Two-tone Signal Research Articles

3.3-4.3 GHz efficient continuous class-F gallium nitride power amplifier based on simplified real frequency technique and harmonic tuning.

In order to implement the fifth generation (5G) communication system for a large number of users, the governments of many countries nominated the low 5G frequency band between 3.3 and 4.3 GHz. This paper proposes a wideband RFPA by designing the input matching network (MN) and output MN of the device using the simplified real frequency technique (SRFT) and the harmonic tuning network. The load-pull and source-pull is applied at multiple points for 100 MHz intervals over the bandwidth to obtain the optimum impedances at the output and input of the 10W Gallium Nitride (GaN) Cree CGH40010F device. To verify the design, the RFPA is simulated, and the performance is measured between 3.3 and 4.3 GHz. According to experimental findings, the measured drain efficiency (DE) throughout the whole bandwidth ranged from 57.5 to 67.5% at the output power of 40 dBm. Moreover, at the 1 dB compression point between 39.2 and 42.2 dBm output power, the drain efficiency (DE) achieves a high value of 81.2% with an output power of 42.2 dBm at a frequency of 3.3 GHz. The RFPA can obtain a maximum gain of 12.4 dB at 3.5 GHz. The linearity of the RFPA with a two-tone signal is measured and the value is less than -22 dBc all over the band.

Testing and Analysis of PIM Performance in a Passive DAS Network - Experimental Approach

Passive intermodulation (PIM) poses a significant challenge in telecommunication networks, with potentially severe impacts on network performance and signal integrity if not addressed during the initial deployment phase. This study investigates PIM levels within a passive distributed antenna system (DAS) network for cellular mobile radio communication across multiple floors of a building. The network comprises coaxial cables, connectors, splitters, combiners, and antennas structured in a systematic plan. This work used the experimental method to test for PIM in the network used for this investigation. Designed as a multicarrier system, it handles RF signals across frequencies of 700/850MHz, 1900MHz, 2100MHz, and 2600MHz. On-site PIM testing was conducted during the network deployment phase to analyze the behavior of high-power RF signals. Utilizing Kaelus iQA-1921C and iQA 850C series PIM analyzers, tests were conducted following known industry codes and standards. High RF power was preset to 43dBm for full band, 35dBm for high bands, and 25dBm for low band. The test equipment was calibrated on high PIM load and low PIM load. Test points were selected at both vertical and horizontal subsystem cabling structures, focusing on riser cables. The standard baseline performance PIM levels was set to -150dBc. The analysis focused on examining the characteristics of PIM signals captured via time-domain PIM traces, investigating the impact of altering the frequency of the two-tone signal on the IM3 frequency component, and highlighting the importance of selecting an appropriate frequency for the two-tone signal that is not positioned near the edges. Results were based on pass or fail test, and resolution measures were taken to mitigate interference.

Design of a Millimeter-Wave Broadband Linearizer Based on an Extended Design Space

In this study, a broadband linearizer design method based on an extended design space is proposed to optimize the design complexity and linearization performance of conventional linearizers for broadband operation. The gain characteristics of the power amplifier (PA) and linearizer are fitted to simplify the analyses and to quickly derive the ideal objective function of the linearizer design. Then, the 1 dB compression point of a nonlinear system is redefined and used to further extend the design space of the linearizer. To verify the proposed design method, a millimeter-wave linearizer prototype based on the extended design space was designed and fabricated. The linearizer was tested with continuous-wave and 100 MHz two-tone signals from 40 GHz to 43 GHz. The measurement results of the linearized PA showed that the output 1 dB power point (OP1dB) was improved by more than 1.7 dB, the phase error was reduced by more than 15°, and the third-order intermodulation distortion (IMD3) was suppressed by 8.6 dB–13.1 dB over the working frequencies. The proposed linearizer achieved good linearization performance, low power consumption, and simple design implementation, and it was not necessary to tune the bias during broadband operation, making it applicable in complex communication scenarios.

Microwave photonics frequency measurement with improved accuracy based on an artificial neural network.

Photonics-assisted techniques for microwave frequency measurement (MFM) show great potential for overcoming electronic bottlenecks, with wild applications in radar and communication. The MFM system based on the stimulated Brillouin scattering (SBS) effect can measure the frequency of multiple high-frequency and wide-band signals. However, the accuracy of the MFM system in multi-tone frequency measurement is constrained by the SBS bandwidth and the nonlinearity of the system. To resolve this problem, a method based on an artificial neural network (ANN) is suggested, which can establish a nonlinear mapping between the measured two-tone signal spectra and the theoretical frequencies. Through simulation verification, the ANN optimized frequencies within the range of (0.5, 27) GHz of the MFM system show 79%, 76%, 70%, 44% reduction in errors separately under four spectral signal-to-noise ratios (SNR) conditions, 20dB, 15dB, 10dB, 0dB, and the frequency resolution is improved from 30MHz to 10MHz.

ADC low-complexity modelling identification and mitigation of baseband intermodulation distortion with instantaneous frequency dependence

The linearization of active electronic components such as power amplifier or analog-to-digital-converter (ADC), is a vast subject. Many issues come into play, including behavioural modelling with the selection of a relevant model in terms of accuracy, complexity, identification, and compensation. In this paper we consider an ADC linearization problem, we propose an original low-complexity modelling identification and mitigation of baseband intermodulation distortion with instantaneous frequency dependence. Thus, we introduce a refinement of a power series model by adding a dependence on the variation of the instantaneous frequency of the signal. Based on this, we describe a method suitable for the model calibration using a two-tone signal. We finally present a measurement bench adapted to the calibration of the coefficients of the model, followed by some results of linearization. All the methods presented are intended to be operated in real time in embedded systems and are therefore studied to present very low computational complexities.

A Joint Design of Radar Sensing, Wireless Power Transfer, and Communication Based on Reconfigurable Software Defined Radio

This paper proposes a compact three-mode base station capable of performing radar sensing, communication, and wireless power transfer (WPT) in collaboration with indoor sensor networks. With regard to the wireless sensor node, the base station transmits two-tone signals in the downlink to support its operation and provides two-way communication. The sensor node sends uplink information through backscattering using the third order intermodulation (IM3) product of the rectification. In the radar mode, a single-tone continuous wave (CW) is used to monitor if there is a moving target in the static environment. If a speed is detected, the transmit signal to the node is stopped, while the single-tone CW excitation will continue until the speed of the target is zero, and then the base station transmits a stepped frequency continuous wave (SFCW) signal to measure the distance of the target. The repeat between the two radar waveforms continues until the target is undetectable within the detection range. The software defined radio PlutoSDR is adopted as the base station. The system can wirelessly supply power and bi-directionally communicate with a CO2 sensor node 2 m away. It gives a range resolution of 2.5 cm and a minimum detectable speed of 0.25 m/s in the radar mode.

Adaptive Distributed Transceiver Synchronization Over a 90 m Microwave Wireless Link

We present an adaptive approach for synchronizing both the phase and frequency of radio frequency transceivers over 90 m wireless links to support distributed antenna array applications. To enable phase-coherent distributed operation between separate wireless nodes, the oscillators in the transceivers must operate at the same frequency, and their phases must be appropriately aligned to support beamsteering. Based on a spectrally sparse waveform, a self-mixing frequency demodulation circuit, and an adaptive control loop, we present a system capable of synchronizing the RF oscillators in separate transceivers over distances of 90 m. The approach is based on a multitone waveform designed for joint internode ranging and frequency transfer. A frequency reference is modulated onto one signal of a two-tone waveform transmitted by the primary node and is then demodulated and used to lock the oscillator of the secondary node. The secondary node retransmits the two-tone signal, which the primary node uses for a high-accuracy range measurement. From this range, the phase of the two transceivers can be aligned to support beamforming. We furthermore implemented an adaptive phase control approach to support high-accuracy phase coordination in changing environmental conditions. We demonstrate continuous high-accuracy links over a 90 m distance in an outdoor environment for durations up to seven days, demonstrating sufficient phase coordination in changing weather conditions to support distributed beamforming at frequencies up to 3 GHz.

Wavelength-Tunable Optical Two-Tone Signals Generated Using Single Mach-Zehnder Optical Modulator in Single Polarization-Mode Sagnac Interferometer

We demonstrate 60 GHz separation optical two-tone signal generation at arbitrary C-band wavelengths without involving complicated optical wavelength filtering. By utilizing a polarizer, the selective suppression of undesired low-order optical sidebands has been proven and optimized based on model analysis. By utilizing this scheme in conjunction with the optimized parameters, more than 20 dB of suppression of undesired optical sidebands have been successfully achieved over a 40 nm wavelength range. This scheme allows us to generate optical two-tone signals at the desired wavelength.

Design of Ultra-Wideband Power Amplifier Based on Extended Resistive Continuous Class B/J Mode

This brief presents the design of an ultra-wideband high-efficiency extended resistive continuous class B/J (ERCB/J) power amplifier (PA). Beyond an octave bandwidth, the conventional class B/J mode is inappropriate. Whereas the existing resistive-reactive class J modes present an overlapped impedance space at the expense of the efficiency and power degradation or voltage swing beyond 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V_{DD}$ </tex-math></inline-formula> . Therefore, this brief presents a novel ERCB/J mode to achieve overlapping impedance space promising high efficiency over a multi-octave bandwidth. A design scheme is presented to map loads of the proposed mode to frequencies in the targeted multi-octave band to design a feasible matching network. For the proof of concept, a PA has been designed based on ERCB/J using commercialized GaN HEMT. This PA operates from 0.5-3.25 GHz, exhibiting fractional bandwidth of 146.7%. The peak drain efficiency of 60-70.1% and peak output power of 39.1-41.75 dBm are obtained at saturation over the operating band. The PA has also been tested with a two-tone signal with 10 MHz spacing and a 10 MHz LTE signal.

Simulation Analysis of RBW Parameters of Spectrum Analyzer Based on Convolution Approach

Resolution Band Width (RBW) represents the 3 dB bandwidth of the internal IF filter of the spectrum analyzer, the setting of which greatly affects the clarity of the output spectrum line of the spectrum analyzer. Its reasonable value is essential to correctly distinguish the signals of different frequencies, especially in the case of aliasing of the output spectrum. Thus, it is of great significance to study the relationship between the setting of RBW and the output spectrum. Due to the expensive spectrum analyzer, the RBW adjustment range, frequency range and output accuracy are limited, so this paper will apply an economic, RBW arbitrary adjustable, high accuracy equivalent convolution method for the simulation of the RBW parameters of the spectrum analyzer, and evaluate the effect of RBW and filter type on the degree of output spectrum aliasing based on a typical equal-amplitude two-tone signal input, and finally give setting suggestions on RBW and filter type.

Design of Wideband Continuous Class-F Power Amplifier Using Low Pass Matching Technique and Harmonic Tuning Network

Many countries have allocated new frequency bands for fifth generation (5G) communication systems. In this paper, a wideband continuous class-F (CCF) radio frequency power amplifier (RFPA) is presented for the new 5G frequency band, from 3.3 GHz to 4.3 GHz using a 10 W Cree CGH40100F device. A unique wideband RFPA design approach for the output matching network (OMN) is also presented by applying a harmonic tuning network (HTN) for the harmonics and a low pass matching technique (LPMT) for the fundamental frequency. The RFPA is fabricated, and promising measurement results show a drain efficiency of 55.9% to 65.3% is achieved at an output power of 40 dBm (&#x00B1; 0.3 dBm) over a frequency range of 3.3 GHz to 4.3 GHz. A two-tone signal with a 10 MHz spacing was also applied to investigate the linearity of the RFPA.

An Undersampling Communication System Based on Compressive Sensing and In-Fiber Grating

An undersampling free-space optical (FSO) communication system based on compressive sensing (CS) and in-fiber grating is proposed. Our proposal drastically mitigates the data scale unfavorable issue and reduces the great amount of required data. Also, our proposal employs low-bandwidth and low-cost photodetectors (PDs) and analog-to-digital converters (ADCs) and decreases the cost of data detection. Besides, the data transmitted in the free space is encrypted, which enhances the security of the system. The in-fiber grating, which has the advantage of highly efficient thanks to its inherent compatibility with optical fiber links, plays the roles of light emitter, in-fiber polarizer, and light diffraction device, simultaneously. A sinusoidal radio frequency (RF) signal with a frequency of 1 GHz is utilized for a 2.4 m data transmission. And each PD with a bandwidth of 300 MHz is employed for detecting the transmitted signal on each channel. The proposal obtains data compression ratios of 25%, 15%, and 5% both in the temporal domain and frequency domain. Besides, a two-tone signal and a random RF signal are applied in the proposed FSO transmission for data transmission. Our proposal not only has the merits of secure, compact, stable, and highly efficient, but also has great potential in extremely secure situations, such as secured indoor and under water data communication.

A multi-tone high efficient bandwidth system with an eliminated even-order distortions using double dual-parallel Mach-Zehnder modulator

In this paper, a linearization of dual RF channels over a single carrier wavelength is proposed and experimentally demonstrated. Multiple microwave signals with a multi-octave bandwidth are modulated by a double dual-parallel Mach-Zehnder modulator (D-DPMZM) and recovered by a differential balanced detector (BPD). The theoretical and experimental model illustrates the elimination of second-order harmonic distortions (SHD) and second-order intermodulation (IMD2), and significant suppression of the third-order intermodulation (IMD3) by controlling the phase of the input RF signal and DPMZM. The proposed photonic link configuration illustrates the modulation of two microwave signals on a single optical carrier wavelength, and each RF channel is tested for Two-tone signals to illustrate the linearization of the channelized analog photonic link (CAPL). Firstly, a mathematical model is presented to illustrate the elimination of optical carrier and even-order distortions by using only single-tone in each RF channel. Secondly, the purity of the system is mathematically and experimentally investigated by introducing two-tones in each RF channel. We have analyzed both test cases, with single-tone and with a two-tone test, to help us understand and compare the performance of the system. For test case 1 and test case 2 of our proposed configuration, we have achieved a fundamental signal-to-interference ratio (S/I) of 60 dB and 65 dB with a spurious-free dynamic range (SFDR) of 110 dB.Hz2/3 and 116 dB.Hz2/3, respectively.

Multiple radio frequency measurements with an improved frequency resolution based on stimulated Brillouin scattering with a reduced gain bandwidth.

A photonic-assisted multiple radio frequency (RF) measurement approach based on stimulated Brillouin scattering (SBS) and frequency-to-time mapping with high accuracy and high frequency resolution is reported. A two-tone signal is a single-sideband (SSB) modulated on an optical carrier via a dual-parallel Mach-Zehnder modulator to construct one SBS gain and two SBS losses for SBS gain bandwidth reduction. The unknown RF signal is also SSB modulated on a carrier that has been modulated by a sweep signal, thus the unknown RF signal is converted to a sweep optical signal along with the sweep optical carrier. The bandwidth-reduced SBS gain spectrum is detected by the sweep optical signals at different specific time, mapping the RF frequencies to the time domain. An experiment is performed. RF frequencies from 0.3 GHz to 7.6 GHz are simultaneously measured with a root mean square error of less than 1 MHz. In addition, the frequency resolution of the measurement can be much lower than 10 MHz, which is now the best result in the RF frequency measurement methods employing the SBS effect.

상호 결합된 차동인덕터를 이용한 GaAs HBT 공정 기반의 1.9 GHz~2.6 GHz 광대역 선형 전력증폭기 설계

This study presents a wideband two-stage linear power amplifier, operating from 1.9 to 2.6 GHz, using a mutually coupled differential inductor based on GaAs hetero-junction bipolar transistor (HBT). A part of the two-section inter-stage matching circuit comprises a mutually coupled differential inductor, which widens the operating band of the matching circuit and reduces the circuit size. In addition, it is optimized to linearly operate in the wide frequency band using a wideband balun at the input and output stages. The fabricated linear power amplifier exhibits a maximum output power of 22.0 dBm~24.0 dBm and efficiency of 33.0 %~39.0 % in the 1.9 GHz~2.6 GHz frequency band. An IMD3 of −30.0 dBc at two-tone signal, with high efficiency of more than 33.0 % was achieved at the linear output power of 22 dBm.

A Compressed Sensing Recovery Algorithm Based on Support Set Selection

The theory of compressed sensing (CS) has shown tremendous potential in many fields, especially in the signal processing area, due to its utility in recovering unknown signals with far lower sampling rates than the Nyquist frequency. In this paper, we present a novel, optimized recovery algorithm named supp-BPDN. The proposed algorithm executes a step of selecting and recording the support set of original signals before using the traditional recovery algorithm mostly used in signal processing called basis pursuit denoising (BPDN). We proved mathematically that even in a noise-affected CS system, the probability of selecting the support set of signals still approaches 1, which means supp-BPDN can maintain good performance in systems in which noise exists. Recovery results are demonstrated to verify the effectiveness and superiority of supp-BPDN. Besides, we set up a photonic-enabled CS system realizing the reconstruction of a two-tone signal with a peak frequency of 350 MHz through a 200 MHz analog-to-digital converter (ADC) and a signal with a peak frequency of 1 GHz by a 500 MHz ADC. Similarly, supp-BPDN showed better reconstruction results than BPDN.

High-SFDR 100.8km ROF link with optical homodyne detection and genetic-algorithm-assisted digital demodulation.

Radio-over-fiber (ROF) link based on phase modulation and coherent detection has been widely proposed for linear transmission. Nowadays, there are increasing demands for long-distance analog radio-frequency (RF) signal transmission, as radars and broadcast systems. In this paper, a high spurious-free-dynamic-range (SFDR) analog coherent ROF link based on optical homodyne detection and genetic-algorithm-assisted digital demodulation is proposed and experimentally investigated. The ROF link is designed for transmitting RF signals ranging from 500 kHz to 100 MHz over a long-distance fiber under the environment of wide temperature. We test the link performance by transmitting different groups of two-tone signals (580 kHz and 600 kHz, 9 MHz and 10 MHz, 49 MHz and 50 MHz, 99 MHz and 100 MHz) over a 100.8-km single-mode fiber (SMF) under the temperature varying from -40°C to 70°C, the shot-noise-limited SFDR of the link are measured to be greater than 122 dB·Hz2/3.

Self-Calibrated Measurement of Frequency Response for Broadband Photodetectors Based on Two-Tone Photonic Sampling

A self-calibrated method to measuring the frequency responses of broadband photodetectors (PDs) is proposed based on photonic pulse sampling of two-tone microwave signal, with the help of a mode-locked laser diode (MLLD) and a Mach-Zehnder modulator (MZM). Firstly, the repetition frequency of the optical comb from the MLLD divides the whole measuring frequency range into several segments. Then, a close-spaced two-tone signal modulates every comb tooth through the MZM and generates the sum- and difference-frequency products, working as the probing signal to extract the frequency response of the PD in every segment. Hyper-fine frequency response of the PD at any frequency point can be obtained in every segment by subtly varying the center frequency of the two-tone signal while keeping the difference frequency fixed. Finally, the whole frequency response of the PD in ultra-wide frequency range is obtained by seamlessly stitching the segmental frequency responses. In our experiment, measurement of a commercial PD is demonstrated up to 49.765 GHz with an optical comb at the repetition frequency of 9.953 GHz and a two-tone modulation up to 4.9765 GHz. The measured results are compared with those by using the traditional methods to check accuracy. Moreover, the uneven responses of the MLLD and the MZM are fully subtracted, verifying the ultra-wideband, hyperfine and self-calibrated measurement of PDs based on the two-tone photonic sampling.

A Complexity-Reduced Harmonic-Cancellation Digital Predistortion for HF Transmitters

High-frequency (HF) transmitter implemented with the multioctave power amplifier (PA) is faced with the problem of high-order harmonics owing to the nonlinearity of the PA. In this letter, a complexity-reduced harmonic-cancellation digital predistortion (CR-HC-DPD) is proposed and a narrow pulse sampling (NPS) method is adopted for model identification. Compared with the previous HC-DPD scheme, the proposed CR-HC-DPD approach greatly decreases the number of sampling points used for modeling and, in turn, reduces the computational complexity. Measurement results on a class-AB GaN PA with a 600-Hz two-tone signal demonstrated that the CR-HC-DPD scheme canceled all the harmonics for being below −60 dBc with less than 5% complexity compared with the HC-DPD scheme.

A 24-GHz CMOS Power Amplifier With Dynamic Feedback and Adaptive Bias Controls

A 24-GHz power amplifier (PA) for 5G communication is implemented with a 65-nm bulk CMOS process, which adopts analog linearization techniques of dynamic feedback control (DFC) and an adaptive bias control (ADB). The DFC decreases feedbacks and the ADB increases a gate bias of common sources (CSs) with an increase of the input signal power so that the DFC improves gain flatness and peak efficiency, and the ADB increases high power gain, saturation power, and peak efficiency. These analog linearization techniques lower the IMD3 by improving the AM-AM and AM-phase modulation (PM) of the PA. The proposed PA shows a saturation power of 18.7 dBm, a 1-stage PA gain of 15.3 dB, and a peak PAE of 37.2% with the 24.29-GHz continuous wave signal measurement. It also shows a linear power of 12.9 dBm and a linear PAE of 14.8% with a two-tone signal measurement that has a center frequency of 24.49 GHz and a bandwidth of 80 MHz.