Summary
International Symposium on Antennas and Propagation
2010
Session Number:4FD3
Session:
Number:4FD3-4
Microstrip Balanced Filter with Common-Mode Transmission Zero
Jin Shi, Quan Xue,
pp.-
Publication Date:2010/11/23
Online ISSN:2188-5079
Summary:
Balanced bandpass filter has become the basic component of the balanced systems, because it can provide the differential-mode bandpass and suppress the common-mode noise at the same time. Therefore, a well-designed balanced filter should possess high common-mode suppression, excellent out-of-band rejection and high selectivity. However, previous reported works [1-3] of the balanced filters are rather limited. One may only achieve a balanced filter with either an extended stopband [2] or common-mode suppression [3]. In [4], using multisection resonator, the stopband is extended up to the fifth harmonic. At the same time, the common-mode rejection ration (CMRR) achieves 46 dB. However, the previous methods can only suppress the common-mode signal outside of the differential-mode passband. As far as we know that no way has been used to reduce the common-mode signal inside the differential-mode passband. In this paper, the common-mode transmission zero is proposed to improve the common-mode suppression inside the differential-mode passband. It is realized by the source-load coupling. A two-order balanced bandpass filter demonstrates the controllability of the common-mode transmission zero. To extend the stopband while keeping the high common-mode suppression, resistor-loaded resonator is adopted to absorb the common-mode signal outside of the differential-mode passband. Therefore, a four-order filter using two resistor-loaded SIRs and two resistor-loaded UIRs is designed and fabricated. As a result, a balanced filter with high common-mode suppression, wide differential-and common-mode stopbands and good selectivity may be realized.