A family of low-temperature cofired ceramics (LTCC) based on mixtures of a commercial dielectric, MgTiO3-CaTiO3. (designated MMT-20) and ZnO, SiO2, and B2O3, has been investigated for microwave applications. The main objective was to optimize the three key properties-relative permittivity (epsilon(r)), dissipation factor (DF), and the temperature dependence of the microwave resonance frequency (tau(f))-through adjustment of the composition. A further objective was to estimate the limits on compositional variability while maintaining acceptable properties. The developed microstructures, after firing at 900degreesC, were studied using X-ray diffractometry and scanning electron microscopy/energy dispersive spectrometry techniques and compared with the dielectric parameters. The optimum composition (wt%) was found to lie in the ranges 45.8-44.9, ZnO; 17.25-17.55, B2O3; 6.95-7.05, SiO2; and 30-30.5, MMT-20, yielding values of epsilon(r) = 8.5-9.5, DF < 0.93 x 10(-3) ppm/K, and tau(f) < +/-10 ppm/K.