A Method for the Evaluation of Radiation Q Based on Modal Approach

Abstract

A new formula for the evaluation of the modal radiation Q factor is derived. The total Q of selected structures is to be calculated from the set of eigenmodes with associated eigen-energies and eigen-powers. Thanks to the analytical expression of these quantities, the procedure is highly accurate, respecting arbitrary current densities flowing along the radiating device. The electric field integral equation, Delaunay triangulation, method of moments, Rao-Wilton-Glisson basis function and the theory of characteristic modes constitute the underlying theoretical background. In terms of the modal radiation Q, all necessary relations are presented and the essential points of implementation are discussed. Calculation of the modal energies and Q factors enable us to study the effect of the radiating shape separately to the feeding. This approach can be very helpful in antenna design. A few examples are given, including a thin-strip dipole, two coupled dipoles a bowtie antenna and an electrically small meander folded dipole. Results are compared with prior estimates and some observations are discussed. Good agreement is observed for different methods.

A method for evaluating radiation efficiency based on a modal approach

“…• The skin depth should be also negligible in comparison with the curvature of the discretized space. • Note the similarity of (22) with the superposition of modal Q factors [21]. This unified concept, in which only the β matrix of unknown coefficients occurs, opens new possibilities in complex optimization of the feeding networks.…”

“…In the case of (22), only the unknown coefficients of the β matrix, or in other words the positions, amplitudes and phases of the feeding points, have to be found. This can be done by any fast optimization algorithm without the need to recalculate of the modal decomposition [21].…”

“…The same matrix β = [β uv ] was obtained for summation of the modal Q factors [21]. Using the same discretization as in the previous section, it is seen from (18) and (9) that the modal power loss is…”

An Introduction to the Source Concept for Antennas

“…It is clear that we may assign antenna parameters (energies, powers, losses, directivities, near and far fields) directly to the modes and gain extra physical insight into the antenna behavior. In [26] we derived the so-called coupling matrix  mn which connects the modes with the real world and is represented by modal excitation coefficients V m [27]     …”

“…The radiation quality factor Q, radiation efficiency and directivity can, then, be compactly expressed using modal quantities as [26], [28] (27) in (26) is related to the modal radiation intensity.…”