Miniaturized differential bandpass filter with improved common-mode suppression for healthcare facilities

Compact differential bandpass filters (BPFs) using coupled ring resonators are investigated in this work. Good differential-mode (DM) filtering performances, improved common-mode (CM) suppression, and miniaturized size are obtained and discussed. Two BPFs named Filter A and Filter B are presented and analyzed to validate the theory, respectively. Compared with Filter A, Filter B shows much improved CM rejection due to the loaded open circuited stubs. In addition, both Filter A and Filter B exhibit more than 85% size reduction by reconstructing the ring resonators scientifically. Simulated and measured results show good agreement in low insertion loss, better than 15 dB return loss, more than 20 dB CM suppression of Filter A and 40 dB of Filter B. These advantages are much required in healthcare facilities.