IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. X, NO. X, XXXXXXX 20XX 1 High-gain S-band Patch Antenna System for Earth-observation Cubesat Satellites Augusto Nascetti, Member, IEEE, Erika Pittella, Paolo Teofilatto, Stefano Pisa, Member, IEEE Abstract—A novel S-band circularly polarized patch antenna system suited for earth-observing cubesats is presented. The antenna consists of four rectangular patches properly excited in order to have the maximum gain in the boresight direction and produce circular polarization. The antenna has a compact size and its geometry and characteristics are compatible with any cubesat standard structure. A 57 mm wide square window allows to accommodate imaging system optics in its center leading to a very compact overall system. A prototype of the designed antenna system has been used to validate simulation results ✿✿✿ that ✿✿✿✿✿✿ showed ✿ a ✿✿✿✿ gain ✿✿ of ✿✿✿✿✿✿✿ 7.3 dBi. Experimental measurements confirm that antenna achieves good impedance match at the desired frequency of 2450 MHz with a gain of 7.3 dBi, a directivity of 8.3 dBi and 60 ◦ 3dB-beamwidth, ✿✿ in ✿✿✿✿✿ good ✿✿✿✿✿✿✿✿ agreement ✿✿✿✿ with ✿✿✿ the ✿✿✿✿✿✿✿✿ simulation ✿✿✿✿✿✿ results. Index Terms—small satellites; patch antennas; high gain; CubeSat; s-band. I. I NTRODUCTION S PACE missions based on cubesat are today continuously increasing [1]. Indeed, this class of nanosatellites is par- ticularly attractive because it enables access to the space at low cost allowing small countries, universities or even minor private companies to gain experience in the aerospace sector. In addition, thanks to the modern technologies, relatively complex missions can be planned e.g. for earth observation [2], remote sensing [3], communication technology experiments [4], hardware validation and other scientific missions as well as educational purposes [5], [6]. Even in case of minor projects, every satellite must satisfy strict requirements not only to ensure successful operation in the harsh space environment but also to comply with safety requirements imposed by the launcher company or organization. In the case of cubesats, they also have to comply with the cubesat-standard [5] that imposes stringent limitations to satellite dimensions and weight, which makes the design of each subsystem a challenge. This holds in particular for all the mission-specific aspects since for those parts, typically, no standard solution is commercially available as instead is the case for the satellite-bus subsystems as e.g. on-board computer, electrical power subsystem and radio. One of the key components of each satellite is the communication sub- system as it ensures the link with the ground station for the A. Nascetti and E. Pittella contributed equally to this work. A. Nascetti and P. Teofilatto are with the Department of Astronautical, Electrical and Energy Engineering, Sapienza University of Rome, Rome, 00138 ITALY, e-mail: (augusto.nascetti , paolo.teofilatto)@uniroma1.it. E. Pittella, S. Pisa are with the Department of Information, Electronics and Communication Engineering, Sapienza University of Rome, Rome, 00184 ITALY, e-mail: (pittella , pisa)@die.uniroma1.it. Manuscript received xxxxxxxxxx; revised xxxxxxxxxx. uplink of telecommands and the downlink of telemetry and payload-data. In particular, the design of the antenna system is a fundamental step as it must take into account mission aspects (e.g. satellite attitude) and comply whit the cubesat size-constraints, while, of course, ensuring good performances. Typically, cubesats rely on VHF/UHF communication systems with deployable monopole or dipole antennas for low bitrate uplink and downlink (telecommands and telemetry) while, for high bitrates, S-band is among the favorite choices as the range 2400 -2450 MHz is one of the International amateur satellite frequency ranges allocated by the International Telecommuni- cation Union [7]. One of the most frequent high bitrate payloads is that of cameras or other remote sensing systems like spectrometers. This kind of payload impacts on many satellite aspects making its design more complex due to the size and weight limitations of the cubesat standard and the consequent limits on power budget. However, some aspects can also be favorably used as an advantage in the design of the antenna system: for example the need of a nadir pointing attitude for earth observation can be exploited by using high-gain directive antennas and therefore employing lower transmitting power to achieve the same link performances. Starting from a practical case, namely the design of the Tigrisat satellite, a patch antenna has been designed that combines several advantages making it a suitable general solution for earth-observing cubesat missions. Tigrisat is a 3U cubesat, i.e. three times the basic cubesat unit (1U is a cube of 10 cm side) with a mission of dust storms detection over Iraq. Tigrisat has been developed at the School of Aerospace Engineering of Sapienza University of Rome within an international collaboration between Italy and the Republic of Iraq and has been successfully launched on June 19 th 2014 from Yasni cosmodrome in Russia. II. SYSTEM DESIGN In Fig. 1, a picture of the Tigrisat satellite taken during the assembling phase is shown as a reference to illustrate the position of the camera and the constrains adopted for the design of the S-band antenna system. The basic idea is to use the small 10 × 10 cm 2 face for the payload in order not to sacrifice the large faces (30 × 10 cm 2 , in case of a 3U structure as the one of Tigrisat) that can be more efficiently employed for hosting solar panels for energy production. In such a configuration, the nadir pointing attitude needed for earth imaging will correspond to the major axis of the satellite aligned with the local vertical direction. In this case the attitude