Full-duplex Applications Research Articles

Metasurface-based dual-sense circularly polarized antenna for MIMO/full-duplex applications.

This paper introduces a two-element antenna array with dual-sense circular polarization, wideband operation, and high isolation characteristics. The antenna consists of two conventional truncated corner patches and an extra layer of metasurface (MS) located above the radiating patches. The overall dimensions of the proposed antenna are 0.92 λ0 × 0.73 λ0 × 0.05 λ0 and the element spacings are 0.02 λ0 and 0.39 λ0 with respect to edge-to-edge and center-to-center spacings. For validation, measurements on a fabricated antenna prototype are carried out. The measured data demonstrate that the presented MS-based antenna has a wide operating bandwidth of 14.5% with high isolation of better than 26 dB. The excellent performance could be concluded from the results of the investigation, which indicates that the proposed MS-based antenna could be a good candidate for multiple-input multiple-output (MIMO) and full-duplex applications.

A [formula omitted]45°dual-polarized co-channel patch antenna array for in-band full-duplex applications

A broadband stacked patch antenna array with high port isolation is presented for in-band full-duplex (IBFD) applications in this article. A co-channel feeding scheme is proposed to simultaneously excite two ports of the patch antenna to achieve ±45°dual polarization. An antenna system is then designed using a 2 × 2 stacked patch array, a parallel feeding network, and a hybrid coupler. The coupling between the Tx and Rx ports due to mismatch and coupling between the antenna elements is analysed in detail and shown to be eliminated completely. A demonstrator is fabricated and measured to endorse the accuracy of the proposed feeding scheme. The measured results show that the developed prototype can operate from 3.15 GHz to 4.0 GHz. The isolation level between Tx and Rx ports is higher than 45 dB within the operating band. The realized gains of two ports are higher than 10.5 dBi throughout the band of interest with the maximum gain of 13.9 dBi, which are congruent with the simulated ones.

A Simultaneously Transmit and Receive Antenna Terminal for In-Band Full-Duplex Applications

In this paper, a low-profile co-linearly polarized simultaneously transmit-receive antenna (STRA) terminal is presented for 5G and upcoming technologies. The proposed STRA terminal comprises of an identical pair of spatially rotated half-circular microstrip antennas for transmission (Tx) and reception (Rx). The challenge of self-interference (SI) is addressed by employing passive SI cancellation techniques such as spatial diversity, field confinement, and surface perturbations. This has been accomplished by using fence-strip structure and V-shaped slots in the ground plane. The STRA was designed, fabricated, and tested for full-duplex operation in a sub-6 GHz band lying from 5.73 to 5.88 GHz, providing high interport isolation ranging from 35.5 dB to a maximum of 46.5 dB. The proposed STRA was implemented using Rogers 3003™ substrate. The measurements yield radiation characteristics with high gain of 5.45-6.0 dBi and 5-6.5 dBi for Tx and Rx antennas, respectively. The measured results are in good conformance with the simulated design. This antenna finds its potential usage in V2X and private 5G networks and can be extended for full-duplex MIMO implementations.

Diplexer Antenna for 5G Full-duplex Application

This work proposes a spiral filter-based diplexer antenna for dual-band full-duplex 5G application in C-band. The shared radiator is formed by a cross-shape Yagi-Uda antenna. The dual-band full-duplex characteristic is obtained by applying a diplexer with two different band-stop filters (BSFs) based on a high-order rectangular spiral-shaped open-stub filter. The proposed diplexer antenna is suitable for modern 5G full-duplex communication system applications with a small frequency ratio and high isolation between two ports by applying a Wilkinson power divider. The diplexer antenna is designed, fabricated, and measured, showing good performance of channel isolations of 27 dB/23 dB and the antenna gain of 4.7 dBi/4.2 dBi at two operation bands from 3.56 GHz to 3.68 GHz and from 3.72 GHz to 3.83 GHz covering the required 100 MHz maximum bandwidth in C-band while its frequency ratio is only 1.04.

Wideband Co-Polarized Stacked Patch Antenna for In-Band Full-Duplex Applications

Wideband Co-Polarized Stacked Patch Antenna for In-Band Full-Duplex Applications

Ultra-wideband 3D-printed vivaldi array for in-band full-duplex applications with a grating lobes reduction approach

This work validates the ability for in-band full-duplex systems to operate over ultra-wide bandwidths. As a proof of concept an ultra-wideband in-band full-duplex antenna array was designed. The array is formed of two wideband microstrip-slotline baluns and four Vivaldi antennas in a 3D-printed single-piece structure. The metal thickness of the 3D-printed Vivaldi antennas makes them sturdier than PCB antennas and more immune to fracturing or breaking, however, they require a coax-to-slot transition as a feeding mechanism. Such transitions are not well documented in the literature, specifically, the effect of metal thickness on the impedance of the 3D-printed slotline. Therefore, impedance curves for the 3D slot are provided as a function of its width and metal thickness. Then, a prototype was realized and measured, achieving about 40 to 80 dB of self-interference cancellation in the frequency range from 4.4 GHz to 28.7 GHz, and an average gain of 9.8 dBi with a directive end-fire radiation pattern. The only drawback of this first prototype is the presence of grating lobes in its radiation pattern due to the separation distance between the opposite antennas which exceeds a half-wavelength. Thus, to mitigate those grating lobes, we propose an approach based on a partial size reduction at the bottom of the antenna. This allows bringing the antennas closer together at their bottom parts, reducing the distance between the radiating slots, which translates to grating lobes reduction especially at higher frequencies. The implementation of this approach results in keeping all sidelobes 10 dB below the main lobe level, while keeping the Figure of Merit of this 2nd ultra-wideband in-band full-duplex antenna system at a higher level compared to existing techniques.

Broadband Dual-Polarized Magnetoelectric Dipole Antenna for In-Band Full-Duplex Application

A broadband dual-polarized magneto-electric (ME) dipole antenna is proposed for in-band full-duplex (IBFD) application. The exploited antenna comprises a cross ME dipole, two П-shaped and Г-shaped feedlines, and a ground with a box-shaped baffle. A wideband 180° power divider is connected to the П-shaped feedline and a coaxial line directly to the Г-shaped feedline to excite the cross ME dipole with dual-polarization. Meanwhile, the introduced baffle will stable the radiation pattern and improve the realized gains over a wideband frequency range. As a result, a broadband hybrid decoupling technique is adopted in this design, and the measured antenna prototype realizes an impedance bandwidth of 1.7 - 2.7 GHz (45.4%) for the 10 dB return loss, high isolation of better than 50 dB and the realized gains of more than 7 dBi. These characteristics make the proposed antenna a promising candidate for IBFD base station systems.

Metamaterial-Based Low-Profile Broadband In-Band Full-Duplex Antenna

A low-profile wideband antenna with extremely high isolation is proposed for in-band full-duplex applications. It is designed in a coplanar structure with a periodic array of non-uniform metamaterial cells, a hook-like feeding probe, and four mushroom-like structures. The non-uniform metamaterial cells are excited by a hook-like feeding probe to achieve horizontal polarization. Meanwhile, two slots at the end of the ground are coupled with microstrip feed lines for vertical polarization. As a result, leakage currents between two symmetrical feed structures are suppressed to realize high isolation in wide operation bandwidth. Furthermore, four mushroom-like structures are embedded in the corners of the metamaterial cells to improve bandwidth and isolation. Measured results demonstrate that the proposed antenna with a low profile of 0.06 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength at the center frequency of the operating band) achieves a -10 dB impedance bandwidth of 24.5% from 3.20 GHz to 4.09 GHz and a high Rx/Tx isolation of more than 50 dB. The proposed design has the merits of low profile, wideband, high isolation, and simple feeding structure, which makes it a competitive candidate for in-band full-duplex applications.

Gain and Frequency-Selectivity Enhancement of Dual- Polarized Filtering IBFD Antenna Using PRS

A dual-polarized filtering Fabry–Perot antenna (FPA) with high selectivity and high isolation is proposed for in-band full-duplex (IBFD) applications. The proposed antenna utilizes a square patch as the feeding element, which is fed by a double differential-fed scheme for dual-polarized radiation with high isolation. The patch is loaded with a symmetrical cross-slot and four shorting pins for a broad passband filtering feature. To enhance broadside gain across a wide frequency range, the patch is incorporated with a partially reflecting surface (PRS), which is composed of two complementary cross-slot and patch arrays. Moreover, the frequency selectivity of PRS is exploited to improve the filtering characteristic. The double differential feeds are realized based on out-of-phase power dividers, which are combined with simple low-pass filters to further improve the out-of-band suppression. The final design was fabricated and measured. The measurement results show excellent results with a 10-dB return loss bandwidth of 21.5% (4.91–6.09 GHz), isolation of greater than 40 dB, peak gain of 13.7 dBi, out-of-band suppression level of better than 27 dB, and a cross-polarization level of less than –27 dB.

Wideband Co-Linearly Polarized Magneto-Electric Dipole Antenna for In-Band Full-Duplex Applications

A wideband co-linearly-polarized magnetoelectric (ME) dipole antenna is proposed for the in-band full-duplex (IBFD) application, having identical radiation properties in the operating frequency band. Good isolation between the transmitting and receiving ports is obtained over a wide frequency range by modifying the shared central part of the ME dipole without a complex feeding structure. The central part is a defected rectangular tube suspended above the ground. To validate the proposed antenna, a prototype is fabricated and measured. The measured port isolation is higher than 22 dB over the operating frequency band from 1.90 to 2.91 GHz (42.0%). The proposed antenna has a simple structure and good wideband radiation performance, with high potential for IBFD applications.

Design of Self-Decoupling Dielectric Resonator Antenna With Shared Radiator

The method of mode cancellation to design a two-port dielectric resonator antenna (DRA) for an in-band full-duplex (IBFD) application is investigated in this communication. The whole antenna structure is straightforward, only composed of a single DRA element, a pair of feeding lines, and a pair of metallic probes. Attributing to the features of different modes used in this design, mutual coupling between the exciting port and the passive port can be suppressed to an extremely low level without using an extra decoupling structure. A prototype is fabricated and measured for verification. The measured results demonstrate that the proposed antenna has broad bandwidth and high isolation level can be achieved throughout the whole working band.

Port isolation improvement of full‐duplex single‐patch antenna by loading full‐wave resonators

In this article, a pair of full-wave microstrip resonators is loaded at the nonradiative edges of the patch to improve port isolation of two-port copolarized single-patch antennas (SPAs) for full-duplex applications. First, the decoupling mechanism and its resulting radiation characteristics are exhaustively analyzed, which indicates that more similar radiation patterns and lower crosspolarization can be achieved based on the directly suppressing port coupling. Then, a transversal-section-like topology composed of an additional interference path and the SPA is proposed to realize this purpose. To clearly illustrate the operation principle in practical design, the phase shifts of both paths, that is, the interference paths from Port 1 to Port 2 via the patch and the full-wave resonators, are exhaustively investigated. Attributing to the realization of a stable 180° out of phase between the two paths, the resultant signal is highly and stably attenuated by the interfering signal, and the desired port isolation is satisfactorily attained by manipulating its amplitude readily. The measured results show a dramatic enhancement in isolation between the two ports from 4 to 55 dB with good impedance matching at the two ports. Most importantly, benefiting from the idea of direct port isolation, the radiation performance is hardly deteriorated, with a maximum gain of 8 dBi, beam squint angle of only 10°, and low crosspolarization in the upper half-space.

Broadband Dual-Polarized Fabry–Perot Antenna With Simple Feed for Full-Duplex Applications

In this letter, we present a simple-feed dual-polarized Fabry–Perot antenna with broadband and high-isolation for in-band full-duplex applications. Its feeding element consists of a two-port patch antenna with one aperture coupled port and one microstrip-line-fed port for a high isolation without adding any out-of-phase power divider. For broadband and high-gain radiation, the two-port patch is incorporated with a stacked-patch and partially reflecting surface while maintaining the structure symmetry. The final design with an overall size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim\! 1.9\lambda _{\text{min}}$</tex-math></inline-formula> × 1.9 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{\text{min}}$</tex-math></inline-formula> × 0.48 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{\text{min}}$</tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _{\text{min}}$</tex-math></inline-formula> is the free-space wavelength at the lowest operational frequency) has been fabricated and tested. The measurements result in a 10 dB return loss bandwidth of 19.1% (4.84–5.86 GHz), an isolation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ge$</tex-math></inline-formula> 43 dB, a realized broadside gain of 12.4–14.2 dBi, cross-polarization level of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\le$</tex-math></inline-formula> −30 dB, and side-lobe level of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\le$</tex-math></inline-formula> −18 dB across 5.00–5.95 GHz.

A Compact, Low-Profile Shorted TM$_{1/2,0}$ Mode Planar Copolarized Microstrip Antenna for Full-Duplex Systems

In this letter, a single-layer compact copolarized shorted TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2,0</sub> mode microstrip patch antenna is presented for in-band full-duplex application. Two shorted TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2,0</sub> mode patch antennas, used for transmission and reception purposes, make the structure compact. The wideband behavior of the patch antenna is obtained by fusing the two resonances, one because of the shorted TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2,0</sub> mode radiating patch and the other because of the λ/4 line resonator. To enhance the isolation between the transmitter and receiver antenna, a novel defected ground structure is used. Slots are introduced into the ground plane to create a weak field region for the basic antenna element. The other antenna element (receiver) is located in the weak field region to enhance isolation. Further enhancement in isolation is achieved by introducing a T-shaped metallic strip into the slots. The structure is proposed with the credits of compactness, enhanced bandwidth, colinear polarization, very less fabrication complexity, low profile, and high isolation. The proposed structure is fabricated and measured. The structure experimentally exhibits a bandwidth (≤ −10 dB) of 2.42–2.52 GHz with the isolation of 25 dB, peak isolation of 36 dB, and an average realized gain of 4 dBi in the entire band.

Non-reciprocal diplexer and power combiner/divider from topological cavities with both splitting and combining functions

Multiplexers and power combiners/dividers are crucial in many applications of electromagnetic waves including microwave and terahertz communication. Full-duplex communication requires the separation of transmitted and received signals; thus, non-reciprocal multiplexers and power combiners/dividers are very essential. In this work, we present and numerically study a design concept for such non-reciprocal circuits from topological cavities. First, a quad-port circulator is made from a topological cavity and two trivial waveguides, which effectively operates as a non-reciprocal band-pass filter. Then, by parallelly connecting multiple circulators together, topological diplexers and power combiners/dividers are formed. These circuits are non-reciprocal due to the nature of photonic topological insulators, yet unlike the previously proposed non-reciprocal multiplexers or power combiners/dividers, they can both split and combine multiple frequencies or multiple power flows. The topological nature of the proposed circuits also makes them robust to any fabrication error and suitable for practical full-duplex communication applications.

Co-Circularly Polarized Planar Antenna With Highly Decoupled Ports for S-Band Full Duplex Applications

This work presents a unidirectional, co-circularly polarized (CP), printed antenna with highly decoupled or isolated transmit (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) and receive (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) ports for 2.4 GHz in-band full duplex (IBFD) applications. The presented antenna topology is based on four similar and sequentially rotated trimmed patches with right hand circular polarized (RHCP) characteristics. The symmetrical placement of two T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> patches with respect to both R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> elements results in equal levels of self interference (SI) which was suppressed through balanced excitation of T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> mode. This mechanism results in effective suppression of SI at each R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> patch. The residual SI is suppressed further through a second balanced feeding network deployed at R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> port of proposed antenna topology. The employed balanced feeding networks provide superior performance of ≤ 0.5 dB and 6° magnitude and phase imbalances respectively between the two balanced output ports over the bandwidth of interest. The measured results for prototype of presented antenna achieve -10 dB bandwidth of better than 100 MHz for both T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> and R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ports. The measured interport coupling for validation model ≤ −70 dB across the entire bandwidth of 100 MHz. As per best of authors’ knowledge, the presented antenna is the first one to report such reduced levels of interport coupling over the whole impedance bandwidth of planar antenna with unidirectional radiation patterns and co-RHCP characteristics for both T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> and R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> modes across the overlapped bandwidth.

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.

A W-Band Low-Profile Dual-Polarized Reflectarray With Integrated Feed for In-Band Full-Duplex Application

A W-band low-profile dual-polarized Cassegrain reflectarray with an integrated feed is designed in this work. High isolation, which is necessary for the in-band full-duplex (IBFD) applications, is realized between two feeding ports corresponding to the orthogonal polarizations. The antenna is composed of two parts, i.e., the dual-polarized planar-array feed and the Cassegrain reflectarray with a small focal-length to diameter ratio ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$F/D)$ </tex-math></inline-formula> . The dual-polarized planar array feed is appressed behind the main-reflectarray, and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$F/D$ </tex-math></inline-formula> is reduced to 0.2 to realize the integration and the low-profile property. For the array feed, high isolation is achieved through the orthogonal-mode isolation and the differential signal cancellation. Its radiation pattern is also manipulated to fit the reflectarray considering the taper and spillover efficiency. For the reflectarray, the rotational symmetry configuration and the dual-layer-patch cell are applied to suit the dual-polarization operation and the large incident angle, respectively. The measured operation band, where the gain variation is within 1 dB, is 93.4–95.6 GHz. At the center frequency, the gains of the Cassegrain reflectarray for the two ports are 31.86 and 30.88 dBi, and the corresponding aperture efficiencies are 31.4% and 25.1%, respectively. The isolation between the two ports is higher than 55 dB within the operation band. This work is a low-profile candidate for W-band point-to-point IBFD communication.

Evolution of Circular Mode Phasing for In-Band Full-Duplex Omnidirectional Antennas

Many in-band full-duplex (IBFD) applications require omnidirectional radiation coverage in addition to multilayered self-interference cancellation (SIC). While system-level SIC approaches often require high-isolation antennas before implementing analog and/or digital methods, maintaining the desired omnidirectional transmit/receive patterns is difficult for compact designs that utilize the same polarization. This article discusses the concept development and design progression of the circular mode phasing technique applied to omnidirectional IBFD antenna arrays. The theoretical fundamentals are presented along with simulation results and then validated through the discussion of two prototype antennas, which were measured to provide up to 60 dB of isolation over 2.4–2.5 GHz, which is the highest reported for this SIC method. Additionally, the evolution of this concept for a collection of measured prototypes is summarized and characterized with a unique figure of merit, which should help advance the application of this technique within future IBFD systems.

High-Isolation Dual-Polarized Leaky-Wave Antenna With Fixed Beam for Full-Duplex Millimeter-Wave Applications

In this article, a high-isolation dual-polarized leaky-wave antenna (LWA) with a fixed beam is proposed for full-duplex millimeter-wave (mm-wave) applications. The proposed antenna consists of a dual-polarized LWA array and an orthogonally differential feeding network. The proposed dual-polarized LWA array is developed based on the proposed LWA unit cell, which is suitable for differential feed, and the open stopband is eliminated. The proposed feeding network provides two pairs of orthogonally differential excitation for the LWA array to realize the fixed beam with orthogonal polarization in boresight direction; the high interport isolation is implemented as well. The prototype for demonstration purposes is fabricated and measured. The measured results show that the proposed antenna exhibits an operating band from 27.6 to 29.5 GHz with a maximum gain of up to 24 dBi. Furthermore, the measured interport isolation is higher than 51 dB within the operating band, where the maximum isolation is up to 60 dB. The measured cross-polarization levels are also very low, less than −27 dB. The proposed antenna features high gain, high interport isolation, and good co-/cross-polarization isolation, achieving a good Tx/Rx separation for the in-band full-duplex applications at mm-wave frequencies.