Final author version. Paper published at Loughborough Antennas & Propagation Conference, Loughborough UK, 2012. The paper is also available on IEEE Xplore Microstrip Patch Antennas on Substrates with Metallic Inclusions C. C. Njoku, W. G. Whittow and J. C. Vardaxoglou School of Electronic, Electrical and Systems Engineering, Loughborough University, Loughborough, LE11 3TU, UK j.c.vardaxoglou@lboro.ac.uk Abstract—This paper considers the design of microwave patch antennas using bespoke substrates. The permittivity of the substrate is controlled by inserting small scale metallic inclusions into a host medium and can be obtained using an S-parameter inversion algorithm on the results of plane-wave simulations. Electromagnetic simulations have been used to compare the performance of the patch on the heterogeneous substrate to standard homogeneous substrate. Keywords- artificial dielectrics, effective media, heterogeneous mixtures, patch antennas I. INTRODUCTION Antennas typically consist of metallic and insulating materials. Several papers have investigated artificial dielectric materials [1–8]. Synthetic materials removes the limitation of having to work with existing materials and allows the ‘creation’ of new materials that can be designed to have the required constitutive parameters, losses and other characteristics pre-determined for the whole antenna system. In 1946, Lewin analytically calculated the effective permittivity and permeability of a material loaded with small spherical particles [7]. This seminal work forms a basis for a combination of different kinds of structures with bespoke electromagnetic (EM) parameters. Technology and fabrication processes have made rapid advances in the last 60 years and nanotechnology [9], [10] can offer exciting new opportunities in terms of constructing new materials with amazing properties. These bespoke materials can be integrated to form complete antennas systems where the metallic and dielectric elements are made in one process, resulting in time and potential cost savings [11], [12], [13]. Patch antennas [14], [15] are currently fabricated using destructive processes where a copper film is printed across the whole surface and then the undesired copper is etched away using environmentally damaging chemicals. Controlling the permittivity allows an extra degree of freedom for antenna designers. Previous work has shown that higher bandwidths can be achieved by varying the permittivity of the substrate as a function of location [16]. It was hypothesized that further improvements could be obtained by using a smooth transition between local dielectric regions as could be achieved with artificial dielectrics [17–19]. A small size, high efficiency antenna can be achieved by using an as yet unrealizable material with equality of permittivity and permeability [20]. An initial study by the authors gave preliminary insight into the behaviour of patch antennas on synthetic media with dielectric inclusions [11], [21]. Section II calculates the real and imaginary effective permittivity of small metallic inclusions embedded in a host medium using an inversion algorithm process on the scattering parameters from plane waves impinging on the heterogeneous medium of different thicknesses. Once these are known, patch antennas with heterogeneous substrates can then be compared with a homogenous patch. A transmission line analysis is given in Section III while the patch antenna results are analysed in Section IV and conclusions are highlighted in Section V. II. PLANE WAVE ANALYSIS It is well known that the electrical properties of a material can be understood by the way it responds to a plane wave (PW) travelling through it. Based on this, the scattering parameters,  ଵଵ and  ଶଵ , and the thickness of the material, when processed using suitable inversion processes, for example as shown in [22–24], gives its electrical properties such as the relative permittivity, ߝ ௥ and permeability, ߤ ௥ . The main property being examined here is the relative permittivity of the material, in this case, a heterogeneous medium within which are embedded metallic cubes in a rectangular lattice, as shown in Fig. 1. In a previous paper [25], the authors have shown that the use of metallic cubes can increase the relative permittivity of the host material by a factor of over 20. The values of permittivity and permeability in this paper are relative values.