摘要:

A rigorous field analysis is carried out to obtain the eigenvalue equation for hybrid modes in a rectangular waveguide periodically loaded with uniform E-plane strips on a dielectric substrate. The eigenvalue equation is in the form of a homogeneous matrix equation for the amplitudes of the spatial harmonics of a field vector defined on the interface of the dielectric substrate where the strips are located. The eigenvalue equations when the field is assumed uniform in the direction of the strips and in the case of narrow strips are then obtained as special cases of the analysis. Sample numerical results for both wide and narrow strips are also given.

DOI:10.1049/ip-h-2.1990.0048

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A radial line slot antenna (RLSA) is a nonresonant multimode waveguide slotted array. The slot coupling to the radial waveguide in this antenna is analysed. A parallel plate waveguide with a periodic boundary condition is used to simulate a sectral region of the circular aperture in a RLSA. A set of integral equations for the fields in the slot is derived, based on the field equivalence theorem, and is solved numerically by Galerkin's method. Theoretical results effectively express the measured effects of the various antenna design parameters on the slot coupling.

DOI:10.1049/ip-h-2.1990.0049

出版商:IEE    

年代:1990

数据来源: IET

摘要:

A modal analysis method is used to investigate scattering from conducting objects of rectangular cross-section, and to determine the variation of the radar cross-section due to the polarisation or direction of the incident wave and the effect of the mode coupling resulting from crosssectional perturbation from a circular cylinder. The traditional approach of surface integral equations in conjunction with a moment method is used to solve the problem numerically. A geometric transformation is used to select entire domain basis functions for the surface current along the cross-section. Subdomain basis functions are used to represent the current component in the plane orthogonal to the cross-section. Owing to the geometric structure of the object the current modes are coupled. The degree of coupling and convergence of the modes are investigated. Representative results for objects of square and rectangular cross-sections are presented and discussed.

DOI:10.1049/ip-h-2.1990.0050

出版商:IEE    

年代:1990

数据来源: IET

摘要:

Results of a study of the influence of the lattice and element configurations on the performance of frequency selective surfaces consisting of arrays of simple tripoles and tripole loops are summarised. The performance indicator is the stability of the main reflection band centre frequency during the alteration of the state of incidence of plane EM waves. Most of the results, presented graphically in terms of the percentage drifts as functions of lattice angles or element separations, refer to incidence from 0° to 45°, although some data are given for 80° incidence. Some lattices produce equal drifts for TE and TM incidence and some give very little drift at all for certain states of incidence. The simple tripole tends to give less stability than the tripole loop for which drifts of two or three percent are typical.

DOI:10.1049/ip-h-2.1990.0051

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The excitation of a semi-infinite sheath helix by the TE11mode of a circular metallic waveguide with the same diameter is studied using the Wiener-Hopf technique. Expressions are presented for the TE11reflection coefficient at the waveguide end and for the relative power in the sheath helix discrete modes. Numerical results corresponding to the current density at the sheath helix surface and to the far-field radiation patterns are presented. These are compared to previous results obtained from the modal analysis of an infinite sheath helix that is excited by a current sheet. Experimental patterns corresponding to a finite length multifilar helix show a satisfactory agreement with the theoretical patterns when the scanning mode is dominant.

DOI:10.1049/ip-h-2.1990.0052

出版商:IEE    

年代:1990

数据来源: IET

摘要:

An iterative algorithm incorporating aperture-domain management and an appropriate measurement strategy are employed to recover the aperture phase of a reflector antenna from a single scan of the radiated field amplitude and a simulated approximation of the aperture amplitude. Simulated and experimental results are presented which validate this reflector antenna metrology technique at millimetre wavelengths. Accelerated convergence is obtained and a new sensitive error metric is introduced to assess convergence to the solution. Measurement conditions are identified for modest signal-to-noise requirements and the prevention of algorithm stagnation.

DOI:10.1049/ip-h-2.1990.0053

出版商:IEE    

年代:1990

数据来源: IET

摘要:

An algorithm suitable for the computer aided analysis of geometrical and resistive discontinuities present in microstrip interconnections on silicon integrated circuit substrates is presented. The distortion and dispersion of an electrical pulse, caused by such discontinuities, as it propagates along the microstrip interconnect is investigated in detail. Studies carried out to assess the use of superconducting tracks for the interconnections in integrated circuits, in the presence of modal dispersion and geometry dependent discontinuities, are also presented. The numerical results are demonstrated on realistic microstrip models for the interconnects which are selected from a practical VLSI prototype.

DOI:10.1049/ip-h-2.1990.0054

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The growing complexity of communication and surveillance systems means that there is an increasing need for antennas with multiple beam capability. Several technologies such as radio frequency (RF), intermediate frequency (IF), digital and optical are available to meet this need but RF beamforming has the advantage of simplicity and a good capability for many applications. This state of the art review of RF beamforming methods for multiple beam antennas aims to introduce the topic and to collate and classify types, giving a critical assessment of comparative performance. The fundamental relationship between the number of active control elements and the number of beams is taken as a measure of beamformer performance and this also indicates that, for a limited number of active elements, high gain antennas with narrow beams will have limited scan range whilst low gain systems have a wide angle capability. This deduction is reinforced by the practical results collected at the end of the review. The beamformer types covered include lens based beamformers such as the Ruze, Rotman, R-KR and nonuniform refractive index types together with objective lenses with separate feed arrays. Reflector based multiple beam antennas based on zero, one or two Fourier transform properties are followed by circuit types including the Blass and Butler matrices. The wide range of information presented is clarified by a summary section giving an indication of comparative performance levels. The very diversity of RF beamformer types and performance are seen to attest the importance of the topic area for current and future antenna systems and point the way to further innovation and development in this very significant field.

DOI:10.1049/ip-h-2.1990.0055

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The effects of both absorption and dispersion in the earth's atmosphere on the propagation of very short pulses in the microwave and millimetre-wavelength regions of the electromagnetic spectrum are calculated for line-of-sight transmissions and for earth–space paths. For pulses as short as 0.1 ns, the effects are found to be severe, both in terms of pulse distortion, in the form of either the broadening or the compression of the pulse, and in terms of a shift in the frequency at which maximum energy in the pulse is received. Pulse compression is found to occur in those regions of the electromagnetic spectrum where the second derivative of the absorption coefficient is negative.

DOI:10.1049/ip-h-2.1990.0056

出版商:IEE    

年代:1990

数据来源: IET

摘要:

The transverse operator method is described for the study of different kinds of dielectric waveguides. The longitudinal section electric (LSE) modes and longitudinal section magnetic (LSM) modes of a corresponding dielectric stratified waveguide, also known as TE-to-xand TM-to-xmodes, have been chosen as the basis eigenfunctions, allowing rapid numerical convergence. The dispersion characteristics of some multidielectric waveguide structures have been obtained, as well as their attenuation constants. The results are compared to those previously published or measured and show good agreement. This formulation can be applied to other multidielectric structures with no modification.

DOI:10.1049/ip-h-2.1990.0057

出版商:IEE    

年代:1990

数据来源: IET