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RF Electronics Chapter 7: RF Filters Page 273 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. In addition there are many filters available for specific IF applications, such as 5.5 MHz and 6 MHz for analogue TV sound IF, 38.9 MHz for Digital Audio Broadcasting (DAB), 44 MHz for digital TV receivers etc. Ceramic resonator filters are also used for RF filtering. The Murata Gigafil range for instance contains many different RF filters covering the 800 to 950 MHz mobile phone band and the 1.4 to 2.4 GHz mobile phone and WLAN bands. Since these ceramic filters are mass-produced, their cost is very low and it may be worthwhile to modify one's design to be able to incorporate these filters. SAW Filters The resonators considered so far have electromagnetic or acoustic resonances with the resonator being a quarter wavelength. Voltages across an input transducer on the surface of a piezo-electric substrate, causes an acoustic wave to travel along the surface of the substrate. These travelling waves then induce voltages on a second transducer, which is used as an output transducer. By correctly designing the shape of these transducers, filtering can be achieved, with independent control over both the amplitude and group delay. Surface Acoustic Wave (SAW) filters are thus normally used for analogue TV IF filters, IF filters for radars and other applications where sharp filtering is required and where the group delay must be absolutely flat. Since the input transducer generates a travelling wave in the direction of the output transducer as well as one in the opposite direction, which must be absorbed, SAW filters have a high insertion loss, typically 12 dB for devices with a centre frequency of 70 MHz and 4 dB for devices operating at 2 GHz [20]. Because of their low cost, small size and good performance, SAW filters are used in many consumer devices. The design of SAW filters is outside the scope of this book. References 1. A. I. Zverev, Handbook of Filter Synthesis, Wiley, 1967, Helical Filters pp 499-521, k and q Filter Tables, p 341, Eqn. 9.4.3 pp 517. 2. G G. Matthaei, L. Young, and E. M. T. Jones, Microwave Filters, Impedance- Matching Networks, and Coupling Structures. Boston, MA: Artech House, 1980. pp.583-650. 3. D. Pozar, Microwave Engineering , Third Edition, Wiley, 2005. pp. 416-438. 4. Kikkert C. J, "The Effect of Amplifier Distortion and Filter Type on BER of WCDMA-UMTS Mobile Radio Systems", 2 nd International Conference on Signal Processing and Communication Systems (ICSPCS 2008), Gold Coast, Australia, 15- 17 December 2008, ISBN: 978-0-9756934-6-9. 5. Mini-Circuits, Reflectionless Filters. https://www.minicircuits.com/pdfs/XHF- 23+.pdf 6. Pairing Mixers with Reflectionless Filters to Improve System performance, Mini- Circuits AN-75-007, https://www.minicircuits.com/app/AN75-007.pdf 7. Morgan M. A. and T. A. Boyd, Synthesis of a New Class of Reflectionless Filter Prototypes, National Radio Astronomy Observatory. https://arxiv.org/ftp/arxiv/ papers/1008/1008.3502.pdf 8. Microwaves 101, Reflectionless filters. https://www.microwaves101.com/ encyclopedias/reflectionless-filters 9. Temwell Corporation, http://www.temwell.com.tw/ RF Electronics: Design and Simulation 273 www.cadence.com/go/awr

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