Antenna structure

July 12, 1960 h. jasik 2,945,232

ANTENNA STRUCTURE

Original Filed March 7, 1949

Sheets-Sheet 1

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July 12, 1960

h. jasik 2,945,232

ANTENNA STRUCTURE

Original Filed March 7, 1949

Sheets-Sheet 2

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INVENTOR.

Fenry Jastk

2,945,232

Patented July 12, 1960

United States Patent Office

2,945,232

ANTENNA STRUCTURE 5

Henry Jasik, Flushing, N.Y., assignor to Andrew Alford, Boston, Mass.

Original application Mar. 7, 1949, Ser. No. 79,969. Divided and this application Mar. 5, 1954, Ser. No. io 414,416

Claims. (Cl. 343—807) means while the upper sleeve 1 is capped by a cover 22 which may be of metal. The base 21 may be considered to be at zero potential. The member 3 is an insulating, collar which may be made of a tough plastic material and having a shape to fit snugly against the outer surface of the sleeve ends with a centrally inwardly extending flange filling the space between the end edges of the sleeves separating the two sleeves 1 and 2 by a desired gap distance. The element 4 is a metallic rod which at one end is secured by welding or by other suitable means to the ground plate 21, making electrical connection and at the other end is threaded as at 24 to receive a washer and nut 25 which is tightened against a conductive plate 26 fitting inside the tube 1 and welded 15 to its inner wall just beyond the end resting on the insulator 3 so that the adjacent ends of the tubes 1 and 2 are pressed against opposite faces respectively of the insulator flange putting the insulator under substantial initial compression. The element 5 is a coaxial cable 20 with an inner conductor 6 and an outer conductor 7 which is conductively connected to sleeve 2. The coaxial cable 5 passes through the plate 21 and is connected to the high frequency line by means of the cable connector 20 which may be silver soldered to the plate 21.

The inner conductor 6 of cable 5 is connected to rod 4 by the connector 13. The rod 4 is connected to plate 26 and hence a potential is set up across the gap separating sleeves 1 and 2. If desired, the plate 26 may be closer to the insulator flange than shown in Figure 1, in 30 which case the series inductance 12 (Figure 2), on one side of the coaxial line would be decreased. The potential which is impressed by the connections of the coaxial cable sets up radiating currents on the outer surfaces of sleeves 1 and 2. The coaxial cable 5 with inner 35 conductors 6 and outer conductor 7, apply a voltage to a shunt reactance formed by the reentrant circuit consisting of outer and inner surfaces of the tube 18, the lower part of rod 4, the inner surface of plate 21, and of the tube 2. The tube 18 has a metallic plug 14 at its 40 upper end through which the rod 4 is threadedly engaged with a washer 27 and nut 28 to clamp tightly the eyelet end of the conductor 13 and the rod 4 to the top surface of the plug. The effect of this reactance is shown as a shunt 13' (Figure 2) across the coaxial cable. This re46 actance is used to help compensate the impedance as seen by the coaxial line.

The radiation impedance 10 (Figure 2) of the antenna proper can be changed by varying the diameter and length of sleeves 1 and 2. Two other variations as noted 50 just below are useful for impedance compensation. The length of the insulating collar 3 is used to control the shunt capacitive reactance across the radiation impedance. A decrease in the gap space will decrease the capacitive reactance. The upper part of rod 4, namely 56 the section 29 together with the plate 26 and the small section of the sleeve 1 to the gap form the series inductance in one conducting element of the coaxial cable which is designated as 12 in Figure 2, as has been stated.

The complete equivalent compensation network, as 60 has been stated, is shown in Figure 2, the elements of which have already been referred to above. In part recapitulation 10 is the radiation impedance of the sleeves 1 and 2, 11 is the capacitive reactance due to the gap spacing, 12 is in the inductive reactance of the upper part 66 of rod 4, and 13' is the reactance as explained above across the coaxial line.

Another embodiment of my invention is shown, in Figure 3. The same elements used in the modification of Figure 1 will bear the same numerals in all of the 70 other figures where there is no structural change. In Figure 3, the rod 4' extends through the cap 22' and compresses the sleeves 1 and 2 together against the insulator

The present invention is a division of my copending 15 patent application, Serial No. 79,969, filed March 7, 1949, now Patent No. 2,700,112.

The need for a high frequency dipole of a simple design, having substantially unchanging characteristics overa wide frequency band has existed for some time. The 20 chief objection to antennas of this general type is that they are mechanically weak because of the stresses placed on the insulators when the antenna is subjected to rough handling.

The antennas described in my invention have wide 25 band characteristics and have a mechanical design such that the insulators are placed only under compressive stresses. Almost all high frequency insulating materials can withstand considerable compression but are quite weak when subjected to tension. In previous designs in- 3° sulators as used are often subjected to tensile stress, with the result that they are frequently fractured thus rendering the antenna useless.

In my invention, two radiating outer sleeves are employed with an insulating spacer separating the sleeves. 35 The end of one of the outer sleeves spaced away from the other end near the insulating collar is at zero potential. A metallic means for spanning the sleeves in their longitudinal direction exerts a compressional stress between opposite faces of the insulating collar. ⁴⁰

The structure of the present invention may be carried out in various forms as for instance, in a completely balanced structure in which a gap exists on either side of the neutral plane or in a unit where the neutral plane is at one end of the structure. The structure may also 46 employ special coupling means connected between coaxial feed cables and the antenna or other special compensating elements which enter individually and in combination to form the distinguishing features of the present invention. 50

Without further discussing the merits and advantages of the present invention which will be more fully learned from the specifications and claims set forth below, the invention in its various embodiments will be described in connection with the drawings forming a part of the 55 specification in which:

Figure 1 is a longitudinal section taken through one form of the antenna.

Figure 2 shows a substantially equivalent electrical circuit diagram for the structures of Figure 1. CO

Figure 3 shows in longitudinal section a modified form of the structure shown in Figure 1.

Figure 4 shows a substantially equivalent bilineal circuit diagram for the structure of Figure 3.

Figure 5 shows a longitudinal section of a further gg modification of the structure shown in Figure 1, and,

Figure 6 shows a substantially equivalent electrical circuit diagram of the structure shown in Figure 5.

In the embodiment of my invention shown in Figure 1, 1 and 2 are sleeve radiating elements of metallic material, the lower part of 2 being electrically connected to a ground plate or base 21 by welding or by other suitable

2,945,332

-.- .- 3 from their extreme.ends by tightening the nut on the rod 4' on the outside of the cap 2-2'. The internal plate is therefore omitted and the·coaxial cable 5 has its internal conductor 6 connected by a short lead 30 to the end oft he· tube 1--adjacent-tile gap. The outer conductor β 7 is;in good- electrical contact with the inside of the tube 2 substantially up to the end adjacent the gap.

The equivalent circuit diagram is shown in Figure 4. The gap reactance is shunted across the coaxial cable as indicated , at 11 with a radiation impedance 1®' also in io shunt across the coaxial cable. Due to the shortness of the connector 30, there is substantially no series reactance on one side of the line as indicated in Figure 2, but there is a considerable shunt inductive reactance made up of the rod 4 , part of the base 21, and part of the upper 15 sleeve 1. The lower section of the rod 4' and base 21 corresponds to a reactance 32 which is substantially equivalent to reactance 13 of Figure 2, while the reactance 31 accounts for the additional upper section of the rod 4'. 20

The arrangement shown in Figure 5 is a balanced system consisting of a structure which electrically differs somewhat from the structure of the other figure. In Figure 5 the structure on the left is the same as that on the right with a neutral mid-plane. 23

The device comprises inner sleeves 41, actually a single tube and outer sleeves 42, spaced by the insulators 43 which correspond to similar elements described in connection with the other modifications. Concentrically positioned and supported within the sleeves and insulators, 30 are the feeder tubes 44 within which is positioned the tie rod 45 which extends from one extreme outer sleeve 42 to the .other and serves as the means for putting the sleeves and insulators under compression. For this purpose plates 46 are secured inside the sleeves 42 near their 35 outer ends by welding the sleeves to those plates while th© rod 45 extends through holes in the center of the plates and on the other side is· drawn tightly by a suitable nut 47. Within the sleeves 42 are plates 48 through which the feeders 44 extend, which feeders are con- 40 centrically positioned with respect to the sleeves. These plates 48 are .also welded to the tubes or sleeves 42 and make good electrical connections both with the inside of the sleeves 42 and the outside of the feeder 44. The position of the· plates 48 with respect to the gap has a 45 substantial effect on the value of the terminal impedance of the concentric feeders consisting of the tubes 44 and 41.. An increase in this spacing has the effect of increasing the inductive reactance in series with impedance of the end part of sleeve 42. The two plates 46 and 48 50 provide strong supports for the tube 44.

The outer ends of the sleeves 42 may be capped by caps. 49 which may be· secured in any desirable way. Insulating discs 50 act as supports for the tie rod 45 and spacers for the tie rod; within the tube 44. 55

The· single tube 41 has an opening at the top center section closed.by a. cover plate 51 fitting on a cover plate mounting 52 so that the device can be reached in the region where the feed lines are brought up to the structure just described. 80

The means and method of feeding the sleeve antenna is optional and may be accomplished by the application of a balanced feed, compensated as desired, between right and left feeders 44. In Figure 5 there is shown a single coaxial cable 53 with an outer conductor 54 connected 65 by a connector 55 to the feeder 44 and an inner conductor56 connected by a connector 57 to the other feeder 44. A section of a compensating reactance 58 is also shown connected to the connector 57. The balanced voltage in this case is supplied between the outer con- 70 ductor 54 and the· connector 57 or the tube 58.

The equivalent circuit diagram is shown in Figure 6. The balanced supply voltage is- shown at 59. This is applied to a-transmission line 60 consisting of the sleeve or tube 44 as the high side and the inner side of the sleeve 75 as the grounded side. Reactance 64 comprises the inside of the tube 44 and the plate 46 to the tie rod 45 and the tie rod 45 to the neutral plane. 61 represents a series inductance which includes the plates 48 and the section of the tube 42 from where the plate 48 is connected to it, to the gap. 68 represents the gap shunted across the line and 63 represents the radiation impedance. It will be understood that the circuit is only a half circuit of Figure 5 since the same elements in the same position are repeated for each side.

In all of the circuits shown, the system has a neutral or ground plane away from the air gap and this distinguishes this type of antenna from the so called dipole antenna. In the balanced system of the present invention, the antenna length may correspond to a half wave length of a frequency chosen in the band width. In the unbalanced system it may correpsond to a quarter of a wave length and is fed in the manner indicated above.