Development of FFT processor for Large Field Radio Patrol Camera

作为数字透镜的FFT处理器：考虑N元等距线阵天线，根据奈奎斯特定理给出实信号的N/2傅里叶分量。当我们在每个天线上附加正交位相延迟线时，我们观察到N的复信号，得到N的傅立叶分量(N/2的实分量和N/2的虚分量)。每个傅里叶分量的复振幅的平方给出了相应方向的每个电磁辐射强度。因此，我们得到了天空的无线电图像。这里的FFT处理器就像光学望远镜中的透镜一样工作。目前的FFT处理器：复八点FFT处理器已于1985年在早稻田大学建造并运行。该处理器旨在通过评估来构建完整的系统。使用FFT处理器的好处是它的扩展能力。在本系统中，16个A/D转换器以20 MHz的频率同时产生8个复数信号。FFT处理器以相同的时钟并行运行。动态范围为8位。对得到的傅立叶分量进行平方、相加和积分。最后将这些数据传输到计算机中。在两块板上有12个蝶形运算符，并且使用55个乘法器-加法器C-MOS LSI(Sony Corporation的CX-7997，S.Iwase等1984)。这些LSI也用作其他两块板上的积分器。

FFT processor as a digital lens: Considering N elements equally spaced linear array of antennas, it gives Fourier components of N/2 for real signals according to Neyquist's theorem. When we use quadrature phase delay lines attached to each antennas, we observe complex signals of N, and obtain Fourier components of N ( real components of N/2 and imaginary components of N/2). Square of complex amplitude of each Fourier component gives the each intensity of electromagnetic radiation of corresponding direction. Thus , we get the radio image of the sky. FFT processor here operates as a lens does in an optical telescope.The present FFT Processor: Complex eight points FFT processor has been constructed and operating at Waseda University in 1985. This processor aims the evaluation to construct the full system. Benefit of using FFT processor is its capability in extension. In the present system, sixteen A/D converters generate eight complex signals simultaneously at 20 MHz. The FFT processor operates parallely at the same clock. The dynamic range is eight bit. Resulting Fourier components are squared, added, and integrated. Finally these data are tranfered to computer. Twelve butterfly operators are on two boards, and fifty five multiplier-adder C-MOS LSIs( CX-7997 of SONY Corporation, S. Iwase et al 1984) are used. These LSIs are also used as integrators on the other two boards.