Analysis and Measurements of Nonradiative Dielectric Waveguide Bends

The coupling theory is applied to analyze loss characteristics of the NRD-guide bends. Besides the operating LSM/sub 01/ mode, the parasitic LSE/sub 01/ mode is generated at bends as a result of the mode conversion. A rigorous expression for the coupling coefficient between these two modes is derived and then employed in the two-mode coupling equations to be solved for the bending loss analysis. Design diagrams, which are useful for optimizing the strip width against a given curvature radius to build a Iossless bend, are constructed for 90 and 180° NRD-guide bends. It is shown that the field profile at a bend always shifts inwards. This confirms the previous experimental prediction. It is found that the periodic spikes on the loss versus frequency curve of a bend, which have been observed before, can be interpreted as being caused by resonances of the parasitic mode between the transition horns fixed at both ends of the bend, and that the true bending loss itself is normally restricted within a reasonable level. As an application of the present theory, a Iossless 180° bend with a curvature radius of 5 mm was fabricated with polystyrene and tested at 50 GHz. The measured bending loss was less than 0.3 dB.     

Nonradiative dielectric waveguide circuit components

The nonradiative dielectric waveguide (NRD-guide) is a newly proposed dielectric waveguide which can substantially suppress radiation at curved sections and discontinuities and is applicable to great advantage for millimeter wave integrated circuits. Basic circuit components such as transitions between a metal waveguide and an NRD-guide, matched terminations, a ring resonator and a bandpass filter were fabricated with polystyrene material and tested successfully at 50 GHz. Measurements showed that each component worked as expected without suffering from undesirable radiation and interferences at all.     

Insulated Nonradiative Dielectric Waveguide for Millimeter-Wave Integrated Circuits

An improved version of the nonradiative dielectric waveguide (NRD-guide), called an insulated nonradiative dielectric waveguide, is proposed for millimeter-wave integrated circuits. This dielectric waveguide can overcome some difficulties which arise when high dielectric material is used in the NRD-guide. Guide wavelengths and transmission losses were measured at 50 GHz and compared with theory. In addition, some basic circuit components such as bends, ring resonators, chip resonators, and T-junctions were fabricated on the basis of the insulated NRD-guide and tested to confirm their usefullness in millimeter-wave integrated circuits. The fabricated components operated as expected without suffering from any appreciable radiation at curved sections and discontinuities.     

Nonlinear TE waves in an optically nonlinear curved waveguide andpulse compression

The propagation properties of the TE₀ mode in an optically nonlinear curved waveguide are examined in detail. As the input power increases, the self-focusing effect of the nonlinear core is found to largely reduce the radiation loss and to moderately reduce the mode-conversion loss. It is made clear from detailed examinations of the power transmissivity that the nonlinear curved guide can be used as a threshold device for a logical AND gate or an optical amplifier, and that the device property improves with the bend length and curvature radius. The optical pulse compression using the curved guide is also considered. It is shown that larger values of the bend length and peak input power are preferable for shorter output-pulse widths and lower power losses, respectively     

A Novel UWB Antenna with Small Side-Leakage

A successful design for a UWB (ultra-wideband antennas) antenna based on NRD-guide (nonradiative dielectric waveguide) with small side-leakage is presented. The rule of the theoretical selection of its parameters, if NRD-guide is used as the UWB antennas, is studied firstly, then the temporal propagation characteristics of the NRD-guide and the radiation characteristics for an tapered open-ended NRD-guide are calculated by FDTD (finite-difference time-domain) method.     

Ultra-wide-band NRD-guide Antenna

A new ultra-wide-band(UWB) horn antenna based on the nonradiative dielectric waveguide (NRD-guide) was proposed to solve the problem of UWB antennas, TEM horns for example, generally suffer from large side leakage. The rule of the theoretical selection of its parameters, if NRD-guide is used as the UWB antennas, is studied firstly, then the radiation characteristics for an open-ended NRD-guide are calculated by FDTD (finite-difference time-domain) method.     

奇模抑制孔缝阵列速度补偿型弯曲共面波导

提出了一种可以抑制奇模的速度补偿型弯曲共面波导结构。该结构采用在弯曲共面波导较长缝隙中的介质上打孔的方式降低其等效介电常数,加快该缝隙中的电波速度,从而使得较长缝隙中的信号经过弯曲段后与较短缝隙中的信号同相输出。仿真和实验结果表明：所提出的结构可以有效抑制奇模辐射,显著降低传输损耗和减小反射。     

The development of nonradiative dielectric waveguide transmitting front-end in Ka-band

The operating theory,design method and experimental results of the nonradiative dielectric waveguide (NRD-guide) transmitting front-end in millimeter wave band are related in details in this paper. As a kind of dielectric waveguide,the NRD-guide possesses fine transmission performances, and it can be used to fabricate the millimeter wave hyterodyne integrated circuits. The two kinds NRD-guide transmitting front-ends substantiated in the paper, the voltage controlling oscillator(VCO) and twin-Gunn-diode power-combiner,have very similar structures to each other and possess compact sizes, fine machinery and electric performances.For the VCO front-end in Ka-band, the frequency modulation band is greater than 150MHz, the output power is larger than 20mW.For the power-combiner, the output power is larger than 40mW,the combination efficiency is better than 90%,the frequency stabilization reaches 1.68×10^?5. Combined with the receiving front-end reported before,the transmitter and receiver can be composed to a dielectric waveguide R/T module to be applied in some millimeter wave sub-systems.     

Excitation of a parallel-plate dielectric waveguide using a coaxialprobe-basic characteristics and experiments

In this paper, we study the basic characteristics of a probe excitation to a parallel-plate dielectric waveguide (PPDW), and present design data and experimental results. A coaxial probe has been used in microstrip lines and rectangular waveguides. The present study shows that it is also an effective method to excite/couple a PPDW, thus facilitating the introduction of a new class of PPDW technology in microwave/millimeter-wave integrated circuits. We use here a spectral-domain analysis for analytical modeling of the probe transition, where the probe is approximated by a current strip of an equivalent width. Applying the method of image, the structure is transformed to an infinite-long thin strip inside a dielectric slab, which reduces the transition analysis into a simpler planar geometry. Basic characteristics of the probe excitation, and a complete design data for the radiation loss, excitation efficiency, and input impedance for various transition parameters are computed. Prototype design experiments were conducted, which show that quite efficient excitation can be achieved using; the probe, with insertion loss as low as 0.1 dB. This is contrary to some misconceptions that a probe transition to the fundamental PPDW mode is quite inefficient due to parallel-plate mode radiation     

GaAs/GaAlAs curved rib waveguides

Curved dielectric optical waveguides suffer from radiation loss due to bending. To minimize the bending loss and reduce the radius of curvature, it is necessary to fabricate guides which provide strong optical confinement. This paper gives a brief review of curved waveguide analysis and presents some experimentally measured loss values for GaAs/GaAlAs curved rib waveguides. The rib waveguides, fabricated using ion beam milling, have a large rib height and are tightly guided structures. When corrected for reflection losses and input coupling efficiency, a minimum loss of approximately 3 dB has been achieved for a multimode 90° curved guide with a radius of curvature of 300 μm, and 8.5 dB for a single-mode curved guide with a radius of curvature of 400 μm. It is believed that most of this residual loss is not radiation loss due to bending, but rather scattering loss due to rib wall imperfections.     

Radiation from Bends in Dielectric Rod Transmission Lines

The radiation from the fundamental mode propagating around curved dielectric rod transmission lines is investigated experimentally with microwave frequencies. Three methods are used to determine the attenuation by radiation: measuring the insertion loss of bends, measuring the Q-factor of ring resonators, and measuring the Q-factor of sections of curved dielectric rod transmission lines terminated by large reflecting plates. The attenuation is found to depend mainly on the combination R lambda/sub 0//sup 2/ / r/sub 0//sup 3/ where R is the radius of curvature, lambda/sub 0/ the free space wavelength and r/sub 0/ a measure of the transverse field extent of the HE/sub 11/ mode. The experimental results are compared with theoretical predictions of other authors. The measured values of the attenuation constant are found to be smaller than the theoretical values. The distribution of the electromagnetic field near bends is recorded using a semiautomatic field plotter. From the field pictures, it can be concluded that the curved dielectric waveguide radiates tangentially from the outer side. The results presented will also be useful for understanding the mechanism of radiation from bent optical waveguides.     

Coupler-Type Bend for Pillbox Antennas

A new type of 180/spl deg/ H-plane bend has been developed for use in double-layer pillbox antennas. This bend, called a coupler-type bend, permits complete coupling between two pillbox layers with a minimum of reflection, cross-polarization, and defocusing. It can be used with short focus antennas where large feed angles are involved. The coupler-type bend utilizes a metal plate between the pillbox layers; the plate coutains a pattern of holes which achieves the desired coupling. Analytical and experimental programs have been implemented to determine the optimum hole size and distribution. Simulation techniques in rectangular waveguide were employed for convenience in measurements. The bend design was measured to have a reflection less than 2 dB SWR over a ten percent frequeucy band; this is computed to contribute less than 0.2 dB SWR to the reflection seen by the feed-horn of a double-layer pillbox. The bend introduces less than --22 dB of cross-polarization in the antenna radiation. Measurements of a pillbox model incorporating the bend design have verified the predicted performance of the coupler-type bend.     

Reflection at a Curved Dielectric Lnterface--- Electromagnetic Tunneling

The reflection of a locally plane wave from a curved interface between two nonabsorbing dielectric media is investigated. Our analysis is applicable to an interface of general shape, defined at each point by the two principal radii of curvature. When the wave is incident from the denser medium at angles greater than the critical angle it is only partially reflected, due to a form of electromagnetic tunneling. Generalized Fresnel transmission coefficients and an extension of Snell's law are derived to account for this transmission into the less dense medium. Ray tracing can then be applied to determine such phenomena as the bending losses in optical slab waveguides, and the curvature loss of skew rays within straight optical waveguides of circular cross section.     

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.     

Coupling of Degenerate Modes on Curved Dielectric Slab Sections and Application to Directional Couplers

Approximate expressions are derived for the coupling of degenerate modes on two curved dielectric slab sections. From this analysis a directional coupler is designed in which a finite length coupler is joined to terminal lengths via curved structure sections. The reverse coupling (directivity) and reflection, as well as corrections to the coupling length, are studied. The propagation characteristics and the reflection coefficient due to coupling, as well as the correct 3-dB coupling length are calculated, numerically. Second order effects, that determine the band-width as well as the coupling, have been considered and found to be very substantial. In the examples considered the reflection and directivity due to the coupling process were both more than 35 dB down, and the 3-dB outputs were exactly in quadrature, correct to the first order of approximation.     

Analysis of Open-Type Dielectric Waveguides by the Finite-Element Iterative Method

Dispersion characteristics for open-typed dielectric waveguide structures operated at millimeter-and submillimeter-wave frequencies are calculated by a finite-element iterative procedure with a given criterion on the maximum field strength at the virtual boundary. Numerical results for a rectangular dielectric image guide are presented and compared with results from other methods. The strip dielectric guide and the insulated image guide with finite- or infinite-width substrates are also analyzed.     

Experimental evaluation of bend radiation losses in millimetric dielectric waveguide

A crucial parameter in the design of compact dielectric waveguide integrated circuits is the minimum bend radius below which radiation losses become prohibitive. It is shown that, for waveguides with a relative permittivity of 10, values of bend radii down to four guide wavelengths are acceptable.     

Radiation characteristics of uniform and nonuniform dielectricleaky-wave antennas

An approach based on a waveguide model for analyzing the uniform and nonuniform dielectric leaky-wave structures is proposed for which the Galerkin solution method is applied. In the first part of the paper the far-field radiation of the uniform antenna is determined theoretically and experimentally in the Ku band and also the dependence of beamwidth and sidelobe level as function of strip width and frequency is demonstrated. In addition, an analysis of the antenna with a tapered-strip distribution-is presented. The second part describes a novel tapering procedure, performed by changing the width of the uniform antenna, for obtaining the radiation pattern with lower sidelobe levels. Sinusoidally and exponentially shaped dielectric leaky-wave structures are analyzed as nonuniform antennas. Finally, the radiation and scanning characteristics of these antennas are theoretically presented     

Radiation by a corner reflector with dielectric loaded edges

The first part, of this paper deals with the electromagnetic scattering by a cylindrical dielectric shell with an azimuthal permittivity profile and an internal E-polarized line source or an externally incident plane wave. The integral equation for the resulting scattered electric field is solved approximately by the method of moments and the results for the echo width and polar radiation pattern are displayed graphically for typical geometrical dimensions, frequency and permittivity profiles.

The second part of this paper deals with the cylindrical dielectric shell terminating a conducting strip with one edge coinciding with the axis of the cylinder. The results for the scattered field due to a line source excitation are presented and extended to the case of two such strips whose unloaded edges intersect to form a corner reflector antenna. The resulting radiation pattern is shown to improve for specific dimensions and complex permittivity profiles of the dielectric caps.