An Artificial Coupled Line with Common-Mode Rejection and Its Applications
Date Issued
2012
Date
2012
Author(s)
Tsai, Chung-Hao
Abstract
An artificial coupled-line with broadband even-mode rejection is proposed based on the concept of transmission line metamaterial. It is composed of a pair of coupled lines and a ground plane backed by mushroom structures and called mushroom-backed coupled-line (MBCL). Its equivalent circuit model is established to explain wave propagation property. Based on odd and even mode analyses, the proposed coupled-line behaves like a quasi-TEM transmission line for odd-mode excitation while it possesses a wide stopband for even-mode excitation.
Based on the proposed MBCL, a common mode filter and a passive balun are designed with a compact size and broadband operation. Both structures are realized on the LTCC technology. For the common-mode filter with four unit cells, its size is 0.16 ⼔4;g × 0.26 ⼔4;g corresponding to a real size of 3.2 mm × 5.12 mm. The filter shows over 10 dB reduction for common-mode noise from 3.8 GHz to 7.1 GHz in frequency domain and over 50% suppression for voltage amplitude in time domain. Moreover, a common-mode filter is designed based on a unit-cell equivalent circuit model with two transmission zeros for common mode. The structure is compact and can be designed for surface mounted devices.
As for the broadband balun, a new concept is presented to design it. The realized balun exhibits good amplitude imbalance of less than 0.3 dB and phase imbalance of 179 ± 3°with the return loss greater than 10 dB from 3.3 to 7.1 GHz. Its electrical size is only 0.063 × 0.44 λg2. Furthermore, a compact balun with a fractional bandwidth of 40 % is realized. It can be designed for arbitrary real impedance transformation ratio and its electrical size is only 0.088 λg × 0.078 λg.
Subjects
Low temperature co-fired ceramic (LTCC)
Coupled-line
Common mode choke
Common-mode noise
Balun
System-in-Package (SiP)
Type
thesis
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