Hardware Description

The ELDORA radar system consists of five major functional blocks: the RF signal generator/receiver unit, the high power amplifiers, the signal processor, the antenna/rotodome system, and the radar control equipment. Since the radar system consists of two separate fore- and aft-pointing radars much of the hardware contains two identical modules. Only the basic signal generation equipment and the radar control equipment does not contain duplicate modules.

The entire system is synchronized to a high-precision 10 MHz crystal oscillator which serves the clock and stable reference for the radar. This frequency is used as the basis for synthesis of all frequencies needed by the rest of the system. The 60 MHz intermediate frequency (IF) is generated by the RF signal generation hardware and is used by the receivers, the digital IF signal processors and the master timing module. The timing of the transmitted waveform and the spacing of the range gates are synchronized to the 60 MHz signal.

The master timing module, located within the digital signal processing equipment, generates the 7 optical pulse trains that initiate the major transmit activities of the radar. One of these trains consists of a pulse that occurs each pulse repetition time (PRT) and enables the high power amplifier to transmit if it is fed an RF input. This pulse is often referred to as the video pulse or the pulse repetition frequency (PRF) pulse. Five other pulse trains occur synchronously with the video pulse to turn on the five chips to be transmitted - each chip being a slightly different transmit frequency. The last pulse train turns on a test pulse that is injected into the receiver for calibration purposes.

The RF signal generator continuously generates all four RF frequencies for both the fore and aft radars. For each radar the five frequencies are fed to a five-input, single-output switch that is controlled by the five chip pulse trains generated by the master timing module. The output of the switch is amplified and then fed to the high-power amplifiers in order to generate the transmitted signal.

The received signal consists of the total reflected energy from all transmitted frequencies. The received signals are amplified by a single wide-band, RF low-noise amplifier (LNA), and then fed to a splitter which distributes the received signals to each channel's mixer. There, the received signals are mixed with the appropriate frequencies to create separate IF signals, one for each transmitted frequency. Separate digital IF signal processors then digitize and mix the IF for each frequency down to baseband. Finally, the data from the different frequencies are processed in separate auto-covariance processors, and the results combined to provide the desired output measurements.

The ELDORA output variables include radar reflectivity, radial mean velocity, spectral width, and normalized coherent power. These data products are passed to the data recording and display system over a high-speed parallel link. The fore and aft digital signal processors both sit on this high-speed link, thus enabling the data system to receive all data from both the fore and the aft radars, to tag it with aircraft position information and to record and display the data.