Abstract This invention relates to antennas for simultaneous transmission of sum and difference patterns as in a runway localizer for instrument landing of airplanes. A straight horizontal run of coaxial cable, placed centrally perpendicular to the extension of the runway centerline, is symmetrically fed from both ends by an RF bridge in sum and difference modes. The outer conductor of the cable is periodically interrupted by slots which permit currents to flow on the outside of the outer conductor. The antenna current distributions corresponding to the two modes are controlled by low-resistance shunts placed across the slots and by the relationship between the slots spacing and the internal guide-wavelength. To maintain the relationship over the 4 percent band of localizer frequencies, the guide-wavelength is adjusted always to the same value by filling the cable with the necessary quantity of a gas of relatively high-dielectric constant.
A slotted cable antenna comprising a centrally located hybrid with sum and difference input terminals, first and second transmission lines extending symmetrically outwards from the output terminals of said hybrid, a third length of coaxial transmission line connected at each end respectively to the outer ends of the said first and second transmission lines, a plurality of gaps in the outer conductor of said third transmission line, radiation control means disposed across each of said gaps, said means presenting in each case an impedance, whereby most of the line current is conveyed across the gap, except for a portion of said current which escapes to flow on the outside of said third coaxial line, thereby producing radiation.
Claim 2
Dependent Claim
117 words
A slotted cable antenna comprising a centrally located hybrid with sum and difference input terminals, first and second transmission lines extending symmetrically outwards from the output terminals of said hybrid, a third length of coaxial transmission line connected at each end respectively to the outer ends of the said first and second transmission lines, a plurality of gaps in the outer conductor of said third transmission line, radiation control means disposed across each of said gaps, said means presenting in each case an impedance, whereby most of the line current is conveyed across the gap, except for a portion of said current which escapes to flow on the outside of said third coaxial line, thereby producing radiation.
Claim 3
Dependent Claim
22 words
An antenna as in claim 1, with said radiation control means comprising a metallic shunt connected conductively across each of said gaps.
Claim 4
Dependent Claim
23 words
An antenna as in claim 1, with said radiation control means comprising a metal tube, surrounding each of said gaps, but insulated therefrom.
Claim 5
Dependent Claim
28 words
An antenna as in claim 3, with frequency tuning means comprising a quantity of high-dielectric gas filling the space between inner and outer conductors of said transmission lines.