electronics Article Magnetic-Free Nonreciprocal Multifunction Device Based on Switched Delay Lines Fengchuan Wu, Yuejun Zheng and Yunqi Fu * National University of Defense Technology, Changsha 410073, China * Correspondence: [email protected] Received: 10 July 2019; Accepted: 1 August 2019; Published: 3 August 2019 Abstract: A magnetic-free multifunction nonreciprocal device based on switched delay lines (SDLs) has been proposed in this paper. It is constructed with two double balanced gyrators (DBGs) and four baluns, each pair of differential ports of the balun connect the ports at the same orientation of the two DBGs, respectively. Due to the asymmetry of the clock control signals acting on the switches, the time reversal symmetry of the transmission line between the Gilbert quad-switch-sets (GQSS) can be broken to achieve non-reciprocity. It can be used as a circulator, gyrator, or isolator by setting different control signals. The device has infinite working bandwidth in theory based on the SDLs. Common mode interference can be better suppressed by using differential transmission structures. Moreover, power capacity can be improved compared to the previous work. Then, experiments have been done to verify the device as a circulator. Broadband property and the anti-interference property have been verified. Keywords: anti-interference; circulator; gyrator; isolator; magnetic-free; multifunction; nonreciprocal; power capacity; switched delay lines; ultra-broadband 1. Introduction In the future, wireless cellular network communication and WIFI will be further improved, the integrated full-duplex system is expected to improve the channel capacity or communication speed of wireless cellular networks and WIFI. Circulator and isolator, as full-duplex or decoupling devices between transmitter and receiver, to avoid self-interference, play an irreplaceable role in duplex communication systems. The main feature of circulators and isolators are their nonreciprocity. Conventional nonreciprocal devices usually use magnetic materials such as ferrites [1,2] to achieve non-reciprocal property. However, the ferrite-based nonreciprocal devices are quite bulky and difficult to be integrated, which limits its further miniaturization. Moreover, non-reciprocal is exceptionally strong in structures with near-zero parameters, which is expected to be used to design nonreciprocal devices [3,4]. However, it has not been fully carried out and explored. So, several magnetic-free devices have been proposed to realize integration of nonreciprocal devices [5–17]. For magnetic-free nonreciprocal devices, there are several ways to realize them. Reciprocity can be broken with active transistors, either in discrete circuits or integrated circuits [5,6]. However, the use of active transistors severely limits the linearity and noise performance. Reciprocity can also be broken using nonlinearities [7]. However, nonlinear devices typically exhibit non-reciprocity over a limited range of signal powers, and have limited bandwidth, precluding their application in scenarios where linearity to the desired signal is required. Parametrically modulated coupled-resonator loops have been proposed to construct the magnetic-free circulators with subwavelength dimensions [8,9]. However, they will produce intermodulation and harmonic products, and the working bandwidth is limited. At microwave frequencies, permittivity modulation is typically achieved using varactors that exhibit a limited maximum-to-minimum capacitance ratio ranging from 2 to 4, thus leading to large devices. Electronics 2019, 8, 862; doi:10.3390/electronics8080862 www.mdpi.com/journal/electronics Electronics 20192019,, 88,, 862x FOR PEER REVIEW 22 of of 1213 time varying transmission lines (TVTL) to construct magnetic-free nonreciprocal devices [8], where Shihanthe distributed Qin et al.capacitive proposed mixers the time are used varying to the transmission TVTL. 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Also, the bandwidthIn this paper, of the a frequencymagnetic-free conversion nonreciprocal isolator ismultifunction limited. device, which can be used as a circulator,In this paper,gyrator, a magnetic-freeor isolator by nonreciprocal changing the multifunction clock control device, sign whichals, is can proposed. be used asBesides, a circulator, the gyrator,anti-interference or isolator performance by changing and the po clockwer capacity control signals, of the device is proposed. can be improved Besides, the at the anti-interference same time by performanceusing differential and powertransmission capacity line of thesegments. device canIt also be improvedhas infinite at working the same bandwidth time by using in theory. differential The transmissionproperties mentioned line segments. above It can also be has realized infinite at working the same bandwidth time in this in theory.work. This The paper properties is organized mentioned as abovefollows: can be realized at the same time in this work. This paper is organized as follows: Section2 2introduces introduces the the principle principle of the of magnetic-free the magnetic-free nonreciprocal nonreciprocal device asdevice a gyrator, as a circulator, gyrator, andcirculator, isolator. and Section isolator.3 presents Section 3 the presents simulation the simulation verification verification of the device of the as device a circulator as a circulator and isolator, and andisolator, theanti-interference and the anti-interference performance performance of the device of th ise also device verified. is also Section verified.4 presents Section the 4 presents experiment the ofexperiment the device of as the a circulator.device as a Finally, circulator. a conclusion Finally, a is conclusion made in Section is made5. in Section 5. 2. Principle of the Device 2. Principle of the Device The schematic of the proposed device is shown in Figure1, which consists of two DBGs and four The schematic of the proposed device is shown in Figure 1, which consists of two DBGs and baluns. Each pair of differential ports of the balun connect the ports at the same orientation of the two four baluns. Each pair of differential ports of the balun connect the ports at the same orientation of DBGs, respectively. The GQSS in the DBG are controlled by the clock signals. The switch keeps on (off) the two DBGs, respectively. The GQSS in the DBG are controlled by the clock signals. The switch when at a high (low) level of the control signal acting on the switches. keeps on (off) when at a high (low) level of the control signal acting on the switches. S1(t) S3(t) S2(t) Z0,Td=Ts/4 S4(t) Balun Balun 1 S2(t) Z0,Td=Ts/4 S4(t) 3 S1(t) S3(t) S1(t) S3(t) Z0,Td=Ts/4 S2(t) S4(t) Balun Balun 2 2 4 S (t) Z0,Td=Ts/4 S4(t) S1(t) S3(t) S1(t) S2(t) S3(t) S4(t) Ts/4 Figure 1. Schematic of the proposed magnetic-free device. Figure 1. Schematic of the proposed magnetic-free device. 2.1. Gyrator 2.1. Gyrator For the gyrator, keeping the clock control signal is shown in Figure1. Regard port 1(2) and port 3(4) asFor port the 1 gyrator,+