Polyaniline nano-material backed lens antenna for X-band LEO satellite transceivers

This paper presents the design and implementation of an open-ended waveguide lens antenna engineered to generate a conical-shaped radiation pattern for the X-band fully-duplex communication subsystem of a low Earth orbit (LEO) satellite dedicated to Earth remote sensing. The antenna is designed to maintain reliable links with ground stations at a minimum satellite elevation angle of 10°, corresponding to ± 63° off-nadir, for a near-circular orbit at an altitude of 700 km. Operating within the 9.75-10.25 GHz band, the antenna provides broad coverage over a working sector of approximately 126° × 126° in azimuth and elevation, with peak radiation directed at ± 63° from nadir. It achieves a minimum gain of 5 dBic in these directions and employs right-hand circular polarization (RHCP) for downlink and left-hand circular polarization (LHCP) for uplink. The axial ratio remains below 3 dB across the working sector at the center frequency of 10 GHz, while the input reflection coefficient stays better than - 10 dB over a wide impedance matching bandwidth of 8.75-11.25 GHz. The 3-dB axial ratio bandwidth spans from 9.75 to 10.25 GHz. To further enhance performance particularly circular polarization purity, gain, and axial ratio bandwidth a metallic circular backing plate coated with a polyaniline (PANI) nano-material absorber is integrated between the dielectric lens and the reflector disc. The PANI layer, characterized by tunable dielectric properties and intrinsic microwave loss, improves impedance matching at the lens-waveguide interface and effectively suppresses surface currents and backward radiation. Material characterization via X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirms the semi-crystalline structure and micro-porous morphology of the synthesized PANI, which contribute to enhanced electromagnetic absorption. As a result, the axial ratio at 10 GHz is reduced from 1.0 dB to 0.05 dB, the gain at ± 63° is increased from 4.1 dBic to 6.0 dBic, and the 3-dB axial ratio bandwidth is expanded from 400 MHz to 500 MHz. These findings demonstrate the potential of integrating functional PANI nano-materials into high-performance antenna architectures for advanced satellite communication and Earth observation applications.