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Part of designing an evanescent-mode waveguide filter is to employ effective launchers. Figure 6 illustrates two types of coaxial launchers. Launchers can be coaxial types, propagating waveguide types, and microstrip-to-evanescent waveguide transformers.

6. These diagrams show (a) a magnetic-loop RF launcher and (b) an electric-field-probe RF launcher.

The resistance of an evanescent-mode waveguide filter can be calculated by applying Eq. 35 from ref. 3; it can also be found by experimental methods. To tune the launcher, the probe or the magnetic loop can be moved closer to or further from the first resonator on the filter. An evanescent-mode waveguide filter is a unique type of filter that provides high Q in a relatively small size compared to other types of filters. By using the design methods shown here, reasonable results can be achieved without the long times required for iterative methods.

Dr. John Howard, President

Steve Jalil, Wireless Engineer

Electromagnetic Technologies Industries, Inc., 50 Intervale Rd., Boonton, NJ 07005; (973) 379-1719, FAX: (973) 379-1651.

Acknowledgment

The authors would like to express their thanks to Mr. Sertac Sayin for his helpful comments on the subject.

References

1. John Howard and M. Lavey, “Simplified Method Eases The Design Of Bandpass Filters,” Microwaves & RF, Vol. 39, No, 13, December 2000, pp. 97, 98, 230, 232.

2. G. Craven and C. Mok, “The Design of Evanescent Waveguide Bandpass Filter for a Prescribed Insertion Loss Characteristic,” IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-19, March 1971.

3. John Howard and W. Lin, “Evanescent Mode Filter: Design and Implementation,” Microwave Journal, Vol. 32, October 1983, pp. 121-136.

4. Richard V. Snyder, “New Applications of Evanescent Mode Waveguide Filter Design,” IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-25, December 1977.

5. Seymour B. Cohn, “Direct Coupled Resonator Filters,” Proceedings of the IRE, Vol. MTT-5, February 1957, pp. 187-196.

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