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With the aim of enhancing the performance of Automatic Modulation Classification (AMC), modern researchers tend to adopt architectures based on Recurrent Neural Networks (RNNs) to better extract temporal features from signals. However, the widely adopted vanilla RNN structures incur high parameter and compute overheads, making them challenging to deploy in resource-limited scenarios. In this letter, a plug-and-play architecture based on Gated Recurrent Unit (GRU) is proposed, named Lightweight Grouped Gated Recurrent Unit (LGGRU), which proves highly effective for AMC. We first analyze the detrimental impact of the reset gate in vanilla GRU on feature extraction for modulation signals and suggest its removal. Additionally, a grouped update algorithm for hidden state is innovatively proposed to further reduce redundant parameters. Furthermore, LeakyReLU is employed instead of the hyperbolic tangent (tanh) activation function, making it more adaptable to resource-limited devices. Experimental results confirm the improvement in AMC accuracy with the proposed method, along with a significant reduction in parameter and compute overheads.

Wireless transmitters are affected by the reflection caused by an impedance mismatch between the power amplifier’s (PA) output and the antenna’s input. Isolators can lessen the output mismatch of the PA, but they add the bulk to the transmitter. A reflection-aware augmented PA modeling and Digital Predistortion (DPD) technique are proposed to reduce the influence of the dynamic varying reflection due to the output-load mismatch and the PA’s nonlinearities. This Augmented model includes a term that characterizes the mismatched effect. The proposed DPD with a single set of coefficients is robust and can mitigate the dynamic varying output-load mismatch with the PA nonlinearity.

This article presents a modified transmit/receive (T/R) front-end module (FEM) architecture with improved transmitter (TX) efficiency. Single-pole double-throw (SPDT) switch is commonly adopted in conventional FEM for T/R isolation, but its insertion loss (IL) deteriorates TX efficiency greatly. To alleviate this problem, a post-matching (PM) architecture is proposed to eliminate the switch in the TX branch. Specifically, a PM network (PMN) is employed to transform 50- $\Omega $ impedance at the antenna port into the intrinsic optimal load impedance of the power amplifier (PA), while the output capacitance of the PA is absorbed into a $\lambda $ /4-transmission-line (TL)-based single-pole single-throw (SPST) switch in the receiver (RX) branch. The drain voltage of the PA can also be supplied via the SPST, avoiding the use of an additional choke inductor. The theoretical performance of the T/R switch, including bandwidth, IL, and isolation, is analyzed in depth. A 4.9–7.1-GHz FEM for Wi-Fi 7 application is implemented in a commercial 0.15- $\mu \text{m}$ gallium nitride (GaN)-high-electron-mobility transistor (HEMT) process to validate the proposed architecture, and the chip size is only 2 $\times $ 1.6 mm. The TX mode realizes a saturated power of 37.1–38.6 dBm and a saturated power-added efficiency (PAE) of 45%–52.4%. With MCS9 EHT160 signals, an average PAE of 18.5%–23.3% at an average power of 28–29.9 dBm is measured, while the error vector magnitude (EVM) specification of – 32 dB is met. When digital predistortion (DPD) is applied, MCS13 EHT320 signals are also supported. The RX mode achieves a gain of 9.1–12.1 dB, a noise figure (NF) of 1.6–1.9 dB, and an input-referred third-order intercept point (IIP3) of 20.2–25.4 dBm.

In this investigation, water-soluble N-Acetyl Cysteine Capped-Cadmium Telluride QDs (NAC/CdTe nanocrystals), utilizing N-acetyl cysteine as a stabilizer, were prepared to assess their potential in differentiating between DNA extracted from pathogenic bacteria (e.g. Escherichia coliisolated from urine specimen) and intact DNA (extracted from blood of healthy individuals) for biomedical sensing prospective. Following the optical characterization of the synthesized QDs, the XRD analysis illustrated the construction of NAC-CdTe-QDs with a grain size of 7.1 nm. The prepared NAC-CdTe-QDs exhibited higher PL emission features at of 550 nm and UV-Vis absorption peak at 300 nm. Additionally, the energy gap quantified via PL and UV–Vis were 2.2 eV and 2.3 eV, respectively. The interconnection between the synthesized QDs and the different types of the extracted genomic DNA (both Escherichia coliand healthy subjects) was analyzed optically. This is resulted in a clear shift in the maximum fluorescence emission intensities (observed at 533 nm for an Escherichia coliDNA and 541 for healthy DNA). Overall, the present study findings suggest that prepared QDs could be employed as probes for the detection of pathogenic bacteria DNA from that of healthy subjects.

This article presents a 24–40-GHz broadband beamforming transmit-receive (T/R) front-end (FE) chip for the next-generation millimeter-wave (mm-wave) communication systems. To achieve multiband coverage in a single beamforming front-end IC, the proposed beamforming chip adopts a unified gain and phase control scheme as well as an asymmetric T/R switch circuit, which simplifies the system design and enables broadband operation in both directions. The vector-modulation-based unified phase and gain control (UPGC) scheme eliminates the standalone variable gain amplifier (VGA) in the front end. The bidirectional impedance transformation T/R switch reduces the insertion loss in the TX path and enables Class-F1 operation to improve the bandwidth and efficiency. Based on the proposed UPGC scheme and T/R switch circuit, a high-performance mm-wave front-end chip is implemented using a 0.13- $\mu $ m SiGe BiCMOS technology. The fabricated front-end chip achieves 12.9–16.9-dBm maximum output power in TX mode, up to 14.3-dB gain and 7.4–9.2-dB noise figure (NF) in RX mode over the frequency range of 24–40 GHz. In both TX and RX modes, the proposed chip achieved less than 0.4-dB rms gain error and 2.0° rms phase error. A four-element dual-band phased array module is designed and tested to evaluate the performance of the proposed chip in the 28- and 38-GHz dual-band phased array.

Based on the linear responses and nonlinear (NL) loss effects of ferrite, a filtering–limiting (FT) integrated device applicable to the high-power microwave (HPM) electromagnetic environment is proposed. The small-signal bandpass filtering characteristics of the FT device with polycrystalline yttrium iron garnet (YIG) as a substrate are achieved using the conventional parallel-coupled microstrip structure. When HPM pulses within the operating frequency band are injected, the NL loss effects are excited in this device, achieving power-limiting characteristics. However, the spatial distribution of the RF magnetic fields in such a device is extremely inhomogeneous. There is currently no commercially available simulation tool that can effectively calculate the power loss performance of ferrite materials in the HPM electromagnetic environment. Therefore, combined with the transient-state NL threshold theory, an equivalent iterative simulation method for structure partition is proposed. This method is utilized to quantitatively evaluate the power loss of such resonant structures. The simulated results align well with the measured trends and can successfully indicate the limiting threshold, limiting isolation, and dynamic range of the FT device under HPM conditions.

This article presents an ultra-broadband distributed efficient power amplifier (DEPA) with reactance compensation and adaptive biasing. It is illustrated that the bandwidth of the DEPA can be improved apparently by applying a shunt short-circuited stub at the combining point. The principle of such method is that the back-off impedance variation with frequency can be compensated by the reactance of the shunt stub. Besides, to get over the high gain compression of the conventional DEPA, an adaptive biasing scheme is proposed for the auxiliary PAs. A DEPA is implemented in a 0.25- $\mu \text{m}$ GaN-HEMT process for validation. The shunt stub is realized by a LC tank equivalently for a compact size. The fabricated DEPA achieves a saturated output power of 41.5–43 dBm and an 8-dB back-off drain efficiency (DE) of 38%–46.8% from 1.8 to 5.4 GHz with a chip size of $3.2\times3.2$ mm2. The fractional bandwidth (FBW) is up to 100%. Applying a 100-MHz LTE signal with an 8.5-dB peak-to-average power ratio (PAPR), an average DE of 35%–43% is measured over the entire bandwidth, and adjacent channel power ratio (ACPR) is better than −47 dBc after applying digital predistortion. To the best of our knowledge, the proposed DEPA demonstrates the largest FBW among all reported integrated back-off efficient PAs without using digital techniques or reconfiguration.

With the advent of the fifth generation (5G) New Radio (NR), the Non-Terrestrial Network (NTN) stands out as a solution to enable wider coverage of broadcast satellites. NTN systems require higher data rates and bandwidth. Digital predistortion (DPD) is commonly adopted as an effective method to enhance the power efficiency of broadcast satellites’ NTN systems. With the continuous increase of signal bandwidth, the bandwidth of the feedback loop and the sampling rate of analog-to-digital converters (ADCs) need to be reduced so as to reduce the system cost. The computational complexity and overfitting effect of the existing band-limited DPD (BLDPD) method will raise as the decrease of feedback bandwidth. To address this issue, one deep neural network (DNN) assisted band-limited polynomial digital predistortion (DNN-BLP DPD) is proposed in this paper. This method reduces the computational complexity and the overfitting effect of the band-limited basis functions by grouping a small number of band-limited basis functions for online parameter identification while embedding the DNN in the parameter identification module. Compared with the conventional BLDPD, the experimental results show that the proposed method can achieve a low sampling rate and low computational complexity while ensuring modeling accuracy.

The purpose of this article is to solve the issue that current high-power microwave (HPM) transmission links are used in the rigid metal waveguide, which causes significant installation difficulties to the system integration. In this article, we design the TM01 and TE01 high-power handling corrugated flexible waveguides using a numerical analysis method based on coupled wave theory. The measured results are in good agreement with the numerical calculation method. The designed TM01 corrugated flexible waveguide has a transmission efficiency of up to 98% at bending angles less than ±5°, and correspondingly, the TE01 corrugated flexible waveguide has a transmission efficiency of up to 98% at bending angles less than ±8°. The designed flexible waveguides are all capable of power capacities of more than 3 GW.

An investigation on the phase locking of S-band relativistic magnetrons with an all-cavity-extraction (ACE-RM) structure is carried out. In order not to disrupt the periodic distribution of electric fields in the resonant cavities, an azimuth-uniform coupling structure is introduced, which could achieve a transmission efficiency of over 98% at the operating frequency, with an amplitude difference of only ±3.3%. Furthermore, particle-in-cell (PIC) simulations demonstrate that when five ACE RMs are interconnected through four such coupling structures, phase locking can be achieved, and the relative phase jitters are controlled within ±1%. After establishing stable $\pi $ -mode oscillation in RMs, in each of the 20 ports, an average output power of over 400 MW can be obtained, corresponding to a total power of 8.5 GW and a power conversion efficiency of 45%.

An efficient coaxial superradiant relativistic backward wave oscillator (SR-RBWO) operating at a low magnetic field is proposed and studied. In such SR-RBWO, a coaxial slow wave structure (SWS) is used in the interaction region, the coaxial structure can realize the stable transmission of the intense relativistic electron beam (IREB) in a long interaction region by using the relatively low guiding magnetic field. The existence of an inner conductor can reduce the radial electric field near the cathode emission region, which can reduce radial expansion and improve the quality of IREB. According to the dispersion relations in the coaxial SWS region, when the radiation frequency remains unchanged, the power capacity can be improved by changing the radius of the inner conductor. The particle-in-cell (PIC) simulation results reveal that when this oscillator is applied with a low guiding magnetic field of 0.32 T and diode voltage of 268 kV, the SR pulse with an average power of 1.62 GW corresponding to power conversion efficiency of 140% can be obtained, and output a relatively pure TEM mode at a center frequency of 8.6 GHz.

In this article, the theory and design of high-efficiency broadband continuous class-B/J power amplifiers (PAs) with active second harmonic injection technique have been presented. By injecting the second harmonic component generated by the auxiliary PA, the optimal phase shift parameter $\alpha $ between the drain voltage and current can be selected properly, leading to an efficiency and power improvement of the conventional class-B/J PA. Detailed design guidelines and step-by-step procedure are also suggested. To verify the feasibility of the proposed circuit, a wideband PA operated from 1.1 to 1.7 GHz (fractional bandwidth of 42.9%) has been designed and fabricated. Experimental results show an output power of 40.9–42.6 dBm, drain efficiency of 70.0%–80.9%, and average efficiency (AE) of 74.4%. To the best of our knowledge, this is the highest AE of class-B/J PAs over such bandwidth.

An ${X}$ -band superradiant relativistic backward-wave oscillator (RBWO) operating at a low magnetic field with power conversion efficiency exceeding unity is proposed. The device efficiency is improved from two aspects: beam transmission stability focused by a low guiding magnetic field and microwave transmission efficiency. First, a gradually decaying axial magnetic field is applied. It could not only suppress the initial radial oscillation amplitude of the electron beam envelope but also transform the high transverse momentum of electrons into the axial momentum, which is beneficial to the beam–wave interaction. Second, a novel structure with a front extractor is introduced. The backward wave is extracted into a coaxial channel outside the slow wave structure (SWS) and transmitted in TEM mode to avoid the power loss of the reflected microwave in the SWS caused by the dispersion effects. Particle-in-cell (PIC) simulation results reveal that when the intense relativistic electron beam (IREB) propagating in a 36-period superradiance-RBWO (SR-RBWO) is confined with a magnetic induction intensity that decreases from 0.81 T in cathode region to 0.43 T in interaction region, the output power of 1.04 GW corresponding to conversion factor ${K}$ = 1.55 can be obtained. The merits of low-magnetic-field operation and high efficiency make this tube a promising device used for the miniaturization of high-power SR systems.

In this brief, a highly-efficient Doherty power amplifier (DPA) architecture with generalized parallel-circuit class-EF mode is proposed. With this topology, the ideal harmonic impedance conditions at the deep power back-off (PBO) region and saturation region can remain the same. Based on it, by adding a single harmonic control network (HCN) and an offset line, the carrier PA can be operated at the ideal high-efficiency conditions within the above two regions. In this case, the overall efficiency of the DPA can be improved simultaneously. As an example, a high-efficiency DPA working at 2.6 GHz is designed and fabricated based on a Wolfspeed CGH40010F GaN HEMT transistor. The measured results of the proposed structure demonstrated that a drain efficiency (DE) of 76.7% with the peak outpower of 45.2 dBm, as well as DE of 74.8% at the 6dB power back off region.

In this article, we propose a new robust and highly efficient digital predistortion (DPD) concept for the linearization of wideband RF power amplifiers (PAs). The proposed approach is based on the combination of a parallelized delta-sigma modulator (DSM) and a forward model of the PA. This concept applies multi-rate techniques on a DSM that incorporates the forward PA model in its feedback loop to perform the required signal predistortion. Such a technique eliminates the need of reverse modeling and its associated problems. The multi-rate approach relaxes enormously the clock speed requirement of the DPD, which allows handling high signal bandwidths at feasible sampling rates. Moreover, enhanced performance can be achieved without the need of increasing the order of the modulator which reduces the sensitivity of the system to gain variations and phase distortions caused by the nonlinear PA characteristics. Three time-interleaved parallel DPD (P-DPD) variants are described and introduced, all of them have been shown to offer increased accuracy, and consequently better linearization performance compared to the DSM-based DPD state-of-the-art. The proposed architectures are tested and assessed using extensive real-world RF measurements at the 3.6 GHz band utilizing wideband 100 MHz 5G New Radio (NR) transmit waveforms, evidencing excellent transmit signal quality.

In this brief, a novel impedance matching network (IMN) for designing high-efficiency power amplifiers (PAs) is presented. With this method, the fundamental matching network (FMN) and the harmonic control network (HCN) are incorporated into a single network, which is composed of a $\boldsymbol{\lambda }$ /8 ( $\boldsymbol{\lambda }$ is wavelength) transmission-line (TL) and a $\boldsymbol{\lambda }$ /4 TL. Based on it, the design procedure is more straightforward. Besides, the forbidden regions and feasible regions of the proposed network at the first three harmonics are also analyzed. The results show that the forbidden regions are very small. Finally, as an example, a harmonic tuned (HT) PA is designed and implemented using a GaN HEMT transistor. The measured results demonstrated that the fabricated HT PA working at 3.0 GHz delivers a power-added efficiency (PAE) of 79.2%, a gain of 11.6 dB and an output power ( ${\text{P}}_{out}$ ) of 41.0 dBm.

The parallel-pumped spin-wave instability (SWI) threshold power, $P_{\mathrm {th}}$ , of polycrystalline yttrium iron garnet (YIG) excited by microwave pulses with the varied rising-edge time was investigated theoretically and experimentally. The SWI threshold model associated with the rising-edge time $t_{r}$ is developed in terms of the attributes of half-frequency spin waves in the applied static fields $H_{\mathrm {ext}}$ . The results manifest a significant increase in microwave-excited SWI threshold power level when the rising-edge time $t_{r}$ is shortened from 600 to 100 ns at the X-band. In addition, the rising-edge microwave pulses with different time scale distinctly present different threshold responses under the left-wing field region of the butterfly curves. The SWI thresholds associated with the spin-wave initial amplitude grow with increasing $H_{\mathrm {ext}}$ when $t_{r}$ is smaller than the spin-wave relaxation time ( $t_{r}~ \boldsymbol {\le }~200$ ns), while SWI thresholds are more sensitive to the $k$ -dependent spin-wave linewidth, which decreases with the increasing $H_{\mathrm {ext}}$ as $t_{r}$ exceeds the spin-wave relaxation time ( $t_{r} ~ \boldsymbol {\ge }~400$ ns). The calculated responses of the SWI threshold are in close agreement with the measurements.

The dynamic radio resource management technology is an essential technology in high throughput satellite (HTS) communications. Aiming at the problem that the traditional static radio resource allocation is difficult to meet the dynamic traffic, the dynamic radio resource allocation based on the meta-heuristic algorithm has been extensively studied. Since wireless channel conditions, differentiated services have stochastic properties, and the environment's dynamics are unknown in HTS, the dynamic radio resource allocation based on model-free deep reinforcement learning (DRL) method was used to learn the optimal policy through interactions with the situation. However, the generalization ability of the existing DRL cannot fully meet the great dynamic change in HTS. To address this issue, we explore an advanced heuristic learning approach that combines DRL with one heuristic algorithm. In the proposed approach, we apply the DRL to accelerate the convergence of the heuristic algorithm and verify the proposed method in the dynamic power allocation (DPA) in HTS. Compared with the traditional methods, the simulation results show that the proposed approach can accelerate the convergence of the heuristic method for the allocation of power in HTS and has a low time complexity of the decision. Compared with the traditional methods, our proposed method can reduce the computational overhead by 6.2–94.8%.

High frequency (HF) transmitter implemented with the multioctave broadband power amplifier (PA) is always faced with the problem of harmonics because of the nonlinearity of the PA. With the previous harmonic cancellation digital predistortion (HC-DPD) scheme, harmonics and the fundamental components, as a whole, are modeled with a uniform memory polynomial (MP) model. Although the harmonics can be well canceled, unwanted spurs can be generated when the nonlinearity order of the MP model exceeds the critical point because of the limited sampling rate. In this letter, a spur-free HC-DPD (SF-HC-DPD) scheme is proposed to suppress the spurs. Without increasing the sampling rate, a novel anti-aliasing MP (AA-MP) model is proposed. With the energy-saving linearization technique, the signal quality and robustness of HF communication can be greatly improved. Measurement results show that the harmonic-to-fundamental power ratio, the adjacent channel power ratio (ACPR), and the error vector magnitude (EVM) performances were all improved by nearly 20 dB. In addition, the unwanted spurs can be suppressed for being below −80 dBc, which is more than 26 dB better than the HC-DPD scheme with the MP model.

Simulations and experiments of an ${S}$ -band TEM-output relativistic magnetron (RM) driven by split cathode (SC) are proposed. In the previous researches on SC, as a result of the space-charge-screening effect of squeeze-state electrons accumulated nearby the emission surface, the diode current is limited, which finally results in low output power. To improve the output performance, a bidirectional emission SC (BSC) is introduced. Experimental results on EPA-90 high-voltage electron beam accelerator demonstrate that when the voltage is around 480 kV and the axial magnetic field is 0.49 T, comparing with a conventional unidirectional emission SC, the output power can be enhanced from 124 to 400 MW by adding an extra downstream emitter. This work lays a foundation for further researches to make the SC-fed RM more practical.

A compact relativistic magnetron with diffraction output (MDO) of TEM mode has been investigated experimentally by using the EPA-90 high-voltage electron accelerator. The purpose is to verify the diffraction output in low-order mode predicted by numerical simulations. The diagnostic results have indicated that the MDO with all cavity extraction realizes the TEM mode output. When the diode voltage is 480 kV and the axial magnetic field is 0.49 T, the MDO could generate a microwave at a frequency of 2.42 GHz, corresponding to 950-MW output power and 25.8% conversion efficiency. This work paths a way for MDO to realize the radiation with low-order mode.

In modern wireless compact transmitters, Power Amplifier (PA) behavior is considerably affected by the impedance mismatch between the PA’s output and the antenna’s input. This PA’s output mismatch results in a reflection at the PA–antenna interface. In this brief, reflection-aware PA modeling and digital predistortion (DPD) techniques are proposed to mitigate the negative impact of this mismatch on the forward and reverse models of the PA. An Augmented Convolutional neural network model $(\boldsymbol{\Gamma }$ ACNN) is proposed to linearize a Doherty PA under different values of the output mismatch using a single set of coefficients. The developed DPD shows robust performance metrics like normalized mean square error (NMSE), and adjacent channel power ratio (ACPR) under diverse complex output mismatch levels.

Power amplifier (PA) models, such as the neural network (NN) models and the multilayer NN models, have problems with high complexity. In this article, we first propose a novel behavior model for wideband PAs, using a real-valued time-delay convolutional NN (RVTDCNN). The input data of the model is sorted and arranged as a graph composed of the in-phase and quadrature ( $I/Q$ ) components and envelope-dependent terms of current and past signals. Then, we created a predesigned filter using the convolutional layer to extract the basis functions required for the PA forward or reverse modeling. Finally, the generated rich basis functions are input into a simple, fully connected layer to build the model. Due to the weight sharing characteristics of the convolutional model’s structure, the strong memory effect does not lead to a significant increase in the complexity of the model. Meanwhile, the extraction effect of the predesigned filter also reduces the training complexity of the model. The experimental results show that the performance of the RVTDCNN model is almost the same as the NN models and the multilayer NN models. Meanwhile, compared with the abovementioned models, the coefficient number and computational complexity of the RVTDCNN model are significantly reduced. This advantage is noticeable when the memory effects of the PA are increased by using wider signal bandwidths.

High peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems is one of the major drawbacks in wireless transmitters. In this letter, a novel low complexity PAPR reduction method based on the real-valued neural network (NN) is proposed. This method first builds the PAPR reduction module using the real-valued NN to achieve the reduction of PAPR. To reconstruct the transmission signal, the PAPR decompression module is introduced into the receiving end to recover the signal in order to minimize the bit error rate (BER) of the systems. The PAPR reduction module and the PAPR decompression module can be jointly trained offline, therefore, the reduction of PAPR and the minimization of BER can be achieved simultaneously. To reduce the process rate of the PAPR reduction, the trained model uses multiple parallel processing links to achieve the reduction of the PAPR. The extensive simulations indicate that the proposed method outperforms previously available methods in terms of PAPR and BER, while having low complexity.

The objective of this paper is to design dedicated probing signals for localization based on orthogonal multicarriers that attain the lowest value of the possible fundamental limits. The proposed scheme named Quasi-Optimal Subcarrier Selection (QOSS) attempts to generate the probing signals in positioning systems by minimizing the Cram$\acute{\textrm {e}}$r–Rao lower bound of range estimation in nonoverlapping multipath channels instead, which do indirectly depress the performance bounds in overlapping multipath channels to a certain extent. Based on the optimization of power allocation on orthogonal subcarriers, two kinds of QOSS signals are proposed for: 1) basestation (BS)-based localization networks where mobile station (MS) transmits to all BSs, and 2) MS-based localization networks where multiple BSs simultaneously transmit to the MS. Two adaptive search algorithms have been presented to generate the QOSS signal for MS-based localization networks. The fundamental limits of both QOSS signals are theoretically derived, the close relationship between the bound of range estimation and that of localization is disclosed and the lower bound of position dilution of precision is further obtained. Numerical results and experiments demonstrate our proposed theory.

A digital predistorter, modeled by an augmented real-valued time-delay neural network (ARVTDNN), has been proposed and found suitable to mitigate the nonlinear distortions of the power amplifier (PA) along with modulator imperfections for a wideband direct-conversion transmitter. The input signal of the proposed ARVTDNN consists of Cartesian in-phase and quadrature phase ( $I/Q$ ) components, as well as envelope-dependent terms. Theoretical analysis shows that the proposed model is able to produce a richer basis function containing both the desired odd- and even-order terms, resulting in improved modeling capability and distortion mitigation. Its actual performance has been validated through extensive simulations and experiments. The results show that the compensation and hardware impairment mitigation capabilities of the ARVTDNN are superior to the existing state-of-the-art real-valued focused time-delay neural network (RVFTDNN) by 3–4 dB for the adjacent channel power ratio and by 2–3 dB in terms of the normalized mean square error. Other important features of the proposed model are its reduced complexity, in terms of the number of parameters and floating-point operations, and its improved numerical stability compared to the RVFTDNN model.

This paper presents a technique for suppressing the intermodulation distortion caused by nonlinear multi-band power amplifiers with minimal modeling complexity. The technique is based on generating a narrowband static predistorter for the power amplifier. Then, the intended multi-band signals are resampled and shifted into their representative carrier frequencies before applying the static predistorter in order to accommodate the intermodulation distortion products produced by the nonlinearity. Since the resampling frequency may be high, a study is presented, using filtering techniques to represent low-bandwidth transmitter schemes, to show the accuracy of the intermodulation distortion suppression. Results are presented for the proposed predistorter for two amplifiers: one in a tri-band carrier aggregated LTE scenario in the sub 3 GHz frequencies and another in the millimeter-wave band, demonstrating the effectiveness of reducing the intermodulation products using 5G signals.

This paper investigates the green characteristic of the non-data-bearing orthogonal frequency-division multiplexing (NDB OFDM) transmission in wireless localization, relative to being widely used non-pulse-shaping pseudorandom noise (NPS PN) transmission in current satellite- and ground-based positioning systems. For obtaining a fixed ranging accuracy, the required NDB OFDM transmit energy is proven in this paper to be equal to 30% of the required NPS PN transmit energy, spending less nonrenewable resource, emitting smaller ${\rm CO}_{2} $ and indicating a “green” activity. Furthermore, the localization performance and the optimal network topology for obtaining the best accuracy are mathematically derived. By assuming a positioning system with the proposed optimal network topology, the positioning accuracy is derived, and the total energy saving is reported when using NDB OFDM transmission instead of NPS PN transmission. Numerical results and experimental measurements both show a consistency with our proposed theory.

Although children with acute lymphoblastic leukemia (ALL) generally have a good outcome, some patients do relapse and survival following relapse is poor. Altered DNA methylation is highly prevalent in ALL and raises the possibility that DNA methylation-based biomarkers could predict patient outcome. In this study, genome-wide methylation analysis, using the Illumina Infinium HumanMethylation450 BeadChip platform, was carried out on 52 diagnostic patient samples from 4 genetic subtypes [ETV6-RUNX1, high hyperdiploidy (HeH), TCF3-PBX1and dic(9;20)(p11–13;q11)] in a 1:1 case-control design with patients who went on to relapse (as cases) and patients achieving long-term remission (as controls). Pyrosequencing assays for selected loci were used to confirm the array-generated data. Non-negative matrix factorization consensus clustering readily clustered samples according to genetic subgroups and gene enrichment pathway analysis suggested that this is in part driven by epigenetic disruption of subtype specific signaling pathways. Multiple bioinformatics approaches (including bump hunting and individual locus analysis) were used to identify CpG sites or regions associated with outcome. However, no associations with relapse were identified. Our data revealed that ETV6-RUNX1and dic(9;20) subtypes were mostly associated with hypermethylation; conversely, TCF3-PBX1and HeH were associated with hypomethylation. We observed significant enrichment of the neuroactive ligand-receptor interaction pathway in TCF3-PBX1as well as an enrichment of genes involved in immunity and infection pathways in ETV6-RUNX1subtype. Taken together, our results suggest that altered DNA methylation may have differential impacts in distinct ALL genetic subtypes.

The 15 papers in this special issue have been grouped into four main categories: 1) radio-frequency circuits for CR/SDR (five papers); 2) digital and mixed-mode subsystems for CR/SDR (two papers); 3) receivers and transmitters for CR/SDR (five papers); and 4) signal-processing and communications techniques for CR/SDR (three papers).

AbstractOil obtained from oil sands resources constitute an important portion of the oil industry in Canada. Extraction of the bitumen from oil sands is very crucial process because of its cost and environmental impact. Microwave energy applicators by heating oil sands at microwave frequencies can be an excellent alternative to extract bitumen with the advantages of being potentially cost-effective and environmentally friendly method of extraction. In order to design and manufacture a microwave energy applicator, its dielectric properties must be known. In this study, as the first part of our ultimate microwave energy applicator project, in advance, the complex permittivity of oil sands was measured by using rectangular cavity resonator, designed and fabricated in École Polytechnique de Montréal laboratories, at 2.45 GHz with TE1011mode. The accuracy of the permittivity measurement results obtained with the developed system was verified against those obtained using a commercial open-ended probe system as well the values of well known materials documented in open literature. Since there is no study found in the literature about the complex permittivity values of oil sands at 2.45 GHz, the present study would be of great help and important guide for those who plan to design and manufacture microwave energy applicators in order to extract the bitumen from the oil sands.

This paper reports an extensive experimental investigation of the effects of second harmonic loading on the performance of microwave GaAs MESFET oscillators and strongly driven amplifiers. The measurement system used is an active load system based on six-port techniques. Harmonic load pull measurements were obtained for the NE72084 MESFET; the measurements show how the second harmonic load can influence the power gain and the power added efficiency in strongly driven amplifiers. The device line characterization technique was combined with the harmonic load pull technique; the measurement results illustrate how the output power and the DC to RF conversion efficiency of an oscillator depend on the choice of the second harmonic load. Amplifier and oscillator circuits have been designed using these measurements; the circuits have been constructed and measured. The results validate the experimental approach used and clearly illustrate the importance of properly selecting the second harmonic load in amplifier and oscillator circuits. Significant improvements in gain, output power and efficiency have been achieved by properly selecting the second harmonic load.

The simultaneous measurements of the third-order intermodulation and output power under two-tone excitation have been implemented on a MESFET operated in large-signal mode for load impedances spanning quasi-entirely the Smith chart, using a six-port reflectometer with variable test port impedance. An experimental comparison between single-tone and two-tone output power and power-added efficiency was performed. The experimental results show that the load-pull of the output power capability and power-added efficiency by a twotone test are more accurate than the single-tone characterization for multi-carrier Solid State Power Amplifiers (SSPA’s) design.

Genital bovine papillomavirus infection was observed for the first time in the Al-Ahsa region of Saudi Arabia. The disease involved 1 female and 2 male 2–4-year-old crossbred cattle. Fibropapillomas (warts) were limited to the prepuce and vulva. Electron micrographs of thin sections of the lesions revealed the presence of intranuclear viruslike particles. Using a broadly cross-reactive rabbit polyclonal antiserum directed against papillomavirus group-specific antigens, the infection was confirmed by immunohistochemical staining of paraffin-embedded tissues to be due to a papillomavirus. Staining with a series of monoclonal antibodies of various specificities indicated that the virus was bovine papillomavirus type 1. Attempts to propagate the virus by inoculation of tumor homogenates onto chorioallantoic membranes of chicken embryos were unsuccessful.

In the coexisted world of 3G, 4G, 5G and many other specialized wireless communication systems, billions of connections could be existing for various information transmission types. Unluckily, data show that the increase of network capacity is heavily more than the increase of the network energy efficiency in recent years, which could lead to more energy consumption per transmitted bit in the future network. As basic units in mobile communication systems, microwave/RF components and modules play key roles in energy-efficiency of the wideband/broadband wireless communication systems due to the high peak-to-average power ratio (PAPR) in the modulated signals. This leads to high frequency- spectrum efficiency but low energy-efficiency. With further increasing both PAPR and bandwidth in 4G and 5G systems, the challenge of energy-efficiency originating from microwave components will dramatically increase. That is why the guest editors organized this Special Topic Issue.