Antenna system

April 2, 1946.

G. H. BROWN

2,397,645

ANTENNA SYSTEM

Filed May 30. 1942

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attorney

April 2, 1946.

2,397,645

G. H. BROWN

ANTENNA SYSTEM

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BY

Patented Apr. 2,1946

2,397,645

UNITED STATES PATENT OFFICE

This invention relates to improvements in antenna systems of the type used to establish overlapping radiation fields, and particularly to a system with means for 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 differently 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 object is to provide improved means for directing the plane of the axes of said fields at an angle with respect to the plane of said antenna array. Still another object is to provide improved means for minimizing mutual coupling effects between the antennas of an array of the type described, and for energizing all of said antennas from a single 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 art upon consideration of the following description, with reference to the accompanying drawings, in which Hg. 1 is a schematic diagram of a radio frequency distribution circuit illustrating the principle of operation of the invention; Hg. 2 is a plan view, partly in section, of an antenna array representing one embodiment of the invention; Hgs. 3 and 4 are elevations, partly in section, of parts of Hg. 1; Hg. 5 is a diagram of the connections between the antennas shown in Hg. 1 and a transmitter or other radio device.

Referring to Hg. 1, a length of transmission line 111, which is shown as a coaxial line, is connected in a closed loop. The length of line, jor 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 the other 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 by two paths and in opposite phases, producing zero resultant voltage. Thus there can be no reaction between the sources A and B. Two loads, C and D, are likewise connected at such points that the difference in the

2,397,645 ANTENNA SYSTEM /

George H. Brown, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of &lt; Delaware

Application May 30,1942, Serial No. 445,175

Claims. (CL 250—11) 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.

Referring to Hg. 2, the array which will be used as an example in describing the present invention corhprises two centrally disposed antenna groups I and 3 and four antennas 5, 7, 9 and 11 disposed at the sides. Each of the side antennas is a dipole comprising two radiating sections, each one-quarter wavelength long at the frequency 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 each other. The component quarter wave sections may be constructed of pieces 13 of pipe or tubing, centered on rods 15 running through each group by means of plugs 17, as illustrated in Hg. 3. Metallic tubular supporting members 19 are secured near adjacent ends of the members 13, and are also employed as ' reactance elements, as described hereinafter.

In order to produce the required overlapping radiation fields, the center antennas are energized constantly, while the polarities of the side antennas are alternately reversed. The energy radiated by each side antenna alternately adds to and subtracts from that radiated by the center 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 the purpose of concentrating the radiated fields, and directing the plane of the axis of the overlapping lobes at an angle with respect to the plane of the array. To give the desired difference in direction of the two lobes, each center group is made of four quarter wave sections. 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 &lt;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

2,397,645 the fields produced by the two radiation lobes at that position. Another important problem is the prevention of radiation in directions other than those of the two desired lobes.

In the illustrated array (see Fig. 2) four fifths of the total power is radiated by the center antennas, 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 i, B and 7 are in quadrature phase with those supplied to antennas 3, 9 and 1I, respectively. The currents supplied to the side antenna 5 should be either 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 S and 7 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 respect to the currents in the center antennas.

Referring to Fig. 4, each center group is excited as two half-wave antennas in phase, sectionalized by means of the conductive supporting members 25 and a shorting member 23. The distance Si 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 of the antenna elements, constitutes a high impedance resonant circuit, effectively isolating the two sections. The supports 27 are similarly tuned by shorting members 21, and the loop formed by members 21 and 27 is used as a loading reactance across the input terminals of each of the component dipoles. The effective value of the reactance is determined by the distance S3 between each member 21 and the points where the corresponding supports 27 are attached to the antenna. The supports 19 of the side antennas are likewise employed, in conjunction with shorting members ί ί, as loading reactances or insulators as shown in Fig. 2.

Referring to Fig. 5, the center antennas I and 3 are represented schematically. The component dipoles 31 and 33 of the antenna I, and the corresponding dipoles 35 and 37 of the antenna 3, are connected together and to a transmitter or other radio device 89, by lengths of transmission line 41, 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 fed through a line one-half wavelength longer than the line to the dipole 31, thus producing a 180° phase difference between the currents reaching the two dipoles and causing them to radiate in phase. The total length of line between antennas 31 and 33 is one wavelength, or an integral number of wavelengths. Since the antennas are connected in reverse polarity to the line, any difference 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 37 are connected like the dipoles 31 and 33.

The junctions 45 and 47 are connected as follows to be energized in quadrature phase with respect to each other: A junction point 49 is connected to junction 45 through a three quarter wavelength line and to the junction 47 through a one-quarter wavelength line. Any voltage present at the point 49 will thus result In equal and opposite currents at points 45 and 47, since the difference in the line lengths is one-half wavelength. A junction point 51 is also con5 nected to points 45 and 47 through quarter Wavelength lines. Any voltage at junction 51 will thus produce equal currents in the same direction at the points 45 and 47. Since the points 49 and 51 are thus connected together through two 10 paths differing in length by one-half wavelength, the voltage at each of the two points is cancelled at the other and Can produce no effect. The points 49 and 51 therefore may be energized in quadrature phase relation without interaction. 15 If this is done, the resultant currents at points 45 and 47 will be in quadrature with respect to each other and hence the antennas ί and 3 will be energized in quadrature, notwithstanding any coupling between them or other antennas. If 2Q points 45 and 4T were fed in quadrature directly without the above described network, interaction between their radiation fields would be reflected to the phase shifting networks and make adjustment of the system difficult, if not impossible; ₂₅ 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 51 are connected through 50 lines of different lengths to a junction point 53.

Phasing stubs 55 and 57 are connected in these lines one-quarter wavelength distant from the point 53. The stubs 55 and 57 are tuned off the resonance frequency and thus function as react35 ances 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 51 which are of equal amplitudes and in quadra40 ture phase. In order to compensate the impedance mismatch due to the connection of the two antenna lines at 53 to the line 61 from the transmitter, a matching stub 59 is connected to the line 61 at a suitable point, and adjusted so that 45 no standing waves appear on the line 6 ί between the transmitter and the matching stub. The line 61 may then be made of any convenient length.

Each of the side antennas 5 and 7 is connected through a quarter wavelength line 44 to a junc50 tion point 46. The antennas are connected in opposite polarities to the line, so they will radiate 180° out of phase. The side antennas 9 and ί I are similarly Connected to a point 48. The connections between points 46 and 48 and the 55 transmission line 63 are exactly like those shown in Fig. 5 between points 45 and 47 and the line 61. To provide periodic reversal of the polarities of the side antennas 5, 7, 9 and II, the phase of the voltage fed into the line 63 is reversed. This is 60 done by connecting the line 63 to the transmitter alternately through two paths, one of which is one-half wavelength longer than the other. The lines 67 and 69, forming the two paths, are connected to the line 63 at the point 65, and to a 65 line 71 at point 73. If the line 69 is short-circuited at a point 75, it will present a very high impedance at the points 65 and 73 which are each one-quarter wavelength distant from the short circuit, and no energy will flow into it at 70 either end. Similarly, if the line is short circuited at a point 77, an odd number of quarter wavelengths distant from both points 65 and 73, it will present substantially an open circuit at those points. Thus, if the lines are shortcirculted 75 alternately at points 75 and 77 by means scheΛΒ97.64Β said parallel connected lines at such a point that the lengths of the two paths through the network from one of said latter points of connection to the other differ by an odd number of half wavelengths, whereby the voltage at each of said points is unaffected by that at the other, a third transmissionline connected to both of said supply lines at a common point, and;phasing circuits including reactance elements shunting said supply lines at critical points whereby the voltage at the point of one of said supply lines to said parallel connected lines is maintained in predetermined phase and amplitude relation to that at the point of connection of the other of said supply lines to the other of said parallel connected lines, impedance converting means connected between said source of radio frequency energy and all of 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 different impedances to said source and take correspondingly different proportions of power therefrom.

2. An antenna system, comprising two groups of antennas, each of said groups comprising a centrally positioned antenna and two antennas arranged at the sides of said first antenna, means for energizing each of the antennas of one of said groups in predetermined ,phase with respect to the corresponding antennas of the other of Said groups, comprising, for each pair of corresponding antennas, a transmission line connected in a closed loop, with said pair of antennas connected to said loop at points such that the difference in lengths of the two paths around said loop between said points is one-half wavelength, two lead-in lines connected to said loop at points suck that the difference in lengths of the two paths around said loop between said latter points is one-half wavelength, phasing means including reactance elements shunting each of said lead-in lines, two supply lines, each connected to one pair of said lead-in lines at a common point, switching means arranged in one of said supply lines to vary the effective length of said line, a radio device connected to both of said supply lines at a common point, and impedance inverting means in one of said supply lines arranged to present to said radio ' device an impedance of different magnitude from that presented by the other of said supply lines.

3. A directive antenna system including two groups of radiator elements which are to be en- , ergized in a predetermined phase relationship to ' each other, an electrical network having two pain of conjugate terminals, connections from said groups respectively to one conjugate pair of said network terminals, a common supply line for said elements and branch lines connected from said ¹ common line to the other conjugate pair of said network terminals, said branch lines differing matically indicated at 19, the voltage at the point 69 will be alternately in phase and out of phase with respect to the voltage at the point 73, and polarities of the antennas 6, 7, 9 and tl will be reversed correspondingly. The switching means 79 may be of the type described In U. S. Patent No. 2,189,549 to William D. Hershberger. Power division between the center antennas and the side antennas is accomplished by providing two quarter wavelength sections 81 and 83 in parallel with each other and in series with the line 71. This causes the impedance at the point 87 to be reflected at the point 89 as an impedance onefourth as great.

A quarter wavelength section 85 is provided to act as Impedance inverter, so the impedance presented at the point 91 by the side antenna circuit is four times as high as it is at the point 87, and four times that presented by the center antenna circuit through the line 61. Thus one-fifth of the power supplied from the device 39 through the line will flow to the side antennas, and fourfifths of the power will flow to the center antennas. . The length of the line 61 may be trimmed to secure the required phase relations between the center and side antennas. An impedance matching stub 95 is connected to the line 83 to compensate the mismatch caused by connecting the lines 85 and 61 together to the line 83.

Thus the invention has been described as an 30 antenna system arranged to produce alternately overlapping fields. The various components of the array are energized from a single source, through circuits arranged to minimize the effects of mutual coupling and to provide the phase and power relations between the component antennas required to produce the desired fields. While a single embodiment has been described, this invention may be used in other applications where it is desirable to avoid mutual coupling between radio devices and yet connect a plurality of such devices to a common circuit. For example, a radio transmitter and a radio receiver may be connected to a 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.