Central-fed hemispherical helical antenna
The characteristics of a hemispherical helical antenna with central-fed are investigated by experiment. Results for a 3-turn hemispherical helix indicate that circular polarization can be obtained over a wide angular range with relatively high gain of about 8 dB. The frequency bandwidth for a 3-dB axial ratio criterion is /spl sim/11%, with a nearly resistive input impedance of 163 /spl Omega/.
Radiation characteristics of a spherical helical antenna
A helical antenna, consisting of a winding over a spherical surface, is proposed and investigated, both theoretically and experimentally. The winding is such that a constant spacing between turns is maintained. It is fed coaxially, with the inner conductor forming the helical winding and the outer conductor becoming the ground plane. Radiation characteristics of the proposed spherical helix are calculated, using the method of moments, and compared with the measured results. The results of this investigation indicate that radiation properties of the spherical helix are markedly different from those of the conventional cylindrical helix. Of particular interest is that, over a certain bandwidth, the proposed helix is capable of providing circular polarisation over a broad beamwidth. This property and its compact size make the spherical helix attractive to mobile radio communication systems with low channel capacity.
Women and Politics in Early Tudor England
Political historians working on the early Tudor period have traditionally concentrated on institutions – monarchy, council, parliament, courts, and administrative bodies – that excluded women. The very definition of politics underlying the dominant historiography has thus made it seem both natural and inevitable to write history as if the world of high politics, the world that really counted, were exclusively male.