The far-field distribution of a travelling type triangular array of slots on a circular waveguide is evaluated experimentally. The efficacy of the antenna as a satellite onboard antenna is examined, and it is found that such an antenna can indeed be characterised as a good telemetry antenna. With the dominating mode propagating in the guide, the radiation pattern of a single slot, array of slots and array of arrays is obtained experimentally. The experimentally obtainedE-plane radiation pattern of a single slot in the illuminated region compared with the theoretically obtainedresults of geometrical optics and Shafai and Hassan's modematching technique. In a similar manner GTD is used to confirm the experimentally obtained results in the transition and deep shadow regions. The comparison is found to be very good.