The AT22D filter represents a low frequency design for ceramic technology with the 5 section bandpass design having a centre frequency of 390 MHz and features 6 mm resonators. The pass band is 30 MHz with a rejection of 40 dB at 300 MHz and 480 MHz and the insertion loss is 2.5dB maximum.
Ceramic filters are made from high-dielectric constant ceramic resonators plus a capacitive coupling network to realise an “n” section cavity filter. The AT22D features 5 resonators, however the number of resonators can vary from 2 to 8 or more — dependent upon the required filter response.
Applications for this particular design could be related to any TETRA radio system requirement. However, given the wide frequency range over which these filters can be designed, applications can include, cellular, PMR, avionics or defence, to name a few.
Ceramic filters are less expensive and smaller than either LC or cavity type filters. Typically available with a bandpass response, they are also available in “notch” or band reject configurations. In addition ceramic designs can be configured as duplexers for transmit/receive applications.
Monoblock ceramic filters, formed from a single block of ceramic material are also available. This design of ceramic filter does not have a printed circuit board to secure their elements together, the entire block being surface mounted directly onto the circuit board.