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The theory of superdirective antenna arrays was discussed. The procedure for finding the excitation currents of fixed-geometry arrays, which maximizes the directivity, termed as superdirectivity, for a given direction and polarization, was described. The procedure was based on the solution of an eigenvalue problem including the directivity and matrices of normalized self- and mutual radiation intensities and normalized self- and mutual radiated powers of array elements. For examples of a linear dipole array located above a perfect electric conductor ground plane, this procedure was also combined with the optimization of the parameters of geometry of the array as a spacing of dipoles, or their height above the ground, for various number of dipoles in the array.

A compact three-element shared-aperture waveguide antenna array for the 24–28 GHz microwave-frequency band is presented as a proof-of-concept of an array with steerable directional beam suitable for 5G telecommunication systems. The array is intended for use in a microwave photonic link and is sufficiently steerable only with the progressively phased excitation signals of equal magnitudes. The mutual interactions between the array elements are minimized to maintain the properties of the individual elements, even if they are embedded and closely spaced in the array. The proposed concept could be simply extended by adding more elements to further increase the directivity and enhance the steering properties of the array.

The concept of source currents of a radiating source can be employed to express its directivity in some particular cases analytically. For an antenna array, this concept can be extended to the concept of a generalised directivity based on self- and mutual radiation intensities, self- and mutual radiated powers and excitation currents of array elements. These approaches were applied to examples of the array of two elementary dipoles and the array of two isotropic radiators. Particularly, the evaluation of the directivity of the end-fire arrays, which are of special attention due to superdirective properties, was treated. Novel closed-form expressions for the directivity of these arrays with out-of-phase excitation were derived. It was observed that the end-fire directivity can be further enhanced by optimising the excitation currents of the arrays. Their optimal phase difference and corresponding increased directivity were also found analytically. The results were validated by a full-wave simulator.

[EN] Multi-element antenna beam steering in free-licence higher frequency bands is one of the crucial features of 5G networks enabling better tracking of the users. In this paper, we present an experimental microwave photonics transmission system operating at 26 GHz where beamforming is fully realized in the optical domain. The system is designed to be deployed as a part of the mobile fronthaul network with an optical fiber span of 15 km. As a proof of concept, a planar 3-element antenna array has been developed and radiation patterns were measured in an anechoic chamber with high agreement between experimental and simulation results, The research has been supported by the project from Ministry of Industry and Trade in Czech Republic (FV30427) and COST action CA 16220.

This paper describes the application of the theory of characteristic modes to excite a conducting cylinder representing the chassis of a rocket. Mode excitation is achieved by cutting H-shaped slots on the cylinder at specific locations where the maximum of modal current distribution occurs. The L-matching network is designed to match the impedance of the slots to the input coaxial cable. Finally, the proposed concept is verified during manufacturing and measurement. It is shown that the measured results are in excellent agreement with the simulation.

The theory of characteristic modes is used to analyze antenna arrays. In particular, to study arrays of thin-wire dipoles backed by an infinite electric ground plane. The proposed theory is based on an analytically prescribed current distribution on the dipoles where, when compared with the full method of moments solution, only a self- and mutual impedance matrix relating excitation currents and voltages of array elements is the subject for modal decomposition. Therefore, the impedance matrix of interest has dimension $ \times $ , where $N$ is number of the array elements resulting in an extremely fast approach. The results of the proposed method are validated by a full-wave simulator and show good agreement.

An antenna arrays are widely used due to its properties in comparison to single element antenna. The possible achievable gain can be much higher, also one of the biggest advantage is the possibility to steer the main radiation beam and cover wider area. The problematic part to obtain maximum achievable directivity for antenna arrays is the corresponding feeding. In this paper, we use the one term sinusoidal current density excitation and more precise King’s three-term excitation for optimization of an array of four dipoles for maximum directivity. The goal of this paper is to present a new fast method for antenna array design and to compare its exactness. As an example a four element Yagi-Uda antenna is optimized.

The concept of source currents of a radiating source can be employed to express its directivity in some particular cases analytically. For an antenna array, this concept can be extended to the concept of a generalized directivity based on self- and mutual radiation intensities, self- and mutual radiated powers and excitation currents of array elements. These concepts were applied to example of the array of two isotropic radiators above perfect electric conductor (PEC) ground, where the PEC ground is simulated by mirror image of the original image of isotropic radiators.

The Method of Moment, used for computation of the impedance matrix of the dipole array, is substituted here by faster method using simple approximation by the sinusoidal current. This method is verified by the theory of characteristic modes that provide a set of eigenvectors and eigenvalues, which are determined entirely by a structure's geometry at a certain frequency. When computing over a range of frequencies, the methods for eigenvalue tracking are essential. Proposed eigenvalue perturbation method is a powerful tool in this phenomena.

The Characterlstic Mode Analysis (CMA) provides a set of eigenvalues and eigenvectors that are determined entirely by the antenna array structure at a particular frequency. The presented method solely relies on the mutual impedance matri:s: of elements of the array. In turn, the proposed approach is yery fast. Various modal decompositions are performed on an array of parallel dipoles placed horizontally above an infinite electric ground plane. The dipoles have prescribed sinusoidal currents. The results are validated by a full-wave simulator FEKO, showing good agreement.

A dielectric rod antenna designed for maximal gain at the frequency band of 5-6 GHz is presented in this paper. A simulation using CST Microwave Studio results in gains of 12 to 15 dBi with beamwidths of 30° in both E and H planes making the dielectric rod antenna a sensible alternative to Yagi-Uda antennas as it performs in a similar fashion and is less sensitive to manufacturing tolerances. Multiple polymers were measured in order to find proper material for the rod resulting in using a cheap, affordable and low-loss material plexiglass.

Various modal decompositions are performed on an array of dipoles backed by electric ground plane. The theory is based on analytically prescribed current on dipoles so the decomposition returns directly excitation coefficients of an array with respect to given quantity.

Two different array of dipoles above infinite electric ground plane are optimized for bandwidth using particle swarm optimizer, concept of self and mutual impedances and impedance quality factor. It is found that it is the interaction of mutual radiated power that limits the bandwidth, rather than stored energies.