Showing papers on "Q factor published in 1971"

The accurate measurement of permittivity by means of an open resonator

Abstract: A method for the measurement of permittivity at microwave frequencies using an open resonator is proposed. The theory of the method is developed, and an experimental procedure is evolved and justified. It is shown that the present method has advantages over other open resonator methods which have been proposed, and a thorough experimental study of the method has shown that experimental errors can be made very small indeed. Since the very beginnings of modern microwave techniques in the 1940s, many alternative methods of measuring the complex permittivity of gases, liquids and solids have been devised. Most of these have employed a cavity resonator or a length of waveguide as a means of defining the configuration of the electromagnetic field with the precision needed for accurate quantitative analysis of the experimental results. Although very satisfactory results have been obtained using such methods, they become increasingly difficult to apply as the wavelength decreases. For the solid dielectric materials with which the present paper is exclusively concerned, a major problem is the accurate machining of a specimen of the material to fit closely into the resonator or waveguide. Even very small air gaps between the dielectric material and the metal wall can cause large errors, and this problem is obviously more serious at shorter wavelengths since the fractional error corresponding to a given absolute error in the dimensions of the specimen is inversely proportional to the wavelength. Another difficulty is encountered at very high frequencies in the resonant cavity method of measurement of the loss tangent of a dielectric material when this has a small value. The accuracy of measurement begins to decrease when the loss tangent falls below the reciprocal of the Q factor of the empty resonant cavity. Since this Q factor varies as fo , where f0 is the resonant frequency it is clear that the method is unsatisfactory for low-loss materials at high frequencies. The pioneer work of Culshaw & Anderson (I962) on the measurement of permittivity and dielectric loss with a millimetre wave Fabry-Perot interferometer was the first successful attempt to use an open resonator for this purpose. However, the use of parallel-plane mirrors rather than spherical mirrors gives rise to a field distribution within the resonator which is not readily amenable to mathematical analysis. Moreover, the diffraction losses are much larger than is the case when spherical mirrors are used in a suitable configuration.

Transit-time oscillator with velocity-limited injection

Abstract: The basic theory of a space-charge transit-time oscillator is outlined in which phase lag of current is caused by using low-velocity injection. Large negative resistances are anticipated at microwave frequencies, giving generation of moderate power levels with low-noise operation. Approximate design calculations for a representative idealised structure 100 ?m square, based on silicon and operating at a frequency of 10 GHz, suggest a negative resistance of ?50 ? and a negative Q factor of -?/2, with a maximum output power of about 1 W and an efficiency of about 7%.

Analytical and Experimental Study on Landau Damping of Surface Wave along a Plasma Column

Abstract: A resonator method is used to demonstrate Landau‐damping of surface waves along a plasma column. As a method of plasma diagnostics, an open plasma resonator utilizing longitudinal resonance of the surface wave has been proposed by one of us. This work presents an analysis of anomalous damping in terms of the Q factor observed in the open plasma resonator. In the analysis, the effect of energy absorption by the thermal electrons travelling across the side boundaries of the resonator is accounted for. A method of single‐mode excitation which is convenient for experimental determination of the Q factor is also described. The results of Q measurements are compared with the computer solutions; the Landau‐damping mechanism which is responsible for the anomalous damping in the Q factor is examined.

Investigation of the emission by a ruby laser under self-Q-switching conditions

Abstract: An investigation was made of the generation of giant pulses in a ruby laser which did not contain any switching elements. The self-switching of the Q factor was achieved by the use of unstable configurations of the laser resonator.

Design Study of a Superconducting Deflecting Cavity

Abstract: The superconducting RF beam separator now being constructed at Karlsruhe requires two 3m-long niobium deflectors, which are capable of operating with an equivalent deflecting field of at least 2 MV/m corresponding to an RF peak field of about 250 G. At present, a series of uniform periodic n/2-mode structures are investigated to determine a suitable fabrication technique, but it is anticipated to build the final deflector with a bi-periodic ?/2-mode structure. The problem of mechanical tolerances is analysed by means of equivalent circuits. Questions which arise in connection with the coupling system, frequency tuner, end cells, joints, and mode stabilizers are discussed. Measurements on a test structure yielded a residual quality factor of Q?109 and a peak field of ?200 G after firing the cavity at 1400°C in a vacuum furnace.

Tuning and Excitation of A Prolate Spheroidal Cavity Resonator for Microwave Drying

Abstract: The analytical and experimental results for the eigenfrequencies, electric and magnetic field distributions, Q factor and a coupling system for an empty TMl1m prolate spheroidal cavity resonator are presented.

Grating coupled compound resonators

Abstract: A simple model, based on a simple boundary condition at the grating coupling surface, is constructed for a grating coupled cavity The physical meaning of the boundary condition is discussed, and the gain factor and phase shift of the coupled resonator are studied in terms of the properties of the grating and the reflectivities of the mirrors