disclosed is a planar dual mode microstrip filter with the coupling between similar modes on different patches governed by the spacing between the patches rather than by microstrip coupling lines between the patches . the patches are shaped to allow dual mode coupling . the materials used in building this filter were an alumina substrate with gold metalization . the filter is encased in a conducting box made from a conducting material . one advantage of the proximity coupled structure is that it reduces the number of parts , complexity and allows the filter to be realized in a smaller space than in previous dual mode designs . this filter is useful in satellite communications , radar , and cellular communications . high temperature superconductor materials can be used in a planar microstrip form .