Various filter technologies suitable for use in communications systems have been investigated. Active microwave filters have been constructed and exhibit infinite Q- Factor. This could be a useful technique for realising MMIC bandpass filters with low insertion loss. However the inherant nonlinear behavior of active devices will cause intermodulation products to be produced when multiple signals are filtered. For this reason the authors believe that miniature passive filters are ultimately a better solution for products such as wireless LAN's. To this end high dielectric ceramic materials used in a miniature line configuration have been investigat and encouraging results for a 2 pole end coupled filter have been demonstrated. The prototype filter exhibited an unloaded resonator Q factor of greater than 300. With this technique miniature surface mount filters can be realized with a variety of transfer characteristics. E-Plane filter technology for use in millimeter wave radio systems has been investigated and a new type of E-Plane filter with an asymmetric frequency response has been demonstrated. This will be of particular use in diplexer applications. It is further proposed to combine the E-Plane and ceramic technologies to produce miniature high Q waveguide filters.