US2984183A - Auxiliary compensating antenna - Google Patents

Description

y 1961 A1. HOPPER 2,984,183

AUXILIARY COMPENSATING ANTENNA Filed March 29, 1950 I rates 1 assignments, to the United States of America as represented by the Secretary of the Army Filed Mar. -29,- -'1950,Ser. No. 152,689

3 Claims. (G1; 102 7012) My invention relates to electric proximity fuses utilizing the Doppler principle, and has particular reference to an arrangement for minimizing the effect of moisture on such a fuse.

One widely used circuit for proximity fuses employs a tuned diode voltmeter across the antenna terminals, with the diode-antenna tuning coil individually coupled to a stable oscillator operated at full power capability. This arrangement requires an adjustable Vernier tuning capacitance for individually resonating the diode-antenna circuit to the power oscillator assembly. This design is very sensitive to changes in antenna reactance. Unless the diode circuit is tuned exactly, its sharp response makes it a frequency discriminator, resulting in spurious signals for any small variation in triode capacitances. A small change in antenna capacity or oscillator frequency results in an appreciable change of diode voltage in this type of fuse.

It has been noted that under high moisture conditions the diode voltage may be lowered by as much as 50%. Under these conditions, by retuning the diode circuit, the voltage can be brought back to normal. The difficulty is caused by moisture increasing the capacity between the antenna and ground. According to my invention, I neutralize this capacity change by adding another electrode, exposed to rain or moisture to a degree proportioned to the exposure of the antenna, and connected to a point in the circuit such that the capacity effect above noted will be neutralized. Such a point may be the high side of either the plate or the grid coils, as will be more fully described below so that moisture will change the frequency of the oscillator and the diode coil in about the same degree so that the diode voltage will remain constant.

The specific nature of the invention, as well as other objects and advantages thereof, will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing in which:

Fig. 1 is a schematic general view of a fused projectile incorporating my invention,

Fig. 2 is a schematic circuit diagram showing the principle of my invention and Fig. 3 is a detail of the circuit of the Fig. 2 showing a modification of my invention.

Referring to Fig. 1 projectile 1, which may be a bomb or rocket or any other projectile, is provided with a proximity fuse 2, screwed into the nose thereof at 3 in conventional fashion. The antenna is a modified dipole type wherein the ring member 6 comprises one of the radiating members and conducting projectile body 1 with fuse body 2 comprises the other radiating member. The main fuse body 4 carries ring member 6 spaced by suitable insulation from the main body 4 to provide a desired relation pattern, as is well known. Spaced between ring member 6 and fuse body 4 is an insulated supplemental element or neutralizing ring 7, the purpose of which will be more fully explained below. The fuse body 4 ordinarily contains the arming device, electric 2,984,183 Patented May 16, 1961 circuit, power supply, detector, and booster, as is well known, while the radio oscillator and other tube circuits are usually located as close to the forward end of the fuse as is practicable. However, the placement of these elements is well known and forms no part of my invention.

' pending on the physical construction and position of these "elementsand indicated schematically by the dotted'lines "at 9. There is similarly an elfective capacitance between the ring member 6 and fuse body 2 as indicated at 11. The value of capacitance 11 affects the resonant frequency of the antenna-diode circuit which is established primarily by diode coil 14 and adjustable condenser 15.

The modified dipole antenna radiates energy supplied by oscillator 12 through plate coil 13 inductive to diode coil 14. The diode antenna circuit is tuned to the frequency of the oscillator and this tuning must be accurate to secure the desired sensitivity. Changes in the reflected impedance of the antenna due to the presence of a nearby reflecting body show up in the diode circuit as apparent changes in antenna radiation resistance and thus affect the output of diode 17. When the projectile and reflecting target have a definite relative velocity toward each other these changes appear as the well known Doppler frequency which is amplified and used to activate a thyratron to cause detonation in known fashion. In order to compensate for the detuning of the antenna due to moisture, 1 connect the neutralizing ring 7 to the high side of plate coil 13 as shown in Fig. 2. Alternatively i may connect neutralizing ring 7 to the high side of grid coil 16 in which case the action is similar except that the circuit parameters are different and must be adjusted accordingly. If the neutralizing ring 7 is correctly dimensioned and proportioned, it will be affected by extraneous moisture in the proper degree so that the oscillator frequency is altered by the same amount and in the same sense as the resonant frequency of the antennadiode circuit. Thus there is no net change in frequency and a resonant antenna-diode circuit remains at its point of maximum sensitivity.

The moisture referred to may be moisture on the surface of the fuse due to rain, or it may be merely a change in the moisture conditions of the atmosphere through which the fuse passes. The effect of moisture may be minimized by completing the encasing antenna in molded insulating material as described in U.S. patent application of Custer and Hopper, Serial No. 124,522 filed October 31, 1949, entitled Antenna for Proximity Fuse." This expedient may be utilized together with the present invention to elfect practically complete neutralization of all extraneous moisture efiects.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of my invention as defined in the appended claims.

I claim:

1. An object detecting system comprising an antenna having two relatively fixed radiating members insulated and spaced from each other, an oscillator coupled to said members, said oscillator setting up a high frequency radiant energy field between said members, a detector operatively coupled to said members for detecting the effect of reflecting objects in said field, and an exposed conducting element, said element positioned in said field and in fixed relationship to at least one of said members and directly coupled to said oscillator, said element so coupled to said oscillator whereby a capacitance change between said radiating members due to the presence of a distributed amount of conducting matter in the vicinity of said mem- 3. hers is compensated by an increasing capacitance change between said element and at least one of said members.

2. The invention according to claim 1 wherein said radiating members comprise a modified dipole antenna, an antenna-detector input circuitjsaid circuit coupling said detector with said antenna and comprising the tuning means of said detector, said circuit being resonant at the frequency of said oscillator, said element functioning to change the frequency of said oscillator by the same amount and in the same sense as the tuning of the antenna-detector input is changed by the presence of said 7 distributed conducting matter.

3. A proximity fuse for projectiles comprising an antenna having two fixed radiating elements insulated and spaced from each other, a high frequency oscillator ineluding a thermionic tube having its output coupled to said antenna, a diode-detector, a resonant circuit for tuning said diode-detector to the frequency of said oscillator, an auxiliary antenna element positioned intermediate the said elements and insulated therefrom, the radiating elements of said antenna directly coupled to said resonant circuit and said auxiliary antenna directly coupled to said high frequency oscillator whereby to compensate for capacitance changes between said radiatin elements. I

References Cited in the file of this patent FOREIGN PATENTS 581,163 Great Britain Oct. 3, 1946

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