A novel technique for the elimination of the open stopband in one-dimensional periodic printed leaky-wave antennas is presented. A quarter-wave transformer, or alternatively a matching stub, is introduced into the unit cell of the antenna, which forces the Bloch-wave impedance of the structure to remain real and non-zero at broadside. The effectiveness of the proposed technique is first demonstrated on a printed periodic microstrip leaky-wave antenna consisting of a single radiating stub per unit cell, which exhibits a significant stopband at broadside. The technique is then also applied to a structure consisting of two radiating stubs per unit cell, which is capable of mitigating, but not eliminating, the open stopband. In both cases the open stopband at broadside is completely suppressed.

A Novel Technique for Open-Stopband Suppression in 1-D Periodic Printed Leaky-Wave Antennas

Here, we propose a fully metallic implementation of a Luneburg lens operating at Ka-band with potential use for 5G communications. The lens is implemented with a parallel plate that is loaded with glide-symmetric holes. These holes are employed to produce the required equivalent refractive index profile of a Lune-burg lens. Glide symmetry and inner metallic pins are employed to increase the equivalent refractive index. The lens is fed with rectangular waveguides designed to match the height of the parallel plate, and it is ended with a flare to minimize the reflections.

Glide-Symmetric Fully Metallic Luneburg Lens for 5G Communications at K a -Band

Metasurfaces are thin two-dimensional metamaterial layers that allow or inhibit the propagation of electromagnetic waves in desired directions. For example, metasurfaces have been demonstrated to p ...

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Roadmap on metasurfaces

We present a novel electromagnetic bandgap (EBG) structure, which can be used to manufacture low-cost waveguiding structures at high frequencies. The unit cell of the proposed EBG consists of glide-symmetric holes in parallel plate waveguide. Using this unit cell in groove gap waveguide technology has a number of advantages over pin-type EBG at high frequencies, such as acquiring higher accuracy because of larger periodicity as well as an easier and cheaper manufacturing process. The performance of the proposed waveguiding structure is demonstrated using both a straight and a double 90° bent lines through simulation and measurement.

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Cost-Effective Gap Waveguide Technology Based on Glide-Symmetric Holey EBG Structures

The application of symmetry analysis to uniform waveguides is discussed. Symmetry analysis provides exact information concerning mode classification, mode degeneracy, modal electromagnetic-field symmetries, and the minimum waveguide sectors which completely determine the modes in each mode class. Tables are presented which list the possible mode classes and their degeneracies for the two general symmetry families, C/sub n/ and C/sub nv/, of uniform waveguides. Tables showing the azimuthal dependence of the longitudinal components of the electric and magnetic fields for each mode class are given. Based on this azimuthal dependence, figures showing the minimum waveguide sectors which are necessary and sufficient to completely determine the modes of the various mode classes are presented. The application of symmetry analysis is illustrated by considering uniform waveguides with C/sub 4/ and C/sub 6v/ symmetry.

Symmetry-Induced Modal Characteristics of Uniform Waveguides --- I: Summary of Results

A generalization of Floquet's theorem is presented for periodically loaded closed waveguides possessing a certain class of higher symmetries which includes the screw and glide symmetries. These symmetries frequently appear in microwave structures such as filters, traveling-wave tubes, and traveling-wave antennas. The theorem states that the natural modes are eigenvectors of the symmetry operator characterizing the structure. An alternative derivation of the theorem using an equivalent network representation leads naturally to a simple method for constructing the qualitative dispersion (Brillouin) diagrams for structures with screw or glide symmetry.

Propagation in periodically loaded waveguides with higher symmetries

In this Letter, we use radio-frequency digital-to-analog converters (DACs) operating in different frequency response modes to generate a high spectral-efficiency multi-band (MB) filter bank multicarrier (FBMC) signal. In the receiver, the undersampling technique is employed to realize down-conversions. No electrical mixers are required. Besides, discrete Fourier transform and orthogonal circulant matrix transform precoding techniques combined with channel-independent digital pre-equalization are enabled to enhance transmission performance. Both numerical simulations and offline experiments are performed. The relevant results show that the MB-FBMC without a cyclic prefix (CP) is robust against inter-symbol interference induced by the band-pass filtering. By using precoding and pre-equalization techniques, the bit error rate can be improved by more than one order of magnitude. In contrast, an additional 12.5% CP overhead is required for the MB orthogonal frequency division multiplexing system to achieve such an improvement.

Ming Hui Chen

Papers

Propagation in periodically loaded waveguides with higher symmetries

Precoded and pre-equalized multi-band FBMC transmission enabled by radio-frequency DACs and the undersampling technique.