Large Signal Bandwidth Research Articles

Memory-electroluminescence for multiple action-potentials combination in bio-inspired afferent nerves

The development of optoelectronics mimicking the functions of the biological nervous system is important to artificial intelligence. This work demonstrates an optoelectronic, artificial, afferent-nerve strategy based on memory-electroluminescence spikes, which can realize multiple action-potentials combination through a single optical channel. The memory-electroluminescence spikes have diverse morphologies due to their history-dependent characteristics and can be used to encode distributed sensor signals. As the key to successful functioning of the optoelectronic, artificial afferent nerve, a driving mode for light-emitting diodes, namely, the non-carrier injection mode, is proposed, allowing it to drive nanoscale light-emitting diodes to generate a memory-electroluminescence spikes that has multiple sub-peaks. Moreover, multiplexing of the spikes can be obtained by using optical signals with different wavelengths, allowing for a large signal bandwidth, and the multiple action-potentials transmission process in afferent nerves can be demonstrated. Finally, sensor-position recognition with the bio-inspired afferent nerve is developed and shown to have a high recognition accuracy of 98.88%. This work demonstrates a strategy for mimicking biological afferent nerves and offers insights into the construction of artificial perception systems.

Preliminary Results of Marine Gravity Recovery by Tiangong-2 Interferometric Imaging Radar Altimeter

This paper presents for the first time the results of marine gravity recovery using the ocean observation data acquired by Tiangong-2 interferometric imaging radar altimeter (TG2 InIRA) which demonstrate not only the balanced accuracies of the north and east components of deflection of the vertical (DOV) as envisaged, but also the improved spatial resolutions of DOV compared with that by conventional altimeters (CAs). Moreover, much higher measurement efficiency owing to the wide-swath capability and the great potential in accuracy improvement of marine gravity field are also demonstrated. TG2 InIRA adopts the interferometry with short baseline and takes small incidence angles, by which wide-swath sea surface height (SSH) can be measured with high accuracy. Gravity recovery experiments in the Western Pacific area are conducted to demonstrate the performance, advantages and capability of TG2 InIRA. SSH data processing algorithms and DOV calculation have been designed by taking the wide-swath feature into account, based on which, the gravity anomalies are then calculated using the inverse Vening Meinesz formula. The derived gravity anomalies are compared with both the published gravity models and the shipborne gravity measurements. The results show that the accuracy of TG2 InIRA is equivalent to, or even a little better than, that of CAs. The fused gravity result using equal TG2 InIRA data and CAs data performs better than those using TG2 InIRA data alone or CAs data alone. Due to the signal bandwidth of TG2 InIRA is only 40 MHz which is much smaller than that of CAs, much higher accuracy can be hopefully achieved for future missions if larger signal bandwidth is used.

100 kHz Large-Signal Bandwidth GaN-Based 10 kVA Class-D Power Amplifier With 4.8 MHz Switching Frequency

Power amplifiers (PAs) are widely used, for example, to emulate the behavior of the power grid or electric machines under critical operating conditions, to measure the impedance of the power grid, or to generate specific impedance profiles in power-hardware-in-the-loop (P-HIL) tests. To accurately emulate dynamic effects and to characterize power electronic systems featuring wide-bandgap power semiconductors, PAs with very high output voltage quality and ever higher bandwidth (BW) at full output power are required, motivating the development of ultrahigh bandwidth power amplifiers (UHBW-PAs). While linear UHBW-PAs achieve very high signal fidelity and BW, they suffer from a tremendously bad efficiency, demanding large cooling effort and resulting in uneconomical operation, particular at high power levels and/or during long-term tests. Therefore, this article investigates possibilities for a switch-mode realization of UHBW-PAs with significantly higher efficiency and power density compared to existing solutions. There are two key concepts, namely series- and parallel-interleaving of multiple switching and/or converter cells, that allow to increase the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">effective</i> switching frequency relevant to output filtering without increasing the individual device switching frequency that determines the per device switching losses. This article analyzes comprehensively the advantages and disadvantages of a combination of series- and parallel-interleaving in terms of losses, volume and complexity scaling. Finally, a UHBW-PA with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {10}$</tex-math></inline-formula> kVA output power (single-phase), a nominal rms output voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {230}$</tex-math></inline-formula> V, a full-power BW of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {100}$</tex-math></inline-formula> kHz, very high output voltage quality (third and fifth harmonic <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {&lt; 2.5}$</tex-math></inline-formula> V and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {&lt; 1.2}$</tex-math></inline-formula> V, respectively), an efficiency <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {&gt;95\%}$</tex-math></inline-formula> , a power density of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {25}$</tex-math></inline-formula> kW/dm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {^{3}}$</tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {410}$</tex-math></inline-formula> W/in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {^{3}}$</tex-math></inline-formula> ), and a switching frequency of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {4.8}$</tex-math></inline-formula> MHz is presented. A hardware demonstrator is built and extensive measurements verify the system performance and confirm the calculation from the initial analyses with loss models.

OFDM Radar With Subcarrier Aliasing—Reducing the ADC Sampling Frequency Without Losing Range Resolution

Many radar applications require a high range resolution, entailing the necessity for a large signal bandwidth. When employing an orthogonal frequency-division multiplexing (OFDM) radar system in its standard implementation, the radar system must operate at a high sampling frequency to ensure covering the entire signal bandwidth, thus imposing significant challenges on its implementation. Therefore, methods for reducing the sampling frequency are topic of recent research. In this work, a method for reducing the analog-to-digital converter (ADC) sampling frequency at the receiver without losing range resolution is proposed. This is achieved by activating only a fraction of the subcarriers at the transmitter, while simultaneously allowing for systematic aliasing due to undersampling in the receiver. This aliasing is designed such that the active subcarriers do not interfere with each other, which ensures a simple separation of them in the frequency domain. The proposed concept, denoted as subcarrier aliasing (SA), allows reducing the ADC sampling frequency in the receiver, but lacks in reducing the digital-to-analog converter (DAC) sampling frequency in the transmitter. However, the key asset of SA-OFDM lies in the properties of its waveform, making it especially suitable for joint radar and communication applications over other waveforms, e.g., stepped-carrier OFDM.

RIS-Enabled SISO Localization Under User Mobility and Spatial-Wideband Effects

Reconfigurable intelligent surface (RIS) is a promising technological enabler for the 6th generation (6G) of wireless systems with applications in localization and communication. In this paper, we consider the problem of positioning a single-antenna user in 3D space based on the received signal from a single-antenna base station and reflected signal from an RIS by taking into account the mobility of the user and spatial-wideband (WB) effects. To do so, we first derive the spatial-WB channel model under the far-field assumption, for orthogonal frequency-division multiplexing signal transmission with the user having a constant velocity. We derive the Cramer Rao bounds to serve as a benchmark. Furthermore, we devise a low-complexity estimator that attains the bounds in high signal-to-noise ratios. Our estimator neglects the spatial-WB effects and deals with the user mobility by estimating the radial velocities and compensating for their effects in an iterative fashion. We show that the spatial-WB effects can degrade the localization accuracy for large RIS sizes and large signal bandwidths as the direction of arrival or departure deviate from the RIS normal. In particular, for a 64X64 RIS, the proposed estimator is resilient against the spatial-WB effects up to 140 MHz bandwidth. Regarding user mobility, our results suggest that the velocity of the user influences neither the bounds nor the accuracy of our estimator. Specifically, we observe that the state of the user with a high speed (42 m/s) can be estimated virtually with the same accuracy as a static user.

A modified broadband weighted magnitude‐selective behavioral model for digital predistortion of radio frequency power amplifiers

With the increasing demand for large signal bandwidth in communication systems, the complexity of the behavioral model of power amplifier (PA) will also increase. In this paper, a modified weighted magnitude-selective model based on magnitude-selective affine (MSA) function based model and weighted memory polynomial model is proposed to ensure low complexity and good modeling performance under broadband signal excitation. This model is constructed by using the power-dependent weighted function instead of the sum of multiple MSA functions in MSA. It can not only be used to solve the nonlinearity of PA excited by large bandwidth signal but also reducing the model coefficients without affecting the modeling performance makes the digital predistortion of large bandwidth signals more simple and effective. In this paper, a 100 MHz broadband signal is used for simulation and experiment on a wideband PA. The results show that for the same performance the WMA model required approximately 80% less coefficients.

Efficient Joint DOA and TOA Estimation for Indoor Positioning With 5G Picocell Base Stations

The ubiquity, large bandwidth, and spatial diversity of the fifth generation (5G) cellular signal render it a promising candidate for accurate positioning in indoor environments where the global navigation satellite system (GNSS) signal is absent. In this paper, a joint angle and delay estimation (JADE) scheme is designed for 5G picocell base stations (gNBs) which addresses two crucial issues to make it both effective and efficient in realistic indoor environments. Firstly, the direction-dependence of the array modeling error for picocell gNB as well as its impact on JADE is revealed. This error is mitigated by fitting the array response measurements to a vector-valued function and pre-calibrating the ideal steering-vector with the fitted function. Secondly, based on the deployment reality that 5G picocell gNBs only have a small-scale antenna array but have a large signal bandwidth, the proposed scheme decouples the estimation of time-of-arrival (TOA) and direction-of-arrival (DOA) to reduce the huge complexity induced by two-dimensional joint processing. It employs the iterative-adaptive-approach to resolve multipath signals in the TOA domain, followed by a conventional beamformer to retrieve the desired line-of-sight DOA. By further exploiting a dimension-reducing pre-processing module and accelerating spectrum computing by fast Fourier transforms, an efficient implementation is achieved for real-time JADE. Numerical simulations demonstrate the superiority of the proposed method in terms of DOA estimation accuracy. Field tests show that a triangulation positioning error of 0.44 m is achieved for 90% cases using only DOAs estimated at two separated receiving points.

Track and Hold Amplifier Investigation for 100-GHz Bandwidth, 200-GS/s ADC Front Ends

We report on the track and hold amplifier (THA) topology choice and design details of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times $ </tex-math></inline-formula> time-interleaved 200-GS/s SiGe BiCMOS ADC front end with a measured SNDR > 25 dB up to 63 GHz, and with a large signal bandwidth of 58 GHz when subsampling at 5 GS/s. We show that by replacing the current-mode-logic (CML) MOS switch with a quasi-CML switch and increasing the tail current, a THA with a measured small-signal bandwidth of 101 GHz is obtained in the same 55-nm SiGe BiCMOS technology. The ADC front end bandwidth could thus be further improved at the same sampling rate.

Secrecy Capacity of Time Reversal Beamforming for Multi-User MIMO System under Spatial Correlation

In this paper, for strengthening the security of wireless transmission system, the time reversal (TR) beamforming method is proposed for the downlink of multi-user MIMO system with multiple users who potentially act as eavesdroppers. We develop a multi-input, single-output, multi-eavesdropper (MISOME) wiretap channel model in which Rayleigh fading and spatial correlation are taken into account. Using the proposed model, we further analyze the confidentiality provided by TR beamforming and we use achievable secrecy rates as our performance metrics. In particular, we derive novel closed-formed expressions for the average secrecy-SINR and the mean secrecy sum-rate in order to characterize the influences of propagation conditions on network secrecy metrics. These expressions provide deeper insights into the impact of network interference on communication confidentiality. We find that TR beamforming can deliver the maximum secrecy capacity potential in uncorrelated Rayleigh channels and achieve perfect confidential communication without any extra secrecy cost. On the other hand, even weak inter-user correlation may cause a significant loss of achievable secrecy sum-rate and therefore result in high secrecy cost. But benefiting more from larger signal bandwidth and rich-scattering environment, the TR beamforming technique is still an attractive and cost-effective solution for low-power indoor applications.

Narrowband and wideband EMW path loss in underwater wireless sensor network

PurposeUtilization of electromagnetic wave (EMW) sensors in an underwater environment has the potential to increase the data rate compared to acoustic-based sensors because of the ability to use larger signal bandwidth. Nevertheless, EMW signals has the drawback of large signal attenuation in underwater, attributed to the high relative permittivity and conductivity of water compared to the atmosphere, hence employment of wide signal bandwidth is necessary to balance the data rate-attenuation trade-off. The purpose of this paper is to analyze the characteristics of both narrowband and wideband EMW signal propagation underwater and devise a path loss model for both cases.Design/methodology/approachPath loss measurement was conducted using a point-to-point configuration in a laboratory water tank while transmitting narrowband and wideband signals between a pair of wideband underwater antennas. The wideband underwater antennas use buffer-layer structures as the impedance matching layer to optimize the antenna performance when operating underwater. The path loss for narrowband signal was modeled using a multi-layer propagation equation in lossy medium considering losses at the medium boundaries. For the case of the wideband signal, a modified version of the model introducing power integration over bandwidth is adopted. These models were formulated through numerical simulations and verified by measurements.FindingsThe measured narrowband path loss marked an 80 dB attenuation using 800 MHz at 2 m distance. The proposed narrowband model agrees well with the measurements, with approximately 3 dB modeling error. Utilization of the proposed wideband path loss model resulted in a reduction of the gradient of the path loss curve compared to the case of the narrowband signal. The measured wideband path loss at 2 m distance underwater was approximately −65 dB, which has been shown to enable a working signal-to-noise ratio of 15 dB. This proves the potential of realizing high data rate transmission using the wideband signal.Originality/valueThe paper proposed a wideband propagation model for an underwater EMW sensor network, using power integration over bandwidth. The effectiveness of using wideband EMW signals in reducing path loss is highlighted, which is seldom discussed in the literature. This result will be of useful reference for using wideband signals in designing a high data rate transmission system in underwater wireless sensor networks, for example, in link budget, performance estimation and parameter design of suitable transmission scheme.

Limitations and Implementation Strategies of Interstage Matching in a 6-W, 28–38-GHz GaN Power Amplifier MMIC

In this article, we summarize the theoretical matching boundaries and show the limitations they implicate for real-world amplifier design. Starting with a common schematic prototype, we investigate the question of how to realize its electrical response in a densely routed, massively parallelized layout. To that end, we develop a comprehensive study on the application of space-mapping techniques toward the design of high-power amplifiers (HPAs). We derive three reference design procedures and compare their performance in terms of convergence, speed, and practicality when laying out a densely routed HPA interstage matching network. Subsequently, we demonstrate the usefulness of the study by designing the networks of a compact three-stage eight-way wideband HPA in the Ka-band. The processed monolithic microwave integrated circuit features a 1-dB large-signal bandwidth of more than 11 GHz (a fractional bandwidth of 32.8%) and thus covers most of the Ka-band with an output power exceeding 6 W in 3 dB of gain compression. This demonstrates the highest combination of power and bandwidth to date using a reactively matched topology in the Ka-band.

Frequency Multiplier-Based Millimeter-Wave Vector Signal Transmitter Using Digital Predistortion With Constrained Feedback Bandwidth

We have demonstrated a frequency multiplier-based multiplying transmitter (MT) architecture, which shows the transmission of wideband modulated signals from the lower frequency band to the millimeter-wave (mm-wave) through the frequency multiplier directly is a viable option. To compensate for the severe nonlinear distortions exhibited by the frequency multiplier in a more efficient way, a two-stage cascaded digital predistortion (DPD) scheme with constrained feedback bandwidth is proposed. The complexity-reduced generalized memory polynomial (GMP) and $N$ th-order power/root module are used for nonlinear behavioral modeling. Furthermore, the spectral extrapolation and band-divided (BD) modeling methods are employed to achieve more accurate linearization performance of the frequency multiplier over the limited feedback bandwidth. The MT experimental system with an active frequency quadrupler at the Q-band was set up to evaluate the linearization capacity of the proposed BD $N$ th-order cascaded complexity-reduced GMP (BD-N-CGMP) DPD scheme. In the test for 24-MHz bandwidth 16 quadrature amplitude modulation (QAM) signal, the frequency quadrupler’s linearized output at 48.6 GHz with error vector magnitude (EVM) of 1.94% and adjacent channel power ratio (ACPR) of −47.2 dBc could be achieved, even when the feedback bandwidth was limited from 480 to 78 MHz. This demonstrated system significantly decreased the requirement of the digital-to-analog converters (DACs) and analog-to-digital converters (ADCs) sampling rate, and showed promising performances for future MT architecture at mm-wave and sub-terahertz (sub-THz) frequencies with large signal bandwidth.

A new method for improving the inductively coupled data transmission rate of mooring buoy based on carrier signal frequency selection

In the inductively coupled data transmission system of the mooring buoy, the carrier signal frequency of the transmission channel is limited due to the inherent characteristics of the system, resulting in limited channel bandwidth. The limited channel bandwidth limits the increase in inductively coupled data transmission rate. In order to improve the inductively coupled data transmission rate of mooring buoy as much as possible without damaging the data transmission performance, a new method was proposed in this paper. The method is proposed to improve the data transmission rate by selecting the appropriate carrier signal frequencies based on the principle of maximizing the amplitude value of amplitude-frequency characteristic curve of the system. Research has been done according to this method as follows. Firstly, according to the inductively coupled transmission mooring buoy structure, the inductively coupled data transmission circuit model was established. The binary frequency shift keying (2FSK) digital signal modulation mode was selected. Through theoretical analysis, the relation between the carrier signal frequency and the data transmission performance, the relation between the carrier signal frequency and the 2FSK signal bandwidth were obtained. Secondly, the performance and the bandwidth of the signal transmission were studied for the inherent characteristics of the actual inductively coupled data transmission system. The amplitude-frequency characteristic of the system was analyzed by experiments. By selecting the appropriate carrier signal frequency parameters, an excellent data transmission performance was guaranteed and a large 2FSK signal bandwidth was obtained. Finally, an inductively coupled data transmission rate optimization experiment and a bit error rate analysis experiment were designed and carried out. The results show that the high-speed and reliable data transmission of the system was realized and the rate can reach 100 kbps.

Robust Data Detection for MIMO Systems With One-Bit ADCs: A Reinforcement Learning Approach

The use of one-bit analog-to-digital converters (ADCs) at a receiver is a power-efficient solution for future wireless systems operating with a large signal bandwidth and/or a massive number of receive radio frequency chains. This solution, however, induces a high channel estimation error and therefore makes it difficult to perform the optimal data detection that requires perfect knowledge of likelihood functions at the receiver. In this paper, we propose a likelihood function learning method for multiple-input multiple-output (MIMO) systems with one-bit ADCs using a reinforcement learning approach. The key idea is to exploit input-output samples obtained from data detection, to compensate the mismatch in the likelihood function. The underlying difficulty of this idea is a label uncertainty in the samples caused by a data detection error. To resolve this problem, we define a Markov decision process (MDP) to maximize the accuracy of the likelihood function learned from the samples. We then develop a reinforcement learning algorithm that efficiently finds the optimal policy by approximating the transition function and the optimal state of the MDP. Simulation results demonstrate that the proposed method provides significant performance gains for the optimal data detection methods that suffer from the mismatch in the likelihood function.

Sampling Rate Reduction for Digital Predistortion of Broadband RF Power Amplifiers

In this article, we present a novel technique to build digital predistorters that can linearize broadband power amplifiers (PAs) using reduced sampling rates. In contrast to conventional digital predistortion (DPD) where oversampling is necessary to avoid aliasing effect, the proposed method cancels the aliasing distortion using a sliced multistage cancellation scheme. A large reduction of sampling rate can be achieved in digital implementation of DPD, significantly reducing power consumption and implementation cost. Experimental results show that a DPD with a sampling rate of merely 1.5×, instead of 5×, signal bandwidth, can still produce satisfactory performance within the linearization bandwidth but consume only one-third of power, compared with that using the conventional approaches. The proposed technique provides a promising solution for the next-generation 5G systems, where large signal bandwidths are required.

A 4-GHz Low-Power, Multi-User Approximate Zero-IF FM-UWB Transceiver for IoT

This paper presents a 4-GHz FM ultra-wideband (UWB) transceiver designed for the Internet of Things and body area network applications. Robustness to interferers and low power spectral density allow FM-UWB to coexist with narrowband radios, while large signal bandwidth strongly relaxes constraints on the frequency synthesis blocks enabling the full integration of the radio at low power. The transceiver, integrated with a 65-nm standard CMOS technology, consists of a transmitter and two receivers that provide two modes of operation. The transmitter consumes 575 μW while transmitting a 100-kb/s signal at 4 GHz at an output power of -11.4 dBm. A single RF IO pad is used and the fully integrated matching network is shared among the transmitter and the receivers. The low-power receiver consumes 267 μW and provides a single communication channel at 100 kb/s in the 4-GHz band, with a -57-dBm sensitivity. The second receiver provides a better performance and takes full advantage of the FM-UWB features, as it implements wireless communication with up to four parallel channels sharing the same RF band. It consumes 550 μW and provides -68-dBm sensitivity at 100 kb/s per channel. The FM-UWB architecture can tolerate a very large reference frequency offset of up to ±8000 ppm. This unique feature potentially allows for a quartzfree synthesizer, resulting in a radio with no off-chip components.

Photonic implementation of a highly reconfigurable wideband RF spectral shaper

In emerging Radio Frequency (RF) systems, the capability to dynamically process a wide range of frequency bands is highly desired due to the multi-frequency operation in multi-function RF systems and the large signal bandwidth usage associated with data-intensive applications. As the operation bandwidth increases, the frequency response uniformity of both RF components and microwave transmission medium degrades, that leads to the need of broadband RF spectrum equalization to support wideband high-quality services. Therefore, a wideband and reconfigurable RF spectral shaper is highly desired for dynamically manipulating the RF spectrum from low- to high-frequency band. Unfortunately, it is very challenging for conventional RF electronics to achieve dynamic spectral control over a wide operation bandwidth. In this paper, we take advantages of photonics and demonstrate a highly-reconfigurable RF spectral shaper that can manipulate an RF spectrum of tens of GHz wide. The proposed scheme is based on a microwave photonic filter architecture with multiple tunable, reconfigurable and switchable passbands. By manipulating the shape, bandwidth, and frequency of the passbands, highly reconfigurable wideband frequency responses for spectral equalization are experimentally achieved, covering the entire 0 to 10 GHz frequency range with adjustable attenuation up to 40 dB. Various RF equalization functions including tunable positive/negative slope, non/inverted parabolic, and multi-point spectral control with tunable floor are experimentally demonstrated using the proposed system. Several of the demonstrated RF functions have also been applied to arbitrary pulse shaping. The RF spectral shaper can be tuned to adapt to different scenarios dynamically, which could benefit a variety of applications including RF signal processing systems and communication networks.

Multifrequency Subpulse SAR: Exploiting Chirp Bandwidth for an Increased Coverage

Spatial resolution and swath width are fundamental quality parameters for spaceborne synthetic aperture radar (SAR) products. They have driven the research on new spaceborne SAR system concepts in the last decades, and a new generation of SAR systems is emerging. Main feature of these future systems is the use of multiple digital channels and new SAR processing techniques. A further characteristic is that they can resort to a large radar signal bandwidth. In this letter, a novel SAR operational mode is presented, denoted as multifrequency subpulse (MFSP). The MFSP exploits the available radar signal bandwidth to increase the imaged swath extension, without the emergence of range ambiguities. The proposed approach is explained both theoretically and by a design example, based on the future German X-band SAR system, HRWS. Moreover, the achievable SAR imaging quality is investigated.

DESIGN AND VERIFICATION FLOW OF MULTI-STAGE SIGMA-DELTA ADC DIGITAL CORE

There is a need for analog-to-digital converters with high signal-to-noise ratio and large signal bandwidth to solve a number of radiolocation problems. Developing such ADC is a challenge in the analog core, digital core and verification. The design flow of the digital core must take into account the possibility of changing the analog core specification at any design stage, provide the ability to quickly obtain the synthesizable RTL code of the device and conduct its functional verification. Automation tools were used to reduce the time spent on development and verification. This article describes the developed software package that generates the synthesizable RTL code and the verification environment configurations for each stage of development of the analog core of the multi-stage sigma-delta ADC.

A &lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;${D}$ &lt;/tex-math&gt; &lt;/inline-formula&gt;-Band Digital Transmitter with 64-QAM and OFDM Free-Space Constellation Formation

A ${D}$ -band I/Q RF-DAC featuring two 6-bit DAC elements driven in quadrature, each with its own on-die antenna, and a total effective isotropic radiated power (EIRP) of 13.2 dBm, is demonstrated in a 45-nm SOI-CMOS technology. The carrier signal is first amplified by the 30-dB gain LO path and is directly modulated by the 12 baseband bit streams, without linear upconversion or power amplification. QPSK, 8-PSK, 16-QAM, 32-QAM, and 64-QAM single-carrier (SC) and OFDM constellations are formed in free space and measured above the die at data rates up to 12 Gb/s and at distances over 15 cm. The large-signal bandwidth—from the carrier input pad to the output of the transmitter above the antennas—is 130–142 GHz and was obtained by sweeping the frequency of the ${D}$ -band external carrier, modulating it on die at 0.4 Gb/s using 16-QAM format, and measuring the error vector magnitude (EVM) with an instrumentation receiver. The highest data rate of 12 Gb/s was measured for QPSK SC modulation with a corresponding EVM of −12.2 dB. Lower maximum data rates of 7 Gb/s with −14.3-dB EVM and 3.6 Gb/s with −19-dB EVM were observed for 16-QAM and 64-QAM formats, respectively. Spectral shaping and OFDM transmission were also demonstrated at up to 2.5 Gb/s. The prototype consumes a total of 1.25 W, with an energy efficiency of 104 pJ/b.