An experimental investigation of dielectric-coated antennas

The characteristics of a monopole antenna embedded in a cylinder of low-loss dielectric have been measured. A cylinder of infinite length was approximated by extending the length of a finite cylinder until the admittance did not change. Admittance and current distribution data are represented as a function of antenna length for various diameters and dielectric constants of the cylinders. The results compare well with a theoretical analysis by Ting. The effect of the cylinder is to increase the electrical length of the antenna and decrease the bandwidth.     

An experimental and theoretical study of the monopole embedded in a cylinder of anisotropic dielectric

The characteristics of a monopole antenna embedded in an anisotropic cylinder of semi-infinite length were studied. The anisotropic medium was created artificially by thin layers of lossless material whose dielectric constant alternated between two values, 15.0 and 1.06. A theoretical and experimental analysis was carried out for the axially anisotropic (uniaxial) orientation of the dielectric medium with curves shown for input admittance and current distribution. An experimental investigation was also carried out for the radially anisotropic orientation with measurements made for the input admittance, axial charge distribution, and the angular and axial current distributions.     

Novel approach to the production of band branching filters for microwave frequencies

A new type of microwave branching filter is proposed, using a curved slotted-waveguide array to focus different frequencies into different receiving apertures in a near-field focal plane. An example of a theoretical response for a 7-channel filter is given.     

The transient response of the coaxial cone antenna

A coaxial cone antenna whose aperture is in the plane of a ground plane has been described theoretically and experimentally in the time domain. Its response to an incident step along the ground plane is essentially a pulse whose width is equal to the diameter of the outer conductor at the aperture. Limitations on the cone dimensions are also discussed.     

Capacitively tuned dipole

Capacitive tuning of a dipole of almost any electrical length is demonstrated with an antenna configuration that is similar to the folded dipole. If variable-capacitance diodes are substituted for the capacitors, tuning over a very wide band of frequencies is possible.     

Reduced striatal tyrosine hydroxylase activity is not accompanied by change in responsiveness of dopaminergic receptors following chronic treatment with deprenyl

Deprenyl is the only selective monoamine oxidase B (MAO-B) inhibitor that is in clinical use for the treatment of Parkinson's disease. Our previous studies showed that chronic treatment of rats with low (MAO-B selective) doses of deprenyl inhibited dopamine (DA) re-uptake and enhanced DA release in the striatum. These changes could affect DA synthesis rate by activation of negative feedback loops. Chronic deprenyl treatment has also been suggested to cause down-regulation of release-modulating DA receptors. The effects of chronic and acute treatment with deprenyl on ex vivo striatal tyrosine hydroxylase activity were therefore studied, by determination of steady-state tissue level of DOPA following administration of NSD-1015 (100 mg/kg i.p.). In addition, we assessed changes in the in vivo sensitivity of dopaminergic receptors from the reduction in DOPA extracellular level after systemic apomorphine administration (2.5 mg/kg s.c.), following elevation of microdialysate DOPA by systemic or local aromatic amino acid decarboxylase inhibition with NSD-1015. Chronic treatment with deprenyl (0.25 mg/kg s.c. daily for 21 days) caused a significant reduction in tyrosine hydroxylase activity to 60% of control, with no change in the apomorphine-induced reduction of microdialysate DOPA and DOPAC. The reduction in tyrosine hydroxylase activity is compatible with our previous results showing an increase in striatal DA extracellular level following chronic treatment with deprenyl. The increased extracellular striatal DA level could reduce tyrosine hydroxylase activity through activation of a negative feedback loop, by activation of either presynaptic or postsynaptic DA receptors.