Previously, satellite communications systems used a separate component for delay equalisation. The additional degrees of freedom obtained from cross-coupled filters held out the possibility of designing a flat delay into a filter without compromising other performance parameters. A component that simultaneously functioned as both filter and equaliser would save valuable weight and space. The needs of satellite communication also drove research into the more exotic resonator modes in the 1970s. Of particular prominence in this respect is the work of E. L. Griffin and F. A. Young, who investigated better modes for the band when this began to be used for satellites in the mid-1970s. Another space-saving innovation was the dielectric resonator, which can be used in other filter formats as well as waveguide. The first use of these in a filter was by S. B. Cohn in 1965, using titanium dioxide as the dielectric material. Dielectric resonators used in the 1960s, however, had very poor temperature coefficients, typically 500 times worse than a mechanical resonator made of invar, which led to instability of filter parameters. Dielectric materials of the time with better temperature coefficients had too low a dielectric constant to be useful for space saving. This changed with the introduction of ceramic resonators with very low temperature coefficients in the 1970s. The first of these was from Massé and Pucel using barium tetratitanate at Raytheon in 1972. Further improvements were reported in 1979 by Bell Labs and Murata Manufacturing. Bell Labs' barium nonatitanate resonator had a dielectric constant of 40 and "Q" of 5000–10,000 at . Modern temperature-stable materials have a dielectric constant of about 90 at microwave frequencies, but research is continuing to find materials with both low loss and high permittivity; lower permittivity materials, such as zirconium stannate titanate (ZST) with a dielectric constant of 38, are still sometimes used for their low loss property. An alternative approach to designing smaller waveguide filters was provided by the use of non-propagating evanescent modes. Jaynes and Edson proposed evanescent mode waveguide filters in the late 1950s. Methods for designing these filters were created by Craven and Young in 1966. Since then, evanescent mode waveguide filters have seen successful use where waveguide size or weight are important considerations. A relatively recent technology being used inside hollow-metal-waveguide filters is finline, a kind of planar dielectric waveguide.