Reflected fields from twist reflector in twist reflector scanning antenna configuration

Theory is presented for calculating the variation of cross-polarisation suppression ratio and loss in the desired polarisation of a twist reflector in different scanning planes in a twist-reflector scanning antenna system. Theoretical and experimental results for a W-band twist reflector are described.<>     

Novel frequency-selective twist polariser

A new type of twist polariser that has a frequency selective property is investigated. The polariser consists of two sheets of photoetched dipole array FSSs (frequency selective surfaces), spaced about one-quarter wavelength apart. Such a polariser reflects waves at the desired frequency band in the usual manner, but lets the other frequency waves pass through.<>     

A broad-band twist reflector

Polarization twisting reflectors, or twist reflectors, consisting of a wire grid spaced approximately3 lambda/8from a ground plane [1], [2] have a bandwidth of at most 30 percent. It is shown that the inclusion of an additional wire grid in front of the first grid makes bandwidths of 100 percent possible. Design formulas, theoretical performance in terms of cross polarization attenuation, and some experimental results for a twist reflector with two wire grids are given.     

Long period fibre grating torsion sensor measuring twist rate and determining twist direction simultaneously

A fibre-optic torsion sensor based on a long-period fiber grating written by high-frequency CO/sub 2/ laser pulses is proposed and has been demonstrated. Such a torsion sensor cannot only measure the applied twist rate directly, but also determine the twist direction simultaneously.     

Wide-band waveguide and ridge waveguide T-junctions for diplexerapplications

Scattering parameters of E- and H-plane stepped waveguide and E-plane ridge waveguide stepped T-junctions are obtained using an extension of the three-plane mode matching method. An optimization process is applied to find the T-junctions and step dimensions that yield a low reflection coefficient in one of the T-junctions arms over a wide frequency band. An example of the design of a wideband T-junction diplexer is presented. The diplexer filters are inductive window waveguide filters, and are rigorously modeled using mode matching and a novel two-dimensional curve fitting method, which greatly reduces the CPU time for optimization. The diplexer optimization procedure, as well as the filter modeling method, are described. Experimental results on the optimized T-junction and the diplexer are presented; both show excellent agreement with their computed optimum results, without any adjustments or tuning     

Magneto-inductive waveguide

A new magnetic waveguide is described, the operation of which is based on inductive coupling between resonant elements. The general form of the dispersion equation is shown. For a particular embodiment of the waveguide, consisting of 26 elements, the relative values of the currents are plotted and the travel of power from the first to the last element is shown by the streamlines of the Poynting vector. Application, as a magnetic guide for magnetic resonance imaging (MRI) is proposed     

Broadband transition between air-filled waveguide and substrate integrated waveguide

A Ka-band broadband transition between an air-filled waveguide and a substrate integrated waveguide (SIW) is proposed. The transition is realised by using a radial probe inserted into the height-tapered metal waveguide. Results show that an insertion loss less than 2.5 dB and a return loss better than 14 dB in the frequency band 28.3-39.5 GHz are obtained for a back-to-back structure     

Measurement of optical waveguide coupling coefficients usingmultiple waveguide systems

A method for simply and accurately determining the coupling coefficient between integrated optical waveguides is presented. Measurement of only a few features of the output power distribution from a linear array of identical guides is required. The result is most accurate for long samples, but approximates the coupling coefficient to well within a few percent even for samples shorter than one two-guide coupling length. Since waveguides in the array would be fabricated in the same way, perhaps the same substrate, as the device structures of interest, the method ought to be a useful and convenient one for device designers     

A dielectric rod waveguide coupled with metal rectangular waveguide

Measurements have been done in the millimeter wave region on a composite waveguide which comprises a dielectric rod waveguide connecting two metal rectangular waveguides. Such a waveguide has been used by us in a Josephson harmonic mixer installed in a small metal cryostat, to prevent the thermal invasion from outside environment and to transmit both signal and LO waves with small losses. The measured transmission loss, that is caused mainly by the coupling loss between metal rectangular waveguides (TE₁₀ mode) and a dielectric rod waveguide (HE₁₁ mode), has been less than 2dB in the frequency range of 52–104 GHz.     

Millimeter wave twist reflector design aspects

A millimeter-wave twist reflector design procedure is described. An effective dielectric constant for capacitive susceptance correction for a unidirectional planar grating at the interface of free space and dielectric material in the twist reflector environment is introduced. The loss factor of the dielectric material is taken into account for the prediction of twist reflector performance. With the introduction of these corrections experimental results are found to be in close agreement with the theory. Normalized curves for the design of twist reflectors in terms of grating parameters, dielectric substrate relative permittivity, and dielectric material thickness are presented. Experimental results are given     

改进型圆-矩波导模式转换器的研究

在某些特定频段上,传统的圆-矩波导模式转换器无法满足其性能要求。针对这一问题,提出一种结构紧凑、反射系数小且波形转换效率高的改进型波导模式转换器,其工作在4.7 GHz,带宽800 MHz。采用切比雪夫阻抗法对其进行理论分析,并计算得到结构尺寸。最后测量结果与仿真结果吻合良好,在工作频带内电压驻波比均小于1.1,证明了该方法的可行性。     

Broadband substrate integrated waveguide to rectangular waveguide transition with fin-line

A novel broadband transition from a substrate integrated waveguide to a rectangle waveguide with an antipodal fin-line in its quasi-TE mode is presented. Impedance match and field mode gradual changing of transition circuits have been carefully analysed and performed. Experimental results show about a 1.6 dB insertion loss and greater than 12 dB return loss for back-to-back transitions over 10 GHz bandwidth from 26.5 to 40 GHz, so single transition insertion loss is about 0.8 dB. The transition is proposed for low-loss front-end circuits in the millimetre-wave band.     

Optical waveguide transmission

As optical communication systems are being studied in more detail, the need for many different types of optical waveguides becomes apparent. The applications range from miniature optical circuit connections to long-distance high-capacity transmission links. The requirements with respect to cost, attenuation, dispersion, or flexibility are vastly different. As different as the specifications are the guides evolving for various purposes. We describe the state of the art and give a survey of those guides which show the greatest future potential.     

Electromagnetic helical waveguide

The H0nmodes for helical waveguide are obtained rigorously from a newly introduced system of coordinates. It is also found that a coaxial line can support slow waves of magnetic type.     

Coupled waveguide antennas

A structure consisting of two coupled waveguides is proposed as a leaky-wave antenna. The analysis of this device is based on coupled-mode theory. Previous coupled-mode treatments are extended, since radiative loss is not neglected and the asymmetry of the structure is taken into account. Two cases are considered: the coupling parameter constant with distancezalong the antenna and the coupling as a function ofz. In both, the radiative attenuation is maintained constant. It is found that the first case permits two "normal modes" to propagate and, if both modes are excited, the patterns may be superposed to produce desirable overall results. An example is given of an approximation to a pencil beam pattern. By means of the second method, essentially any of the common excitation functions may be produced. An example is given of an antenna to achieve a cosine-on-a-pedestal excitation. Experimental results are given and compared to theory. Suggestions are presented for further work.     

Coaxial waveguide gyro-peniotron

A coaxial waveguide gyro-peniotron with largeorbit beam is proposed. The linear thoery of 3-D model is given to describe this device. The influences of the beam radius and beam current on the normalized growth rate are discussed in terms of numerical analysis.     

Microstrip waveguide transitions

Excitation of a microstrip waveguide by means of a microstrip line and waveguide transitions between microstrip waveguides characterized by different parameters are investigated theoretically.     

Glass waveguide laser

A channel waveguide fabricated in a Nd³⁺-doped laser glass by the ion exchange method is discussed. The device was end-fire pumped by a diode-laser operating at 802 nm. Continuous-wave (CW) lasing was observed at 1054 nm, and maximum output power was higher than 150 mW. The large output power was achieved by increasing the radius of the waveguide