The present invention relates to 3-D structures having high temperature stability and improved micro-porosity as well as processes of making and using same. The disclosed 3-D are advantageous because they have low densities and low permittivities. When compared to previous 3-D structures, the present structures maintain their low permittivities over a broader range of electromagnetic frequencies. Thus, when used in communication devices such as array antennas, can provided higher communication performance in high temperature environments.