Tx Antennas Research Articles

Adaptive Matching Transmitter With Dual-Band Antenna for Intraoral Tongue Drive System

The intraoral Tongue Drive System (iTDS) is a wireless assistive technology that detects users' voluntary tongue gestures, and converts them to user-defined commands, enabling them to access computers and navigate powered wheelchairs. In this paper, we presented a transmitter (Tx) with adaptive matching and three bands (27, 433, and 915MHz) to create a robust wireless link between iTDS and an external receiver (Rx) by addressing the effects of external RF interference and impedance variations of the Tx antenna in the dynamic mouth environment. The upper two Tx bands share a dual-band antenna, while the lower band drives a coil. The Tx antenna is simulated in a simplified human mouth model in HFSS as well as a real human head model. The adaptive triple-band Tx chip was fabricated in a 0.35-μm 4P2M standard CMOS process. The Tx chip and antenna have been characterized in a human subject as part of an iTDS prototype under open-and closed-mouth scenarios, which present the peak gain of -24.4 and -15.63 dBi at 433 and 915MHz, respectively. Two adaptive matching networks for these bands compensate variations of the Tx antenna impedance via a feedback mechanism. The measured S11 tuning range of the proposed network can cover up to 60 and 75 jΩ at 433 and 915MHz, respectively.

Numerical and Experimental Investigations of Base Station Antenna Height on Cellular Network Coverage

A test setup is deployed to study the influence of base station antenna height on the cellular network coverage. Both the numerical and experimental investigations are undertaken to evaluate the received electric field levels for different heights of the transmitting (TX) antenna and several distances between the transmitter and the receiver. The numerical simulation results demonstrate that when the TX antenna is mounted high above the ground, more fluctuations are induced in the electric field levels, resulting in possible dead zones for mobile communications. The measured received levels and data rates confirm the numerical simulation results.

A Channel Sounder for Massive MIMO and MmWave Channels

Both massive multiple-input multiple-output (MIMO) technology and use of frequencies in the range 24100 GHz are considered essential for upcoming 5G systems. Measurements of the new type of channels are needed, but this is challenging due to the large number of channels in massive MIMO and the short wavelength in the 24100 GHz channels (so-called mmWave channels). This article describes a sounder system capable of measurements in both types of channels. While the same sounder system supports simultaneous massive MIMO and mmWave channels, the number of channels in each band and in total is in practice limited. For massive MIMO in the 3006000 MHz band alone, arrays with up to 128 receiver (Rx) elements are possible, receiving from 16 independent mobile transmitter (Tx) antennas, where all channels are measured within 1.3 ms and in a 200 MHz bandwidth. To the authors' knowledge, this is the first sounding system with this number of channels and a speed necessary for measuring the dynamic channels in typical application scenarios. For mmWave channels, the sounder operates in the range 1840 GHz. For these bands up to 2 Tx elements and 16 Rx elements can be measured. In addition, the article describes some measurements in both a massive MIMO setup in an indoor sports arena and an mmWave setup with a

Design of a MMIC low‐noise amplifier in industrial gallium arsenide technology for E‐band 5G transceivers

AbstractThe technology, design procedure and measurements of an E‐band (71‐86 GHz) high performance gallium arsenide (GaAs) low‐noise amplifier (LNA) are presented. The latter provides a gain in excess of 20 dB, an average in‐band noise figure (NF) of 2.3 dB, absorbing 60 mW DC bias power. A European space‐qualified technology (OMMIC's GaAs 70 nm process) has been selected to demonstrate the feasibility of employing the proposed LNA for production‐ready wireless backhaul point‐to‐point communication systems. A possible installation scenario has been depicted, in order to verify the maximum distance at which TX and RX antennas can be placed and employing the proposed LNA as first amplifying stage of the receiver chain.

Sensor Antenna Transmitter System for Material Detection in Wireless-Sensor-Node Applications

This paper presents a fully combined sensor-antenna transmitter system for sensing relative permittivity of material at microwave frequencies. The transmit (Tx) antenna senses the relative permittivity of specimen and loads the radio frequency (RF) oscillator which translates the relative permittivity to the operational frequency of the carrier signal. At the same time, independent data, which can be the Radio Frequency Identification (RFID) information, are ON-OFF keying modulated over the carrier. At the receiver, a demodulator system extracts the data stream as well as recovers the carrier frequency using a zero-crossing detector. Therefore, the relative permittivity of the sample can be obtained from the extracted frequency shift as a digital number. As all the sensing elements in the proposed structure are passive, the sensor does not increase the power consumption of the system. The sensor-transceiver capability at low powers makes it ideal for sensor nodes in the Internet of Things applications. Since the sensing and demodulation are implemented at the same time, the complexity for detection reduces significantly compared with traditional RF/microwave sensing techniques which need complicated frequency spectrum monitoring equipment. The output of the system is a digital number correlated to the dielectric constant of the specimen and the independent data stream for communication. The proposed sensor node is fabricated at the 2.45-GHz ISM band as an evaluation and the measurement results with some known samples are presented.

Channel Characterization and Path Loss Modeling in Indoor Environment at 4.5, 28, and 38 GHz for 5G Cellular Networks

The current propagation models used for frequency bands less than 6 GHz are not appropriate and cannot be applied for path loss modeling and channel characteristics for frequency bands above 6 GHz millimeter wave (mmWave) bands, due to the difference of signal propagation characteristics between existing frequency bands and mmWave frequency bands. Thus, extensive studies on channel characterization and path loss modeling are required to develop a general and appropriate channel model that can be suitable for a wide range of mmWave frequency bands in its modeling parameter. This paper presents a study of well-known channel models for an indoor environment on the 4.5, 28, and 38 GHz frequency bands. A new path loss model is proposed for the 28 GHz and 38 GHz frequency bands. Measurements for the indoor line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios were taken every meter over a separation distance of 23 m between the TX and RX antenna locations to compare the well-known and the new large-scale generic path loss models. This measurement was conducted in a new wireless communication center WCC block P15a at Universiti Teknologi Malaysia UTM Johor, Malaysia, and the results were analyzed based on the well-known and proposed path loss models for single-frequency and multifrequency models and for directional and omnidirectional path loss models. Results show that the large-scale path loss over distance could be modeled better with good accuracy by using the simple proposed model with one parameter path loss exponent PLE (n) that is physically based to the transmitter power, rather than using the well-known models that have no physical base to the transmitted power, more complications (require more parameters), and lack of anticipation when explaining model parameters. The PLE values for the LOS scenario were 0.92, 0.90, and 1.07 for the V-V, V-H, and V-Omni antenna polarizations, respectively, at the 28 GHz frequency and were 2.30, 2.24, and 2.40 for the V-V, V-H, and V-Omni antenna polarizations, respectively, at the 38 GHz frequency.

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.

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.

Simplified Antenna Group Determination of RS Overhead Reduced Massive MIMO for Wireless Sensor Networks.

Massive multiple-input multiple-output (MIMO) systems can be applied to support numerous internet of things (IoT) devices using its excessive amount of transmitter (TX) antennas. However, one of the big obstacles for the realization of the massive MIMO system is the overhead of reference signal (RS), because the number of RS is proportional to the number of TX antennas and/or related user equipments (UEs). It has been already reported that antenna group-based RS overhead reduction can be very effective to the efficient operation of massive MIMO, but the method of deciding the number of antennas needed in each group is at question. In this paper, we propose a simplified determination scheme of the number of antennas needed in each group for RS overhead reduced massive MIMO to support many IoT devices. Supporting many distributed IoT devices is a framework to configure wireless sensor networks. Our contribution can be divided into two parts. First, we derive simple closed-form approximations of the achievable spectral efficiency (SE) by using zero-forcing (ZF) and matched filtering (MF) precoding for the RS overhead reduced massive MIMO systems with channel estimation error. The closed-form approximations include a channel error factor that can be adjusted according to the method of the channel estimation. Second, based on the closed-form approximation, we present an efficient algorithm determining the number of antennas needed in each group for the group-based RS overhead reduction scheme. The algorithm depends on the exact inverse functions of the derived closed-form approximations of SE. It is verified with theoretical analysis and simulation that the proposed algorithm works well, and thus can be used as an important tool for massive MIMO systems to support many distributed IoT devices.

Analysis of Antenna Structure for Energy Beamforming in Wireless Power Transfer

The technology to send a magnetic field in a particular direction, known as energy beamforming, has been recently introduced as a magnetic field shaping technology in nonradiative wireless power transmission. In general, one of the most efficient conditions for energy beamforming is that the magnetic fields induced by each antenna should be synthesized to head the same direction. To synthesize the magnetic fields induced at each antenna, interference by mutual inductance that can occur between transmitting (TX) antennas should be minimized. In addition, energy should not be exchanged between the TXs, otherwise it lowers the transmission efficiencies of TX and receiving antenna. In this paper, we present an optimal antenna structure that minimizes the mutual inductance between two TX antennas. First, we have analyzed the mutual inductance between TX antennas that have asymmetric sizes with different antenna lengths and arrangement angles. The directivity of the magnetic field vector is also investigated through an experimental analysis of an antenna structure. Finally, it has been verified that the optimal TX antennas for energy beamforming should be symmetric, which means that all the length of antennas are same and disposed perpendicular to each other. The experimental results show that the deviations of magnetic field directivity for symmetric and asymmetric antennas are 0.045 and 0.355, respectively, which shows that the symmetric structure shows 8.2 times larger consistency over the asymmetric structure.

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.

Generalization of the Phase Shift Condition in “Intrinsic ICI-Free Alamouti Coded FBMC”

The condition given in (5) of the paper “Intrinsic ICI-Free Alamouti Coded FBMC” accomplishes the desired property, i.e., ICI-free performance of frequency reversal alamouti coded FBMC. However, this condition is sufficient but not necessary as it corresponds to a subset of the solutions. We show that this condition can be relaxed to cover more general solutions. This generalization allows more beneficial waveform generation such as decoupling peak power minimization at the two TX antennas and no need of null insertion to the center subcarrier.

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.

Iterative detection for frequency-asynchronous distributed Alamouti-coded (FADAC) OFDM

We propose a near intercarrier interference (ICI)-free and very low complexity iterative detector for frequency-asynchronous distributed Alamouti-coded (FADAC) orthogonal frequency division multiplexing (OFDM). In the previous cancelation schemes, the entire subcarrier signals from one transmit (TX) antenna are estimated and canceled in the received signal from the other TX antenna and vice versa. However, the reliability of the estimated symbols are revealed to significantly vary across the subcarriers and thus, the poorly estimated symbols lead to the incorrect cancelation. Motivated from this, we first propose a scheme which does not cancel the interfering subcarrier(s) at the half band edges which undergo very high interference in FADAC-OFDM. For further improvement, we propose a so-called selective scheme which instantly measures the reliability of the detected symbols at each iteration and then exclude the unreliable symbols in the estimated interference generation.Moreover, the proposed scheme has a drastically reduced complexity by converting the cancelation process from the subcarrier domain to the time domain. In accordance with the analysis on the considered reliability measures, the numerical results show that the proposed scheme achieves the near ICI-free level only within three or four iterations for wide ranges of SNR, frequency offset, and delay spread.

Optimal transmission power determination to increase energy efficiency of large-scale MIMO antenna systems

Large-scale (LS) MIMO antenna systems use excessive amount of TX antennas and serve limited number of users to make very high channel gain, and it is obvious that the channel gain increases spectral efficiency of the system. The transmission power of LS-MIMO systems also can be reduced from the increment of channel gain to increase energy efficiency (EE). In this situation, a determination of transmission power which is reduced from total available transmission power can be an important scheme to achieve high EE. This paper proposes a determination scheme of the EE optimum transmission power for LS-MIMO systems. The approximated optimum transmission power is derived analytically as a closed-form function based on various parameters, such as number of TX antennas, number of users, system bandwidth, interference, and so on. Using the closed-form function with the measurable parameters, we can easily get the optimum EE transmission power in real-time. The effectiveness of proposed scheme is validated with numerical simulations. According to the results, the proposed scheme can significantly increase the EE with fairly small loss of channel capacity, compared with ordinary LS-MIMO systems.