Tx Antennas Research Articles

Detection of breast tumor with a frequency selective surface loaded ultra-wide band antenna system

Breast tumors are a significant cause to the global death rate among women. However, the fatality rate can be lowered through early detection. This paper presents an ultra-wideband, modified patch antenna of a compact size that can be used for microwave-sensing biomedical applications in the detection of breast cancer. A partial ground plane and slots are implemented in a transformed patch antenna to enhance the impedance bandwidth. The antenna is backed by a uniform frequency selective surface of 5 × 5 unit cells to achieve the necessary antenna characteristics, specifically directivity and gain, for microwave detection applications. Through optimization and fabrication, the final design maintained (|S11|< −10 dB) over the entire frequency band of 11.6 GHz (3.1–14.7 GHz) and achieved an average gain of over 5 dBi. Other metrics, such as group delay and the fidelity factor in different setups, are also simulated to observe the expected performance in the required frequency range. Finally, based on simulation, a model is suggested that comprises various configurations of antenna arrays, including one Tx antenna and one to seven Rx antennas. Further, breast phantom with different tumor sizes and locations were used in the simulation. The simulation results successfully validated the detection of breast cancer cells. We believe these technologies can open possibilities in healthcare applications for identifying tumors.

New indoor propagation model proposed for future B5G/6G rollout

Abstract The rollout of the fifth-generation (5G) mobile network was completed in 2020. Now, the focus shifts towards exploring the new perspectives of Beyond 5G (B5G) and 6G. Despite being a key enabler of 5G, millimeter wave technology has not yet been fully implemented due to various deployment challenges. Over the past decade, numerous efforts have been dedicated to modeling the propagation channel across the spectrum from 0.5 to 100 GHz. Propagation models such as Close-In (CI), Floating Intercept (FI), and single frequency Alpha-Beta-Gamma (ABG) have been extensively utilized. However, a significant deviation between co- and cross-polarization models has been observed in many estimated models in the literature. In this paper, we propose an optimization of the classic CI model by considering both TX and RX antenna heights, along with a correction coefficient. Initially, we estimate the propagation channel using the classic CI model in indoor environments, revealing a notable deviation between co- and cross-polarization models. Subsequently, we introduce a new model aimed at reducing this deviation and optimizing the Path Loss Exponent (PLE). With our proposed model, the estimated channel depolarization in Line-of-Sight (LOS) conditions stands at 2.8 dB, 5.6 dB, and 2.9 dB for room, corridor, and stairwell environments, respectively. In contrast, utilizing the conventional model yields channel depolarization figures of 4.8 dB, 8.2 dB, and 7 dB for the same environments. This disparity in channel depolarization can have significant implications for millimeter wave propagation, particularly during meteorological events such as rainfall.

A cross-polarized antenna sensor based on U-shaped resonator for crack sensing

To address the insufficient strain transfer ratio of monolithic antenna sensors and signal self-jamming in wireless interrogation, this paper presents a cross-polarized antenna sensor based on a U-shaped resonator for crack sensing. The sensor comprises an Rx antenna, a Tx antenna, and a sensing element. Employing cross polarization between Rx and Tx antennas mitigates ambient reflection, and the channel model of the sensing system based on cross polarization technique is demonstrated to reveal the working mechanism. Within the sensing element, a U-shaped resonator and movable shorted unit form an unstressed resonator, encoding the crack width in both the amplitude and phase in the retransmission signal, which are utilized to extract the sensor’s resonant frequency. The equivalent circuit model is established to analyze the monitoring mechanism comprehensively. The operational performance of the sensor is simulated in CST and validated by experiment. Results demonstrate a good linear relationship between the sensor’s resonant frequency and the crack width.

A Simultaneously Transmit and Receive Antenna Terminal for In-Band Full-Duplex Applications

In this paper, a low-profile co-linearly polarized simultaneously transmit-receive antenna (STRA) terminal is presented for 5G and upcoming technologies. The proposed STRA terminal comprises of an identical pair of spatially rotated half-circular microstrip antennas for transmission (Tx) and reception (Rx). The challenge of self-interference (SI) is addressed by employing passive SI cancellation techniques such as spatial diversity, field confinement, and surface perturbations. This has been accomplished by using fence-strip structure and V-shaped slots in the ground plane. The STRA was designed, fabricated, and tested for full-duplex operation in a sub-6 GHz band lying from 5.73 to 5.88 GHz, providing high interport isolation ranging from 35.5 dB to a maximum of 46.5 dB. The proposed STRA was implemented using Rogers 3003™ substrate. The measurements yield radiation characteristics with high gain of 5.45-6.0 dBi and 5-6.5 dBi for Tx and Rx antennas, respectively. The measured results are in good conformance with the simulated design. This antenna finds its potential usage in V2X and private 5G networks and can be extended for full-duplex MIMO implementations.

26‐GHz Testbed performance evaluation using system EVM characterization for 5G communication

SummaryThe millimeter‐wave (mmW) band has been chosen to obtain multi‐gigabit per second in the fifth generation (5G) communication and beyond. The knowledge of this frequency band is still the focus of research today. After UTI announced its choice of mmW for 5G communication, massive studies were carried out on this band. Among these studies, many optimization methods were proposed to reduce the impact of degradation sources. In this paper, we propose a new method to optimize the system error vector magnitude (EVM) of complex systems with many different calibration sources. A difference of 0.1% is observed between our optimization method and old methods. This small improvement of the EVM system can push the 3GPP system EVM (EVM at the receiver) limits by a few centimeters, which is not negligible in a high‐frequency transmission. Moreover, we have also proposed a new method to compute the throughput that takes into account the TX and RX directional antenna heights. The measurement campaigns and simulation results have shown an improvement from 0% to 6% of throughput. The results depend on indoor environment study and different obstacles in NLOS (non‐line of sight) conditions.

Range and Velocity Resolution of Linear- Frequency-Modulated Signals on Subarray-Mimo Radar

The most important radar system performance is determining the range-velocity of the detected target. This performance is obtained from processing an ambiguity-function (AF) between signals from target reflections and radar radiation signals. Selection of the appropriate waveform transmitted by the radar is a key factor in supporting high resolution radar performance in the AF. There are many waveforms that have been studied in radar systems, especially for multi-antenna radars, i.e., subarray-MIMO (SMIMO) radar which can form phased array (PA) and MIMO radars simultaneously, in the form of linear-frequency-modulated (LFM) signals. In this paper, we examine the use of LFM waveforms combined with SMIMO radar to produce plots of three-dimensional AF as a function of time delay and Doppler shift. The results of the comparison with the Hadamard signal determine the effectiveness of the observed AF performance on parameters such as magnitude, range-velocity resolution, peak sidelobe level ratio, and integrated sidelobe ratio by taking into account the factors of the number of Tx antennas on the PA radar and the number of Tx subarrays on the MIMO radar. The evaluation results of the SMIMO radar configuration (M = 6) with the number of Tx-Rx antenna elements the being 8 provide the best mainlobe magnitude, sidelobe magnitude, range resolution, velocity resolution, PSLR, and ISLR of AF LFM signals compared to conventional radars are 235.2dB, 7.54dB, 37.5m, 75km/s, 29.89dB, and 29.8dB, respectively. Meanwhile, the LFM signal is far superior to the Hadamard signal which has PSLR and ISLR 1.16dB and -3.36dB, respectively.

Design and Verification of a Miniaturized Multifunctional Transmitarray Unit Cell for the S-Band

In this paper, a miniaturized multifunctional unit cell structure of a transmitarray operating at S-band and its verification method using a waveguide structure is presented. The unit cell of a multifunctional transmitarray antenna is a critical component because it controls the phase and polarization of an incident wave. The proposed unit cell consists of three main parts: an Rx antenna, a Tx antenna, and a control circuit for phase and polarization. The performance of the designed unit cell is verified by a rectangular waveguide structure. The waveguide structure feeds an electromagnetic wave propagating in a TE&lt;sub&gt;10&lt;/sub&gt; mode to a 1 × 2 unit cell array to verify polarization and phase shifting capability of the unit cell. The phase shifting and polarization conversion capabilities of the proposed unit cell are directly measured by the radiation patterns and polarization of the transmitted wave.

A Trigger-Free Multi-Active-Probe Anechoic Chamber System for 5G/6G Millimeter Wave OTA Test

The multi-probe anechoic chamber (MPAC) approach is one of the most promising candidates for fifth-generation (5G)-advanced/sixth-generation (6G) massive multiple-input-multiple-output (MIMO) over-the-air (OTA) performance testing. In this article, a trigger-free multi-active-probe anechoic chamber system (MAPAC) is proposed for 5G/6G millimeter wave (mmWave) OTA test, which allocates the transmitting (Tx) and receiving (Rx) probes separately and then avoids the requirement for uplink (UL)/downlink (DL) switching signals. The system architecture is proposed, and a figure of merit for the UL/DL channel reciprocity is provided. For system design, simulations are conducted on essential items, such as the measurement distance, probe density, Tx/Rx probe spacing, etc. A novel dual-polarization active probe (AP) with independent Tx and Rx antennas is developed for the test system, which has the advantages of low loss, low cost, and high integration. The accuracy of the trigger-free mmWave MAPAC is experimentally verified by 3rd Generation Partnership Project (3GPP) clustered delay line (CDL)-A and CDL-C channels with promising application potential.

A Planar Shared-Aperture Co-Polarized Array Antenna With a High Isolation for Millimeter-Wave Full Duplex Communication

We provide the design of a co-polarized simultaneous transmit and receive (STAR) array antenna, aiming to address the issue of undesired isolation in the antenna domain of the millimeter-wave (mm-Wave) full-duplex co-polarized communication system. As the cornerstone for the design and development of the antenna, the guided-wave structures of the virtual-electric-wall (VEW)-based ridge substrate-integrated waveguide (RSIW) and ridge parallel plate waveguide (RPPW) are proposed and applied to the full-duplex antenna design. Compared with conventional RSIW, VEW-based RSIW has the merits of lower ohmic loss and releasing the fabrication tolerance in the array antenna. Additionally, on the basis of parallel plate waveguide (PPW), the proposed RPPW exhibits a Chebyshev filtering response. The radiating part of the proposed array employs a slot-pair array excited along orthogonal directions by using the preceding guided-wave structures. Among them, the RSIW array serves as the Tx antenna, and the RPPW array is regarded as the Rx antenna. To achieve co-polarized radiation patterns in the boresight direction, the substrate-integrated waveguide (SIW) feed network is integrated into the reverse side of the antenna, providing differential and common-mode excitations for the RSIW-excited and RPPW-fed arrays. Furthermore, the inter-port isolation is effectively ameliorated by inserting the mushroom-type metamaterial between linear arrays. As a proof-of-concept, a shared-aperture full-duplex array operating in the Q-band is developed and fabricated to demonstrate the above concept by using standard printed circuited board technology. The measured overlapped impedance bandwidth covers from 38.18 GHz to 39.13 GHz. The measured Tx-to-Rx isolation is greater than 25.5dB in the Q-band. The measured peak gains in Tx- and Rx-mode are 18.4 dBi and 17.8 dBi. The simulation and measurement results show good consistency, verifying the effectiveness of the proposed array in inter-port isolation, array size, planarization, and lightweight, making it suitable for mm-Wave shared-aperture full-duplex communication systems.

A Wideband Co-Linearly Polarized Full-Duplex Antenna-in-Package With High Isolation for Integrated Sensing and Communication

In this letter, a novel co-linearly polarized full-duplex antenna-in-package (AiP) with high Tx/Rx isolation and wide decoupled bandwidth is proposed for integrated sensing and communication (ISAC). Fan-out wafer-level packaging technology is employed, and the preparation process is discussed in details. To improve Tx/Rx isolation, the current direction of the patch elements is orthogonal to that of the feeding ports. Two identical 1×2 patch antenna arrays are used as Tx and Rx antennas, respectively. To further suppress mutual coupling, a decoupling loop is proposed to enhance Tx/Rx isolation. In addition, a wideband full-duplex AiP with high isolation and wide decoupled bandwidth is also proposed by using the parasitic technique and the proposed decoupling method. Prototypes are fabricated and measured to verify the proposed AiPs. The measurement results demonstrate that the proposed AiP possesses the merits of high Tx/Rx isolation (up to 53 dB), wide isolation bandwidth (up to 9.2%) and low cost, providing a foundation for chip-level applications in ISAC.

A Co-Linearly Polarized Shared Radiator-Based Full-Duplex Antenna With High Tx-Rx Isolation Using vias and Stub Resonator

In this paper, a co-linearly polarized shared radiator (SR) based in-band full-duplex (FD) microstrip antenna with high Tx-Rx isolation is proposed. The Tx and Rx terminals of the proposed FD antenna are designed on a single patch, where a series of vias are loaded in the central line of the patch followed by two L-shaped stubs at either end, which leads to high Tx-Rx isolation (≈60 dB). The via loading makes the Tx and Rx antennas individually operate in TM0,1/2 mode. The proposed SR-FD antenna demonstrates Tx-Rx isolation of 60.8 dB at 5.9 GHz operating frequency. Both Tx and Rx terminals of the FD antenna exhibit identical radiation property with peak realized gain of 6.65 dBi and co-to-cross polarization isolation >18 dB. The working mechanism of the proposed FD antenna is explained by both EM and circuit simulation, as well as verified with measurements on the fabricated prototype. The proposed SR-FD antenna has the merits of being planar, reduced footprint, simple feeding mechanism, and desired isolation bandwidth for IEEE 802.11p which renders it suitable for V2X-ITS application.

Prototype Design of Radio Frequency Energy Harvesting for Lighting Applications

The prototype resonant frequency is designed to work at 150 MHz. The signal source prototype is the signal that comes from handy talky (HT). There are two subsystems, which are Matching Impedance and Voltage Multiplier. The resonant frequency of the matching impedance subsystem at 143 MHz from 0.053 mH inductor and 0.0233 pF capacitor. The output of the matching impedance subsystem is then amplified by the multiplier voltage subsystem using parallel PH4148 diodes with the 6-stage multiplier. Load prototype is a CR-151 LED that works at 12 volts 1 watt. When the HT battery has a voltage of 7.3 volts, the prototype can turn on the lamp with the distance between the TX antenna and the antenna on the prototype less than 36 cm. The maximum voltage on the load is 6.8 volts with a length of 5 cm between the antenna and the lamp 774 lumen.

High-Isolation 5G Repeater Antenna Using a Novel DGS and an EBG

Repeaters have been widely used to improve communication quality and extend the coverage areas of wireless communication systems. However, mutual coupling between the Tx and Rx antennas significantly deteriorates the performance of repeater systems. This work presents a high-isolation repeater antenna operating in a frequency range of 3.6–3.7 GHz in a 5G communication system. Perpendicularly arranged microstrip patch antennas are used because this arrangement can lead to greater isolation than a parallel arrangement. However, the perpendicular arrangement results in radiation pattern distortion due to the ground mode. A novel defected ground structure (DGS) is developed to suppress the ground mode and simultaneously reduce the mutual coupling between the Tx and Rx antennas. An electromagnetic bandgap (EBG) is additionally employed to further increase isolation. The measurement results of a fabricated repeater antenna show no radiation pattern deformation and an isolation improvement of 28 dB over the repeater antenna without the DGS and EBG.

Highly Integrated In-Band Full-Duplex TRx Antennas for mmWave V2X Communications

A compact mmWave co-circularly polarized (CP) Tx and Rx (TRx) antenna array for in-band full-duplex (IBFDX) V2X communications is proposed. The proposed TRx antenna is based on highly integrated coplanar TRx antenna elements with high Tx-to-Rx isolation maintained in n257 5G NR band. The TRx antenna elements are coplanar patches with the same CP and concentrically integrated to form individual 2 × 2 array on the same substrate. The proposed mmWave IBFDX antenna is designed at 28 GHz with a multilayered printed circuit board (PCB) having sequetially rotated feed networks. Also, the designed antenna is fabricated with the size of 1.867 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 1.867 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.087 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> including both CP feed network and ground plane. The measured 2 × 2 Tx impedance bandwith and peak gain at 28 GHz are 27.14% and 8.43 dBic, respectively. Also, the measured 2 × 2 Rx impedance bandwith and peak gain at 28 GHz are 28.57% and 6.17 dBic, respectively. Further, IBFDX operation of the proposed antenna is verified by n257 5G NR 256-QAM test signals with the maximum 400 MHz bandwidth.

Beam-Level Frequency-Domain Digital Predistortion for OFDM Massive MIMO Transmitters

In this article, a novel digital predistortion (DPD) solution for fully digital multiple-input–multiple-output (MIMO) transmitters (TXs) is proposed. Opposed to classical DPD solutions that operate at TX chain or antenna level, the proposed DPD operates at the stream or beam level, and hence, its complexity is proportional to the number of spatially multiplexed streams or users rather than to the number of antennas. In addition, the proposed beam-level DPD operates in the frequency domain (FD), which makes it possible to provide flexible frequency-dependent linearization of the transmit waveforms. This feature is very well suited to the linearity requirements applicable at the 5G new radio (NR) frequency-range 2 (FR2), where the inband quality requirements commonly limit the feasible TX power and can also vary significantly within the channel bandwidth depending on the utilized data modulation and coding schemes of the different frequency-multiplexed users. Altogether, the proposed solution enables a large reduction in the computational complexity of the overall DPD system, and its performance is demonstrated and verified through both experimental and simulation-based results.

A Dual-Band Patch Antenna Employing a Folded Probe Feed for Nonlinear Radar Applications

In this work, we design a novel, integrated transmit (TX)/receive (RX) dual-band folded-probe-fed patch (DFPFP) antenna to improve nonlinear radar (NLR) system performance. Designed for down-looking, airborne NLR applications, the DFPFP antenna occupies an improved form factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.9\lambda \times 0.9\lambda \times 0.1\lambda $ </tex-math></inline-formula> , 1.8 kg) over existing commercial-off-the-shelf (COTS) designs and additionally offers minimal drag in airborne applications due to its low profile. The DFPFP antenna is simulated, fabricated, and tested, and excellent gain (9 dBi) and bandwidth (15%) performance are demonstrated. Iterations of the design from single, standalone TX and RX antennas to the final, integrated design are presented and discussed. The final DFPFP is compared to a pair of COTS antennas that are currently used for NLR system testing. Evaluated in the context of an NLR system, the custom DFPFP antenna significantly outperforms the COTS antennas, with signal-to-noise ratio (SNR) improvements as high as 17 dB, while offering significantly improved size, weight, and power (SWaP) performance.

Time-Switching Symmetric Transmitter Array to Increase Sweet Region for Far-Field Wireless Power Transmission Under Receiver Rotation and Location Variation

For wireless power transfer using linear-polarized transmitter (TX) and receiver antennas, the rotation and movement of receiving antenna cause received power variation. The received power pattern is proposed to describe the received power variation from a specific TX antenna under receiver rotation. By placing the peak of the received power pattern of additional TX antennas in null directions of the previous TX antenna, received power variation due to rotation can be compensated. With symmetrically placed TX antennas, the power variation due to location variation can be compensated. This article proposes a time-switching symmetric transmitting array combining both techniques to increase the sweet region for far-field wireless power transfer under rotation and location variation. A sweet region is an area in the 2-D case or volume in the 3-D case, which is defined as an area or a volume inside the TX array that can get guaranteed minimum received power under rotation. The received power calculation using the Friis equation with short dipole antenna pattern shows that a symmetric TX array can achieve a larger sweet region than an asymmetric TX array under the same total transmitted power. The efficiency for the receiver at the origin is 1/2 at the 2-D case and 1/3 at the 3-D case. In the experiment, a linear-polarized TX array at 915 MHz with monopole receiver antenna and power detector is used as the receiver to measure received power under rotation and location variation. Measurement results at 2-D and 3-D cases confirm the received power level predicted by calculation using the Friis equation. The power budget calculation for wirelessly powering a sensor module attached on a bee inside a beehive using the proposed 3-D TX array shows that it is feasible to deliver sufficient power to the sensor module regardless of the orientation and location of the bee inside the beehive.

Efficiency Bound Estimation for a Practical Microwave and mmWave Wireless Power Transfer System Design

In this study, we present an efficient method to find the power transfer efficiency (PTE) bound for practical microwave and mmWave wireless power transfer (MPT) systems composed of transmitter (Tx) and receiver (Rx) array antennas. The PTE bound of the MPT system is obtained by formulating it as a convex optimization problem (CVP) that maximizes the power received at the Rx array under the transmit power constraint. The channel state information (CSI) between each element of the Tx and the Rx is the input parameter of the proposed CVP. The CSI is estimated using the Friis transmission equation and the active element pattern of the array antenna because the Tx and the Rx are assumed to be large arrays. For an MPT system designed at 10 GHz and 24 GHz, the estimated PTE bound is compared to those in previous studies while varying the distance and tilted angle between the Tx and the Rx. The computation times required for the methods are compared. The numerical results show that the proposed method provides a faster and more accurate PTE bound without full electromagnetic simulation of the MPT system consisting of Tx and Rx array antennas. This study's results will serve as guidelines for practical MPT system design in the future.

Range-Division Multiplexing for MIMO OFDM Joint Radar and Communications

An orthogonal frequency-division multiplexing (OFDM) waveform enables simultaneous radar sensing and communications. In the multiple-input multiple-output (MIMO) case with several transmit (Tx) antennas, multiplexing the transmit signals is usually implemented using equidistant subcarrier interleaving (ESI), thus allowing the separation of the transmit signals in frequency domain. In this work, a multiplexing technique denoted as range-division multiplexing (RDMult) is analyzed, which allows separating signals radiated by different Tx antennas along the range axis of a range-Doppler map. This work also investigates the effects of RDMult on the communication task. It turns out that RDMult heavily distorts the channel statistics by introducing a repetitive pattern of deep fading holes, which severely distort the transmission of data. To combat this issue, this work proposes a communication system especially designed for RDMult, including methods for data estimation, channel estimation and synchronization. Simulations confirm the effectiveness of these concepts in terms of bit error ratio (BER) performance.

Isolation Improvement in Reflectarray Antenna-Based FMCW Radar Systems.

This paper presents an optimization of reflectarray-based RF sensors for detecting UAV and human presence. Our previous human detection radar system adapted a center-fed reflectarray antenna to a commercially available radar system, successfully increasing the gains of the transmit (TX) and receive (RX) antennas by 21.18 dB and the range for detecting human targets 3.4 times. However, because the TX and RX antennas were placed in the focal point of the reflectarray, the TX signal reflected by the reflectarray was directly propagated into the RX antenna, causing desensitization or damage to the receiving circuit if high powers were used. To reduce this direct reflection, we propose a novel radar antenna configuration in which the TX and RX antennas are placed back-to-back with each other. In this configuration, the RX antenna does not directly face the reflectarray, thus direct path between the TX to RX through the reflectarray is removed. The results demonstrate that this approach achieves the optimum isolation level of 51.3 dB. With the reflectarray, the TX antenna gain increases to 30.6 dBi, but the RX antenna gain remains at 16 dBi since the RX antenna does not utilize the reflectarray. The TX and RX gain difference (14.6 dB) is a trade-off for good isolation and may be reduced by utilizing a high-gain receiver amplifier.