Receiver Antenna Research Articles

X-band RADAR Reflected Signal Measurement of Gallium-based Liquid Metal

RADAR(Radio Detection and Ranging) is an important system for surveillance and reconnaissance by detecting a reflected signal which obtains the range from the radar to the target, and the velocity of the target. The magnitude of the reflected signal varies due to the radar cross section of the target, characteristic of the transmission and reception antenna, distance between the radar and the target, and power and wavelength of the transmitted signal. Thus, the RCS is the important characteristic of the target to determine if the target can be observed by the RADAR system. It is based on the material and shape of the target. We have measured the reflection signal of a simple square-shaped (20 × 20 cm) target made of a new material, a gallium-based liquid metal alloy and compared that of well-known metals including copper, aluminum. The magnitude of reflected signal of the aluminum target was the largest and it was 2.4 times larger than that of the liquid metal target. We also investigated the effect of the shape by measuring reflectance of the F-22 3D model(~1/95 ratio) target covered with/without copper, aluminium, and liquid metal. The largest magnitude of the reflected signal measured from side-view with the copper-covered F-22 model was 2.6 times greater than that of liquid metal. The reflectance study of the liquid metal would be helpful for liquid metal-based frequency selective surface or metamaterials.

On Detection of Anomalous VHF Propagation over the Adriatic Sea Utilising a Software-Defined Automatic Identification System Receiver

This paper represents observations on detection of Very High Frequency (VHF) anomalous propagation over the area of the Adriatic Sea. During the research campaign, a Software Defined Radio (SDR) Automatic Identification System (AIS) receiver was employed for collection of AIS data packets at a fixed location in the Northern Adriatic. Data were collected during the 24-h period (25 February 2023 15:32 LT to 26 February 2023 15:32 LT), providing information from 115 AIS targets, or 159 965 AIS packets with 54.3% Packet Error Rate (PER), respectively. Subsequent analysis and post-processing of successfully demodulated signals and decoded packets was presented further. In certain instances, the SDR AIS receiver detected, received and decoded data packets from AIS targets distant several orders of magnitude larger than the VHF nominal ranges. To determine the magnitude of line-of-sight and over-the-horizon radio waves propagation, the great circle distances between the SDR AIS receiver antenna and AIS packets’ decoded positions were calculated, revealing hundreds of Nautical Miles (NM). Possible reasons for these occurrences, including tropospheric scattering, diffraction, ionospheric sporadic E layer and refraction were discussed and evaluated, in accordance, among others, with the previous research. By exclusion criteria and neglection of possible causes, it was concluded that the enhanced, over-the-horizon propagation of AIS signals occurred as a result of refraction effects, namely trapping/ducting, subrefraction and superrefraction. Data from nine World Meteorological Organization (WMO) radiosondes surrounding the greater reception area were collected for the same observation periods. Atmospheric profiles were created using Advanced Refractive Effects Prediction System (AREPS) program, and analysed for each individual station measurement. The results confirmed anomalous, over-the-horizon enhanced propagation and their probable origins, i.e., the occurrence of refractive conditions in the atmosphere over the Adriatic Sea area. These findings provide a solid foundation for further research in the area of propagation of VHF signals and their anomalous features caused by the atmospheric phenomenon effects.

Flexible Spatial Modulation With Transmit Antenna Selection for MIMO Systems

This article introduces flexible spatial modulation with transmit antenna selection (FSM-TAS) for future multiple-input multiple-output systems. In this scheme, the number of active antennas varies in each time interval depending on the incoming bits. After determining the number of active antennas, channel coefficients corresponding to each possible active antenna combination are added up. Then, a certain number of antenna combinations with largest gains is selected to apply spatial modulation (SM). For the proposed system, complexity and outage probability analyses are performed. In addition, it has been shown by Monte Carlo simulations that FSM-TAS provides better bit error rate performance than the benchmark enhanced SM with generalized antenna selection under the same spectral efficiency and the same number of transmitter and receiver antennas.

Reducing Non-Through Body Energy Transfer in Microwave Imaging Systems.

On-body antennas for use in microwave imaging (MI) systems can direct energy around the body instead of through the body, thus degrading the overall signal-to-noise ratio (SNR) of the system. This work introduces and quantifies the usage of modern metal-backed RF absorbing foam in conjunction with on-body antennas to dampen energy flowing around the body, using both simulations and experiments. A head imaging system is demonstrated herein but the principle can be applied to any part of the body including the torso or extremities. A computational model was simulated numerically using Ansys HFSS. A physical prototype in the form of a helmet with embedded antennas was built to compare simulations with measured data. Simulations and measurements demonstrate that usage of such metal-backed RF-absorbing foams can significantly reduce around-body coupling from Transmit (Tx) and Receive (Rx) antennas by approximately 10dB. Thus, the overall SNR of the MI system can be substantially improved using this low-cost and affordable method.

Estimation of antenna phase center offsets for BDS-3 satellites with the metadata and receiver antenna calibrations

Estimation of antenna phase center offsets for BDS-3 satellites with the metadata and receiver antenna calibrations

Method of locating a target with a Mimo radar distributed at the international airport of Ndjili in Kinshasa

This system is based on a UWB wave distributed radar using a trilateration algorithm for localization. Before describing the complete system, we detail some signal processing techniques on the UWB signals acquired directly at the output of the reception antenna. To apply the trilateration algorithm, the signals coming from the reception antennas must first be shaped. The necessary processing is to improve the signal to noise ratio (S/N), to extract the signal envelope and to determine the propagation time. Once the propagation time is known, the trilateration algorithm is used to locate the targets.

Performance Analysis of Channel Imbalance Control and Azimuth Ambiguity Suppression in Azimuth Dual Receiving Antenna Mode of LT-1 Spaceborne SAR System

The LuTan-1(LT-1), known as the L-band differential interferometric synthetic aperture radar (SAR) satellite system, is an essential piece of civil infrastructure in China, providing extensive applications such as surface deformation monitoring and topographic mapping. To achieve high-resolution and wide-swath (HRWS) observation abilities, the LT-1 takes the dual receiving antenna (DRA) imaging mode as its working mode. However, amplitude and phase errors between channels lead to a mismatch between the reconstruction filter and the multichannel echo signal, worsen the reconstructed azimuth spectrum, and introduce ambiguity targets in the final imaging results, seriously affecting the final imaging quality. In order to better evaluate the channel error and azimuth ambiguity performance of the LT-1 system, this paper proposed an advanced channel consistency correction method and conducted many measured data experiments. The experimental results show that the proposed method is effective, and the LT-1 system has excellent channel error control and azimuth ambiguity performance.

Joint Spatial and Reflecting Modulation for Active IRS Assisted MIMO Communications

This paper proposes an active-intelligent reflecting surface (IRS) assisted joint spatial and reflecting modulation (A-IRS-JSRM). The proposed A-IRS-JSRM engages an active IRS with sub-connected architecture in which several reflecting elements are grouped into panels, and the elements within a panel have the same amplification factor but different reflection angles. Transmit and receive spatial modulation are employed at the base station (BS) and user equipment (UE) by activating a set of transmit antennas and selecting a receiver antenna. Further, only a subset of panels is switched to the ON state in the active IRS, which is determined by the information bits and thus invokes reflecting modulation. The active IRS panels in the ON state also aid in maximizing the received energy in the chosen receiver antenna at the UE. We present the theoretical analysis of the performance of the proposed A-IRS-JSRM system and validate them with simulation results. Further, we have discussed a low-complexity approach for receiver processing in the compressive sensing framework. We compare the proposed A-IRS-JSRM with closely related IRS-assisted spatial modulation schemes in the literature and demonstrate the outperformance of our proposed approach in terms of achievable rate, bit error rate, and outage probability.

Full-Rate Space-Time Line Code With Asymptotic SNR Gain

In this letter, we introduce a novel quasi-orthogonal full-rate space-time line code (FR-QSTLC) for an arbitrary number of transmit antennas and four receiver antennas. Its fully analytical examination and the benchmark of full-rate STLCs are provided, and the results are compared in terms of average bit error ratio (ABER) and diversity gain. Due to its quasi-orthogonal properties, the proposed FR-QSTLC exhibits an asymptotic SNR gain of up to 3 dB compared to its orthogonal two-antenna counterpart and outperforms all the other linearly-decoded full-rate STLCs.

Analysis of Characteristics for Inter-System Bias on Multi-GNSS Undifferenced and Uncombined Precise Point Positioning

Multi Global Navigation Satellite System (GNSS) Precise Point Positioning (PPP) has become the mainstream of PPP technology. Due to the differences in the coordinates and time references of each GNSS, multi-GNSS PPP must include additional Inter-System Bias (ISB) parameters to ensure compatibility between different GNSSs. Therefore, research on the characteristics of ISB is also essential. To analyze the short- and long-term time characteristics of multi-GNSS ISBs, as well as their relationship with receiver type and receiver antenna type, the Undifferenced and Uncombined (UDUC) PPP model of Global Positioning System (GPS), BeiDou navigation satellite system (BDS), and Galileo satellite navigation system (Galileo) was rigorously derived, and the physical of ISBs was elaborated in depth. ISB parameters were estimated and analyzed using 31 days of data from the 31 Multi-GNSS Experimental stations (MGEX). The results indicate that: (1) the ISB value is dependent on the station receiver type, receiver antenna type, analysis center product utilized, and GNSS system. (2) The short-term time characteristics of ISB-COM, ISB-WUM, and ISB-GBM are similar for the same station but not for the long term. In addition, ISBs are more stable in the short term. (3) There is little correlation between the ISB time characteristics, the receiver type, and the receiver antenna type, and the day-boundary discontinuity(DBD) on the ISB can be ignored for the concussive days’ process.

A New Generation of Fast and Low-Memory Smart Digital/Geometrical Beamforming MIMO Antenna

Smart multiple-input multiple-output (MIMO) antennas with advanced signal processing algorithms are necessary in future wireless networks, such as 6G and beyond, for accurate space division multiplexing and beamforming. Such a MIMO antenna will yield better network coverage and tracking. This paper presents a smart MIMO antenna configuration with a highly innovative beamforming technique using several nonlinear configurations of dipole arrays. Phase delay factors are optimized at the transmitter to form a single beam and then to steer the beam towards a particular direction. A number of phase shifters are added in order to obtain maximum directional gain. This configuration also significantly increases the power gain of the MIMO antenna at a low cost and with operational simplicity. The paper also demonstrates how the beam width and beamsteering can be effectively controlled. Wolfram Mathematica software was used to generate the three-dimensional radiated beam patterns of the transmitter antenna. There are two approaches to configure the receiver antenna. In the first approach, the received signal magnitude is maximized by aligning the contribution of all elements of the receiver antenna to the same phase. With this approach, the field gain of the proposed system is 25.52 (14.07 dBi). The signal processing gain at the receiver is 64 (18.06 dBi). Therefore, the overall power gain for this proposed new digital/geometrical smart MIMO system is 32.13 dBi. In the second approach, the receiver beam is directed towards the transmitter by optimizing the phase delay coefficients of the receiver. Here, the overall gain of the system is found to be 134.56 (21.28 dBi). Even though the system gain in the second approach is lower, it has the advantage of low interference at the receiver side.

Deep Neural Networks for Direction of Arrival Estimation of Multiple Targets With Sparse Prior for Line-of-Sight Scenarios

Received signal Direction of Arrival (DOA) estimation represents a significant problem with multiple applications, ranging from wireless communications to radars. This problem presents significant challenges, mainly given by a large number of closely located transmitters being difficultly separable. Currently available state of the art approaches fail in providing sufficient resolution to separate and recognize the DOA of closely located transmitters, unless using a large number of antennas and hence increasing the deployment and operation costs. In this paper, we present a deep learning framework for DOA estimation under Line-of-Sight scenarios, which able to distinguish a number of closely located sources higher than the number of receivers' antennas. We first propose a formulation that maps the received signal to a higher dimensional space that allows for better identification of signal sources. Secondly, we introduce a Deep Neural Network that learns the mapping from the receiver antenna space to the extended space to avoid relying on specific receiver antenna array structures. Thanks to our approach, we reduce the hardware complexity compared to state of the art solutions and allow reconfigurability of the receiver channels. Via extensive numerical simulations, we demonstrate the superiority of our proposed method compared to state-of-the-art deep learning-based DOA estimation methods, especially in demanding scenarios with low Signal-to-Noise Ratio and limited number of snapshots.

Multitarget 2-D DOA Estimation Using Wideband LFMCW Signal and Triangle Array Composed of Three Receiver Antennas

Direction of arrival (DOA) estimation has been a primary focus of research for many years. Research on DOA estimation continues to be immensely popular in the fields of the internet of things, radar, and smart driving. In this paper, a simple new two-dimensional DOA framework is proposed in which a triangular array is used to receive wideband linear frequency modulated continuous wave signals. The mixed echo signals from various targets are separated into a series of single-tone signals. The unwrapping algorithm is applied to the phase difference function of the single-tone signals. By using the least-squares method to fit the unwrapped phase difference function, the DOA information of each target is obtained. Theoretical analysis and simulation demonstrate that the framework has the following advantages. Unlike traditional phase goniometry, the framework can resolve the trade-off between antenna spacing and goniometric accuracy. The number of detected targets is not limited by the number of antennas. Moreover, the framework can obtain highly accurate DOA estimation results.

Multi-antennas PAPR Reduction for FBMC/OQAM System

Background: The filter bank multicarrier (FBMC) with offset quadrature amplitude modulation (OQAM) is a promising future generation of wireless systems. However, like multicarrier modulations (MCM), FBMC/OQAM has a high peak-to-average power ratio (PAPR), which allows the FBMC/OQAM signal to pass through the nonlinear region of the high-power amplifier (HPA) in the time domain and causes in-band and out of band (OOB) distortion. Methods: In this paper, a new method to overcome this problem called multi-antennas PAPR (MAP) reduction is proposed. It consists of using I antennas in transmission and reception to transmit I FBMC/OQAM sub-signals with low PAPR. The complementary cumulative distribution function (CCDF), the bit error rate (BER), and the energy efficiency are used to evaluate the method's performance. Results: The simulation results showed that the new technique can reduce the PAPR of the original signal by more than half, achieve BER comparable to that of the original signal without HPA, and when the input back-off (IBO) equals 3dB, the error vector magnitude (EVM) result can be reduced from 19% to 7%. Conclusion: The PAPR, BER, and EVM of MAP technique are much better than the original system.

A Wideband Dual-Circularly Polarized, Simultaneous Transmit and Receive (STAR) Antenna Array for Integrated Sensing and Communication in IoT

This article presents a novel 5.8-GHz ISM-band dual-circularly polarized (CP) simultaneous transmit and receive (STAR) common-aperture antenna array (CAAA) for integrated sensing and communication (ISAC) in Internet of Things (IoT). A new near-field cancellation technique based on differential feeding and geometrical symmetry is proposed for dual-CP to realize high TX/RX isolation. In addition, a high-impedance surface is introduced to further improve the TX/RX isolation. Furthermore, the parasitic patches are added to enhance the gain and isolation bandwidth (BW). The simulation results demonstrate that the proposed CAAA possesses the merits of high isolation (up to 67 dB), wide isolation BW (better than 40 dB for 240 MHz BW), high gains (up to 10/10.5 dB for right-hand CP (RHCP)/left-hand CP (LHCP)), wide 1-dB gain BWs (better than 230/350 MHz BW for RHCP/LHCP), and low-axial ratios (lower than 1.4 dB). The designed CAAAs are fully characterized and the experimental results meet the simulation very well. For the first time, systematic validations for both wireless communication and radar sensing have been thoroughly carried out by integrating the proposed CAAA in the custom-designed full-duplex radio system. The experimental results not only prove the validity of the design methodology but also the feasibility of employing the proposed CAAA for ISAC, which indicates potential applications in IoT era.

Computer Modeling of the Outgoing GPR Signal

This paper considers a mathematical model to reconstruct the shape and tabular value of the source based on real signal data from a Loza-V series GPR receiver. A geoelectric equation in a cylindrical coordinate system is chosen as the mathematical model. Experiments, using GPR, were conducted on a homogeneous area of clean river sand, with known geoelectric properties. In this case, the equation in question is reduced to the Riccati differential equation using a special function substitution. This allowed us to obtain an explicit expression linking the spectrum function describing the response of the medium (the real radar data) and the spectrum function describing the source behavior. From the found source spectra, using inverse Fourier transforms, the emitted source itself is reconstructed in tabular form. The methodology of source reconstruction was carried out at different locations of the receiver antenna from the source antenna. In practice, geophysicists are interested in the physical characteristics of heterogeneity depending on spatial coordinates. For numerical solution of inverse coefficient problem it is necessary to have tabular value of disturbance source and tabular values of reflected signals (GPR data) at measurement points. To solve these problems we have developed an algorithm of source reconstruction and, as a consequence, determination of media response corresponding to real GPR data at the points of observation. A series of numerical calculations demonstrating the effectiveness of the considered computer model for source recovery have been carried out.

Wirelessly powered deformable electronic stent for noninvasive electrical stimulation of lower esophageal sphincter

Electrical stimulation is a promising method to modulate gastrointestinal disorders. However, conventional stimulators need invasive implantation and removal surgeries associated with risks of infection and secondary injuries. Here, we report a battery-free and deformable electronic esophageal stent for wireless stimulation of the lower esophageal sphincter in a noninvasive fashion. The stent consists of an elastic receiver antenna infilled with liquid metal (eutectic gallium-indium), a superelastic nitinol stent skeleton, and a stretchable pulse generator that jointly enables 150% axial elongation and 50% radial compression for transoral delivery through the narrow esophagus. The compliant stent adaptive to the dynamic environment of the esophagus can wirelessly harvest energy through deep tissue. Continuous electrical stimulations delivered by the stent in vivo using pig models significantly increase the pressure of the lower esophageal sphincter. The electronic stent provides a noninvasive platform for bioelectronic therapies in the gastrointestinal tract without the need for open surgery.

Channel estimation and detection with space–time transmission scheme in colocated multiple‐input and multiple‐output system

AbstractIn this study, a space–time transmission scheme is proposed to tackle the limitations of channel estimation with orthogonal pilot information in colocated multiple‐input multiple‐output systems with several transmitting and receiving antennas. Channel information is obtained using orthogonal pilots. Channel estimation introduces pilot heads required to estimate a channel. This leads to bandwidth insufficiency. As a result, trade‐offs exist between the number of pilots required to estimate a channel versus spectral efficiency. The detection of data symbols is performed using the maximum likelihood decoding method as it provides a consistent approach to parameter estimation problems. The moment‐generating function of the instantaneous signal‐to‐noise ratio is used to drive an approximate expression of the symbol error rate for the proposed scheme. Furthermore, the order of diversity is less by one than the number of receiver antennas used in the proposed scheme. The effect of the length of a pilot sequence on the proposed scheme's performance is also investigated.

A Unification of LoS, Non-LoS, and Quasi-LoS Signal Propagation in Wireless Channels

The modeling of wireless communication channels is often broken down into two distinct states, defined according to the optical viewpoints of the transmitter (TX) and receiver (RX) antennas, namely, line-of-sight (LoS) and non-LoS (NLoS). Movement of the TX, RX, both and/or objects in the surrounding environment means that channel conditions may transition between LoS and NLoS leading to a third state of signal propagation, namely, quasi-LoS (QLoS). Unfortunately, this state is largely ignored in the analysis of signal propagation in wireless channels. We, therefore, propose a new statistical framework that unifies signal propagation for LoS, NLoS, and QLoS channel conditions, leading to the creation of the three-state model (TSM). The TSM has a strong physical motivation, whereby the signal propagation mechanisms underlying each state are considered to be similar to those responsible for Rician fading. However, in the TSM, the dominant signal component, if present, can be subject to shadowing. To support the use of the TSM, we develop novel formulations for the probability density functions of the in-phase and quadrature components of the complex received signal, the received signal envelope, and the received signal phase. In addition, we derive an expression for the complex autocorrelation function of the TSM, which will be of particular importance in understanding and simulating its time correlation properties. Finally, we show that the TSM provides a good fit to field measurements obtained for two different body-centric wireless channels operating at 2.45 GHz, which are known to be subject to the phenomena underlying the TSM.

Two-Dimensional Phased-Array Receiver Based on Integrated Silicon True Time Delay Lines

In this work, we first demonstrate a complete 2-D photonics-aided phased-array antenna (PAA) receiver with so far the largest scale of 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 8 by utilizing highly integrated silicon true-time delay line chips. The prototype utilizes the wavelength-division-multiplexing technology to build the crucial optical beamforming network (OBFN) module so as to dramatically reduce the type and amount of silicon binary integrated optical time delay lines. The measured beam scanning range in the frequency range from 2 to 6 GHz is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$90^{\circ }\,\,\times \,\,90^{\circ }$ </tex-math></inline-formula> with a beam-pointing step of 1°. Furthermore, due to the online channelized signal processing module, we systematically characterize sensitivity, RF gain, and dynamic range of the photonics-aided PAA. Considering that we first utilize the photonic integration technology to realize a 2-D PAA demonstrator with the largest scale and the highest technological maturity, we believe that it presents a milestone in the development of future microwave photonics-based radar systems.