Canan Toker

High-Power 20-100-MHz Linear and Efficient Power-Amplifier Design

This paper presents modeling and analysis of the realization of high-power broadband RF power amplifiers (PAs) and power combiners. In the scope of the study, a model is proposed for a transmission line with a ferrite core, which is the basic building block for the transmission line transformers (TLTs) used in broadband high-power amplifiers and power combiner/divider networks as a building block. Simulated performances of the designed networks using the proposed model possess high conformity with the empirical performance of the corresponding realized networks. Therefore, broadband TLT networks with low insertion loss, high power-handling capability, and low return loss are realized. RF power combiner/divider networks with wide frequency bandwidth and high isolation are also implemented. By using class-B biased pushpull network topology, a linear and wideband RF PA is realized with high drain efficiency at high output power levels. In order to broaden the operating frequency range of the indicated amplifier, a novel technique for TLT utilization that matches the output impedance of the RF power transistor in wideband is proposed and realized. Measurement results satisfy the design specifications.

Branch-line couplers using unequal line lengths

General solutions for branch-line couplers using different line lengths are provided in this paper. Explicit expressions are derived with which a hybrid with any given power division ratio can be designed. In the design, one of the characteristic impedances or lengths of the branches can be chosen arbitrarily to suit a given design specification. This approach brings flexibility in choosing the characteristic impedances or the lengths of the branches, and is helpful especially in monolithic-microwave integrated-circuit applications where restrictions imposed on microstrip transmission lines do not allow the use of conventional branch-line couplers employing quarter-wave-long lines. However, the resultant bandwidth is narrower compared to that of the conventional coupler.

Microstructure of boron nitride coated on nuclear fuels by plasma enhanced chemical vapor deposition

Abstract Three nuclear fuels, pure urania, 5% and 10% gadolinia containing fuels were coated with boron nitride to improve nuclear and physical properties. Coating was done by plasma enhanced chemical vapor deposition technique by using boron trichloride and ammonia. The specimens were examined under a scanning electron microscope. Boron nitride formed a grainy structure on all fuels. Gadolinia decreased the grain size of boron nitride. The fractal dimensions of fragmentation and of area–perimeter relation were determined.

Design of an active microstrip array using a microwave circuit simulator

An active antenna array design and simulation of this design with a microwave circuit simulator are presented. This active antenna array is a TV receive only (TVRO) antenna operating at 10 GHz. It is a 8/spl times/4 array of rectangular microstrip patch antennas. Eight low noise pHEMTs are placed in the antenna. Passive antenna characteristics are usually obtained by analytical techniques or using special softwares for this purpose. The numerical representation as well as the nonreciprocal nature of the active device necessitates the use of a circuit simulator. In this work, both the antenna and the active circuit characteristics are obtained in the same medium, using microwave circuit simulator LIBRA. The array structure is simulated with LIBRA for gain, noise temperature, radiation pattern, directivity and bandwidth.

Comments on "Branch-line couplers using unequal line lengths

For original paper see Toker et al., ibid., vol.49. no.4, pp.718-21, 2001. In the above paper, Toker et al. maintain that the general solution of branch-line couplers is provided. In fact, the more general coupler was published previously by the author (see ibid., vol.40, pp.253-62, 1992). Simplifying the general structure in this paper by removing the lumped elements, one can get the branch-line coupler. A reply to these comments by Toker et al. is included.

Noise in the Presence of Coupling Among Antenna Elements

Noise temperature calculation and minimum noise temperature design of feed structures for large scale antenna arrays is given in Demir et al. (1)-(3). In those studies the portion of internally generated noise power appearing at the antenna element terminals was not calculated because the feed system is assumed to be matched to the antenna elements and therefore reflections do not occur and all the noise power dissipates on or radiates through the antenna elements. However, even in the matched case, some part of the noise power may return back to the output port if there is coupling among antenna elements. In this study, it is assumed that internal noise power at the antenna element terminals is coupled to the neighboring antenna elements and received as noise power input. This consideration has two aspects: the noise power at the output terminal is changed and noise signals at the output terminal are not any more uncorrelated and therefore requires a special treatment.

Design criteria for a lumped-element directional coupler

The lumped-elernent directional coupler described in this paper uses one inductor and one capacitor as the lossless junction of a four-port network. The directional coupler effect and the infinite directivity are frequency independent, at least, from d.c. to the frequencies at which the inductor and/or the capacitor deviates from the idea), but the coupling properties are frequency dependent. However, the forward coupling from the Input arm and the reversed coupling from the output arm form a ratio which is also frequency independent.A technique is described to obtain wide-band operation which is particularly useful for large coupling. By this technique multi-decade bandwidth operation is possible.The properties are expressed in terms of the scattering matrix and the frequency dependence of the coupling and the insertion loss are formulated. General design criteria for single frequency (narrow-band) and wide-band operations are provided by means of which a directional coupler with required characteristics...

Weissfloch transformer for antenna impedance measurements

An antenna impedance measurement technique based on the Weissfloch transformer theorem is described. In this method the antenna impedance is compared to a normalizing load whose value can be determined to a high degree of precision. The method provides a perfect transformer action between the antenna terminals and a point in the input transmission line, with the known transformer ratio. Baluns and other auxiliary antenna components are treated as a discontinuity and their intervening effects in the measurement accuracy are eliminated.