Broadband active receiver antenna design for ionospheric remote sensing and low frequency radio astronomy applications

Today, due to the demands for high bandwidth and compact design, many communication applications use UHF and higher frequency bands. In addition to these bands, the unique characteristics of the sub-UHF frequency bands continue to maintain interest in them. Observations in these bands, especially in scientific studies such as ionospheric radar and low frequency (< 100 MHz) radio astronomy applications, indicate intensive use of the relevant bands. The decrease in frequency in these bands increases the wavelength, which brings various challenges. With the decrease in frequency, the physical sizes of the antennas increase, and the mechanical structure of the antennas can become overly complex for applications requiring high bandwidth. As a solution to this situation, the literature suggests the use of active antenna structures designed with transistorized pre-amplifiers. The antenna sizes can be significantly reduced with an active circuit directly connected to the passive radiator terminals. In radio astronomy studies, the high resolution demanded by astronomers results in antenna sizes that are practically unfeasible for low-frequency radio astronomy. As a solution, the use of electrically short antennas within an interferometric array has been introduced. In low-frequency radio astronomy applications, high resolution is achieved through the simultaneous use of thousands of receiving antennas in an interferometric arrangement. This increase in the number of antennas leads to design requirements such as low cost, easy production, and easy installation for the antennas to be used in the interferometry array. These requirements imply that the antennas are designed on a project basis. In this study, an active receiving antenna design for ionospheric radar and low-frequency radio astronomy applications in the 1 – 50 MHz range is proposed. The designed antenna consists of a passive radiator structure, an active antenna, and an antenna skeleton. For the design of the passive radiator structure, antenna topologies found in the literature were examined, and as a result, the Inverted-V dipole antenna topology was selected due to requirements such as low cost, ease of production, and installation. The natural frequency response of the chosen passive radiator structure was decisive in the design of the active antenna. The active antenna structure, directly connected to the terminals of the passive radiator, was designed using the voltage sampling method. The measurements of the designed and manufactured active circuit were conducted using the Red Pitaya SDR, and it has been demonstrated that the active circuit provides the required 30 dB amplification ratio.