Radiation-Enhancement Properties of an X-Band Woodpile EBG and Its Application to a Planar Antenna

Abstract

A woodpile Electromagnetic Bandgap (EBG) material has been designed, by using an in-house code that implements the Fourier Modal Method (FMM). A couple of alumina-woodpile samples have been fabricated. Several results have been collected for the transmission behaviour of the woodpile and of resonators with woodpile mirrors, in a shielded anechoic chamber, by using a vector network analyzer, in the 8–12 GHz range. These new experimental data highlight interesting properties of 3D EBG resonators and suggest possible innovative applications. Comparisons of the collected results with FMM show a satisfactory agreement. An application of the EBG resonator has been considered, for gain enhancement of a microstrip antenna: an increase of about 10 dB in the broadside gain has been measured; experimental data and numerical results obtained with the commercial software HFSS show a good agreement. A comparison is presented between EBG resonator antennas and two-dimensional uniform arrays. Finally, HFSS results are provided for EBG resonator antennas working at higher frequencies or with a more selective superstrate: a gain enhancement of more than 18 dB is achieved by such antennas.

Experimental Analysis of a Directive Antenna with a 3D-EBG Superstrate

“…A woodpile with square-section rods is often preferred, because easier to fabricate. The aim of our paper is to complement the work published in [11], by presenting several new experimental results. These results highlight the role of the periodic superstrate in the directivity enhancement and we believe that they al-low researchers interested in EBG resonator antennas to achieve a deeper understanding of the electromagnetic phenomena involved in this kind of structures.…”

“…The design is described in [19] and resumed in [11], where the electromagnetic behavior of the proposed woodpile is also analyzed. The crystal consists of four periodic layers of alumina rods, with square section having side length w = 3.18 mm.…”

“…The diameter tolerance of the rods is ±3%, their straightness is represented by a camber/length parameter ≤ 0.003, and the maximum twist is 2 o per 30.48 cm. For more details about the woodpile fabrication see [11]. We realized a microstrip antenna, from a 0.76 mm thick Rogers/RT Duroid 5870 laminate (relative permittivity 2.33), printed on both sides with 36-µm thick copper.…”

“…When used as planar reflectors [4], substrates [5], or high-impedance ground-planes [6], are able to eliminate the drawbacks of conducting ground-planes, to prevent the propagation of surface waves also allowing a lowering of the antenna profile, and to improve the radiation efficiency. In EBG resonator antennas [7]- [11], an electromagnetic crystal is employed as a superstrate on a primary radiator, backed with a ground plane, and its main effect is a considerable increase in the directivity. Else, it is possible to obtain a highly-directive antenna by embedding a source in an EBG working near its band gap [12], thanks to the limited angular propagation allowed within the crystal.…”

“…The design was carried out by using an in-house code that implements the Fourier Modal Method (FMM) [20]. Woodpile samples were fabricated, by means of alumina rods with square cross-section [11]. A rectangular patch antenna was realized, resonating at 10.3 GHz.…”