Behrouz Khayatian

InP HEMT low-noise amplifier-based millimeter-wave radiometers from 90 to 180 GHz with internal calibration for remote sensing of atmospheric wet-path delay

The recent introduction of 35-nm gate length InP MMIC low-noise amplifiers has enabled significant advances in Earth remote sensing. These low-noise amplifiers achieve 2-dB and 3-dB noise figure at 180 GHz and 90 GHz, respectively, at room temperature. For Earth remote sensing using ocean surface altimeters, the design of new millimeter-wave radiometers is motivated by the fact that these missions include nadir-viewing, co-located 18–37 GHz microwave radiometers to measure wet-tropospheric path delay. However, due to the substantial area of the surface instantaneous fields of view (IFOV) at these frequencies, the accuracy of wet path retrievals begins to degrade at approximately 50 km from the coasts. In addition, conventional microwave radiometers do not provide wet-path delay over land. For a maximum antenna aperture size on Earth observation satellites, the addition of higher-frequency millimeter-wave (90–170 GHz) radiometers to current Jason-class radiometers is expected to improve retrievals of wet-tropospheric delay in coastal areas and to increase the potential for over-land retrievals.

The DESDynI synthetic aperture radar array-fed reflector antenna

DESDynI is a mission being developed by NASA with radar and lidar instruments for Earth-orbit remote sensing. This paper focuses on the design of a large-aperture antenna for the radar instrument. The antenna comprises a deployable reflector antenna and an active switched array of patch elements fed by transmit / receive modules. The antenna and radar architecture facilitates a new mode of synthetic aperture radar imaging called ‘SweepSAR’. A system-level description of the antenna is provided, along with predictions of antenna performance.

A novel antenna concept for future solar sails: application of Fresnel antennas

Recent studies have shown that interplanetary missions may be made possible using inflatable solar sails that employ solar-flux power, providing thrust for spacecraft while reducing onboard fuel requirements. These sails require a large surface area (i.e., 100 m in diameter) to capture enough solar flux for spacecraft navigation. In this paper, a novel communication antenna concept is proposed for future solar-sail missions, taking advantage of the large sail surface area via application of Fresnel-zone (FZ) antennas. This study focuses on utilizing a design/analysis methodology using physical optics (PO) and method of moments (MoM) for Fresnel-type antennas applicable to the solar-sail missions. Extensive parametric studies of Fresnel-zone antenna radiation characteristics have been performed, and the analytical methodologies were verified using a series of measurements. Fresnel-zone antenna gain is studied under different antenna configurations. Furthermore, a Fresnel-zone antenna under surface deformation is investigated to characterize Fresnel-zone antenna performance in the reflective mode. In addition, a new bandwidth-enhancement technique is introduced for Fresnel-zone antennas, to accommodate the dual-band operation ( X band uplink and downlink) of the antenna for the deep space network (DSN).

The deep space network's X/X/Ka feed: Modifications for 100 kW CW uplink operation

The Deep Space Network, which provides communication services for NASAs robotic missions, consists of a number of 34m beam waveguide antennas and conventional 70m dual-reflector antennas located around the globe, [1]. The 34m beam waveguide antennas employ a three-band feed covering the deep space uplink band near 7.2 GHz, and downlink bands at 8.45 and 32 GHz. Simultaneous uplink commanding at 25 kW CW and ultra low noise reception in both bands is supported along with monopulse tracking at 32 GHz, [2]. An existing uplink capability of 25 kW is also available on the 70m antennas using a more conventional X/X diplexing feed. In order to provide an equivalent uplink capability with the 34m antennas the X/X/Ka feed is currently being modified for 100 kW CW operation, [3]. Here we will discuss both the existing feed and the 100 kW modifications which are underway.

Multi-step Ka/Ka dichroic plate with rounded corners for NASA's 34m Beam Waveguide antenna

A multi-step Ka/Ka dichroic plate (Frequency Selective Surface (FSS)) is designed, manufactured and tested for use in NASAs Deep Space Network (DSN) 34m Beam Waveguide (BWG) antennas. The proposed design allows ease of manufacturing and ability to handle the increased transmit power (reflected off the FSS) of the DSN BWG antennas from 20kW to 100 kW. The dichroic is designed using HFSS and results agree well with measured data considering the manufacturing tolerances that could be achieved on the dichroic.

Strut shaping of 34m Beam Waveguide antenna for reductions in near-field RF and noise temperature

Strut shaping of NASAs Deep Space Network (DSN) 34m Beam Waveguide (BWG) antenna has been implemented to reduce near-field RF exposure while improving the antenna noise temperature. Strut shaping was achieved by introducing an RF shield that does not compromise the structural integrity of the existing antenna. Reduction in the RF near-field level will compensate for the planned transmit power increase of the antenna from 20 kW to 80 kW while satisfying safety requirements for RF exposure. Measured antenna noise temperature was also improved by as much as 1.5 K for the low elevation angles and 0.5 K in other areas.

Development of internally-calibrated, MMIC-based millimeter-wave radiometers to enable correction of wet-tropospheric delay for coastal zone altimetry

Critical microwave component and receiver technologies are under development to reduce the risk, cost, volume, mass, and development time for a high-frequency microwave radiometer needed to enable wet-tropospheric correction in the coastal zone and over land as part of the accelerated Tier-2 NRC Decadal Survey-recommended Surface Water and Ocean Topography (SWOT) Mission. Current satellite ocean altimeters include a nadir-viewing, co-located 18–37 GHz multi-channel microwave radiometer to measure wet-tropospheric path delay. However, due to the area of the instantaneous fields of view on the surface at these frequencies, the accuracy of wet path retrievals begins to degrade at approximately 50 km from the coasts. Additional higher-frequency microwave channels added to the Jason-class radiometers on the recommended SWOT mission will improve retrievals in coastal regions since their surface footprints are about five times smaller than the lower frequency ones. Specifically, high-frequency window channels at 92, 130 and 166 GHz are optimum for wet path delay retrievals in coastal regions. New, high-sensitivity, wide-bandwidth mm-wave radiometers using both window and sounding channels show good potential for over-land wet-path delay retrievals.