Periodically Nonuniform Coupled Microstrip Lines with Equalized Even- and Odd-Mode Velocities for Harmonic Suppression in Filter Design

Sheng SUN
Lei ZHU

Publication
IEICE TRANSACTIONS on Communications   Vol.E88-B    No.6    pp.2377-2382
Publication Date: 2005/06/01
Online ISSN: 
DOI: 10.1093/ietcom/e88-b.6.2377
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on 2004 International Symposium on Antennas and Propagation)
Category: 
Keyword: 
coupled microstrip line,  periodic structure,  bandpass filter,  even- and odd-mode,  transmission zero,  

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Summary: 
Periodically nonuniform coupled microstrip line (PNC-ML) loaded with transverse slits is characterized using the fullwave method of moments and short-open calibration technique. Guided-wave characteristics of both even- and odd-modes are thoroughly investigated in terms of two extracted per-unit-length transmission parameters, i.e., phase constants and characteristic impedances. As such, frequency-dependent coupling between the lines of the finite-extended PNCML is exposed via two dissimilar impedances. Meanwhile, two phase constants try to be equalized at a certain frequency by properly adjusting the slit depth and periodicity, aiming at realizing the transmission zero. Further, equivalent J-inverter network parameters of this finite-length PNCML are derived to reveal the relationship between the transmission zero and harmonic resonance. By allocating this zero to the frequency twice the fundamental passband, one-stage and two-stage PNCML filters are then designed, fabricated and measured to showcase the advantageous capacity of the proposed technique in harmonic suppression.