(A) broadband X/ka band antenna for SAR application

Abstract

In this thesis detail design of microwave components and antenna is presented which were designed for SAR and radar project. A novel rotary joint for drone radar is presented. The rotary joint was used for interface between antenna and transceiver. The antenna and transceiver both had WR-75 interface and a rotary joint using multiple transitions from assymetric mode to symmetric mode is designed and presented. A symmetric mode TM\textsubscript{01} is used in centre waveguide which also includes the joint with a ball bearing mechanism. The problem of discontinuity for joint was solved with matching the length of slot at discontinuity to avoid impedance mismatching. A gaussian antenna for air borne SAR application with very low sidelobes used in ViSAR is also given. The antenna was designed using hyperbolic and gaussian profiles and the mode content at apertures was adjusted to achieve low sidelobe and cross polarisation. The antennas used a corrugated surface with slot depth of $\lambda$/4 to achieve balanced hybrid condition in the profile and a transition of $\lambda$/2-$\lambda$/4 in the transition region for better impedance matching. A slotted waveguide array for SAR applications is given using infinite periodic boundary model. A resonant slot array with centre inclined slots is used to feed the radiating aperture comprising of 12x16 antenna elements. Uniform aperture distribution is taken with centre inclined slots for maximum aperture efficiency. In addition to that a travelling wave slot array with progressive phase difference with $\pm$$45^{\circ}$ is also presented. A feeding network with a ferrite switch and a combination of hybrids and power dividers is presented. An axially displaced ka-band reflector antenna is designed with no blockage from subreflector with a self supported feed system. A potter horn is designed with very low sidelobes is used to illuminate the sub reflector.