RF Front-end Research Articles

6-20 GHz 30% ScAlN Lateral Field-Excited Cross-Sectional Lamé Mode Resonators for Future Mobile RF Front Ends.

This article reports on 30% scandium-doped AlN (ScAlN) lateral field-excited (LFE) cross-sectional Lame' mode resonators (CLMRs) with unprecedented performance in the 6-20 GHz range. By combining high-crystallinity 30% ScAlN piezoelectric thin films, a lithographic tunability of the resonance frequency, and a simple three-mask post-CMOS compatible fabrication process, we propose a technology platform that can enable the mass production of low-loss, wideband, and compact microacoustic filtering devices spanning a wide spectrum portion on the same chip for the next-generation radio frequency front ends (RFFEs) of handsets. This article demonstrates a successful scaling of the microacoustic technology well beyond the sub-6-GHz fifth-generation (5G) band, as well as the outstanding capabilities of high-crystallinity 30% ScAlN piezoelectric layers in delivering high-quality factor ( Q ) and high-electromechanical coupling ( kt2 ) resonators, notably exceeding the state of the art in terms of relevant figures of merit (FOMs). Furthermore, we experimentally investigate the impact of geometrical parameters, such as tethering configuration and width-over-length ratio on the devices' 3-dB quality factor ( [Formula: see text]), power linearity (PL), and temperature coefficient of frequency (TCF). By adopting a statistical approach for data analysis, we determine the optimal geometry to maximize the Q value. Moreover, we experimentally demonstrate that a fully tethered device's configuration ensures superior PL, lower TCF, and higher device yield and select that as the best design tradeoff between all the variables under consideration. Finally, we discuss a further scaling of LFE CLMRs, both in terms of higher doping levels in the piezoelectric layer, in order to enhance the performance of microacoustic filters, and in terms of higher operation frequencies, in order to reach and cover the mm-wave spectrum.

Analysis and Compensation of Tx and Rx IQ Imbalances in Uplink IM-OFDMA Systems

Index modulation-based orthogonal division multiple access (IM-OFDMA) has recently been proposed as a potential technique for future wireless communication systems due to its superior spectral efficiency and error performance over conventional multiple access schemes. However, its performance is still under investigation by researchers in light of a variety of scenarios and assumptions. Following this direction, in this paper, the individual and joint effects of the transmitter (Tx) and receiver (Rx) in-phase and quadrature imbalances (IQI) on the bit-error-rate (BER) performance of the uplink IM-OFDMA scheme are investigated by considering whether each user's RF front-end is identical or not. Moreover, to reduce the detrimental effect of IQI, a preamble-based estimation and compensation method is proposed for IM-OFDMA. Closed-form expressions for the average BER of IM-OFDMA are obtained by considering the physical effect of the Tx and Rx IQI. Also, using Monte Carlo simulations, the derived expressions are verified under different system configurations. Analytical and simulation results reveal that Tx and Rx IQI cause an error floor in the BER performance of IM-OFDMA schemes. However, the proposed estimation and compensation method not only reduces the impact of IQI but also leads to a better BER performance compared to the case of no IQI, which mainly refers to the frequency diversity caused by the IQI.

Partially Etched Piezoelectric Film Filled with SiO2 Structure Applied to A1 Mode Resonators for Transverse Modes Suppression.

With the arrival of the Fifth Generation (5G) communication era, there has been an urgent demand for acoustic filters with a high frequency and ultrawide bandwidth used in radio-frequency (RF) front-ends filtering and signal processing. First-order antisymmetric (A1) lamb mode resonators based on LiNbO3 film have attracted wide attention due to their scalable, high operating frequency and large electromechanical coupling coefficients (K2), making them promising candidates for sub-6 GHz wideband filters. However, A1 mode resonators suffer from the occurrence of transverse modes, which should be addressed to make these devices suitable for applications. In this work, theoretical analysis is performed by finite element method (FEM), and the admittance characteristics of an A1 mode resonator and displacement of transverse modes near the resonant frequency (fr) are investigated. We propose a novel Dielectric-Embedded Piston Mode (DEPM) structure, achieved by partially etching a piezoelectric film filled with SiO2, which can almost suppress the transverse modes between the resonant frequency (fr) and anti-resonant frequency (fa) when applied on ZY-cut LiNbO3-based A1 mode resonators. This indicates that compared with Broadband Piston Mode (BPM), Filled-broadband Piston Mode (FPM) and standard structures, the DEPM structure is superior. Furthermore, the design parameters of the resonator are optimized by adjusting the width, depth and filled materials in the etched window of the DEPM structure to obtain a better suppression of transverse modes. The optimized A1 mode resonator using a DEPM structure exhibits a transverse-free response with a high fr of 3.22 GHz and a large K2 of ~30%, which promotes the application of A1 mode devices for use in 5G RF front-ends.

Considerations, Advances, and Challenges Associated with the Use of Specific Emitter Identification in the Security of Internet of Things Deployments: A Survey

Initially introduced almost thirty years ago for the express purpose of providing electronic warfare systems the capabilities to detect, characterize, and identify radar emitters, Specific Emitter Identification (SEI) has recently received a lot of attention within the research community as a physical layer technique for securing Internet of Things (IoT) deployments. This attention is largely due to SEI’s demonstrated success in passively and uniquely identifying wireless emitters using traditional machine learning and the success of Deep Learning (DL) within the natural language processing and computer vision areas. SEI exploits distinct and unintentional features present within an emitter’s transmitted signals. These distinctive and unintentional features are attributed to slight manufacturing and assembly variations within and between the components, sub-systems, and systems comprising an emitter’s Radio Frequency (RF) front end. Although sufficient to facilitate SEI, these features do not hinder normal operations such as detection, channel estimation, timing, and demodulation. However, despite the plethora of SEI publications, it has remained largely a focus of academic endeavors, primarily focusing on proof-of-concept demonstration and little to no use in operational networks for various reasons. The focus of this survey is a review of SEI publications from the perspective of its use as a practical, effective, and usable IoT security mechanism; thus, we use IoT requirements and constraints (e.g., wireless standard, nature of their deployment) as a lens through which each reviewed paper is analyzed. Previous surveys have not taken such an approach and have only used IoT as motivation, a setting, or a context. In this survey, we consider operating conditions, SEI threats, SEI at scale, publicly available data sets, and SEI considerations that are dictated by the fact that it is to be employed by IoT devices or IoT infrastructure.

Steerable Simultaneous Multibeam Antenna Based on Reconfigurable Reflectarray

Multi-beam system is a core part for wireless concurrent communication and massive MIMO applications. Traditional concurrent communication techniques, like phased-array or digital beam-forming (DBF) system, suffer from massive RF frontends or power-hungry high speed ADCs, which makes them complex and expensive in fabrication. Inheriting the advantages of reflectarray and passive multi-beam system, we reported in this letter a novel and cost-effective concept of steerable simultaneous multi-beam antenna (SMBA). New features and the practicality of it are fully verified with theoretical analysis and experimental implementation of a prototype working at 7GHz with 300MHz bandwidth. With multiple beams steered simultaneously, the SMBA can eliminate the crossover regions between adjacent beams of passive multi-beam antenna. Experimental results indicate its potential in the design of diverse concurrent communication systems such as base stations and point-to-point links.

Design of Compact and Superdirective Metamaterial-Inspired Two- and Three-Elements Antenna Arrays

This paper presents the development of a miniature antenna array in a small space in order to achieve superdirectivity for long-range communication. The proposed structures consist of a superdirective metamaterial-inspired array based on a capacitively loaded loop (CLL) driven by an electrically small monopole antenna. This elementary antenna is then used in two- and three-array configurations separated by a fixed interelement distance of 0.1λ to achieve a higher directivity and compact size (with λ the wavelength calculated at the operation frequency 1.850 GHz). The design of the elementary antenna, its simulated radiation performances, as well as those of the parasitic array are also reported. The results of the optimization of two- and three-antenna arrays are discussed. For this study, three corresponding prototypes were fabricated and tested. The measured impedance mismatch and radiation pattern results are presented and shown to be in good agreement with their simulated values. The maximum measured directivity is equal to 5.9 dBi and 4.75 dBi in the case of the two- and three- elements, respectively. The proposed antenna arrays can serve for the realization of point-to-point wireless links and can have a significant impact on compact and high-directive radiofrequency front-ends of a wireless system and for wireless power transfer applications.

Improved TDD operation on Software-Defined Radio platforms towards future wireless standards

Software-Defined Radio (SDR) platforms are valuable for research and development activities or high-end systems that demand flexible wireless protocols. While low-latency digital baseband processing can be achieved using a dedicated processing unit, like an FPGA or hardware accelerator, its multi-purpose Radio Frequency (RF) front-end often poses a limitation. Zero Intermediate Frequency (ZIF) transceivers are favorable for SDR, however, even for Time Division Duplex (TDD) systems, these transceivers suffer from self-interference when the transmitting and receiving Local Oscillator (LO) is set to the same frequency. To achieve low self-interference, switching from receiving to transmitting mode is needed. However, the time this takes (turnaround time, TT) for configurable RF front-ends often violates the strict timing requirements of protocols like Wi-Fi and 5G, which require response times in the order of microseconds. In this work, we first evaluate the advantages and disadvantages of several methods to suppress self-interference of a ZIF transceiver. Next, a novel approach is proposed, which can reduce the TT to as low as 640ns using the widely used AD9361 configurable ZIF RF front-end, while the noise floor is at the same level as achieved by the conventional way of switching between transmit and receive mode. We have realized and validated this approach using openwifi — an open-source Wi-Fi implementation on SDR. As a result, the receiver sensitivity is improved by up to 17dB in the 2.4GHz band and 9.5dB in the 5GHz band, for over-the-air transmissions.

Research on Bulk Acoustic Wave Resonator Based on Phononic Crystal

Abstract With the continuous advancement of information technology and the rapid development of mobile communication technology, from smart home to automatic driving of cars, and then to the application and development of virtual reality, communication technology has evolved from the earliest communication between people to communication between things. The frequency band supported by smart phones and various small mobile terminals is increasing, and their communication frequency is also gradually increasing, which brings some challenges to the traditional RF front-end devices. The traditional RF filter can not meet the current market demand because of its own performance and size constraints. As the best option to integrate with RF circuit or microwave circuit, bulk acoustic wave filter has great development and application prospects in modern RF communication system. This paper will focus on the solid-state assembled resonators based on one-dimensional and two-dimensional phononic crystals, analyze the influence and change law of the performance of bulk acoustic wave devices based on two-dimensional phononic crystals, then explore the main loss mechanism existing in solid-state assembled devices, and propose improvement schemes, which lays a foundation for the application of solid-state assembled resonators in today’s RF front-end.

Design of a Microstrip Filtering Antenna for 4G and 5G Wireless Networks

The filtering antenna provides both radiation and filtering features and is an important component for the RF front-end of wireless devices. The main function of a filtering antenna is to reject out-of-band signals, thus reducing the interference from adjacent channels. The aim of the present work is to design a 2.6 GHz microstrip filtering antenna for 4G and 5G global mobile services. The filtering antenna is designed using a hairpin bandpass filter integrated with an elliptical microstrip aerial. Good impedance matching is obtained by using appropriate dimensions of the hairpin bandpass filter. The 10 dB return loss bandwidth of the filtering antenna is approx. 5.7%, with the maximum gain for the elliptical filtering antenna of approx. 2.2 dB. Good agreements between the measured and simulated results are obtained for the proposed filtering antenna and the bandwidth covers almost the entire 2.6 GHz band.

Dual‐band filtering power amplifier with extended passband bandwidths and wide stopband rejection

AbstractThis article presents a dual‐band filtering power amplifier (DB‐FPA) with extended passband bandwidths and wide stopband rejection, which is helpful in reducing the number of microwave components in the dual‐band radio frequency front end, resulting in compact circuit size and low loss. In the designed DB‐FPA, a wideband low‐pass filter is applied as the input matching network (IMN) to provide wideband impedance matching and good stopband rejection, while a dual‐band filtering impedance transformation is adopted as the output matching network (OMN) to provide dual‐band impedance matchings and filtering responses simultaneously. Specifically, the IMN is constructed by high‐impedance transmission‐line sections and low‐impedance open‐circuit stubs. The OMN is designed based on the specific external quality factors and coupling coefficients during two bands, resulting in dual‐band impedance transformations and dual‐band filtering responses. Then, based on the above IMN and OMN, the design procedure of the presented DB‐FPA is summarised. To verify the proposed idea, a novel DB‐FPA has been fabricated and measured. During the two frequency bands, the measured maximum power added efficiencies are 55.11% and 47.78% within 33.0 dBm input power, while the measured peak gains are 15.4 and 14.0 dB within 15.0 dBm input power.

Circularly polarized differential intra-oral antenna design validation and characterization for tongue drive system

Assistive devices are becoming increasingly popular for physically disabled persons suffering tetraplegia and spinal cord injuries. Intraoral tongue drive system (iTDS) is one of the most feasible and non-invasive assistive technology (AT), which utilises the transferring and inferring of user intentions through different tongue gestures. Wireless transferring is of prime importance and requires a suitable design of the intra-oral antenna. In this paper, a compact circularly polarized differential intra-oral antenna is designed, and its performance is analysed within heterogeneous multilayer mouth and head models. It works at 2.4 GHz in the Industrial, Scientific, and Medical (ISM) band. The footprint of the differential antenna prototype is 0.271 λgtimes 0.271 λgtimes 0.015 λg. It is achieved using two pairs of spiral segments loaded in diagonal form near the edges of the central rotated square slot and a high dielectric constant substrate. Its spiral-slotted geometry further provides the desired swirling and miniaturization at the desired frequency band for both mouth scenarios. Additionally, corner triangular slits on the radiating patch assist in tuning the axial ratio (< 3 dB) in the desired ISM band. To validate the performance of the proposed in-mouth antenna, the measurement was carried out using the minced pork and the saline solution for closed and opened mouth cases, respectively. The measured − 10 dB impedance bandwidth and peak gain values in the minced pork are from 2.28 to 2.53 GHz (10.39%) and − 18.17 dBi, respectively, and in the saline solution, are from 2.3 to 2.54 GHz (9.92%) and − 15.47 dBi, respectively. Further, the specific absorption rate (SAR) is estimated, and the data communication link is computed with and without a balun loss. This confirms that the proposed differential intraoral antenna can establish direct interfacing at the RF front end of the intraoral tongue drive system.

Multicoset-based deterministic measurement matrices for compressed sensing of sparse multiband signals

Signal acquisition is a basic function in signal processing systems. In the context of digital communications, the analog-to-digital (ADC) converters have to be carefully designed as part of the radio frequency front end, to reduce power consumption while avoiding aliasing. When operating with sparse multiband signals, compressive sampling becomes an attractive alternative to enable low sampling rates at the front end. Starting from previous results on multicoset sampling and compressed sensing, we analyze sampling strategies for sparse multiband signals based on the operation of a set of ADC converters working in parallel. Different architectures are considered, with equal and different sampling rates in the ADCs, and their associated deterministic measurement matrices and sampling patterns are studied. The matrices involved in the corresponding reconstruction equations for the different architectures are also analyzed in terms of their mutual coherence. As a result, we are able to design different universal multicoset sampling patterns. We obtain the parameters for the different sampling architectures that guarantee reconstruction of the multiband sparse signal, even at high compression rates. Simulation results show the effectiveness of the theoretical designs for sparse reconstruction of this type of signals.

Reconfigurable Antennas for RF Energy Harvesting Application: Current Trends, Challenges, and Solutions from Design Perspective

Due to the widespread use of low-power embedded devices in both industrial and consumer applications, research into the use of alternate energy sources has been sparked by the requirement for continuous power. Due to its accessibility and ability to be implanted, RF energy is always taken into consideration among the traditional energy sources that are currently available. There is a significant necessity for efficient RF front-ends, which must provide effective circular polarization (CP) features, effectiveness, feasibility from a design standpoint, and optimal usage of ambient RF signals accessible in the environment. So, for understanding their utilization in RF energy harvesting, a metasurface reflector-inspired CP-printed reconfigurable antenna integrated with a Greinacher voltage divider (GVD) rectifier circuit is reported. It offers broadband CP with fractional bandwidth &gt; 25%, CP gain &gt; 8.35 dBic, and directional radiation with the 3 dB angular beamwidth &gt; 100° in the 3.5/5 GHz bands. With the integration of the rectifier circuit, a theoretical DC output &gt; 4.8 V at 12 dBm is obtained. The acceptable impedance bandwidth, axial ratio bandwidth, antenna gain, antenna efficiency, and directional radiation with a 3 dB angular beamwidth value are studied and subsequently matched with the trade-offs (usage of diodes, complexity of DC biasing circuits, and attainment of polarization reconfigurability) obtained from the state of the art. A comprehensive study of the reconfigurable antennas is reported to highlight the findings as a widespread solution for these limitations in RF energy harvesting application.

Loss Mitigation in Self-Biased Microstrip Circulators

Integration of the ferrite devices in the RF front-end and active antennas is hindered by the need for external magnets, biasing soft microwave ferrites. The hexaferrite-based self-biased nonreciprocal devices can operate without external magnets at mm-wave frequencies but the currently available hexaferrite materials inflict high RF losses at lower frequencies, particularly in the wireless communication bands. In this paper, the parameters of La-Co-substituted hexaferrite compounds are used for the self-biased circulators in the low GHz frequency bands, and a means of the dissipation loss reduction are discussed.

A 28 GHz 8 × 8 Gapwaveguide Phased Array Employing GaN Front-End With 60 dBm EIRP

A cost-efficient, high equivalent isotropic radiated power (60 dBm), large-bandwidth (26.5-29.5 GHz) active phased array antenna system has been designed and experimentally verified. The proposed design methodology results in a reduction of production costs by employing GaN-based radio frequency front-ends with 31 dBm output power allowing a reduced number of antenna elements. A fully metallic gapwaveguide technology has been employed achieving efficient heat dissipation per aperture area of the array as well as low-loss easy-to-manufacture antenna elements. The phased array is realized by subarraying an 8×8 slot array antenna with horizontal polarization. A ±60° analog beamforming in the E-plane is demonstrated. The presented antenna is a potential candidate for compact-size high-performance 5G base station antennas with excellent temperature stability.

Erratum

Microwave and Optical Technology LettersEarly View ERRATUMFree Access Erratum This article corrects the following: A fully integrated rf front end for DVB-SH Hugo García-Vázquez, Sunil L. Khemchandani, Dailos Ramos-Valido, Aitor Juanicorena, Carmen Luján-Martínez, Javier del Pino, Volume 54Issue 8Microwave and Optical Technology Letters pages: 1944-1949 First Published online: May 16, 2012 First published: 27 April 2023 https://doi.org/10.1002/mop.33726AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Erratum to “A fully integrated rf front end for DVB-SH” Microwave and Optical Technology Letters, by García-Vázquez, H., Khemchandani, S.L., Ramos-Valido, D., Juanicorena, A., Luján-Martínez, C. and del Pino, J. In the published article, an unintentional error occurred, which resulted in the name of the penultimate author being miswritten when it was first published online. It should read as: Clara I. Luján-Martínez We apologise for the error. REFERENCE 1García-Vázquez, H., Khemchandani, S.L., Ramos-Valido, D., Juanicorena, A., Luján-Martínez, C. and del Pino, J. (2012), A fully integrated rf front end for DVB-SH. Microwave and Optical Technology Letters, 54: 1944- 1949. doi:10.1002/mop.26974 Early ViewOnline Version of Record before inclusion in an issue ReferencesRelatedInformation

Design and FPGA-Based Hardware Implementation of NB-IoT Physical Uplink Shared Channel Transmitter and Physical Downlink Shared Channel Receiver

With the anticipated growth of the internet of things (IoT) market, many low-power wide-area (LPWA) technologies have been introduced to connect a wide range of IoT devices with varying performance requirements. The narrowband internet of things (NB-IoT) is a 3rd generation partnership project (3GPP) standardized LPWA technology that meets most IoT service requirements. In this paper, the design and implementation of the physical uplink transmitting chain as well as the physical downlink receiving chain of the NB-IoT user equipment (UE) are presented. Both chains’ main blocks are designed to follow the 3GPP NB-IoT LTE standard Release 14 (Rel-14). The whole design is experimentally implemented on the Virtex 7 (VC 709) Connectivity kit, and all performance metrics are reported. Moreover, an NB-IoT base station is implemented and integrated with the two prototyped UEs to set-up an NB-IoT system, which is employed to send data from one UE to another UE through the NB-IoT base station using two FPGAs (one to implement the sending UE and the other one to implement the receiving UE) and three universal software radio peripherals (USRPs) B200 (one to implement the RF front-end of the transmitting UE FPGA, one to implement the base station RF front-end, and one to implement the RF front-end of the receiving UE FPGA). Experimental results show that the implemented NB-IoT system is working successfully, as the two NB-IoT UEs communicate together successfully through the NB-IoT base station and exchange the data properly.

Radio Frequency Fingerprint Identification Based on Metric Learning

With the popularization of the internet of things (IoT), its security has become increasingly prominent. Radio-frequency fingerprinting (RFF) is used as a physical-layer security method to provide security in wireless networks. However, the problems of poor performance in a highly noisy environment and less consideration of calculation resources are urgent to be resolved in a practical RFF application domain. The authors propose a new RFF identification method based on metric learning. They used power spectrum density (PSD) to extract the RFF from the nonlinearity of the RF front end. Then they adopted the large margin nearest neighbor (LMNN) classification algorithm to identify eight software-defined radio (SDR) devices. Different from existing RFF identification algorithms, the proposed LMNN method is more general and can learn the optimal metric from the wireless communication environment. Furthermore, they propose a new training and test strategy based on mixed SNR, which significantly improves the performance of conventional low-complexity RFF identification methods. Experimental results show that the proposed method can achieve 99.8% identification accuracy with 30dB SNR and 96.83% with 10dB SNR. In conclusion, the study demonstrates the effectiveness of the proposed method in recognition efficiency and computational complexity.

Monolithically Integrated Directly Pumped Time-Varying Transmission Lines

A novel directly pumped time-varying transmission line (DP-TVTL) is proposed here and implemented on gallium arsenide (GaAs) microwave monolithic integrated circuit (MMIC). Comparing to existing TVTL architectures where the pump wave is launched through the transmission line, the pump wave in the DP-TVTL is directly fed to the different parts of the transmission line through a parallel power division network. The impedance of TVTL is modulated by the pump through diode bridges that isolate the signal path from the pump path. The power division network creates a phase delay emulating that of a traveling-wave delay line yet without launching the physical pump wave on the TVTL. This avoids the loss of the pump energy propagating through the transmission line. It also adds more freedom in the design of the bandgap properties of TVTL and simplifies the combination/separation circuitry for waves at different frequencies in and out of the TVTL. The resulting MMIC TVTL offers exceptional, broadband conversion gain performance of up to 4.2 dB, a low noise figure of 3 dB, and input referred P1dB of 12 dBm when used as a parametric mixer. It may be used in an RF front end as a mixer first receiver or an RF correlator.

How 3D-Printing Is Changing RF Front-End Design for Space Applications

3D-printing is leading to a major transformation in many industrial and application sectors, ranging from medical to aerospace. In the space sector, 3D-printing has firstly been adopted for the development of structural and thermal parts, such as brackets and heat pipes. In more recent years, thanks to improvements in precision and surface roughness, 3D-printing technologies have steadily been investigated also for the development of radio frequency components and advanced payloads. Indeed, the unique features of 3D-printing, including the free-form capability and the ease for customization, make these manufacturing technologies very appealing in the development of complex radio-frequency front-ends for space applications, including New Space constellations and next generation software-defined communication satellites. They also enable a drastic simplification of mechanical designs by reducing the number of interfaces and assembling screws of large radio-frequency front-ends, thus leading to significant mass savings and higher integration. This paper briefly reports on recent advances in 3D-printing that have been carried out according to the current trends in radio-frequency front-ends for satellite communications.