Array trade-off study using multilayer parasitic subarrays

The use of multilayer parasitic patch arrays in a microstrip phased array offers many potential advantages. An analytical study of microstrip arrays with high gain multilayer parasitic patch subarrays and conventional patch antennas is presented. It is indicated that a thinned array of half as many multilayer parasitic patch subarrays (per row and column) at twice the spacing will perform as well as the full array of ordinary patch antennas. The criterion for comparison was array gain, 3 dB beamwidth and sidelobe level. The attendant reduction in the required number of patch antennas and consequently, MMIC phase shifters is very significant in terms of array complexity, cost and power loss

Analysis of MMIC arrays for use in the ACTS Aero Experiment

The Aero Experiment is designed to demonstrate communication from an aircraft to an Earth terminal via the ACTS. This paper describes the link budget and antenna requirements for a 4.8 kbps full-duplex voice link at Ka-Band frequencies. Three arrays, one transmit array developed by TI and two receive arrays developed by GE and Boeing, were analyzed. The predicted performance characteristics of these arrays are presented and discussed in the paper

Visions of Juliana: A Portuguese Woman at the Court of the Mughals

This article discusses Juliana Dias da Costa (d. 1734), an influential Portuguese woman at the court of the Mughal king Bahadur Shah I (d. 1712). Through an analysis of sources that traverse three centuries and several languages, this article demonstrates how visions of Juliana were shaped by the political aspirations of those writing about her. To Jesuits, Juliana was a proxy for their mission in India, and to the Portuguese, she was one of their own, strategically placed at court to serve their interests. And for her impoverished descendants in British India, she was emblematic of times when they held both power and prestige. Concluding with the author\u27s encounter with a descendant of Juliana\u27s in Pakistan, this article addresses questions of belonging that a figure such as Juliana raises today

System overview on electromagnetic compensation for reflector antenna surface distortion

The system requirements and hardware implementation for electromagnetic compensation of antenna performance degradations due to thermal effects was investigated. Future commercial space communication antenna systems will utilize the 20/30 GHz frequency spectrum and support very narrow multiple beams (0.3 deg) over wide angle field of view (15-20 beamwidth). On the ground, portable and inexpensive very small aperture terminals (VSAT) for transmitting and receiving video, facsimile and data will be employed. These types of communication system puts a very stringent requirement on spacecraft antenna beam pointing stability (less than .01 deg), high gain (greater than 50 dB) and very lowside lobes (less than -25 dB). Thermal analysis performed on the advanced communication technology satellite (ACTS) has shown that the reflector surfaces, the mechanical supporting structures and metallic surfaces on the spacecraft body will distort due thermal effects from a varying solar flux. The antenna performance characteristics (e.g., pointing stability, gain, side lobe, etc.) will degrade due to thermal distortion in the reflector surface and supporting structures. Specifically, antenna RF radiation analysis has shown that pointing error is the most sensitive antenna performance parameter to thermal distortions. Other antenna parameters like peak gain, cross polarization level (beam isolation), and side lobe level will also degrade with thermal distortions. In order to restore pointing stability and in general antenna performance several compensation methods were proposed. In general these compensation methods can be classified as being either of mechanical or electromagnetic type. This paper will address only the later one. In this approach an adaptive phased array antenna feed is used to compensate for the antenna performance degradation. Extensive work has been devoted to demonstrate the feasibility of adaptive feed compensation on space communication antenna systems. This paper addresses the system requirements for such a system and identify candidate technologies (analog and digital) for possible hardware implementation

Improvement of adhesive toughness measurement

The double cantilever beam (DCB) method for adhesive toughness measurement was improved by incorporating a sufficiently sharp crack made by a wedge-tapping method. A known route to producing cracks via loading–unloading cycles was proved unreliable because the cycles produced plastic deformation in the adhesive where new cracks propagated. Abnormally high toughness values with large standard deviations were obtained with cracks made by embedding a non-sticky insert. Only instantly propagated cracks made by tapping were sufficiently sharp to produce reproducible, accurate tough-ness measurements. However, toughened resin was insensit

Case study of active array feed compensation with sidelobe control for reflector surface distortion

The feasibility of electromagnetically compensating for reflector surface distortions has been investigated. The performance characteristics (gain, sidelobe levels, etc.) of large communication antenna systems degrade as the reflector surface distorts mainly due to thermal effects from a varying solar flux. The techniques described in this report can be used to maintain the design performance characteristics independently of thermal effects on the reflector surface. With the advent of monolithic microwave integrated circuits (MMIC), a greater flexibility in array-fed reflector system design can be achieved. MMIC arrays provide independent control of amplitude and phase for each of many radiating elements of the feed array. It is assumed that the surface characteristics (x,y,z, its first and second derivatives) under distorted conditions are known