The optimization of antenna parameters such as gain is an important aspect of all antenna design. In the context of leaky-wave antennas (LWAs), it is important to have accurate design rules for optimizing the gain of the antenna for practical finite-length structures. In this work, taking advantage of the recent formulas derived for the accurate evaluation of the beamwidth in finite-size 1-D unidirectional LWAs, we obtain optimum conditions for this general class of antennas. In particular, design rules for minimizing the beamwidth or maximizing the gain are obtained. The latter is evaluated with a fully analytical procedure through the definition of a correction function that improves the accuracy of the common gain–beamwidth relation. The effects of material losses are also discussed to show how they can affect the optimization procedure. These results apply to any 1-D unidirectional LWA, because no assumptions are …