High resolution chirp transform spectrometer

Abstract

In the submillimeter (SMM) region of electro-magnetic spectrum, heterodyne techniques are widely used to achieve high spectral resolution. The SMM source signal and a known local oscillator signal are mixed in a nonlinear device in order to generate an intermediate frequency (IF), which retains the spectrum of SMM source. The IF1 thus obtained from first mixer stage is down converted to required frequency of 1250 MHz to make it suitable for further processing in spectrometer. To extract the spectral information of source signal various spectrometers are used. The chirp transform spectrometer (CTS) is the state-of-the-art spectrometer (Hartogh and Hartmann, 1990) to achieve very high frequency resolution. The key element of CTS is a surface acoustic wave (SAW) based chirp filter capable of providing desired frequency resolution. We present the details of system design of the spectrometer, digital generation of expander chirp signal and the reflective array compressor (RAC) type SAW chirp filter.