GB648277A - Improvements in slot antenna systems - Google Patents

Abstract

648,277. Aerials. RADIO CORPORATION OF AMERICA. Sept. 23, 1947, No. 25858. Convention date, Feb. 28, 1946. [Class 40 (vii)] A broad-band antenna system comprises a number of elongated narrow slots in a conductive. sheet, the slots being arranged in a regular geometric pattern with a conductive walled cavity behind each slot, and a transmission line system from a source of energy being connected to energize the slots in the correct phase relationship to produce a uniform radiation pattern. In Fig. 10, a delta formation of three slots is provided in the conduction skin of an aircraft and is energized in 120 degree phase relationship by coaxial lines 70, 71 and 72, 73 extending from a connector TLC through each of the quarter-wavelengthdeep cavities 60, 62, 64 backing the slots. The electrical length of time between each slot is made 120 degrees, and the impedance presented by each cavity together with the impedance of the coaxial lines is selected to provide a match throughout the system (see Fig. 7, not shown). An adjustable coaxial stud tuning section 75 terminates the coaxial line inner conductor in the cavity 62 and a fixed stub 84 terminates the inner conductor in cavity 60. An alternative arrangement for energizing the slots, Fig. 8 (not shown), employs a branch line to each cavity, the electrical lengths of the branch lines differing from each other by 120 degrees. The impedance presented by a slot is adjustable by selecting the height above the base of the cavity at which the coaxial line connects with the cavity, Figs. 2 and 3 (not shown). The minimum length for a slot is one-half wavelength while the slot width is <SP>1</SP>/ 20 or <SP>1</SP>/ 30 of a wavelength. In the plane of the array of slots the polarization is linear but rotates at the carrier frequency. In the direction normal to the plane the polarization is circular, while in intermediate directions the polarization is elliptical.