• Journal of Biomedical Engineering Research
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• v.19 no.2
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• pp.105-112
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• 1998

In this paper, several bandwidth sampling methods were compared using experimental result in which contains "multi-order sampling", which was proposed for envelope detections in RF ultrasonic signals. A "Quadrature sampling method" and "Second-order sampling method" were compared with it. The resultant image of second-order sampling method introduces too much error as compared with the result of quadrature sampling. But Multi-order sampling method, specialy 5-th sampling method showed quite good envelope detection property. This means that more economical and quite good performance digital beamforming system can be built by adopting this multi-order sampling method.s multi-order sampling method.

• Journal of the Korea Institute of Military Science and Technology
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• v.25 no.4
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• pp.347-354
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• 2022

The synthetic aperture radar(SAR) is an equipment that can acquire images in all weathers day and night based on radar signals. The on-board processor of satellite SAR generates transmission signal by digital signal processing, converts it into an analog signal and transmits to antenna. Until the transmission signal generated by on-board processor is output, the signal passes the transmission cables and analog devices. At this time, these hardware distort the signal and makes SAR performance worse. To improve the performance, pre-distortion technique is used. But, general pre-distortion using taylor series is not sufficient to compensate for the distortion. This paper suggests transmit signal design method with improved pre-distortion. This paper uses envelop sampling method and interpolation filter for frequency domain compensation. The proposed method accurately compensates the hardware distortion and reduces resource usage of FPGA. To analyze proposed method's performance, IRF characteristics are compared when the proposed method applies to signal with errors.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.10
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• pp.185-190
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• 2007

In this paper, minimum sampling rates and method of nonlinear characterization were suggested for low power, quasi-memoryless PAs. So far, the Nyquist rate of the input signal has been used for nonlinear PA modeling, and it is burdening Analog-to-digital converters for wideband signals. This paper shows that the input Nyquist rate sampling is not a necessary condition for successful modeling of quasi-memoryless PAs. Since this sampling requirement relives the bandwidth requirements for Analog-to-digital converters (ADCs) for feedback paths in digital pre-distortion systems, relatively low-cost ADcs can be used to identify nonlinear PAs for wideband signal transmission, even at severe aliasing conditions. Simulation results show that a generic memoryless nonlinear RF power amplifier with AMAM and AMPM distortion can be successfully identified at any sampling rates. Measurement results show the modeling error variation is less than 0.8dB over any sampling rates.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.5
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• pp.419-425
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• 2017

This paper presents CMOS UWB RFIC based radar system for high speed target detection. The system can achieve resolution of 15 cm and detection range of 15 m. For developed system, single chip CMOS UWB IC is implemented. To reduce the measuring and processing time, envelope detection and equivalent time sampling technique are used. Measurement results show that the bandwidth and center frequency of UWB pulse can be adjusted in the range of 0.5 GHz~1.0 GHz, 3.5 GHz~4.5 GHz, respectively. Signal processing time including scan time over 15 m distance is about $150{\mu}sec$.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.4
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• pp.34-40
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• 2004

In this paper, we have studied the OCT(Optical Coherence Tomography) system which has been advantages of high resolution, 2-D cross-sectional images, low cost and small size configuration. The characteristics of light source determine the resolution and coherence length. The light source has a commercial SLD with a central wavelength of 1,285 ill11, 35.3 nm(FWHM). The optical delay line is necessary to make equal with the optical path length to scattered light or reflected light from a sample. In order to make equal the optical path length, the stage that is attached to a reference mirror is controled by a step motor. And the interferometer is configured with the Michelson interferometer by using a single mode fiber, and the scanner can be focused on the sample by using a reference ann Also, the 2-dimension cross-sectional images were measured with scanning the transverse direction of the sample by using a step motor. After detecting the internal signal of lateral direction, a scanner is moved to obtain the cross-sectional image of 2-dimension by using step motor. A photodiode, which has high detection sensitivity and excellent noise characteristics has been used. The detected small signal has a noise and interference. After filtering and amplifying the signal, the output signal is demodulated the waveform And then, a cross-sectional image is seen through converting this signal into a digitalized signal by using an AID converter. The resolution of the sample is about 30${\mu}{\textrm}{m}$, which corresponds to the theoretical resolution. Also, the cross-sectional images of onion cells were measured in real time scheme.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2004.04a
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• pp.5-9
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• 2004

In this paper, we studied the OCT(Optical Coherence Tomography) system which it has been extensively studied because of having some advantages such as high resolution cross-sectional images, low cost, and small size configuration. A basic principle of OCT system is Michelson interferometer. The characteristics of light source determine the resolution and the transmission depth. As a results, the light source have a commercial SLD with a central wavelength of 1,285 nm and FWHM(Full Width at Half Maximum) of 35.3 nm. The optical delay line part is necessary to equal of the optical path length with scattered light or reflected light from sample. In order to equal the optical path length, the stage which is attached to reference mirror is moved linearly by step motor And the interferometer is configured with the Michelson interferometer using single mod fiber, the scanner can be focused of the sample by using the reference arm. Also, the 2-dimensional cross-sectional images were measured with scanning the transverse direction of the sample by using step motor. After detecting the internal signal of lateral direction at a paint of sample, scanner is moved to obtain the cross-sectional image of 2-demensional by using step motor. Photodiode has been used which has high detection sensitivity, excellent noise characteristic, and dynamic range from 800 nm to 1,700 nm. It is detected mixed small signal between noise and interference signal with high frequency After filtering and amplifying this signal, only envelope curve of interference signal is detected. And then, cross-sectional image is shown through converting this signal into digitalized signal using A／D converter. The resolution of the OCT system is about 30$\mu\textrm{m}$ which corresponds to the theoretical resolution. Also, the cross-sectional image of ping-pong ball is measured. The OCT system is configured with Michelson interferometer which has a low contrast because of reducing the power of feedback interference light. Such a problem is overcomed by using the improved inteferometer. Also, in order to obtain the cross-sectional image within a short time, it is necessary to reduce the measurement time for improving the optical delay line.