The use of printed antenna techniques at millimetre wavelengths to create planar linear travelling wave antennas is commonly considered to be inhibited by the microstrip feeder loss and the alternate use of low loss dielectric feeders is thus attractive. In this investigation an additional source of unwanted loss is considered and a complete assessment, more favourable to microstrip, emerges. The fields of an insular guide antenna feeder are computed by a mode matching method to provide accurate data for the guide attenuation and also the launcher radiation loss when the insular guide is connected to a conventional rectangular metal waveguide using a horn launcher transition. This latter analysis is based both on a chopped surface wave distribution method and an alternative variational method. Similar loss data is computed for microstrip antenna feeders using existing theories and some experimental data presented. A comparison of total unwanted losses for both types of feeders establishes that microstrip is advantageous for feeder lengths up to about 20 wavelengths long, the precise condition for equality depending on many other factors which are discussed. If however the feeders are assumed to be fully integrated with an electrically compatible guide structure in the receiver or transmitter to remove the source of launcher radiation loss, insular guide is distinctly advantageous, thus highlighting the need for new technological developments in integrated millimetre linear antenna systems.