This paper presents a family of four-port electronic circulators adhering to a new topology symmetry that enables linear, low-loss transistor-based circuit implementations. The underlying principle of operation employs a property of the 90^∘ non-reciprocal phase shifter (NRPS) derived in this article. Under quadrature excitation, the NRPS transfers or reflects exciting signals depending on their respective phase lead. The fundamental topology consists of two back-to-back quadrature hybrid couplers with a 90^∘ NRPS connected in parallel over the line of symmetry, interrupting the circuit’s reciprocity to achieve circular propagation by bypassing or reflecting at the NRPS but not through. We break down the circuit into three fundamental four-port sub-circuits. The transfer function of the cascaded sub-circuits enables an analysis with specific hybrid couplers. It also allows a synthesis of other four-port passive sub-circuits that, with an NRPS, achieve a four-port circulator transfer function by solving a matrix equation. Some of the mathematical solutions have circuit realizations, which are adjusted quadrature hybrid structures that differ from each other by the characteristic impedance of their arms. Two familiar solutions, including the standard quadrature hybrid and a modified design with equal Z_0 , λ /4 arms, are simulated utilizing lossless lumped element arms and a 4-Path, 65-nm NMOS 90^∘ NRPS. The simulation results verify the theoretical analysis and enable a comparison between the performance of the two circuit solutions around 1 GHz. The four-port circulator with equal arms is implemented on a PCB and measured, yielding better than 1.5 dB insertion loss between the circulator ports, over 17 dB port-to-port reverse isolation, and better than 20 dBr port matching around 1 GHz.

Abstract This paper presents a family of four-port electronic circulators adhering to a new topology symmetry that enables linear, low-loss transistor-based circuit implementations. The underlying principle of operation employs a property of the $$90^\circ $$ 90 ∘ non-reciprocal phase shifter (NRPS) derived in this article. Under quadrature excitation, the NRPS transfers or reflects exciting signals depending on their respective phase lead. The fundamental topology consists of two back-to-back quadrature hybrid couplers with a $$90^\circ $$ 90 ∘ NRPS connected in parallel over the line of symmetry, interrupting the circuit’s reciprocity to achieve circular propagation by bypassing or reflecting at the NRPS but not through. We break down the circuit into three fundamental four-port sub-circuits. The transfer function of the cascaded sub-circuits enables an analysis with specific hybrid couplers. It also allows a synthesis of other four-port passive sub-circuits that, with an NRPS, achieve a four-port circulator transfer function by solving a matrix equation. Some of the mathematical solutions have circuit realizations, which are adjusted quadrature hybrid structures that differ from each other by the characteristic impedance of their arms. Two familiar solutions, including the standard quadrature hybrid and a modified design with equal $$Z_0$$ Z 0 , $$\lambda /4$$ λ / 4 arms, are simulated utilizing lossless lumped element arms and a 4-Path, 65-nm NMOS $$90^\circ $$ 90 ∘ NRPS. The simulation results verify the theoretical analysis and enable a comparison between the performance of the two circuit solutions around 1 GHz. The four-port circulator with equal arms is implemented on a PCB and measured, yielding better than 1.5 dB insertion loss between the circulator ports, over 17 dB port-to-port reverse isolation, and better than 20 dBr port matching around 1 GHz.

This paper presents a family of four-port electronic circulators adhering to a new topology symmetry that enables linear, low-loss transistor-based circuit implementations. The underlying principle of operation employs a property of the [Formula: see text] non-reciprocal phase shifter (NRPS) derived in this article. Under quadrature excitation, the NRPS transfers or reflects exciting signals depending on their respective phase lead. The fundamental topology consists of two back-to-back quadrature hybrid couplers with a [Formula: see text] NRPS connected in parallel over the line of symmetry, interrupting the circuit's reciprocity to achieve circular propagation by bypassing or reflecting at the NRPS but not through. We break down the circuit into three fundamental four-port sub-circuits. The transfer function of the cascaded sub-circuits enables an analysis with specific hybrid couplers. It also allows a synthesis of other four-port passive sub-circuits that, with an NRPS, achieve a four-port circulator transfer function by solving a matrix equation. Some of the mathematical solutions have circuit realizations, which are adjusted quadrature hybrid structures that differ from each other by the characteristic impedance of their arms. Two familiar solutions, including the standard quadrature hybrid and a modified design with equal [Formula: see text], [Formula: see text] arms, are simulated utilizing lossless lumped element arms and a 4-Path, 65-nm NMOS [Formula: see text] NRPS. The simulation results verify the theoretical analysis and enable a comparison between the performance of the two circuit solutions around 1 GHz. The four-port circulator with equal arms is implemented on a PCB and measured, yielding better than 1.5 dB insertion loss between the circulator ports, over 17 dB port-to-port reverse isolation, and better than 20 dBr port matching around 1 GHz.

This work presents a 5–6 GHz full-duplex (FD) multiple-input and multiple-output (MIMO) transmitter front-end based on a quadrature balanced power amplifier (QBPA) topology and wideband digital interference cancellation. The proposed architecture benefits from low implementation complexity and is compatible with MIMO scaling with no additional hardware and power consumption penalties. The QBPA chip was fabricated in 180 nm CMOS and assembled on a four-element PCB MIMO array. The system was measured using a 320 MHz OFDM signal with 11 dB PAPR at 4 dBm TX power per element. 44 dB of combined self and cross-interference (XI) cancellation in the RF domain is demonstrated while requiring only −17 dBm of canceling signal power, along with −32 dB of TX EVM and 0.7 and 1.8 dB of TX and RX insertion losses (ILs), respectively. The standalone QBPA chip delivers $P_{\text {sat}}$ and peak PAE of >19.3 dBm and >31%, respectively, between 5 and 6 GHz.

This article presents a new four-port electronic circulating duplexer (CD) that enables similar functionality to that of a four port circulator. The proposed CD is formed by connecting a quadrature hybrid (QH) and a quasi-circulating quadrature hybrid (QCQH). We derive the S-matrix of the CD by employing Mason's rule and verify the analytical results by simulations in which the 90° NRPS of the QCQH is implemented as a behavioral 8-Path NRPS. The functionality of CD enables implementation as a simultaneous transmit-receive (STR) RF front end that includes transmit (TX), antenna (ANT), self-interference cancellation (SIC) and receive (RX) dedicated ports. Measurements of a CD with a commercial QH connected to a QCQH that employs 65-nm NMOS 4-path NRPS integrated on PCB, show a 1.6 dB TX-to-ANT, less than 2 dB ANT-SIC and 2.9 dB SIC-to-RX losses over 40MHz bandwidth. TX-RX and TX-SIC isolation are also measured showing 18 and 13.5 dB respectively. A 5 dBm modulated TX signal at 970 MHz achieved a total isolation of 55 dB with active SIC injection along with a TX EVM of −39 dB.

This article presents a new four-port electronic device – the directional quadrature hybrid isolator (DQHI). The topology of this duplexer is similar to the four-arm quadrature hybrid (QH) except for a 90° non-reciprocal phase shifter (NRPS) replacing one of the λ/4 Z 0 arms. We derive the DQHI S-parameters and show that it performs a 0°/90° power division for an incident signal at port 2 into ports 3 and 4 exactly like a QH, functions as an ideal isolator between ports 1 and 2, enables high-isolation between port 1 to ports 3 and 4 and facilitates injection of self-interference cancellation (SIC) signal from port 4 into 3. Analytic evaluation of a dual-port N-path circuit as an NRPS is performed and the theoretical impact on the DQHI performance is examined. An 8-path, 65-nm NMOS design is utilized to simulate the performance with a 1 GHz clock resulting in 1.7 dB TX-to-antenna loss, antenna-RX loss of 3 dB, SIC-to-RX loss of 6.6 dB, TX-RX and TX-SIC isolations of 26 and 12.5 dB respectively.

This article presents a new electronic device – the four-port quasi-circulating quadrature hybrid (QCQH), which combines desirable features of electronic circulators and quadrature hybrids. The QCQH comprises three quarter-wavelength transmission lines and a 90° non-reciprocal phase shifter (NRPS) and is suitable for inband full duplex applications. We derive the four-port S-parameter matrix of the QCQH and the transfer functions under termination scenarios of interest. The resulting closed-form expressions are compared with the prior art electronic circulator. A 90° transmission line and lumped transformer alternatives are considered for designing a QCQH based on a two-port N-path circuit. TX isolation and transmission expressions are derived and verified against simulations, and a new wideband leakage cancellation approach is proposed. A TSMC 65 nm CMOS N-path chip is integrated on-board with a discrete, lumped, LCL transformer implementation. TX-to-antenna insertion loss of 1.4 dB and an RX NF of 4.7 dB at the frequency of 1 GHz were measured with a primary passive TX-RX isolation of 21 dB. Total isolation of more than 50 dB for an 80 MHz OFDM WiFi TX signal employing digitally equalized active leakage cancellation was achieved along with better than −40 dB TX EVM with SIC ON.

This paper presents a quadrature balanced RF Front-End architecture with a built-in primary isolation for a single antenna Full Duplex and Time Division Duplex wireless communications. Self-interference cancellation is implemented by injecting a digitally synthesized cancellation signal into a dedicated input port that enables wideband cancellation of the leaking transmit signal at the receiver. A closed form analytical expression of the cancellation signal as a function of the channel frequency response is derived, together with a nonlinear analysis that predicts distortion fundamentals at both transmit and receive channels. Simulations at the 5-6GHz Wi-Fi band verify the theoretical results and demonstrate leakage cancellation better than 60dB for 160MHz and 320MHz channels for linear and nonlinear operation conditions.

This paper presents a quadrature balanced RF Front-End transceiver architecture and a digital self-interference cancellation (SIC) algorithm for simultaneous transmit-receive (Tx-Rx) in next generation half-duplex and full-duplex radios. Tx-Rx isolation of >57dB is measured for CW signals over 80MHz BW, and >40dB for an actual 80MHz 802.11ac OFDM signal within the 2.4GHz Wi-Fi band, along with EVM of -37dB of the Tx signal for a concurrent Tx-SIC operation. Measured Rx loss is lower than 1.8dB within the operating frequency band.

This article presents a quadrature balanced radio-frequency (RF) front-end transmitter (TX) architecture assisted by a digital self-interference cancellation (SIC) algorithm for simultaneous transmission and reception in next-generation full-duplex radios. The proposed quadrature balanced power amplifier (QBPA) topology is a four-port circuit with an embedded passive primary isolation (PI) between the antenna and the receiver (RX) low-noise amplifier (LNA), along with a very low power SIC injection mechanism that reuses the TX's gain. A transmit receive (TR) isolation of >57 dB is measured for continuous-wave (CW) signals over an 80 MHz bandwidth (BW). A TR isolation of >50 and >56 dB is demonstrated for an 80 MHz 802.1 lac orthogonal frequency-division multiplexing (OFDM) signal at 10- and 20 dB backoff from 30 drim peak TX power (P-TX,P-max), respectively, within the 2.4 GHz Wi-Fi band. A digital predistortion algorithm is applied to linearize the TX at the high output power case, achieving error vector magnitude (EVM) lower than 34.7 dB for concurrent TX-SIC operation. A simultaneous TR scenario is demonstrated, measuring an RX signal EVM of 22 dB, while P-TX,P-max = 30 dBm. Measured RX loss is lower than 1.8 dB within the operating frequency band.

This paper presents a quadrature balanced transmitter, assisted by a digital equalization and predistortion self-interference cancellation technique for Full-Duplex wireless applications. An analysis of design trade-offs between low receiver (Rx) loss and high transmitter (Tx) efficiency is laid out and demonstrated on a 5GHz to 6GHz class AB power amplifier implemented in 180nm CMOS. Wideband cancellation of >48dB and >57dB at 20dBm and 10dBm Tx output power, respectively, is measured in CW. Cancellation of >30dB for an actual 160MHz 802.11ac OFDM packet around a carrier frequency of 5.2GHz together with EVM of -33dB is demonstrated. Measured Tx power added efficiency (PAE) for concurrent Tx-SIC operation is 35% and 6.4% at peak and RMS (10dB backoff) power, respectively. Rx loss is lower than 1.6dB at RMS Tx power within the signal frequency band.

An RF front-end (RFFE) architecture for dual-mode half and full duplex operation, employing a modified quadrature balanced power amplifier (QBPA), is proposed, where the receive channel is connected to the QBPA transmit isolated output. In this RFFE, the receive signal is reconstructed from inherent output reflections of the two internal power amplifiers employed in the modified QBPA. Re-configurable transmit signal isolation at the receive port enables safe LNA operation at half-duplex and relaxed RF self-interference cancellation (SIC) requirements for full-duplex operation. The S-parameter signal flow diagram of the proposed RFFE is described and analyzed, yielding transmit-receive transfer functions of interest in the presence of antenna back-reflected transmit signal. Transmit-receive isolation compensation for antenna reflections is analytically derived. Circuit simulations of the proposed topology verify the model and theoretical analysis.

A new architecture for multi-channel carrier aggregation receivers is proposed for eliminating risks of VCO injection pulling and mitigating performance degradation resulting from Multi-Lomutual coupling. A fully integrated receiver front-end is implemented, enabling the realization of a robust multi-LO triple-carrier-aggregation system operating in the 5.2-5.8 GHz band. The RFIC demonstrates EVM better than 30dB for all three noncontiguous 80MHz channels. It is implemented in 65nm CMOS LP process and occupies a die area of 1mm 2 .

Carrier aggregation supports an increased total bandwidth, data rate and utilization of available fragmented spectrum, where the latter is a core component of next generation Wi-Fi and Cellular networks, including 5G. Wireless communications receivers with intra-band non-contiguous CA, employing conventional complex mixers and base-band circuitry, are desirable, however risks of VCO injection pulling and LO coupling may hinder adoption of simplistic parallel receive channels. Furthermore, in-band strong blockers are expected in such environment and the CA receiver should be designed to tolerate such signals. This paper introduces a scalable CA receiver architecture, enabling co-existence of multiple LO signals and respective down conversion of recentered, offset signals of flexibly spaced component carriers. The architecture presented here supports an aggregation of intra-band, inter-band and inter-standard component channels, employing conventional base-band signals, where the performance per receive channel is compatible with Legacy (single channel) performance. A flexible CA receiver demonstrating this architecture with 3 component channels is implemented in 65nm CMOS LP process and occupies a die area of 1mm2, operating at 5.2-5.8GHz.

This work presents a parallel direct-conversion and double-conversion transceiver to solve the problems of crosstalk and LO pulling in the carrier aggregation scenario. An EVM of -34.9 dB is obtained when the output power of the PA driver is 0.4 dBm. Three aggregated carriers with 80 MHz 256-QAM modulation are demonstrated. To the authors' best knowledge, this work is the first CMOS integrated transceiver for IEEE 802.11 WLAN carrier aggregation application.

Multiple antenna techniques are used to enhance wireless links and therefore have been studied extensively. Many practical systems that differ from ideal schemes have been discussed in the literature. One example is a system that lacks precise channel information at the transmitter. We evaluate analytically the performance of a multiple input multiple output (MIMO) technique that uses partial channel knowledge. Specifically, we analyze a scheme with M transmit antennas and N receive antennas, employing eigenbeamforming at the transmitter and maximal ratio combining (MRC) at the receiver, where the receiver antennas experience correlated fading. We assume that only partial channel matrix is known to the transmitter, specifically only P out of N rows of the channel matrix are known. In addition, the transmitter is endowed with knowledge of the receive channel correlations. We derive the optimal beamformer for a single stream transmission case and show that it is the principal eigenvector of the known channel submatrix and the expected value of the unknown channel submatrix given the known channel. We show that the diversity order of a transmission scheme where such a preceder is used is MP+N-P and further show that increasing the value of P by one increases the diversity order by M - 1. We also derive the array gain for this scheme. We further show that, as expected, the effect of the correlation is only an array gain reduction. All the results are supported by simulations.

Multiple antenna techniques are used to enhance wireless links and therefore have been studied extensively. Many practical systems differ from the ideal schemes discussed in the literature. One example is the lack of precise channel information at the transmitter. We evaluate analytically the performance of a beamforming technique that uses partial channel knowledge. Specifically, we analyze a suboptimal M ×N scheme employing Maximal Ratio Transmission at the transmitter and MRC at the receiver, assuming only one out of M rows of the channel matrix is known at the transmitter. We show that the diversity order and array gain of such a scheme is M+N -1. The performance of this scheme, which is supported by both Worldwide Inter-operability for Microwave Access (WiMAX) and Long Term Evolution (LTE) systems, is identical to that of an MRC system with M+N -1 antennas. All the results are supported by simulations.

The mounting evidence, that cellular radiation may adversely affect the health of its users, results in growing concern among the general public. This concern only grows as cellular technologies become an essential part of modern life (mobile e-mail, social networking, etc.). Radiating antennas in the proximity of the user, such as antennas of mobile phones are of special interest for this matter. In this paper we study the performance of a recently proposed architecture for wireless networks, aiming at minimal emission from mobile stations, without any additional radiation sources. The new architecture, dubbed Green Cellular, abandons the classical transceiver base station design and suggests the augmentation of transceiver base stations with receive only devices. These devices, dubbed Green Antennas, are not aiming at coverage extension but rather at minimizing the emission from mobile stations. We employ indoor and outdoor propagation simulation tools and field experiments to study the expected impact of the Green Cellular architecture on emission from mobile stations. Our results reveal a significant, up to 50dB, decrease in emission power and respective exposure to radiation.

In recent years, cellular technology has become very widespread, with over 4 billion users worldwide. The increase in usage has been accompanied by a growing concern related to the possible adverse effects of the cellular radiation on human health. The radiation from the cellular phone, which is in close proximity to the user, is of special interest for this matter. In this paper we propose a new handover mechanism for cellular networks, aiming at minimal emission from mobile phones. The criterion for handover in common cellular systems is based on the received downlink signal strength or signal quality. This criterion makes sense when the uplink and downlink are symmetric. However, the advent of MIMO technology changes this assumption since MIMO transmission and reception techniques may significantly alter the uplink and downlink characteristics. For example, the number of transmit antennas may differ from the number of receive antennas. Alternatively, the techniques may significantly differ, such as when the transmitter broadcasts the downlink signal whereas the receiver performs beamforming. Consequently a mobile phone may receive Cell A with best quality, whereas Cell B may receive the mobile at better quality than Cell A, and hence Cell B requires minimal emission from the mobile phone. The new handover mechanism uses this concept and chooses, among neighboring cells with sufficient downlink, the cell for which the emission from the mobile phone is minimized. This mechanism requires methods to estimate the expected uplink emission. We propose several such methods. These include procedures where cells broadcast their uplink reception capabilities or request mobiles to perform test transmissions. Finally, we discuss the application of the proposed handover mechanism to create a new bidding procedure aiming at minimal uplink transmission power and minimal exposure to radiation.

Wireless systems, which include cellular phones, have become an essential part of the modern life. However the mounting evidence that cellular radiation might adversely affect the health of its users, leads to a growing concern among authorities and the general public. Radiating antennas in the proximity of the user, such as antennas of mobile phones are of special interest for this matter. In this paper we suggest a new architecture for wireless networks, aiming at minimal emission from mobile stations, without any additional radiation sources. The new architecture, dubbed Green Cellular, abandons the classical transceiver base station design and suggests the augmentation of transceiver base stations with receive only devices. These devices, dubbed Green Antennas, are not aiming at coverage extension but rather at minimizing the emission from mobile stations. We discuss the implications of the Green Cellular architecture on 3G and 4G cellular technologies. We conclude by showing that employing the Green Cellular approach may lead to a significant decrease in the emission from mobile stations, especially in indoor scenarios. This is achieved without exposing the user to any additional radiation source.