ORIGINAL PAPER Space Electromagnetic and Plasma Sensor (SEAPS): A Laboratory Prototype for a Space Payload K. Makhija*, R. Borade, G. Shaifullah, S. Gujare, S. Ananthakrishnan and D. C. Gharpure Department of Electronic Science, Savitribai Phule Pune University, Pune, India Received: 29 February 2016 / Accepted: 06 June 2016 Ó Metrology Society of India 2016 Abstract: Space electromagnetic and plasma sensor is a proposed space payload consisting of an electric field vector sensor—a tri-axial arrangement of monopoles in a mutually orthogonal configuration—and a magnetic field vector sensor, which is a tri-axial arrangement of mutually perpendicular loop antennas. Both operate between 0.5 and 20 MHz in order to acquire the complete 3D polarization matrix. The antennas, which are meant to be electrically short, are matched with a high input impedance amplifier, followed by gain blocks, filters and a six-channel data acquisition system. Some of the proposed goals of the project include study of the low frequency Sun, plasma interactions between the solar wind and Earth’s magnetosphere, lunar atmosphere, and radio emission from other planets within the solar system. This article describes the construction of a laboratory prototype and preliminary calibration results. Keywords: Active antennas; Low frequency; Radio astronomy; Plasma 1. Introduction The opacity of the ionosphere at lower frequencies ( \ 20 MHz) requires the largely overlooked study of the low frequency universe to be done only from outer space. This is an important frequency regime as it can yield valuable information about radio bursts from solar flares and Coronal Mass Ejections (CMEs) and plasma interactions between the solar wind and Earth’s magnetosphere. Dipole antennas are the preferred choice as receiving elements due to their inherently large effective area. However, the large size and weight of half-wave dipoles at these wavelengths leads to an expensive payload. Although several other space missions have had similar instruments [1, 2], space electromagnetic and plasma sensor (SEAPS) proposes a novel payload [3, 4] consisting of electrically short 1 active antennas for reducing the size and weight. Its field-programmable gate array (FPGA) based backend consists of a data acquisition and analysis system based on the use of frequency binning to reduce the size of the data. When used in an interferometric array for higher angular resolution and sensitivity, SEAPS can be used to detect decametric radiation from other planets within the solar system or exo-planets, supernova remnants, continuum emission from pulsars, etc. [5, 6]. As a single receiver system, it can serve as a precursor to a future space- based radio telescope for probing the heretofore unseen cosmic dark ages ([7, 8], and references therein). A brief overview of the payload and description of its laboratory prototype is presented in this paper. 2. Practical and Astrophysical Considerations 2.1. Impedance and Practical Considerations of Small Antennas The cost of launching a payload increases dramatically with its size and weight. For these reasons and for reducing the coupling between the antenna elements and the satellite body, smaller receiving elements need to be realized. However, the impedance of electrically short monopoles and loops becomes highly reactive with a very low—albeit non-zero—resistive impedance [9] as shown in Fig. 1. This makes passive impedance matching over large bandwidths impossible and other options need to be considered. The *Corresponding author, E-mail: krishnamakhija@gmail.com 1 Antennas whose conducting elements are typically of lengths l  0.1k. M  APAN-Journal of Metrology Society of India DOI 10.1007/s12647-016-0188-y 123