摘要:

Information concerning the subwavelength structure of an object is normally irretrievable from its radiated spatial-frequency distribution: consequently such fine detail is classically irresolvable. It is shown that supcrdirectivc data processing may be used to extrapolate beyond the visible spatial-frequency range so that the individual wires in an array of three 0-6 λ-spaced wire scatterers are resolved. A new development of this technique, based on synthetic evanescent-wave illumination, aids recovery of extrapolated spatial frequencies which subsequently provide even greater resolution.

DOI:10.1049/ij-moa.1979.0009

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The paper examines the application of a technqiue known as reactance compensation to the problem of broadband impedance matching of passive loads. A theory is developed which enables a Cheby̅shev frequency response to be obtained for different loads in alternative compensation circuits. An additional relationship is developed which relates the reflection coefficient of a compensated arbitrary admittance to the reflection coefficient of the uncompensated admittance. This relationship is confirmed experimentally using a microwave detector diode as the load.

DOI:10.1049/ij-moa.1979.0010

出版商:IEE    

年代:1979

数据来源: IET

摘要:

A novel dielectric waveguide that simulates optical graded index fibre is proposed for millimetre-wave applications. It is shown that a gradually varying refractive index across the guide can result in a well confined, single-mode propagation even in a guide several wavelengths wide. The desired index profile is achieved by varying the thickness or height of the waveguide. The effective-dielectric-parameter concept is introduced and used in generating the thickness profile which is approximated by a roof-top. Experimental results for a trial guide are presented and discussed together with the relative merits of this guide.

DOI:10.1049/ij-moa.1979.0011

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Approximate expressions are derived for the coupling of degenerate modes on two nonparallel, dielectric-slab waveguides when the waveguides are symmetrically located about a plane. Numerical examples are given when the waveguides are either both straight or both curved. These results have applications in the design of waveguide junctions and couplers for integrated optical circuits.

DOI:10.1049/ij-moa.1979.0012

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Planar waveguides like microstrip and microslot have been used not only as waveguides but also for radiation purposes (microstrip antennas). Therefore, this paper tries to give a clear description of waveguide characteristics as well as radiation characteristics of planar waveguides. The differences between the several modes, i.e. the guided modes, the radiation modes and the leaky waves, are clarified. Moreover, computed results as well as experimental results of different mode characteristics are presented.

DOI:10.1049/ij-moa.1979.0013

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Symmetrical edge-coupled sections have been used as octave-band microstrip d.c. blocks1as well as building blocks for filters, directional couplers, impedance transformers and other important transmission-line devices. In this paper, the possibility of utilising coupled sections as parts of the input and the output impedance matching networks for transistor amplifiers operating at microwave frequencies is specifically investigated including the effects of dissipation. The experimental results agree very well with the theory and confirm that low-loss transformers can be realised.

DOI:10.1049/ij-moa.1979.0014

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The insertion loss between ports 1 and 3 of a 3-port junction circulator terminated in a variable short circuit at port 2 varies between one and three times that between adjacent ports. Whereas a phcinenological explanation of this behaviour is not possible on the basis of a sequence of travelling waves, it may be understood by taking a linear combination of standing-wave patterns in an ideal circulator. The minimum attenuation condition is obtained by superimposing two such solutions in antiphase. This combination leads to a reversal in the direction of circulation in the junction, and in this case the insertion loss becomes the loss between adjacent ports. The maximum attenuation is obtained by adding the two standing-wave solutions in phase.

DOI:10.1049/ij-moa.1979.0018

出版商:IEE    

年代:1979

数据来源: IET

摘要:

Edge effects in planar resonators may be described by subdividing the resonators into thin strips and replacing each strip by an equivalent waveguide transmission line. The discontinuity between adjacent strips is accounted for by using a lumped-element inductor. The resonant frequency of the overall network is calculated by forming a transverse resonance condition. This approach has been used to obtain mode charts for planar triangular resonators on an alumina substrate and on a demagnetised-garnet substrate, and for circular and rectangular resonators on rexolite substrates. Experimental points show good agreement in each case. A theoretical mode chart for a hexagonal resonator, not previously described, is also evaluated.

DOI:10.1049/ij-moa.1979.0019

出版商:IEE    

年代:1979

数据来源: IET

摘要:

A completely new geometrical method of optical design is proposed using the combined concepts of the phase front of zero distance and the inversion theorem of Damien. Ray tracing is not used and the method is applied to the design of two surface reflecting and refracting systems with sources at finite or infinite distances. When extended, the method can apply to caustics and other forms of extended source distribution. The process is illustrated for fundamental systems and the application to shaped-beam antennas is outlined.

DOI:10.1049/ij-moa.1979.0020

出版商:IEE    

年代:1979

数据来源: IET

摘要:

The effect of motion on the signal received from a source in translation is investigated. The Courier spectrum of the signal is evaluated by the method of steepest descent. The spectrum associated with a monochromatic source turns out to be bandlimited, and to have two infinite peaks. These peaks disappear when the receiver is activated during part of the time only. Finally, the spectrum of the signal received from a sinusoidal transmitter modulated by a Gaussian pulse is discussed. There, again, the infinite peaks disappear.

DOI:10.1049/ij-moa.1979.0021

出版商:IEE    

年代:1979

数据来源: IET