Patch antenna design with a photonic bandgap substrate

Beatriz Martinez, Public university of Navarra, Spain

Recently, a new, multidisciplinary field of study called "Photonic BandGap" (P. B. G.) structures have been developed. In analogy with electronic bandgaps in periodic semiconductor crystal lattices, a periodic lattice of dielectric "atoms" can yield a gap of forbidden electromagnetic energies. The operation key is its periodicity, the dielectric contrast, the pattern and the repetitive spacing between "atoms".

These structures present a very useful feature, do not allow the propagation of any electromagnetic wave in a frequency range for certain space directions.

One of the most attractive applications is in the antennas field. The Photonic BandGap structures can be used as substrates in different kind of antenna configurations. Two-dimension PBG substrates used in patch antenna configurations and three-dimension PBG substrates in dipole structures are two examples that are under study with very promising results.

There are high-performance applications like aircraft, spacecraft, satellite, mobile radio and wireless communications where size, weight, cost, performance, ease of installation are constrains where can be required low profile antennas. Microstrip antennas are the preferred solution in these cases because they are low-profile, conformable to planar and non-planar surfaces, simple, inexpensive to manufacture and robust.

Main operational disadvantages of microstrip antennas are their low efficiency, low power, high Q, poor polarization purity and very narrow frequency bandwidth.

There are applications where broader bandwidth and high efficiencies are desirable. To meet these requirements, methods like increasing the height of the substrate can be used. However, this method leads to increase at the same time the surface waves which extract power from the direct radiation degrading the pattern and the efficiency of the antenna.

In order to avoid this effect, a Photonic Bandgap substrate can be used. The benefits from using such photonic crystals will be the improving of the antenna efficiency, the reduction of the side lobe level and an increasing in the antenna gain by reducing the surface wave propagation.

In this paper, a two-dimensional structure formed by a patch antenna in a PBG substrate has been studied and will be presented. An important reduction in the surface wave levels has been observed in the simulations, which has lead to an improvement in the gain, efficiency and side lobe level parameters.