image line use, and in fact, these plastics have such good electrical and physical properties that they should be useful in many microwave applications. A qualitative measure of field extent is given for several image lines at 35 or 70 kmc, and various image lines and associated components are discussed. A new type of image line, called the tape line, is described.     

毫米波段复介电常数测量的开放腔法改进

为实现毫米波段低损耗电介质材料的复介电常数高精度测量,文章主要关注开放腔法宽频带内腔长的精确确定、相对介电常数反演的多值解、误差的完整分析、测试系统检验以及自动测量等理论和技术难题.显然,这些问题的存在会影响开放腔法测量的正确性和精确性.通过研制和构建Ka波段上的开放腔自动测试系统,成功解决上述问题,完善和发展了开放腔测量理论.误差分析表明:本测试系统对相对介电常数和损耗正切的相对不确定度分别小于0.17%和20.4%.自动测试系统操作简便,测试结果可信且精度高.     

Resotron: A Novel Tunable Millimeter and Submillimeter Wave Source of Radiation

The need for tunable radiation sources in the millimeter and submillimeter range for spectroscopic purposes is still a research area of great interest. The tunable radiation source, proposed in this paper, is a special free electron laser device with the prerequisite of low electron energy. The output power density in the millimeter (GHz)-range is of the order of MW/cm² and in the submillimeter (THz)-range of the order of kW/cm². The device consists of an electron source with electron optics, wiggler/microwiggler, and a longitudinal magnetic field. The wiggler for the THz-regime has a very short wiggler period of approximately 400 μm and could be manufactured with laser micromachining techniques. The free electron laser operates in magnetoresonance and shows surprisingly stable electron orbits and therefore narrow output frequencies. Computational results of the temporal behavior of the output power done with a multi-frequency code are reported.