Wideband Linear Frequency Modulated Waveform Compensation Using System Predistortion and Phase Coefficients Extraction Method

Kim, Seyoung; Myung, Noh‐Hoon

doi:10.1109/lmwc.2007.908061

Cited by 19 publications

(3 citation statements)

References 4 publications

(9 reference statements)

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“…Therefore, an openloop concept, such as the predistortion technique [15], is used to realize the FM time in the range of 10-100 µs. The nonlinearity of a VCO's output frequency versus tuning voltage is curve-fitted as a polynomial with several coefficients and a VCO tuning voltage waveform, which will linearize FM, is calculated based on the coefficients [25]. Because low-order polynomial fitting to nonlinear curves is inaccurate over a wide frequency range, most open-loop-based LFM systems operate in a narrow bandwidth.…”

Section: Plasma Movementmentioning

confidence: 99%

Fluctuation effects on the plasma density profiles measured by using a frequency modulated continuous wave reflectometer

Seo¹

2022

Plasma Phys. Control. Fusion

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Scanning diagnostics require that the target should not move during scan for the correct measurement. However, even if a frequency modulated continuous wave (FMCW) reflectometer is operated with a frequency modulation (FM) time of 10 μs, the high temperature fusion plasma is fluctuating even for such a short duration. The fluctuation effect on the reflectometer measurements is investigated by simulating the reflectometer response for various plasma conditions. Because the uncertainty of zero density position might give additional distortion to the reconstructed profile, this effect is also investigated. The simulation results show that the density profile reconstruction is not very sensitive to the zero density position but very sensitive to the fluctuations. The FM rate must be 100 times faster than the fluctuation frequency to suppress the radial distortion below about 20 % of the fluctuation radial amplitude. An algorithm is proposed to reduce the distortion more effectively even at much lower FM rate. The distortion is canceled out by averaging two profiles one of which is measured as increasing the frequency and the other as decreasing the frequency. This algorithm is applied to the experimental data analysis to confirm the simulation results. Through this study, it is concluded that the FM time of the KSTAR reflectometer should be reduced to 2 μs$s to be able to measure the H-mode plasma density profiles.

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Section: Plasma Movementmentioning

confidence: 99%

Fluctuation effects on the plasma density profiles measured by using a frequency modulated continuous wave reflectometer

Seo¹

2022

Plasma Phys. Control. Fusion

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“…A previous research shows that the parameter extraction technique is reliable, but it is cumbersome procedure [6]. In this system, the amplitude is compensated by the impulse response function of the DAC.…”

Section: Fmcw Radar Mode Operationmentioning

confidence: 99%

An FMCW and chirp pulse‐doppler radar system for surveillance in X‐band

Park

2013

Micro & Optical Tech Letters

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A narrow band radar system based on a field programmable gate array is proposed for dual‐mode operation.Frequency‐modulated continuous‐wave (FMCW) radar mode is for short‐range target detection and pulse‐Doppler (PD) radar mode is for long‐range target detection. Precomputed codes are used to generate linear frequency modulation signals in both FMCW and PD radar mode. The bandwidths of FMCW and PD radar modes are 10 and 1 MHz. Experiments have been carried out to confirm the system operation. In FMCW radar mode, nonlinear amplitude response can be corrected by precomputed code. In PD radar mode, the RX signals have been checked in the pulse width of 4 μs with a compressed echo signal response. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:474–479, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27343

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“…In a high-resolution SAR system, the LFM generator produces in-phase/quadrature (I/Q) signals of a wide bandwidth to simplify the implementation [22]. After they have been filtered through low-pass filters, the I/Q signals are modulated by a quadrature modulation unit in a radio-frequency (RF) circuit to the carrier frequency.…”

Section: Introductionmentioning

confidence: 99%

A Novel Real-Time Processing Wideband Waveform Generator of Airborne Synthetic Aperture Radar

Chen,

Wei,

et al. 2024

Remote Sensing

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This paper investigates a real-time process generator of wideband signals, which calculates waveforms in a field-programmable gate array (FPGA) using the high-level synthesis (HLS) method. To obtain high-resolution and wide-swath images, the generator must produce multiple modes of large time-bandwidth product (TBP) linear frequency modulation (LFM) signals. However, the conventional storage method is unrealistic as it requires huge storage resources to save pre-computed waveforms. Therefore, this paper proposes a novel processing approach that calculates waveforms in real-time based simply on parameters such as the sampling frequency, bandwidth, and time width. Additionally, this paper implements predistortion through the polynomial curve to approximate phase errors of the system. The parallelizing process in the FPGA is necessary to satisfy the high-speed requirement of a digital-to-analog converter (DAC); however, repeatedly multiplexing real-time calculation consumes extensive logic and DSP resources, potentially exceeding FPGA limitations. To address this, this paper proposes a piecewise linear algorithm to conserve resources, which processes the polynomial only once, acquires the difference in two adjacent values through the register and pipeline, and then adds this increment to facilitate parallel computations. The performance of this proposed generator is validated through simulation and implemented in experiments with an X-band airborne SAR system.

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Wideband Linear Frequency Modulated Waveform Compensation Using System Predistortion and Phase Coefficients Extraction Method

Cited by 19 publications

References 4 publications

Fluctuation effects on the plasma density profiles measured by using a frequency modulated continuous wave reflectometer

Fluctuation effects on the plasma density profiles measured by using a frequency modulated continuous wave reflectometer

An FMCW and chirp pulse‐doppler radar system for surveillance in X‐band

A Novel Real-Time Processing Wideband Waveform Generator of Airborne Synthetic Aperture Radar

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