Esperanza Alfonso

Experimental Demonstration of Local Quasi-TEM Gap Modes in Single-Hard-Wall Waveguides

This letter reports an experimental study of a gap waveguide which is able to support a plurality of degenerate local quasi-TEM modes. No sidewalls are needed to separate these modes, which is a very useful property in the upper microwave and millimeter-wave bands. The waveguiding media is formed in the gap between a conducting plate and a hard surface. The working principle is described first. Next a practical realization is explained and tested experimentally.

Gap Waveguides Using a Suspended Strip on a Bed of Nails

This letter discusses the feasibility of a new type of waveguide consisting of a strip suspended on a bed of nails. The bed of nails enforces a stopband, while the strip opens a propagating path that can be used to design circuits and feeding networks for the microwave and millimeter-wave bands. Advantages and drawbacks with respect to existing ridge gap waveguide are discussed. Experimental demonstration is also given.

Design of microwave circuits in ridge-gap waveguide technology

This paper presents recent advances is a new waveguiding technology referred to as ridge gap waveguides. The main advantages of the ridge gap waveguides compared to hollow waveguides are that they are planar and much cheaper to manufacture, in particular at high frequencies such as for millimeter and submillimeter waves. In these waveguides there are no mechanical joints across which electric currents must float. The gap waveguides have lower losses than microstrip lines, and they are completely shielded by metal so no additional packaging is needed, in contrast to the severe packaging problems associated with microstrip circuits. The gap waveguides are realized in a narrow gap between two parallel metal plates by using a texture on one of the surfaces. The waves follow metal ridges in the textured surface. All wave propagation in other directions is prohibited (in cutoff) by realizing a high impedance (ideally a perfect magnetic conductor) through the textured surface at both sides of all ridges. Thereby, cavity resonances do not appear within the band of operation. The paper studies the characteristic impedance of the line and presents simulations and measurements of circuits designed using this technology.

Study of local quasi-TEM waves in oversized waveguides with one hard wall for killing higher order global modes

An oversized rectangular waveguide with one hard wall was previously demonstrated to be suitable for feeding a planar slot array because it has higher-order-mode-killing properties, i.e. it supports propagation of a single quasi-TEM parallel-plate-type mode, and no higher order modes. In the present paper we detect instead many local quasi-TEM waves that follow the hard surface with identical propagation constants. The local quasi-TEM waves can be excited to produce a combined mode that is the single quasi-TEM parallel-plate-type mode. We propose to characterize this interesting feed guide in terms of the performance of the local quasi-TEM waves.

Design of transition from coaxial line to ridge gap waveguide

This paper presents the design of a simple transition from ridge gap waveguide to coaxial line transition. First, a straight ridge gap waveguide with single transition on end is simulated. Then a ridge gap waveguide with two 90° bends is simulated with two transitions on each end. Available commercial FDTD simulation tool was used to design the transitions. A return loss of −10 dB was achieved over the frequency band of 12– 15.75 GHz.

Study of the characteristic impedance of a ridge gap waveguide

This paper presents a study of the characteristic impedance of a ridge gap waveguide. Ridge gap waveguides belongs to a new metamaterial-based waveguide technology for millimeter and submillimeter waves which emerged recently. A formula for the characteristic impedance of an ideal PEC-over-PMC ridge gap waveguide has been derived. A preliminary numerical study of the characteristic impedance of a real ridge gap waveguide where the PMC is realized by a bed of nails is also presented.

Oversized waveguides for TEM propagation using hard surfaces

We propose a new structure to force a quasi-TEM mode to propagate inside an oversized closed rectangular waveguide. A hard surface is employed. Simulation results confirm a good performance. The structure means a promising first step toward a waveguide slot array with high efficiency and directivity

Moment Method Analysis of Corrugated Surfaces Using the Aperture Integral Equation

This communication describes a method of moments formulation to analyze the scattering from corrugated surfaces. The approach is based on the aperture integral equation. Such approach decouples the analysis of the impedance effect of the grooves from the external coupling among grooves and allows us to deal accurately with grooves of any shape. Advantage is taken of the geometrical properties of the problem to solve it efficiently using a conjugate gradient-FFT algorithm.

Wideband, lowloss, low-cost, quasi-TEM metamaterial-based local waveguides in air gaps between parallel metal plates

The paper presents a new waveguide appearing in the air gap between two parallel metal plates. One of the plates has a metal texture, and confined local waves follow ridges in the texture whereas they are prohibited from propagating in other directions by metal pins in the texture. The pins (or bed of nails) provide a high impedance surface that creates a stop band when used together with a metal surface, i.e. a parallel plate cut-off. The principle performance of the ridge gap waveguide is explained by numerical simulations of the dispersion diagram, both to show the parallel plate cut-off generated by the pin surface, but also to see the quasi-TEM wave propagating along the ridge. The performance is validated by numerical simulations and experimentally of a ridge gap waveguide with two 90 deg bends, including transitions to coaxial connectors. The ridge gap waveguide has a large potential for use up to THz because it can be realized without conducting joints between metal parts, and it lends itself to co-design and integration with active components.

Optimized design of beam-tilted linearly-polarized radial-line slot-array antennas

High-gain low-profile antennas for microwave and millimeter-wave applications have been a topic of exhaustive research during last decades. More specifically, radial-line slot array-antennas (RLSAs) demonstrated their suitability for massive production in low-cost applications, e.g. TV-DBS. In this context, RLSAs became very attractive due to their simplicity, low profile, low fabrication cost and high efficiency. In a standard RLSA design, slots are arrayed on the upper plate of a radial line, i.e. parallel plate waveguide, which is fed at its center, typically by a coaxial probe. Overall, any polarization and radiation pattern can be synthesized by a proper arrangement of slots. Unfortunately, while the circularly-polarized RLSA (CP-RLSA) demonstrates an excellent performance, its counterpart with linear polarization (LP-RLSA) [1] presents an annoying drawback. Standard arrangement distributes slots in concentric rings spaced half wavelength so as to produce a directive beam pointing to broadside direction with linear polarization. Such disposition exhibits rather poor matching performance, which is inherent in traveling-wave series-fed broadside arrays because of coherent reflections.