Eva Rajo-Iglesias

Local Metamaterial-Based Waveguides in Gaps Between Parallel Metal Plates

This letter presents a new metamaterial-based waveguide 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 sub- millimeter waves. The latter is due to the fact that 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 or multilayer structure 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 surface impedance (ideally a perfect magnetic conductor) in the textured surface at both sides of all ridges. Thereby, cavity resonances do not appear either within the band of operation. The present letter introduces the gap waveguide and presents some initial simulated results.

Mutual Coupling Reduction in Patch Antenna Arrays by Using a Planar EBG Structure and a Multilayer Dielectric Substrate

Periodic structures can help in the reduction of mutual coupling by using their capability of suppressing surface waves propagation in a given frequency range. The purpose of this work is to show the viability of using a planar electromagnetic band gap (EBG) structure based on a truncated frequency selective surface (FSS) grounded slab to this aim. The goal is to use it in patch antenna arrays, keeping both the element separation smaller than for grating lobes avoidance (assuming broadside case) and the patch antenna size large enough to have a good antenna directivity. To this aim, a multilayer dielectric substrate composed of high and low permittivity layers is convenient. This allows the use of a planar EBG structure made of small elements printed on the high permittivity material and, at the same time, the low permittivity layer helps the bandwidth and the directivity of the antenna to be increased. The EBG structure was designed under these premises and optimized for the particular application via an external optimization algorithm based on evolutionary computation: ant colony optimization (ACO). The mutual coupling reduction has been measured and it is larger than 10 dB with a completely planar structure.

Ant Colony Optimization in Thinned Array Synthesis With Minimum Sidelobe Level

The synthesis of unequally spaced large arrays is computationally unapproachable without using an optimization technique. In complex structures, gradient implementations converge to local minima and cannot be used to obtain a desired solution. Thus, global search methods are necessary to get specific design characteristics. In this letter, we propose the ant colony optimization (ACO) as an useful alternative in the thinned array design, using the sidelobe level (SLL) as the desirability parameter. Some examples have been proposed and solved to demonstrate the functionality of this technique for both linear and planar arrays

Parallel Plate Cavity Mode Suppression in Microstrip Circuit Packages Using a Lid of Nails

The suppression of parallel plate and cavity modes in shielded microstrip circuits is presented. To this aim a textured metal lid consisting of periodically located pins known as a bed of nails is employed. The mode suppression has a bandwidth of more than 2:1, and it does not interfere much with the microstrip circuit. Thereby, this mode suppression technique introduces a new advantageous packaging technology for high frequency circuits.

Approximate analysis of short circuited ring patch antenna working at TM/sub 01/ mode

This paper presents a study of the short circuited ring patch antenna based on the cavity model. Special attention has been paid to the fundamental mode in this geometry: the TM/sub 01/ mode. Analytical expressions for resonant frequency, fields, radiation pattern and input impedance based on this model have been developed. Simulations based on this theoretical model and experimental results show good agreement. The interesting radiation characteristics and resonant frequency of this mode are presented.

Size Reduction of Mushroom-Type EBG Surfaces by Using Edge-Located Vias

Periodic surfaces made of patches with metallized via holes or grounding pins (ldquomushroomsrdquo) have been shown to have bandgaps in their dispersion diagrams, inside which surface waves cannot propagate. These bandgaps are defined in all directions in the surface structure. The purpose of this work is to show how by changing the position of the metallic via of the mushroom from its center to its edge, the bandgap moves towards lower frequencies. This allows an easy structure size reduction which is critical in many applications. Results prove a size reduction of the unit cell size by approximately 20% by only moving the via position. The conclusions have been validated with measurements.

High Isolation Proximity Coupled Multilayer Patch Antenna for Dual-Frequency Operation

A new method to enhance the isolation between two ports in a dual-frequency proximity coupled patch antenna is presented. The dual-polarized patch antenna has a multilayer substrate configuration to achieve a compact design. In addition, two periodic structures have been included under the two feeding lines to have stopband behavior in the other frequency port. These electromagnetic bandgap (EBG) filters have been realized by introducing mushroom type resonators underneath the antenna feeding lines. Measurements show how the isolation between the feeding ports can be improved by selecting a suitable size for the resonators. The proposed antenna design achieves an isolation higher than 55 dB in the first frequency band (2.1 GHz) and better than 40 dB in the second one (2.45 GHz). Radiation patterns are not affected by the proposed structures showing low cross-polarization levels in both planes at the two frequency bands.

Planar Soft Surfaces and Their Application to Mutual Coupling Reduction

This paper presents a numerical study of the behavior of a planar version of traditional soft surfaces. The application of these structures, although limited to one direction, can be enough for many applications where the directions along which the waves must be suppressed are clearly defined. The proposed soft surface is compact and its design is flexible due to the different parameters of the structure. This work analyzes the effects of all these parameters in both the position and size of the bandgap or stop band. Also a practical application to reduce mutual coupling in patch antennas is presented. The work is supported by experimental results.

Planar Dual-Mode Horn Array With Corporate-Feed Network in Inverted Microstrip Gap Waveguide

The gap waveguide technology was recently introduced as an alternative to hollow waveguides and substrate integrated waveguides for millimeter-wave applications. This paper presents the design of a 4 ×4 planar dual-mode horn array with low loss corporate feed network realized by using an inverted microstrip gap waveguide. The dual-mode horns are compact and designed to reduce the power losses in grating lobes. It is because the diameters of the horn apertures are larger than two wavelengths to allow more space for the feed network and thereby lower conductive losses. The measurements show very good agreement with simulations, with 10% bandwidth of the return loss, 25 dBi realized gain and about 60% aperture efficiency.

New Microstrip Gap Waveguide on Mushroom-Type EBG for Packaging of Microwave Components

The gap waveguide has been recently presented as a new transmission line technology using artificial magnetic conductors (AMCs) to allow the wave propagation only along a desired path. The first validation has been provided using a lid of metal pins as AMC for high frequency applications. In this letter, simulations and measurement results are presented for another version called microstrip gap waveguide, working as inverted microstrip line and realized using a mushroom-type EBG surface. The transmission line is surrounded by mushrooms which create a parallel plate stop band, suppressing cavity modes and unwanted radiations compared to standard packaged microstrip transmission lines. The field propagates in the air gap between the upper lid and the mushrooms layer, providing a low loss compact circuit made in printed technology.