Miniature stubs‐loaded square open‐loop bandpass filter with asymmetrical feeders

Abstract

AbstractA miniaturized microstrip stubs‐loaded square open‐loop bandpass filter (BPF) with asymmetrical feeder lines is proposed.Using this filter structure, the improved out‐of‐band rejection characteristics and higher transmission zero can be possible. The filter is based on a combination of electric and magnetic couplings in the central open‐gaps of the square loop resonators. Hence, the combined couplings generate an electromagnetic (EM) flux between the two square open‐loop resonators. The maximum coupling can be obtained by adjusting the open‐loop gap, mounting the two open‐loop resonators spacing, and the orientation of loaded‐stubs inside the loop resonators. The asymmetrical port terminals also help to couple EM energy by maintaining 50 Ω impedance matching with input/output devices. The open‐gap between the two loops of the filter structure strongly prohibit to flow DC current and out band signals. In this article, the presented BPF generates 5.85 GHz resonant frequency. The insertion loss (S21) was measured as −1.6 dB, and the return loss (S11) was −24.8 dB. The simulated predictions are quite agreed with the measurement results. The proposed filter can be implemented in the RFID systems. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:329–332, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27318