Calculation of nonconverting taper structure for TE/sub 01/ modes in gyrotron
Calculations and analysis of nonconverting taper for circular waveguide with operating TE/sub 01/ mode are presented. Calculations are carried out on the basis of discretely defined T-functions. The results obtained were checked by alternative method of finite elements which is incorporated in widely spread program.
Theoretical evaluation of nonlinear tapers for a high-power gyrotron
The theoretical performance of two nonlinear circular waveguide tapers constructed for a 10-GHz, 30-MW amplifier utilizing the lowest circular electric mode is evaluated. Mode coupling is estimated with a code that solves the generalized telegraphist's equations numerically and is compared with the results of a cascaded scattering matrix code. It is found that assuming a sufficiently lossy conducting boundary allows evaluation of modes that pass through cutoff and that consideration of backward modes usually results in small changes in the forward modes that reconcile the two numerical procedures. A comparison of the raised cosine profile with other taper shapes is made. It is shown that, under some conditions, a raised cosine profile yields less mode conversion than the modified Dolph-Chebyshev profile. >
Ceramic microwave antennas for mobile applications
Due to their medium to high permittivity values, ceramic microwave materials are attractive as building blocks for miniaturised antenna solutions. Further advantages are low dielectric losses and an excellent temperature stability of standard ceramic materials. Yet, the permittivity of the ceramic material also has a strong influence on the radiation efficiency and bandwidth of the antenna. This implies that in the design process a suitable compromise has to be found between the degree of miniaturisation on the one hand and the antenna efficiency and bandwidth on the other. We describe two approaches towards efficient miniaturised ceramic microwave antennas: the dielectric resonator antenna (DRA) with partial metallisation and the shorting post patch antenna. We focus on design steps taken to ensure both a high degree of miniaturisation and high values of the radiation efficiency, the choice of the ceramic material and the experimental performance of the antennas.