Analysis and Design of Helical Antenna for Capture of Meteorological Images of NOAA Satellites

Abstract

This article presents the design, the characterization and the construction of a helical antenna in axial mode to receive weather images of Colombia transmitted from NOAA (National Oceanic and Atmospheric Administration) satellites. The antenna has been located in Bogota (latitude: 4°36'34''N, longitude: 74°04'54''W; 25822 m above sea level), it has received Automatic Picture Transmission (APT) signals of good quality with circular polarization on the right (RHCP); those ones have been fed to a sharp SDR (generic software RTL-SDR) and decoded through the WXtoImg software in the receiver. In order to improve the performance of the antenna, the helix has been built with a coaxial cable of 0.0047λ diameter (RG-213 / U), the length of the feed cable has been minimized to 55 cm, (less than λ/2), and an impedance coupling network using a series stub has been designed. The physical design has represented an important aspect, since some wrong dimensions have caused distortions in the received signal. The experimental results show radiation diagrams with a gain of eight dBi and bandwidth of 30 kHz with respect to 3dB at the central frequency of 137 MHz, which are comparable with the simulations and theoretical analysis. With the above, the design of the circuit is validated; it guarantees its performance and confirms the practical utility of the antenna.