US2397645A - Antenna system - Google Patents

Description

April'2, 1946. I G. H. BROWN ANTENNA SYSTEM Filed May 30. 1942 2 Sheets-Sheet 1 Zsnventor George Brown v j va i wfimw F Fl n 5.; m fl m .0 0 H m 1 bu -mm U 14 m aulrflv 1| 7:. z T a 7 r/ a u i Z m mm ,5 2/1. a m m 7 u n ,i fi/ F; Z d 4 k I (Ittomeg G. H. BROWN ANTENNA SYSTEM Filed May 30. 1942 April 2, 1946.

2 -Sheets-Sheet 2 I DEV/CE I N VEN TOR. fiwrKHBrmr/m BY 1 Arron/5r Patented Apr-2,1946, g

George H. Brown, Haddonfleld, N. J., assignor to Radio Corporation of Americas corporation, of i Delaware Application May 36, 1942, Serial No. 445,175

4 Claims. (Cl. 25 -11) This invention relates to improvements in antenna systems of the ty'peused to establish overlapping radiation fields, and particularly to a system with meansfor minimizing the mutual coupling between the several antennas of an array and for reversing alternately the phase of the currents applied to certain of. the antennas with respect to the phase of the. currents applied to another group of antennas, whereby diflerently directed field patterns are obtained in synchronism with said phase reversals.

One-of the objects of this invention is to provide improved means for establishing two alternately differently directed and overlapping radio frequency'fields. A further'ob'iect is to provide improved means for directing the plane of the axes of said fields atan angle with respect to object is to provide improved means for minimizing mutual coupling efi'ects between the antennas of an array of the type described, and

for energizing all of said antennas from a single I source-in proper phase and power relationship to produce the desired field patterns. These and other and incidental objects will become apparent to those skilled in the artupon consideration of the following description; with reference to the accompanying drawings, in which Fig. 1 is a' schematic diagram of a radio frequency distribution circuit illustrating the principle of operation of the invention; Fig. 2 is aplan view, partly in section, of an antenna array representing one embodiment of the invention; Figs. -3 and 4 are elevations, partly in section, of parts of Fig. 1; Fig. 5 is adiagram. of the connections between the antennas shown in Fig. l and a transmitter or other radio device. Referring to Fig. 1, a line I, which is shown as a coaxialline, is connected in a closed loop. The length of line, pr perimeter of the loop, is made one and one-half wavelengths long at the frequency at which the system is to operate. Two sources, A and B (not shown), are connected as indicated at points.

spaced one-half wavelength apart around the loop in one direction. The distance between the two points in theother direction is one wavelength; the difference between the two distances is one-half wavelength. Therefore, any voltage at one of the points of connection will reach the other point bytwo paths and in opposite phases, producing rer'o resultant voltage. Thus there can be no reaction between the. sources A and B. Two loads, C and D, are likewise connected at suchpoints that-the difference in the length of transmission the'plane of said antenna array. Still another lengths of the two paths between them through the line is one-half wavelength, and there can be no reaction between them through the network. However, the voltage at each of the loads is a resultant of the voltages at the two sources,

and by providing suitable amplitude and phase relations between the two source voltages, any desired relation between the two load voltages may be obtained while maintaining isolation between the individual loads and, the individual sources. I

Referring to Fig; 2, the array which will be used as an example in describing the present invention comprises two centrally disposed antenna groups I and 3 and four antennas 5, I, 9 and ii disposed at the sides. Each of the side antennas is a dipole comprising two radiating sections, each one-quarter wavelength long at the irequency for which the system is designed; and

arranged end to end. Each of the groups I and 3 comprises four quarter, wave sections arranged end to end and connected as two dipoles energized in phase with eac other. The component quarter wave sections may be constructed of' pieces is of pipe or tubing, centered on rods it running through each group by means of plugs [1, as illustrated in Fig. 3. Metallic tubular supporting members l9 are secured near adjacent ends of the members i3, and are also employed as reactance elements, as described hereinafter.

In order to produce the required overlapping radiation fields, the center antennas are enerv gized constantly, while the polarities oi the side antennas are alternately reversed. The energy radiated by each side antenna alternately adds,

to and subtracts from that radiated by the centhe radiated fields, and directing theplane of the axis of the overlapping lobes at an angle with respect to the plane of the array. To give the,

ter antennas, thus producing a resultant field which is deflected alternately from side to side with respect to a center reference line. Two

central, groups of antennas and two pairs of side antennas are employed in the illustrated arrangement for thepurpose of concentrating desired difference in direction of the two lobes, each center group is made of four quarter wave sections. 1 The particular arrangement to be used, in any case is a matter of design, determined by the requirements. Ordinarily it is desirable. to

design the system so that the boundaries of the overlapping portion of the two ,lobes-are nearly parallel to each other, so that a'small deviation in position from-the axis of the overlapping area results in a'large difference in the intensities of the fields produced by the two radiation lobes at of the total power is radiated by the centerantennas, without switching, and one-fifth is radiated by the side antennas, which are, switched so that they are periodically reversed in phase.

The currents supplied to the antennas l, 5 and I are in quadrature phase with those supplied to antennas 3, 9 and II, respectively. The currents supplied to'the side antenna 5 should be either v exactly in phase or exactly 180 out of phase with that of the center antenna I, depending on which lobe is being radiated, if the side antennas 5 and I were arranged in line with the corresponding center antenna I. Since the side antennas are not in line with the center antennas, their currents must be shifted in phase with rev spect to the currents in the center antennas.

Referring to Fig. 4, each center group is excited as two hali-wa've antennasin phase, sectionalized by means of the conductive support-- ing members 25 anda shorting member 23. The distance S4 of the member 23 from the points where the supports 25 are attached to the antenna is adjusted so that the loop formed by the members 25 and the member 23, together with the capacitance between the adjacent ends 01' the antenna elements, constitutes a high impedance resonant circuit, eflectively isolating the two sections. The supports 21 are similarly tuned by shorting members II, and the loop formed by members 2i and 21 is used as a loading reactance across the input terminals of each or the component dipoles. The e'flfective value of the reactance is determined by the distance Si between each,

member 2| and the points where the corresponding supports 21 are attached to the antenna. The supports I9 of the side antennas are likewise employed, in conjunction with shorting members 28, gas loading reactances or insulators as shown in 8. 2. Referring to Fig. 5, the center antennas I and 3 are represented schematically. The component dipoles 3| and 33 of the antenna I, and the cors,so7,o4o

present at the point 43 will thus result in .edual and opposite currents at points 45 and 41, since the difference in the line lengths is one-half wavelength. A junction point 5| is also connected to points 45 and 41 through quarter wavelength lines. Any voltage at junction 5| will thus produce equal currents in the same direction at the points 45 and 41. Since the points 49 and 5| are thus connected together through two paths difiering in length by one hali wavelength, the voltage at each of the two points is cancelled at the other and can produce no effect. The points 49 and 5| therefore may be energized in quadrature phase relation without interaction.

If this is done, the resultant currents at points 45 and '41 will be in quadrature with respect to each other and hence the antennas I-and ,3 will be energizedv in quadrature, notwithstandingany coupling between them or other antennas. It points and 41 were fed inquadrature directly without the above described network, interaction between their radiation fields would be reflectedto th phase shifting networks and make adjustment of the system difficult, if not impossible; coupling with the side antenna groups would affect the adjustment, and since the side antennas are periodically reversed, the problem would be further complicated.

The points 49 and 5| are connected through lines of diflerent lengths to a junction point 53. Phasing stubs 5,5 and 51 are connected in these lines one-quarter wavelength distant from the point 53. The stubs 55 and 5'! are tuned off the resonance frequency and thus function as reactances connected .across the lines. The line lengths and the positions and lengths of the phasing stubs are adjusted so that a voltage applied at the point 53 produces voltages at 49 and 5i which are of equal. amplitudes and in quadrature phase. In order to compensate the impedance mismatch due to the connection of the two antenna lines at 53 to the line 6! from the transmltter, a matching stub 58 is connected to the responding dipoles 35 and 31o! the antenna 3. e

are connected together and to a transmitter or other radio device 35, by lengths of transmission line 4|, which in this case is shown as concentric line. The component dipoles of the antenna I are excited to radiate in phase; since, as shown in Fig. 3, their respective connections to the inner conductor 43' are reversed, the dipole 33 is led through a line one-half wavelength longer than the line to the dipole 3|, thus producing a 180 phase diflerence between the currents reaching the two dipoles and causing them to radiate in phase. The total length of line between antennas 3i and 33 is one wavelength. or an integral number 0! wavelengths. Since the antennas are connected in reverse polarity to the line, any diflerence in their currents. such .as might tend to result from coupling with the side antennas, is prevented by transfer of energy from one antenna to the other through the line. The dipoles 35 and 31 are connected like the dipoles 3| and 33. The junctions 45 and 41 are connected as follows to be energized in quadrature phase with respect to each other: A junction point 49 is conline M at a suitable point, and adjusted so that no standing waves appear on the line 5i between the transmitter and the matching stub. The line 6i may then be made 01' any convenient length.

Each of the side antennas 5 and I is connected through a quarter wavelength line 44 to a junction point 46. The antennas are. connected in opposite polaritiesrto the line, so they will radiate 180 out of phase. The side antennas 9 and nected to junction through a three quarter Y wavelength line and to the junction 41 through a one-quarter wavelength line. Any voltage I I are similarly connected to a point 48. The connections between points 46 and 48 and the transmission line 83 are exactly like those shown in Fig. 5 between points 45 and 41 and the line 6|. To provide periodic reversal oi the polarities of the side antennas 5, I, 3 and II, the phase of the voltage fed into the line 63 is reversed. This is done by connecting the line 53 to the transmitter alternately through two paths, one of which is one-half wavelength longer than the other.

Thelines 81 and 58, forming the two paths. are connected to the line 53 at the point 65, and to a line II at point I3. If the line 69 is short-circuited at. a point 15, it will present a very high impedance at the points 85 and 13 which are each one-quarter wavelength distant from the short circuit, and no energy will flow into it at either end, Similarly. if the line is short circuited at a point vH, an odd number oi quarter wavelengths distant from both points 35 and 13.

it will present substantially an open circuit at those points. Thus, it the lines are shortcircuited alternately at points 15 and I'I by means scheaeeaecs inatically indicated at 19, the voltage at the point 85 will be alternately in phase and out 01' phase 7 with respect to the voltage at the point 13, and

' polarities oi the antennas s, 1, a and will be reversed correspondingly. The switchingmeam 19 may be of the type described in U. 8. Patent No. 2,189,549 to William D. Hershberger. Power division between the center antennas and the side at a common point, and/phasing circuits 'includ-" antennas is accomplished by providing two quarfer wavelength sections 81 and 83 in parallel with each other :and inseries with the line II. This causes the impedance atthe point 81 to be reflected at the point 89 as an impedance oneiourth as great.

A quarter wavelength section. is provided to the lengths o! the two paths through the network from one of said latter points oi connection .to the other diiier by anodd number of hall, wavelengths, whereby the voltage at each oi said points is unaflected by that at the other, a thirdtransmission line connected to bothof said supply-lines ingreactanee elements shunting said supply lines,

at critical points whereby the volta e at the point of one of said supply linesto said parallel con- I nected lines is maintained in predetermined phase act as impedance inverter, so the impedance presented at the point'9l by the side antenna circuit.

' is four times as highas it is at the point 81, and four times that presented by the center antenna circuit through the line 8!. Thus one-fifth oi the power supplied from thedevice 39 through the line will flow to the side antennas, andv iourfifths of the power will 'fiow-to the .center antennash The length of the line 6| may be trimmed to secure the required phase relations between the center and side antennas. An impedance matching stub Sils connected to the line 03' to compensate the mismatch caused by connecting the lines 85 and 6| together to the line 93.

Thus the invention has been described as an antenna system arranged to produce alternately tion'may be used in other applications where it is desirable to avoid mutual coupling between radio devices and yet connect a plurality oi such and amplitude relation to that at theIpoint of connection or the other 01 said supply lines to the other of said parallel connected lines, impedance converting means connected between said source of radio frequency energy and all oi said'side antennas comprising two quarter wavelength line sections connected in parallel with each other and in series with a third quarter wavelength line section, whereby said side antenna circuit and said center antenna circuit present diil'erent impedances to said source'and take correspondingly different proportions oi power. therefrom.

2. An antenna system, 'comprlsing two groups oi antennas, each of said groups comprising a centrally positioned antenna and two antennas arranged at the sides-oi said first antenna, means for energizing each of the antennas or one of said groups in predetermined ,phase with respect to the corresponding antennas of the other of said groups, comprising,ior each pair of correspond-5 (sing antennas, a on line connected in a closed loop, with said pair of antennas connected to said loop at points such that the difference in lengths or the two paths around said loop between said points is one-halt wavelength, two lead-in line's connected to said loop at points such that devices to a common circuit. For example, a radio transmitter and a radio receiver may be;

connected 'tola common antenna system by a network according to the invention, and arranged so that no energy is transferred from one to the other through the circuit.

.. I claim as my invention:

-1. A system for producing overlapping radia- I tion fields including two groups of antennas, each oi said groups comprising a centrally positioned energy so as to be energized constantly, and two side antennas arranged at the'sides of said first antenna, switching means, and connections from said source through said switching means to said side. antennas so as to periodically reverse said side antennas in phase, means for energizing the antennas of one of said groupsin predetermined,

phase with respect to the corresponding antennas of the other oilsaidgroups comprising two transmission lines, each an integral number of half antenna. connected to a source oi'radio frequency wavelengths long at the irequencyat which the Y I system is to operate, extending in parallel con-- nection-between correspondingpoints in the circuits or said antenna groups, said lines differing in length by an odd number 0! half wave-lengths,

7 tionship. Y 4. 'iheinventionassetiorthinclaimswherein the difierence in lengths of the two paths around said loop between said latter points is one-hall wavelength, phasing means including reactanceelements shunting eachoi said lead-in lines, two 1 supply linesgeach connected to one pair of said lead-in lines at a commonpoint, switching means arranged in oneoi said supp y" lines to vary the eilective length or saidiine, a radio device con,- nected to both 01' said supply lines at a common point, and impedance inverting means in one of said supplylines arrangedto present at said radio A device an impedance of diflerent magnitude from that presented by the other r said supply lines.

3. A directiv'eiantenna vsystem including two groups or radiator elements whichare to be en-" ergized'in a predetermined phase relationship to each other, an electrical network having two pairs 1 of conjugate terminals, connections from said groups respectively to one conju te pair of said network terminals, 0. common supply line for said elements and branch-lines connected from said common line to the other conjugate pair oi said network terminals, said branch lines diilering 'i'romeachotherinlength byan amount related in a predetermined manner to said phase relsv said network includes a transmission line 1% whereby the voltage at each 0! said corresponding points is ,imafiected by that at the other 02- said' points, two supply lines, each connected to one or long connectedin a closed loop and" .said coniutateterminals comprise points la svelens 'saertonaidune.

' amass n.

l 3* said parallel connected lines at such a point that

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