Yee Kit Chan

AN INTRODUCTION TO SYNTHETIC APERTURE RADAR (SAR)

This paper outlines basic principle of Synthetic Aperture Radar (SAR). Matched filter approaches for processing the received data and pulse compression technique are presented. Besides the SAR radar equation, the linear frequency modulation (LFM) waveform and matched filter response are also discussed. Finally the system design consideration of various parameters and aspects are also highlighted.

A new unmanned aerial vehicle synthetic aperture radar for environmental monitoring

A new Unmanned Aerial Vehicle (UAV) Synthetic Aperture Radar (SAR) has been developed at Multimedia University, in collaboration with Agency of Remote Sensing Malaysia. The SAR operates at C-band, single V V -polarization, with 5m £ 5m spatial resolution. Its unique features include compact in size, light weight, low power and capable of performing real-time imaging. A series of fleld measurements and ∞ight tests has been conducted and good quality SAR images have been obtained. The system will be used for monitoring and management of earth resources such as paddy flelds, oil palm plantation and soil surface. This paper reports the system design and development, as well as some preliminary results of the UAVSAR.

TRANSMITTER AND RECEIVER DESIGN OF AN EXPERIMENTAL AIRBORNE SYNTHETIC APERTURE RADAR SENSOR

An Experimental Airborne Synthetic Aperture Radar (SAR) Sensor has been designed and,developed at Multimedia University, Malaysia. The airborne system is an inexpensive C-band, single polarization, linear-FM airborne radar sensor. An innovative cancellation network is implemented to overcome the poor isolation of the circulator thus allow a single antenna to be used for transmitting and receiving the radar signal. The system will be used for monitoring and management of earth resources such as paddy fields, oil palm plantation and soil surface. This paper highlights the design and development of the SAR transmitter and receiver, as well as the evaluation result of the sensor. Calibration has been performed in the laboratory to verify the performance of the radar sensor. External calibration is accomplished by using three artificial point targets, i.e., 12” conducting sphere, 4”×8” dihedral corner reflector and 8” trihedral corner reflector. The field measurements are conducted in an empty car park, which is a low reflection outdoor environment. Both range detection and radar cross section (RCS) measurement capability are verified in the field experiments.

SIDELOBES REDUCTION USING SIMPLE TWO AND TRI-STAGES NON LINEAR FREQUENCY MODULATION (NLFM)

The Linear Frequency Modulation (LFM) waveform is the most commonly and extensively used signal in practical radar system. However a compressed LFM signal at the receiver will produce the flrst sidelobe at a level of i13dB to the peak of the main lobe. A weighting function is needed to apply in order to reduce the sidelobes. However, the penalty of mismatch loss is clearly evident. It may reduce output SNR, typically by 1 to 2dB. Every single dB of additional SNR can have great efiects in reducing false alarm rates in target detection applications. In an efiort to achieve low autocorrelation sidelobe level without applying weighting function, Non-Linear Frequency Modulation (NLFM) signal has been investigated. This paper describes the sidelobe reduction techniques using simple two-stage FM waveform, modifled two-stage FM waveform and tri-stage FM waveform. Simulation results of the proposed NLFM signal are presented. Sidelobe reduction of more than i19dB can be achieved by this design without any weighting technique applied.

THE MASAR PROJECT: DESIGN AND DEVELOPMENT

In 2002, the MASAR (Malaysian Airborne Synthetic Aperture Radar) project was initiated at Multimedia University (MMU), in collaboration with the Malaysian Centre for Remote Sensing (MACRES). The main objective of this project is to construct an instrument for earth resource monitoring in Malaysia. The proposed SAR system is a C-band, single polarization, linear FM radar. This paper outlines the major design issues and considerations for MASAR. In particular, the design and construction of the microwave system, microstrip antenna, and a high-speed data recording system are described. The SAR processing algorithm which incorporates motion compensation capability for high resolution image generation is also outlined.

Design and Development of a C-Band RF Transceiver for Uavsar

An experimental Unmanned Aerial Vehicle (UAV) Synthetic Aperture Radar (SAR) Sensor has been designed and developed at Multimedia University, Malaysia. This airborne system is an inexpensive C-band, single polarisation, linear FM airborne radar sensor. The system will be used for monitoring and management of earth resources such as paddy fields, oil palm plantation and soil surface. A series of field measurements and flight test has been conducted to verify the performance of the RF transceiver. This paper highlights the design and development of the SAR RF transceiver, as well as its evaluation result.

Multiple Phase Difference Method for Real-Time SAR Autofocus

This paper deals with the SAR autofocus problem, with the aim to implement the proposed autofocus algorithm in real-time. The crux of the SAR autofocus problem is to estimate the phase error e (·) based on the uncompensated SAR raw signal, and subsequently eliminate the phase error from the SAR data. The existing autofocus algorithms are mostly performed off-line as part of the post-processing step. This is due to the fact that the conventional autofocus methods require the entire synthetic aperture length for phase error estimation and hence, they are time-consuming and not practical for real-time implementation. The proposed algorithm, called the Multiple Phase Difference (MPD) Autofocus, utilises the maximum likelihood (ML) principle to solve the phase estimation problem. It is shown that the ML solution can essentially achieve better performance with minimum computational burden by employing the sub-aperture approach.

A CANCELLATION NETWORK FOR FULL-DUPLEX FRONT END CIRCUIT

A circulator is needed in a C-band airborne synthetic aperture radar system which employs single antenna configuration. The circulator provides full-duplex capability to transmit high-power RF signal and receive the echo signal via the same antenna simultaneously. Commercially available circulators with moderate isolation are inadequate for this application. An innovative Cancellation Network (CN) has been designed to enhance the performance of the conventional circulator. This paper highlights the conceptual design and measurement results of the CN. An improvement of more than 27 dB has been achieved

MODIFIED ALGORITHM FOR REAL TIME SAR SIGNAL PROCESSING

The generation of the picture out of the SAR raw data is a computational intensive task. Both range compression and azimuth compression utilized Fast Fourier Transform (FFT) algorithms and Inverse Fast Fourier Transform (IFFT) in order to perform convolution with respective reference signal. Thus FFT and IFFT occupied about 70% of the total computation operation in SAR image formation. In this paper a modified algorithm based on conventional FFT is proposed to optimize the computation performance. It is shown that the proposed algorithm can essentially achieve better performance with minimum computational burden compare to conventional FFT.

Conceptual Design of A High Resolution, Low Cost X-Band Airborne Synthetic Aperture Radar System

This paper describes the conceptual design of a low cost airborne Synthetic Aper- ture Radar (SAR) capable to obtain high-resolution image. The proposed system is an X-band, single polarization, high bandwidth linear FM radar and high resolution airborne SAR system. The system can be used as monitoring and management of earth resources such as paddy fleld, oil palm plantation and soil surface. First of all, the high level design will be discussed and detail design parameters are presented. It followed by radar electronics design, which outlined the detail in radar transmitter and receiver.