RF Front-end Research Articles

A Cost-Effective W-Band Antenna-in-Package Using IPD and PCB Technologies

This paper presents a cost-effective millimeter-wave (W-band) cavity-backed slot antenna-in-package (AiP) built by using commercially available integrated passive device (IPD), printed circuit board (PCB), and flip-chip assembly technologies. An IPD-PCB resonant cavity is formed by flipping an IPD chip on a PCB substrate with surrounding solder bumps to provide radiation through a square slot, which is patterned on one of the IPD metal layers. Moreover, a substrate integrated waveguide (SIW) cavity under the IPD-PCB cavity and a wideband grounded coplanar waveguide (GCPW) are built in the PCB substrate for the transition between a radio-frequency front-end (RFFE) and the IPD-PCB cavity. The fabricated AiP achieves a 3.75-dBi gain at 94.5 GHz (TE210 mode) and a 10-dB impedance bandwidth of 1.9 GHz with a 3.61 mm2 IPD chip area.

A Near-Field Motion Detection Technique Based on a Resonant Magnetic Probe

This letter proposes a near-field motion detection technique based on a resonant magnetic-field probe. The resonant magnetic-field probe consists of a parallel metal plate and a quarter-wave impedance transformer to make the input impedance 50 &#x03A9;. The 5.8-GHz radio frequency (RF) front-end is designed, which consists of a hybrid coupler and the proposed resonant magnetic-field probe that can be regarded as a full duplex antenna. Then, a 5.8-GHz continuous-wave Doppler radar transceiver is designed and integrated with the RF front-end to build the near-field radar system. The equivalent circuit of the RF front-end while detecting the targets in near-field is analyzed, in which the probe loop and the matching circuitry are modeled as a parallel <i>RLC</i> circuit and the coupler and transmission lines are equivalent to a lossy transmission line and an attenuator. The experimental results demonstrate that the proposed system can detect submillimeter displacement motions in the near-field.

Efficient RF-PA Two-Chip Supply Modulator Architecture for 4G LTE and 5G NR Dual-Connectivity RF Front End

This article presents a two-chip supply modulation architecture for efficient RF power amplification using a fully switched-mode supply modulator (SM) and a linear-assisted hybrid SM to support simultaneous transmission on long-term evolution (LTE) and 5G bands. The designed fully switched-mode SM consists of a fast switching buck converter and a slow switching buck converter, and it achieves 88.2% peak efficiency and a low receiver (RX) band noise of −140 dBm/Hz at the SM output. The fully switched-mode SM tracks the envelope of LTE 5-/10-/20-MHz signals with the average switching frequencies of 50/70/120 MHz, respectively. The ET-PA measured using the fully switched-mode SM and LTE band-3 power amplifier module integrated duplexer (PAMiD) saves the dc power consumption of 320 mW at a 23-dBm output power compared to an average power tracking (APT)-PA. The designed 5G new radio (NR) SM consisting of a class-AB linear amplifier (LA) and an interleaved three-level buck–boost converter provides a 160-MHz 3-dB bandwidth to track the envelope of a 100-MHz NR signal. The measured peak SM efficiency is 84.1% at a 3.53-W output power. The measured ET-PA with 5G NR SM and 5G n77 PAMiD achieves an ACLR of −36.9 dBc at a 27.45-dBm output power with a 6-dB peak-to-average-power ratio DFT-spread-OFDM NR 100-MHz quadrature phase shift keying (QPSK) signal. It saves the dc power consumption of 950 mW at a 27-dBm output power compared to APT-PA. An optimal RF power amplifier (RF-PA) supply deployment using the two SMs efficiently supports multiple RF-PA loads while satisfying the dual-transmission requirements of E-UTRAN new radio dual-connectivity (EN-DC) and 5G 100-MHz ET operation. The fully switched-mode SM is implemented in a 130-nm CMOS process, and the die size is 4.0 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The 5G NR SM is implemented in a 90-nm CMOS process, and the die size is 6.75 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

Chip Design of an All-Digital Frequency Synthesizer with Reference Spur Reduction Technique for Radar Sensing

5.2-GHz all-digital frequency synthesizer implemented proposed reference spur reducing with the tsmc 0.18 µm CMOS technology is proposed. It can be used for radar equipped applications and radar-communication control. It provides one ration frequency ranged from 4.68 GHz to 5.36 GHz for the local oscillator in RF frontend circuits. Adopting a phase detector that only delivers phase error raw data when phase error is investigated and reduces the updating frequency for DCO handling code achieves a decreased reference spur. Since an all-digital phase-locked loop is designed, the prototype not only optimized the chip dimensions, but also precludes the influence of process shrinks and has the advantage of noise immunity. The elements of novelties of this article are low phase noise and low power consumption. With 1.8 V supply voltage and locking at 5.22 GHz, measured results find that the output signal power is −8.03 dBm, the phase noise is −110.74 dBc/Hz at 1 MHz offset frequency and the power dissipation is 16.2 mW, while the die dimensions are 0.901 × 0.935 mm2.

Design of Compact Complex Impedance Transformer with Frequency and Terminal Impedance Tunability

In the paper, a compact complex impedance transformer (CIT) composed of the cascading of three varactors loaded coupled lines and two variable shunt susceptances was proposed. Highly flexible tunability functions including only frequency tunable, only impedance tunable, and both frequency and impedance tunable can be achieved by tuning the capacitance of two types of varactors and the value of the susceptance. Design equations were derived using the even–odd mode analysis and examples are given for descripting the design procedures. For validation, a prototype was designed and fabricated. During measurement, three cases were exhibited. When the termination impedance was fixed, the measured center frequency can be tuned in the range of 1.1–2.1 GHz (62.5%). When the frequency was determined, different terminal impedances can be matched by the prototype. The function of frequency tunable at different terminal impedances is also trated by the measured results. After comparison, the potential of the proposed CIT for applications in radio frequency front-end were demonstrated.

Single-crystalline LiNbO3 film based wideband SAW devices with spurious-free responses for future RF front-ends

This work demonstrates super-high frequency wave-guided surface acoustic wave (SAW) devices based on LiNbO3/SiO2/Si layered substrates. SAW resonators with fundamental operating frequency to the 7-GHz range were developed, and wave modes like the Rayleigh, Shear-horizontal (SH), Pseudo-Bulk, etc., were observed. Furthermore, effective coupling coefficients (k2eff) and quality factor (Q) of the devices have been investigated systematically. Specifically, spurious-free SAW resonators with the SH wave frequency over 7.40 GHz and the high k2eff value of ∼7.8% were obtained at a nanoscale wavelength of 480 nm. Finally, high-performance filters with a bandwidth over 300 MHz were achieved. The demonstrated filters show sharp roll-off and spurious-free responses within the passband with insertion loss &amp;lt;−5 dB and a small temperature coefficient of frequency of ∼−45.8 ppm/K at a super-high frequency of 7.17 GHz. Upon further optimizations, high-performance SAW devices built on a single crystalline LiNbO3 film can potentially enable the low-loss and wideband signal processing functions, promising for the next-generation radio frequency front-end system applications.

A 60‐GHz low‐noise amplifier with +7.258‐dBm third‐order input intercept point using current reuse feedforward distortion cancellation for 5G emerging communication

AbstractIn the ever‐growing 5G technology, the millimetre‐wave (mmWave) frequency spectrum is the inevitable mainstream for high‐speed wireless communication. The wide‐ranging spectrum bandwidth of the mmWave frequency attracts interest in radio frequency (RF) front‐end design which will be very much beneficial for security and cellular‐based applications such as intersatellite communication and automotive vehicle‐to‐vehicle communication. The RF front end requires low‐power and low‐noise receiver architecture for effective satellite communication, and it needs high throughput with maximum data transfer for cellular‐based applications. To address these challenges, this paper presents a novel low‐noise amplifier (LNA) operating from 57.12‐ to 66.25‐GHz frequency. The design is implemented using UMC 65‐nm CMOS process technology, and the post‐layout simulations are carried out using the Cadence Spectre RF tool. At 60 GHz, the LNA exhibits a power gain of 15.46 dB, minimum noise figure (NF) of 1.32 dB while consuming 6.59 mW from a 1.2‐V supply. The LNA employs the current reuse feedforward distortion cancelation technique to improve the third‐order input intercept point (IIP3) to +7.258 dBm. The proposed LNA provides a relatively better figure of merit compared to some of the recently proposed mmWave LNA architectures.

Wideband RF Transmit-Receive Switch for Multi-Nuclei NMR Spectrometers

The utility of wideband high field nuclear magnetic resonance (NMR) spectrometers is significant in many applications. Wideband radio frequency (RF) front-ends are critical for the realization of multi-nuclei spectrometers. To realize such systems, wideband Transmit-Receive (TR) switches and low noise amplifiers (LNA) should be implemented at the RF front-end (FE) of the system. Most of the common designs used nowadays on NMR spectrometers are either inherently narrowband and/or of relatively high noise-figure which limit the overall system performance to a large extent. To improve upon the conventional FE performance, a new design of wideband high-power TR switch which could be devised for multi-nuclei NMR spectrometers is introduced in this brief. The developed wideband TR switch employs PIN diode switching technique and a dual-driver circuit. A prototype was constructed and experimentally characterized. The small-signal measurement results show that the switch has a bandwidth from 30 – 200MHz where the return loss is maintained below 18 dB with insertion loss of 0.09 - 0.2dB in the transmit mode and 0.11 – 0.37dB in the receive mode. It also exhibits a very high isolation of 63 - 80dB over the entire bandwidth. It is demonstrated that the switch can withstand continuous-wave RF input with power levels as high as 125 W while maintaining low insertion loss and high isolation.

Flexible and Transparent Circularly Polarized Patch Antenna for Reliable Unobtrusive Wearable Wireless Communications

This paper presents a circularly polarized flexible and transparent circular patch antenna suitable for body-worn wireless-communications. Circular polarization is highly beneficial in wearable wireless communications, where antennas, as a key component of the RF front-end, operate in dynamic environments, such as the human body. The demonstrated antenna is realized with highly flexible, robust and transparent conductive-fabric-polymer composite. The performance of the explored flexible-transparent antenna is also compared with its non-transparent counterpart manufactured with non-transparent conductive fabric. This comparison further demonstrates the suitability of the proposed materials for the target unobtrusive wearable applications. Detailed numerical and experimental investigations are explored in this paper to verify the proposed design. Moreover, the compatibility of the antenna in wearable applications is evaluated by testing the performance on a forearm phantom and calculating the specific absorption rate (SAR).

A novel piezoelectric RF-MEMS resonator with enhanced quality factor

This work presents a novel ultra-high frequency Lamb mode Aluminum nitride piezoelectric resonator with enhanced quality factors (Q). With slots introduced in the vicinity of the tether support end, the elastic waves leaking from the tether sidewalls can be reflected, which effectively reduces the anchor loss while retaining size compactness and mechanical robustness. Comprehensive analysis was carried out to provide helpful guidance for obtaining optimal slot designs. For various resonators with frequencies ranging from 630 MHz to 1.97 GHz, promising Q enhancements up to 2 times have all been achieved. The 1.97 GHz resonator implemented excellent f × Q product up to 6.72 × 1012 and low motional resistance down to 340 Ω, which is one of the highest performances among the reported devices. The devices with enhanced Q values as well as compact size possess potential application in advanced radio frequency front end transceivers.

Wireless powered hybrid backscatter-active communications with hardware impairments

Wireless powered hybrid backscatter-active communication can full make use of the different tradeoff between power consumption and achievable rate of the active and backscatter communications, and thus achieving a better performance than wireless powered active or backscatter communications. In this paper, we design a throughput maximization-based resource allocation scheme for a wireless powered hybrid backscatter-active communication network, while considering the hardware impairments at all RF front ends of each transceiver. Towards this end, we formulate a problem by jointly optimizing the transmit power of the dedicated energy source, the time for pure energy harvesting, backscatter and active communications, the power reflection coefficient, and the transmit power of each IoT node during active communications. The formulated problem is non-convex and different to solve. Subsequently an iterative algorithm based on the block coordinated decent technology is proposed to address the above problem. Simulation results verify that our proposed iterative algorithm converges very fast and that the proposed scheme outperforms the baseline schemes in terms of the throughput.

GNSS User Technology: State-of-the-Art and Future Trends

Advances in the miniaturization, computational capabilities, and cost reduction of semiconductor technology have made global navigation satellite systems (GNSSs) the favorite choice for positioning. Currently, positioning is a key factor for many essential tasks in our modern society and will become even more important with the advent of new concepts such as the Internet of Things (IoT), smart cities and autonomous driving. The extensive use of GNSSs in a wide range of applications has caused their migration from the professional segment to the mass-market segment in terms of both technology and performance. This presents new and more stringent requirements in terms of accuracy, robustness, ubiquity, and continuity for the original “open sky” GNSS design. GNSS technology has experienced an unprecedented evolution in the last decade, and it is expected to exponentially evolve in the next decade. This evolution is considered in this paper with the aim of providing a unified reference for current GNSS receiver technologies and solutions and its expected evolution in the next decade. We consider receiver concepts, antennae, RF front ends, digital signal processing, and positioning algorithms. The impacts on the different GNSS market segments and applications are also analyzed.

A Compact 28 GHz Millimeter Wave Antenna for Future Wireless Communication

This article presents a novel modified chuck wagon dinner bell shaped millimeter wave (mm-wave) antenna at 28 GHz. The proposed design has ultra-thin Rogers 5880 substrate with relative permittivity of 2.2. The design consists of T shaped resonating elements and two open ended side stubs. The desired 28 GHz frequency response is achieved by careful parametric modeling of the proposed structure. The maximum achieved single element gain at the desired resonance frequency is 3.45 dBi. The efficiency of the proposed design over the operating band is more than 88%. The impedance bandwidth achieved for −10 dB reference value is nearly 2.9 GHz. The proposed antenna is transformed into four element linear array which increases the gain up to 10.5 dBi. The fabricated prototype is tested for the measured results. It is observed that measured results closely match the simulated results. By considering its simple structure and focused radiation patterns, the proposed design is well suited for IoT (Internet of Things), mmWave microwave sensing, 5G and future RF (Radio Frequency) front-ends.

Physical Layer-Based IoT Security: An Investigation Into Improving Preamble-Based SEI Performance When Using Multiple Waveform Collections

The Internet of Things (IoT) is a collection of inexpensive, semi-autonomous, Internet-connected devices that sense and interact within the physical world. IoT security is of paramount concern, because most IoT devices use weak or no encryption at all. This concern is exacerbated by the fact that the number of IoT deployments continues grow, IoT devices are being integrated into key infrastructures, and their weak or lack of encryption is being exploited. Specific Emitter Identification (SEI) is being investigated as an effective, cost-saving IoT security approach, because it is a passive technique that exploits inherent, distinct features that are unintentionally imparted to the waveform during its formation and transmission by the IoT device’s Radio Frequency (RF) front-end. Despite the amount of research conducted, SEI still faces roadblocks that hinder its integration within operational networks. Our work focuses on the lack of feature permanence across time and environments, which is designated herein as the “multi-day” problem. We present results and analysis for six distinct experiments focused on improving multi-day SEI performance through the use of multiple waveform representations, deeper Convolutional Neural Networks (CNNs), increasing numbers of waveforms, channel model impacts, and two channel mitigation techniques. Our work shows improved multi-day SEI performance using the waveform’s frequency-domain representation and a CNN comprised of four convolutional layers. However, the traditional channel model and both channel mitigation techniques fail to sufficiently mitigate or remove real-world channel impacts, which suggests that the channel may not be the dominant effect hindering multi-day SEI performance.

Advances in Wirelessly Powered Backscatter Communications: From Antenna/RF Circuitry Design to Printed Flexible Electronics

Backscatter communication is an emerging paradigm for pervasive connectivity of low-power communication devices. Wirelessly powered backscattering wireless sensor networks (WSNs) become particularly important to meet the upcoming era of the Internet of Things (IoT), which requires the massive deployment of self-sustainable and maintenance-free low-cost sensing and communication devices. This article will introduce the state-of-the-art antenna design and radio frequency (RF) system integration for wirelessly powered backscatter communications, covering both the node and the base unit. We capture the latest development in ultralow-power RF front ends and coding schemes for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{W}$ </tex-math></inline-formula> -level backscatter modulators, as well as the latest progress in wireless power transfer (WPT) and energy harvesting (EH) techniques. Newly emerged rectenna system, waveform design, and channel optimization are reviewed in light of the opportunities for adaptively optimizing the WPT/EH efficiency for low-power signals with varying conditions. In addition, advanced device packaging and integration technologies in, e.g., additively manufactured RF components and modules for microwave and millimeter-wave ubiquitous sensing and backscattering energy-autonomous RF structures are reported. Inkjet printing for the sustainable and ultralow-cost fabrication of flexible RF devices and sensors will be reviewed to provide a prospective insight into the future packaging of backscatter communications from the chip-level design to complete system integration. Finally, this article will also address the challenges in fully wireless powered backscatter radio networks and discuss the future directions of backscatter communication in terms of “Green IoT” and “Low Carbon” smart home, smart city, smart skin, and machine-to-machine (M2M) applications.

Design of a Compact Novel Stub Loaded Pentaband Bandpass Filter for Next Generation Wireless RF Front Ends

This paper presents a compact novel pentaband bandpass filter using a dual path stub loaded step impedance resonator (SLSIR). The proposed topology consists of a dual path λ/4 and 2λ/3 long uniform impedance resonator centered separated by 2λ/3 open and λ/12 short circuit stubs respectively. The superposition of signals from the two transmission routes results in a fifth-order pentaband bandpass response with six finite frequency transmission zeroes and out-of-band rejection of 11dB from 12 GHz up to 20 GHz. The filter produces five frequency bands at 1.06 GHz, 3.24 GHz, 5.36 GHz, 8.55 GHz and 10.78 GHz with fractional bandwidth (FBW) of 25.59%, 22.22%, 19.48%, 16.03% and 17.17% respectively. The proposed design is fabricated on a high-frequency substrate with a physical size of (0.23λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>g</i></sub> × 0.14 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>g</i></sub> ). The new pentaband bandpass filter has a simple and compact design with good electrical performance. A fair match can be found between the simulated and experimental results.

A Reconfigurable Power-Efficient Quantized Analog RF Front-End With Smart Calibration

A power scalable RF front-end using Quantized Analog signal processing is presented. The front-end is based on a voltage-mode power scalable approach which allows the power dissipation to be scaled upon the operative scenario and to performing an agile calibration for mismatch impairments. Power and input dynamic range can be scaled upon the desired 1dBCP (from -15.3dBm to 0.5dBm) while keeping the same sensitivity with 2.5dB NF. Signal path power can vary between 3.3mW to 6.4mW while clock generation and distribution power can vary between 1.6mW/GHz to 18.5mW/GHz, with a PN as low as -171.2dBc/Hz. After calibration, IM2 and IM3 improved up to 33dB while 1dBCP improved by 1dB, which resulted in achieving an IIP3 of 26.1dBm and IIP2 of 71dBm at 0dBm 1dBCP.

DeepAoANet: Learning Angle of Arrival From Software Defined Radios With Deep Neural Networks

Direction finding and positioning systems based on RF signals are significantly impacted by multipath propagation, particularly in indoor environments. Existing algorithms (e.g MUSIC) perform poorly in resolving Angle of Arrival (AoA) in the presence of multipath or when operating in a weak signal regime. We note that digitally sampled RF frontends allow for the easy analysis of signals, and their delayed components. Low-cost Software-Defined Radio (SDR) modules enable Channel State Information (CSI) extraction across a wide spectrum, motivating the design of an enhanced AoA solution. We propose a Deep Learning approach for deriving AoA from a single snapshot of the SDR multichannel data. We compare and contrast deep-learning based angle classification and regression models, to estimate up to two AoAs accurately. We have implemented the inference engines on different platforms to extract AoAs in real-time, demonstrating the computational tractability of our approach. To demonstrate the utility of our approach we have collected IQ (In-phase and Quadrature components) samples from a four-element Universal Linear Array (ULA) in various Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) environments, and published the dataset. Our proposed method demonstrates excellent reliability in determining number of impinging signals and realized mean absolute AoA errors less than 2°.

Research on Continuous Wave Electromagnetic Effect in Swept Frequency Radar

In order to establish the prediction model of radar equipment in multisource complex electromagnetic environment, the blocking effect and false alarm interference effect caused by single-frequency CW (continuous wave) electromagnetic interference on typical radar equipment are studied. Taking a certain sweep radar as the research object, the equivalent injection test of EMI (electromagnetic interference) is carried out. Based on the theory of radar front door coupling, the interference mechanism of EMI to radar receiver RF front end is revealed, and the variation law of blocking target and false alarm target level is analyzed. The results show that, under the single-frequency CW-EMI, the target echo level decreases with the increase of the interference field strength, and the false alarm level increases with the increase of the interference field strength. The blocking jamming sensitive bandwidth is about f 0 ± 200 MHz , and the false alarm jamming sensitive bandwidth is about f 0 ± 80 MHz .

Piezoelectric MEMS—evolution from sensing technology to diversified applications in the 5G/Internet of Things (IoT) era

The rapid development of the fifth-generation mobile networks (5G) and Internet of Things (IoT) is inseparable from a large number of miniature, low-cost, and low-power sensors and actuators. Piezoelectric microelectromechanical system (MEMS) devices, fabricated by micromachining technologies, provide a versatile platform for various high-performance sensors, actuators, energy harvesters, filters and oscillators (main building blocks in radio frequency front-ends for wireless communication). In this paper, we provide a comprehensive review of the working mechanism, structural design, and diversified applications of piezoelectric MEMS devices. Firstly, various piezoelectric MEMS sensors are introduced, including contact and non-contact types, aiming for the applications in physical, chemical and biological sensing. This is followed by a presentation of the advances in piezoelectric MEMS actuators for different application scenarios. Meanwhile, piezoelectric MEMS energy harvesters, with the ability to power other MEMS devices, are orderly enumerated. Furthermore, as a representative of piezoelectric resonators, Lamb wave resonators are exhibited with manifold performance improvements. Finally, the development trends of wearable and implantable piezoelectric MEMS devices are discussed.