LUNAR ROVER

Antennas

Considering the low-power constraints placed upon the rover communication system, intelligent design of the transmitting antennas is critical. The primary communication link passes from the rover, through the lander, and to the earth station. When designing the primary antenna, the directivity and form factor are the most important factors. First, the antenna needs to radiate with an Omni-directional pattern in the horizontal plane, allowing the rover to transmit while maneuvering without the need for a mechanically or electrically steered beam. Second, the form factor must be small enough to fit onto the rover, which is difficult at the UHF transmit frequency. After considering several options, an off-the-shelf Omni-directional antenna is selected which satisfies the required design criteria. The antenna is built by Monteria which makes customized antennas.

Rover-to-Lander Antenna (USM1000D)

Operating Frequency

730 MHz (UHF)

Dimensions

100mm x 140mm x 30mm

Gain

7 dBi

Table 1. Monopole Antenna Properties

The secondary communication link (direct link between the rover and the Earth) would be utilized in case the primary link fails. In contrast to the primary antenna, the wavelength at X-band is sufficiently small such that antenna size is not a major concern, and a more directive beam is desirable for the higher gain. A Yagi-Uda antenna, consisting of a reflector and three directors, was chosen because it meets these requirements and can be mounted along the periscope to point toward the earth station. The beamwidth of this antenna is wide enough to provide full coverage to the earth as the rover drives over sloped terrain without the need for mechanical or electrical steering.

Rover-to-Earth Antenna: Yagi-Uda

Operating Frequency

8.4 GHz (X Band)

Number of Elements

5

Driver Length

1.707 cm (0.4781λ)

Reflector Length

1.720 cm (0.482λ)

Director Length

1.528 cm (0.428λ)

Element Spacing

7.14 mm (0.2λ)

Wire Diameter

0.303 mm (0.0085λ)

Gain

11.35 dBi

Half-Power Beamwidth

~60º