Jose I. Herranz

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.

Periodic Leaky-Wave Antenna on Planar Goubau Line at Millimeter-Wave Frequencies

A periodic leaky-wave antenna on a planar Goubau line is presented. This transmission line is formed by a planar single-wire waveguide on a thin dielectric substrate. Leakage is produced by adding dipoles along the line on the bottom face of the substrate. A coplanar waveguide is used to feed the antenna, which acts as a smooth transition between the input coaxial cable and the planar Goubau line. The advantage of using this line lies on its losses, lower than those of typical microstrip lines due to the absence of a ground plane. As a result, a higher radiation efficiency than in microstrip-fed antennas can be obtained while keeping similar advantages, e.g., low profile or low production cost. A prototype of the antenna at 40 GHz has been fabricated. Measurements of this prototype are presented in this letter.

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

Optimization of Beam-Tilted Linearly Polarized Radial-Line Slot-Array Antennas

This letter investigates the performance of beam-tilting technique when applied to improve matching of linearly polarized radial-line slot-array antennas. The application of a full-wave analysis reveals a severe deterioration of radiation patterns even for small tilt angles. An iterative optimization procedure is proposed in order to restore the radiation performance in conjunction with the desired matching enhancement. Performance and limitations of the correction procedure are discussed in terms of the beam pointing direction. One prototype is fabricated, and measurements are reported to validate the conclusions of this letter.

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.

Low-Loss Circularly Polarized Periodic Leaky-Wave Antenna

This letter presents a periodic leaky-wave array antenna with circular polarization at millimeter-wave frequencies. The antenna is designed on the low-loss planar Goubau transmission line to maximize the radiation efficiency of the antenna. The unit cell of the array is formed by four dipoles located on both faces of the Goubau lines substrate. A prototype has been fabricated and measured. Experimental results show an impedance bandwidth above 15% for |S11| <; -10 dB and a 3-dB axial-ratio bandwidth of 7.6%. The radiation efficiency and maximum gain of the prototype are above 90% and 15.6 dBi, respectively, from 38 to 41 GHz. The maximum gain and the minimum axial ratio present the characteristic steering behavior of leaky-wave antennas.

Single-Layer Cavity-Backed Slot Array Fed by Groove Gap Waveguide

An effective feeding procedure for slotted waveguide arrays in the context of so-called groove gap waveguides (GGWs) is presented. Slots are fed through a corporate feed network with E-plane splitters and backed by coaxial cavities, which are more compact than conventional cavities. The coaxial cavity is integrated within the same bed of nails used to host the groove in the gap waveguide. The cavity resonance is generated by merely lowering the height of the desired nail with respect to the surrounding ones. Therefore, no increase in complexity is introduced. The feeding network is built in the same layer as the cavities and the slots, considerably reducing array volume compared to multilayer topologies. A