The measured equation of invariance and its application to transmission line modelling

The Measured Equation of Invariance (MEI) is a geometry-dependent Finite Difference equation that can be used to terminate a mesh extremely close to the object of interest. The mesh can be terminated much closer than what absorbing boundary conditions would allow, but still keeping the locality of the equations. In this paper, this new concept is applied to the numerical simulation of transmission lines and their discontinuities.Peer ReviewedPostprint (published version

Application of the measured equation of invariance to radiation and scattering by flat surfaces

Because on flat surfaces the electric currents are confined to two dimensions, a simple vector potential formulation can be used. The problem of radiation and scattering by rectangular strip dipoles is solved, including the transversal variation of the current across the dipole width. Also of interest are the currents induced on antennas with step variations in width, and with bends and T-junctions.Peer ReviewedPostprint (published version

The measured equation of invariance: a new concept in field computation

Computations of electromagnetic fields are based either on differential equations or on integral equations. The differential equation approach using finite difference or finite element methods results in sparse matrices, which is an advantage, but has to cover large volumes, which is a disadvantage. The integral equation approach using the method of moments (MOM) limits the mesh to the surface of the object, which is an advantage, but results in full matrices, which is a disadvantage. It is noted that the ideal case would be to reduce the finite difference type equations close to the object surface and still preserve the sparsity of the matrices. The measured equation of invariance is a new concept in field computation capable of approaching this ideal situation. The mathematics and reasonings to reach a novel computational method based on this concept are presented. It is shown that the method is robust for both convex and concave objects, is much faster than the MOM, and uses a fraction of the memory.Peer ReviewedPostprint (published version

Measured equation of invariance: a new concept in field computations

Numerical computations of frequency domain field problems or elliptical partial differential equations may be based on differential equations or integral equations. The new concept of field computation presented in this paper is based on the postulate of the existence of linear equations of the discretized nodal values of the fields, different from the conventional equations, but leading to the same solutions. The postulated equations are local and invariant to excitation. It is shown how the equations can be determined by a sequence ofPeer ReviewedPostprint (published version

Perturbation of the sierpinski antenna to allocate the operating bands

A scheme for modifying the spacing between the bands of the Sierpinski antenna is introduced. Experimental results of two novel designs of fractal antennas suggest that the fractal structure can be perturbed to enable the log-period to be changed while still maintaining the multiband behaviour of the antenna.Peer ReviewedPostprint (published version

Application of the measured equation of invariance to transmission.

The MEI (measured equation of invariance) method can easily be applied to static analyses of uniform transmission lines, such as single and coupled microstrip lines. Laplace's equation is solved for the static electric potential, and the total charges on the metal structures are found. Solving the problem with the correct permittivity values for the dielectrics yields the capacitance of the structures, while solving the problem with all permittivities equal to the free-space value yields the inductances. The quasi-static impedance values may then be obtained. Planar microstrip-type structures, where currents are confined to two dimensions are also considered. Results are presented for cases where no dielectric is present. This simplifies the Green's function calculation for the present purposes, but the method may be applied to more general cases.Peer ReviewedPostprint (published version

Small but long koch fractal monopole

A small but long wire fractal antenna based on the Koch curve is presented. Experimental and numerical results show that the antenna improves the features of a common linear monopole. The radiation resistance is increased and the Q is reduced at each fractal iteration, approaching the fundamental limit on small antennas.Peer ReviewedPostprint (published version

On the behavior of the Sierpinski multiband fractal antenna

The multiband behavior of the fractal Sierpinski antenna is described. Due to its mainly triangular shape, the antenna is compared to the well-known single-band bow-tie antenna. Both experimental and numerical results show that the self-similarity properties of the fractal shape are translated into its electromagnetic behavior. A deeper physical insight on such a behavior is achieved by means of the computed current densities over the antenna surface, which also display some similarity properties through the bands.Peer Reviewe

Accuracy considerations in microstrip surface impedance measurements

An approach is proposed for the design, measurement and data extraction of superconducting microstrip resonators used in determination of surface resistance and penetration depth. Major sources of error are analyzed and procedures to minimize them are givenPeer Reviewe

Full wave modelling of hts dual mode patch filters and staggered coupled-line filters

In order to obtain high-power handling, dual-mode patch HTS filters have been analyzed through Green's function and desegmentation techniques. A precise circuit model has been obtained and applied to the filter design process, and useful design curves relating filter parameters and physical dimensions of the square patch have been plotted. Several designs have been made using them and then optimized with the Method of Moments in the Spectral Domain. For higher order circuits, staggered coupled-line HTS filters have been considered. The designs have been made using the method of moments to compute the coupling capacitances, and then optimized with the Method of Moments in the Spectral Domain. One dual-mode patch filter and one staggered coupled-line filter have been fabricated on a YBCO film. Measurements agree well with simulationsPeer Reviewe