Traveling wave antennas for the millimeter wave range face two main problems: increased metal loss, and fabrication difficulties due to the smaller wavelengths. To overcome these two problems, a new class of uniform leaky wave antennas have been introduced. The antennas are longitudinally continuous to minimize the fabrication problems, and they are based on low-loss waveguides, such as groove guide and nonradiative dielectric (NRD) guide, to reduce the effects of higher loss. New techniques for obtaining controlled leakage have also been investigated. Four different leaky wave antenna structures are discussed here, two based on groove guide and two on NRD guide.