Analysis and modelling of rampart line antennas

A new, efficient, and accurate analytical model is introduced for estimating the beam direction of rampart line antennas with microstrip radiators that can change beam direction with feeding frequency. The model takes its origins from 1-D array theory, in which the bends represent the radiating elements, and the interconnecting lines represent the phase shifters. A mathematical expression accounting for the equivalent length of the bends for the correct estimation of the distance between the radiators is introduced. The model was tested for various substrate relative permittivity values ranging from 2.9 to 6.45. This model can be used for arbitrary rampart line configurations by providing the equivalent dipole direction, depending on the orientation of the bends. An alternative geometry was proposed to reduce the coupling between the parallel line segments. A prototype operating in a bandwidth of 1 GHz around 7.8 GHz was realized on a Rogers RO4350B high-frequency laminate with a thickness of 1.524 mm. Both the radiation pattern and the reflection coefficient were measured and show a good agreement with the proposed analytical model and commercial full-wave simulation tool results.