Rx Antennas Research Articles

Investigation of indoor propagation of WLAN signals

<p>The propagation of radio waves inside a typical university building is investigated by simulation and measurements. The Line of sight (LOS) and Obstructed Line of sight (OLOS) propagation scenarios were considered. The received power from a WLAN access point operating at 2.45GHz was determined from the simulations and measurements at various positions, orientations, and heights of the Tx and Rx antennas. The path loss exponents were estimated from the obtained simulation and measurement results of the received power variation with distance. The obtained path loss exponent values were found between 1.15-1.63 for LOS propagation and 2.14-2.55 for OLOS.</p>

A Software-Defined Radio Receiver for Wireless Recording From Freely Behaving Animals.

To eliminate tethering effects on the small animals' behavior during electrophysiology experiments, such as neural interfacing, a robust and wideband wireless data link is needed for communicating with the implanted sensing elements without blind spots. We present a software-defined radio (SDR) based scalable data acquisition system, which can be programmed to provide coverage over standard-sized or customized experimental arenas. The incoming RF signal with the highest power among SDRs is selected in real-time to prevent data loss in the presence of spatial and angular misalignments between the transmitter (Tx) and receiver (Rx) antennas. A 32-channel wireless neural recording system-on-a-chip (SoC), known as WINeRS-8, is embedded in a headstage and transmits digitalized raw neural signals, which are sampled at 25 kHz/ch, at 9 Mbps via on-off keying (OOK) of a 434 MHz RF carrier. Measurement results show that the dual-SDR Rx system reduces the packet loss down to 0.12%, on average, by eliminating the blind spots caused by the moving Tx directionality. The system operation is verified in vivo on a freely behaving rat and compared with a commercial hardwired system.

Antenna pairing for highly efficient wireless power transmission in the reactive near‐field region based on mutual coupled impedance compensation

This study presents the design of an antenna pair for short-distance wireless power transmission (WPT) in the reactive near-field (NF) region. Instead of designing each antenna alone to achieve good reflection coefficients, the transmitting (TX) and receiving (RX) antennas as a pair are designed to maximise the transmission coefficients. Thus, the antenna pair can mutually compensate the impedance mismatching caused by the coupling between them to enhance energy transfer efficiency. Based on this concept, the developed RX antenna, a key component of rectennas, has a dual functionality to retain relatively stable reflection coefficients when it is moved far away from the NF TX antenna, for example, to pair with other conventional far-field WPT TX antennas with larger separation distances. The electromagnetic field and energy transfer characteristics, as well as system experiments, are presented to validate the design.

Analytical and Experimental Investigation of Ultra Wideband Channel Characteristics in the Presence of Door/Window Glass

This paper presents ultra-wideband channel characteristics in the presence of float glass slab as obstacle of varied thickness (4 mm, 8 mm, 12 mm, 19 mm) in an indoor environment. Two different sets of measurements are performed related to variation in the Tx–Rx antenna position and rotation of the glass slab at angles varying from 0° to 90° to mimic the glass door/window movement. The channel characterization of various Tx–Rx links are carried out by analyzing various parameters such as RMS delay spread, peak magnitude of the power delay profile and received signal amplitude. Different direct path, partial and total obstructed path situations are observed depending on the position of the Rx antenna, rotation angle of the glass slab and also the position of the Tx–Rx antennas with respect to the glass slab. Results indicate higher multipath and RMS delay spread for glass edge scattering and direct through glass propagation. Decrease in signal strength is more prominent for 12/19 mm glass thickness in comparison to 4 mm glass sheets for partial NLOS and NLOS scenarios. For LOS situations, channel parameters for various glass thickness show similar range of values and are comparable with the scenario when no-glass in present.

A Compact Rx Antenna Integration for 3D Direction-Finding Passive Radar

A Compact Rx Antenna Integration for 3D Direction-Finding Passive Radar

Improvement of GPR SAR-Based Techniques for Accurate Detection and Imaging of Buried Objects

This paper introduces three methodologies to improve synthetic aperture radar (SAR)-based techniques used in ground-penetrating radar (GPR) systems. They consist of: 1) equalization of the frequency response of the transmitting (Tx) and receiving (Rx) antennas; 2) processing of SAR images using partially overlapped frequency subbands; and 3) imaging domain clustering. The goal is to combine ground penetration capabilities of lower frequency bands with the resolution achieved when increasing the overall frequency band, resulting in enhanced detection and imaging capabilities. Validation of these techniques has been done at three levels: first using simulations, next by means of measurements in a controlled scenario, and, finally, using a portable setup deployed in a realistic scenario.

A Wearable RF Sensor for Monitoring Respiratory Patterns.

We present a non-invasive approach for continuous monitoring of respiration dynamics using a wearable radio-frequency (RF) sensor based on near-field coherent sensing. A continuous-wave RF signal at 1.8 GHz is generated by a software-defined radio, with both transmitter (Tx) and receiver (Rx) antennas placed close to the xiphoid process. The experimental prototype of the mobile sensor can modulate the internal organ motion in the near-field region of the Tx antenna and is then received by the nearby Rx antenna to be demodulated and sampled. Through peak detection, we have identified inhalation and exhalation peaks of each breath cycle to estimate the breath rate and the lung volume. The extracted respiratory parameters are compared with the conventional chest belts data for various simulated respiratory conditions including voluntary deep, fast-shallow and slow-shallow breathing. We also characterized simulated central sleep apneas, Cheyne-Stokes, Biot's, ataxic and coughing conditions. To accurately identify obstructive apnea, we presented a two-sensor approach that can capture paradoxical movement of thorax and abdomen. The on-line recognition of these respiratory patterns can be employed not only to continuously monitor patients with chronic respiratory disorders but also to provide real-time feedback for future therapeutic purposes.

Noncontact Vital Sensing With a Miniaturized 2.4 GHz Circularly Polarized Doppler Radar

Conventionally, in Doppler radar vital sign detection, two separate linearly polarized TX and RX antennas are used and often placed more than half wavelength away from each other to mitigate mutual coupling. However, the overall footprint of the radar system with separate TX/RX antennas may make it difficult to be integrated into compact consumer devices. In this article, a single dual circularly polarized circular patch antenna was presented to help to achieve a miniature Doppler radar system. The proposed antenna was designed, integrated, and demonstrated with a 2.4 GHz radar transceiver module, but the design method and approach could be extended to higher frequencies to help to reduce the antenna area needed for radar sensing. The designed antenna at 2.4 GHz has the largest dimension of no larger than 5 cm and TX/RX isolation of better than 30 dB, ensuring good detection sensitivity. With a low output power of 0 dBm, both respiration and heartbeat movements of human test subjects can be detected accurately.

A 24 GHz ISM-Band Doppler Radar Antenna With High Isolation Characteristic for Moving Target Sensing Applications

A 24 GHz Industrial, Scientific, and Medical (ISM)-band Doppler radar antenna with high isolation is proposed for moving target sensing applications. Both transmit (Tx) and receive (Rx) antennas consist of 2 × 2 microstrip patch antenna arrays. High isolation of the proposed antenna is achieved by inserting periodic Jerusalem cross slot array between Tx port and Rx port, and thus the surface wave from Tx port to Rx port is significantly suppressed. The −10 dB reflection coefficient bandwidth of the proposed antenna is 510 MHz, and the isolation between Tx port and Rx port is higher than 36.7 dB over the 24 GHz ISM band. The simulated half-power beamwidths are 58.53° for E -plane and 47.54° for H -plane. Experimental results show that high isolation can lead to improve Doppler radar performance. The proposed antenna can be a good candidate for contact-free monitoring of the heart rate and respiration rate in healthcare applications.

Compact Co-Horizontally Polarized Full-Duplex Antenna With Omnidirectional Patterns

This letter presents a compact co-horizontally polarized (HP) in-band full-duplex (IBFD) antenna with omnidirectional patterns. The Tx antenna is a variant turnstile antenna with four 90° progressively phased T-shaped monopoles, whereas the Rx antenna is an in-phase loop antenna with four symmetrically excited dipoles. The polarizations and radiation patterns of both antennas are horizontally polarized and omnidirectional patterns in the azimuth plane. Nevertheless, a high measured isolation of more than 37 dB across the desired band is achieved with an orthogonal spatial phase diversity approach. To the best of our knowledge, this is the first time two co-HP omnidirectional antennas are integrated with a high isolation for the IBFD communication. The proposed antenna has the potential to double the spectral efficiency of wireless communication systems and to combat the polarization variations in the rich multipath environments.

Packaging Solution Based on Low-Temperature Cofired Ceramic Technology for Frequencies Beyond 100 GHz

In this paper, a package concept based on low-temperature cofired ceramic (LTCC) technology is illustrated. The concept is specifically designed for frequencies beyond 100 GHz, taking into consideration the inherent LTCC manufacturing defects, e.g., shrinkage, layer misalignment, and warping. Simple techniques are used for package assembly which can be automated using standard industrial processes. The proposed concept is implemented by integrating a 122-GHz silicon-germanium (SiGe) radar transceiver chip in an LTCC-based package. The off-chip components of the package, operating at 122 GHz, include a transmit (Tx) and a receive (Rx) aperture-coupled patch antenna array, a stripline to grounded coplanar waveguide signal transition feeding each of the antenna arrays, and three parallel, self-matched ground-signal-ground wirebonds connecting the SiGe radar transceiver chip and the LTCC package on Tx and Rx side. The simulation and measurement results of the Tx and Rx antenna arrays along with the signal transitions in the frequency range of 110–140 GHz are shown. The radar front end (RFE) is encapsulated using an epoxy molding compound, Polytec TC 430-T with suitable dielectric characteristics in the desired frequency range. The encapsulated RFE is surface mounted on a baseband printed circuit board, thereby realizing a fully functional 122-GHz frequency modulated continuous wave (FMCW) radar. The FMCW radar is used to measure the distance of a target, and the measurement results are compared with those of a commercial 122-GHz RFE.

Ambient Backscattering Transponder With Independently Switchable Rx and Tx Antennas

This article presents an ambient backscattering transponder with independently beam-switchable receive and transmit antennas. The independently switchable antennas make it possible to collect ambient waves from the direction where they are the strongest and further modulate and redirect the waves toward the receiver possible in a direction other than the ambient source. The transponder consists of patch antennas, circulators, low-power RF switches, and a diode-based modulator.

A Compact, Low-Profile Simultaneous Transmit and Receive Antenna With Monopole-Like Radiation Characteristics

A compact, vertically polarized simultaneous transmit and receive (STAR) antenna with a high transmit–receive isolation level and an omnidirectional radiation pattern in the azimuth plane is presented. The proposed STAR antenna consists of transmit (TX) and receive (RX) antennas whose phase centers are collocated. The TX antenna is a monopole with top-hat loading, placed directly below the central point of the crossed loop. The RX antenna consists of a pair of orthogonal half-loops, each capacitively fed at both of its ends with a $\text{180}^\circ$ phase difference. The four ports of the RX antenna are fed with the same amplitude and relative phase values of $\text{0}^\circ$ , $\text{90}^\circ$ , $\text{180}^\circ$ , and $\text{270}^\circ$ to produce an omnidirectional radiation pattern and high isolation with the TX antenna. The STAR antenna was designed for operation in the 2.45 GHz ISM band with electrical dimensions of $D \times H=$ $0.44\lambda \times 0.15\lambda$ (diameter × height). A prototype of this antenna was fabricated and experimentally characterized. Measurement results show that the antenna has a TX/RX isolation level better than 38 dB and maintains monopole-like patterns for both TX and RX modes over a frequency range of 2.4–2.7 GHz.

Passive RFID Uplink and Downlink Link Budget and Comparison of ASK and BPSK Backscatter Modulations

Complete link budget for forward and backward link in a RFID system are given with constituent parts. Backward link signal levels with current improvements requires separate TX and RX antenna bistatic configuration to overcome reader threshold. To further elaborate on link budgets, reflection coefficient and power equations are obtained from a RFID front-end model with circuit theory and shown on a passive RFID system. It is demonstrated that both forward and backward links have limitations on the range depending upon tag power dissipation, antennas in use and type of modulation. To make two distances equal, parameters are found from two way link equations. Then, ASK and BPSK modulations are compared on communication distance for given average backscatter difference power, minimum SNR to targeted BER on the reader by the equations obtained on the circuit model and MATLAB simulations.

Measurement-Based Massive MIMO Polarimetric Channel Characterization in Outdoor Environment

This paper introduces a measurement campaign to investigate the characteristics of massive multiple-input multiple-output (MIMO) channels in both line-of-sight (LoS) and obstructed LoS suburban outdoor environments. The measurements are conducted at the center frequency of 3.5 GHz with a bandwidth of 160 MHz. The transmitter is equipped with a 4 × 8 planar patch antenna array and the receiver is equipped with a 4 × 8 cylindrical patch antenna array. Each patch consists of two antenna ports which have main polarizations of +45° and -45°, respectively, resulting in a total of 64 × 64 sub-channels. We examined the influence of different polarization combinations on channel characteristics such as power delay profile (PDP), K-factor and delay spread for both LoS and obstructed LoS scenarios. Results show that the characteristics are more dependent on the Rx antennas rather than the Tx antennas. When the Rx antennas are facing the Tx antenna array, the received power is higher, the K-factor is lower and the delay spread is lower in cross-polarization cases with respect to the co-polarization ones in general. When the Rx antennas are back-facing the Tx antenna array, lower powers, higher K-factors and higher delay spreads can be observed in cross-polarization cases with respect to the co-polarization cases. In conclusion, the polarimetric influence on the channel characteristics depends on the antenna structure as well as the environment.

A 250-mW 60-GHz CMOS Transceiver SoC Integrated With a Four-Element AiP Providing Broad Angular Link Coverage

In this article, we present a low-power, small form-factor, 60-GHz packaged radio featuring broad beam coverage. We increase angular coverage by beam switching between two orthogonally pointed low directivity beams that are created using two different antennas integrated in package. The resulting wide angular coverage of the radio makes radio links robust to movement and rotation; this improvement overcomes a key challenge for millimeter-wave (mmWave) deployment in portable electronics. We incorporate a 3.2 mm $\times $ 3.2 mm 32-nm CMOS radio integrated circuit (IC) in the package for radio functions. The IC includes TX and RX RF front ends, up- and down-conversion mixers, TX and RX analog baseband circuits, a common PLL, TX and RX LO chains, and ADCs and a micro-controller for built-in self-test (BIST). The IC is flip-chip packaged on a four-layer organic package comprising two TX antennas and two RX antennas. In board-level over-the-air measurements of the half-duplex packaged radio, 17.1-dBm effective isotropic radiated power (EIRP) and 6.1-dB noise figure are achieved in the TX and RX modes respectively, with power consumption below 250 mW in either mode. We characterized the radio over the air using 802.11ad waveforms; the radio is 802.11ad compliant in both TX and RX modes at data rates up to the maximum 802.11ad PHY rate of 4.62 Gb/s (raw data rate >7 Gb/s) with a TX EVM $\pi $ steradians in first-of-a-kind measurements. The radio maintains 802.11ad compliance over 2.9 $\pi $ steradians solid angle.

Analytical Performance Assessment of THz Wireless Systems

This paper is focused on providing the analytical framework for the quantification and evaluation of the joint effect of misalignment fading and hardware imperfections in the presence of multipath fading at terahertz (THz) wireless fiber extenders. In this context, we present the appropriate system model that incorporates the different operation, design, and environmental parameters. In more detail, it takes into account the transceivers antenna gains, the operation frequency, the distance between the transmitter (TX) and the receiver (RX), the environmental conditions, i.e., temperature, humidity, and pressure, the spatial jitter between the TX and RX antennas that results to antennas misalignment, the level of transceivers' hardware imperfections, and the stochastic characteristics of the wireless channel. Based on this model, we analyze and quantify the joint impact of misalignment and multipath fading by providing novel closed-form expressions for the probability and cumulative density functions of the composite channel. Moreover, we derive exact closed-form expressions for the outage probability for both cases of ideal and non-ideal radio frequency (RF) front-end. In addition, in order to quantify the detrimental effect of misalignment fading, we analytically obtain the outage probability in the absence of misalignment cases for both cases of ideal and non-ideal RF front-end. In addition, we extract the novel closed-form expressions for the ergodic capacity for the case of the ideal RF front-end and tight upper bounds for both the cases of ideal and non-ideal RF front-end. Finally, an insightful ergodic capacity ceiling for the non-ideal RF front-end case is provided.

Microwave Imaging of Non-Rigid Moving Target Using 2D Sparse MIMO Array

This paper develops a microwave/mmw (millimeter-wave) imaging method for moving objects of non-rigid body which can be used in the heavy traffic scenarios. This method is proposed with a 2D sparse MIMO (multiple-input multiple-output) array composed of two orthogonal linear arrays. In comparison to the RX antennas, a smaller number of TX antennas is used to decrease the data acquisition time of this system when using TDM (time division multiplexing) signal transmitting technique. The 2D sparse MIMO array is deployed with wide-band signals transmitted to reconstruct the backscattering coefficient in 3D space using synthetic aperture imaging technique. Then a series of synthesized 3D snapshot images are generated during the motion of the target. The non-rigid human body target is decomposed into 25 joints tracked by an optical device which is Kinect in this paper. After the decomposition, the movement of each joint can be described as a space-time trajectory tracked by Kinect, providing a preliminary indication of the 3D position of each joint. With the indication, we divide every microwave/mmw image into 25 sub-images corresponding to the joints’ position to form an image sequence of each joint. Subsequently, a segmental joint estimation method is proposed to estimate the accurate motion parameters of each joint from the image sequence. The decorrelation of the images in large angle observation can be significantly reduced by the segmental estimation which leads global optimized motion parameters. Consequently, the estimated parameters are taken into the effective movement compensation of each component. Meanwhile, the image refocusing method is presented to generate the well-focused image of each component. Finally, all the images of components are fused into one image of the whole target to reconstruct the 3D high-resolution image. Imaging simulations and measuring data experiments show that this method is efficient.

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.

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.