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RF Electronics Chapter 7: RF Filters Page 208 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Chapter 7 RF Filters Introduction Filters used for RF signals are nearly always Bandpass filters using coupled resonator design techniques. The basic properties of the most common types of filters are: Electrical Filters LC Bandpass Filters. Typical unloaded Q valued are 60-150, resulting in a large % Bandwidth filter with a high insertion loss. Frequency range 455 kHz to 2 GHz. Helical Filters. Typical unloaded Q values > 1000. The Q value can be increased, by increasing the size of the resonator cavity. Frequency range 30 MHz – 1 GHz. Coaxial Filters. Typical unloaded Q value > 5000. Frequency range 80 MHz – 2 GHz. Using a Ceramic dielectric results in a small size, for mobile radio use. Air dielectric coaxial filters are used for high power diplexers in Radio and TV transmitters. Microstrip and Stripline filters. Made using lines on PCB. Typical unloaded Q value 250. Wide % bandwidth. Transmission Line Filters. Designs based on Short or open circuited stubs. Wide Bandwidth. Interdigital Filters. High Q and < 10% bandwidth. Acoustic filters Ceramic filters. Commonly used frequencies only. 455 kHz, 10.7 MHz IF filters, 800 MHz and 1.9 GHz diplexers for cellular phones. Crystal Filters. Very High Q values and very low bandwidths. Typical 6 kHz Bandwidth at 10.7 MHz. Used for SSB filters. High cost compared to other filters. SAW filters. Frequencies from 40MHz to 3 GHz. Relatively high insertion loss. The amplitude response and group delay can be controlled independently. Several of the above filter types are discussed in detail in these notes. Filter Design Revision For this chapter, it is assumed that the reader knows about basic filter requirements and the resulting specifications of filtering characteristics if required, please refer to filter design texts, such as Zverev[1]. Most RF filter designs start with a normalised lowpass filter design and that filter has the required specifications in terms of filter order required, amplitude and group delay performance. This normalised lowpass filter is then transformed into the appropriate bandpass filter. There are two starting points: 1 Normalised LC filter tables or equations 2 K and Q filter tables. RF Electronics: Design and Simulation 208 www.cadence.com/go/awr