A new class of E-plane filters based on cross-coupled resonators or over-moded cavities is introduced. The filters exhibit pseudoelliptic transfer functions with steep attenuation slopes. The metal inserts and separating wall between waveguide sections can be fabricated using electro-deposition techniques with the accuracy required for millimeter-wave applications. The filters are mass-producible, are much shorter than traditional E-plane filters, and have less insertion loss. Based on this new type of E-plane filter, highly compact diplexer structures are designed. A comparison between prototype filters and design prediction shows excellent agreement.