US2903695A

US2903695A - Impedance matching feeder for an antenna array

Info

Publication number: US2903695A
Application number: US405269A
Authority: US
Inventors: Hugh W Jamieson
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-01-20
Filing date: 1954-01-20
Publication date: 1959-09-08
Anticipated expiration: 1976-09-08

Description

sept 8, 1959 y H. w. JAMn-:soN 2,903,695

IMPEDANCE MATCHING FEEDER FOR AN ANTENNA ARRAY Filed Jan. 20, 1954 HUGH W JM/ESON A TTORNEYS 42% mar 2,903,695 Patented Sept. 8, 1959 United States Patent-Oiice IMPEDANC'E MATCHING FEEDER FOR AN ANTENNA ARRAY Application January 20, 1954, Serial No. 405,269

s claims. (c1. 34a-852)' This invention relates generally to antenna arrays, and more speciiically to an improved sandwich type feeder for an antenna array.

In the use of an antenna system for radiating or receiving R-F energy, maximum eiiciency of the antenna system demands that each link in the path from transmitter to antenna, and from antenna to receiver, accurately control the R-F energy in the system in both amplitude and phase.

Prior to this time, feeders of the sandwich type for an antenna array have been constructed ordinarily with junctions of simple T-shape, and have not operated satisfactorily insofar as eicient distribution of current and power are concerned. The lumped inductance existing at these junctions resulted in an excessive loss of energy.

Accordingly it is an object of this invention to provide a sandwich-type feeder for an antenna array which has a minimum of energy lossl at its junctions.

Still a further object of the invention isthe provision of an antenna array feeder system wherein there is correspondence between the electrical lengths and physical lengths of the trunk and of the feeder branches.

relation therebetween. The multibranch inner or center conductor 31 is thus contained within an enclosure formed between the bottom wall or ground plane 32 of the beam forming structure 10 and an opposed wall 33. The conductor 31 is made up of a series of lines and junctions arranged as described infra to provide feeder connections for the antenna dipoles l2--17. The couductor 3l is held in spaced apart relation from the

conductors

32 and 33 as by suitable insulating spacers (not shown). Itwill be seen that the sandwich assembly is somewhat analogous to a coaxial line and comprises an outer

hollow conductor

32, 33 of generally rectangular cross-section and a flat substantially rectangular inner conductor 31.

In the feeder system 30, the conductor 31 is formed into a series of conductive lengths. This conductor is formed into an input line 34 which is connected through an impedance transformation, as indicated at 35, to the trunk 37 of a Y-junction, indicated generally by the numeral 36.

-It being necessary to make a right angle turn from the line 34 to the trunk 37, and from the trunk 37 to the branch lines 40 and 51, the trunk and the arms 38, 39 are arcuately shaped, instead of sharply angled as is the usual case. This greatly reduces the lumped inductances which would otherwise be present at junction 36.

1, In order to get maximum power transfer from the truuk 37 to the branch lines 40 and 51, it is necessary that there be a minimum of reactance at the junction point., It is an important feature of this invention that this is accomplished. To this end the trunk 37 and arms 3 8, 39 are arcuate, as described supra, to reduce the It is still a further object of the invention to provide-a 'l feeder for an antenna array wherein the reactance at the junctions of the feeder branches is reduced to a-minimum by cancellation thereof.

, Still a further object is to reduce the lumped inductive reactance normally present at the junctions of a feeder for an antenna array.

Other objects and many of the attendant 'advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. l shows the general conformation of an antenna array utilizing a feeder system constructed in accordance with my invention;

Fig. 2 is a cross sectional schematic view taken along the lines II-ll of Fig. 1; and

Fig. 3 is a plan view of a part of the feeder system for the antenna array, constructed in accordance with my invention.

Referring to the drawings my improved feeder is 1llustrated as feeding an antenna having a plurality of aligned radiating-receiving elements, such as dipoles 12 17. The antenna array in the illustrated embodiment has a reflector, generally designated 10, which may be formed of suitable sheet material. Dipoles 12-17 extend through openings 18 in the ground plane 32. These dipoles are free at one end and suitably connected, as by a screw connection (not shown) at their other end to the branches of a feeder system, generally designated 30. External connection between the feeder system and a coaxial line may be made by means of a coaxial tting conventionally indicated at 29.

The feeder system 30 consists of a sandwich assembly made up of a pair of parallel

conductive sheets

32 and 33 having a flat center conductor` 31 held in spaced lumped inductive reactance at the junction, and a stub 41 is provided which extends from the center of the Y- junction. The stub 41 provides a capacitive reactance which substantially cancels the remaining lumped inductive reactance at the junction. This stub is of a length less than one-quarter wave length at the operating frequency in order to provide a capacitive reactance, the exact length being dependent upon the amount of inductive reactance required to be compensated.

The arm 38 connects to branch line 40 through a twostep step-down impedance transformation, as indicated at 42, 43, the branch line 40 being matched in impedance with the dipole 12.

The arm 39 connects through a two-step step-down impedance transformation 44, 4S to the branch line 51 which'forms the trunk of a second Y-junction, generally indicated by the numeral 50. The Y-junction 50 is similar in construction to the Y-junction 36 having an arcuate trunk 51, capacitive reactance stub 52, and arms 53, S4, which connect through step down transformations to a dipole feeder line 56 and the trunk 62 of a third similar Y-junction 61. The Y-junction 61 in turn feeds a dipole feeder line 63 and the trunk 72 of a fourth Y-junction 71. The dipole feeder line 73 and the trunk 81 are connected through impedance transformations 74 and 75, 76, respectively, to Y-junction 71. Y-junction fed by its trunk line 81 branches off and feeds through

suitable impedance transformations

82 and 83, 84, the dipole feeder lines 85 and 86.

Dipoles 22-27 may be fed by a system (not shown) similar to system 30, and the two systems may be joined together at the input end of line 34 and the corresponding line in the complementary system by a stubbed V- junction arrangement, as described in conjunction with system 30 to form a single feeder system for the dipoles 12-17 and 22-27. In such case the input line to the trunk of this Y-junction (not shown) may be suitably matched to the input source (not shown).

It will be apparent to those skilled in the art that more or less dipoles would require correspondingly more or Obviously many modifications and variations ofl the` present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

l. A low energy loss feeder for an antenna array, said feeder comprising a first `leg forming the trunk of a Y-junction having a pair of branch legs, one of said branch legs being arcuate and arranged for connection to a radiating or receiving element of an antenna array between a branch and its trunk whereby the lumped inductance at said junction is of a reduced value as compared to a sharp angle junction, said junction having a capacitive reactance stub extending7 therefrom to substantially cancel the inductive reactance at said junction.

2. A low energy loss feeder for an antenna array, said feeder comprising a first leg forming the trunk of a Y- junction having a pair of branch legs, one of said branch legs being arranged for connection to a first radiating or receiving element of an antenna array, the other of said branch legs forming the trunk of a second Y-junction having a pair of branch legs, one of said last mentioned' branch legs being arranged for connection to a second radiating or receiving element of an antenna array and the other of said last mentioned branches forming the trunk of a third Y-junction having branch legs each of which is arranged for connection respectively to a third and fourth radiating or receiving element of an antenna array, each of said branches having arcuate arms at said junction to provide a smooth change in direction, each of said junctions having a capacitive reactance stub extending therefrom in a direction opposite to the trunk direction to substantially cancel the inductive reactance at said junctions.

3. A feeder for an antenna array, said feeder comprising la sandwich of two spaced apart fiat substantially parallel conductors, at least one of said conductors having a Y-shaped junction having a trunk and two branches, and a stub extending from said junction between the branches thereof.

4. A feeder for an antenna array, said feeder comprising a sandwich of at least two spaced apart fiat substantially parallel conductors, at least one of said conductors having a Y-shaped junction having a trunk and two branches, and a stub extending from said junction, said stub being of a length less than one quarter wave length at the operatingv frequency, whereby a capacitive reactance is set up at said junction to cancel the normally existing lumped inductive reactance thereat.

5. A feeder as defined in claim 4 wherein said branches of said junction are arcuate in shape.

6. An antenna array feeder comprising a sandwich of two conductors, one of said conductorsl having a, Y- junction with a trunk and two arms, said trunk being operably connected through an impedance matching transformer section to an input branch, andeach of said armsv feeding through an impedance matching transformer section to a feeder branch' matched in impedance for connectionv to a radiating element of an antenna array, and a capacitive reactance stub extending from said Y-junction, said stub having a capacitive reactance at the operating frequency of such value as to substantially cancel the inductive reactance at said junction.

7:. An antenna array comprising a plurality of radiatingv elements, each of said elements being operahly connected to and fed by branches of la feeder system, said: feeder system having any input. leg, said input leg feeding the trunk of a Y-junctionv through an impedance matchin'g transformer, each of the arms. of said Y-junction: beingA arcuate and feeding a branch through. anv impedance transformer, one of s-aid branches being operably.v connected to and matched in impedance with one of said radiating elements, the other of said branches being operably connected to and feeding the trunk' of a secondI Y-junction, the arms of said second Y-junction feeding a trunk of a third Y-junction and a second one of said`v radiating elements, respectively, there being a plurality of' said branch fed Y-junctions of a number equal to one less than the number of radiating elements, each of the arms of. one of said Y-junctions being operably con-v nected to branches matched in impedance with and feedinga` radiating element, and a capacitive reactance stub extending from each ofV said Y-junctions between the arms` thereof to substantially cancelany inductive reactance at said junctions.

8. A high frequency feeder comprising an outer conductor formed byk parallel spaced conductive sheets, a multi-branch conductor in sandwiched spaced apart relation between said sheets, said multi-branch conductor having Y-shaped junctions, each of said junctions having a capacitive compensating stub.

Hershberger Nov. 5, 1946 Rumsey July 8, 1952