RESUMO
This article describes the development of a high-gain, broadband, circularly polarized Fabry-Perot cavity (FPC) antenna for high-data-rate communication in CubeSat/SmallSat applications. In this work, the concept of spatially separated superstrate area excitation is developed for the first time in FPC antennas. This concept is then validated and applied to increase the gain and the axial ratio bandwidth of a conventional narrowband circularly polarized source patch antenna. The antenna's design leverages independent control of polarization at different frequencies, resulting in a large overall bandwidth. The fabricated prototype antenna provides right hand circular polarization with a peak measured gain of 15.73 dBic over a common bandwidth of 1.03 GHz ranging from 7.99 GHz to 9.02 GHz. The gain variation over the bandwidth is less than 1.3 dBic. The antenna measures 80 mm × 80 mm × 21.14 mm and is simple, lightweight, easily integrable with CubeSat body, and useful for X-Band data downlink. When integrated with the metallic body of a 1U CubeSat, the simulated gain of the antenna increases to 17.23 dBic, with a peak measured gain of 16.83 dBic. A deployment method is proposed for this antenna that results in a total stowed volume of only 2.13λo × 2.13λo × 0.084λo (0.38 [Formula: see text]).
RESUMO
The increasing use of wireless communication devices has raised major concerns towards deleterious effects of microwave radiation on human health. The aim of the study was to demonstrate the effect of low-intensity microwave radiation on levels of monoamine neurotransmitters and gene expression of their key regulating enzymes in brain of Fischer rats. Animals were exposed to 900 MHz and 1800 MHz microwave radiation for 30 days (2 h/day, 5 days/week) with respective specific absorption rates as 5.953 × 10(-4) and 5.835 × 10(-4) W/kg. The levels of monoamine neurotransmitters viz. dopamine (DA), norepinephrine (NE), epinephrine (E) and serotonin (5-HT) were detected using LC-MS/MS in hippocampus of all experimental animals. In addition, mRNA expression of key regulating enzymes for these neurotransmitters viz. tyrosine hydroxylase (TH) (for DA, NE and E) and tryptophan hydroxylase (TPH1 and TPH2) (for serotonin) was also estimated. Results showed significant reduction in levels of DA, NE, E and 5-HT in hippocampus of microwave-exposed animals in comparison with sham-exposed (control) animals. In addition, significant downregulation in mRNA expression of TH, TPH1 and TPH2 was also observed in microwave-exposed animals (p < 0.05). In conclusion, the results indicate that low-intensity microwave radiation may cause learning and memory disturbances by altering levels of brain monoamine neurotransmitters at mRNA and protein levels.
