Miniaturized tunable antenna for general electromagnetic radiation and sensing with particular application to TV and FM

Abstract

Abstract A miniaturized thin-wire multi-turn series-connected helical loop antenna, the volutes of which are concentric turns, closely spaced so as to exhibit strong mutual coupling effects. A lumped impedance, fixed or variable, is disposed electrically in series with one of the turns, and a selectively actuable multi-position switch interconnects the turns and the lumped impedance to maximize efficiency. BACKGROUND OF THE INVENTION 1. Field of the Invention The subject invention relates to miniaturized multi-turn series-connected loop antennas. 2. Description of the Prior Art The theoretical solution for multi-turn loop antennas, whether transmitting or receiving, is initially based on the solution for a single-turn loop. The single-turn solution can be obtained by considering the antenna to be a transducer which converts concentrated or distributed voltages into distributed fields and vice-versa. The phenomenon which accomplishes this is the flow of current on the antenna conductor. Thus, if one can postulate the true form of the current and the resulting fields in space in response to timevarying driving forces, the solution for the single-turn loop, whether transmitting or receiving, can be obtained. A previous patent issued to me on Feb. 19, 1963, U.S. Pat. No. 3,078,462, was titled "One-Turn Loop Antenna". This patent discloses the basic solution for a thinwire, one-turn loop antenna in air, without and with inserted impedances. Although the one turn loop antenna described in the aforesaid patent was a distinct advance over available loop antennas, its limitation to a single loop design subjects it to several limitations. The extension of the theoretical analysis of the operational characteristics to multi-turn loop antennas had not been accomplished, probably because of the difficulty in developing a solution which takes into account the interconnection discontinuity between turns of a multi-turn series connected loop antenna having concentric planar turns. Without such a usable theoretical analysis, prediction of the operation of a multi-turn loop, or the effects of various modifications thereof are well-nigh impossible. As a result, the development of loop antennas today has not progressed much beyond the level of my aforesaid patent. I have now developed a complete mathematical theory for the characteristics of a multi-turn, series-connected loop antenna formed of planar turns that are closely spaced and exhibit strong mutual coupling effects. The theory from which the multi-turn loop has been developed is applicable not only to miniaturized antennas, but to any electrical size. Hence, the ability to control radiation coverage and antenna impedance of a transmitting antenna, and the ability to control response to incident fields and the antenna impedance of a receiving antenna, apply also to an antenna of any electrical size constructed in accordance with the principles and teachings of the present invention. SUMMARY OF THE INVENTION The present invention relates to a multi-turn thin-wire series-connected loop antenna formed of, planar concentric turns, cylindrical turns, or any three-dimensional geometric configuration, having turns that are closely spaced so as to exhibit strong mutual coupling effects. A lumped impedance, fixed or variable, is disposed at a selected point in the periphery of one or more turns, and a multi-position switch is interconnected between the turns and the lumped impedance to maximize efficiency. In accordance with the present invention, there is provided a miniaturized antenna capable of achieving high radiation efficiency such as 50% or more for a miniaturized antenna whose maximum dimension is less than 0.07λ over a 10 to 1 frequency range and having an impedance that can be easily adjusted to almost any desired value. The radiation pattern can be selected to conform to many desired coverages. When utilized for reception, the miniaturized receiving antenna converts incident fields into a maximal signal voltage at the input of a receiver over a frequency range of as much as 16 to 1 by utilizing the ability to control the antenna impedance. Being miniaturized, the receiving antenna can act as a probe in space so as to finely select and respond to a particular incident field in the presence of a number of simultaneous incident fields. In essence, it can reduce the undesirable "ghost" effect. Such a receiving antenna responds to both horizontally and vertically polarized fields. Hence, its physical attitude can be easily adjusted to provide polarization sensitivity. Accordingly, it is an object of my invention to provide a miniaturized transmitting antenna in a concentric multi-turn series-connected loop configuration, planar and non-planar, smaller than any other transmitting antenna presently known, where the radiation efficiency is an appreciable fraction of 100%. Another object of my invention is to provide a miniaturized transmitting antenna in a multi-turn series-connected loop configuration capable of covering frequency bands of as much as 16 to 1: (a) by the use of a single tuning condenser inserted in a single turn of the multi-turn loop; (b) by the use of switches to switch opens to shorts and vice-versa in one or more turns. A further object of my invention is to provide a transmitting antenna in which, regardless of size, a prescribed and desired field pattern and a desired impedance level can be easily adjusted by using inserted impedances, fixed and/or variable, in one or more turns of a multi-turn loop to select and/or repress particular current modes. Still another object of my invention is to provide a multi-turn series-connected loop antenna configuration for radiation and/or reception of electromagnetic waves in which turns can be connected in single spiral form, in double spiral form, in reversed turn form, and in partial turn form, so as to achieve characteristics such as broad-banding, field pattern control, impedance level control. Another object of my invention is to provide a miniaturized passive probe antenna in a concentric multi-turn series-connected loop configuration, planar and non-planar, for reception of VHF black and white and color TV and FM, with maximum loop antenna diameter being less than five inches. A further object of my invention is to provide a miniaturized passive probe antenna for VHF black and white and color TV and FM, capable of minimizing "ghosts" by universal adjustment of the plane of the multi-turn series-connected loop. Another object of the invention is to provide a miniaturized passive probe antenna for VHF black and white and color TV and FM which uses internal antenna tuning in the form of a single miniature tuning condenser inserted in one turn of a multi-turn series-connected loop to maximize the signal voltage developed across the input impedance of the TV or FM receiving set. A further object of my invention is to provide a miniaturized passive probe receiving antenna capable of covering frequency bands of as much as 16 to 1 by the use of switching configurations which change opens to shorts and vice-versa in one or more turns of a multi-turn series-connected loop antenna. A distinct and important advantage of the present invention is that the foregoing objects can be achieved through a frequency spectrum from a few hertz up to the point where physical limitations preclude practical embodiment which is about 5000 MHZ.

Inventors

• 👤 Julius Herman

Bibliographic Details