RF Front-end Research Articles

Emerging trends in advanced rf/microwave filters for wireless applications, part i [from the guest editor's desk

The articles in this special section focus on emerging trends in advanced radio frequency/microwave filters for wireless applications. Currently, there is a progressive trend toward the development of highly flexible and miniaturized RF front ends that support emerging multipurpose/multistandard wireless communications systems, i.e., for satellite or mobile communications (e.g., 5G) and multifunction radar applications. Consequently, significant research is geared toward the design of advanced enhanced-performance RF components as the enabling hardware for next-generation high-frequency systems. Such research includes microwave filters and multiplexers as major components because they are essential RF blocks to perform the signal-band selection processes needed by wireless systems to efficiently reject out-of-band power-/frequency-agile interference and noise.

CMOS Channel-Selection Low-Noise Amplifier With High-$Q$ RF Band-Pass/Band-Rejection Filter for Highly Integrated RF Front-Ends

In this letter, a CMOS tunable channel-selection low-noise amplifier (LNA) employing a high- ${Q}$ RF band-pass (BP)/band-rejection (BR) filter is proposed for highly integrated RF front-ends in cellular applications. The proposed LNA implements a high- ${Q}$ RF BP/BR filter characteristic based on a four-path filter theory from a baseband polyphase filter and a low-pass filter. It also provides a high rejection ratio for close-in transmitter leakage signal and out-of-band blockers. Therefore, it compensates for the limited filtering performance of the CMOS duplexer and improves the blocker-tolerance and linearity of the receiver. The proposed LNA is implemented in 65-nm CMOS technology. It achieves a maximum voltage gain of 20.4 dB, a minimum NF of 3.24 dB, and a notch rejection ratio of more than 56.4 dB. It can also cover a low-band and a mid-band from 0.7 up to 2.2 GHz in cellular applications. It draws an average current of 13 mA from a supply voltage of 1.2 V and has an active area of 0.62 mm2.

A Baseband Wireless Spectrum Hypervisor for Multiplexing Concurrent OFDM Signals.

The next generation of wireless and mobile networks will have to handle a significant increase in traffic load compared to the current ones. This situation calls for novel ways to increase the spectral efficiency. Therefore, in this paper, we propose a wireless spectrum hypervisor architecture that abstracts a radio frequency (RF) front-end into a configurable number of virtual RF front ends. The proposed architecture has the ability to enable flexible spectrum access in existing wireless and mobile networks, which is a challenging task due to the limited spectrum programmability, i.e., the capability a system has to change the spectral properties of a given signal to fit an arbitrary frequency allocation. The proposed architecture is a non-intrusive and highly optimized wireless hypervisor that multiplexes the signals of several different and concurrent multi-carrier-based radio access technologies with numerologies that are multiple integers of one another, which are also referred in our work as radio access technologies with correlated numerology. For example, the proposed architecture can multiplex the signals of several Wi-Fi access points, several LTE base stations, several WiMAX base stations, etc. As it able to multiplex the signals of radio access technologies with correlated numerology, it can, for instance, multiplex the signals of LTE, 5G-NR and NB-IoT base stations. It abstracts a radio frequency front-end into a configurable number of virtual RF front ends, making it possible for such different technologies to share the same RF front-end and consequently reduce the costs and increasing the spectral efficiency by employing densification, once several networks share the same infrastructure or by dynamically accessing free chunks of spectrum. Therefore, the main goal of the proposed approach is to improve spectral efficiency by efficiently using vacant gaps in congested spectrum bandwidths or adopting network densification through infrastructure sharing. We demonstrate mathematically how our proposed approach works and present several simulation results proving its functionality and efficiency. Additionally, we designed and implemented an open-source and free proof of concept prototype of the proposed architecture, which can be used by researchers and developers to run experiments or extend the concept to other applications. We present several experimental results used to validate the proposed prototype. We demonstrate that the prototype can easily handle up to 12 concurrent physical layers.

A Compact UWB Bandpass Chip Filter on a GaAs Substrate with Modified Chebyshev Structure

Ultra-Wideband (UWB) systems are widely used in low-power, high-speed, high-security short-range wireless communication systems throughout digital homes and offices. In the RF front-end of a UWB system, bandpass filters (BPFs) are used to put through the passband signals and reject the stopband signals. Most UWB BPFs are designed with dielectric materials on circuit boards or LTCC technology. In this paper, a very compact fully integrated UWB chip filter is proposed and designed on a GaAs substrate with nitride as dielectric layers to meet the small size requirement of portable devices for next-generation UWB applications. The filter is constructed with a modified Chebyshev structure. The final filter circuit contains only four inductors instead of six for the conventional Chebyshev filter, which makes the chip more compact and cost effective. The filter is designed and fabricated on a 0.25 μm GaAs pHEMT technology with a chip size of only 0.73 mm × 0.51 mm including the chip edge and scribe line area, while the filter core area is only 0.61 mm × 0.39 mm, including bonding PADs. The measurement results illustrated that the proposed BPF shows a passband covering the frequency range of 3.1–9.0 GHz, the minimum passband insertion loss is only 1.5 dB, the stopband rejection is better than −30 dB throughout frequencies below 2 GHz and above 12 GHz, S11 is less than −16 dB, and S22 is better than −11 dB during the whole passband range. It demonstrated that the proposed filter can be considered as one of the most compact UWB filters.

Performance Aspects of Multiband Microwave Planar Devices for Wireless Applications

The RF front end receiver plays a key role to fulfill the demands of the numerous applications in the wireless communication .This article of lettering portrays about the analysis of planar microstriplines based multiband passive microwave devices which are simulated in ADS (Advanced Design System) software. Also we have designed a multiband band pass filter, and multiband hybrid coupler which are essential in the front ends design of receivers such as software defined radio and cognitive radio. Here BPF covers the frequency range from 400 MHz-2GHz and hybrid coupler covers from 1-5GHz. With the use of these components the single band RF front end will become the multiband front end receiver architecture.

Performance Analysis of Modular RF Front End for RF Fingerprinting of Bluetooth Devices

Radio frequency fingerprinting (RFF) could provide an efficient solution to address the security issues in wireless networks. The data acquisition system constitutes an important part of RFF. In this context, this paper presents an implementation of a modular RF front end system to be used in data acquisition for RFF. Modularity of the system provides flexible implementation options to suit diverse frequency bands with different applications. Moreover, the system is able to collect data by means of any digitizer, and enable to record the data at lower frequencies. Therefore, proposed RF front end system becomes a low-cost alternative to existing devices used in data acquisition. In its implementation, Bluetooth (BT) signals were used. Initially, transients of BT signals were detected by utilizing a large number of BT devices (smartphones). From the detected transients, distinctive signal features were extracted. Then, support vector machine (SVM) and neural networks (NN) classifiers were implemented to the extracted features for evaluating the feasibility of proposed system in RFF. As a result, 96.9% and 96.5% classification accuracies on BT devices have been demonstrated for SVM and NN classifiers respectively.

A flexible LEO satellite modem with Ka‐band RF frontend for a data relay satellite system

SummaryFrom a geostationary Earth orbit (GEO) satellite's perspective, a low Earth orbit (LEO) satellite is visible on more than half of its orbit. Albeit the free‐space loss of an inter‐satellite link is much higher than the one of a direct ground link, considerable data rates and download volumes can be achieved. In this paper, we describe the system architecture of an integrated approach for a data relay satellite system and the development of LEO satellite and ground station modems. The approach allows serving several small and inexpensive LEO satellites at the same time both with low rate telemetry/telecommand links and with high rate download of sensor data.

A Fully Passive RF Front End With 13-dB Gain Exploiting Implicit Capacitive Stacking in a Bottom-Plate N-Path Filter/Mixer

A low-power interferer-robust mixer-first receiver front end that uses a novel capacitive stacking technique in a bottom-plate N-path filter/mixer is proposed. Capacitive stacking is achieved by reading out the voltage from the bottom plate of N-path capacitors instead of their top plate, which provides a $2\times $ voltage gain after downconversion. A step-up transformer is used to improve the out-of-band (OOB) linearity performance of small switches in the N-path mixer, thereby reducing the power consumption of switch drivers. This article explains the concept of implicit capacitive stacking and analyzes its transfer characteristics. A prototype chip, fabricated in 22-nm fully depleted silicon on insulator (FDSOI) technology, achieves a voltage gain of 13 dB and OOB IIP3/IIP2 of +25/+66 dBm with 5-dB noise figure while consuming only 600 $\mu \text{W}$ of power at $f_{\mathrm{ LO}}=1$ GHz. Thanks to the transformer, the prototype can operate in the input frequency range of 0.6–1.2 GHz with more than 10-dB voltage gain and 5–9-dB noise figure. Thus, it opens up the possibility of low-power software-defined radios.

New Agile Matrix Antenna for Nano-satellite Telemetry Using Bimodal Pattern Reconfiguration

This review deals with the design of a new reconfigurable beam antenna used to improve the efficiency of spatial telemetry links on Nano-Satellite. Advances in this domain show the needs to serve some applications with special electromagnetic beams and polarization patterns especially from LEO and MEO Space-Earth links. The RF front end must be capable to switch from high gain directive pattern to special pattern called Isoflux where the gain must be concentrated at high elevation angles with another challenge also the circular polarization. The content is a part of the CNES project that serves for multimode beam forming applications. This agile beam antenna is not built on the well-known array concept: AESA stands for Agile Electronically Scanned Array but using a new approach called ARMA standing for Agile Radiating Matrix Antenna. Contributions will show the small size elementary antenna of ARMA called Pixel, the polarization circuits that fit the challenges of the Nano-Satellite dimensions, the enhancement in the circular polarization requirements and theoretical and experimental comparison. Special beam forming required in the telemetry applications are achieved with better gain especially for the aim of wide beams. The use of the new approach will show the beam forming advantage of radiating the energy to high elevation angles.

Multi-Tone Signal Optimization for Wireless Power Transfer in the Presence of Wireless Communication Links

In this paper, we study optimization of multi-tone signals for wireless power transfer (WPT) systems. We investigate different non-linear energy harvesting models. Two of them are adopted to optimize the multi-tone signal according to the channel state information available at the transmitter. We show that a second-order polynomial curve-fitting model can be utilized to optimize the multi-tone signal for any RF energy harvester design. We consider both single-antenna and multi-antenna WPT systems. In-band co-existing communication links are also considered in this work by imposing a constraint on the received power at the nearby information receiver to prevent its RF front end from saturation. We emphasize the importance of imposing such constraint by explaining how inter-modulation products, due to saturation, can cause high interference at the information receiver in the case of multi-tone signals. The multi-tone optimization problem is formulated as a non-convex linearly constrained quadratic program. Two globally optimal solution approaches using mixed-integer linear programming and finite branch-and-bound techniques are proposed to solve the problem. The achieved improvement resulting from applying both solution methods to the multi-tone optimization problem is highlighted through simulations and comparisons with other solutions existing in the literature.

Sub-Nyquist Spectrum Sensing of Sparse Wideband Signals Using Low-Density Measurement Matrices

The problem of wideband spectrum sensing/sampling in the sub-Nyquist domain is solved in this paper using sparse (low-density) binary-valued measurement matrices. Key objectives are (i) to achieve an efficient compression ratio, and (ii) improve the signal reconstruction performance. We propose a novel RF front-end with parallel branches that we have called Low-Density Wideband Converter (LDWC). We show that the LDWC implements a binary Low-Density Parity Check (LDPC) matrix as the compressive sensing (CS) measurement matrix. We evaluate, using an Information-Theoretic approach, the asymptotic bound on the required number of LDWC parallel branches for sparsity detection. We develop two new belief propagation (BP) algorithms that operate on the Tanner graph of the CS measurements. We have derived the first algorithm by assuming independence among the variable nodes (VNs) of the Tanner graph. For the second method, we have accounted for the joint probability distribution of the VNs. Analytical and simulated performance results prove the concepts of the LDWC and the proposed BP algorithms and quantify the attainment of objectives (i) and (ii) stated above.

An Ultra Low Cost Highly Reliable 18–22 GHz T/R Front-End With Adaptive Sensitivity, Rx Absorptive Calibration, and Fast Switching Time for Phased-Array Radars Applications

This letter proposes a fully integrated K-band front-end architecture for radars targeting extremely low NRE and RE. The RF front-end is composed of an SPDT-less half-duplex low-noise variable gain amplifier (LNVGA) co-designed with a power amplifier (PA) and an Rx coupler for A/ ${\varphi }$ calibration. The design architecture is built to answer to the multirange detection requirement of many phased-array applications and optimize their calibration in an array configuration. The half-duplex receiver has a gain ≥25 dB between 18 and 22 GHz and is integrating a current steering gain control mechanism for changing the Rx IP1dB up to −5 dBm. For this lowest sensitivity, the minimum 6.5-dB noise figure is affected by only 0.3 dB and conserves an AM-to-PM ≤2°. The half-duplex transmitter has a 34-dB small-signal gain and delivers at 20 GHz an output power of +18 dBm with a PAE of 16 % at 4-dB compression. The calibration circuit degrades the Rx noise figure by only 0.1-dB NF while acting as a coupler with 18-dB coupling and 21-dB directivity. The circuit with all its periphery can switch between Tx and Rx in less than 15 ns. Compared to the previous works in similar technology, performances were significantly improved. Despite the very low cost 180-nm CMOS process used, this SPDT-less T/R front-end architecture demonstrates excellent performances for radar applications at K-band frequencies, therefore, presenting a high performance-to-cost ratio. In terms of reliability, this circuit is designed for a life time of more than 106 h under HCI and TTBD degradations at continuous waves.

Ultra-high resolution microwave photonic radar with post-bandwidth synthesis

We demonstrate microwave photonic radar with post-bandwidth synthesis, which can realize target detection with ultra-high range resolution using relatively small-bandwidth radio frequency (RF) frontends. In the proposed radar, two temporal-overlapped linear frequency-modulated (LFM) signals with the same chirp rate and different center frequencies are transmitted. By post-processing the de-chirped echoes in the receiver, a signal equivalent to that de-chirped from an LFM signal with the combined bandwidth is achieved. In a proof-of-concept experiment, two LFM signals with bandwidths of 8.4 GHz are exploited to achieve radar detection with an equivalent bandwidth of 16 GHz, and a range resolution of 1 cm is obtained.

Three-Hop Untrusted Relay Networks With Hardware Imperfections and Channel Estimation Errors for Internet of Things

Cooperative relaying can be introduced as a promising approach for data communication in the Internet of Things (IoT), where the source and the destination may be placed far away. In this paper, by taking a variety of realistic hardware imperfections (HWIs) and channels estimation errors (CEEs) into account, the secrecy performance of a three-hop cooperative network with a source, a destination and two consecutive amplify-and-forward (AF) relays is investigated. The relays are considered to be untrusted, i.e., while they are mandatory helpers for data transmission, they may overhear the received signals. We adopt the artificial noise injection scheme, to keep the source message secret from being captured by the untrusted relays. Given this system model, a novel closed-form expression is obtained in the high signal-to-noise ratio (SNR) regime for the ergodic secrecy rate (ESR) performance over Nakagami-m fading. Our simulation results highlight that the secrecy performance of the system is improved when the tolerable HWIs are distributed beneficially across the transmission and reception radio-frequency (RF) front-ends of each node. Our work reveals that unlike the ideal case, the realistic scenario of non-ideal hardware with CEEs faces with the secrecy rate ceiling. Finally, under a constraint on the total energy consumption which is applicable for battery-limited IoT equipment, we maximize the achievable secrecy rate. Our results highlight the importance of the destination's jamming cooperation and the first relay's role on the secrecy performance.

Improved Real Time GPS RF Data Capturing for GNSS SDR Applications

Global Navigation Satellite System (GNSS) software-defined radio (SDR) is a programmable software receiver, primarily used to receive satellite data and provide user position. It is flexible and cost-effective compared to conventional satellite receivers. In GNSS SDR, recording the live raw data in real-time is a challenging task as large data are sent by the satellites at a very high speed. These data are further processed by the baseband algorithms which provide the user location. The accuracy of the tracked location depends on the precision of the data captured. Among the available hardware receivers, USRP RF front end kit provides flexibility. This paper proposes an efficient approach to capture the real-time GPS data by using the USRP N210 kit. If the receiver is not tuned with the exact parameters, the problems of data overflow and underflow occur. A novel data controlling queue thread method is introduced to overcome this problem. It is evident that the results obtained from our method are very close to those of Ublox GPS.

A Reconfigurable Passive Switched-Capacitor TX RF Front End With −57 dB ACLR2

This letter presents a wireless transmitter (TX) front end in which the functionalities of digital-to-analog conversion, baseband filtering, and signal upconversion are implemented by a passive switched-capacitor (PSC) network. The result is a versatile architecture that fully benefits from CMOS scaling. The front end was integrated in a 65-nm CMOS technology and can support various channel bandwidths simply by adjusting the switching frequency for the PSC network. Thanks to its third-order reconfigurable filter, it maintains a thermal noise floor better than −156 dBc/Hz at a power dissipation of 45 mW. The measured prototype achieves an ACLR2 of −57 dB and an EVM of −31 dB for a 20-MHz 64-QAM OFDM and a 20-MHz 16-QAM signal, respectively.

Cavity-Backed Patch Filtenna for Harmonic Suppression

A co-design consisting of a filtering antenna integrating a cavity-backed patch antenna and a low-pass coaxial filter is proposed for size reduction of the RF front-end. The cavity-backed patch antenna is developed to exhibit a broad impedance bandwidth and a unidirectional radiation pattern. The low-pass coaxial filter is implemented to suppress harmonic resonances and gain in the stop-band of the antenna and is embedded directly inside the antenna cavity to realize a compact small-footprint co-designed filtering antenna structure. Two prototypes of the proposed filtering antennas, which integrate cavity-backed patch antennas with $4^{\textit {th}}$ and $5^{\textit {th}}$ order low-pass coaxial filters and with the overall dimensions of $0.697\lambda _{0} \times 0.585\lambda _{0} \times 0.236\lambda _{0}$ and $0.697\lambda _{0} \times 0.585\lambda _{0} \times 0.320\lambda _{0}$ (where $\lambda _{0}$ is the free space wavelength at 3.15 GHz), respectively, are fabricated and measured. The experimental results show fractional bandwidths of 25% and 23.8% and gain suppression levels exceeding 11 dB and 22 dB in the stop-bands for the filtering antennas with the $4^{\textit {th}}$ and $5^{\textit {th}}$ order filters, respectively. The measured gain is more than 6.5 dBi in the pass-band for both filtering antennas. In addition, excellent agreement is obtained between the simulated and measured results.

第５世代移動通信基地局向けミリ波アンテナ・RFフロントエンド技術

第5 世代移動通信システム(5G) では，多種多様なアプリケーション実現に向けて，通信の大容量化・高速化に対応するために広い周波数帯域を確保可能なミリ波等の高周波数帯の活用が見込まれている．ミリ波帯利用による伝搬損の増大を補償するには，多数の素子アンテナから成るMassive アンテナを用いた高精度なビーム制御が有効である．本稿では，5G におけるミリ波帯向けのMassive アンテナとして，ビーム形成を担うアンテナ・RF フロントエンドの開発事例を概説する．

Performance of Efficient CMOS Power Amplifier for ISM Band Applications

Power amplifiers are one of the most important functional blocks in the Radio Frequency (RF) frontend for reliable wireless communications. The power amplifiers amplify and boost the input signal to needed output power. The signal is amplified to create it sufficiently high for the transmitter to propagate the needed distance to the receiver. Such as power amplifiers are expected to need low-power communication while producing a relatively high output power with more efficiency. The trans-receiver has various blocks such as filters, Voltage Control Oscillator (VCO), Low Noise Amplifier (LNA) and power amplifier. Among these, the most power hungry device is a power amplifier. The efficiency of the power amplifier can be 100%, but practically it is just 55%. So, the scope of improvement in efficiency in a power amplifier will be an interesting and most challenging task. As well defined architecture, including linear functional block synthesis, which is complex in designing CMOS power amplifier for different applications. This article describes the different state-of-the-art design biasing class and advanced RF CMOS power amplifier for Industrial, Scientific, and Medical (ISM) band applications.

Implementation of Stepped Frequency Modulation Pulse Compression on NI Suite

In Radars and Sonar, the pulse compression technique is used continuously to increase the range resolution, range detection and the signal-to noise ratio (SNR). This can be achieved by modulating the transmitted pulse and then correlating it to the received pulse with the transmitted signal. This transforms short pulse into long pulse and is used to increase long pulse bandwidth by some form of modulation such as linear frequency modulation (LFM), so that Range Resolution is not compromised. The proposed Stepped Frequency Modulation (SFM) is a common Pulse Compression Method, which is useful to increase the Radar Range Resolution without losing the capability of target detection. Step Frequency Continuous Wave (SFCW) is also one of the techniques used in the Pulse Compression Technique, where the return echo step is used to determine range and is used for different purposes. This type of setup is widely used in RADAR design and testing. This Paper proposes the implementation of various Modulation techniques such as LFM, SFM and SFCW for proposed Stepped frequency Modulation using NI suite hardware PXI system which has a configurable FPGA and RF front end to generate custom waveform in wide range of frequencies with bandwidth up to 1GHz design and testing.