Optimization of a Multi-port Amplifier Using a Least Squares Evolutionary Relaxation Method
A satellite designed for mobile telecommunications applications may contain a large aperture reflector fed by an array at its principle focus. Each radiator element of the array has a one-to-one correspondence with a spot on the earth, so that radiation patterns are pointed at different locations on the Earth by different combinations of elements. Before the signals arrive at the array with their specified complex weights they must undergo amplification. This can be provided by a beam forming network composed of between 10 and 20 multiport amplifiers (MPA). The object of this paper is to describe an optimization method that will improve the performance of the beam forming network
MODELLING OF A MULTIPORT AMPLIFIER FOR A MOBILE COMMUNICATIONS SATELLITE
Some communication satellites have an antenna that consists of a fixed parabolic reflector that is fed by an array. Such antenna systems can be programmed to produce a variety of fixed beams in response to traffic demands and can be built so that each array element is fed by its own high power amplifier. However benefits can accrue if the amplifiers are incorporated into Multiport Power Amplifiers (MPAs). Ideally all the MPA inputs are divided equally between all amplifiers and there is a one to one correspondence between the MPA feed ports and the MPA array ports. Due to imperfections in the INET and the ONET, and differences between the amplifiers, the ideal behaviour is never realized in practice. To optimize the performance of any manufactured MPA a deliberate offset in the gain and phase shift of each amplifier has to be introduced to compensate for the imperfections introduced by the INET, the ONET and their associated cabling. This paper shows how the RF modelling of an MPA has been performed by computer modelling using HFSS, Matlab and the Agilent ADS software.
Pharmacokinetics of amikacin and chloramphenicol in the aqueous humor of rabbits
Composite data describing ocular pharmacokinetics are unreliable because of intersubject variation. To address this problem, an animal model was developed in which multiple aqueous samples from single subjects were obtained. Following direct anterior chamber or intravenous administration of amikacin or chloramphenicol, pharmacokinetic analysis of drug concentrations in the serum and anterior chamber was performed by using a nonlinear least-squares regression program. The number of anterior chamber paracenteses performed did not alter the beta elimination rates or percent penetration into the anterior chamber. The aqueous humor and peripheral-compartment terminal slopes were identical. These data indicate that complete ocular concentration-time curves can be obtained without altering antibiotic pharmacokinetics. Following direct injection into the anterior chamber, the elimination rates for both antibiotics followed a one-compartment model, whereas those following intravenous administration best fit an open, first-order, two-compartment model. Following intravenous administration, the anterior chamber elimination rate constants for both drugs were equal to that of the serum and significantly longer than that following direct injection. The elimination rates of both drugs following direct injection were similar. Systemic administration resulted in drug levels in aqueous humor that persisted longer than those following direct injection. Chloramphenicol, a lipophilic compound, gave higher mean concentrations in aqueous humor than did amikacin. Our model provides a new approach which rigorously examines ocular pharmacokinetics and provides data which suggest that for selected compounds the parenteral route of administration is preferable.