Compact Mixed-Cross Coupled Bandpass Filter With Enhanced Frequency Selectivity

Abstract

In this paper, a compact three-order mixed-cross coupled bandpass filter (BPF) with enhanced frequency selectivity is proposed. Multiple transmission zeros (TZs) can be obtained near the passband for high frequency selectivity by introducing mixed-cross coupling between the nonadjacent resonators. The frequency-dependent mixedcross coupling matrix of the proposed filter is presented to explain the occurrence of the TZs caused by mixed-cross coupling. A new BPF centered at 2.7 GHz with 11.5% fractional bandwidth has been designed and fabricated to verify the validity of the proposed method. The measurement result shows four finite TZs in the stopband, located at 1.74 GHz with 52.16 dB rejection, 2.53 GHz with 24.67 dB rejection, 3.83 GHz with 47.52 dB rejection, and 7.75 GHz with 54.83 dB rejection, respectively. The circuit only occupies 6.2×7.6 mm 2 .

Design of Miniaturized Bandpass Filters Using Quasi-Lumped Multilayer Resonators

“…In order to reduce the footprint of the¯lter, the multilayer implementations [6][7][8][9][10][11][12][13] have been considered. In this approach, the¯lter components are positioned in a 3D structure so the overall occupied area is reduced compared with the single layer approach.…”

“…However, in those cases higher-order¯lters are usually required to achieve¯lter speci¯cations. The patch-via-spiral resonators [9][10][11] have been used to further reduce the footprint. Patch-via-spiral resonators are usually implemented with two types of feeders: tapped-line feeder and capacitively coupled feeder.…”

“…In order to obtain a better selectivity, higher order¯lters and/or cross coupling is necessary. 11 In our earlier research 14,15 we have proposed and implemented a compact multilayer bandpass¯lter with resonators comprised of quasi-lumped elements. Capacitive coupling between the feeder and the resonator has been proposed.…”

Novel Compact Tri-Band Bandpass Filter Using Multi-Stub-Loaded Resonator

“…In [1][2][3], miniaturized BPFs with high selectivity and enhanced out-of-band performance are designed for wireless communication systems. In recent years, with the development of different wireless standards, such as global system for mobile communication (GSM), wireless local-area network (WLAN) and world interoperability for microwave access (WiMAX), designing multi-band BPFs with miniaturized size, high selectivity and controllable frequencies has become a trend.…”