A mobile robot includes a chassis, a shell moveably mounted on the chassis, and a cutting assembly mounted to the chassis. The mobile robot also includes a communication system that includes an antenna module disposed on a rear portion of the mobile robot. The antenna module includes a base assembly, and an antenna assembly mounted to the base assembly by a spring. The antenna assembly includes a ranging antenna, and at least three angle antennas arranged axisymmetrically about the ranging antenna, such that the ranging antenna and the three angle antennas define a tetrahedral geometry for determining an angle of arrival for one or more incident signals.