Dynamic Frequency Passive Millemeter-Wave Radiometer Based on Optical Up-Conversion

Passive microwave sensors aboard satellites provide valuable information regarding weather conditions by measuring atmospheric attenuation over a broad range of frequencies from 0-200 GHz. Additional ground-based sensors are desirable to provide complementary upward looking measurements that can be used to refine existing attenuation models. Operating over such a large bandwidth, however, places significant demands on the receiver architecture; a common approach to this challenge involves channelizing the receiver for each frequency band of interest. Unfortunately, this limits the flexibility of the system and finding components that can operate at these higher frequencies is challenging. The approach is taken by Phase Sensitive Innovations involves conversion of the collected radio frequency signals to optical frequencies, where these signals are relatively narrowband and can be processed using conventional photonic components. Optical up-conversion is accomplished using our own high speed (up to 300 GHz) lithium niobate phase modulators acting as broadband mixers. Subsequently an optical heterodyne mixer is used to tune the receiver and bring the desired frequency signals to baseband for detection. Such an approach offers significant advantages in terms of overall simplicity of the receiver design and the ability to operate efficiently at high frequencies up to and exceeding 200 GHz.