A single-aperture, low-profile antenna design has been developed that supports dual-polarization and simultaneous operation at two wavelengths. It realizes multiple beams in the elevation plane, and supports radiometric, radar, and conical scanning applications.
This antenna consists of multiple azimuth sticks, with each stick being a multilayer, hybrid design. Each stick forms the h-plane pattern of the C and Ku-band vertically and horizontally polarized antenna beams. By combining several azimuth sticks together, the elevation beam is formed. With a separate transceiver for each stick, the transmit phase and amplitude of each stick can be controlled to synthesize a beam at a specific incidence angle and to realize a particular side-lobe pattern. By changing the transmit phase distribution through the transceivers, the transmit antenna beam can be steered to different incidence angles. By controlling the amplitude distribution, different side-lobe patterns and efficiencies can be realized. The receive beams are formed using digital beam synthesis techniques, resulting in very little loss in the receive path, thus enabling a very-low-loss receive antenna to support passive measurements.
Each azimuth stick consists of a dual-polarized Ku-band slotted waveguide linear array that is one-half of a Ku-band wavelength wide and is center-fed. The latter ensures that grating lobes will not be produced in the full array. The linear array has two sections, one supporting broadside slots and the other “edge” slots. For the broadside slots, a ridge waveguide is used to reduce the width of the waveguide section well below one-half wavelength.
For the initial instrument design, the full array will implement phase steering to form the transmit beam and digital beam synthesis to form the receive beam. The phase and amplitude of the transmit signal delivered to each vertically and horizontally polarized C and Ku-band port on the array will be controlled through dedicated, phase-locked transceivers. The array will be conically scanned to map a large surface swath beneath the aircraft and provide multiple looks at each along and cross track pixel within the swath. This will permit ocean vector wind scatterometry techniques to be applied. The coincident passive measurements obtained with this antenna will allow the atmospheric attenuation to be estimated and used to aid the ocean vector wind retrieval process, especially in the presence of precipitation where the Ku-band receive signals will be attenuated.
This antenna’s compact design will reduce deployment costs for ground-based applications, and will be ideal for mobile applications where space is often limited. Its ability to separate transmit and receive modes permits very low losses to be achieved during the receive phase, allowing for coincident active and passive measurements. Its flexibility to support frequency, phase, and digital beam synthesis techniques allows it to service a broad market, and its scalability will enable it to be customized to commercial applications at very little cost.
This system has application in monitoring the ocean surface vector wind in tropical cyclones and other severe ocean storms. In defense applications, it has uses where an imaging and mapping dual-band, dual-polarized antenna would provide strategic advantages. Search and rescue missions also can benefit from this antenna technology.
This work was done by James R. Carswell of Remote Sensing Solutions, Inc. for Goddard Space Flight Center. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Physical Sciences category. GSC-15706-1