Annular Cavity Horn Antenna Provides a Fivefold Increase of the Power Density in BEM Experiments in the 60-GHz Band

ABSTRACTHigh electron mobility transistors (HEMTs) based on the InAlAs/InGaAs heterostructure have been grown on InP by molecular beam epitaxy. At room temperature, typical sheet charge densities of 2.1–3.0×1012 cm−2 and Hall electron mobilities over 10000 cm2 /V-s are obtained. An electron mobility as high as 13000 cm2 /V-s is achieved with a pseudomorphic Iny Ga1−y As channel and a y value of 0.70.HEMTs with a T- or Γ-shaped gate and with gate lengths ranging from 0.1–0.25 urn have been fabricated. A record low noise figure of 0.7 dB with an associated gain of 8.6 dB at 62 GHz has been achieved with 0.1 μm Γ-gate devices, while T-gate devices exhibit a minimum noise figure of 1.2 dB with 7.2 dB associated gain at 94 GHz. Separately, a record fmax value of 455 GHz was determined by extrapolating at -6 dB/octave from the measured gain of 13.6 dB at 95 GHz.Power HEMTs using a double heterojunction structure exhibit a record peak power-added efficiency (P.A.E.) of 49% with 8.6 dB power gain and 0.30 W/mm power density measured at 60 GHz. When biased and tuned for maximum output power, our best 60 GHz output power density to date is 0.52 W/mm with 33% P.A.E. and 5.9 dB power gain using a single heterojunction HEMT scheme with pseudomorphic channel. A similar device also yields peak P.A.E. of 26% with 0.20 W/mm power density and 4.9 dB gain at 94 GHz. These results represent the highest P.A.E.S and power gains ever reported for any transistor at these frequencies.

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Adjustments in metabolic heat production by squirrel monkeys exposed to microwaves

Journal of Applied Physiology ◽

10.1152/jappl.1982.52.4.1049 ◽

1982 ◽

Vol 52 (4) ◽

pp. 1049-1058 ◽

Cited By ~ 19

Author(s):

E. R. Adair ◽

B. W. Adams

Keyword(s):

Power Density ◽

Heat Production ◽

Horn Antenna ◽

Threshold Level ◽

Squirrel Monkeys ◽

Metabolic Heat Production ◽

Oxygen Deficit ◽

Whole Body ◽

Saimiri Sciureus ◽

Metabolic Heat

Squirrel monkeys (Saimiri sciureus) were exposed in the far field of a horn antenna to both brief (10-min) and prolonged (90-min) periods of 2,450-MHz continuous microwaves. Ambient temperature (Ta) was constant at 15, 20, or 25 degrees C. Microwave power density ranged from 2.5 to 10 mW/cm2, representing a range of whole-body energy absorption from 0.4 to 1.5 W/kg. Reliable reductions in metabolic heat production (M), calculated from oxygen deficit in the monkey's expired air, were initiated at all Ta by 10-min whole-body exposures to power densities of 4 mW/cm2 (2 monkeys) or 6 mW/cm2 (1 monkey) and above. The magnitude of M reduction was linearly related to microwave intensity above the threshold level. Termination of microwaves was followed by a rapid M rebound. The change in M produced by a given power density was nearly the same in Ta = 15 and 20 degrees C. During 90-min exposures at Ta = 20 degrees C, the vigorous M reduction to microwave onset adapted slowly, ensuring continual precise regulation of internal body temperature. Thus cold-exposed endotherms readily compensate for microwave-induced body heating by reducing endogenous heat production.

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