Dec._3, 1946- R. c. LONGFELLOW V DIRECTIVE RADIO ‘ SYSTEM Filed Sept. 26, 1941 2,412,150 - ‘ ' 3 Sheets-Sheet’ 1 75.3.1. kg, F" 31% '31?“ - “ 0%41.31‘ I ‘ ' Re cel'ver Fansm/éter - Inventor“: Richard C.L0n Fellow, byiv? 'éfii His ‘ btorney. ' Dec. 3, 1946. _R. c. LONGFELLOW" - I 2,412,160 DIRECTIVE RADIO SYSTEM Filed Sept. 26, 1941 ‘ 3 Sheets-éheet 2 Fig.2. Invehtor": Richard C. Longfellow, His tborney Dec- 3, 1946- R.‘c. LONGFELLOW 2,412,160 ' DIRECTIVE RADIO SYSTEM ' ‘Fig.5. f/ . ' Inventor‘ -..*-1'~_/:r Richard C. Lon gfellow 2 '- ' byHis ‘.mVZaaMM t’cobney _ ‘2,412,160 Patented Dec. 3, 1946 UNITED STATES PATENT oF-rice ‘ Richard C. Longfellow, Schenectady, N. Y., as si'gnor- to“ General Electric Company, a corpo ration‘ of New York Application September 26, 1941, SerialENo. li12,452 10'Clairns‘. (Cl. 250-11) . 14 . 2‘ . which,- at the: same time. is somewhat simpler My invention relates; to; directive radio sys tems‘ and more particularly to means for vary-. and more economical to- construct. the location of distant objects-f moving’ craft,- and the like, it is desirable that the directivity of energy is carried are avoided. ‘ An object» of my invention is to provide an im proved system for- varying. the ‘directivity of. such 0 systems. ‘ _ > three or more directions by variationof the phase relation of the waves supplied to the different 7 _ In copendingapplication of'Lawrence M. Leeds, Serial No. 410,836} ?led-y, simultaneously herewith, i method of operation, together with further ob Fig. 4 represents the capacitance switch utilized entitled. Directive radio systems, and which is in the form of the invention shown in‘ Fig. 1; Fig. 5 represents the structure of the diode em-v ployed in my invention, and Figure 6 is a dia grammatical showing of a modi?cation. of my‘ in assigned to the same assignee as my present ap- - plication, is shown a system involving four ra diators located at the corners of a rectangle. Each’ of? these radiators is connected‘ through transmissionlines to the respective corners of a transmissionv line loop. or “phasing rectangle.” ’ The novel features which I' believe to be char acteristic of my invention are set forthwith par ticularity in the appended claims. My invention itself, however, both as to its organization and jects and advantages thereof, may best be im-v derstood by reference to the following descrip tion taken in connection with the accompany ing. drawings in. which Fig. 1 represents a dia grammatical showing of an embodiment of’ my invention; Fig. 2" represents‘a modi?cation there} of; Fig. 3' represents the antenna array employed; Another object of my invention is to simplify systems in which the 'directivity is variable in antennae. i ' leading ‘to, different antennae in which no useful Li the antennae arrays employed be readily and electrically variable; ' Another object of- my invention. is to provide a system, in which interconnections betweenv lines ing/ the directivity of such‘ systems.» _ In directive systems‘ such as- are employed for vention. 25 Transmission lines? then extend from interine~> diate points on all of- the sides of the loop, or ’ " Referring to‘ Fig‘. l of the drawings, I have shown therein four antennae, I, 2, 3' and 4‘, ar ranged at the respective corners of a rectangle. Theseantennae preferably‘ are disposed in van “phasing rectangle” to the radio apparatus, array and mounted for orientation both in‘ eleva which may comprise either a transmitter, orja receiver,‘ or’ both. Means are‘ provided‘ whereby 30 tion and in‘ azimuth, or train. In Fig. 3, I have shown the antennae l, 2, 3 and 4’ as mounted transmission‘ over any three of these latter lines in a suitable array and arranged for rotation in may be simultaneously‘ interrupted thereby‘ to the vertical plane about a pivot 5‘. This pivot 5 con?ne transmission to‘ any single one of the is arranged in the support 6 which may be‘ ro lines extending to the radio apparatus. Thus energy transmitted‘ over any line excites one pair , tated in the‘ horizontal plane-whereby the array of antennae'may be ‘oriented both in the_ hori of adj acent' antennae inj phase‘,and' it excites the zontal plane and in the vertical plane. remaining‘ adjacent pair in phase; but the latter In accordance with my invention as illuse pair is excited in displaced phase relation with respect to the ?rst‘ pair by an amount equal to the electrical length of the‘ “phasing rectangle.” Thus the antenna array has‘ maximum e?e'ct ‘dated in the embodiment of Fig. _1, the direction 4.0 directions about the normal ofthe array. As illustrated in the‘ drawings, each of ‘the an tennae: l, 2, 3 and 4- comprises four dipoles, a, b, with respect to a direction at an angle to the normal to the plane‘ of the‘ array. This effect may be varied through any of four directions about‘ the normal to the array by changing the c and d, the dipoles a and b being positioned end to‘ end and the‘ dipoles c and (1 being positioned line through which transmission between the radio‘ apparatus and. the “phasing rectangle” is con?ned. of maximum effect of the array‘ when oriented in any'direction may be shifted to any one ‘of ,four end to end parallel with the dipoles a and Debut at a distance one half of a wave length there ‘ Such‘ a system possesses certain very desirable from. The dipoles themselves, of course, have advantages. An object of my invention is to pro- - a length equal to half of a wave length of the wave at which they operate. The end of di pole b adjacent dipole d is connected to theend of dipole 0 adjacent dipole d and similarly dipole a is connected to dipole d. The antenna l is also positioned in end-toeend. relation with the Vide a system having improved capabilities with respect to the angle through which the direction of maximum effect of the antenna may be shifted.v ,Aiurther object of my present invention isto: provide such; an improved systemv and one 55 2,412,160 3 antenna 2, and similarly antenna 3 is positioned in end-to-end relation with antenna 4, and an tennae 3 and 4 are positioned a half wave length from the antennae I and 2, all, of course, in the same plane. While this relative spacing of the different antennae has been departed from in Fig. 1 for the purposeof clearness of that draw ing, the antennae are shown so relatively spaced in Fig. 3. While I have shown and described a particular form of directive antenna, it will of course be understood that any desired form of antenna may be used at the corners of the rectangle, as, for example, simple dipoles. ' -' The antennae positioned‘ at diagonally oppo site corners of the rectangle are connected to gether through a transmission line; that is, the antenna I is connected to the antenna 4 through a transmission line ‘I, and antenna 2 is connected to antenna 3 through a transmission line 8. These transmission lines may be of the concentric conductor type in which the outer conductor may be -maintained at ground potential. The inner conductor ‘I, or 8, is connected to one side of the feed point of each of the antennae to which it is connected. Conductor ‘I, for example, is con nected to the left-hand terminal of the feed point A of antenna I and to the left-hand terminal of the feed point D of antenna 4. Since the imped ance of the dipolesvat the feed points-A, B, C and’ D is balanced with respect to ground, means must ‘be provided to effect'the connection between the balance'impedance of the antennae vand the sin ‘ gle-ended transmission line. This is effected by means of a sleeve I9 positioned about the end of each transmission line, this sleeve having a length ‘equal to a quarter of a wave length of the wave at which the system operates. The sleeve is con ductively connected to the outer sheath of the transmission line at a vpoint'one quarter of a wave ‘length from the end ‘of that sheath, and ,forms with the end quarter of a‘wave length of the sheath a' transmission linehaving a length of a quarter of a wave length and which ‘is'short circuited at the end remote'from the antenna. These sleeves I0 are grounded and insulated from the end quarter of a wave length of the sheath. Since they form a quarter .wave length transmis Sion line with the end of the sheath, ‘those ends oscillate with respect to ground in opposed phase ' relation to the inner conductor and .thus the inner conductor and the end of the sheath have an impedance between them which is balanced .with respectv to ground and which may be con nected directly across the respective feed points A, B, C or D. - ' ' ' _ ~These antennae I, 2, 3 and 4 are connected through transmission lines to radio apparatus ~comprising a transmitter I1 and a‘ receiver I9, both shown near the bottom of the drawing. These connections comprise transmission lines I I, ,I2, I3 and I4, as shown on the drawing, all of which are connected together at the point I5 and thence through transmission line It to the trans mitter I'I and‘through transmission line I8 to the receiver 1I9.. Transmission lines II-and I2 are connected to points on the line] removed from Lines I3 and I4 are similarly connected to line 3. Means are provided whereby only two of these II, I2, I3 and I4 are employed at a time, one being connected to the line 'I and the other to the line 8, This means comprises the capaci tance switch 20. e y This capacitance devicev comprises four station ary capacitance electrodes 2|, 22, 23 and 24, each of which is connected through the inner conduc tor of concentric transmission lines 25, 26, 21, 28 to a point on-the respective transmission lines II, I3, I2 and I4 respectively. This capacitance de~ vice also comprises a rotating capacitance elec trode 29, which is grounded as at 30 and which may be in the form of half of a disk whereby it simultaneously cooperates with any two of the electrodes 2I, 22, 23 and 24 depending upon its position about pivot point 3I. Thus in the po sition shown, this ‘electrode 29 cooperates with electrodes 2I and 22 producing high capacitance between it and electrodes 2I and 22. 7' Similarly,‘ low capacitance exists between electrodes 23 and 29, and between electrodes 24 and 29. ' _ ’ Electrode 2| is connected through the line 28, which has a length equal to’ an odd number' of quarter Wave lengths, to the point 32 on line I4. Since line 28' is an odd number of quarter wave lengths in length, the low impedance between electrodes 2| and 29 produces a high impedance at the point 32 whereby the line 28 has little effect upon the transfer of energy through the line H past point 32. ' _ > " Electrode 22 is similarly connected through the line 2'! to the point 33 on line I2 and for vthe same reason has little e?ect upon the transfer of energy through the line I2 past point 33. " Electrodes 23 and 24, being similarly connected to points 34_and 35 respectively on transmission lines II and I3, have very great e?‘ect upon the transfer of energy through the lines I I and‘ I3 since high impedance exists between these elece trodes and the electrode 29. That is, these var ious lines 25, 26, 21 and 28 operate as impedance inversion networks producing high impedance at the respective points 32, 33, 34‘ and 35' when low impedance exists between the corresponding ?xed electrode and the rotor 29,'and producing low impedance at the points 32, 33, 34, 35 when high impedance exists between the respective ?xed capacitance electrode and the electrode 29'. Thus it will be seen that with‘, electrode 29 in the position shown, conductorsII' and I3 are vef fectively short circuited in the points 34 and 35. A short circuit at the'p'oint 34 does not affect transmission of energy through line, 7, however, .because the length or" lin'e'I I between point, 34 and the point of connection with line 7 is also an odd number of quarter wave lengths in length. Also a'short circuit» at point 34 does'not impair transfer of energy past point I5 on‘any of the other circuits because the length of 'line II from point '34 to point I5 is also an odd number of quarter wave lengths in length. This same re‘ ' llationship between the lengths of'the different sections of the transmission line I I is true of each of the other transmission lines I2, I3 and.I4. ;the midpoint of that line so that each line II. or Thus, with electrode 29 inthe positionshown, , ,I2 is connected to the line ‘I at a point nearer to transfer of energy over lines- II'and I3, either in one of the antennae I and 4 than it is to the other. 70 transmission or reception, is interrupted. Such Thus if energy be suppliedv over linev II to the transmission, however, takes place over lines I2 vlines‘! itexcites antennae I and 4 with a phase fdi?erence equal to the electrical difference in the lengths of the path over which thewaves are ‘supplied to the'respective antennae. ' ' v and I4. 1' ‘ ' During transmission, energy is supplied rover "lines I2 and I4 and lines ‘I and 8 to all of the different radiators‘ I,l2»,~ 3 and-4. 5This» energy 2,412,160. 5 6 is supplied to the radiators 2 and It in phase since transmitter, high voltageis produced upon the. the lengths of the paths leading to these radia anode of the diode 31 and this diode becomes conducting, producing'low impedance across. the end of the stub transmission line 38 during. the transmitted impulses. This low impedance, how ever, does not exist during reception because the diode is. not then conducting. 'This low imped ance of the diode 31 doesnot impair transmission tors are equal. It is also supplied to the radi ators I" and 3 in phase since the lengths of the paths'leading to these radiators are equal. The energy supplied to the radiators I and 3 is de layed in phase with respect to the energy sup plied to radiators 2 and 4, and accordingly the direction of maximum e?ect of the array is shift. over the line I6 because the stub line 38 has a ed~ from the normal of the array in the horizontal 10 length equal to a. half of a wave length so that plane by an angle corresponding to the difference the diode 3'I-v produces. low impedance at the point in the length of the’ paths leading to the an 39. The distance between the points 39'I‘and1 36 tennae 2 and- l% from those. leading to the an is an odd number of quarter wave lengths so tennae I and 3. that the. diode has the effect of producing high Nowlet- us suppose thatr the capacitance elec 15 impedance at the point 36. trode 29 is rotated clockwise through 90°. Then Fig. 2 shows a form of my invention involving low impedance exists between electrodes 22 and only three antennae I, 2 and 3-, these antennae 29-, and between electrodes 24 and 29. This ren being positioned at the vertices of a triangle ders lines I72 and i3 free for transmission of en rather than at the corners of a rectangle as in ergy between the radio apparatus and the an 20 tennae, and produces short circuits at the p ints 32 and 34 thereby interrupting transfer of en ergy- through conductors I I and I4. Now for the Fig. 1. Each of these: antennae is connected to the transmitter through respective transmission lines 59, El and 52, these lines being- intercon nected by lines 53, 54 and‘ 55', which may bewof same reason as that previously described, an equal lengths. tennae‘ I and 2 are energized with currents in delayed phase relation with respect to the cur rent supplied to antennae 3 and 4, and the direc tion of maximum effect of the array is shifted from the normal in the vertical plane by an amount corresponding to the electrical difference " in the length of the various paths. If condenser 29 be shifted from the position shown through 189°, the beam will be shifted from the normal in the horizontal plane in the opposite direction and- by an equal amount from Capacitance device» 564 is also employed but is of slightly different character from that‘ shown in that in which it is shifted with the condenser 28in the position shown. If it be shifted through 2'70°- in clockwise direc tion, then the beam will be shifted downward in the vertical plane. The receiver i9 is connected to the transmis sion line at the point 35 distant from the trans Fig. 1 in that its rotor is in the form of an arc 40 low the connection to the receiver is made at a point 36 distant from the transmitter by a quar ter wave length or odd multiple thereof, whereby, because of the impedance inversion effect of the section of line between point 35 and the trans mitter, the transmitter impedance, as viewed from point 36 is high. System such as that described may be em ployed in'connection with echo systems in which impulses are transmitted at a very rapid rate and echoes thereof are received in the intervals between the transmitted impulses. It is desirable, therefore, that the receiver be protected from the'inten‘se impulses produced by the transmitter. Unless such protection is provided the intense transmitted impulses may impair the sensitivity subtending approximately 120° rather than 180°. This condenser com-prises three ?xed electrodes 51, 58 and 59, each connected to the‘ respective transmission line 50, 5|, 52 through transmis sion lines 80, SI‘ and 62 respectively. These lat ter lines 69, BI and (52V have a length equal to an odd‘ number of quarter wave lengths, as explained before whereby, with the" capacitance electrode 63 of- swi'tching- device 56 in the position shown, the electrodes 5-? and 59 produce low“ impedance at the points. 64 and‘ I56 on the‘lines 5i] and 52' and thus impair transmission over‘ these lines. These points, however, arepositioned an odd number of quarter wave lengths from the point I5. so that the short circuit at the'points 64 and 66 does not mitter by an amount such that the impedance of- the transmitter as viewed from the point 35 is high. For example; if the transmitter impedance be , Li impair transmission over line 51' past the point l5. Electrode 58', having low impedance‘ to elec trode 63, produces a high impedance at the point 55. and thus line El is in transmitting condition. Energy is transmitted up line 5| to the point 68 Where it ‘divides one portion passing to antenna 2 and another portion passing, to antennae I and 3 through’ line 55-, and line '53 andiil in one case, and 515‘v and 52-1 in the, other. The 'sec'tionlof line between'points ‘61 and 65 is an odd number‘ of quarter wave lengths in length so that the short at point ?é'does not impair transmission-from line 53 to antenna I past point 61‘. The same‘ is true with respect to the section of line between points so. and s9 and also-between points. as and 63. -' The-points 61‘, 68' and'?dv are so positioned‘ and ‘the connections 53, 54 and 55v are of such length that the array, when operating through the line 51, has a maximum effect in the vertical plane at ‘ an. angle to the» normal. ' of'vthe receiver and the receiver will not have suf If electrode 63 be rotated through 120" in clock ficient time in which to recover before reception wise direction, then transmission takes place over by- it is required. The result is that it may be 65 line 52‘ and transmission over lines 50' and 5| is insensitive during the time when the impulses interrupted. ‘ The beam is now shifted through tobe received arrive. For this reason the diode .3115 is employed, the anode thereof being con~ nected to the end- of the inner conductor of a an’ arc of approximately 120° about the normal to the plane-of the array. If the-electrode 56 be rotated to its third posi stubtransmission line 33 extending from the 70 tion, theidirection of maximum effect of the array pointx39 on transmission line IS. The cathode of ‘willbe shifted through a further 120°. .thediodeB'I is connected to ground and through Fig. 4 shows in greater detail'the condenser albattery 40 to the outer conductor of the con structure of the form of theinventionshown in .centric. transmission line, 38. During the trans Fig. 1,, the electrodes 2|, 22', _23,' 24‘and. 29 all mission of'the intense impulses produced b‘y'the‘ 75 ‘being housed‘ within ‘a housing 65‘to which the 2,412,100. 7 8 outer conductors of the various transmission lines are securely connected electrically as indi cated at 66. These electrodes are equally spaced 26, 21 and 28 in association with the capacitance about a circumference to cooperate in succession device 20 is more particularly described and is claimed in the copending application of Franklin G, Patterson, Serial No. 421,126, ?led December 1, with rotating electrode 29. .Fig. 5 represents the diode employed in con is assigned to the same assignee as my present 1941, entitled Transmission systems and which application. nection with my invention. It comprises an an ode 10 and a cathode ‘H, the latter of which may I have found, when operating. at certain fre quencies, that di?iculty may be encountered in be indirectly heated by heater ‘I2 energized from a transformer 13'. The cathode is mounted upon 10 obtaining the impedances within the capacitance switching device necessary for operation of the a conducting plate 14 which closes the end of the transmission line 15 but which is insulated there from by means of insulating material 16. The anode 10 of the diode is provided with a screw-threaded projection 11 at the top of which 15 lines connected thereto in the two modes de scribed. No difficulty is encountered in producing the quarter wave length mode of operation be cause this merely requires adding capacity be tween the stationary electrodes and ground. This may easily be done by adding trimmer electrodes the transmission line. This anode is provided arranged in adjustable spaced relation with re with a ?ange portion 19, the outer periphery of spect to the stationary electrodes. In the half which is sealed in the edge of a glass cylinder 80, the lower edge of which is securely sealed to the 20 Wave mode of operation larger capacity between the rotor electrode and stationary electrode is plate 14 whereby the interior space between the present. The circuit then extends from the sta electrodes may be evacuated. tionary electrode to the rotor, which is in mesh _ If desired, a source of potential 40 may be con therewith, and then through the shaft of the r0 nected between the plate 14 and the outer con tor to ‘ground. This path not only has capacity ductor 15 of the transmission line thereby to ren but also inductance, which must be adjusted for der the anode of the diode somewhat negative the half wave mode. This may be done by proper with respect to the cathode normally in order proportioning of the parts. to prevent the ?ow of electrons to the anode by reason of thermal agitation and the like. The In accordance with my invention, however, the arrangement of Fig. 6 may be employed. In this connection to the anode for direct current is, of Fig. 6 I have shown conductors H and 25 of Fig. course, completed through any apparatus that l joined at point 34. Conductor 25 leads to the may be connected between the outer conductor electrode 23 of the capacitance switch 20. In this and the inner conductor of the transmission line. switch the capacitance between the electrode 23 I have described certain transmission line sec tions as having a length equal to a odd multiple and ground, when the rotor is removed from elec trode 23, is represented by the dotted linesat 80. of a quarter of a wave length. It will, of course, This capacity may be adjusted, as by trimmer be understood that I include the multiple one since frequently any of these lines may be of but electrodes, to produce the quarter wave mode of screws into the end of the inner conductor 18 of operation. a quarter of a wave length in length. I have mentioned lines 25, 26, 21 and 28 as 40 being of an odd number of quarter wave lengths in length; if desired, however, these lines may be of different lengths. For example, the line it self may, if desired, have a length equal to an A further component of impedance between electrode 23 and ground, when the rotor meshes with this electrode is represented as comprising a series combination of capacitance 8| and an eighth of a wave length, or to an eighth of a wave inductance 82, in parallel with capacitance 80. These impedances may be adjusted for the half length plus a half wave length, or multiple wave mode of operation. thereof. If line 25, for example, has such a venient, however, to provide the stub line 83 at point 34, this stub line being of adjustable length, length, the capacitance between electrode 23 and ground, assuming electrode 29 in the position shown, may be adjusted, as by means of variable I have found it con as by telescoping inner and outer conductors, as conventionally represented on the drawings. The length of this stub line may be adjusted to cause it to resonate with any reactance presentedby tance device to cooperate with the line 25 to cause line 25 at point 34 to produce very high shunt im it to have an electrical length equal to a quarter pedance between point 34 and ground. That is, ofa wave length and thus to produce an effective short circuit at the point 34. The same may be 55 capacitance 88 may now be adjusted to- produce a short circuit between the inner and outer con true with respect to the line 26. The lines 21 ductors at point 34 when the rotor is in its most and 28 being connected respectively to electrodes 22 and 2| having higher capacity to ground, as remote position from electrode 23, and line 83 may be adjusted in length to produce very high suming electrode 29 in the position shown, may then have a wave length equal to a half a wave 60 impedance between the inner and outer conduc length such that they produce high impedance at tors at point 34 when the rotor meshes with trimmer electrodes, not shown, within the capacie the points 33 and 32. That is, the lines 25, 26, 21 and 29 operate in either of two modes, the open circuit quarter wave mode or the open circuit half electrode 23. 7 It will be observed that my invention offers a very satisfactory system for shifting, in two or 65 more planes at an angle to each other, the direc tion of maximum effect of the antenna array, whether it be a radiator, a receiver, or both, the wave mode dependent upon the capacitance be tween the respective ?xed electrode within the capacitance device 20 and ground, and these ca pacitances for the two modes may be separately shift being brought about by simple rotation adjusted within the capacitance device 20. In of the rotor Of the capacitance switch. Any in this way the overall operation previously de 70 terconnections between lines leading to different scribed may be secured but the action may be somewhat improved by reason of thesharper antennae, and which, at least at times, carry no useful energy, are avoided. The avoidance of resonance effects of the various lines 25, 26, v2'! such interconnections increases the capabilities of the system with respect to the angle through ‘and 28 when so adjusted. ‘ This proportioning and tuning of the lines 25, 3 75 which the direction of maximum effect of the sys- . 2,412,160 '10 tern may be shifted. This results from the~ avoid of transmission lines extending from said appara ‘tus to respective points on each‘ of said intercon ance of reactance, or impedance effects‘, of such interconnections upon the system. Moreover, the nections, said points being so positioned that the avoidance of such interconnections very greatly path from any antenna to said apparatus is simpli?es the problem of impedance matching longer over one of said lines extending from the throughout the length of the lines between the respective interconnection than the other, and radio apparatus and the different antennae. In means to select one line in each pair to transfer fact, in the systems Of my invention the problem energy between said apparatus and each corre of impedance matching throughout these lines sponding pair of antennae thereby to control the is no more di?‘icult than it is in the usual trans 10. direction in which said array has maximum ef mission systems between a radio apparatus and fect. ‘ one or more antennae. 4. In combination, a plurality of antennae po While I have shown particular embodiments of sitionedv at the vertices of a polygon, ‘a plurality my invention, it will, of course, be understood that of interconnections, each interconnection'extend I do not wish to be limited thereto since different 15 ing between antennae positioned at opposite cor modi?cations both in circuit: arrangements and ners of said polygonyradio apparatus, a pair of in the instrumentalities employed may be made, transmission l-inesextending from said apparatus and I contemplate by the appended claims to to respective points on each of said interconnec cover any such modi?cations as fall within the tions, said points being so positioned that the true spirit and scope of my invention. 20 path from any antenna to said apparatus is longer What I claim as new and desire to secure by Letters Patent of the United States, is: 1. In combination, a plurality of antennae po sitioned in an array to produce maximum eifect of said array with respect to certain directions, radio apparatus. a plurality of permanent trans mission lines, each line extending from said appa ratus to a corresponding one of said antennae, a connection between different of said lines near over one of said lines extending from the respec tive interconnection than the'other, and means to interrupt transmission through either line in each pair while maintaining transmission through the other line of each pair thereby to Vary the directivity of the array comprising said antennae. 5. In combination, a plurality of antennae po sitioned at the vertices of a polygon, a, plurality of interconnections, each interconnection extending the antenna ends thereof, the path through any 30 between antennae positioned at opposite corners line to its corresponding one antenna being of said polygon, radio apparatus, a pair of trans shorter than the path through the same line to mission lines extending from said apparatus to any other of said antennae, means to select'any respective points on each of said interconnections, of said lines in accordance with the direction in said points being so positioned that the path from which said array is to have maximum effect, the lengths of the paths from said apparatus to all the antennae being so proportioned as to produce maximum effect in the direction corresponding to the line selection made by said means, said means comprising an impedance device having a moving 40 member, and means whereby said lines are al ternately shorted at respective points thereof in response to movement of said moving member, said points being so positioned on the respective lines as to prevent impairment of transmission through another line to an antenna correspond ing to a line shorted by said impedance device. 2. In combination, a plurality of antennae po sitioned in an array to produce maximum effect of said array with respect to certain directions, a radio apparatus, a plurality of transmission lines, each line corresponding to one of said an tennae and extending from said apparatus to its corresponding antennae, a connection from a point near the antenna end of one line to a point near the antenna end of another line, the path from said apparatus through said line to the an tenna corresponding thereto being shorter than ' the path through said line to another antenna, means to short ?rst one and then another of said lines alternately while maintaining unshorte'd lines in energy transferring condition, the dis tance of any short on any line from said connec— tion being such that transmission through said connection is not impaired by said short and the lengths of the said connection being such that the any antenna to said apparatus is longer over one of said lines extending from the respective inter connections than over the other, and means to produce low impedance across either line in each pair to impair transmission therethrough, said low impedance being produced‘ at a point such that high impedance is presented by the respec tive line to the other lines over which transmis sion is not impaired. 6. In combination, a plurality of directive an tennae arranged at the corners of a rectangle, the antennae at diagonally opposite corners of said rectangle being connected together through respective transmission lines, radio apparatus, two pairs of transmission lines, the lines of each pair of extending from respective points spaced apart on one of said ?rst mentioned lines corre sponding to the respective pair, all of said two pairs of lines extending to said apparatus, and means to interrupt transmission through any two of said last-mentioned lines while maintaining transmission through the other two of said lines. 7. In combination, a plurality of directive an tennae arranged at the corners of a rectangle, the antennae at diagonally opposite corners of said rectangle being connected together through respective transmission lines, radio apparatus, two pairs of transmission lines, the lines of each pair extending from respective points spaced apart on one of said ?rst-mentioned lines corre spending to the respective pair, all of said two pairs of lines extending to a common point and direction with respect to which said array has thence to said apparatus, and means selectively maximum e?ect is dependent upon the line over to produce low impedance across any two of said which energy is transferred between said appa two pairs of lines at points thereon such that ratus and said array. 70 transmission over the other lines of said two pairs 3. In combination, a plurality of antennae po ‘of said antennae and said apparatus is not im sitioned at the vertices of a polygon, a plurality paired by such low impedance. ‘of interconnections, each interconnection extend 8. In combination, a plurality of antennae ele ing between antennae positioned at different ments arranged at the vertices of a triangle, an vertices of said polygon, radio apparatus, a pair ‘ individual connection from each antenna element 2,412,160 11 ’ to a common point, a radio apparatus, an indi 12 10. In combination, a transmission line, a sec ond line connected to a. point on said ?rst line vidual transmission line extending from each of said connections to said apparatus, and means to and having a length different from any'integral disable all but one of said lines while maintaining said one line in condition to transmit energy be multiple of a quarter of a wave length, a capaci tance connected across the end of said second line tween all of said antennae and said apparatus. 9. In combination, a plurality of antenna ele proportioned to produce low impedance at said point substantially equal to that of an open line having a length equal to a quarter of the operat ing wave length and variable to increase said im pedance, and a third transmission line connected ments arranged at the vertices of a triangle, an individual connection from each antenna vto a common point, radio apparatus, an individual connection extending from a point on each of said to said point .to resonate with reactance pro connections to said apparatus, means to con?ne duced by said second line when said impedance is transmission of energy between said apparatus increased by variation of said ?rst-mentioned ca and the different antenna elements .to one of said pacitance thereby further to increase the imped last-mentioned connections at a time, said points 15 ance at said point to‘a value approaching that of being so positioned that said ‘antenna elements an open transmission line having a. length equal have a direction of maximum effect dependent upon that one of said last individual connection to which transmission is~ con?ned. to half of the operating wave length. " RICHARD C. LONGFEILOW.