Solid solutions in the Ag(NbxTa1−x)O3 (where 0 ≤ × ≤ 1) system exhibit excellent dielectric properties at microwave frequency including high dielectric constant (200<k<400), low loss (tanΔ ∼ 0.004) and a composition controlled temperature coefficient of capacitance (TCC). For Ta-rich and Nb-rich solid solutions, the TCC values are negative and positive, respectively, and two-phase mixtures provided an average TCC close to zero. Series, parallel, and logarithmic mixing rules were applied to predict dielectric constant and TCC of polyphase assemblages (45wt%Ag(Nb0.65Ta0.35)O3+55wt% Ag(Nb0.35Ta0.65)O3) yielded an average dielectric constant of 450 and a TCC of 180ppm/°C. Microstructure analysis revealed that a CuO-rich liquid remains at the grain boundary and transmission electron microscopy shows that the CuO resides at triple points. Ag(Nb
)O3 ceramics were successfully integrated into LTCC for embedded capacitors. The addition of CuO lowered the sintering temperature to below 900°C and a low TCC was maintained for fine grained microstructures.