TEM coupling between orthogonal crossing wires: a closed-formapproximation

The equations describing the coupling mechanism between two crossing, orthogonal thin wires over a perfectly conducting ground plane are derived from first principles. Cast in the form of two cross-coupled Fredholm integral equations of the second kind, the equations are manipulated in such a way as to show the nature of the coupling between the TEM modes, the evanescent modes and the radiation terms. The assumption is made that the coupling between the evanescent and radiation terms to the TEM mode is weak after the first wave bounce. By neglecting such effects, we derive a closed-form approximation for the equivalent lumped junction capacitances. The resulting expressions are surprisingly simple and are amenable to desktop calculation. The final formulas are numerically compared with previously published data     

H-plane coupling between rectangular microstrip antennas

A new model that theoretically characterises mutual coupling effects between two rectangular microstrip antennas is presented. Numerical S-parameter results exhibiting mutual coupling effects are reported.     

On Lewin's theory of waveguide coupling by rectangular slots

It is shown that Lewin's waveguide coupling formula, when suitably modified, is in good agreement with the results obtained by variational methods. The connection between the modified Lewin formula and the results of the Bethe-Cohn theory is pointed out. It is doubtful if Lewin's theory can be improved to yield the correct slot length for resonance.     

E-plane coupling between two rectangular microstrip antennas

A model which theoretically characterises end coupling (E-plane coupling) between two rectangular microstrip antennas is discussed. Computer generated S-parameter results for this particular type of mutual coupling are presented.     

Mutual coupling between cylindrical rectangular microstrip antennas

The effect of curvature and separation on the mutual coupling between probe feed rectangular microstrip antennas printed on a cylindrical surface is studied theoretically and experimentally. To incorporate the interactions between patches through the space wave as well as the surface wave, the rigorous spectral domain approach is adopted. The experiment is performed for the purpose of validation of the theoretical results     

Study of the magnetic coupling between a SQUID and wires integratedon a chip

Magnetic coupling between a SQUID and wires in an integrated circuit has been studied. Using test integrated circuits, the coupling is measured by varying the distance from the SQUID to each wire. The coupling between the SQUID and the wires with and without a groundplane decreases with an increase in the distance. The coupling for the wires with the groundplane is smaller than that for the wires without the groundplane at distances less than 595 μm. However, the rate of the decrease in the coupling for the wires with the groundplane falls off for distances more than 595 μm and the coupling converges to around 2.9 pH. From two dimensional simulations for the magnetic flux coupling, the origin of the residual inductance is found to be the coupling between the SQUID, and shielding current in the groundplane. The value of the distance, 595 μm, does not depend on the size of the SQUID. To decrease the coupling, the use of wires with stripline structure or coplanar structure is desirable     

Electromagnetic random field models for analysis of coupling inside mode tuned chambers

The statistics of interference sources, induced by the electromagnetic fields of a mode tuned chamber (MTC), in electronic equipment is computed from the field's spatial covariance operator and a deterministic current distribution on the system under test. An example shows that the computed results, obtained with two canonical random field models, compare very well with measurements. In addition, a new and interesting relation between the variances of two-port S-parameters is established, which can be used to detect bad stirring in MTC.     

Mutual coupling between circular waveguide-fed apertures in a rectangular ground plane

A method is presented whereby the infinite ground plane analytical model for the self- and mutual admittances of waveguide-fed apertures can be supplemented (using the geometrical theory of diffraction) to include the edge effects of a rectangular ground plane. TheH-plane coupling between twoTE_{11}mode excited circular apertures is calculated and compared with measurements.     

Electromagnetic field inside a surface current distribution

The electromagnetic field and a generalised electric Green's dyad, when the field point is inside a surface current distribution are derived. The Green's dyad is represented by the sum of the dyadic Green's function in free space and a source dyad determined by the shape of the principal area that surrounds the singularities of the Green's function.<>     

Radio frequency coupling between an antenna and two unshieldedparallel wires above a metal sheet-measurement precautions

An unshielded 1 m transmission line, made of two parallel wires suspended 0.1 m above a plane metal sheet, is illuminated in the VHF and UHF bands by a log-periodic dipole array (LPDA). A network analyzer is used to measure the voltage induced at one end of the line. The measured signal is compared to the predictions of a moment method numerical analysis, using the NEC code. The measured and predicted coupling are in reasonable agreement only once two measurement precautions are taken. First, the illuminating antenna has to be well-balanced to suppress common mode radiation from the coaxial cable connecting the transmitter to the antenna. Second, an output balun must be inserted between the unshielded transmission line and the coaxial cable to the network analyzer. This is needed to prevent common mode signals on the coaxial cable from contaminating the measurements. Besides these practical steps, it is also necessary to use physical insight and high frequency circuit theory to develop a good equivalent circuit of the output balun for use in the computational model     

Study of coupling between circular groove guide and rectangular groove guide

On the basis of the studies of single circular groove guide and single rectangular groove guide, the coupling of the two waveguides has been researched and the characteristic equation of circular—rectangular groove guide has been given in this paper.     

Electromagnetic coupling to a cable through apertures

Electromagnetic field penetration through apertures is investigated numerically and experimentally. The coupling to a cable located behind an aperture is determined in terms of the open circuit voltage of the cable. A square and a circular aperture are taken as examples, and the open circuit voltage is calculated and verified by an experiment. The apertures are modeled by employing Babinet's principle and solving the complementary flat plate problem using wire-grid modeling. Comparisons with radar cross section measurements were also made to verify the wire-grid modeling.     

Electromagnetic scattering from arbitrary configurations of wires

A general formulation is presented for the treatment of electromagnetic scattering from an arbitrary configuration of thin wires. A system of integral equations is derived for obtaining the currents in the wires.     

Via coupling within parallel rectangular planes

Convenient formulas which characterize via or probe coupling are presented for both frequency-domain mutual impedance and time-domain voltage waveforms. These expressions are valid for arbitrary via locations and take into account all edge reflections. Skin effect is included within the frequency domain formulas. These results have application to power/ground plane “bounce” in digital circuits. They also provide insight into more general transient behavior. A direct closed-form Fourier inversion back into the time domain is detailed for the negligible loss case. To determine the behavior for finite rise-time excitations, the step response is integrated term-by-term to obtain a ramp response. Responses of other excitations, such as a finite rise-time step current, and various pulse currents, are easily obtained through superposition of appropriately delayed ramp responses. This process is extended to include piecewise-quadratic current excitation waveforms, thereby avoiding all slope discontinuities. These somewhat more involved expressions give “smoother” results which may have greater esthetic appeal     

Folded-type rectangular loop antenna with tunable circuit

A design for a small and tunable loop antenna is presented. This design enables the higher-order mode resonant frequency to become low while keeping the radiation pattern in good shape. The use of a tunable circuit to utilise higher-order mode for bandwidth enhancement has been investigated. The measured and simulated radiation patterns and voltage standing wave ratio are given.     

Analysis of mutual coupling between an infinite phased array ofhorizontal dipoles and vertical wires

A theoretical method is presented to analyze the radiation characteristics of an infinite phased array of horizontal dipoles in the presence of adjacent vertical wires protruding out of the ground plane. Green's functions for vertical and horizontal δ-sources in a unit cell are derived in terms of Floquet modes. By superposition of the Green's functions, the E- and H-fields in a unit cell are obtained. The current distributions and the input radiation impedances of the dipole array are obtained by making use of the method of moments. Numerical examples are given to show the coupling effects. Measurements of the radiation impedances in a waveguide simulator with and without the coupling effects due to the vertical wires have been conducted to verify the theoretical model. The general trend of measured data has been predicted quite well by the theoretical computation     

Measurement of the coupling efficiency between dielectric-loaded rectangular waveguides and dielectric-loaded trough waveguides

The measurement of the coupling efficiency between a dielectric-loaded rectangular waveguide and a dielectric-loaded trough waveguide is described, and the results are compared with theoretical estimates.