Leaky Wave Antenna Based on Substrate Integrated Waveguide Technology

Abstract

Leaky Wave Antenna (LWA) is currently an immensely vibrant topic in the research circles related to Antennas. Leaky Wave Antenna offers some distinct features which are not easy to obtain from its counterpart antennas. One of the key features is its easy beam scanning ability, as its main beam of radiation steers with change in frequency. This aspect of LWA makes it a favorite for applications which demand beam scanning like radars and electromagnetic imaging systems. A design methodology of LWA proposed by Robert S. Elliott was followed to simulate the LWA. Radiation results obtained after simulation were verified by comparing them with Elliott’s experimental results. In order to design an LWA, it is imperative to determine complex propagation constant (i.e. attenuation constant “α” and phase constant “β”). Phase constant β decides the direction of main beam and attenuation constant α determines main lobe’s beamwidth as well as length of antenna. Elliott has described a method to find the values of complex propagation constant but that method helps in finding these values only at a single frequency. Other methods of extracting complex propagation constant were studied and verified by simulating an Elliott’s LWA of 0.3 inch slot length. These simulation results were compared with the experimental data provided by Elliott. Substrate Integrated Waveguide (SIW) Technology offers compactness, planar topology, ease in fabrication and cost effectiveness for microwave circuits. This thesis presents a Leaky Wave Antenna which enjoys the advantages of Substrate Integrated Waveguide Technology. An LWA based on SIW technology was designed and developed. The antenna was designed on RO4003C substrate having dielectric constant of value 3.55 and it operates at a central frequency of 10GHz. The proposed design contains transverse slots, opened at broadside of the antenna, and tapered at both ends. Microstrip to SIW transition and SIW to LWA transition were designed and optimized. Considerable improvement in return loss curve was achieved by the help of these transitions. Simulation results of the proposed SIW LWA shows sidelobe level of -11.7dB, a gain of 8.8dB and a main lobe having a beam width of 10.8 degrees pointing at an angle of 46 degrees. These results were obtained by keeping Perfect Electric Conductor (PEC) as metallic walls of the substrate. In order to make the simulation more realistic copper and nickel materials were used for representing the metallic sides. Degradation in radiation characteristics like gain, sidelobe levels (SLL) and beamwidth was noticed. It was also observed that there is a shift of around 0.15GHz between measured and simulated return loss trace. This difference suggests that the simulated and measured radiation patterns should also be observed with a frequency shift of 0.15GHz. So, the simulated radiation pattern obtained at a frequency of 9.8GHz matched the measured radiation pattern at a frequency of 9.65GHz. Simulated radiation pattern shows a gain of 3.4dB, SLL of -6.9dB, beamwidth of 8.6 degrees and main beam pointing at 30 degrees. Whereas measured radiation pattern shows good agreement with the above mentioned simulated result by showing a gain of 1.7dB, SLL of -4.88dB, beamwidth of 9.6 degrees and the main beam aiming at an angle of 30 degrees.