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趙士傑 2011/07/21

Design of Highly Selective Microstrip Bandpass Filters with a Single Pair of Attenuation Poles at Finite Frequencies. 趙士傑 2011/07/21. Ref: J. Hong and M. J. Lancaster, IEEE Trans. Microwave Theory and Tech., vol. 48, no. 7 , pp. 1098-1107, 2000. Introduction.

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趙士傑 2011/07/21

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  1. Design of Highly Selective MicrostripBandpassFilters with a Single Pair of Attenuation Poles at Finite Frequencies 趙士傑 2011/07/21 Ref: J. Hong and M. J. Lancaster, IEEE Trans. Microwave Theory and Tech., vol. 48, no. 7, pp. 1098-1107, 2000.

  2. Introduction • Narrow-band RF/microwave bandpass filters with high selectivity and low insertion loss are highly demand • One filter with these attractive characteristics is that of quasi-elliptic function response filters with a pair of attenuation poles at finite frequencies • The capability of placing attenuation poles near the cutoff frequencies of the passband improves the selectivity using less resonators

  3. Introduction (cont.) • This type of filter is usually realized using waveguide cavities or dielectric-resonator-loaded cavities • Two technical approaches are normally used to realize this type of filter • The first is to extract poles from both ends of a filter prototype by using shunt resonators • The second approach is to introduce a cross coupling between a pair of nonadjacent resonators (more attractive)

  4. Filter Characteristics • Transfer function : normalized to the passband cutoff freq. frequency attenuation poles

  5. Filter Characteristics (cont.) • Frequency mapping of bandpass filter • The locations of two finite frequency attenuation poles of the bandpassfilter

  6. Chebyshevfilter vs. the Proposed filter

  7. Configurations of MicrostripBandpass Filters

  8. General Coupling Structure for This Class of Filters • It is essential that the sign of cross coupling Mm-1,m+2 opposite to that of Mm,m+1 in order to realize a pair of attenuation poles at finite frequencies, where m=N/2 with N being the degree of the filter • Mm-1,m+2:Electric coupling • Mm,m+1 :Magnetic coupling Out of phase!

  9. Low-pass Prototype for the Filter Synthesis J: Admittance inverter

  10. Design Technique

  11. Design Technique (cont.)

  12. Comparison of Specified Filter Responses

  13. Six-Pole Filter Design Example • Center frequency 955 MHz; • Fractional bandwidth FBW 7.331%; • 40-dB rejection bandwidth 105 MHz; • Passband return loss 20 dB.

  14. Full-wave EM Simulations All resonators have a line width of 1.5 mm and a size of 16 mm x16 mm on the substrate with a relative dielectric constant of 10.8 and a thickness of 1.27 mm

  15. Full-wave EM Simulations (cont.)

  16. Full-wave EM Simulations (cont.)

  17. Fabricated Six-pole MicrostripBandpassfilter Theoretical response

  18. Measured Performance of the Six-pole Microstrip Filter Insertion loss=2 dB

  19. Conclusion • The design of a class of selective microstripbandpassfilters that exhibit a single pair of attenuation poles at finite frequencies has been presented • This class of filters is able to improve the selectivity while maintaining a lower insertion loss • The use of microstripopen-loop resonators not only allows the cross coupling to be realized, but also makes the filters compact • Apractical design technique, including the tabulated design data and formulas for accurate and fast filter synthesis has introduced

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