First Results from CSU-CHILL High Power Solid State Transmitter

The CSU-CHILL weather radar facility has modernized and advanced all parts of the radar subsystem from antenna, receivers, signal processors and displays. Only the transmitter has remained of the original radar. The CSU engineering team has experience developing waveforms and the receive subsystem using solid-state transmitters, demonstrated through two distinct projects namely the CASA WIBEX solid-state radar (George et al, 2010) and the NASA D3R radar (Vega et al 2014). Based on this heritage in collaboration with Raytheon Corporation, CSU-CHILL embarked on an ambitious project to integrate a high power solid-state power amplifier and demonstrate operation equivalent to traditional megawatt Klystron transmitters. Solid-state transmitters have numerous advantages as were discussed widely in the Community Radar Workshop in 2014. Many of the solid-state transmitters used in weather radars so far have been lower power systems. This paper describes the specific features of the high power solid-state transmitter implementation in the CSU-CHILL radar.

The high power solid-state transmitter has reduced peak power relative to the Klystron, and so must use longer transmit pulses to achieve equivalent sensitivity. The paper will demonstrate low-sidelobe pulse compression waveforms and filters that are compatible with the class-C amplifiers used in the transmitter. The advanced waveforms also mitigate the range eclipsing inherent to long transmit pulse radars. The paper presents details of the digital waveform generator and multi-channel pulse compression receiver that have been developed specifically for this radar. An RF up/down conversion subsystem has been designed that is capable of very rapid changes in RF frequency, while exhibiting enough RF bandwidth for the advanced pulse compression waveforms.

In order to validate the high-power solid-state transmitter and demonstrate its viability for weather radar applications, we test the transmitter in conjunction with the existing Klystron tube transmitters installed at CSU-CHILL, and the results will be presented. A waveguide switch was installed connecting both transmitters to the same antenna subsystem, thus allowing scan-by-scan switching between them.

The solid-state system has been developed as a self-contained module, including the transmitter and the receiver such that it could be easily transported and connected to any antenna system. This form factor is chosen for ease of deployment with other S-band radars in the research community such as the NCAR S-Pol and NASA NPOL. One of the main motivations of the solid-state system, apart from all the operational and cost advantages, is the compactness and the ease of remote unattended deployment for weather observations. We expect the integration, test, and validation of the solid-state transmitter to be a pathfinder system for the future of lower life cycle cost, highly reliable S-band weather radar systems. This advantage was widely discussed at both the NSF LAOF workshop in June 2012 and the Community Workshop on Radar Technologies in November 2012. This paper will present the first results from the solid-state high power transmitter at the CSU-CHILL radar facility.