  The potential capabilities of resonators based on two dimensional arrays of
re-entrant posts is demonstrated. Such posts may be regarded as
magnetically-coupled lumped element microwave harmonic oscillators, arranged in
a 2D lattices structure, which is enclosed in a 3D cavity. By arranging these
elements in certain 2D patterns, we demonstrate how to achieve certain
requirements with respect to field localisation and device spectra. Special
attention is paid to symmetries of the lattices, mechanical tuning, design of
areas of high localisation of magnetic energy, which in turn creates unique
discrete mode spectra. We demonstrate analogies between systems designed on the
proposed platform and well known physical phenomena such as polarisation,
frustration and Whispering Gallery Modes. The mechanical tunability of the
cavity with multiple posts is analysed and its consequences to optomechanical
applications is calculated. One particular application to quantum memory is
demonstrated with a cavity design consisting of separate resonators analogous
to discrete Fabry-P\'{e}rot resonators. Finally, we propose a generalised
approach to a microwave system design based on the concept of Programmable
Cavity Arrays.
