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This paper investigates the energy-efficient power allocation strategy for multi-user mmWave non-orthogonal multiple access (NOMA) system with different hybrid precoding (HP) structures. Particularly, we consider the fully-access HP structure and the subarray HP structure, respectively. For these two structures, the finite resolution analog precoder is realized through a low-power switches and inverters (SI) network. In the NOMA system, multiple users are first paired according to their channel correlation and gain difference. Following this, we propose hybrid precoding schemes for the low-power SI-based HP structures. Then, a power allocation (PA) problem is formulated to maximize the energy efficiency of the system, subject to per-cluster power constraints and per-user quality of service constraints. To solve the non-convex PA optimization problem, we devise a suboptimal solution with two-stage PA strategies. Furthermore, the PA problem aiming at conditionally maximizing the spectrum efficiency is also analyzed. Simulation results show that the proposed mmWave-NOMA can achieve higher energy efficiency than the existing mmWave-NOMA scheme and the conventional mmWave orthogonal multiple access scheme.

Antenna-in-package (AiP) technology has been a main design scheme of millimeter-wave (mmWave) phased array antennas for 5G communications. The beamforming pattern of mmWave phased array AiP is steered by controlling the amplitude and phase excitations of AiP elements. It would be helpful to evaluate the control accuracy of complex excitations and to reliably calibrate mmWave AiP. However, these tasks are not trivial and time consuming in practice, especially when the number of AiP elements is large. To address this problem, this article presents an efficient and automated mmWave phased array experimental platform. To reduce measurement time, a control software is developed to automatically control the AiP and measurement instruments simultaneously. This experimental platform has flexible gain and phase control of AiP element excitations, and customized measurements in an automated and efficient way can be realized. The effectiveness of the experimental platform is demonstrated by several measurement campaigns, where control accuracy, array calibration, and beam steering for mmWave phased array AiP are extensively investigated.

A sectored multiprobe anechoic chamber is seen as a promising method to carry out the radiated testing of massive multiple-input–multiple-output (MIMO) base station (BS), and realistic channel environment reconstruction is crucial for the performance assessment of wireless devices, especially for the testing of beamforming procedures, such as beam acquisition, tracking, and so on. This letter proposes a novel probe selection algorithm and corresponding device rotation scheme to enable more accurate channel emulation with specific probe antennas. On the other hand, within the acceptable threshold of error, the number of required probe antennas can be reduced, which will mitigate setup complexity and the number of hardware resources. In the simulation, to verify the robustness of the proposed probe configuration, several metrics are examined with different numbers of selected probes, in terms of spatial correlation and power angular spectrum emulation. The simulation results show that the proposed selection and rotation algorithms perform well in synthesizing the accurate target propagation environment on the BS side.

In this study, a series of rat-race couplers with bandpass filtering responses and impedance transforming characteristics are presented based on novel coupled-line structures. Firstly, a novel filtering rat-race coupler core circuit is proposed by introducing coupled-line structures into conventional rat-race coupler. Then, a series of rat-race couplers with enhanced filtering responses and stopband rejections are constructed by employing various types of impedance transformers. The even- and odd-mode methods are adopted to explain the operating mechanisms. Finally, a filtering rat-race coupler prototype with a fractional bandwidth of 35.2% is designed and measured. The measured results show high passband selectivity, good out-of-band rejection and isolation performances, which is attractive for practical application.

The conventional broadband impedance matching network in low-pass structure cannot present adequate broadband impedance rotation for the optimum broadband operation of the power amplifier (PA), resulting in performance variations and degradations. The underlying constraint is the phenomenon of opposite impedance rotation. Against such a backdrop, this paper presents a methodology using the band-pass topology to compensate the frequency-variable response of the PA. The CGH40010F from Cree is used to verify the effectiveness of this compensation method. The experimental results are in good agreement with the simulation. The proposed PA yields good gain flatness (±0.5 dB), input/output return loss (>13 dB), and high power added efficiency (>60 %) over the band from 1.7 to 2.7 GHz. After digital predistortion, the measured adjacent channel power ratio is about -55 and -50 dBc at ±5 and ±10 MHz offset when the PA is driven by 5- and 10-MHz WCDMA signals at 6.5 ~ 7 dB power back-off.

This paper presents a novel wide-band filtering three-port coupler with inherent DC-blocking function, which is simply comprised of a power divider with wideband filtering function and a broadband phase shifter with a modified coupled line. For demonstration, a designed prototype operating at 3 GHz is simulated, fabricated, and measured. From the simulated and measured results, the coupler shows a 49% filtering bandwidth with 12-dB return loss and 90° ± 590°phase shifting. The amplitude imbalance between the two output ports is less than 0.5 dB. The all-passband isolation is below -13 dB and the 25.7-dB upper stopband rejection is up to 5.4 GHz. Good agreement between the simulated and measured results validates the proposed idea. Hence, the proposed coupler is well suited for the applications of wideband, filtering, and single-layer circuitry integration.

A concurrent dual-band receiver based on a single multiport correlator is proposed in this brief to down-convert dual-band radio frequency signals. The system configuration, output power, as well as its spectrum analysis are discussed, and then a generalized baseband signal recovery theory is put forward. Next, the calibration algorithm based on real-valued time-delay neural network, which can take the system impairments and signal distortions into consideration, is proposed to retrieve two baseband signals, simultaneously. Finally, the six-port receiver is tested under the common modulated signals, and the measured error vector magnitudes between the transmitted and the received signals are all less than 2%.

Out-of-phase balanced-to-unbalanced (B2U) power dividers are popular. However, here we present a new in-phase B2U power divider, which is rarely considered. The presented power divider realizes ultrawideband common-mode suppression, while two additional transmission zeros are added around the edges of the passband, exhibiting wideband filtering response. The circuit schematic is simply composed of coupled/non-coupled lines and stubs. Finally, the simulated design is validated experimentally.

This paper proposes a novel monostatic concurrent multiband radar front-end architecture that can work in several independent bands simultaneously. Compared with the conventional single-band radar, multiband radar has the potential to support different modulation modes in independent frequency bands and multi-functional integration, and has a good ability to adapt to complex electromagnetic environment and flexible applications. In order to demonstrate the validity of this proposed multiband radar front-end architecture, the corresponding dual-band radar and two single-band radar prototypes are fabricated and measured. A good agreement of measured results between the dual-band and two single-band radar front-ends validates the effectiveness and reliability of the proposed new radar architecture.

The phase-difference performance at two desired frequencies of the generalized dual-band unequal coupler is discussed and presented in this comment as supplementary information. The condition of ${\{ \angle {S_{21}} - \angle {S_{31}}\} _{{f_1}}} + {\{ \angle {S_{21}} - \angle {S_{31}}\} _{{f_2}}} = \pi $ and the analytical equations for ${\{ \angle {S_{21}} - \angle {S_{31}}\} _{{f_1} \,\text{or}\, f_{2}}}$ are provided. It can be concluded that the dual-frequency output phase differences are constant and equal to 90° when ${R_2} = {R_3},$ but the values of ${R_1}$ and ${R_4}$ can be varied. Finally, the calculated results show that the phase-difference variations about $ \pm 11\% $ in the whole useful bandwidths of these branch-line couplers are objective and acceptable in common practical applications when ${R_2}$ and ${R_3}$ are in the range of 30–100 Ω $({R_2} \ne {R_3})$ .

In this paper, a new method to design a digitally assisted and spurious-free direct carrier mixerless modulator based on the six-port correlator is proposed. The calibration of the modulator based on modified Cartesian memory polynomial (MCMP) is used to linearize and mitigate hardware impairment of the whole system. The modulation and the up conversion are performed by using the variable loads controlled by the differential in-phase and quadrature-phase baseband voltages together with common-mode voltages. The proposed MCMP is able to compensate for nonlinearity, frequency responses, residual carrier leakage, crosstalk between the in-phase and the quadrature-phase data. The proof-of-concept of digitally assisted mixerless modulator is developed and its performance is assessed at 2.6 GHz with modern communication signals. The error vector magnitudes between the input ideal baseband signals and the up-converted radio frequency signals are all between 2% and 4%. The residual carrier leakage, which remains present after imperfect suppression through hardware means, degrades the overall system performance and it can be suppressed completely by means of the proposed memory polynomial model.

A simple and planar design structure for dual-band bandpass filter (BPF) with multiple transmission poles and zeros is proposed in this brief. According to frequency response transformation, two passbands are realized on both sides of the operation frequency. Sharp selectivity and high isolation level with eight transmission poles and seven transmission zeros are achieved just by employing three-section coupled lines and three short-circuit stubs. Besides, the analytical (closed-form) extraction process for the transmission poles and zeros of the proposed dual-band BPF is presented based on the rigorous scattering-parameters theory and the even- and odd-mode analysis method. A prototype for the dual-band BPF with 3-dB fractional bandwidth of 41.1% and 19.0% is designed and fabricated. The measured and simulated results are in good agreement to verify the validity of the proposed design principle.

A novel and simple dual-band out-of-phase balanced-to-single-ended (BTSE) power divider with filtering response and enhanced bandwidth is proposed in this article. The dual-band filtering response is realized by the embedded Π-type network with short-circuited stubs, leading to an enhanced operating bandwidth. The good isolation within the whole passband is implemented only using the ground resistor. The complete theoretical analysis and closed-form equations are presented based on the equivalent even- and odd-mode circuits. And then the higher-order circuit model with the improved frequency selectivity is established based on the proposed BTSE PD. For demonstration, a brand-new and simple planar BTSE power divider operating at 1 and 2.2 GHz is simulated, fabricated, and measured, which includes outstanding advantages for filtering response, return loss, insertion loss, isolation, and common-mode suppression. Finally, a good agreement between the simulated and measured results verifies the proposed design.

Complexity and computation effective design of multiport-based receiver system is proposed in this paper, and a simple calibration algorithm based on modified memory polynomial for the five-port receiver is used to demodulate the desired baseband signals from the received radio frequency signals. The theoretical foundation for the baseband signal recovery for the multiport system, basic circuit theory of the five-port receiver, and the proposed algorithm about how to retrieve the baseband signals from three output voltage signals are discussed. Finally, common modulated signals are used in the five-port receiver to validate the proposed calibration algorithm, and the measured performance in terms of error vector magnitude between the transmitted and the received signals are all less than 2%. Also, the performance comparison with the state-of-the-art multiport receivers is made to conclude that the five-port receiver with the proposed model can be one of the best cost and computation effective choices to accurately complete the signal recovery.

This paper proposes a novel approach for digital predistortion, based on direct learning architecture (DLA), to reduce the computational complexity. In power amplifier (PA) behavioral models, the coefficients of a Volterra polynomial or a simplified Volterra polynomial are extracted by calculating the inverse of a time-varying matrix, which is resource-consuming, time-consuming, and power-consuming due to its matrix dimension and inverse operation in a field-programmable gate array. To speed up the computation and save hardware resources, we propose a low computational complexity DLA with covariance matrix that uses the constant covariance matrix to replace the time-varying input signal filled matrix based on a stationary ergodic random process. To verify the proposed method, it was applied to a wideband Doherty gallium nitride (GaN) PA at 2.6 GHz with a 40-MHz orthogonal frequency division multiplexing signal, and to a dual-band Doherty GaN PA at 1.9 and 2.6 GHz with two 20-MHz long-term evolution signals. Experimental results show that the proposed algorithm achieves almost the same performance as the traditional approach, with less than one fifth of the computational quantity.

In this paper, a novel design method of generalized dual-band unequal filtering power divider (DUFPD) is proposed. Using this method, the power divider (PD) could be designed to realize the dual-band filtering response with arbitrary power division, arbitrary frequency ratio, arbitrary real terminated impedances, independently controllable bandwidth, and excellent isolation. To satisfy these characteristics, a proper dual-band filtering structure is selected to replace the conventional quarter-wave length transmission line in the PD. In addition, a single resistor structure is utilized to obtain effective isolation between the output ports. Furthermore, the complete design procedures and analytical equations of the proposed generalized DUFPD are presented based on the circuit and transmission line theories. To demonstrate the validity of the proposed design method, a DUFPD with different real terminated impedances is designed, fabricated, and measured. We show that there is a good agreement between the simulated and measured results.

In modern wireless communications, it is getting urgent to make a better trade-off between reliability and effectiveness in wireless systems. In fact, the use of coded cooperation (e.g. space time coding) in multiple input and multiple output (MIMO) system has drawn much attention for this purpose. However, it needs to be further investigated how to select the space time codes (STC) adaptively. On the other hand, continuous phase modulation (CPM) is a promising technology for its merits of power and spectrum efficiency. This study is to consider adaptive space time coded CPM systems. The criterion of adaptive switching is based on the Frobenius norm and the thresholds between STC schemes. Analysis and simulation are made to the proposed system in terms of frame error rate and data rate.

In this paper, a novel planar compact coupled-line circuit is proposed to design a single-ended-to-balanced power divider (PD) that can be used in numerous balanced circuits and systems. By using the matrix transformation between the mixed-mode (MM) scattering parameters and the single-ended scattering parameters, the constraint rules are deduced to realize the performance of equal power division with in-phase, good input (output) port matching, high isolation between two balanced outputs, high suppression of the common-mode (CM) noise, as well as the mode-conversion suppression between differential-mode signals and CM noise. Then, the closed-form design equations are derived using the even- and odd-mode analysis. Finally, a microstrip PD, which works at 1 GHz, is designed and fabricated. The measured (simulated) operating relative bandwidth is 37% (38%) from 0.76 (0.83 GHz) to 1.13 GHz (1.21 GHz). The consistency between the simulated and measured MM scattering parameters verifies the correctness of the design theory.

For the first time, this paper presents a novel approach for designing a coupler with arbitrary division, optional phase difference, and alternative input/output impedances. In the section of theoretical analysis, rigorous closed-form design equations are derived, and explicit methodology for computer-aided design is given based on the equations. To validate the idea, several numerical examples extracted from the design procedure are constructed and demonstrated. Eventually, three prototypes of the coupler are fabricated, and experiments are carried out. The excellent agreement between the theoretical and experimental results sufficiently verifies the theoretical methodology. This proposed coupler is well applicable to the applications that require high flexibility in couplers’ performances.

Wideband spectrum sensing in cognitive radio networks has gained significant research interests in the recent years. In the context of noise uncertainty, the noise variance has no access to accurate estimation which brings about an imprecise decision threshold. This paper investigates this subject from a novel perspective. Multistage Wiener filter (MSWF) is adopted in the conventional minimum description length (MDL) criterion to enhance the detection performance. By seeking the value that minimizes the MSWF aided MDL criterion, the number of occupied sub-channels in the wideband spectrum is determined. And then the accurate locations can be obtained based on the received energy of each channel. The proposed scheme is robust to noise uncertainty since it requires no estimation of noise variance. Meanwhile, having no demand for the estimation of covariance matrix or its eigenvalue decomposition makes our approach computational attractive. In addition, the proposal partitions the array data into the cleaner signal and noise subspace components and can thereby improve the detection performance. Numerical results verify our approach and show that it is superior to other existing sensing algorithms in the previous works.

A systematic design methodology including novel crest factor reduction (CFR) and power amplifier (PA) efficiency enhancement techniques for concurrent dual-band transmitters is proposed to improve performance under concurrent modulated stimulus, in terms of both efficiency and output power. Conventional energy efficient PAs are typically implemented separately in analog circuit or digital signal domains. However, the proposed method combines a digital domain 2-D power distribution reshaping (2-D-PDR) method to adaptively reshape the signals’ distribution to fit the target PA’s characterization and an analog domain inter-modulation tuning design to enhance the PA’s output capability. Based on the proposed method, an example of concurrent dual-band Doherty PA (DPA) working at 1.9–2.6 GHz LTE bands was designed using two 10-Watt GaN HEMTs. A 2-D-PDR procedure was developed for the designed DPA. The fabricated DPA was measured in concurrent mode under the stimulus of a pair of 10 MHz LTE signals. According to the measured results, the proposed DPA achieved a drain efficiency of 46.6% at an output power of 6.2 W while maintaining a good adjacent channel power ratio and error vector magnitude. To the best of the authors’ acknowledge, this is the state-of-the-art performance for concurrent dual-band PAs. Additionally, measurements are performed on three varied type of PAs using the proposed 2-D-PDR. According to the measured results, about 0.3~0.8 dB power improvement and 1.5%~3% efficiency improvement can be achieved using the proposed 2-D-PDR compared with the conventional 2-D-CFR, proving the feasibility of the proposed technique.

In this paper, a novel terminated coupled line structure (TCLS) is introduced, which is constructed by a coupled line section and four terminations loaded on it. Introducing different kinds of terminations, three types of bandpass filters (BPFs) based on TCLSs are proposed, theoretically analyzed, and fabricated, including two single-ended wideband BPFs with fractional bandwidths (FBWs) of 67% and 40% respectively, and a wideband differential BPF with 74% differential-mode FBW. These BPFs can achieve wide passband bandwidth, low in-band insertion loss, high passband selectivity, as well as deep stopband rejection performance simultaneously, benefited from the multiple transmission zeros and transmission poles obtained by the TCLSs. The practical design procedures of these BPFs are presented and explained. The agreement among theoretical predictions, EM-simulated, and measured results validates our proposed filter structures. Finally, the generalized multistage filter topology based on TCLSs is proposed to design high-order filters with better filtering performances.

A planar microstrip circuit is proposed in this article to design a dual-band balanced-to-unbalanced out-of-phase power divider with inherent impedance transformation. This balanced-to-unbalanced power divider, which essentially consists of two pairs of cascaded coupled lines, two dual-band 90° phase shifters, and a grounded resistor, features the dual-band application with inherent impedance transformation, the equal power division with out of phase, high isolation between two outputs, good ports (A, 3, and 4) matching, and high common-mode noise suppression as well as the excellent conversion inhibition between the differential-mode signals and the common-mode noise. The closed-form solutions are obtained by using the traditional odd- and even-mode analytical methods. Finally, a practical microstrip balanced-to-unbalanced power divider, which operates at 0.9 GHz and 1.8 GHz, is designed and fabricated. The simulated and measured results verify the correctness of the circuit and the design theory.

A concurrent dual-band six-port receiver based on real-valued time-delay neural network (RVTDNN) is proposed in this paper to retrieve two baseband signals from a dual-band radio frequency signal, concurrently. Different from the traditional six-port correlator, the new passive circuit correlator, which is composed of one power divider and three quadrature couplers, has three inputs and three outputs, resulting in the decreased hardware complexity as well as circuit size, and a reduced power consumption for the system. The new six-port correlator, its output power as well as the baseband signal recovery theory are described and analyzed in detail. The calibration algorithm based on the RVTDNN is adopted to verify the feasibility of the concurrent dual-band receiver based on the proposed correlator circuit. Finally, a practical wideband six-port receiver test bench, which operates from 2 to 3 GHz, is built and tested using the common modulated signals. The calculated error vector magnitudes are all less than 2% verifying the correctness of this novel system implementation approach.

In this study, the authors propose a generalised multiband impedance transformer (MIT), which can transform the frequency-dependent complex loads at multiple arbitrary bands simultaneously. The proposed transformer has two parts: the multiple frequency-selection sections consisted of the series–parallel branches and the π-shape impedance transformer is composed of the multiple series transmission lines. Analytical equations are derived for the closed-form solutions and the rules of electrical parameters. Numerical examples are examined to verify the validity. On the basis of printed circuit board, a single-stage tri-band low-noise amplifier (LNA) with the proposed MIT is designed, simulated, and measured for practical application. The measured LNA maintains the tri-band performance and the 3 dB bandwidths are 400, 250, and 50 MHz with the 15, 12, and 7 dB minimum gain, respectively. The minimum input return losses are −24, −13, and −11 dB corresponding to the three bands, and the output return loss is lower than −10 dB from 1.5 to 2.6 GHz. The minimum input third-order intercept points are 4.1, 6.2, and 14.7 dBm, respectively. Besides, the noise figures (NFs) are 1.9, 2.6, and 5.0 dB separately at the centre frequencies of 1.8, 2.23, and 2.47 GHz.

A new planar dual-band balun with filtering response and output isolations is proposed in this letter. The balun is constructed on a three-layer PCB, whose out-of-phase operation is realized by antisymmetric output configuration. By introducing dual-band resonators and admittance inverters, the circuit is able to operate with designated filtering response, and the source/load impedances could be different. Additionally, the output isolation is reserved by employing two isolation resistors. The experimental results prove that this new balun is a good candidate for multi-standard and multi-functional communications.

In this paper, a novel broadband Doherty power amplifier based on the continuous-mode technique (C-DPA) is proposed. The amplifier is focused on manipulating harmonic components in a Doherty power amplifier (DPA) structure to achieve improved bandwidth and efficiency. In a conventional DPA, harmonic isolation is typically required between the two transistors to prevent them from modulating each other at harmonic frequencies. However, as presented in this paper, such isolation is not actually necessary. On the contrary, by allowing the two transistors to modulate each other at harmonic frequencies with the help of a properly designed postharmonic tuning network, a series of highly efficient DPA modes can be created over a continuous frequency band, leading to a broadband C-DPA. Based on the proposed method, an example of a C-DPA working from 1.65 to 2.75 GHz was designed. According to the measured results, the designed C-DPA exhibits a 52%–66% efficiency at a −6 dB power backoff and a power utilization factor higher than 1.08 over the 1.1-GHz band. In addition, when simulated by a 7.5-dB peak-to-average power ratio 20-MHz LTE signal, the example C-DPA exhibits an efficiency of 46%–62% while maintaining an adjacent channel power ratio below −45 dBc after linearization over the full 1.1-GHz band. To the best of our knowledge, this is the first proposed C-DPA and a state-of-the-art performance for broadband DPAs.

A concurrent dual-band low intermediate frequency receiver, which is based on the multiport correlator, is proposed in this letter. Only one single local oscillator signal is used to demodulate the dual-band RF signals at the same time, which greatly reduce the receiver complexity. The system configuration, output power theory, as well as the power spectrum are analyzed in detail, and then an appropriate baseband signal recovery theory is put forward. Finally, a concurrent dual-band six-port receiver is tested under the long-term evolution signals with 3- and 5-MHz bandwidths. The measured error vector magnitudes are all lower than 2%, which verify the proposed system structure and the signal recovery theory.

This letter reports a novel synthesis method to design an extended dual-band power amplifier (PA). The proposed matching networks exhibit dual-band impedance rotation, leading the transistor to yield flat gain at the two designed passbands and suppressed gain responses at frequencies outsides the passbands. The fabricated PA represents a competitive solution in multiband and multimode applications as compared with the conventional dual-band PA based on the multifrequency techniques. The transistor CGH40010F from Cree is employed for verification. At 1.4 and 2.4 GHz, the bandwidth has been extended over 150 MHz at each individual passband. The implemented PA can deliver the saturated output power of 10 W minimum, and power-added efficiency of 65% minimum has been measured.

A novel impedance transformer (IT), which transforms different terminations at multiple bands is reported. This transformer is especially suitable for extremely low and high impedances. By utilising the impedance buffer method and introducing ladder networks, this IT is generalised and is available to arbitrary number of bands theoretically. For verification, a quad-band prototype is fabricated and measured. The results show good agreement with the design expectations.

In this paper, a novel reconfigurable wideband/dual-band filtering antenna loaded with coupled lines and stepped-impedance stubs is proposed for Wireless Communication Systems. The proposed antenna consists of a reconfigurable filter and a wideband antenna. In this design, a wideband band pass filter (WBPF) with high selectivity is presented by employing two-section coupled lines, a short-circuit stub, and two open-circuit stepped-impedance stubs. After adding a coupled line, the WBPF is transformed to a dual-band band pass filter (DBPF). A reconfigurable wideband/dual-band filtering antenna is obtained through the integration of the reconfigurable filter and a wide-band monopole antenna. The functions of the filtering antenna are controlled by the PIN diodes. The operating impedance bandwidth of the wideband filtering antenna is from 1.27 to 3.47 GHz, while the dual-band filtering antenna is from 1.25 to 1.88 GHz and from 2.84 to 3.24 GHz. Details of the antenna design are shown, and the simulation for the constructed prototype are also exhibited and discussed.

Based on current waveform shaping, a novel concurrent inverse Class-F (Class-F−1) mode is presented for the concurrent dual-band power amplifier (PA). According to the analysis of proposed concurrent modes, the optimal load impedances are given for output matching circuit design at fundamental, harmonic and intermodulation (IM) frequency. The process of engineering current and voltage adopts the strong nonlinear model of PA and reveals that concurrent Class-F−1 mode may have better linearity performance because of class-A bias point. The theoretical results show that the proposed mode show more than 3.8 dB output power promotion compared with concurrent Class-B mode, which are driven by two CW signals with same amplitudes, which provides an opportunity and potential to design concurrent power amplifier.

Automatic modulation recognition (AMR) plays an indispensable role in many fields, such as cognitive radio, spectrum sensing, non-cooperative link adaptation, and other civilian and military fields. OFDM-IM is an innovative OFDM-based scheme which has better bit error performance than classical OFDM scheme especially in high mobility cases. Different from OFDM, the modulation parameters include both M-ary signal constellations and indices of the subcarriers in OFDM- IM scheme. In this paper, we studied a deep neural network (DNN) based AMR method in orthogonal frequency division multiplexing with index modulation (OFDM-IM) scheme.

By exploring embedding transversal signal-interference sections in a Wilkinson power divider, this letter proposes a novel methodology for the filter and power divider co-design. The structure realizes simultaneous power division and filtering in a single uniplanar circuit. In this letter, the equations as well as the detailed design methodology are given. In the last section, simulations and experiments are carried out, the results of which show a filtering power-division performance with 90% bandwidth (15-dB return loss) and two transmission zeros at the passband edges.

A novel digital predistortion (DPD) with an ultralow feedback sampling rate is proposed for wideband wireless communications. Analytical groundwork is carried out to support the rationale of the proposed method. Due to the power amplifier (PA) spectral expansion, the sampling rate of the feedback loop in the DPD architecture generally requires several times the input signal bandwidth, which presents challenges for the analog-to-digital converter, especially in broadband applications. In order to remove this bottleneck in real-world implementation, a forward behavioral modeling method with low-rate aliasing PA output signals is adopted to estimate the model coefficients. The obtained coefficients are then used to predict the high-rate PA output, using the input signal with an adequate sampling rate, and to further generate the predistorter for the nonlinear PA with the conventional indirect learning architecture. To validate the proposed method, different PAs driven with a 40-MHz two-carrier Long Term Evolution are used for linearization purposes. Experimental results based on the instrument platform show that the proposed algorithm achieves almost equivalent results with only a 2.5 Msamples/s feedback sampling rate. Further experimental verification is also demonstrated on an FPGA platform, which achieves an adjacent channel power ratio that is better than −47 dBc for 40-MHz signals with a feedback sampling rate of 20 Msamples/s.

In this paper, a novel calibration algorithm based on real-valued time-delay neural network (RVTDNN) is proposed for the multiport receiver to recover I/Q signals from the received modulated signals, especially from wideband signals. All the system impairments, including the nonideal six-port correlator, the nonlinearity of the diodes, and the memory effects under the excitation of the wideband signals, are taken into consideration. The RVTDNN, which has three layers, consists of four inputs and two outputs (in-phase and quadrature signals), and its parameters (biases and weights) are all real-valued and are determined by the backpropagation algorithm. Finally, the proposed calibration method is validated by a 2–18-GHz six-port receiver under 3G and 4G signals. The performance of the error vector magnitude between the transmitted signals and received signals is always less than 1.8%, which validates the correctness of the proposed model.

A novel small-size filtering power divider (PD) featured four-function integration is proposed. These four integrated functions are high-selectivity filtering, inherent DC block, high all-frequency isolation, and high-power applications. Using single-layer planar circuit technology, this proposed PD can be implemented easily. The measured results of a prototype show that it can operate at 2 GHz with a −10 dB matching bandwidth of 6% and all-frequency −15 dB isolation.

A novel dual-band out-of-phase power divider with inherent impedance transformation and high power-handling capability is presented in this article. This proposed power divider essentially consists of four sections of double-sided parallel striplines for the signal transmission, an inserted middle conductor plane as the common ground, and two resistors to improve the isolation between two outputs. Closed-form design equations are derived based on the conventional even- and odd-mode analytical methods and the transmission-line theory. Finally, a practical three-layer out-of-phase power divider is designed and fabricated. The experimental results show that good ports matching, excellent isolation between two outputs, and out-of-phase performance are simultaneously achieved at both 1 and 2.6 GHz.

In this paper, a novel coupled-line tunable Wilkinson power divider with perfect port match and isolation in a continuously tunable passband is presented. The proposed tunable power divider consists of an isolation resistor, two coupled lines, and two types of varactors. By providing these varactors with suitable bias voltages, the operating frequency of the proposed power divider can be flexibly changed as desired. Meanwhile, perfect port match and isolation are maintained at all tunable operating frequencies. After applying the even-odd mode analysis method, the closed-form equations of the design parameters are derived to illuminate the effects on the minimum and maximum operating frequencies. These equations exhibit that the proposed power divider has a wide frequency tuning range and a high tunability (more than 110% in ideal conditions). Owing to the limitation of manufacturing process, a microstrip power divider with a tunable frequency of 0.54–1.41 GHz (89.23%) is designed and simulated based on the provided closed-form equations. The measured results show a frequency tuning range from 0.56 to 1.39 GHz (85.13%) with a more than 20-dB return loss and isolation in the entire tuning range, agreeing well with the simulation results.

This paper presents a novel compact power divider (PD) with bandpass response and improved out-of-band rejection performance, which features flexible bandwidth adjustment and high passband selectivity. The proposed filtering PD consists of two coupled-line sections, two short-circuited transmission line sections (TLSs), and two cascaded stepped impedance TLSs in symmetrical arrangement. The unique loading point of isolation resistor is proposed to provide enhanced isolation performance, different from that of the conventional Wilkinson PD where the isolation resistor loaded between the output ports. Theoretical investigation adopting even–odd-mode method is presented to explain the operating mechanism. For verification, a filtering PD centered at 2.4 GHz is designed and measured. The measured results agree well with the simulated ones.

This letter presented a novel compact continuously tunable low-pass filter (LPF) using varactor-loaded coupled rhombic stubs. The proposed LPF demonstrated excellent roll-off selectivity, wide stopband range as well as good cut-off frequency tunability. This LPF consisted of three varactor-tuned coupled rhombic stubs loaded on a section of high-impedance microstrip line symmetrically and two coupled line LPFs which could further improve the stopband performance. A detailed explanation of the tuning mechanism was illustrated by adopting lumped-element equivalent circuit model. The measured results showed not only a wide cut-off frequency tuning range of 56% from 350 to 800 MHz, but also an excellent steepness factor of less than 1.14. Additionally, a rejection level of greater than 20 dB up to 8 GHz (>10 fc) was observed in the stopband. The proposed ideas were verified by the measured results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1641–1644, 2016

There is an ever increasing demand for both function integration and improved performance in wireless communication devices. Therefore, the integration of efficient linearizing amplifying and bandpass filtering functions is proposed for the first time in this paper. A new Doherty amplifier configuration with attractive behaviors including bandpass filtering, wideband harmonic suppression, and enhanced efficiency, is presented. A component crucial to the successful implementation of the proposed configuration is the bandpass quadrature coupler with arbitrary coupling coefficient. Owing to the flexibility of a circular patch in locating the frequencies of different operational modes, it is thus possible to implement good bandpass characteristics. With the introduction of this new component, the Main and Auxiliary amplifiers can be driven more efficiently, resulting in both linearity and efficiency improvements. To verify the validity of the proposed configuration, a Doherty amplifier has been designed and fabricated. Its measured performance is compared with the conventional design and found to exhibit a bandpass filtering characteristics with a wide suppression band up to the third harmonic frequency. Meanwhile, the proposed amplifier achieves a measured power-added-efficiency improvement of 10% and an ACLR improvement better than 5.8 dB at the higher output power region.

A compact coupled-line circuit is proposed in this article to design a kind of dual-band Gysel power divider (Gysel, 1975). This circuit inherently consists of three pairs of coupled lines, an open stub, two output extension lines, and two grounded isolation resistors. Besides the high power-handling capability, this Gysel power divider features dual-band operating performance, wide frequency ratios, flexible impedance transformation, etc. Using the transmission-line theory and rigorous even- and odd-mode analysis, closed-form solutions for the electrical parameters are obtained. A practical Gysel power divider, which works at 0.92 and 2.45 GHz, simultaneously, is designed and fabricated for radio frequency identification application. Good agreement between the simulated and measured results verify the correctness of the design theory.