175 Defence Science Journal, Vol. 70, No. 2, March 2020, pp. 175-182, DOI : 10.14429/dsj.70.14725  2020, DESIDOC Low-profle Compact Printed Monopole Antenna for Satellite-based AIS Application Prithish Chand S.P., Amar D. Chaudhari * , Rahul Keley, and K.P. Ray DRDO-Defence Institute of Advanced Technology, Pune - 411 025, India * E-mail: amar_pee18@diat.ac.in AbStrACt In this paper, a simple, low profle compact printed monopole antenna has been proposed for satellite based automatic identifcation system (SB-AIS). The design consists of a printed monopole, which has been meandered to achieve optimum size reduction. The detailed investigation in terms of bending of the arms of monopole, width of the patch and dimensions of the ground plane on the resonance frequency and input impedance is presented. The antenna is matched to a typical 50 Ω coaxial line without any requirement of external matching structures. The prototype of the antenna is fabricated and tested at an operating frequency of 161 MHz for SB-AIS, with compact size of 44.5 × 17 cm 2 . The measured results show that the antenna has a bandwidth of 15 MHz (9.3 per cent), gain of 1.87 dBi and beam-width of 82° in the elevation and omnidirectional in azimuthal plane. The size reduction is 53.8 per cent as compared to a linear printed monopole antenna. Keywords: Satellite based-automatic identifcation system; Printed monopole antenna; Meandered monopole antenna; VHF antenna; Compact monopole antenna 1. IntroduCtIon A traditional line of site based automatic identifcation system (AIS) has limited communication range, to extend the range of the communication (>80 km), it has to be undertaken through a satellite, which also makes the data worldwide 1 . Satellite based-automatic identifcation system (SB-AIS) is a maritime surveillance system working on VHF band of 161 MHz over the channel 1 and channel 2 2,3 . It fnds its application in Navy, Coast guard and Maritime patrol police to secure the coastal and maritime environment. The SB-AIS, being in VHF range, the antennas of these satellites becomes large in comparison with the size of satellite itself. Thus, it becomes difcult for satellites to accommodate these large VHF antennas. The mass and the volume of the satellite are the two fundamental driving factors for the choice of an antenna arrangement. Several approaches have been proposed for the choice of an antenna for SB-AIS such as, deployable wire monopole antenna 4 and helical antenna 5 . The conventional deployable monopole and helical antenna have linear dimension of a quarter wavelength and 4m, respectively, and weighs up to several kilograms. The deployable nature of this heavy antenna also required high core strength and good spring stifness. The special mechanism is needed for maintaining the stability of satellite during deployment of these large antennas, which also adds mass to the satellite. Owing to such bulky structure and the other mechanisms, planar/printed antennas would become the natural choice for on-board applications. With the advent of technology and miniaturisation of satellite payloads, there has been a need to develop compact and easily integrable on- board antennas. This led to popularisation of printed/patch/ planar antennas 6 . Printed antennas, have a variety of benefcial properties including mechanical durability, conformability, compactness and cost-efective manufacturability. As such, they have a range of applications in both the military and the commercial sectors, and are often mounted on the exterior of the aircraft and spacecraft as well as incorporated into mobile radio communication devices. Recently, a compact array of patch antenna was developed 7 for space based AIS with overall dimension of 50 × 50 cm 2 and mass of approximately 3.9 kg. In order to reduce the profle, patch array antenna based on an artifcial magnetic material (AMM) was presented 8 . However, for manufacturing of these elements, aluminum slabs were machined using high precision CNC and laser cutting technology, which were very cumbersome and expensive. In another method, a printed folded line fed by a short probe monopole, using a concept of capacitive coupling, was presented 9 , which sufered from very poor gain of -11.6 dBi. In the last decade, wide range of monopole structures have been studied such as T-shape 10 , rectangular-shape 11 , elliptical-shape 12 , metamaterial inspired monopole 13 . All these structures, when considered for AIS applications, are not suitable as they are bulky and do not meet its required specifcations 2 . A quarter-wave linear printed monopole antenna (LPMA) has been considered for SB-AIS. In this paper, investigations have been carried out to reduce the size of a LPMA. It is proposed to achieve the size-reduction by meandering the monopole antenna, which is an efective way to reduce the length for the given resonance frequency. The parametric study leading to an optimum design of a compact meander line printed monopole antenna (MLPMA) has been presented. A compact MLPMA of overall size of 44.5 × 17 × 0.159 cm 3 has been realised on a low-cost Glass Received : 25 June 2019, Revised : 04 November 2019 Accepted : 06 February 2020, Online published : 09 March 2020