The sintering behavior and dielectric properties of perovskite Ag(Nb1-xTax)O-3 (0 < x < 1) solid solutions and two-phase composite assemblages were explored. A small amount of CuO (1 wt%) was used for liquid-phase sintering and led to high densification at temperatures < 950degreesC. The temperature coefficient of capacitance, TCC, was adjusted by varying the Nb:Ta ratio within the solid-solution series and by creating composite microstructures. Two-phase assemblages consisting of Ag(Nb3/4Ta1/4)O-3 and Ag(Nb1/4Ta3/4)O-3 were synthesized to achieve a temperature-stable dielectric material for high-frequency applications. The composite dielectric. with CuO addition had an average dielectric constant of 390 and a Q X f factor of 410 GHz at 2 GHz, with a stable TCC (0 to -180 ppm/degreesC) in the temperature range from -20degrees to +60degreesC. In addition, process compatibility with a silver conductor was confirmed by high-frequency ring-resonator measurements and microstructural characterization. The Ag(Nb1-xTax)O-3 solid solutions and composites are promising candidates as embedded capacitors for radio-frequency/microwave applications.