Omnidirectional WLAN Antenna For Unmanned Aerial Vehicle

The unmanned aerial vehicle (UAV) is an unmanned aircraft that can be operated by a telecontrol device and a self-contained programming controller. As the most frequently-used type among the UAV family, a four-rotor UAV is characterized by its small size, low cost, ability of vertical-takeoff-and-landing, simple structure and operational flexibility. In fact, the UAV has already played a very significant role in military and civil use. However, to design an antenna for the four-rotor UAV that fulfils the requirements of omnidirectional radiating and reduced unroundness can be very challenging. In view of these difficulties and based on the state-of-the-art of four-rotor UAVs and its application prospects, three antenna schemes, which can be operated over the WLAN bands (2.4 GHz?2.484 GHz,5.15 GHz?5.35 GHz and 5.75 GHz?5.825 GHz), are proposed in this thesis.As the prerequisite of antenna measurements, a UAV model is self-made at first.Since the in-flight four-rotor UAV are controlled by land remote radio and exchanges information with the operator at the same time, the UAV antennas are required to be vested with good omnidirectional radiating and excellent unroundness. The first scheme in this thesis is that four loop antennas are respectively located on each side of the UAV's fuselage. The antennas are operated at 2.45 GHz, and excited by a one-to-four microstrip power divider. The simulations and measurements show that the designed antennas can realize excellent omnidirectional radiating and unroundness in the horizontal plane.Secondly, a vertically-crossed dipole patch antenna for UAVs is proposed. The scheme is implemented by utilizing two mutually perpendicular dipole patch antennas,which consequently induce a 45° angular offset for the radiating patterns. The four uniform antennas are excited with equal-amplitude and in-phase feeding provided by a top-mounted one-to-four power divider. According to the simulations and experiments,proper adjustments of the antenna locations could bring better omnidirectional radiating and unroundness. However, one drawback of this scheme is that the crossed dipole patch antenna is large in size when operating over the 2.4 GHz ?2.484 GHz band. To address this problem, some attempts have been carried out. The most effective one is bending the patch antenna arm and installing its bent portion at the edge of its microstrip substrate (with the thickness of 2 mm). The obtained antenna can be operated over the WLAN band (2.4?2.484 GHz),and has a good omnidirectional radiating performance and efficiency as well.Finally, a rectangular waveguide slot antenna with small size, simple structure and machining flexibility is also presented. This antenna performs better than the previous two proposed schemes. The antenna occupies an overall area of 22×22×6mm . Four identical antennas are excited by a one-to-four power divider and respectively located at the center of each side of the UAV's fuselage. By rotating its angles and locations, the antennas can correspondingly radiate various patterns. According to this approach, the antennas are successfully optimized to achieve the dual WLAN operating bandwidths(2.4 GHz?2.484 GHz band and 5.75 GHz ?5.825 GHz band).