**2.3 Verification for launch and environmental effects**

In order to verify that antennas can perform functionally in space environment and withstand launch effect mentioned above, some tests should be performed as addition to functional tests before mission started. These environmental verifications can be listed as:


*Advanced Radio Frequency Antennas for Modern Communication and Medical Systems*

by International Telecommunication Union (ITU).

maintain link margin positively.

**2.1 Launch phase**

adversely.

**2.2 Space environment**

**2. Antennas exposed to effects of space environment**

In space not only functionality should be taken into consideration but also durability and reliability of antennas should be taken into account. Consequently, in design phase of antennas to be used in space applications, environmental conditions are decisive factors. Materials to be used on space antennas should meet requirements based on space qualifications and factors [3]. These factors can be listed under two main subjects: *effects due to the launching activity* and *space environment.*

During launch of spacecraft, acoustic vibrations, shocks, mechanical stress based on static loads, dynamic loads and sudden atmospheric pressure fall occur and those effects should be taken into account in the course of antenna design step. In addition, in commissioning phase pyrotechnical shocks are generated while deploying solar panels and payloads like deployable antennas. All of those may affect objects, for example antennas, detached to surface of spacecraft,

After LEOP, antennas will be exposed to harsh space environment. Those can be listed as vacuum, high temperature changes regarding nonconductive thermal feature of vacuum typically between −150 and 150°C, outgassing or material sublimation which can create contamination for payloads especially on lens of cameras, ionizing or cosmic radiation (beta, gamma, and X-rays), solar radiation, atomic oxygen oxidation or erosion due to atmospheric effect of low earth orbiting.

Antennas used in LEO-type satellites can be divided into three types: payload data transmission (PDT) antennas for downloading high-density data to the ground station or inter satellite link (ISL) communication, payload antennas for special missions like mobile communication, GNSS services or remote sensing operations and TM/TC antennas to control the satellite and receive health parameters to monitor its functionality. The frequency ranges allocated for LEO satellites vary according to the characteristics of the payload on the satellite, but are determined

After a LEO satellite is launched, it must be brought to desired position or orbit in order to fulfill the function of the satellite or be required to stabilize tumbling. This phase is called as Launch and Early Orbiting Phase (LEOP). In this case, hemispherical or omnidirectional antennas are very beneficial and used for the transmitting and receiving TM/TCs since they have wide coverage capability [2]. Antennas having directional or shaped conical radiation pattern are preferred in order to transmit telemetry and payload data to the ground station after it has been commissioned. Since line of sight (LOS) communication time interval is limited over one ground station, it is desirable to use this interval in the most efficient manner. This can be acquired by starting downlink and uplink communication at low elevation angles of the satellite. Because it will provide more time to download high-density payload data from the satellite. Therefore, at lower elevation angles of the satellite, a higher antenna gain is required, whereas in the case where the satellite is at higher elevation angle with respect to ground station, the antenna gain may be relatively lower so as to

**142**


To verify the modules, requirements and tests have been defined by NASA and ESA in their published standards. For space programs, the related requirements and tests are prepared based on those standards. Some important and general ones can be listed as:


which have been published by ESA and


which have been published by NASA.
