TX-RX Isolation Research Articles

The design and decoupling of TX/RX antenna with omnidirectional conical beam operating at V band

Abstract In this work, a high isolation transmitter–receiver antenna with omnidirectional conical beam operating at 61.5 GHz is presented. The proposed dual-antenna system consists of a transmitter (TX) antenna and a receiver (RX) antenna with the same structure, composed of a circular metal patch with ring slot and metal shorting vias, fed by a coaxial probe at their respective geometric center. And both antennas are placed on a circular metal platform, positioned symmetrically with each other. To increase the isolation between them, three different decoupling methods are proposed, and the one with an electromagnetic band gap (EBG) structure added in-between shows the most promising decoupling effect, as the surface wave current can be maximally suppressed. The overall size of the antenna system is 2.2552 × π × 0.579 λ 0 3, where λ 0 is the free space wavelength at 61.5 GHz. A prototype of the proposed antenna system with EBG decoupling structure is fabricated and measured, demonstrating that the TX–RX isolation is 57.9 dB at 61.5 GHz, 21.6 dB better than that without decoupling structure, with omnidirectional conical beam radiation achieved at the same time.

A Co-Linearly Polarized Shared Radiator-Based Full-Duplex Antenna With High Tx-Rx Isolation Using vias and Stub Resonator

In this paper, a co-linearly polarized shared radiator (SR) based in-band full-duplex (FD) microstrip antenna with high Tx-Rx isolation is proposed. The Tx and Rx terminals of the proposed FD antenna are designed on a single patch, where a series of vias are loaded in the central line of the patch followed by two L-shaped stubs at either end, which leads to high Tx-Rx isolation (≈60 dB). The via loading makes the Tx and Rx antennas individually operate in TM0,1/2 mode. The proposed SR-FD antenna demonstrates Tx-Rx isolation of 60.8 dB at 5.9 GHz operating frequency. Both Tx and Rx terminals of the FD antenna exhibit identical radiation property with peak realized gain of 6.65 dBi and co-to-cross polarization isolation >18 dB. The working mechanism of the proposed FD antenna is explained by both EM and circuit simulation, as well as verified with measurements on the fabricated prototype. The proposed SR-FD antenna has the merits of being planar, reduced footprint, simple feeding mechanism, and desired isolation bandwidth for IEEE 802.11p which renders it suitable for V2X-ITS application.

Decoupling Network for Closely Spaced Tx/Rx Antennas Using a Directional Coupler and Transmission Lines

This paper presents an efficient decoupling network using a single directional coupler and transmission lines for closely spaced Tx/Rx antennas in single polarized radar applications. The isolation between both antennas can be enhanced by controlling the phase of the Tx leakage signal and the coupling coefficient of the directional coupler. Its structure provides no loss of Tx/Rx paths excepting minute loss due to the coupling of the directional coupler. The Tx leakage is more insensitive to the antenna impedance variation compared with a conventional monostatic system. The design process is as follows: First, closely separated Tx/Rx antennas were designed and their isolation ( I a ) was extracted. Second, the directional coupler was designed with its coupling coefficient = I a . Finally, both were connected by transmission lines, of which phases were adjusted for the coupled and antenna-isolated signals with 180° phase difference. The Tx/Rx antennas without and with the decoupling network have 15-dB bandwidths of 23.98–24.43/23.98–24.50 GHz and 23.80–24.36/23.80–24.45 GHz, respectively. Gains of 8.17/8.39 and 8.72/8.73 dBi and efficiencies of 60.56%/60.77% and 63.0%/61.8% in the Tx/Rx antennas without and with the decoupling network were achieved at 24.1 GHz, respectively. The dimension of the proposed antenna is 1.62λ0 × 2.09λ0 × 0.0204λ0. The K-band antennas show a good Tx-Rx isolation of 29.3–67.9 dB which was superior at least 9 dB to the conventional antennas.

A 140-GHz FMCW TX/RX-Antenna-Sharing Transceiver With Low-Inherent-Loss Duplexing and Adaptive Self-Interference Cancellation

This article presents a 140-GHz frequency-modulated continuous-wave (FMCW) radar transceiver featuring transmit/receive (TX/RX) antenna sharing that address a TX/RX beam misalignment problem when large-aperture lenses/mirrors/reflectarrays are used for pencil beam forming. A full-duplexing technique based on circular polarization and geometrical symmetry is applied to mitigate the 3 dB + 3 dB insertion loss inherent to conventionally adopted directional couplers, while still maintaining high TX-to-RX isolation. In addition, a self-adaptive self-interference cancellation (SIC) is implemented to suppress extra leakage due to antenna mismatch from a desired frontside radiation scheme. The TX/RX antenna sharing enables the pairing with a large 3-D printed planar lens and boosts the measured effective isotropic radiated power (EIRP) to 25.2 dBm. The measured total radiated power and minimum single-sideband noise figure (SSB NF) including antenna and duplexer losses are 6.2 dBm and 20.2 dB, respectively. The measured total TX-RX isolation is 33.3 dB under 14-GHz wide FMCW chirps. Based on a 65-nm complimentary metal–oxide–semiconductor (CMOS) technology, the chip has a die area of 3.1 mm2 and consumes 405 mW of dc power. Among all reported sub-THz transceivers with TX/RX antenna sharing, this work demonstrates the highest total radiated power and is the only work that has >30 dB of TX-RX isolation while mitigating the inherent 6 dB coupler loss.

A Colinearly Polarized Full-Duplex Antenna With Extremely High Tx–Rx Isolation

In this letter, we present a colinearly polarized in-band full-duplex (FD) microstrip antenna system with passive self-interference cancelation achieved from extremely high interport isolation. The proposed FD antenna achieves this isolation enhancement without the use of any circulator, hybrid or complex feed-network, by adopting a novel combination of: 1) field-confinement near individual antennas due to metallic vias, and 2) U-shaped slots etched from the ground plane. The proposed FD antenna demonstrates interport isolation values of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;\!\!54$</tex-math></inline-formula> dB over the operating band of 5850–5945 MHz (IEEE 802.11p band for V2X-ITS) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\approx \!\!90$</tex-math></inline-formula> dB at 5.9 GHz, along with broadside gain of 5.63 dBi and X-pol level less than 20 dB. The design procedure of the proposed planar FD antenna is explained and verified by CST-MWS full-wave simulations along with experimental results on fabricated antenna prototype.

A Portable 5.8 GHz Dual Circularly Polarized Interferometric Radar Sensor for Short-Range Motion Sensing

The conventional short-range interferometric radar sensors usually employ two separate transmitting (TX) and receiving (RX) antennas for improved TX–RX isolation. However, they are subject to increased system size and misalignment of the TX/RX radiation patterns. In this article, a portable 5.8 GHz dual circularly polarized (CP) interferometric radar sensor is presented, which leverages the proposed dual CP common-aperture antenna that reduces the size of the entire radar system. The common-aperture nature gets rid of the radiation pattern misalignment and ensures that the object can be in the optimal boresight direction. Cross polarization, i.e., right-hand CP (RHCP) for TX and left-hand CP (LHCP) for RX or vice versa, was employed based on the sequentially rotated array (SRA), which not only improves the TX–RX isolation but also adapts with the polarization change in radar sensing. Moreover, a near-field cancellation technique was proposed to further increase the TX–RX isolation in the small form factor. A portable 5.8 GHz radar sensor integrated with the proposed dual CP antenna was custom-designed. Compared to the conventional two-antenna architecture, the proposed radar sensor is reduced in size by 140% but can still achieve a high TX–RX isolation of >60 dB at 5.8 GHz. Experiments were carried and the results illustrate that the proposed radar sensor has high micrometer accuracy in detecting the predefined displacement motions and is able to precisely track the human vital signs in the office environment.

Design and Analysis of an Electrical Balance Duplexer With Independent and Concurrent Dual-Band TX-RX Isolation

An electrical balance duplexer (EBD) supports dual-band TX-RX isolation enabling frequency-division duplexing (FDD) operation at 5-7 GHz for Wi-Fi 6/6E. A programmable balance network in the EBD can balance the antenna impedance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Z_{\text {ANT}}$ </tex-math></inline-formula> ) in the TX channel and RX channel independently and simultaneously. An on-chip passive bandstop filter as a part of the balance network is implemented, achieving sub-2-dB passband insertion loss (IL) and >20-dB stopband rejection with 10% frequency spacing. This filter separates two impedance tuners in the balance network and enables the independent tunability at two bands. A comprehensive and rigorous analysis of general <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCR</i> two-ports shows the limit of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$s_{21}$ </tex-math></inline-formula> frequency selectivity when built with finite- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> elements. The analysis guides the filter design, which guarantees the maximum frequency selectivity. The analysis is then extended to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCR</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${N}$ </tex-math></inline-formula> -ports as the complete analysis. The EBD provides >40-dB isolation in an 80-MHz channel bandwidth in the TX band (5-6 GHz), for any <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Z_{\text {ANT}}(f_{\text {TX}})$ </tex-math></inline-formula> within VSWR = 2, and independently in the RX band (6-7 GHz) when <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{\text {ANT}}&lt; 4.3$ </tex-math></inline-formula> . The EBD is designed for ≤4-dB RX IL and ≤3.8-dB TX IL, and it supports +29-dBm TX output. The EBD is implemented in Towerjazz 65-nm RF silicon-on-insulator (SOI) CMOS technology and occupies an area of 2.3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Analysis and Design of Quasi-Circulating Quadrature Hybrid for Full-Duplex Wireless

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.

Stacked patch antenna with wider impedance bandwidth and high interport isolation for 2.4 GHz IBFD transceiver

AbstractThis paper reports a bi-port, wideband, parasitic-fed, single/shared patch antenna with enhanced interport isolation for 2.4 GHz in-band full duplex (IBFD) applications. The employed parasitic feeding provides comparatively the wider impedance bandwidth and better gain for the presented antenna. The improved self-interference cancellation (SIC) levels across the required bandwidth are obtained through differentially-driven receive (Rx) mode operation. The differential Rx operation performs effective cancellation of in-band self-interference (SI) through signal inversion mechanism to achieve the additional isolation on the top of the intrinsic isolation of polarization diversity. The validation model for the presented antenna features ≥88 dB peak isolation between the dual-polarized Tx and Rx ports. In addition, the measured Tx–Rx isolation for prototype is &gt;70 dB across the 10 dB return loss bandwidth of 100 MHz (2.42–2.52 GHz). The measured gain for each mode is better than 7.0 dBi. The novelty of this work is that compared to previously reported designs, the presented antenna offers wider impedance bandwidth and improved SIC levels in addition to superior gain performance. To the best of our knowledge, this is the first single/shared patch antenna which provides better than 70 dB interport isolation across the 10 dB return loss bandwidth of 100 MHz along with 7.0 dBi gain for Tx/Rx modes.

Low NF and High P1dB Wideband Quasi-Circulator With Unequal Power Split and Reconfigurable Inter-Stage Matching

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.

A Survey and Quantitative Evaluation of Integrated Circuit-Based Antenna Interfaces and Self-Interference Cancellers for Full-Duplex

Full-duplex (FD) wireless - simultaneous transmission and reception on the same frequency - is a promising technique that can significantly improve spectrum efficiency and reduce communication latency in future wireless networks. To enable FD operation, the powerful self-interference (SI) signal leaking from the transmitter (TX) into the receiver (RX) needs to be suppressed and canceled to an extreme degree at the antenna interface as well as in the RF/analog and digital domains. Various approaches to achieve TX-RX isolation at the antenna interface and SI cancellation (SIC) in the RF/analog and digital domains have been demonstrated, with a focus on using bench-top off-the-shelf components. Recent advances in integrated circuit (IC) implementations of various types of shared antenna interfaces and cancellers in the RF and/or analog baseband (BB) domains have further pushed the frontier of realizing FD wireless in small-form-factor/hand-held devices. Moreover, it is still important to fundamentally study the SIC performance that can be achieved by different types of cancellers. In this paper, we present a first-of-its-kind comprehensive overview on the implementation and comparison of various state-of-the-art integrated shared antenna interfaces and SI cancellers in both the RF and analog BB domains. We define two figures of merit (FOM) for the IC-based shared antenna interfaces and SI cancellers, which capture various design considerations and performance tradeoffs including the achievable isolation/SIC, bandwidth, noise figure degradation, TX/SI power handling, and power consumption. In particular, we focus on two types of integrated shared antenna interfaces including electrical-balance duplexers and circulators. We also discuss two types of SI cancellers based on the time-domain and frequency-domain approaches, which respectively employ parallel delay lines and bandpass filters to emulate the SI channel. Based on realistic measurements, we perform extensive numerical evaluations to illustrate and compare the achievable RF SIC performance in different scenarios, as well as discuss various design tradeoffs. Finally, we provide an overview of the IC-based implementations and performance evaluations of both types of cancellers based on our recent work.

Triple-Resonance Chipless RFID Tag With Dual Circularly-Polarized Wideband Reader Antenna for Wirelessly Differentiating Liquid

To wirelessly differentiate specified liquid samples, this article presents a radio-frequency identification (RFID) front-end including wideband reader antenna with chipless tag. The proposed reader antenna employs left-handed circularly-polarized (LHCP) antenna for transmitter (Tx) and right-handed circularly-polarized (RHCP) antenna for receiver (Rx), to improve the Tx-Rx isolation and also liberate the orientation and polarization of chipless tags. This dual circularly-polarized (dual-CP) configuration also features wide bandwidths of impedance and axial ratio, by using sequentially-rotated structure. Moreover, the proposed chipless tag has three resonances, among them, one independent resonance provides a lookup table for fast and easy identification, and another two resonances can be used to reconfirm the identification results. For validation, dual-CP reader antenna array and chipless tag are numerically optimized, experimentally measured, and also in-vivo demonstrated to wirelessly differentiate liquid samples.

25–53 GHz ultra‐wideband high‐isolation passive balanced duplexer on 0.18‐ μ m BiCMOS for 5G applications

A new ultra-wideband millimetre-wave passive balanced duplexer (DUX), employing a lumped-element Wilkinson power divider and grounded-centre-tap transformer, has been developed using 0.18-m BiCMOS process for fifth generation operations at 28, 37, 39 GHz, and beyond. The developed DUX is configured single-ended transmitter (TX) and antenna (ANT) ports and differential receiver (RX) port. It has an inherent matching at TX, RX and ANT ports, high TX–RX isolation, and highly balanced differential RX waveforms, and is ready for direct integration with a differential low-noise amplifier. Analysis has been performed to confirm the DUX's characteristics and assess its performance. Measured isolation from TX to each single-ended RX port is higher than 50 and 40 dB from dc-20 GHz and dc-60 GHz, respectively. Measured insertion loss from TX to antenna is better than 6.3 dB across 13–53 GHz. Measured insertion loss from ANT to differential RX port is lower than 13.8 dB from 25 to 57 GHz with 10.8 dB at 40 GHz. The core chip only occupies 0.3 mm2.

Multi-port monostatic antenna system with improved interport isolation for 2.4GHz full duplex MIMO applications

ABSTRACT This paper presents a five (05)-port proximity coupled monostatic patch antenna having four (04) linearly co-polarized ports (same polarization for two-transmit and two-receive ports) for 2.4 GHz in-band full duplex (IBFD) 2-order MIMO (multi-input multi-output) wireless applications. The employed differential receive mode mechanism and single-tap self-interference cancellation (SIC) circuit achieves high isolation between transmit (Tx) and receive (Rx) ports for IBFD operation. The fifth port is dual polarized with respect to the first four (04) ports to provide intrinsic isolation through polarization diversity. The implemented antenna system provides 10 dB return-loss bandwidth of more than 200 MHz for all five ports. The measured MIMO isolation (Tx-Tx ports and Rx-Rx ports) is better than 15 dB and full duplex Tx-Rx isolation ≈ 20 dB between linearly co-polarized ports for 200 MHz bandwidth. Moreover, the interport isolation between Tx ports (Rx ports) and dual polarized port (port 5) > 30 dB (25 dB) in 200 MHz bandwidth in addition to better than 60 dB (27 dB) peak isolation. To the best of our knowledge, it is the first type of such monostatic antenna with multiple co-polarized and dual polarized ports for full duplex MIMO applications.

In-Band Full-Duplex Radar-Communication System

In-band full-duplex (IBFD) technology is a promising solution to boost the throughput of wireless networks. To bring IBFD to reality, the modem has to cancel the self-interference (SI) signal, which includes the strong direct Tx leakage signal and the weaker reflected Tx signal from the surroundings. Adaptive analog and digital SI cancelation schemes have been proposed. It becomes then interesting to understand, although, how the echoed SI could be exploited for enabling radar functionality while reusing the waveform and the already-existing hardware. This article formulates the monostatic radar system model starting from the communication system model. Beside simulation-based assessment, the performance is also evaluated by an IBFD system prototype, which consists of both analog and digital SI canceller modules, enabling $>$ 85 dB Tx–Rx isolation. The system is enhanced with Doppler radar functionality, reusing as much as possible the existing IBFD functional blocks. The experimental result shows the accuracy of the proposed system to measure the velocity of mobile objects at various speeds between 0.2 and 1 m/s while the device is simultaneously served as a node to perform in-band bidirectional communication. This ability suits the proposed system for a broad spectrum of opportunistic remote sensing applications, such as body and hand gesture detection.

Compact structure with high TX-RX isolation for frequency domain duplexing on printed circuit boards

When developing compact and lightweight antenna systems for unmanned aerial systems, achieving high isolation between transmit and receive signal paths is challenging. To address this issue, we demonstrate a prototype isolation design on a printed circuit board for a frequency division duplexed X band antenna system. Key components include a microstrip defected ground plane notch filter and a copper grating barrier that provides 20 dB higher isolation than free space separation between the transmit and receive antennas. The hardware provides at least 105 dB of transmit isolation into the receiver low noise amplifier in the transmit band. The proposed design is lighter and more compact than traditional machined metal waveguide isolation techniques used for ground-based systems yet achieves similar isolation performance.

Full-Duplex OFDM Radar With LTE and 5G NR Waveforms: Challenges, Solutions, and Measurements

This paper studies the processing principles, implementation challenges, and performance of OFDM-based radars, with particular focus on the fourth-generation Long-Term Evolution (LTE) and fifth-generation (5G) New Radio (NR) mobile networks' base stations and their utilization for radar/sensing purposes. First, we address the problem stemming from the unused subcarriers within the LTE and NR transmit signal passbands, and their impact on frequency-domain radar processing. Particularly, we formulate and adopt a computationally efficient interpolation approach to mitigate the effects of such empty subcarriers in the radar processing. We evaluate the target detection and the corresponding range and velocity estimation performance through computer simulations, and show that high-quality target detection as well as high-precision range and velocity estimation can be achieved. Especially 5G NR waveforms, through their impressive channel bandwidths and configurable subcarrier spacing, are shown to provide very good radar/sensing performance. Then, a fundamental implementation challenge of transmitter-receiver (TX-RX) isolation in OFDM radars is addressed, with specific emphasis on shared-antenna cases, where the TX-RX isolation challenges are the largest. It is confirmed that from the OFDM radar processing perspective, limited TX-RX isolation is primarily a concern in detection of static targets while moving targets are inherently more robust to transmitter self-interference. Properly tailored analog/RF and digital self-interference cancellation solutions for OFDM radars are also described and implemented, and shown through RF measurements to be key technical ingredients for practical deployments, particularly from static and slowly moving targets' point of view.

Tunable Quasi-Circulator Based on a Compact Fully-Reconfigurable 180° Hybrid for Full-Duplex Transceivers

In this paper, a tunable quasi-circulator (QC) is proposed, which consists of a compact fully-reconfigurable 180° hybrid and two amplifier stages in the transmitter (TX)- and receiver (RX)-paths, respectively. Such hybrid is implemented by six varactor-tuned phase shifters, which can not only achieve the frequency tuning operation but also suppress the signal leaking from the TX to the RX in the proposed QC. To further enhance the TX-RX isolation, a variable-impedance balance resistor based on the PIN diode is introduced and tapped on the hybrid. Meanwhile, at the TX- and RX-paths of the QC, two amplifier stages with inter-stage matching networks are connected to the hybrid, respectively, which can achieve the nonreciprocity operation of the proposed QC with high performance. To verify the mechanism of the structures mentioned above, a tunable QC operating at 2.88–3.56 GHz is implemented and fabricated. The measurement has merits of the in-band TX-RX isolation greater than 34 dB, RX gain higher than 4.3 dB, and noise figure lower than 5.5 dB. Besides, the minimum gain of the TX path is 6.8 dB, and an output 1-dB compression point of 21.7 dBm with a power efficiency of 20% at 3.2 GHz is achieved, respectively.

Tunable Duplexers: Downlink Band Isolation Requirements for LTE User Equipment

Tunable duplexers based on self-interference cancellation present a promising alternative to fixed-frequency duplexers (e.g., surface acoustic wave devices), however the level of transmit-to-receive (Tx–Rx) isolation they provide is typically lower compared to acoustic devices. This letter quantifies the impact of reduced isolation on receiver (Rx) noise figure (NF), and determines minimum isolation requirements for Tx-Rx isolation in cellular handset transceivers. Measurements of Tx noise power spectral density from a cellular handset power amplifier are combined with theoretical analysis and long term evolution (LTE) downlink throughput simulations to assess the impact of isolation on the NF and sensitivity. Although lower duplexer isolation can lead to substantial desensitization for some duplex separation/bandwidth combinations, achieving LTE compliant sensitivity requires only 38 dB of isolation in the Rx band. LTE sensitivity specification compliance is therefore readily achievable with current tunable duplexing technologies.

Co‐polarized monostatic antenna with high Tx–Rx isolation for 2.4 GHz single channel full duplex applications

AbstractThis article presents a linear co‐polarized (same polarization for transmit and receive modes), proximity coupled monostatic patch antenna with high port to port RF isolation for 2.4 GHz single channel full duplex (SCFD) wireless applications. The presented proximity coupled monostatic patch antenna deploys differential feeding for receive (Rx) mode to significantly suppress RF leakage from transmit (Tx) port and external single‐tap self‐interference cancellation (SIC) circuit provides additional interport isolation. The measurements for implemented prototype of antenna in lab environment provide around 50 dB Tx–Rx isolation for 50 MHz bandwidth in addition to better than 75 dB peak isolation. Moreover, the deployed single‐tap RF SIC circuit can be used to suppress SI resulted from environmental reflections and 50 MHz SIC bandwidth with 50 dB isolation can be tuned within antenna's 10 dB return loss impedance bandwidth of 150 MHz.