IEE Journal on Microwaves, Optics and Acoustics
Volume 3, Issue 5, September 1979
Volume 3, Issue 5
September 1979
Measured and predicted performance of a compensating subreflector
- Author(s): R.J. Langley ; A.J. Drinkwater ; E.A. Parker
- Source: IEE Journal on Microwaves, Optics and Acoustics, Volume 3, Issue 5, p. 169 –171
- DOI: 10.1049/ij-moa.1979.0040
- Type: Article
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p.
169
–171
(3)
The intensity and phase scattering patterns of a profile error-compensating mirror, 30 cm in diameter, have been computed at 34 and 68 GHz. The mirror had been used previously between 28 and 40 GHz to compensate for errors on the surface of a paraboloid 2.8 m in diameter. The results are compared with measured patterns and also the patterns needed to achieve maximum phase compensation. Good agreement was obtained between the measured and computed patterns. Generally the mirror compensated successfully for profile errors with correlation intervals greater than D/10. The residual phase differences between the required and computed patterns were consistent with those deduced previously from the performance of the complete compensated antenna. At 34 GHz they amounted to about 20° r.m.s., giving a shortfall in gain of (0.5 ± 0.3) dB. Results at 68 GHz suggest that the reflector could be operated efficiently at much higher frequencies.
Mode coupling in a planar circular waveguide array
- Author(s): T.S. Bird
- Source: IEE Journal on Microwaves, Optics and Acoustics, Volume 3, Issue 5, p. 172 –180
- DOI: 10.1049/ij-moa.1979.0041
- Type: Article
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p.
172
–180
(9)
By means of an integral-equation approach, expressions are derived for all mode coupling occuring in a finite, planar circular waveguide array. Modes coupling in the aperture of each waveguide yield terms dependent upon contour integrals. These are placed in a suitable form for numerical integration. A new asymptotic formula is obtained for the coupling between modes in separate waveguides. Theoretical results are presented for the TE11 mode admittance of flanged circular waveguide and for two waveguides coupling in the H-plane. These results are shown to correlate satisfactorily with previously published experimental data.
Ray tracing in a general nonhomogeneous cylindrical medium
- Author(s): S. Cornbleet
- Source: IEE Journal on Microwaves, Optics and Acoustics, Volume 3, Issue 5, p. 181 –185
- DOI: 10.1049/ij-moa.1979.0042
- Type: Article
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181
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(5)
The complete ray equations are derived for a generalised cylindrical co-ordinate system obtained by the translation of a plane orthogonal system parallel to the cylinder axis. The condition that a ray is confined to a surface of a constant co-ordinate value is shown to lead to complete integrability of the reduced equations. Ray traces can then be made in specific refractive-index media, such as the parabolic. Alternatively, specified ray behaviour such as coherent refocusing, gives the required refractive index. In the latter case, this is shown to be a generalisation of the sech law for a circularly symmetrical medium.
Radiation from bends in optical waveguides: the volume-current method
- Author(s): I.A. White
- Source: IEE Journal on Microwaves, Optics and Acoustics, Volume 3, Issue 5, p. 186 –188
- DOI: 10.1049/ij-moa.1979.0043
- Type: Article
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p.
186
–188
(3)
A new simple and direct method for the determination of radiation losses due to bends in the axes of open waveguides is presented. For weakly guiding dielectric waveguides, this analysis reduces to an integral of the transverse electric field of the incident wave over the volume of the bent waveguide core. A formula for the power attenuation coefficient for such optical fibres, valid for all dielectric profiles of the core, is presented.
Synthesis of inhomogeneous dielectric-slab waveguide
- Author(s): L.M. Andrushko
- Source: IEE Journal on Microwaves, Optics and Acoustics, Volume 3, Issue 5, p. 189 –196
- DOI: 10.1049/ij-moa.1979.0044
- Type: Article
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189
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(8)
A method for the synthesis of inhomogeneous dielectric-slab waveguides is described. The function ε(x), which specifies the variation of the dielectric constant, is determined from the given spectrum of cutoff frequencies and the group velocities at the cutoff frequencies. The method is based on the solution of the inverse Sturm-Liouville problem, and it is illustrated by a number of solutions.
Switching characteristics of phase modulators
- Author(s): Klaus Schünemann ; Frank Sporleder ; Laszlo Szabo
- Source: IEE Journal on Microwaves, Optics and Acoustics, Volume 3, Issue 5, p. 197 –204
- DOI: 10.1049/ij-moa.1979.0045
- Type: Article
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197
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The influence of the p-i-n-diode switching transients on the performance of digital phase modulators is studied. To this end two models are introduced: a diode model which allows one to calculate the transient impedances, and a black-box model of a phase modulator which can be incorporated in network analysis programs in order to simulate system performance. Based on these models, guidlines are given for an optimum choice of various design parameters as for example the i-layer width of the p-i-n-diode, the switching-current ratio, the switching-current waveforms and the modulator bandwidth.
High-frequency behaviour of microstrip open-circuit terminations
- Author(s): J.R. James and A. Henderson
- Source: IEE Journal on Microwaves, Optics and Acoustics, Volume 3, Issue 5, p. 205 –218
- DOI: 10.1049/ij-moa.1979.0046
- Type: Article
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205
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The extensive use of open-circuit microstrip terminations as tuning stubs and, more recently, as antenna elements, demands design data on the frequency-dependent characteristics of the termination. A variational solution for the end admittance is formulated using discrete and continuous mode distributions to represent the radiation, evanescent and substrate surface-wave fields. Computed results for a variety of line widths on polyguide and alumina substrates are compared with available experimental and theoretical data. It is established that useful admittance curves can be readily calculated using a simple trial aperture field, and the functional form of the curves is independently predicted by a Hilbert-transform relationship. The frequency-dependent end admittance reveals the lower frequency range over which a given substrate is suitable for unshielded high-Q circuit applications and the higher-frequency region for microstrip antenna applications. The generation of substrate surface waves increases with frequency, and sets an upper frequency limit for microstrip antenna applications. Other practical issues of interest such as radiation patterns, intercircuit coupling and resonator losses are briefly considered and the usefulness of this approximate analysis, which represents the most complete treatment to date, is evident.
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