摘要:

Surface-acoustic-wave (s.a.w.) energy, radiated by short normal and rare interdigitai transducers (i.d.t.s) with arbitrary metallisation ratios, is obtained in a novel manner that has an intimate contact with the physical situation. The basic assumption used is that the static mechanical energy generated isk2times the applied electrostatic energy in a piezoelectric insulator, wherekis the appropriate electromechanical coupling factor. By comparison with other models, it is shown thatk2thus defined is equal to 2 {(vo—vM)/v0}, wherevoandvmare s.a.w. velocities on, respectively, free and metallised surfaces of the piezoelectric in the concerned direction, and that the electric field components, both normal and parallel to the direction of wave propagation in an i.d.t., are equally significant in s.a.w. excitation.Experimental results on s.a.w. amplitude radiated by a rare i.d.t. are presented in the time domain; they agree with the calculations.

DOI:10.1049/ij-moa.1978.0014

出版商:IEE    

年代:1978

数据来源: IET

摘要:

In the paper, mixers are described that consist ofMresistive diodes, e.g. Schottky-barrier diodes in a parallel connection. When such mixers are used in frequency convertors, the diodes are pumped by signals having a frequencyMtimes lower than the frequency of conventional local oscillators. A phase shift equal to multiples of 2π/Mis necessary between the pump signals. The frequency multiplication, which is usually carried out in the local-oscillator circuit, is done in the mixer. For this reason it is possible to use pump sources that are much simpler than conventional local oscillators. Often the harmonic mixers proposed in the paper are more complicated than the mixers used so far. Sometimes, however, circuits of moderate complexity can be found, so that a simplification of the frequency convertors is possible. This will be shown by mixers that are pumped at the first or second subharmonic, respectively. Theoretical investigations show that the conversion losses of harmonic mixers are slightly higher than those of conventional mixers.

DOI:10.1049/ij-moa.1978.0015

出版商:IEE    

年代:1978

数据来源: IET

摘要:

A new system has been developed for determining precisely the Q-factor of an X-band open resonator. The new system differs from previous systems in its use of an injection-locked phase-shifting technique to provide electronically a ± π/4 phase shift for Q-factor measurement. The ± π/4 phase change is produced at an i.f. frequency with a total uncertainy that is an order of magnitude lower than is possible with conventional phase shifters. The phase-shifting technique employs a crystal-controlled reference oscillator and a second oscillator whose free running frequency is close to that of the reference oscillator. The output of the second oscillator is injection-locked to the 8th harmonic of the reference-oscillator signal. A π/4 phase shift on the output of the second locked oscillator is achieved by unlocking it from one cycle of the 8th harmonic of the reference oscillator and relocking it to an adjacent cycle. The new system uses single-sideband homodyne detection. Single-sideband modulation is achieved by using the open resonator as a high-Q filter to remove all but the required sideband from the output of a double-sideband modulator. The new system incorporates the injection-locked phase-shifting technique and the homodyne detection system in a phase-locked loop to provide rapid Q-factor measurements.

DOI:10.1049/ij-moa.1978.0016

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The resolution of long-wavelength imaging systems is normally limited by the effective recording-aperture dimension, and may preclude target recognition. It is shown that, for imaging systems in which complex field values are recorded, the aperture can be effectively extrapolated by a superdirective weighting function, thereby restoring essential features to a severely diffraction-limited image. Limitations to image enhancement arising from spatial noise in the object plane are discussed.

DOI:10.1049/ij-moa.1978.0017

出版商:IEE    

年代:1978

数据来源: IET

摘要:

The theoretical design of a long backfire antenna containing a dielectric structure is discussed. The analysis contains a detailed description of the effective aperture radiation, the direct radiation from the feed, the g.t.d. corrections and the multiple-reflection effect. The results are compared with experimental data at 10 GHz.

DOI:10.1049/ij-moa.1978.0018

出版商:IEE    

年代:1978

数据来源: IET

DOI:10.1049/ij-moa.1978.0019

出版商:IEE    

年代:1978

数据来源: IET