A frequency of 32 GHz was chosen because the Deep Space Network (DSN) is able to receive such a frequency. It allows for a higher gain, and lowers the diameter of antenna, while also keeping the power low. The receiver antenna diameters used were 34 m and 70 m. The 34 m DSN antennas are always usable, but the availability of the 70 m antennas is suspect so both versions of the link budget are included. The required power was determined to be less then 100 W because of margin considerations.
To communicate with Earth the SOM will have a high gain antenna (HGA) placed on top as viewed from its landing position on Europa. The HGA is a gimbaled, parabolic dish. The HGA is used to downlink data at a high rate over the highly focused carrier signal. The antenna gimbals so that DSN is accessible as often as possible.
The data rates used for the link budget consisted of spacecraft telemetry and data from the scientific instruments. The total data rate was calculated to be 50 kbps. The transmitter antenna diameter is calculated to be 2.2 m. Furthermore, the power output needed for the HGA is 50 W.
The power output for the transmitter was kept below 100 W so that the margin of the link budget would be positive. Not enough margin (i.e., negative or very small) could lead to excessive bit error rates. The higher frequency is chosen because, even though the space loss is greater, the antenna diameter can be smaller, so it still attains a desirable gain.
The transmit antenna gain expected from the HGA is approximately 53 dB. Also the HGA is expected to transmit 50 kbps if the receive antenna diameter is 70 m and 10 kbps if the diameter is 34 m. The margin is also expected to be around 2 dB.
The antenna diameter is kept around 2 m for mass and structure considerations. Also, if a smaller, and therefore cheaper, launch vehicle can be used, the dynamic envelope will be smaller, dictating that the antenna also be small. The material chosen for the antenna is a carbon/epoxy composite chosen so that it will not out-gas into space. The carbon will allow the structure to be light, but still strong. The mechanical parts of the communication system are aluminum because of its lightweight properties and machinablilty.