High-performance conformal antennas
On top of the cost of integration, conformal antennas also suffer from constraints imposed on their design due to the predefined shape of the area with which they need to conform. Often counterproductive, the shape of a 2D yet not planar surface affects not only antenna performance but also element spacing and relative signal phase. It is therefore necessary to investigate complex antenna shapes in order to compensate for these constraints. The aim of the EU-funded project CONFORMAL (New theoretical developments with application in the area of cylindrical microstrip antennas) was to address the most problematic points in the design of cylindrically conformal antennas. To this end, researchers developed a numerical model for cylindrical microstrip antennas (CMAs) with patches of different shapes. For the analysis of antenna characteristics, the method of moments in the spectral domain was implemented. The model includes further innovations like the use of piecewise sinusoidal basis functions. Several patch shapes were considered, including cylindrical, rectangular patches with a horizontal slot or a slotted frame. Researchers rigorously analysed the input impedance and the far-field radiation patterns of CMAs with patches of all different shapes fed by a microstrip line. The results opened the way to the design of a large CMA array. Specifically, the CMA array consists of five pairs of coupled slotted strip-framed patches fed by a microstrip line of about five wavelengths. With the newly developed model taking into account all electromagnetic couplings between patches and feeding line, researchers were able to evaluate for the first time the performance of such an array in detail. The advantages of this CMA array include the effective patch-to-microstrip line coupling being solely controlled by the space between them. Neither slot size nor patch shape need to be changed. Moreover, standard current distributions are supported on the elements, like cosine, which is of importance in the design of base stations for wireless network communication. Before the end of CONFORMAL, two new types of omnidirectional CMAs had been designed, one with vertical and one with horizontal polarisation. According to calculations, an increase of 20 % in their bandwidth could be achieved with the use of low-permittivity textile substrates and patches made of conducting textiles.
Keywords
Conformal, conformal antennas, software, cylindrical microstrip antennas, wireless network
