THE DIGITAL WIDE BAND CHIRP PULSE GENERATOR AND PROCESSOR FOR PI-SAR2

BRIEF CONCLUSION This paper shows the digital wide band chirp pulse generator and processor for Pi-SAR2, and the history of its development at NEC. This generator and processor can generate the 150, 300 or 500MHz bandwidth chirp pulse and process the same bandwidth video signal. The offset video method is applied for this component in order to achieve small phase error, instead of I/Q video method for the conventional SAR system. Pi-SAR2 realized 0.3m resolution with the 500 MHz bandwidth by this component. After that, we had developed the experimental model of the digital wide band chirp pulse generator and processor for the airborne and spaceborne SAR in 2005. This model adopted the offset video method for the high performance, instead of the conventional I/Q video method. It had capabilities to generate the 300MHz bandwidth chirp pulse and to process video signals at 720MHz sampling rate for the input with 300MHz bandwidth. For the conventional signal generator by the I/Q video method, it is necessary to generate the In-phase(I) and Quadraturephase(Q) signals and to mix two signals using an analog I/Q modulator. The frequency of output signal from the wide band chirp generator is much higher than that of the conventional narrow one. Therefore mutual timing condition should be strictly required for the generation of two signals (I and Q) and its mixing. Otherwise the phase error of I/Q modulation would be large. On the other hand, it is not necessary to mix I/Q signals for the chirp pulse generation with the offset video method. Therefore there is no phase error of I/Q modulation in this method. This i

Monostatic Airborne Synthetic Aperture Radar Using Commercial WiMAX Transceivers In the License-exempt Spectrum

The past half-century witnessed an evolution of synthetic aperture radar (SAR). Boosted by digital signal processing (DSP), a variety of SAR imaging algorithms have been developed, in which the wavenumber domain algorithm is mature for airborne SAR and independent of signal waveforms. Apart from the algorithm development, there is a growing interest in how to acquire the raw data of targets’ echoes before the DSP for SAR imaging in a cost-effective way. For the data acquisition, various studies over the past 15 years have shed light on utilizing the signal generated from the ubiquitous broadband wireless technology – orthogonal frequency division multiplexing (OFDM). However, the purpose of this thesis is to enable commercial OFDM-based wireless systems to work as an airborne SAR sensor. The unlicensed devices of Worldwide interoperability for Microwave Access (WiMAX) are the first option, owing to their accessibility, similarity and economy. This dissertation first demonstrates the feasibility of applying WiMAX to SAR by discussing their similar features. Despite the similarities they share, the compatibility of the two technologies is undermined by a series of problems resulted from WiMAX transceiver mechanisms and industrial rules for radiated power. In order to directly apply commercial WiMAX base station transceivers in unlicensed band to airborne SAR application, we propose a radio-frequency (RF) front design together with a signal processing means. To be specific, a double-pole, double-throw (DPDT) switch is inserted between an antenna and two WiMAX transceivers for generating pulsed signal. By simulations, the transmitted power of the SAR sensor is lower than 0dBm, while its imaging range can be over 10km for targets with relatively large radar cross section (RCS), such as a ship. Its range resolution is 9.6m whereas its cross-range resolution is finer than 1m. Equipped with the multi-mode, this SAR sensor is further enhanced to satisfy the requirements of diversified SAR applications. For example, the width of the scan-mode SAR’s range swath is 2.1km, over five times the width of other modes. Vital developed Matlab code is given in Appendix D, and its correctness is shown by comparing with the image of chirped SAR. To summarize, the significance of this dissertation is to propose, for the first time, a design of directly leveraging commercial OFDM-based systems for airborne SAR imaging. Compared with existing designs of airborne SAR, it is a promising low-cost solution