Beam-switched ESPAR Antenna with Embedded Matching Network for V2X Communications

A planar ESPAR antenna with one active and two parasitic printed monopoles has been examined to fulfil the demands of Intelligent Transportation Systems (ITS) for V2X communications at the allocated frequency of 5.9 GHz. This antenna has the ability to switch between three different radiation patterns (one omni-directional for broadcasting and two directive) and dynamically adapt to the environment. The pattern reconfigurability is achieved by controlling the mutual coupling between the active and the parasitic elements with PIN diodes switches connected to the parasitic elements. A reconfigurable (switched) open microstrip stub acting as an impedance matching network is integrated in the antenna design to correct the deviations between the different states of the ESPAR antenna in the reflection coefficient results (S ₁₁ ). The compact antenna size due to the close distance between the active and parasitic elements (λ/5) enables the integration of the antenna inside the shark-fin structure found in modern cars. Analytical simulation results (S ₁₁ , gain, radiation pattern) are presented for both the free space and installed antenna performance. A satisfactory impedance matching due to the employment of the impedance matching network is guaranteed for all the states and a significant 5 dB gain increase between the omnidirectional and the directive state.