This paper presents the approach to optimal TTC patch antennas placement onboard minispacrafts. The construction of the antennas is briefly discussed and chosen schemes of antennas placement are introduced. Influence of solar panels is also investigated and countermeasures against failure of their deployment are proposed. The results of the analysis were obtained with the use of Moment Method simulations and measurements. Alternative, computationally more efficient ray-tracing method is mentioned and compared with full-wave simulations. STATEMENT OF THE PROBLEMAccording to SSTL (Surrey Space Technology Limited) classification [10], minisatellite is a spacecraft which weight doesn't exceed 500kg. Small spacecrafts, i.e. SSETI (Students Space Exploration and Technology Initiative) minisatellites SSETI Express or ESEO [9] let decrease the time of construction and gives possibility to launch the spacecraft either as an auxiliary payload by large launchers or with the use of small rockets. Due to small dimensions and weight of the minisatellites, the access to the space is accelerated, but also specific, small weight communication devices have to be used. For the needs of SSETI missions we have developed the set of S-band TTC (Telemetry and Telecommand) patch antennas.For small spacecrafts, that are to be launched by small launcher or as an auxiliary payload, it's important to maintain the assumed envelope. Developed low profile LGA antennas are extruded no more than 10mm from the main satellite's body. The gain of the antennas is relatively small (lower than 8dBi), so the set of 3 or 4 antennas is enough to create fairly omnidirectional combined radiation pattern. Moreover, such low gain antenna may be used also onboard larger spacecrafts, especially those changing often their orientation in space. However to obtain the desired shape of radiation pattern, antennas number and placement should be optimized. There are three main objectives of optimization of antennas placement [5], [6]:(i) If possible omnidirectional coverage, if notpossibly narrow minima in resultant radiation pattern of the whole antennas set (ii) Ensuring link stability while maneuvering close to other spacecraft (iii) Maintaining the radio link in case of failure to a proper deployment of solar panels and other deployable instruments. The importance of the optimization of the antennas placement will probably increase after starting direct intersatellite communication and TCP Space protocol for communications between satellites.We've investigated the ideas of antennas placement to obtain the best omnidirectivity of the radiation pattern for various minispacecrafts configurations. The analyses were run with the use of full-wave methods which are good enough for small structures and relatively low frequencies. Fig. 1 presents the developed TTC Low Gain Antenna, which is manufactured in microstrip technology. The major advantages of this technology -with respect to applications on mini-satellite -are: a lightweight structure, a lack of deployable mechan...

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Telemetry, Teleranging and Telecommand (TTC) communication is essential to maintain space missions. Antennas for TTC applications must feature wide -or even omnidirectional -radiation properties. In this paper we present results of our investigations on small size cylindrical arrays which can ensure such radiation properties. Due to small volume required they can be mounted at top and bottom of small spacecraft. Our interest is focused on the S-band, however, results can be extended onto upper microwave frequency bands. We attempted to optimize radiation and impedance properties of patch elements conformal to a small radius cylindrical surface, which is about a wavelength in diameter. The considered cylindrical arrays consist of three to seven probe-fed patches. As a further upgrade to the investigated cylindrical antenna we propose to use a spherical patch on a top of such cylindrical arrays. With use of less expensive materials, the proposed antenna concepts can be applied in wireless communication and in electronic instruments.

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