Design of Multi-band Microwave Branch-line Couplers with Size Reduction
Date Issued
2011
Date
2011
Author(s)
Lin, Yuan-Li
Abstract
The thesis aims at the realization and improvement of compact multi-band branch-line couplers using lumped elements. The first part designs a dual-band branch-line coupler by substituting the λ/4 transmission lines in the conventional coupler with dual-band lumped circuits. The second part designs a tri-band branch-line coupler with conventional transmission lines and LC resonators.
In the first part, the conventional transmission lines are substituted by the dual-band transmission models with the phase reversion characteristics before and after resonance which are equivalent to the low-pass and high-pass lumped models, respectively. With compact lumped elements realized in integrated passive device (IPD) technology, the coupler achieves dual-band characteristic and size reduction at the same time.
The second part, the series circuits composed by LC shunt resonators and open stubs are shunted at each end of the transmission lines to adjust for 90º phase. Based on this concept, the coupler is realized by using the conventional transmission lines for the branches and the shunted series circuits. Because of the limit of the electric length and impedance of the transmission line, the tri bands of the coupler will be equally spaced. For three arbitrary frequencies, the stepped-impedance transmission line is introduced. With the flexible phase and impedance responses of the stepped-impedance section and the slow-wave effect contributed by the open stubs and the resonance of the LC shunt resonators, the tri-band branch-line coupler with arbitrary operating frequencies is realized. Besides, because of using the stepped-impedance section, the circuit area of this design is smaller than the one using the uniform-impedance one.
Subjects
Branch-line coupler
dual-band
lumped elements
IPD (Integrated Passive Device)
tri-band
Type
thesis
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