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Double layer and edge-location via techniques are combined for electromagnetic band gap (EBG) size reduction. The study of the required number of elements and their dimensions is carried out in order to suppress the surface wave propagation modes and consequently to reduce the mutual coupling between radiating elements in low-permittivity substrates. By applying these techniques, the size of the EBG mushroom is reduced by 30%; however, the bandwidth operation maintains its value, and these structures can be integrated between radiating elements in broad bandwidth antennas.

Low-profile integrated antennas are demanded to be small [

The most common mutual coupling reduction techniques are cavity structures [

Patch antennas are found to have very strong mutual coupling due to the severe surface waves on thick and high-permittivity substrates. In the literature, it can be found a variety of works which apply metamaterials for the reduction of this effect. In [

The main goal of this work is to combine multilayer technique with edge-location via [

EBG technique appears as an application of truncated frequency selective surfaces (FSSs) [

High impedance surface and its model with parallel resonant LC circuit. The substrate is transparent in order to get better visualization of metallic vias.

When the period is small compared to the wavelength of interest, it is possible to analyze the material as an effective medium with a surface impedance (metamaterial with electrical properties [

Layer and top views of traditional EBG structures (a) and multilayered F structure (b).

The behavior of this structure is similar to an LC circuit in (

Nearby

Analytically, it can be noticed that the band gap operation band is proportional to

Finally, EGB structures can be seen as bend corrugations, where the length of the corrugation is the sum of the via and the patch multiplied by two, as it is depicted in Figure

Thanks to the high surface impedance, horizontal or vertical modes are not allowed in the mushroom structures at certain frequencies. In order to find the allowed frequencies for each wave vector, a single unit cell with periodic conditions is simulated. The

Unit cell scheme for eigenmode solutions.

Original mushroom

Double layer mushroom

Double layer and edge-location via mushroom (F shape)

All the studied structures are developed in a low-permittivity substrate

The electric field is described in terms of an eigenvalue equation, which is solved numerically. In Figures

Brillouin diagram for original mushrooms.

Brillouin diagram for double layer mushrooms.

Brillouin diagram for F shape mushrooms.

In this work, the combination of multilayer structure [

The size of the mushroom patches and the necessary number of periods for mutual coupling reduction are higher than the available space between radiating elements for low-permittivity substrates. For example, for steering arrays antennas, separation must not be higher than 0.6

Simulation scheme for

In order to validate the whole process, prototypes of four and seven rows are built. Six prototype transmission lines (TLs) with EBG ground plane are mounted in Figure

Samples of single and multilayered EBG mushrooms with different shapes and number of elements.

All the substrates used have permittivity of

Multilayered mushroom with rectangular shape, 4 elements and edge-located via (F-shape).

Schematic

Prototype

In Figures

Transmission parameters (

Transmission parameters (

Transmission parameters (

Finally, the tradeoff solution between isolation and available space is carried out, being the necessary number of periods for surface wave suppression:

In order to prove this solutions four rows of double-layered edge-located via, EBG mushrooms are introduced between two round patches with double circular polarization. The radiating elements are integrated in the same substrate, and they are circular polarized. The elements are fed by a 90°/3 dB branch line coupler in order to get the double circular polarization.

In Figure

Without EBG structures

With EBG structures

This paper presents and proposes a combination of double layer and edge-location via techniques for EBG size reduction. With these techniques, a 30% of size reduction in comparison to the original mushroom shapes is achieved. This F shape mushrooms maintain the broad bandwidth operation, and these are used in order to suppress the surface wave modes and consequently to reduce the mutual coupling between radiating elements in low-permittivity substrates.

The simulations contained in this work have been carried out using CST Microwave Studio Suite 2011 under a cooperation agreement between Computer Simulation Technology (CST) and Universidad Politécnica de Madrid. The authors kindly thank the company NELTEC S.A. for giving samples of the substrates, in which the prototypes were built. This work has been supported by a UPM Grant no. CH/003/2011 and the sicomoro project with Reference no. TEC2011-28789-C02-01.