Array Of Open-ended Waveguides Research Articles

A Fast and Efficient Calibration Method for Phased Array Antennas Using Fourier-Structured Excitation Matrix

This article presents a novel phased array antenna calibration method. Unlike conventional phased array calibration methods equipped with only one probe antenna in the far-field setup, multiple measurement probes are introduced in the proposed algorithm to significantly improve the measurement efficiency. Specifically, a novel construction method for an excitation matrix (which contains excitation coefficients for phased array elements) is proposed, where phase differences introduced by the spatial locations of the multiple probes are perfectly incorporated into the Fourier-structured excitation matrix, thereby presenting the best measurement efficiency without sacrificing the array calibration accuracy. The proposed method can offer robust array calibration results (guaranteed by the low condition number of the constructed excitation matrix with Fourier structure) and high measurement efficiency (offered by multiprobe setups). To experimentally validate the proposed algorithm, a multichannel (i.e., multiprobe) far-field measurement setup was utilized. A four-element open-ended waveguide array operating at 2.6 GHz and two-probe far-field systems were employed as the antenna under test (AUT) and multiple probes, respectively, to validate the effectiveness and robustness of the proposed phased array calibration algorithm. The proposed algorithm will be highly valuable for efficient phased array calibration, especially for future antenna systems equipped with large-scale antenna configurations.

Connecting Networks for Two-Dimensional Butler Matrices Generating a Triangular Lattice of Beams

Connecting networks for two-dimensional beamforming matrices are discussed. They provide a suitable interconnection between the output ports of a Butler matrix and antenna array ports, transforming a square (and more generally, rectangular) lattice of beams into a triangular lattice of beams. This change in lattice improves the crossover between beams, reducing gain roll-off over the field of view for a given multiple fixed beam coverage. A general description of the concept is provided and numerical results are reported, which confirm a reduction in crossover level between 1 and 1.5 dB. The proposed solution is further validated through the design and test of a 4 × 4 open-ended waveguide array in K-band. The connecting network has a length of 70 mm, compared to 226 mm for the 2D Butler matrix, with a design frequency of 19.55 GHz. Good agreement is found between simulated and measured data. The desired triangular lattice of beams is confirmed with the measured multiple beams. This solution is of interest for multiple-beam millimeter-wave communication systems, considered for next generation of terrestrial and non-terrestrial networks.

On Multimode Equivalent Network Representation of Finite Arrays of Open-Ended Waveguides

This communication describes a multimode equivalent network (MEN) representation of a finite array of open-ended lossless waveguides on an infinite ground plane. The derivation is based on an integral equation formulated at the interface between the waveguides and the free-space region. The MEN is formulated using the concept of accessible and localized modes, and includes ports for the free-space plane waves. The MEN derived can be easily combined with the MENs of other microwave components, thus allowing for the accurate analysis and design of more complex systems composed of waveguide elements and radiating apertures. Both simulated and experimental results are presented showing a very good agreement, thereby fully validating the proposed equivalent network representation.

Fundamental Directivity Limitations of Dense Array Antennas: A Numerical Study Using Hannan’s Embedded Element Efficiency

Hannan introduced in 1964 an embedded element efficiency concept that explains the so-called element-gain paradox in antenna arrays, i.e., that the array gain always is smaller than the sum of the element gains. In the present letter, we show for the first time the usefulness of his approach by evaluating directivities and aperture efficiencies of an array of open-ended waveguides by commercial full-wave electromagnetic (EM) solvers for a large range of element spacing. The results show also that by using embedded element analysis, the realized gain of regular arrays actually becomes equal to the sum of the realized gains of the embedded elements. Thus, the embedded element efficiency is more practical to use in design and numerical analysis than the more commonly used active element pattern approach. We also show that the embedded element efficiency can be approximated by a simple formula when the element spacing is smaller than half-wavelength.

Array Pattern Synthesis of Real Antennas Using the Infinite-Array Approach and Linear Programming

This work proposes an efficient optimization methodology of antenna array excitations accounting for the effects of mutual couplings and real radiating patterns of array elements with complex geometry. The method is formulated as a linear programming problem providing multibeam patterns with specified beamwidths, constraints on sidelobe and cross-polar levels, and null pointing directions. A matrix formulation is used to integrate the optimization procedure and a finite-array analysis based on the infinite-array approach, in which the periodic radiating element is characterized by a full-wave and hybrid procedure, combining the domain decomposition technique, the finite-element method, and modal analysis. Numerical examples of arrays of open-ended waveguides, microstrip antennas, and dielectric resonator antennas are presented.

Accuracy of Floquet Model in Predicting Performances of Finite Arrays

This letter studies the accuracy of the Floquet model for finite array analysis. The Floquet model and the Plane Wave Spectum model are compared for open-ended waveguide arrays. The numerical results indicate that for arrays larger than 2 wavelengths, the Floquet model can predict the performance accurately. The Floquet model was found to also compare well to finite element analysis in the case of a small patch array.

Multiband SRR Loaded Rectangular Waveguide

This work proposes the combined use of split ring resonators (SRR) in a middle slab position with side slab ones to create two different passbands (stopbands) below (above) the cutoff frequency in a rectangular waveguide. The same effect can be achieved by using only SRR loadings on the side walls with different sizes of the elements on each side. Furthermore, by combining both techniques, three bands can be obtained. By adjusting the SRR sizes and with the dielectric materials, the passbands (stopbands) can be targeted at the desired frequencies. Both types of multiband structures could find application in multifunction array antennas comprising interlaced arrays of open-ended waveguides. The work is supported by experimental results.

Truncated floquet wave full-wave analysis of large phased arrays of open-ended waveguides with a nonuniform amplitude excitation

Recently, an efficient hybrid asymptotic-method of moments (MoM) approach has been proposed for the analysis of large periodic planar arrays of elements excited with equal amplitude and linear phase. The aforementioned method, which is based on a Floquet wave diffraction representation of the array Green's function (AGF), is here extended to treat arrays with tapered amplitude excitation. To this end, the asymptotic AGF is refined by introducing additional "slope" diffraction contributions. An appropriate "fringe" integral equation, solved via a MoM scheme, provides the effects of array truncation in addition to the infinite array solution. The dimension of the corresponding linear algebraic system is independent of the number of elements of the array. Numerical results are provided to prove the accuracy and the efficiency of this method with respect to an ordinary element-by-element MoM.

Efficient analysis of in-line waveguide filters and frequency-selective surfaces with stepped holes

This paper presents a novel method for the analysis of large classes of microwave and mm-wave passive components, including in-line waveguide filters, single- and multi-layer frequency selective surfaces, and open-ended waveguide array antennas. This method is based on the segmentation technique, which permits us to reduce complex components to cascaded waveguide step discontinuities, which are separately characterized through their generalized impedance matrices, as calculated by the integral equation (IE) technique and the boundary integral-resonant mode expansion (BI-RME) method. Some examples demonstrate the flexibility and efficiency of the IE/BI-RME method, and its utility in investigating novel structures not requiring costly fabrication techniques. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 306–315, 2003.

CAD of waveguide array antennas based on "Filter" concepts

In this paper, an alternative approach for the design of open-ended waveguide array antennas is presented. The approach is based on microwave filter concepts. The exploitation of this alternative viewpoint has been made possible by the availability of a very efficient computer-aided design (CAD) tool which is based on a full-wave modal analysis technique. In this paper, we first outline the technique for the efficient analysis of open-ended waveguide array antennas. Using the software developed and following the alternative design approach, two different application examples are then shown, indicating how the alternative viewpoint introduced gives indeed significant additional degrees of freedom.

Millimeter wave imaging lens antenna

The factors which influence the design of lenses suitable for imaging at millimetre wavelengths are discussed. Examples are given of optical designs for a military tracking application, firstly for use with an open ended waveguide array, and secondly for use with monolithic arrays, each covering a field of view of ±20°.