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.

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.

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.

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.

The purpose of this work is to propose a new method to suppress the harmonic radiation from a microstrip patch antenna with proximity coupled feeding line implemented in a multilayer substrate. The goal of the design is the suppression of the resonances at the 2nd and 3rd harmonic frequencies to reduce spurious radiation due to the corresponding patch modes to avoid the radiation of harmonic signals generated by non-linear devices at the amplifying stage. The study shows the possibility of controlling the second harmonic resonance matching by varying the length of the feeding line. On the other hand, the suppression of the third harmonic is achieved by using a compact resonator. This resonator consists of a printed metallization with a via connected to the ground plane (mushroom type) in a multilayer configuration. Comparing with conventional electromagnetically coupled patch antenna, the radiated power of the proposed antenna at the 2nd and 3rd harmonic frequencies is reduced by 14 dB and 8 dB, respectively.

The use of planar soft surfaces to reduce mutual coupling in a new type of planar inverted-F antenna (PIFA) is demonstrated in this work. The proposed antenna is dual-band, single-port, and quite compact, especially for the low frequency of operation. At that frequency band, the mutual coupling is more critical. With the purpose of decreasing this coupling, a solution based on soft surfaces made of simple printed strips with grounded vias is presented, achieving a simultaneous reduction on the mutual coupling level at the two bands of operation of the antenna. In this particular example, only two strips are used and a reduction on the coupling of more than 6 dB is experimentally verified for these two bands and for different distances between elements. The use of a multilayer substrate is a key aspect in the proposed design.