New experiments on the behaviour of the hybrid TEM-dual surface wave in a coaxial cable

A new series of experiments, using a standing-wave method of measurement as well as a repetition of the previous resonant-cavity work, endorses the conclusion that a significant reduction of attenuation is possible, when the inner conductor of a coaxial cable is coated with a dielectric of higher permittivity than that of the surrounding medium, between the two conductors.     

Experimental investigation of the hybrid TEM-dual surface wave

The conditions for minimum attenuation of this wave supported in one case by a coaxial guide and in another by a parallel-wire transmission line have been investigated experimentally and shown to comply with the earlier theoretical predictions. The best results are obtained by loading one or other of the two supporting surfaces and not both simultaneously.     

Possible physical explanation of the observed behaviour of the hybrid TEM-dual surface wave in a coaxial cable having an electrically loaded inner conductor

Numerical calculations for power distribution over the cross-section of a coaxial cable have been made for the particular case investigated experimentally, giving minimum attenuation at 3 GHz. The results reveal illuminating information about the behaviour of the hybrid and quasi-TEM waves in these circumstances.     

Transferred surface currents in braided coaxial cables

It is shown that the transfer of longitudinal current to the outer surface of a long length of braided coaxial cable, such as might be used in a `leaky-feeder? radiocommunication system, is a function of other parameters besides the surface-transfer impedance of the braid. The dielectric is particularly significant.     

Application of inhomogeneous dielectric loading to coaxial resonators

A technique for improving the Q factor of air-filled coaxial resonators by inhomogeneous dielectric loading is reported.     

降低多模光纤衰减的技术途径

文章从多模光纤的应用需求出发，从多方面探讨了影响多模光纤衰减的因素和降低多模光纤衰减的思路，得出了许多有益的结论．     

同轴气体激光器二球面镜腔内光束的传输特性

本文以多程(臂)环形腔近似替代的方法分析同轴气体激光器二球面镜腔内光束的传输特性,得到一些有用的结果。     

Study of the surface properties of thermally oxidized silicon using surface acoustic wave attenuation

In the separate media space charged coupled convolver, the interaction of a surface acoustic wave (SAW) with the free carriers in an adjacent semiconductor results in attenuation of the acoustic wave. The magnitude of the attenuation is dependent on the concentration of the free carriers near the surface. An externally applied d.c. voltage changes the surface carrier concentration and this change is reflected in SAW attenuation. Analysis of the SAW attenuation caused by a continuous d.c. field gives an estimate of the surface state density. The time required for the SAW attenuation to reach steady state after the semiconductor is driven into deep depletion is an indication of the rate of carrier generation in the depletion region. Transient effects have also been observed using a synchronously applied d.c. pulse.     

Propagation characteristics of the TM01 surface-wave mode in dielectric-lined coaxial cables

Accurate calculations of the propagation coefficients of the TM01 surface-wave mode in coaxial cables with dielectric linings on the inner, outer or both conductors were carried out using a perturbation method, and were checked by solving the exact characteristic equations. The calculations show that the perturbation method yields very accurate results, and that the attenuation coefficients cannot be reduced below that of the quasi-TEM mode in the unlined cable.     

Theory and analysis of leaky coaxial cables with periodic slots

Frequency band and coupling loss are the two important parameters of leaky coaxial cables with periodic slots. The frequency band can be predicted by analyzing the arrangement of the slots on the outer shield of the cable, but the coupling loss is not so easy to determine by classical methods. In this paper, the finite-difference time-domain (FDTD) method is used to calculate the electric field distribution in the slot cut in the outer conductor of the coaxial cable. The dyadic Green's function is then used to calculate the radiation field of the equivalent surface magnetic current densities. By these two methods, the coupling losses of the leaky coaxial cables with different periods, sizes and shapes of the slots can be accurately obtained. Some results in this paper were verified by the experimental results of leaky coaxial cables designed for railway mobile communications with a frequency band of 100-500 MHz     

Azimuthal selection of modes in free-electron masers with coaxial Bragg resonators

A comparative analysis of the selective characteristics of Bragg resonators with various types of periodic corrugation is performed. In the simplest case of the azimuthal symmetric corrugation in a highly overmoded resonator (a large ratio of the perimeter to the wavelength), the Q factors of modes with different numbers of azimuthal variations are almost equal and the mode frequencies are close on the scale of the gain band of electron flow. A certain rarefaction of the mode spectrum can be attained using the helical corrugation when the traveling wave is coupled with the whispering-gallery modes and the frequency interval between the high-Q modes of the resonator with different azimuthal indices is determined by the interval between the critical frequencies of the whispering-gallery modes. The doubly periodic corrugation employed in the 2D Bragg resonators at the same (as in the case of the helical corrugation) intermode distance allows the Q-factor selection of a single azimuthal symmetric mode. The analysis is based on the method of coupled waves and the direct numerical simulation using standard codes.     

Cold tests of open coaxial resonators in the range 9–17 GHz

A study of selective properties of coaxial open cylindrical resonators have been conducted experimentally and compared with theory. The resonator consists of an inner circular cylinder symmetrically located inside an outer weakly irregular open waveguide. Several fundamental TE modes were identified over the range 9 to 17 GHz through measurements of the resonant frequencies and the associated loaded quality factors. It has been verified that the structure and the number of resonant modes are both strongly dependent on the diameter of the coaxial insert. Such an electrodynamical system proves to be useful in guided wave applications requiring, for example, filters, frequency-tunable resonators and devices for analyzing the modal composition of a signal.     

Optical image scanning by electronic control of surface acoustic wave attenuation in CdS

A new technique of reading optical images in a CdS surface acoustic wave delay line is presented. The principle is based on controlling surface-acoustic wave propagation loss by applied gate bias.     

Measurement of the attenuation coefficient of inhomogeneous dielectric-filled cables using the standing-wave technique

When the standing-wave technique is used to measure the attenuation coefficient of an inhomogeneously filled transmission line terminated by a short circuit, the usual expression for the losses in the termination is incorrect. By use of the perturbation technique, a correction factor to this expression may be obtained, and this is evaluated for three examples of inhomogeneously filled cable.     

Experiments on a two-wire line resonator supporting the hybrid tem-dual surface wave

When one of the two wires, forming a resonant transmission line short-circuited at both ends, is coated with polythene, the losses are observed to fall, and the general behaviour appears to be very similar to that of the equivalent coaxial-cable arrangement.     

A procedure for measuring the Q factor of and attenuation in microwave composite acoustic resonators

A procedure for measuring the Q factor of a microwave composite acoustic resonator is described. The resonator consists of a relatively thick crystal plate and a piezoelectric film with electrodes that is deposited on the plate. The procedure is based on mathematical processing of the array of measurement data on the coefficient of the electromagnetic-wave reflection from the resonator structure connected to a microwave reflectometer. Via this procedure, it is possible to obtain data on the Q factor at the resonance and antiresonance frequencies.