Circularly polarized dedicated short range communications antenna for vehicle-to-everything applications

The research works in this thesis mainly focusses on the development of circularly polarized (CP) Dedicated Short Range Communications (DSRC) antenna for Vehicle-to-Everything (V2X) applications. Its CP characteristic is enabled by a sequential phase (SP) feeding network designed on top of the substrate. It has features of balanced signals of equal magnitude and ≈90° phase difference in sequence between ports. The length of the SP feeding network to each port designed in the different form of meander lines are the key to control the generated phase at the center frequency. It also contributes to the smaller final size of the antenna. The implementation of 90° sequentially rotated (SR) elements in correspondence with the SP feeding network are used to boost the performance of circular polarization, enhancing directivity and gain. Besides that, the implementation of folded dipoles on the antenna design helps also in size miniaturization. This thesis proposes three antennas which are CP DSRC antenna with two pairs of parallel dipoles (Antenna 1), CP DSRC antenna with two pair of folded dipoles (Antenna 2) and flexible CP DSRC antenna with two pairs of folded dipoles (Antenna 3). All antennas are designed by using 3D simulator software Computer Simulation Technology (CST) to study and verify the effect of each technique on the performances of the antenna. All the proposed antennas consist of two pairs of complementary dipoles connected to the SP feeding network in a square-shaped substrate. Each pair of dipoles is positioned in the x- and y- axis, respectively, in a perpendicular arrangement. Antenna 1 and Antenna 2 are fabricated on Rogers RT/duroid 5880 substrate with dielectric constant of er=2.2, loss tangent of tan δ=0.0009 and thickness of h=1.02 mm. Antenna 3 is printed on polyethelene terepthalate (PET) substrate with dielectric constant of er=2.8, loss tangent of tan δ=0.003 and thickness of h=1 mm. Both measured and simulated results show an enhancement in bandwidth for all CP DSRC antennas which covering 100% of the required frequencies from 5.85 to 5.925 GHz when SP feed and SR elements techniques are employed to the conventional microstrip patch antenna. Furthermore, 52.4 and 58.6% volume reduction with respect to a circular microstrip patch antenna (MPA) using metallic posts (MPs) (Samanta, S., 2020) are achieved for Antenna 1 and Antenna 2, respectively. In this work, the use of flexible PET on CP antenna based on SP feeding network, SR elements and folded techniques is presented for the first time, for specifically designed for the application of DSRC, to the author's best knowledge. The use of flexible PET on Antenna 3 enables the antenna to be mount on various shapes and surfaces of vehicle. These antennas maintain input impedance approximately 50 Ω over DSRC frequency. The measured results agree well with the simulated results. All antennas exhibit high gains of between 4 to 7 dBi and stable radiation pattern within 5.85 to 5.925 GHz frequency range. The proposed antennas recorded circular polarization and bidirectional patterns due to the presence of the complimentary dipoles located on the opposite side of the substrate. These features indicate the suitability of the proposed antennas in compliance to the ITS-G5 OBU V2X standard.