Transmit-receive Isolation Research Articles

Design of four-port antenna with two sets of orthogonal CO-CP performance

This work presents a four-port in-band full-duplex (IBFD) antenna that allows transmitting and receiving two sets of orthogonal co-circularly polarized signals, facilitating IBFD system applications. The single-element antenna is constructed using a six-port isolation network (SPIN) without the need for circulators, helping to reduce cost and facilitate integration. The transmit-receive isolation is accomplished via the isolation of power dividers and the cancellation guided by the coupling path of SPIN. The microwave network analysis method perfectly analyzes the operating mechanism of isolation and orthogonal co-circular polarization. The measured results confirm that this design achieves excellent two sets of orthogonal co-circular polarization. The measured results show that the 10-dB impedance bandwidth is 24.2%, the 3-dB axial-ratio bandwidth is 23.5%, and the measured 30-dB isolation bandwidth is 3.52-4.15 GHz (16.4%) with a maximum isolation of 53.2 dB.

Transmit–receive isolation improvement by a switch sequence adjustment for MMW linear-arrays imaging

High transmit-receive isolation between any two adjacent elements in sequentially switched linear arrays guarantees the performance of high-resolution close-range imaging. However, the transmit-receive antenna spacing required in wavelength order makes its isolation deteriorated rapidly in the millimeter wave and higher frequency bands. In this paper, we propose a simple yet effective method to improve transmit-receive isolation by a switch sequence adjustment on the traditional linear arrays. The new switch-mode aims to simply increase the vertical spacing between each transmit-receive pair. To maintain the densely uniform-spatial effective sampling and Fourier transform-based image reconstruction, the principle of equivalent phase center is utilized to analyze the maximum of the possible vertical spacing of each transmit-receive pair is four wavelengths. Experiments verify that the method can efficiently improve transmit-receive isolation by up to 11.5 dB and guarantee the high performance of MMW imaging.

On the effect of S-parameter stability of antenna and coupler on electrical balance duplexing

Electrical Balance Duplexers (EBDs) provide transmit-receive isolation to implement a form of self-interference cancellation to facilitate simultaneous transmission and reception from a single antenna in systems like In-Band Full-duplex (IBFD) transceivers. EBD works by coupling transmitter, receiver, antenna, and balancing impedance using a hybrid coupler. In recent pieces of literature, antenna impedance variations are considered the main factor limiting the EBD isolation bandwidth, while the EBD balancing impedance needs to be equal as much as possible to the antenna impedance to achieve high isolation. But hybrid couplers are also not ideal elements, and their S-parameters are not stable in the frequency domain. In this work, five broadband RF devices (two antennas, two couplers, and a 50-Ohm RF-load) are used to form four EBD set-ups. One of the antennas, designed by the authors, has more impedance stability in the frequency domain than the other one, which is a commercial antenna. Also, one of the couplers, designed by the authors, has more S-parameter stability in Ultra-Wideband (UWB) frequency domain than the other one, which is a commercial UWB coupler. The implemented EBDs show that when both antenna and coupler have strong S-parameter stabilities in the frequency domain, wider isolation bandwidth (UWB 1.5–3.5 GHz range) and higher EBD isolation are obtained.

Analysis and mitigation of noise in simultaneous transmission and reception in MRI.

In simultaneous transmission and reception (STAR) MRI, along with the coupling of the excitation pulse to the received signal, noise, and undesired distortions (spurs) coming from the transmit chain also leak into the acquired signal and degrade image quality. Here, properties of this coupled noise and its relationship with the transmit amplifier gain, transmit chain noise density, isolation performance, and imaging bandwidth are analyzed. It is demonstrated that by utilizing a recently proposed STAR technique, the transmit noise can be reduced. The importance of achieving high isolation and careful selection of the corresponding parameters are demonstrated. A cancellation algorithm, together with a vector modulator, is used for transmit-receive isolation. The scanner is modeled as a pipeline of blocks to demonstrate the noise contribution from each block. With higher isolation, coupled transmit noise can be reduced to the point that the dominant noise source becomes acquisition noise, as in the case for pulsed MRI. Amplifiers with different gain and noise properties are used in the experiments to verify the derived noise-transmit parameter relation. With the proposed technique, more than 80 dB isolation in the analog domain is achieved. The leakage noise and the spurs coupled from the transmit chain, are reduced. It is shown that the transmit gain plays the most critical role in determining sufficient isolation, whereas the amplifier noise figure does not contribute as much. The transmit noise and the spurs in STAR imaging are analyzed and mitigated by using a vector modulator.

Analysis and test of transmit-receive isolation of off-axis three-mirror anastigmat optical antenna applied to laser communication

The bi-directional duplex working mode of a transmit-receive integrated optical antenna in laser communication systems has a rigorous requirement on transmission and receiver(T/R) isolation. By using an off-axis three-mirror anastigmat (TMA) optical antenna, backscattered can be significantly reduced, thus achieving high T/R isolation. This paper proposes to design the light exit angle of 5° or larger in the off-axis TMA optical antenna and use the equivalent surface roughness (ESR) to evaluate the surface scattering characteristics of reflector in optical antenna. Therefore, by increasing the ESR of reflector, the isolation of the optical antenna can be improved. In an isolation measurement experiment, the measured isolation of the F150mm off-axis TMA optical antenna was 73 dB, which is consistent with the simulation result. The achieved T/R isolation level meets the requirements for acquiring, tracking, and communication of satellite laser communication systems.

An Integrated, Software-Defined FDD Transceiver: Distributed Duplexing Theory and Operation

Implementing flexible, software-defined duplexing transceivers remains challenging due to the inherent self-interference from TX to RX that requires cancellation in the RF/analog domain. Previously, we presented a novel, duplexing, integrated, single antenna transceiver architecture that used an M-stage distributed amplifier combined with an artificial transmission line to achieve high transmit-receive isolation across more than an octave in center frequency. In this paper, we explain and explore the trade-offs and limits on this class of distributed, duplexing transceivers as a function of system and sub-circuit parameters.

A Self-Interference Suppression Structure for Collinear Dipoles

In this letter, a broadband self-interference (SI) suppression structure is presented for collinear dipoles. By using this structure, an average SI improvement of 21.6 dB is realized within the frequency band of 2.2–2.7 GHz. It has a 14.8% operating bandwidth of transmit-receive isolation higher than 50 dB. The working mechanism and bandwidth extension are discussed. Moreover, the key parameters and the influence of the proposed structure to the dipoles were also studied and presented. Measured results demonstrate that this design provides a wider operating bandwidth, omnidirectional radiation patterns, and ideal distribution distance. It is effective and suitable for reducing the SI between collinear dipoles.

2.2–4.6-GHz Active Quasi-Circulator with > 24-dB Transmit–Receive Isolation

An active quasi-circulator (AQC) integrated circuit is designed and fabricated in a 0.18-[Formula: see text]m CMOS process. The proposed design is based on a parallel combination of a common-source (CS) stage and a combined common-drain (CD) and common-gate (CG) topology. Scattering matrix of the core AQC circuit is derived considering MOSFET’s secondary effects, particularly the body effect as well as output loading effects. Measurements of the quasi-circulator reveal an insertion loss of [Formula: see text] dB between transmitter-to-antenna ports ([Formula: see text]) and of [Formula: see text] dB between antenna-to-receiver ports ([Formula: see text]), within a frequency band of 2.2–4.6 GHz. The isolation between the transmitter and the receiver ports ([Formula: see text]) is better than 24 dB with a maximum value of 29.5[Formula: see text]dB @ 3.6[Formula: see text]GHz. The power dissipation of the proposed AQC is 40[Formula: see text]mW and it covers an active chip area of 0.677[Formula: see text]mm2.

An Efficient Digital Background Control for Hybrid Transformer-Based Receivers

The design and hardware implementation of a digital control system tailored to a hybrid transformer-based duplexer is proposed. Working at Nyquist sampling frequency, it finds the optimal transmit-receive isolation in about 150 $\mu \text{s}$ even when modulated signals with high PAPR (16-QAM) are transmitted. A simple tracking algorithm, operating in background, preserves this condition over time. Uninterrupted system operation can be guaranteed through an auxiliary receiver with sub-mW power dissipation, minimizing the overhead of the entire control system. The algorithms are implemented on FPGA to carry out the experimental validation of the full hardware implementation. Moreover, the hardware overhead of the digital control algorithm is analyzed, synthesizing the digital circuit in 40-nm CMOS technology.

Jamming Wideband Radar Using Interrupted-Sampling Repeater

Interrupted-sampling repeater jamming (ISRJ) provides a novel coherent-jamming mode against wideband radar. ISRJ allows the single-antenna jammer to periodically sample and repeat a fraction of the intercepted signal, which reduces the sampling rate and achieves transmit-receive isolation. The coherent-jamming signal generated by ISRJ can form multiple verisimilar false targets when received and processed by the victim radar receiver. Moreover, some false targets can precede the real target. This paper surveys the use of ISRJ in linear frequency modulated (LFM) radar jamming. The theory and application of ISRJ has been researched for more than one decade, but what is missing is a completed summary for the framework of this technique. In this paper, mathematic principles of ISRJ against LFM radars, which utilize matched-filter processing, stretch processing, and range-Doppler processing, are developed. The unique jamming effects in radar systems are focused on when the interrupted sampling frequency of the jammer is smaller than the bandwidth of the radar signal. Specifically, the false-target characteristics, including amplitude, space distribution, and phase, are discussed, respectively. On this basis, the key jamming elements, which determine these false-target characteristics, are pointed out and analyzed in detail. At last, simulation and real data are used to verify the correctness of the analyses. Experimental results highlight the potential application of the proposed jamming mode.

卡塞格伦光学天线收发隔离度分析与测试

卡塞格伦光学天线收发隔离度分析与测试

Transmit–Receive Isolation Improvement of Antenna Arrays by Using EBG Structures

The mushroom-like electromagnetic band-gap (EBG) structure combined with a choke structure is applied to improve the transmit-receive (T/R) isolation of two X-band large antenna arrays. The basic idea presented is to suppress the surface wave propagation between the T/R arrays by utilizing EBG walls formed through a vertical configuration of the EBG cells, so as to improve the T/R isolation. The isolation level of the arrays with the EBG walls and a metal choke is measured and compared to other isolation methods applied. The experimental results show that by using this combined structure, the isolation level can be improved by at least 30 dB in the radar's operation band, which shows its high efficiency.

Distributed Phased Arrays and Wireless Beamforming Networks

Distributed phased arrays have advantages over conventional arrays in many radar and communication applications. Additional advantages are realized by replacing the microwave beamforming circuit by a wireless network, thus forming a wirelessly networked distributed sensor array. This article examines various aspects of a distributed phased array that incorporates wireless beamforming. First, the fundamental array theory and digital signal processing are reviewed. Basic equations are presented and compared to simulations for a ship-based radar application. Next the basic array architecture is described and the critical techniques and components that are required to realize the design are discussed. Methods are introduced for time and phase synchronization, transmit-receive isolation, sensor location issues, and bandwidth and frequency dispersion.

Dual-linear polarised antenna module with enhanced transmit-receive isolation

A dual-linear polarised antenna module for frequency-domain duplex base-station antenna arrays is described. Designed for the frequency bands 1.92–1.98 and 2.11–2.17 GHz, the antenna radiators are matched to −17 dB return loss. The antenna modules have been arranged in a dual-linear polarised array. Inter-element coupling has been reduced by insertion of conducting walls. The module features separate feeds for transmit and receive signals, and realises an isolation of 20 dB in the described array arrangement. The balanced-fed radiator elements are surface-mounted onto a printed circuit board, which serves as a groundplane and provides the balun structures. Radiators are made of three-dimensional parts suited for injection moulding. Prototypes built using a stereolithography process verify expected performance by measurements.

An integrated active circulator antenna

An active circulator is integrated with a quarter-wave short-circuited microstrip patch antenna to produce a fully duplexed transceiver with transmit and receive operation at the same frequency and with the same polarization. The active circulator antenna is shown to have 14-dBi transmit gain and 7.4-dBi receive gain with a transmit-receive isolation of 26.9 dB at 3.745 GHz. This active antenna has potential uses in both short-range communication and radar systems.

Integrated active antenna with full duplex operation

This paper discusses the design and implementation of a novel two-element active transmit-receive array using dual linear polarization and sequential rotation. Each element includes an integrated oscillator and amplifier mounted on orthogonal edges of a square patch, such that the transmit and receive paths are isolated and polarization duplexed. The array gives in excess of 45-dB transmit-receive isolation with an output power of 5.4 dBm and a receive gain of 8.2 dB at 4.05 GHz. Link budget calculations are used to show expected system performances. These active antennas have potential uses in both short-range communication and radar systems.

Integrated active antenna with simultaneous transmit-receiveoperation

The authors present results for a novel two element active transmit-receive array using dual linear polarisation and sequential rotation. Each element includes an integrated oscillator and amplifier mounted on orthogonal edges of a square patch, such that transmit and receive paths are isolated and polarisation duplexed. The array gives in excess of 55 dB transmit-receive isolation at 3.77 GHz.