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위상 오차 보상을 이용한 DDS 첩 신호 발생기 연구
- Alternative Title
- Heein Yang
- Author(s)
- Yang Heein
- Alternative Author(s)
- Heein Yang
- Advisor
- 김재현
- Department
- 일반대학원 전자공학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2015-02
- Language
- eng
- Keyword
- DDS
- Alternative Abstract
- As a kind of active sensor, the synthetic aperture radar (SAR) uses microwave signal for its own illumination source. Due to the property of microwave, SAR is recognized as a powerful surveillance radar and it provides the high-resolution images of a target regardless of the weather conditions. Therefore, several countries already have and use the satellite on-board SAR. Loaded on unmanned aerial vehicles (UAVs) or satellites with small antenna (usually 2.5 - 10 m long), SAR transmits and receives the microwave signals in sequence. SAR system o_x000B_ffers a high range resolution up to 0.5m. SAR uses a chirp signal its frequency increases or decreases linearly according to the time. It is also called linear frequency modulation (LFM) signal and it can provide the signal with widebandwidth. With the help of pulse compression technique, SAR system can achieve the high range resolution with relatively small power and wide-bandwidth. In this thesis, a chirp signal generator based on direct digital synthesizer (DDS) structure is designed. There are several types of chirp signal generators based on DDS, however, DDS itself has the phase error because of the truncation. Consequently, the phase error increases spurious of whole signal and decreases the signal to noise ratio (SNR) which defines the resolution of SAR system. Undesired signal, the spurious, is often called spurs and it is occurred from spectrum regrowth components in side-lobe. Compared with ideal chirp signal, the conventional DDS chirp signal generator has 28 dB lower spectrum amplitude in maximum. We propose the phase error compensation method that eliminates phase error ideally and decreases spurious components significantly. To eliminate the phase error, we extract the phase components from both ideal and DDS chirp signals. Next we define the phase error by subtracting the each of phase value. The conventional DDS chirp signal generator only has the phase error of 1st order polynomial and it indicates that DDS has the error in frequency accumulator. Because DDS generates the 1st order polynomial as the frequency accumulator output. The coeffi_x000E_cient of 1st order polynomial is modeled as frequency o_x000B_set value and we inserted this value between the frequency accumulator and the mod mod(2_x0019_) operator. Successfully the phase signal has been compensated. Proposed chirp signal generator has been investigated in the respect of time and frequency domain signal plots and impulse response function (IRF). In time and frequency domain signal plot, a proposed chirp signal generator output traces the ideal chirp signal plot similarly. In addition, an IRF has been investigated to evaluate the chirp signal generator performance. Compared with the conventional DDS, a peak side-lobe ratio (PSLR) has been increased 0:2645 dB, and integrated sidelobe ratio (ISLR) has been enhanced 0:1788 dB.
- Fulltext
- Appears in Collections:
- Graduate School of Ajou University > Department of Electronic Engineering > 3. Theses(Master)
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