Dual-band shared aperture reflector/reflectarray antenna: Designs, technologies and demonstrations for nasa's ACE radar

NASA's planned Aerosol, Cloud and Ecosystems (ACE) mission will provide RF measurements for studying the role of aerosols on cloud development. The space-borne radar requires a fixed-beam at W-band and a wide-swath (>100 km) scanning beam at Ka-band. The full scale antenna is comprised of a parabolic cylinder reflector/reflectarray with a fixed W-band feed and a Ka-band Active Electronic Scanning Array (AESA) feed. Cassegrain folded optics is employed to reduce the required mass, volume, mechanical complexity and cost. An innovative reflectarray design provides a focused low-loss pencil beam at W-band, and is RF transparent at Ka-band. The AESA transmit/receive (T/R) modules provide high RF output power and low noise figure. Several planar reflector/reflectarray prototypes were designed and fabricated to validate the novel reflectarray element/surface technology and design methodology. The measured W/Ka band reflector/reflectarray gains and patterns agree very well with predictions thereby confirming the viability of the full scale design.

I. Dual-band Antenna Architecture

The proposed ACE dual-band reflector/reflectarray antenna system design, first described in [1]–[5], is shown in Figure 1. For Ka-band (35 GHz) operation, the parabolic cylinder reflector is fed by an AESA line feed located at the virtual focal line of the parabolic cylinder (Cassegrain optics) and degree azimuth beam steering is provided by electronically scanning the feed in one dimension (azimuth). Array fed offset reflector trades were performed using the COTS code, and a T/R module design was developed in parallel to meet radar performance requirements such as sensitivity and side lobes. System trades were used to develop a module design (shown in Figure 2) to meet critical requirements, while also addressing mechanical and thermal concerns. Four elements are needed in the elevation (vertical) plane to provide proper secondary reflector illumination taper and meet stressing sidelobe requirements.