Oscar Quevedo-Teruel

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

Linear array synthesis using an ant-colony-optimization-based algorithm

The aim of this work is to show the use of a well-known type of evolutionary computational optimization technique, ant colony optimization (ACO), in a typical electromagnetic problem: linear array synthesis. To this aim, an algorithm based on the fundamentals of ant colony optimization has been developed. The algorithm uses real numbers. Some examples using different optimization criteria are presented. Also, some guidelines for the use of the algorithm, especially for creating the desirability function, are supplied. The algorithm has been demonstrated to be versatile and useful for this problem. The purpose of the work is to show (via this particular application) the flexibility and easy implementation of this algorithm family, which makes it suitable for use in other electromagnetic optimization problems.

Transformation optics for antennas: why limit the bandwidth with metamaterials?

In the last decade, a technique termed transformation optics has been developed for the design of novel electromagnetic devices. This method defines the exact modification of magnetic and dielectric constants required, so that the electromagnetic behaviour remains invariant after a transformation to a new coordinate system. Despite the apparently infinite possibilities that this mathematical tool introduces, one restriction has repeatedly recurred since its conception: limited frequency bands of operation. Here we circumvent this problem with the proposal of a full dielectric implementation of a transformed planar hyperbolic lens which retains the same focusing properties of an original curved lens. The redesigned lens demonstrates operation with high directivity and low side lobe levels for an ultra-wide band of frequencies, spanning over three octaves. The methodology proposed in this paper can be applied to revolutionise the design of many electromagnetic devices overcoming bandwidth limitations.

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.

Reconfigurable Loaded Planar Inverted-F Antenna Using Varactor Diodes

This letter presents a compact reconfigurable multiband microstrip antenna. The multiplicity of bands is achieved by the use of concentric external metallic semirings around a central internal semicircular microstrip patch. These are all shorted to the ground plane via a vertical metallic wall through the common diametric plane, thereby adopting the concept of the planar inverted-F antenna (PIFA) for size reduction and thus compactness. The operation frequencies are tuned by varactor diodes placed between the inner semicircular patch and the outer half-rings. In addition to tunability, the overall bandwidth may also be widened by combining the tunable range. Theoretical simulations and measurements of manufactured prototypes agree well with each other.

Waveguided spoof surface plasmons with deep-subwavelength lateral confinement

We present a new type of waveguide scheme for terahertz circuitry based on the concept of spoof surface plasmons. This structure is composed of a one-dimensional array of L-shaped metallic elements horizontally attached to a metal surface. The dispersion relation of the surface electromagnetic modes supported by this system presents a very weak dependence with the lateral dimension and the modes are very deep-subwavelength confined with a long-enough propagation length.

Compact Multimode Patch Antennas for MIMO Applications [Wireless Corner]

This work presents the design of compact multimode patch antennas for application in medium-size MIMO terminals combining spatial and radiation-pattern diversity. This design was inspired by previous work, which proposed the use of patch antennas providing two services at two frequency bands that required different radiation patterns. These precedents are briefly reviewed, before extending the concept of the dual-pattern two-frequency case to one in which diversity is demanded at a single frequency. A design with three modes at a single frequency is also accomplished. Some prototypes have been manufactured and measured. An example of the advantages of using these multimode antennas in terms of spectral efficiency in MIMO systems is also included. The key aspect of this work is the use of short-circuited ring patch (SCRP) antennas.

Compact Loaded PIFA for Multifrequency Applications

A new multifrequency microstrip patch antenna is presented. The antenna can be considered a PIFA since it has a metallic wall on one of its sides. The different bands of operation are independent of each other, and different radiation patterns for each band can be achieved if desired. In addition, a circuital model is introduced to explain the operation of the antenna. This model presents some similarities with composite right left handed models presented in the literature. Some prototypes have been manufactured and measurements of return losses, efficiencies and radiation patterns, have been performed for a thorough characterization of the antenna as well as to validate the simulation results.

Dual-Band Patch Antennas Based on Short-Circuited Split Ring Resonators

A study of an innovative antenna based on split ring resonators (SSRs) is presented. SSRs have been exhaustively used in the literature as the unit cell of periodic structures for obtaining left-handed media, whose interesting characteristics can be applied to waveguides or antennas. In this work, the authors propose the use of only one unit cell of a double SRR as a radiator. The double SRR is printed on a grounded dielectric slab, acting as the radiating element of a microstrip patch antenna, and grounded pins are used to short-circuit the structure for size reduction. A compact dual band antenna is obtained in this way. For example, a particular design making use of PP (εr = 2.2) as substrate allows a size of 0.05 λ0 x 0.05 λ0 for the lower frequency of operation with an acceptable radiation efficiency. Simulated and measured results of return losses, gain and radiation efficiency of this new type of patch antenna are provided.