Rx Antennas Research Articles

Millimeter-wave propagation measurements and models at 28 GHz and 38 GHz in a dining room for 5G wireless networks

To meet 5G requirements, industries are looking forward to a new set of frequency allocation in the millimeter spectrum space, where there is huge amount of bandwidth for wireless gigabit communications. In this paper, the statistics of large-scale path loss and time dispersion parameters are investigated based on ultra-wideband measurements using a steerable directional horn antenna at transmitter (Tx) and omni-directional antenna at the receiver (Rx). The measurement was conducted in a dining room line-of-sight (LOS) scenario, which represents a typical closed-plan for in-building communication. The single-frequency, multi-frequency directional and omni-directional large-scale path loss models are evaluated at 28 GHz and 38 GHz bands based on data acquired from unique Tx and Rx antennas with combination pointing angles. The results show that the large-scale path loss models for indoor propagation developed in this paper is less complex, and yet more physically-based than those used in the third-generation partnership project (3GPP) systems, which involve additional model parameters but yield less accurate results. The time dispersion statistics for mmWave systems using directional antennas and omni-omni antennas configuration at both Tx and Rx are presented for co-polarization scenarios. We show that the multipath root mean square delay spread can be reduced when Tx and Rx antenna are pointed to each other, which results in the strongest received power.

Design of an Antenna Decoupling Structure for an Inband Full-Duplex Collinear Dipole Array

Single-frequency full-duplex (SFD) wireless communication can increase the efficiency of bandwidth utilization by ideally doubling the spectral efficiency. SFD can be achieved by reducing the level of the self-interference between the transmitter (TX) and receiver (RX) to the RX noise floor. This communication describes a novel decoupling structure to increase the isolation for a collinear dipole array which retains the omnidirectional radiation patterns of the dipole antennas. The structure is based on a parasitic element which couples power from the TX antenna and reradiates it with orthogonal polarized elements canceling the original field around the RX antenna. A novel analysis is presented for the decoupling structure in which the phase and amplitude radiation pattern of the decoupling structure is calculated. The obtained isolation is more than 50 dB according to the simulation and measurement results for a bandwidth of 11%, fulfilling the required electromagnetic isolation for a full-duplex system in indoor device-to-device communications.

In-Band Full-Duplex Multimode Lens-Loaded Eight-Arm Spiral Antenna

A multimode lens-loaded eight-arm spiral aperture is proposed for in-band full-duplex applications. Specifically, the single eight-arm spiral antenna is composed of a four-arm spiral for transmitting (TX) and a 45° spatially rotated four-arm spiral for receiving (RX). The eight-arm spiral antenna is connected into two $4 \times 4$ Butler matrix beamforming networks (BFNs) to differentiate between the TX and RX arms/ports and distinguish their functionalities. In the absence of BFN imbalances and antenna geometry asymmetries, the isolation is theoretically infinite due to full cancellation at the RX antenna ports and RX beamformer ports. This approach also enables diverse co-polarized TX and RX radiation modes while maintaining theoretically infinite isolation. The considered spiral aperture modes are mode 1, with a broadside pattern, and modes 2 and 3, with conical patterns. The aperture is loaded with a hyperhemispherical dielectric lens to improve the far-field performance. The operational principles are discussed first under ideal conditions, followed by the computational and experimental results. Average measured isolation >38 dB is achieved over 3:1, 1.5:1, and 1.3:1 bandwidths for the radiating TX and RX modes 1–3, respectively. Once the TX and RX are driven with identical modes, similar radiation patterns with high envelope correlation coefficient are obtained.

Design and analysis of a novel wireless resistive analog passive sensor technique

Unobtrusive monitoring of physiological signals in natural settings is important for precision diagnostics. Fully-passive wireless body-worn sensors are viable and promising for unobtrusive monitoring. In this study, the authors present a new class of fully-passive sensor, namely wireless resistive analog passive (WRAP) sensor. It uses resistive transducers at the sensors for converting physical stimulus to load modulation of carrier wireless signal at 13.56 MHz at low power (–20 to 0 dBm). The sensor is simply composed of a loop antenna, a tuning capacitor, and a resistive transducer suitable for the type of physiological signals to be measured. The authors report the characterisation of WRAP sensors for various resistive loads of 1.2 ω to 82 kω at various co-axial distances (5–40 mm) between the TX and RX antennas. They have prototyped and characterised multiple WRAP sensors with several practical measurements of physiological signals such as heart rate, temperature, and pulse oximetry. They also demonstrate bio-potential measurement (down to 400 μVpp) using metal–oxide–semiconductor field-effect transistor as the transducer. These results show the feasibility of developing a new type of body-worn fully-passive WRAP sensors for unobtrusive physiological signal monitoring at real-life settings for precision diagnostics of many disorders and tracking person-centric therapy efficacy.

Outdoor large-scale path loss characterization in an urban environment at 26, 28, 36, and 38 GHz

Most of the existing channel models cannot be applied to emerging millimeter-wave (mmWave) systems due to the difference between the characteristics of existing operating frequency bands and mmWave frequency bands. Thus, extensive studies on channel characterization and modeling are required to develop a general and suitable channel model that can accommodate a wide range of mmWave frequency bands in its modeling parameter. This paper presents a study of well-known channel models and their authentications for outdoor scenarios on the 26, 28, 36, and 38 GHz frequency bands. A new generalized path loss model for a range of mmWave frequency bands is proposed. Measurements for the outdoor line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios were taken every meter over a separation distance of 114 m between the TX and RX antenna locations to compare the well-known and the new large-scale generic path loss models. This outdoor channel characterization and modeling was conducted in Malaysia, which represents a tropical region environment, and the outcomes were investigated based on the proposed and the well-known path loss models for single- and multi-frequency schemes. Results show that the proposed model is simple and accurate in terms of frequency and environment signal attenuation. The path loss exponent values are 1.54 and 3.05 for the 20 GHz and 30 GHz bands, respectively.

Isolation Improvement Techniques for Wideband Millimeter-Wave Repeaters

Two passive approaches for improving the isolation between flush-mounted transmitting (TX) and receiving (RX) antennas over 45–110 GHz are investigated. Both configurations exploit a reactive impedance surface (RIS) that suppresses TM polarized surface waves propagating on the ground plane between the TX and RX antennas. Quarter-wavelength corrugated one-dimensional (1-D) RIS is shown to improve isolation by ∼20 dB in an octave bandwidth (45–90 GHz), whereas concentric corrugations around the antennas improve isolation over the same bandwidth with better antenna radiation characteristics at the low end. On the other hand, an isolation improvement of ∼15 dB over the entire bandwidth is obtained with an array of grounded circular patches 2-D RIS. Computational studies are validated with measurements of quad-ridge horns with 3-D printed corrugations and printed circuit board 2-D RIS patches.

Predicting Wireless MmWave Massive MIMO Channel Characteristics Using Machine Learning Algorithms

This paper proposes a procedure of predicting channel characteristics based on a well‐known machine learning (ML) algorithm and convolutional neural network (CNN), for three‐dimensional (3D) millimetre wave (mmWave) massive multiple‐input multiple‐output (MIMO) indoor channels. The channel parameters, such as amplitude, delay, azimuth angle of departure (AAoD), elevation angle of departure (EAoD), azimuth angle of arrival (AAoA), and elevation angle of arrival (EAoA), are generated by a ray tracing software. After the data preprocessing, we can obtain the channel statistical characteristics (including expectations and spreads of the above‐mentioned parameters) to train the CNN. The channel statistical characteristics of any subchannels in a specified indoor scenario can be predicted when the location information of the transmitter (Tx) antenna and receiver (Rx) antenna is input into the CNN trained by limited data. The predicted channel statistical characteristics can well fit the real channel statistical characteristics. The probability density functions (PDFs) of error square and root mean square errors (RMSEs) of channel statistical characteristics are also analyzed.

Adaptive Spur Cancellation Technique in All-Digital Phase-Locked Loops

The phenomenon of periodic phase errors (also known as spurs) in phase-locked loops (PLLs) is widely acknowledged and is responsible for posing considerable challenge on development of miniaturized wireless communication devices. The common approach employed today for spur mitigation calls for a digital notch filter within the receive chain, while there is no similar digital scheme for the transmit chain. In addition, this notch filter is not perfect and usually degrades the overall receiver sensitivity. This brief puts forward a novel idea, which is to cancel the spurs inside the PLL such that the local oscillator signal and consequently TX and RX antenna ports become spur-free. The technique is based on a least-mean squares algorithm that features a self-learning capability. The method has been silicon proven in a digital PLL of a transceiver radio test chip realized in a standard nanoscale CMOS technology.

Wideband Decoupling Techniques for Dual-Polarized Bi-Static Simultaneous Transmit and Receive Antenna Subsystem

A wideband, bistatic, and dual-polarized simultaneous transmit and receive antenna subsystem with isolation >60 dB over 6–19 GHz band is demonstrated. The proposed configuration employs two quad-ridge horns fed by a ridge waveguide ortho-mode transducer (OMT) as transmitting (TX) and receiving (RX) antennas. The OMT enables dual-polarized high-power operation for the TX antenna over the entire bandwidth. The TX/RX antennas are flush mounted in a flat ground plane and oriented in D-plane to achieve similar isolation for both polarizations. Different decoupling techniques for increasing isolation between TX/RX antennas are investigated. Specifically, a high capacitive reactance bed of nails is designed to suppress TM polarized surface waves on the metallic ground plane. Moreover, a wideband planar and low-profile high-impedance surface is developed and performance thereof is compared to that of the other considered surfaces. Effect of recessing the RX antenna in an absorber is also discussed. Computational and experimental studies are conducted to demonstrate and validate the performance of the proposed antenna subsystem. Good impedance match, excellent radiation characteristics, and high isolation are achieved.

Measured 21.5 GHz Indoor Channels With User-Held Handset Antenna Array

For mobile systems involving hand-held devices, the influence of the user on system performance has to be considered. Extensive studies below 6 GHz have demonstrated large effects on system performance. However, the impact of user influence at potential frequency bands for upcoming 5G mobile networks is still to be investigated. This paper investigates how the user affects the performance of a 5G handset mock-up. The user impact is studied by channel sounding in an indoor scenario, with and without the presence of different users. The mock-up handset has a uniform linear array of receive (Rx) antennas operated at 21.5 GHz. A dual-polarized horn antenna with a wide beamwidth is transmit antenna and a fast channel sounder is used, allowing for dynamic and realistic channels. The results show that the mean influence of the user on the power varies considerably depending on the scenario, with more than 12 dB loss in some cases, while a gain of 4 dB is seen in other. An important finding is that the mean power among the seven Rx branches may be very different. Branch power ratios in the typical range of 2–10 dB were found, depending on the user and scenario.

X-Duplex Relaying: Adaptive Antenna Configuration

In this letter, we propose a joint transmission mode and transmit/receive (Tx/Rx) antenna configuration scheme referred to as X-duplex in the relay network with one source, one amplify-and-forward (AF) relay and one destination. The relay is equipped with two antennas, each of which is capable of reception and transmission. In the proposed scheme, the relay adaptively selects its Tx and Rx antenna, operating in either full-duplex (FD) or half-duplex (HD) mode. The proposed scheme is based on minimizing the symbol error rate (SER) of the relay system. The asymptotic expressions of the cumulative distribution function (CDF) for the end-to-end signal to interference plus noise ratio (SINR), average SER and diversity order are derived and validated by simulations. Results show that the X-duplex scheme achieves additional spatial diversity, significantly reduces the performance floor at high SNR and improves the system performance.

Directional Full-Duplex RF Booster for 2450 MHz ISM Band

A directional repeater system with simple architecture composed of wideband receive and transmit antennas, a high gain low-power amplifier, and a bandpass filter is proposed for the 2450-MHz ISM band. The repeater system does not require down-conversion and up-conversion with frequency translation and does not rely on any operational protocol to manage users. As a result, the repeater (RF booster) can support all users, channels, modulation themes, and devices simultaneously. Close to 70 dB of isolation between the Tx and Rx antennas over the entire band (~100 MHz) is achieved for a compact structure with lateral dimensions of 8 cm $\times $ 12 cm and thickness of 1 cm. The isolation between the Tx and Rx antennas is achieved using polarization mismatch between orthogonal double-stack patch antennas and a novel two-element Rx antenna whose elements are appropriately located with respect to the Tx antenna to cancel the signal leakage from the Tx antenna to the Rx antennas. Two types of repeaters, one utilizing only the ground plane and polarization mismatch, and the second using the two-element Rx antenna in addition to polarization mismatch, are fabricated and tested in different environments. It is shown that more than 30 dB improvement in coverage can be achieved.

Spatiotemporal-MIMO Channel Estimator and Beamformer for 5G

With requirements of spiraling data rates and limited spectrum availability, there is an increased interest in mm-wave beamformer-based communications for 5G. For upcoming cellular networks, the critical point is to exploit the increased number of employable antennas at both Tx and Rx to: 1) combat increased path loss; 2) tackle higher interference due to higher user density; and 3) handle multipath effects in frequency selective channels. Toward this, a multi-beam spatiotemporal superresolution beamforming framework is proposed in this paper as a promising candidate to design beampatterns that mitigate/suppress co-channel interference and deliver massive gain in the desired directions. Initially, channel and signal models suitable for the mm-wave MIMO system are presented using the manifold vectors of both Tx and Rx antenna arrays. Based on these models, a novel subspace-based channel estimator is employed, which estimates delays, directions, velocities, and fading coefficients of the desired signal paths. This information is then exploited by the proposed spatiotemporal beamformer to provide a massive array gain that combats path loss without increasing the number of antenna array elements and to be tolerant to the near-far problem in a high interference environment. The performance of the proposed channel estimator and beamformer is examined using computer simulation studies.

All-Directions Through-the-Wall Radar Imaging Using a Small Number of Moving Transceivers

Through-the-wall radar imaging systems are utilized for mapping buildings' interiors and detecting static and moving objects hidden behind the walls. The current techniques rely on large linear antenna arrays with directional radiation pattern for obtaining high cross-range resolution, and their imaging capability is limited by the low array processing gain and field of view. This paper introduces a new technique for through-the-wall radar imaging in which the linear array is replaced by a dense 2-D synthetic array formed by an ad hoc network of moving transceivers with omnidirectional antennas. Applying this method enables imaging of building interiors from outside or inside with 360° field of view. As receivers move, the direct and reflected signals from a stationary transmitter are sampled at different positions within the roaming domain, and by combining such signal samples using an appropriate beam-forming technique, a large and dense array is synthesized to provide an accurate radar map of the buildings' interiors and hidden objects in all directions. To increase the system dynamic range, the direct signals between the transmitter (Tx) and receiver (Rx) antennas are reduced, utilizing orthogonal polarizations for Tx and Rx. To improve the range resolution and reduce the background noise, a new method based on the generalized pencil of function method is proposed. This method can accurately detect the locations of the reflecting points within the image which, in combination with the standard back-projection focusing, provides high-quality radar images. A finite-element method for a simple building structure and ray tracing for a large 3-D building structure are used to evaluate the performance of the proposed method.

A Radio Channel Sounder for Mobile Millimeter-Wave Communications: System Implementation and Measurement Assessment

We describe a state-of-the-art channel sounder to support channel-model development for mobile millimeterwave (mm-wave) communications. The system can measure the complex amplitude, delay, and angle of arrival of the multipath components of indoor and outdoor channels. Specifically, a custom multiplexer (MUX) records the channel impulse response across a 16-element receive (RX) antenna array in 65.5 μs, while the channel is static. The delay resolution of the system is 1 ns and, because the elements are oriented in a 3-D space, both azimuth and elevation angles can be extracted. The robust link budget, comprising high-gain directional RX antennas, enables indoor link measurement beyond 150 m in line-of-sight and 20 m in non-line-of-sight conditions. The RX array is mounted on a location-aware robot, which is battery operated. Combined with the speed of the MUX, untethered acquisition of mobile-channel data is possible. To the best of our knowledge, this paper contributes the first sounder that is capable of mobile measurements at mm-wave frequencies. The hardware implementation of a functional 83.5-GHz system is described in this paper, and some illustrative results, including small-scale statistics and Doppler, are presented.

Measurement and Evaluation of Tx/ Rx Antennas for X-Band Radar System

This paper presents the performance evaluation of antennas for microwave transmission and reception in X-band radar systems. The transmitter (Tx) and receiver (Rx) antennas are fabricated on microstrip array structures. The antennas are connected to microwave circuits with transmission lines, coaxial cables, and microwave combiners and splitters. The designed antennas in X-band microwave operation for Tx and Rx parts were fabricated identically by 4x64 microstrip patch antennasin an array structure. The fabricated antennas were measured for return loss (S11), VSWR, radiation pattern, and Gain. The detail methods for the measurements are reported and their results are also discussed. The measured antenna gain of ~20dBi, and beam-width of ~20degreecan be obtained using the fabricated antennas at 9.4GHz microwave operation.

Investigating signal propagation and strength distribution characteristics of wireless sensor networks in date palm orchards

To efficiently plan and deploy wireless sensor networks in palm orchards, it is crucial to obtain preliminary knowledge of radio signal propagation and strength distribution characteristics. Various received signal strength indicator (RSSI) measurements were taken with antennas, operating with a 2.4-GHz band and located 0.05m away from trunks. The RSSI measurements, at seven different antenna heights along one certain horizontal line, revealed that there were three distinct signal propagation characteristics resulting from the morphological features of the date palm trees. Compared with other heights, the attenuation rate was lower when the antennas were placed below the crown base due to the relative lack of obstacles in the propagation paths, which also provided good options for installing the antennas. In addition, off-shoots had a slightly negative impact on signal propagation. Comparison analyses showed that the logarithm model was the most accurate and convenient of all the empirical signal attenuation models for predicting low power wireless signal propagation characteristics in date palm orchards. Further measurements were conducted to investigate the received signal strength distribution around individual trunks and between the orchards of different ages. Results indicated that the reliable communication range showed an increasing trend with increasing orchard age. Moreover, the trunks negatively impacted the signal propagation, and the interference strength depended on the position relationship among the trunks, the Tx and Rx antennas. Finally, the specific and detailed references were provided for the planning and deployment of wireless sensor networks in date palm orchards. Concluding remarks address potential future research.

Dual smoothing DOA estimation of two-channel FMCW radar

We proposed a dual smoothing superresolution direction-of-arrival (DOA) estimation for multitarget detection with two-channel frequency modulated continuous-wave (FMCW) radar. For the conventional superresolution FMCW radar, the number of detectable targets for DOA estimation is limited by the number of RX antenna arrays. To enable DOA estimation for more targets than the number of receiving channels, we propose exploiting a dual shift invariant structure of dual smoothed matrix. We implemented two-channel FMCW radar and tested the performance of the proposed method.

Analysis and Augmented Spatial Processing for Uplink OFDMA MU-MIMO Receiver With Transceiver I/Q Imbalance and External Interference

We address receiver (RX) signal processing in MIMO systems under in-phase/quadrature (I/Q) imbalance, which causes cross-talk of mirror-subcarriers in OFDM systems. We extend the typically reported single-user studies to uplink OFDMA-based multiuser MIMO, with simultaneous user multiplexing in frequency and spatial domains. We also incorporate multiple external interferers, for modeling challenging conditions in heterogeneous networks. In the signal processing developments, we exploit the augmented subcarrier processing, which processes each subcarrier jointly with its counterpart at the image subcarrier, and jointly across RX antennas. Furthermore, we derive an augmented LMMSE RX. The novel approach integrates the I/Q imbalance mitigation, interference suppression and data stream separation into a single processing stage, thus avoiding a separate transceiver calibration. Our numerical results show the signal-to-interference-plus-noise ratio and symbol-error rate of an arbitrary data stream after RX processing as a function of different system parameters. The per-subcarrier processing is shown to suffer heavily under I/Q imbalances, and being particularly sensitive to external interferers, whereas the augmented method provides efficient data stream separation and interference suppression. Finally, we extend the studies to massive MIMO framework and show that the per-subcarrier processing still suffers from performance degradation, whereas the augmented approach can fully exploit the array gain.

Robust Scheduling and Resource Allocation in the Downlink of Spatially Correlated MIMO-OFDMA Wireless Systems With Imperfect CSIT

Multiple-input-multiple-output (MIMO) orthogonal frequency-division multiple access (OFDMA) has been selected as the core physical-layer access scheme for the downlink of state-of-the-art and next-generation wireless communications standards. In these systems, scheduling and resource allocation (SRA) algorithms, jointly assigning transmission data rates, bandwidth, and power, become crucial in optimizing resource utilization while providing support to multimedia applications with heterogeneous quality-of-service (QoS) requirements. To this end, the transmitter is assumed to have channel state information at the transmitter (CSIT) that will typically be imperfect. This paper introduces a unified analytical framework for robust channel- and queue-aware QoS-guaranteed cross-layer SRA algorithms for the downlink of MIMO-OFDMA networks with imperfect CSIT. The framework is based on the statistical characterization of the signal-to-noise ratio (SNR) under imperfect CSIT and is general enough to encompass spatial correlation effects in the Tx and Rx antenna arrays, different types of traffic, uniform and continuous power allocation, discrete and continuous rate allocation, and protocols with different amounts of channel and queue awareness. Simulation results using parameters drawn from the Third-Generation Partnership Project Long-Term Evolution (3GPP-LTE) standard demonstrate the validity and advantages of the proposed robust cross-layer unified approach.