Oct. 15,1946. R. c. SANDERS, JR., er AL . 2,409,449 PHASE IODULATOR Filed Dec. 30, 1943A é _ ¿af-'c'.L--vn/.ReA . f! ,~ 9Í _ ß 7/ « 2 Sheets-Sheet 1 _'ßñ if ¿000 ' e . 5 ., _ A’ 'I l ¿yy Z ven/v5.4! ° ' _L L _L-Lona #_ _ ¿aan .g §- | è ’ . pm A3f _/ fr“ . Y 11d I] _ 9' H Piaf/Vie _.3 . 7 ' »H 311mm: RDYDEN DSRNDERS, J R. » WILLIRM R. MERÉER '8f Dn IEÀ BLITZ nag . C‘ävulu. Ottomeg R. c. SANDERS, JR., ETAL 2,409,449 Filed Dec. 30, 1943 2125 27 £56. :îT--Il--w 2, f ' Y 2 y 57 ¿Effi @zy 2 Sheets-Sheet 2 ` ¿z5 WILLIHM RMERUER ag Dawg-L BuTz 35 l M Óttomeg 2,409,449 3 4 Any number of coupling points may be intro duced simultaneously. If these points are spaced multiples of 180 degrees apart, they will add sig 23. The shield member 21 (Figure 5) is shaped like a rotary shutter, with gaps 90 electrical de grees wide, spaced 180 electrical degrees apart. nal components at the receiver which are all in phase with each other. If the coupling of any The shield 21 serves to prevent coupling be tween the parallel lines except at the gaps. point is broadened over a. length of line to in The open wire lines 2| are each made an clude, for example, everything between plus 45 integral number of wavelengths long, so that the degrees and minus 45 degrees from its center, couplings at the two gaps are additive, as ex the received signal will contain components of all plained above in connection with Figure 1 of the phases between plus 90 degrees and minus 90 de 10 drawings. In the structure illustrated in Fig grees. These components will add vectorially to ure 5, the lines are one wavelength long. produce a signal of the same phase as would re The spacing between the two open lines 2l is sult from coupling only at the mean point, but a compromise between the considerations of vari of much larger amplitude. . ations in characteristic impedance resulting Referring to Figure 2, the parallel lines 3 and from close proximity of the shutter blades to the 9 are curved into a circle having a circumference lines, and incomplete coupling because of dis an integral number of wavelengths long. The tance between the lines. Variations of line im signal at the point i1 at the beginning of the circle pedance cause reflections, which make the phase is in phase with that at the point I9 at the end shift non-linear with respect to angle of shutter of the circle, and the point of coupling may be rotation and change the amplitude of the re moved across the gap without discontinuity in ceived signal with change in phase. Low cou phase of the‘ received signal. If the point of cou pling between the two lines results in high at pling is revolved about the center of the circle tenuation. so as to sweep along the lines 3 and 9 the signal High shutter rotation speeds may be required phase at the receiver 1 is uniformly and contin under certain conditions, involving undesirably uously advanced or retarded by an angle: large centrifugal forces, with consequent vibra tion and bearing load problems. To avoid this difficulty, the diameter required for a given fre Where A0 is the change in angle in radians, n quency of operation may be reduced by provid is the circumference of the circle in wavelengths, 30 ing dielectric material between the lines and their and T is the number of turns made by the cou ground planes, thus lowering the propagation pling point. If the coupling point is continu velocity through the lines and hence reducing ously moved in one direction at s revolutions per second for a period of t seconds, The instantaneous signal voltage at the re ceiver is proportional to sin 21rfrt=sin (21rfLt-l-0l) where fr is the received frequency, ft is the trans mitted frequency, and @t is the total phase differ ence between the transmitter and the receiver. Assuming an initial angle a between the trans mitter and receiver, the wavelength. Figures 6 and 7 show a structure of this type. Reference numerals in Figures 6 and '1 corre spond to those used to designate correspondingr parts of Figures 3, 4 and 5. The lines 2| are supported in circular grooves cut in the faces of boards 3i of insulating material such as “Bake 40 lite” or the like, backed by the conducting sur faces 23. To prevent transmission of energy across the shutter member 21, the two blades 33 are insulated from each other by means of a “Bakelite” block 35 which is secured to the shaft 45 29 by a bushing 31. The open sections into which signal is introduced should be placed 90 elec trical degrees apart to reduce the effect of any discontinuity caused by incorrect line length. The invention has been described as a phase modulator system including two transmission lines disposed parallel to each other and shielded from each other except at certain coupling points. The lines are curved to circular formation and the 55 coupling points are continuously swept over the lengths of the lines, by rotation of the shield. One end of each line is connected to the circuit in which the modulation is to be produced. Mo In reflection type speed measuring systems, a tion of the coupling points varies the effective reflecting object wth a velocity V relative to a source of signal of wavelength A returns an echo 60 length of line included in the circuit, causing cor signal differing in frequency from the transmit responding variations in the transmission delay ted signal by 2V/>\. The same difference in fre and hence phase modulation. quency may be obtained by revolving the coupling point of the system of Figure 2 at a speed We claim as our invention: 1. A phase modulator system including two 65 spaced parallel transmission lines, means for ap plying radio frequency energy to one end of one of said lines, means for absorbing radio fre mission lines may be an open wire 2| supported quency energy from the corresponding end of above a conductive ground plane 23 on standoff the other of said lines, movable shield means dis insulators 25. The two curved lines are placed 70 posed between said lìnes, said shield means pro with their planes parallel to each other with the vided with at least one gap whereby coupling open sides facing each other as shown in Figure between said lines is prevented except at said 4. A conductive shield member 21 is supported gap, and motion of said shield means moves said between the two lines on a shaft 29 extending coupling longitudinally with respect to said lines through the center of the lower ground plane 75 to vary the effective length of the transmission Referring to Figure 3 each of the curved trans 2,409,449 5 path between said means for applying energy and said means for absorbing energy. 2. The invention as set forth in claim 1 where in said transmission lines are curved to substan tially a circular outline an integral number of 6 ly circular form, a rotary shield member lying between said conductors and provided with at least one gap in its periphery, and two ground planes, each disposed adjacent to one of said conductors and on the opposite side thereof fram wavelengths in circumference at the frequency at which the system is to operate. 3. The invention as set forth in claim 1 where cluding two plates of insulating material, each in each of said lines is terminated in a load of such impedance as to match the impedance pre spective adjacent ground plane. sented by said line. 4. The invention as set forth in claim 1 where in said lines are curved to substantially circu lar outline and said shield means comprises a ro 15 tary shutter-like structure. 5. A phase modulator structure comprising two spaced parallel conductors curved to substantial said shield member. - 6. The invention as set forth in claim 5, in lying between one of said conductors and the re 7. The invention as set forth in claim 5 where in said shield’member is in theíorm of a rotary shutter comprising at least two blades, and means for insulating said blades from each other. ROYDEN C. SANDERS, JR. WILLIAM R. MERCER. DANIEL BLITZ.