Simultaneous Transmit And Receive Research Articles

Antenna Systems for Simultaneous Transmit and Receive (STAR) Applications

Abstract Several novel wideband co-polarized circulator-less monostatic antenna and array designs for co-channel simultaneous transmit and receive (STAR) applications are presented. The monostatic STAR apertures are demonstrated first by utilizing multi-arm spiral antennas where a set of arms is used for transmitting (TX) and the other set for receiving (RX). Then, square and hexagonal broadside STAR arrays utilizing closely-spaced spiral antennas are introduced. Finally, (quasi) omnidirectional circular STAR arrays based on phase modes orthogonality principles are realized using four wideband monocone antenna elements. The studied configurations are integrated with the proper beamforming networks to excite the desired modes of TX/RX operations leading to theoretically infinite isolation between TX and RX ports. Practically, the achieved isolation is limited by the electrical asymmetries of the used components. Overall, consistent wideband operation, high isolation, and decent far-field performance are achieved for all proposed STAR approaches.

Monostatic Co-Polarized Full-Duplex Antenna With Left- or Right-Hand Circular Polarization

A monostatic dual-polarized simultaneous transmit and receive (STAR) antenna system with high isolation is introduced. A beamforming network (BFN) producing 0°, ±90°, ±180°, and ±270° phase progression is used to feed TX and RX ports of four dual-polarized antenna elements arranged in a sequential rotation array (SRA). Due to the phase progression and geometrical symmetry of SRA, the coupling from TX to RX ports is canceled at the RX port of the BFN; therefore, infinite system isolation is theoretically obtained. Full-wave simulations are used to verify the theory and study effects of element spacing and BFN imbalances. An additional cancelation layer is designed and used to compensate for the imbalances by the BFN and nearby scatterers. The proposed STAR antenna system is prototyped and tested in the 2.4–2.5 GHz industrial, scientific, and medical band where the measured isolation and return loss are above 47 and 22 dB, respectively. A dual circularly polarized antenna performance with realized gains above 7 dBic, broadside axial ratio <1.6 dB, and symmetric beams is demonstrated. An ability of the proposed monostatic STAR antenna system to achieve wideband operation is also demonstrated with a quad-ridge horn as an element.

Wideband Multimode Monostatic Spiral Antenna STAR Subsystem

A wideband, multimode, and monostatic simultaneous transmit and receive (STAR) antenna subsystem is proposed. The configuration is composed of a single four-arm spiral and two analog circuit layers designed to maximize isolation between the transmitting (TX) and receiving (RX) channels. The first layer consists of two Butler matrix beamformer networks (BFNs); one for each TX and RX. The second layer integrates four, ideally phase-matched, circulators between the spiral arms and the BFNs. Theoretically, this configuration achieves infinite isolation irrespective of circulator’s quality. However, the BFN imbalances and the dissimilarities between the four circulators degrade the overall isolation. The operational principles are discussed under the ideal conditions and in the presence of circuit imperfections. For a four-arm spiral, the utilized BFN provides orthogonal modes 1, −1, 2, and 3, allowing STAR capability with multimode and diverse radiation patterns. The subsystem isolation and far-field performances are characterized experimentally and computationally for different modes of operation. A simple approach to achieve a dual-polarized STAR operation over narrower bandwidth with the proposed subsystem is also discussed. The multimode subsystem is demonstrated over 4:1 bandwidth with high isolation, VSWR < 2, consistent patterns, axial ratio < 3 dB over a wide field of view for the broadside modes (1, −1) and < 4.2 dB for other conical modes (2, 3).

Asymmetric Simultaneous Transmit and Receive in WiFi Networks

Many researchers expect to see the efficiency of wireless local area networks (WLANs) increased by in-band simultaneous transmit and receive (STR). While insufficient suppression of self-interference has been a major obstacle to implementing the STR capability, an even bigger obstacle is the fact that enabling STR involves significant modification to the current IEEE 802.11 medium access control (MAC) protocol. In this paper, we propose MASTaR , a novel MAC protocol that enables STR in 802.11 WLAN using standard-compliant methods. The feasibility and performance of MASTaR are extensively evaluated via 3-D ray-tracing-based simulation. The simulation results demonstrate that significant performance enhancement, e.g., up to $2.58\times $ higher throughput than the current 802.11 MAC protocol, can be achieved by an STR-capable access point.

Wideband Antenna Array for Simultaneous Transmit and Receive (STAR) Applications

Design and performance of a nonscanning antenna array with wideband simultaneous transmit and receive capability are discussed. The proposed configuration utilizes a four-arm spiral antenna as a unit cell to achieve high isolation between transmit (TX) and receive (RX) ports and decent far-field performance. It is shown that the analytically derived system isolation is theoretically infinite for symmetric array under ideal conditions. The proposed antenna is composed of seven four-arm spirals arranged in a hexagonal configuration. Each spiral has two arms for TX, and two arms for RX. Planar microstrip feeds are used to excite each two-arm spiral and eliminate the need for 180° hybrids. The spiral arms are resistively loaded to improve VSWR and axial ratio and reduce interaction with the ground plane. Isolation between the collocated TX and RX arrays > 27 dB, as well as VSWRs < 2, sidelobe levels < –10 dB, and good patterns for both arrays are measured over more than two-octave bandwidth.

Wideband Monostatic Simultaneous Transmit and Receive (STAR) Antenna

A monostatic ultra-wideband simultaneous transmit and receive (STAR) antenna subsystem is introduced. An inherent geometrical symmetry of a four-arm spiral antenna and feeding rearrangement are exploited to achieve the simultaneous transmit (TX) and receive (RX) functionalities without any time, polarization, or frequency multiplexing. The antenna is configured such that one arm-pair is used for TX and the other for RX. Thus, even though the two antennas are spatially separated by 90°, they still share the same aperture and the system is considered monostatic. Theoretical and computational studies are conducted to demonstrate the feasibility of the proposed approach under ideal conditions as well as in the presence of feed network non-idealities. The experimental data indicate that isolation levels greater than 39.6–50 dB over multiple octaves are achievable with realistic components. To improve the TX and RX far-field patterns, the planar four-arm spiral aperture is grounded via resistor-loaded quadrifilar helix with the two-arm TX/two-arm RX feed arrangement preserved. Furthermore, to simplify the feed network and reduce the impact of hybrid imbalances, an impedance-transforming microstrip feed is integrated with each arm pair. Isolation $> {37}\;{\text {dB}}$ and similar with high-quality measured and simulated TX/RX radiation patterns are obtained over the operating bandwidth.

Relay Performance Analysis of TTR and STR Relay Modes in IEEE 802.16j MMR System

The IEEE802.16j standard uses non-transparent relay stations to extend coverage. There are two types of non-transparent relay modes, that is, the time-division transmit and receive (TTR) relay mode which can operate with one of two types of frame structures, a single-frame and multiframe structure, and the simultaneous transmit and receive (STR) relay mode. In this paper, we analyze the relay performance of TTR and STR relay modes in IEEE 802.16j MMR system. We also propose a fair resource allocation scheme for the downlink relay frame. Numerical results show that relay performance of the TTR with a single-frame or a multiframe structure and that of the STR relay modes are almost the same in a two-hop system. However, in a three-hop system, the TTR mode with a single-frame structure outperforms other relay modes.

MMIC-Based Quadrature Hybrid Quasi-Circulators for Simultaneous Transmit and Receive

This paper presents a new type of monolithic microwave integrated circuit (MMIC)-based active quasi-circulator using phase cancellation and combination techniques for simultaneous transmit and receive (STAR) phased-array applications. The device consists of a passive core of three quadrature hybrids and active components to provide active quasi-circulation operation. The core of three quadrature hybrids can be implemented using Lange couplers. The device is capable of high isolation performance, high-frequency operation, broadband performance, and improvement of the noise figure (NF) at the receive port by suppressing transmit noise. For passive quasi-circulation operation, the device can achieve 35-dB isolation between the transmit and receive port with 2.6-GHz bandwidth (BW) and insertion loss of 4.5 dB at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -band. For active quasi-operation, the device is shown to have 2.3-GHz BW of 30-dB isolation with 1.5-dB transmit-to-antenna gain and 4.7-dB antenna-to-receive insertion loss, while the NF at the receive port is approximately 5.5 dB. The device is capable of a power stress test up to 34 dBm at the output ports at 10.5 GHz. For operation with typical 25-dB isolation, the device is capable of operation up to 5.6-GHz BW at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -band. The device is also shown to be operable up to <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> -band by simulation with ~15-GHz BW of 20-dB isolation. The proposed architecture is suitable for MMIC integration and system-on-chip applications.

Orthogonal Channel Coding for Simultaneous Co- and Cross-Polarization Measurements

Abstract Dual-polarization weather radars typically measure the radar reflectivity at more than one polarization state for transmission and reception. Historically, dual-polarization radars have been operated at copolar and cross-polar states defined with respect to the transmit polarization states. Recently, based on the improved understanding of the propagation properties of electromagnetic waves in precipitation media, the simultaneous transmit and receive (STAR) mode has become common to simplify the hardware. In the STAR mode of operation, horizontal and vertical polarization states are transmitted simultaneously and samples of both horizontal and vertical copolar returns are obtained. A drawback of the current implementation of STAR mode is its inability to measure parameters obtained from cross-polar signals such as linear depolarization ratio (LDR). In this paper, a technique to obtain cross-polar signals with STAR mode waveform is presented. In this technique, the horizontally and vertically polarized transmit waveforms are coded with orthogonal phase sequences. The performance of the phase-coded waveform is determined by the properties of the phase codes. This orthogonal phase coding technique is implemented in the Colorado State University–University of Chicago–Illinois State Water Survey (CSU–CHILL) radar. This paper outlines the methodology and presents the performance of the cross-polar and copolar parameter estimation based on the simulation as well as data collected from the CSU–CHILL radar.