Design of compact size excitation device for antenna pattern using fractal architectures

This paper presents the design and the implementation of a device which can properly feeds an antenna composed of three simple radiating elements operating at 2.45 GHz. The designed antenna is of planar type, compact and quite isotropic. Compact size means that the excitation device has to be as small as possible in order to be integrated on the same substrate as the radiating elements. On the hand the excitation device must not affects significantly the radiation pattern. There are several ways to obtain a phase shift of 90deg or 180deg: by using couplers or by splitting the signal into two parts and adjusting the length of the microstrip lines. It is clear however that both these solutions would require a lot of space and an oversized ground plane. For this reason, we decided to design a device using fractal architectures. Its main advantage is that it does not affect the radiation pattern too much and respects the size specifications. A complete antenna has been realized on epoxy substrate. Experimental results confirm the theoretical prediction. In addition, this principle could be used to create even smaller devices by using higher permittivity substrates such as alumina