Antennas and metamaterials for aerospace applications

In this thesis, four antenna designs, two of which are radio altimeters and two are TCAS antennas, and one polarizer are presented for use in aviation. A radio altimeter is a navigation device that measures the altitude of an aircraft above the ground. Operating at a center frequency of about 4,3 GHz, the two-layer MIMO radio altimeter antennas, consisting of a reflector and a top antenna, were designed using techniques based on electromagnetic band gap (EBG) structures' phase response to gather the scattered pattern in the first study and to facilitate fabrication in the second study. Both designs meet the radio altimeter antenna criteria with high gain and directivity values. In the third and fourth studies, antennas were developed for TCAS, another important navigation aid for aviation safety. TCAS is a system used to prevent aircraft collisions. TCAS antennas operate at 1,03 GHz interrogation and 1,09 GHz reply frequencies. The feed network dimensions of the antennas were reduced by downsizing the branch line couplers and the appropriate radiating parts were designed. The antennas presented in the relevant section are successful TCAS antennas capable of scanning a total area of 360° with a beamwidth of 100°. The last section presents the design of a thin-structured polarizer with wide frequency bands that changes polarization while reflecting the incident wave. This polarizer provides polarization rotation over a total frequency range of 1,44 GHz and linear to circular polarization conversion over a total frequency range of 8,94 GHz. In the design, frequency bands suitable for aviation use were selected. The measurement results of all the studies in the thesis support the simulation results performed with an electromagnetic analysis program that uses the finite integration method. In addition, based on transmission line theory, the analysis of the couplers designed for TCAS antennas was performed by coding through a mathematical calculation program and thus the verification was realized.