Surface mount RF and microwave filters using high dielectric constant ceramics

With the use of increasingly high transmission frequencies for future mobile communications and wireless LAN systems there is a need for high production volume, low cost, high performance miniature microwave filters. Two existing technologies are inapplicable: SAW filters suffer from frequency limitations and MMIC active filters have poor intermodulation performance. For these reasons the authors have investigated the potential of passive integrated filters for these applications. An existing design is the engine block filter which consists of a monolithic block of ceramic with internally plated holes forming coupled coaxial transmission lines. The use of a high permittivity ceramic gives a small physical size and low loss due to the large surface area of the holes. However, as the frequency accuracy of the filter is proportional to the dimensional tolerance of the filter, tuning is necessary which increases the unit cost significantly. This paper presents a method to overcome these limitations by using a printed circuit configuration