Abstract
In this article, a wideband quasi-circulator (QC) with the low noise figure (NF) and high 1-dB compression point ( P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 dB</sub> ) is proposed. The slotline-based 180° hybrid is introduced to achieve the wideband high transmitter-receiver (TX-RX) isolation. Meanwhile, the bidirectional in-phase stage and the nonreciprocal out-of-phase stage are utilized to obtain specific power-split ratios for the low insertion loss and high antenna-transmitter (ANT-TX) isolation. By using the unequal power split, the proposed QC is without the fundamental 3-dB loss seen in reciprocal ANT interfaces. Besides, to further enhance the TX-RX isolation within a wideband, a reconfigurable inter-stage matching network based on a varactor-tuned capacitor is implemented. To verify the mechanisms mentioned above, a reconfigurable wideband QC operating at 1.75-2.9 GHz is implemented and fabricated. The total power consumption is 224 mW. The measurement exhibits in-band TX-RX isolation of 27-58 dB. The TX-ANT and ANT-RX insertion losses are 4.3-5.0 dB and 1.0-1.9 dB, respectively. The QC also achieves the minimum in-band ANT-RX NF of 3.4 dB. Meanwhile, the measured TX-ANT and ANT-RX IIP3s are 39.4 and 32.5 dBm, respectively. The TX input P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 dB</sub> is greater than 28.78 dBm, while the RX input P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 dB</sub> is 23 dBm. The TX-induced ANT-RX P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1 dB</sub> is measured to be 28 dBm.
Highlights
W ITH the ever-increasing demand for high data rates in modern wireless communications, there are urgent requirements of wireless channels with large capacity and high spectral efficiency in recent years
To the authors’ best knowledge, it is the first time that the QC uses the unequal power split without additional modulated signals to omit the fundamental 3-dB loss seen in reciprocal ANT interfaces, while achieves low noise figure (NF) and high P1 dB
It is worth pointing out that the more power transmit to the RX path1, the larger gain of the outof-phase stage is required to obtain the high ANT-TX isolation, which leads to lower RX NF
Summary
W ITH the ever-increasing demand for high data rates in modern wireless communications, there are urgent requirements of wireless channels with large capacity and high spectral efficiency in recent years. A tunable QC using the compact fully reconfigurable 180◦ hybrid and amplifier stages is proposed to improve the isolation performance [25] Such a combined-type of QC suffers from the fundamental 3-dB path loss introduced by the reciprocal passive devices, while the operation frequency range still needs to be further expanded. A wideband QC with the low RX NF and high 1-dB compression point (P1 dB) is proposed in our conference article [26] Such QC utilizes a nonreciprocal network connecting to a 180◦ hybrid to achieve the ANT-TX reverse isolation instead of using an amplifier. To the authors’ best knowledge, it is the first time that the QC uses the unequal power split without additional modulated signals to omit the fundamental 3-dB loss seen in reciprocal ANT interfaces, while achieves low NF and high P1 dB.
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