The recent discovery of high-temperature superconductors (HTS's) has generated a substantial amount of interest in microstrip antenna applications. However, the high permittivity of substrates compatible with HTS causes difficulty in feeding such antennas because of the high patch edge impedance. In this paper, two methods for feeding HTS microstrip antennas at K and Ka-band are examined. Superconducting microstrip antennas that are directly coupled and gap-coupled to a microstrip transmission line have been designed and fabricated on lanthanum aluminate substrates using Y-Ba-Cu-0 superconducting thin films. Measurements from these antennas, including input impedance, bandwidth, efficiency, and patterns, are presented and compared with published mdels. The measured results demonstrate that usable antennas can be constructed using either of these architectures, although the antennas suffer from narrow bandwidths. In each case, the HTS antenna shows a substantial improvement over an identical antenna made with normal metals.

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Abstract-NASA's future communications services will be supplied through a space communications network that mirrors the terrestrial Internet in its capabilities and flexibility. The notional requirements for future data gathering and distribution by this Space Internet have been gathered from NASA's Earth Science Enterprise (ESE), the Human Exploration and Development in Space (HEDS), and the Space Science Enterprise (SSE). This paper describes a communications infrastructure for the Space Internet, the architectures within the infrastructure, and the elements that make up the architectures. The architectures meet the requirements of the enterprises beyond 2010 with Internet compatible technologies and functionality. The elements of an architecture include the backbone, access, inter-spacecraft, and proximity communication parts. From the architectures, technologies have been identified which have the most impact and are critical for the implementation of the architectures.

A b s t r a c t N a t i o n a l Aeronautics and Space A d m i n i s t r a t i o n Lewis Research Center Cleveland, Ohio 44135 D i r e c t c u r r e n t and a l s o t h e microwave c h a r a c t e r i s t i c s o f o p t i c a l l y i l l u m i n a t e dAlGaAs/GaAs HEMT a r e e x p e r i m e n t a l l y measured f o r t h e f i r s t t i m e and compared w i t h t h a t o f GaAs MESFET. The r e s u l t s showed t h a t t h e average increase i n t h e g a i n i s 2.8 dB under 1.7 mWlcn? o p t i c a l i n t e n s i t y a t 0.83 pm. F u r t h e r , t h e e f f e c t o f i l l u m i n a t i o n on S-parameters i s more pronounced when t h e devices a r e biased c l o s e t o pinch-off. Novel a p p l i c a t i o n s o f o p t i c a l l y i l l u m i n a t e d HEMT as a v a r i a b l e g a i n a m p l i f i e r , high-speed h i g hfrequency photo detector, and mixer are demonstrated. I n t r o d u c t i o nUse o f d i r e c t o p t i c a l c o n t r o l o f microwave semiconductor devices f o r o p t i c a l i n j e c t i o n locking, phase s h i f t i n g , and s i g c a l d i s t r i b u t i o n has t h e p o t e n t i a l t o enhance t h e performance f f u t u r e space borne phased a r r a y antenna systems.P*2 Previously, several authors have e x p e r i m e n t a l l y i n v e s t i g a t e d t h e e f f e c t o f l i g h t on t h e dc as w e l l as t h e microwave c h a r a c t e r i s t i c s o f IMPATT diodes and GaAs MESFETS.~-~ T h e i r i n v e s t i g a t i o n s show t h a t these changes i n t h e c h a r a c t e r i s t i c s a r e due t o p h o t o c o n d u c t i v i t y and p h o t o v o l t a i c e f f e c t s . F u r t h e r , an a n a l y t i c a l study, by t h e authors t a k i n g i n t o c o n s i d e r a t i o n m a t e r i a l p r o p e r t i e s o f hetros t r u c t u r e s showed t h a t t h e h e t r o s t r u c t u r e s have a h i g h e r s e n s i t i v i t y t o o p t i c a l i l l u m i n a t i o n . When t h i s i n v e s t i g a t i o n was extended t o microwave device s t r u c t u r e s , i t was observed t h a t t h e dc characteri s t i c s o f an AlGaAs/GaAs High E l e c t r o n M o b i l i t y T r a n s i s t o r (HEMT), when compared t o t h a t o f a GaAs MESFET, a r e more s e n s i t i v e t o o p t i c a l i l l u m i n a t i o n g r e a t e r t h a n t h e semiconductor band gap.7 e x t e n s i v e experimental r e s u l t s which show t h e sens i t i v i t y t o o p t i c a l i l l u m i n a t i o n , t h a t i s , t h e l i g h t induced v o l t a g e and as a consequence t h e changes i n t h e d r a i n t o source c u r r e n t , t h e i n t r i ns i c transconductance, t h e s c a t t e r i n q parameters, I n t h i s paper, we present f o r t h e f i r s t t i m e *National Research Council -NASA Research Associate. and t h e q a i n o f an AlGaAs/GaAs HEMT. fromthe de-embedded HEMT s c a t t e r i n g parameters, t h e changes i n t h e e q u i v a l e n t c i r c u i t element values due t o o p t i c a l i l l u m i n a t i o n a r e a l s o computed. I n o...