Fabrication of Compact Microstrip Line-Based Balun-Bandpass Filter with High Common-Mode Suppression

Abstract

A new type of balun-bandpass filter was proposed based on the traditional coupled-line theory and folded open-loop ring resonators (OLRRs) configuration. For that, a new device with both filter-type and balun-type characteristics was investigated and fabricated. Both magnetic and electric coupling structures were implemented to provide high performance balun-bandpass responses. The fabricated balun-bandpass filters had a wide bandwidth more than 200 MHz and a low insertion loss less than 2.51 dB at a center frequency of 2.6 GHz. The differences between the two outputs were below 0.4 dB in magnitude and within 180 ± 7° in phase. Also, the balun-bandpass filter presented an excellent common-mode rejection ratio over 25 dB in the passband. An advanced design methodology had been adopted based on EM simulation for making these designed parameters of OLRRs, microstrip lines, and open stubs. The measured frequency responses agreed well with simulated ones.

Using Open Stubs and Tuning the Width of Output Microstrip Lines of a Balun Diplexer to Obtain the Matching Output Impendence With Rf Output Transceiver

“…4 and 5). Magnetic coupling was easily achieved when each coupled resonator's side with maximum magnetic field was placed next to the other's [8,9]. The simulation results showed that the optimum coupling space between the microstrip lines and the OLRR resonators was 0.2 mm and between the two OLRR resonators was 0.61 mm.…”

“…discriminative coupling [8,9]. The center valley of the OLRR resonators for the two different resonant frequencies had to be positioned at the proper location to obtain maximum magnetic coupling.…”

“…The center frequency of the balun BPF could easily be adjusted by changing the path length of the OLRR resonators [4]. Subsequently, we adopted an advanced design methodology to achieve a balun BPF with an excellent common-mode rejection ratio of over 25 dB in the passband by tuning the length of the open stubs [8]. We also investigated a simple, effective structure based on traditional coupled-line theory and folded OLRR resonators to design a balanced-to-unbalanced (balun) diplexer.…”

“…As mentioned above, we previously fabricated and investigated a new device with both filter-type and balun-type characteristics [8]; tuning the sizes of the open stubs and the length of the microstrip lines allowed the balanced impedance of a balun BPF to be tuned. Xue et al proposed that a stub-loaded resonator not only has an extra degree of freedom to realize the desired coupling scheme but also can reduce the circuit size and enlarge the frequency separation of the first differential and common-mode resonant frequencies.…”

Compact 30:1 Bandwidth Ratio Balun for Printed Balanced Antennas

“…Therefore, research on wideband high performance balun is meaningful for RF frond-ends. Over the past few years, much effort has been focused on this area [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16].…”