This article investigates the superdirectivity limits of end-fire linear arrays based on closely spaced radiating elements. First, directivity upper bounds have been derived analytically in the case of Huygens-source-and electrical-dipole-based arrays using spherical wave expansion (SWE). The fundamental bounds are derived when the interelement spacing d tends to 0 and as a function of the number of the elements (P) composing the array. Furthermore, the complex excitation coefficients associated with end-fire arrays of P infinitesimal Huygens sources and electrical dipoles are synthesized as a function of d to achieve maximum directivity. For this purpose, synthesis procedures based on SWE and array theory are used. When d tends to 0, the numerical results are in excellent agreement with the proposed upper bounds. The maximum superdirectivity approaches a value of P-2 + 2 P and P-2 + P - 1/2, respectively, in the case of Huygens sources and electrical dipoles. A numerical method to estimate the antenna gain, when the arrays are optimized in terms of directivity, is also provided. The theoretical results are then successfully validated through electromagnetic simulations in the case of half-wavelength-dipole-based arrays as a function of P and d. Three prototypes are designed and experimentally characterized as well to demonstrate the proposed analysis.

This paper presents the experimental validation of a three-dipole array optimized for maximum gain. The complex excitation coefficients associated to the array are calculated using a synthesis procedure based on the array factor. A parasitic array architecture has been selected to implement the proposed antenna solution. The high gain reached (8.6 dBi for a ka of 1.4) shows the interest of the proposed optimization method. Furthermore, it was shown that this optimization method decreases the sensitivity to errors in the dipole excitation coefficients at the cost of a lower directivity compared to the superdirectivity.

This paper presents the results of the optimization of two three-element end-fire linear arrays based on straight- and bent-electrical dipoles, respectively. To achieve a compact architecture, the inter-element distance is fixed to 0.12$\lambda$ with $\lambda$ the wavelength calculated at the operation frequency (850 MHz). The array complex excitation coefficients have been optimized to achieve either maximum directivity or maximum gain. The synthesis procedure is based on the optimization of the directivity or gain formulas considering the array factor and the active element patterns. The numerical results have been validated by 3D full-wave electromagnetic simulations. The maximum directivity is equal to 10.0 (gain 2.91 dBi) and 9.83 dBi (gain 3.67 dBi) in the case on the straight- and bent- electrical dipole based arrays, respectively. Instead, the maximum gain is equal to 6.81 (directivity 8.84 dBi) and 7.85 dBi (directivity 9.19 dBi), respectively.

In this paper, the possibility to optimize supergain end-fire arrays is numerically investigated. Firstly, the optimization problems in terms of directivity and gain are introduced. Then, infinitesimal-dipole based end-fire arrays have been optimized as a function of the number of elements and inter-element spacing. It is shown that, their radiation efficiency can be predicted and, for close inter-element spacing, even optimized to provide a higher gain than the one obtained with the classical directivity optimization methods. The numerical analysis is detailed and validated by full wave simulations in the case of three half-wavelength dipoles.

The spherical wave expansion characterizing the radiated field of a two-infinitesimal-dipole-end-fire array is analyzed in this work and optimized to achieve the maximum directivity. In particular, the paper shows how the maximum directivity can be analytically derived in the case where the inter-element spacing tends to zero. Analytic excitation coefficients needed to reach that maximum directivity are also derived in the proposed study. A general expression of the maximum directivity achievable by P-dipole end-fire arrays is then proposed. This limit can be considered as an upper bound and generalizes the analysis proposed by Uzkov in the case of isotropic source based end-fire arrays. A numerical analysis is also proposed to validate the upper bound when infinitesimal electrical dipoles are used.

It is well known from previous works, that a maximum directivity close to P 2 + 2P could be obtained when P Huygens sources are used to implement compact end-fire arrays with reduced inter-element distance (e.g. < 0.3λ). This result has been theoretically demonstrated with infinitesimal Huygens sources, but practical antenna architectures are not yet presented. In this paper, a method to design Huygens source based superdirective arrays is numerically demonstrated through full-wave electromagnetic simulations considering a two-element array with an inter-element distance equal to 0.2λ and kro = 133 (where r 0 indicates the radius of the minimum sphere enclosing the antenna). The strong mutual coupling between the array elements is taken into account in the optimization procedure based on spherical wave expansion. End-fire directivity and gain equal to 8.7 and 7.8 dBi have been respectively obtained. These results have also been compared to the case of the two-element arrays based on magnetic and electrical dipoles.

In this paper, the sensitivity of superdirective end-fire arrays to the precision of the excitation coefficients associated to its elements is studied through the notion of sensitivity factor. Starting from the array factor with optimized coefficients and the general sensitivity factor expression previously defined in the literature, this work provides formulas that can predict the precision requirements for the realization of superdirective arrays. The theoretical formulas are validated through numerical results obtained using an ad-hoc synthesis procedure based on spherical wave expansion.

In this paper, the directivity limit of end-fire arrays based on Huygens source elements has been numerically investigated. Firstly, the elementary infinitesimal Huygens source behavior is introduced and studied through Spherical Wave Expansion (SWE). Then, the maximum theoretical directivity of two-, three- and four-element arrays is calculated as a function of the inter-elements spacing. The optimization has been performed using a synthesis method based on SWE. For an inter-element spacing of a tenth of the wavelength, the obtained directivities are equal to 9.0 dBi, 11.7 dBi and 13.7 dBi for the two-, three- and four-element arrays, respectively.

In-band full-duplex transceivers are considered for future generations of cellular network systems. This paper proposes to evaluate the performance of in-band full-duplex transceivers using a modified architecture based on hardware available for multiple-input multiple-output transceivers. A hybrid self-interference cancellation technique using an auxiliary transmitter is therefore introduced. Performance is evaluated using simulation models and is confirmed by hardware experimentation. The main limiting factors of the proposed architecture are analyzed and improvements to the architecture are then suggested.