Dispersion characteristics of broadside coupled dielectric image guide at millimeter wave frequencies

Dispersion characteristics and wave impedance for the even and odd modes of the broad side coupled dielectric image guides are computed by using mode matching techniques. Dispersion curves for broadside image guide are plotted for various dielectric materials and dimensional parameters as a function of frequency. Normalized electric field for dominant electric field component E of TM even and odd modes for various half spacings between two dielectric slabs of broadside coupled image guide have been plotted. Polysterene ( r=2.56) and Stycast ( r=3.4) have been used as dielectric materials in fabricating broadside coupled image guide. This broadside coupled dielectric guide is very convenient as compared to the other dielectric guides. Since in case of broadside coupled image guide the dielectric slab can be bonded to the side metallic walls using some low loss adhesive material, while in other coupled dielectric guides the dielectric slab have to be supported by some low dielectric constant material (Eccofoam with r=1.02) to maintain the proper distance of side metallic walls from the dielectric slab. Since this structure is symmetrical, this configuration can be analysed in terms of even and odd mode phase velocities. The difference in these even and off mode phase velocities can be used to determine the coupling between coupled dielectric slab. Various couplers in this configuration can be realised.     

Phase Relations for the Electromagnetic Wave Components Reflected from and Transmitted by a Dielectric Layer

An important property of electromagnetic waves, which follows from Fresnel's formulas but has not been clearly defined as yet in the scientific and educational literature, is considered: the phase difference between the wave components reflected from and transmitted through a plane dielectric layer located between optically identical media is equal to /2, irrespective of the optical parameters of the layer and surrounding media, the wavelength, and the wave polarization state.     

Optical propagation of the HE11 mode and Gaussian beams in hollow circular waveguides

The propagation of the HE₁₁ mode and Gaussian beams in hollow oversized circular waveguides is analyzed using optical theories. Different types of waveguides are considered : hollow dielectric or conducting waveguides, dielectric-lined waveguides, corrugated waveguides. General formulas are derived which give the power transmission through these different guides. The best wall materials and structures are determined from a comparison of the waveguide transmissions, at the infrared and millimeter wavelengths. The question of the coupling between the HE₁₁ mode and Gaussian beams is discussed and from a review of coupling coefficients derived before, an optimum value is pointed out. The problem of matching a Gaussian beam into circular waveguides in order to achieve the maximum power transmission is analyzed. These results are of interest for infrared lasers or waveguide applications and for Electron Cyclotron Wave (ECW) systems at the millimeter wavelength.     

A new type of millimeter wave-integrated directional couplers

In this paper a new type of millimeter wave integrated directional coupler is proposed. The coupling mechanism on the narrow wall of waveguide consists of a series of bilateral E-plane slots deposited on a dielectric substrate by photo-etching technique. The modified generalized transmission parameters considering the thickness effects of the strips and higher order mode interactions at the step discontinuities in the coupling region are used in optimizing program. The calculated performance of a 3-dB 12-slot directional coupler at Ka-band is given. A prototype Ka-band coupler has been tested. The measured results agree with the theoretical prediction satisfactorily.     

An experimental investigation of high permittivity dielectric resonators for millimeter-wave microstrip components

This paper proposes a new type of high permittivity whispering gallery mode cylindrical dielectric resonators with a geometry which is very suitable for use in microstrip type integrated circuits. These oversized resonators, together with high Q factors and ease of fabrication, are potentially interesting for millimeter wave integrated filters and oscillators. In this paper, we report an experimental investigation of such resonators carried out in Ka band (26.5–40 GHz). Measured results including resonant frequencies and loaded quality factors will be presented. Application to millimeter wave filters will also be demonstrated.     

Image guide couplers used in millimeter wave integrated circuits

The dispersion and coupling characteristics of the coupled image guides are studied by using the odd-even mode principle and effective dielectric constant method. The practical design of the image guide directional couplers is presented. The experiments of 3-dB and 10-dB couplers in ka band show several good features which are very useful to millimeter wave integrated circuits with flat coupling, easy design and fabrication, mechanical stability and low losses.     

Study on BMT Millimeter Wave Dielectric Resonators

The microwave dielectric properties and microstructures of Ba(Mg_1/3Ta_2/3)O₃ (BMT) ceramics were investigated. In order to reduce the evaporation of MgO at high temperature, burying in MgO powders sintered BMT ceramics. The relationship between the composition and Q value of BMT ceramics was discussed. Dielectric resonators using in millimeter wave band have been designed and fabricated. Their attenuations at central resonation frequency (_f) are less than 35dB. Temperature coefficients of resonant frequency are adjustable and less than 2 ppm/°C.     

Application of multilayer structures at millimeter wavelengths

The paper presents results of theoretical analyses and experimental investigations of the optical characteristics of devices based on multilayer dielectric structures and intended for the millimeter wave band. As is shown, multilayer dielectric structures can prove useful in devices with variable optical characteristics representing coupling elements for quasioptical open resonators, adjustable reflection coefficient mirrors in narrow-band interference Fabry-Perot filters or adjustable multilayer polarizers.     

Design of Coupling Structure for MMW Folded Waveguide TWTs

A significant advantage of the folded wave traveling wave tube (TWT) is simple coupling structure. In millimeter wave band, owing to higher frequency, linear double taper can be used as impedance transformer. The design method and calculation results for the folded waveguide TWTs in K-band are given.     

Characterization of polymer strip waveguides by leaky-mode spectroscopy

Strip waveguides, recorded by UV lithography into photopolymer films were characterized as leaky guides. The effective modes indices of the guides have been measured by the prism coupling method. It is demonstrated that application of the effective index method on leaky strip guides allows the determination of the optical pattern parameters throughout an exposure or annealing procedure.     

Millimeter Wave Antenna with Scanning Beam

The results of theoretical analysis and experimental investigation of the millimeter waves antenna with scanning beam are presented. The operation concept of the antenna is based on the effect of transformation of the surface waves of dielectric waveguide in the volume waves. The smooth space scanning of beam has been made by means of change of wave propagation constant inside of the dielectric waveguide. All experiments were made in the four-millimeter wave range. The angle of scanning was =35° and width of directional diagram was 2° in the scanning plane. The lens and the mirror antennas were designed.     

Integral method of nondestructive testing of optically transparent dielectric elements of band-pass filters

The narrow and wide band-pass filters with high electrical parameters both in the centimeter and millimeter wave band developed in the Microwave laboratory are built on the basis of H- and E-plane inserts made of a high Q dielectric monocrystal leukosapphire (tg 6*10^–6 in centimeter wave band). The filters based on the E-plane inserts have a rare spectrum of parasitic modes (up to doubled working frequency and higher) and those based on the H-plane inserts have lower insertion loss in the bandwidth. Fig.1 shows the design of a band-pass filter in which the resonators of both the first and second types are used to improve stability of amplitude-frequency characteristic in response to influence of production process and climatic factors. The electrodynamic calculation of such a filter electrical parameters is carried out according to the technique analogous to the one described in [1]. The prooedure of the band-pass filter manufacture envisages the operation of determining whether a specific dielectric element fits for pasting into the filter body. The most expedient testing method for filter elements is the electromagnetic resonance method. However, since the monocrystal leukosapphire is an anisotropic, opticallytransparent material [2], there exists a possibility of using not only the traditional SHF (Super High Frequency) method but also the method of optical testing of the quality of the dielectric element by the shape of conoscopic figures that enables to increase the output of suitable products with reduction of expenditure. A new approach to the nondestructive testing of optically-transparent filter elements using both methods and their mutual dependence in technological process, has been suggested.     

TM Nonlinear electromagnetic waves guided by an inhomogeneous medium

Analytical dispersion relations and the power flow expression for TM (polarized) nonlinear electromagnetic surface waves propagating along the interface of an inhomogeneous and dielectric nonlinear media have been investigated theoretically. An inhomogeneous dielectric cover has the dielectric permittivity=a+bz, which is contacted with a strongly nonlinear Kerr like layer. The existence conditions for these waves to be propagated are studied. These waves have no counterpart in the linear isotropic regime. The power flow versus the wave index, and the consequence interface nonlinearity might be evaluated for a variety of inhomogeneity parameters, which are found to be inhomogeneity dependent, and could lead to optical hysterisis and bistability.On leave from: Department of Electrical Engineering and Electronics, UMIST, P.O. Box 88, Manchester M60 1QD, U.K.     

A unique method for reducing losses of bends in dielectric optical wave guide

The dielectric optical wave guide is finding growing attention at millimeter wave frequencies. However the dielectric optical waveguide radiates at bends and thus transmission loss increases. These radiations are in the outword direction of bends. This output radiation at output bends arises due to change in phase velocities of the propagating wave at the centre of the dielectric guide and the phase velocity at the outer surface of the dielectric guide. A unique methiod is suggested to avoid these radiation losses.Experimental results are also shown at microwave frequencies.     

A five-channel grating spectrometer for millimeter-waves

A five-channel grating spectrometer for use in millimeter wave band (25100GHz) is described with its design theory of optical path, and measured results of insertion loss and resolving power.     

Efficient coupling of hybrid optical waveguide with a sharp bend structure for high integration

A hybrid optical waveguide with a \(90^{\circ }\) sharp bend comprising a dielectric straight waveguide, a tapered dielectric strip waveguide, and a microscale metal gap waveguide is proposed, modeled, fabricated, and characterized with the aim of improving the efficiency of light coupling between the dielectric and plasmonic waveguides. The simulation result using the full-vector finite-difference time domain shows a total transmissivity of about 63 % at a wavelength of 1,550 nm. A set of hybrid optical waveguide with a \(90^{\circ }\) bend is fabricated via the two-step photolithography and a metal lift-off process. From the measured result for the characteristics of the fabricated hybrid optical waveguide, the transmission loss was estimated to be about 17 dB, which is in stark contrast with the simulation value. Nevertheless, such a novel coupling scheme may be of potential use in high-density photonic integration applications.     

The Optical Design of Relay Optics for Heterodyne Millimeter Wave Focal Plane Arrays

Since the use of focal plane arrays on millimeter and sub-millimeter telescopes has become more and more important during the last years, it has also become evident the need of optimized auxiliary optics that would efficiently couple the telescope to the receiver over large fields of view (i.e., 5-10 beams). In this work we systematically analyze several relay optics configurations for heterodyne focal plane arrays, all based on the Gaussian beam telescope concept. Because in examining the image performance of auxiliary optics design at millimeter wavelengths one cannot follow the usual image quality criteria, we analyze the designs using both the Strehl ratio and the coupling efficiency to evaluate the quality of the off-axis wave-fronts and the loss in the power coupling with the horn. Coupling efficiency and Strehl ratio cannot be included in the optimization procedures of commercial optical modelling packages and we thus describe how to optimize the design using a customized algorithm. We show that the minimization of the appropriate error function can reduce the anamorphism of the exit pupil and reduce the loss in the horn coupling.     

Optical properties of thin metallic film/dielectric superlattices constrained by the size effect

The dispersion relation of the 1D Bloch wave vector accompanied with an incident transverse electromagnetic wave on thin metallic film/dielectric superlattices is crucial to its optical properties. The interference of excited longitudinal plasmons between neighbouring metallic films induces a collective oscillation of the whole superlattice causing coupled plasmon polariton waves. A calculation of the optical reflectance manipulated by the size effect on the dielectric constant induces more allowable bands at < as the specularity parameters p and q decrease, meanwhile the cut-off frequency for band rejection also shows a blue shift.     

A five-channel grating spectrometer for millimeter waves

A five-channel grating spectrometer for use in millimeter wave band (25100GHz) is described with its design theory of optical path, and measured results of insertion loss and resolving power.     

Unilateral Fin Line Directional Coupler

Photonic band gap (PBG) crystals have been used as a perfectly reflecting substrate for many millimeter wave applications. In this work the fin line directional coupler with substrate PBG was analyzed using the TTL - Transverse Transmission Line - method. Compared to other full wave methods the TTL is an efficient tool to determine the coupler characteristics, making possible a significant algebraic simplification of the equations involved in the process. In order to analyze this structure the effective dielectric constant, the attenuation constant and the coupling were determined. The results obtained for this application and the conclusions are presented. This work was partially financed by CNPQ.