US2679631A - Power divider - Google Patents

Description

May 25, 1954 N. KORMAN ETAL POWER DIVIDER Filed Oct. 2, 1950 2 Sheets-Sheet 1 mg 7 a a m ml n 3 4 v r m wk nn m V m W 3 N W May 25, 1954 N. l. KORMAN ETAL POWER DIVIDER 2 Sheets-Sheet 2 Filed Oct; 2, 1950 5: 4 7 4 was b W0 M 5/. w

A aw n W I? wwwf w P x I M Patented May 25, 1954 UNITE STATES fizATZENT OFFICE P. Bollinger, Haddonfield, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application QctoberZ, 195'0, Serial No. 188332 13 Claims.

This invention relates to power dividers for high frequency systems.

In the testing of components, it is often desirable to have available a means of varying the power from a source over wide limits. For example, in the testing of waveguide components for high power carrying capacity, a variable power source is desirable. Heretofore, attenuators have been commonly used to provide the desired power variation. The usual methods, however, are either subject to low power handling capacity or are bulky and awkward.

It is an object of the present invention to provide an improved means of varying the power output along a transmission line.

Another object of the invention is to vary continuously the power output to a transmission line.

Still another object of the invention is to provide a variable power divider network of high -power handling capacity.

Further objects of the invention are to provide a power divider which is compact, the power division of which is readily and easily controlled, and which is reliable in operation. Also a further object of the invention is to provide a phase shifter which shifts ,phase simultaneously in two waveguides.

.In general, it is found preferable to use the principles of power division between two transmission lines rather than attenuation by variable absorption in the conventional manner. The unwanted power is diverted into a preferably fixed load, which may readily absorb high power, and the remaining undiverted power is passed on to the device under test (or vice versa, of course).

In accordance with the invention, a pair of transmission lines have between them a pair of spaced apart directional couplers each characterized by a phase change of substantially '90 degrees in incident energy transferred through the coupler from one line to the other, and means are provided to shift the phase or to vary the efiective line length of at least one of the transmission .lines between the effective points of coupling. With this variation, the energy division between the two waveguides is varied. If the energy in one line is thus increased, that in the other is decreased, and vice versa. Preferably, the efiective line length between the couplers .in one .line :is increased and that in the other decreased simultaneously, and a novel waveguide phase shifting arrangement is employed for the purpose.

The foregoing and other objects, advantages,

2 and :novel deatures :of "the invention will 'be ex- ;plained'morefully connection with the accompanying drawing in which like reference numerals refer to like parts and in which:

Fig. 1 is aifiront'elevational view of :a preferred embodiment of the invention except that a ;portion symmetrical with that shown is omitted;

Eig. :2 is a sectional view along the -lines 12-2 of .1, showing a *directional coupling between itwo waveguides;

Fig. 3 is a sectionalview along the lines 3-3 of Fig. .1 showing a phase shifting means;

:E'ig. 4 is a simplified schematic longitudinal sectional view parallel to the plan view of Fig. -1, especially :useful explaining the operation '01 the embodiment of Fig. 51

Fig. :5 is ra circuit idia'gra'm schematically illus- 'trati-ng employmentfof the device :of Figs. -1 to 4; and

Fig. 6 is a calibration TClllV .for a .zsp'ecific device such 'as that illustrated in Fig. 1.

The directional couplers mentioned above $311 8 exemplified the illustrated preferred embodiment by directional slot couplers between a pair of waveguides, "which exemplify the transmission lines, and the variation in effective line length preferably accomplished :by .a simple, well known iline 'stretcher or phase shifter arrange ment. :line length variation of the :present arrangement in which the variations are reciprocal and complementary is preferred because of the superior performance of this arrangement.

Referring now more particularly to Figs. 1 to 4, a pair of rectangular waveguides l0 and 12 are coupled by a pair of spaced slots 14 and t6 which are directional slot couplers. Each slot .is placed at \one edge boundary of a common wall portion i i-n the narrow walls of the rectangular waveguides. The-slot couplers 1'0, 12 each transfer half the energy incident from one waveguide t'll, 12 to the ather with a degree phase shift. The properties of such couplers are known and described, for example, in the :copending application of Walden P. 'Bollin'ger, Serial No. 73,838, fi led January 31, 19459, :and entitled "Ir-ansmit- Receive Arrangement and also described in the publications cited in the said application.

Various types of linear passive directional cou- 'plers zbetween transmission lines are known in which the energy incident ."in one direction along one transmission line .is 'coupled idirectiona'lly one-half to another transmission line, half the incident energy continuing along the first iine in its initial direction and the other half traveling in one direction along the coupled line and in which the energy in the coupled line is phased 90 degrees with the energy in the first line. See, for example, the article by Henry J. Riblet entitled Mathematical theory of directional couplers, Proceedings of the I. R. E., November 1947, page 1307 and also Technique of Microwave Measurements by, Montgomery et al., Radiation Laboratories Series, volume 11, section 14.8 starting at page 885. The directional coupler selected as a suitable example in the arrangement disclosed herein is a long-slot coupler between hollow pipe waveguides. However, it will be apparent that other types of directional couplers may be employed wherever suitable for the transmission lines used.

Between the slots I4, I6, there is provided a frame I8 which includes frame members I8a. I81), I80, and IBd, which grasp between them a portion of the waveguides I0, I2 through the intermediary of plates 20a, 20b, 20c, and 20d. The frame I8 and the plates are held together rigidly with suitable bolts as shown. Between the waveguides I0, I2 and in the frame is journaled a shaft 22 which is eccentric with respect to its bearings 24, 26 in the frame I8. The shaft 22 is attached to a gear 28 centered on the hearing 26. The gear 28 is driven by a second gear 30 meshing therewith and held in a bearing 32 attached to the frame I8. A knob 33 is also attached to the gear 30 and a dial 34 is engaged with the knob. The dial 34 is read against a dial plate 36 attached to the frame I8. The broad waveguide walls are arranged transverse to the eccentric motion of the eccentric shaft 22 and are slotted with longitudinal slots 31 near the wall portion movable by the eccentric shaft 22. The slots afford elasticity permitting the expansion or compression of the broad dimension of waveguides III or I2. Of course, slots 31 are preferably made narrow to inhibit the escape of any except a negligible amount of energy. The eccentric shaft portion 22 extends between the narrow waveguide walls and affords a reciprocal and complementary motion of the narrow wall portions between slot couplers in the waveguides I0, I2. Those skilled in the art will understand that the adjacent narrow walls of waveguides I0, I2 at the place where the eccentrio bears against them may be considered as a common wall portion illustrated in the simplified schematic of Fig. 4 as a wall 35, the transverse motion of which is indicated in Fig. 4 by the arrows. At its ends the waveguide ID has couplers 38 (only one of which is shown in Fig. and waveguide I2 has couplers 40 which may be of the standard type of choke joint coupling. These afford means for coupling to other circuit elements. In Fig. 1, the remainder of the structure to the right of the dialed portion. may be considered symmetrical with the portion shown to the left of the dialed portion. This right end portion has been omitted in Fig. 1 because it would be difficult to suitably proportion the figure and show all of the details necessary.

In operation (refer also to the much simplified circuit diagram of Fig. for a typical circuit ap-;

plication), assume that energy enters from the left into one of the waveguides, say I2 from a source 42. The energy is incident in direction toward the right as viewed in Fig. 1 or 4 or 5. When the energy arrives at the directional coupler I4, it begins to be transferred into waveguide IU. In accordance with the theory in the publications to which reference has heretofore been made, and as also explained in the said oopending application, the slot I4 has a sufficient length to couple half the energy into waveguide I0. Thus let the total energy have a voltage maximum designated by V. The transferred energy is then The energy remaining in waveguide I2 to the right of the coupling slot I4 is H 12? In the portion between slot I4 and slot I 6, the

energy in waveguide I0 is shifted by an angle +1 and that at waveguide I2 by an angle 4:2. The resultant energy values, relatively considered, still travelling to the right as viewed in Fig. 1 or 4, are

At the slot I6 each of the energy incident from the left in waveguide I0 and in waveguide I2 splits again. The energy from waveguide I0 divides with an amount continuing in waveguide I0 and t I 4n transferred to waveguide I2. The energy incldent toward the right from waveguide I2 divides with transferred to waveguide I I] and iv g continuing in waveguide I2. Accordingly, the components in waveguide I0 can be combined and result in a wav of voltage amplitude For waveguide I2 the voltage amplitude is gin- #2) (2) It is apparent that the power division between waveguides I0 and I2 can be controlled by control of the phase shifts 1 and 52. The phase shifts can be controlled singly, that is, 51 can be controlled or varied without variation of 9122 and vice versa if desired. Preferably, however, in order to provide a more linear calibration curve and in order to make the phase shifting apparatus as symmetrical as possible with respect to the motion thereby tending to compensate for opposite errors and toward linearity of calibration, it is preferred to shift phases in opposite directions from a calibration point in which they differ by 90. This is readily accomplished by the structure shown in greater detail in Figs. 1 to 3. It will be observed that between the couplers I4, I6, both waveguides III and I2 have their broad dimension or width narrowed generally in the vicinity of th slots 31. The narrowed or necked down portions are for the purpose of increasing the variation in phase shift with motion of the narrow effectively common wall. However, it will be observed that the narrowed portion of waveguide I0, is somewhat longer than the narrowed or. necked. down por- "tion of -'vvaveguiide 2. This means that effective length of waveguides I I] and 12 between 'the ef- 'fective points of coupling of the couplers are This effective -diiference in length is rection, One of the waveguides I is squeezed in the necked down portion to have its width further reduced while theother waveguide has its width expanded .or increased simultaneously and vice versa. Thus the difference in line lengths is varied. Preferably, the eccentric is arranged so that the --diiference in the extreme shifts is just 45 and in-opposite directions. Accordingly, the power transfermayextend all the way from -zero reaching absorptive load Mi connected to "waveguide '10, to -00%, and similarly from a 100% reaching the device under test 46 through waveguide l2 to zero. The connections of load 34 and the device under test 46 may be interchanged if desired. The termination 48 may be simply a low power termination and absorbs any power reflected toward it resulting from imperfections in th directional couplers. Ideally, this reflected power is zero. In practice, it is usually very small, of the order of 1 6% of the total power handled. The connections of termination 48 and source 42 may also be interchanged if desired.

A typical calibration curve is illustrated in Fig. 7 of the drawings. It will be understood that the construction is preferably such that a substantially half dial turn is required to obtain a turn of the eccentric in one direction resulting in a 90 phase shift in one direction in each of waveguides I0, 12, and a half dial turn in the other direction is required to obtain a turn of the eccentric in the other direction with an opposite resulting phase shift. Thus the dial reading 50 in Fig. would correspond substantially to a neutral position of the eccentric and the relative power in percent is that transferred to the Waveguide corresponding to waveguide I0 as illustrated in the drawings. The curve is in fact asymmetrical probably due to the difference in the necked down waveguide portions.

It will be understood that it is not necessary that a directional slot coupler between the two waveguides be used since there are other arrangements which electrically are equivalent to that shown. The arrangement illustrated is preferred, however, because it is particularly compact, neat, and considering the frequencies and the power involved (frequencies of the order of 3 centimeters and amplitudes involving 1,000 kilowatts), is fairly simple to construct.

It is apparent that there is disclosed a highly desirable, readily constructed variable power divider. The energy travelling through one of the waveguides l0, [2 may be directed to and dissipated in a dummy absorptive load or the like, in desired proportion whereas the energy travelling in the other branch may go to a device under test. Large amounts of microwave power may thus be readily divided as desired by the device of the invention. There is also disclosed a novel phase shifter of convenient and economical construction for use with two waveguides. It may be noted that the positions of the source 42 may be at either connection on one side and that of the device under test at either connec- 6 .tion on the opp'osite side :of the :divider :toward which the energy is directed.

What we claim as our inventionis:

1. A power divider comprising. anpairuof transmission lines, a pair of :spaced linear passive directional couplers between said lines reach characterized by a phase change of substantially degrees in energy transferred through the coupler from one line to the :other, and each characterized by a transfer of one half theienergy incident at the -coup1er from one line idirectionally into the other, and means teadjaust the effective relative lengths of :said lines between the effective points of coupling Y of said couplers.

2. A power divider-comprising a pairofztransmission lines, a pair of spaced linear passive directional couplers between said lines each characterized by aphase change of substantially 90 degrees energy transferred through the coupler from one line to the:other,-ea'chsaidJline between said couplers b'ei-n'g efiective to transfer energy from one efiective coupling point of said couplers to the other substantially without change in amplitude, and means to adjust the effective relative lengths of said lines between the effective points of coupling of said couplers.

3. A power divider comprising a pair of transmission lines, a pair of spaced linear passive directional couplers between said lines each characterized by a phase change of substantially 90 degrees in energy transferred through the coupler from one line to the other, and means to vary the efiective line lengths between the effective points of coupling of said couplers with one of said lengths increasing while the other decreases and vice versa.

4. The divider claimed in claim 1, said transmission lines being hollow pipe waveguides.

5. The divider claimed in claim 1, said transmission lines being hollow pipe waveguides, said couplers each being a long slot coupler in a common waveguide wall portion.

6. The divider claimed in claim 1, said transmission lines being hollow pipe waveguides, said effective line lengths being varied by variation of a waveguide width.

7. The divider claimed in claim 1, said transmission lines being hollow'pipe waveguides, said Waveguides having a common wall portion between said couplers, the effective line lengths of both said lines being varied reciprocally and simultaneously by transverse motion of said wall portion.

8. A power divider comprising a pair of rectangular hollow pipe waveguides having broad and narrow walls and having between the narrow walls thereof a pair of spaced apart directional slot couplers, and a common wall portion between said couplers, each coupler being characterized by a phase change of substantially 90 degrees in incident energy transferred through the coupler from one guide to the other, and means to move transversely said common narrow wall portion, thereby simultaneously increasing the width of one waveguide and decreasing the width of the other at said common wall portion.

9. The divider claimed in claim 8, said broad walls of said waveguides being longitudinally slotted near said common movable wall portion.

10. The divider claimed in claim 8, further comprising a frame around said waveguides between said slot couplers, a shaft journaled in said frame and having an eccentric portion transversely between said narrow walls whereby rotation of the shaft moves an effectively common wall portion between said couplers simultaneously to increase one waveguide width and decrease that of the other.

11. The divider claimed in claim 10, further comprising a manually adjustable dial geared to said shaft.

12. A power divider comprising a pair of transmission lines, a pair of spaced linear passive directional couplers between said lines characterized by a phase change of substantially 90 degrees in energy transferred through the coupler from one line to the other, and each characterized by a transfer of one half the energy incident at each coupler from one line directionally into the other, each said line between said couplers being effective to transfer energy from one effective coupling point of said couplers to the other substantially without change in amplitude, and means to adjust the effective relative lengths of said lines between the effective points of coupling.

13. A power divider comprising a pair of transmission lines, a pair of spaced linear passive directional couplers between said lines characterized by a phase change of substantially 90 degrees in energy transferred through the coupler from one line to the other, the transmission paths from one said coupler to the other consisting solely of said lines, and means to adjust the effective relative lengths of said lines between the effective points of coupling of said couplers.

References Cited in the file Of this patent UNITED STATES PA'IENTS Number Name Date 2,423,526 Sontheimer et al. July 8, 1947 2,543,425 Strandberg Feb. 27, 1951 2,560,806 Lewis July 1'7, 1951 2,586,993 Riblet Feb. 26, 1952 2,593,120 Dicke Apr. 15, 1952

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