US2736867A - Crossed wave guide variable impedance - Google Patents

Description

Feb. 28, 1956 D. D. MONTGOMERY CROSSED WAVE GUIDE VARIABLE IMPEDANCE Filed Dec. 10, 1945 INVENTOR DOROTHY D. MONTGOMERY ATTORNEY United States Patent CROSSED WAVE GUIDE VARIABLE IMPEDANCE Dorothy D. Montgomery, Belmont, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application December 10, 1945, SerialNo. 634,112

9 Claims. (Cl. -33381) This invention relates in general to wave controlling apparatus and more particularly to that type of such appara-tu's designed for introducing a variable impedance into a wave guide transmission line.

Heretofore, such wave controlling devices have lacked simplicity, introduced loss of R. F. energy, and were" not continuously adjustable over a; wide range of impedances.

A specific object of the present invention is to provide variable wave guide impedance controlling apparatus which can be adjusted by a simple means of control.

Another object is to provide such apparatus having an impedance that is continuously adjustable over a wide range of values.

A further object is to provide such apparatus which introduces no R. F. energy losses, and is purely reactive in efiect'.

To achieve these and other objects, apparatus in accordance with the invention provides two sections of wave guide of the rectangular, hollow-pipe variety 10ngitudinally coupled together with a conventional choke joint and so mounted that one section is fixed and the other rotatable about their common longitudinal axis. With this apparatus, an impedance which is primarily reactive is offered to waves travelling in the guide when the rotatable section is turned at a skew angle relative to the fixed section, and this impedance is controlled by adjustment of the skew angle.

The details and features of typical embodiments of such wave controlling apparatus are described in the following specification and illustrated in the accompanying drawing in which:

Fig. 1 is a perspective view of two collinear wave guide sections, illustrating the principle of the invention;

Fig. 2 is a perspective view of a particular embodiment of the invention;

Fig. 3 illustrates another embodiment of the invention for introducing a variable impedance in series with a 'wave guide; and

Fig. 4 illustrates still another embodiment of the invention for introducing a variable impedance in parallel with a wave guide.

In Fig. 1, a first stationary Wave guide 10 and second wave guide 11 are collinearly disposed along a common longitudinal axis X-X, the second wave guide 11 being rotatable about the longitudinal axis X -X. The rotation of-the second guide 11 may be measured in degrees with respect to a line YY normal to a broad side of the fixed wave guide 10.

In explaining the operation of the apparatus of Fig. 1, it is necessary to understand that impedance olfered to a travelling electromagnetic wave by a wave guide is determined by the size and physical shape of the conducting sheath which is usually rectangular in cross-section. This impedance can be changed in many ways, as for example, by introducing into the guide windows, irises, metallic and dielectric slugs, or any similar type of discontinuity which will affect the travelling electromagnetic fields.

2 Accordingly, the present invention represents a con veniently controlled discontinuity which causes an efiective change of impedance of a wave guide structure.

Analyzing the impedance effect caused by misalignin'g wage guides 10 and 11 of Fig. 1', it can be seen that the conducting end surface 13 of the rotatable wave guide 11 is caused to partially obstruct electromagnet waves travelling from fixed wave guide 10 into said rotatable wave guide 11. A portion of this conducting surface 13 cffectively diminishes the narrow dimension a of the fixed wave guide 10 and thus acts as a capacitive iris, while that portion of the conducting end surface 13 tending to narrow the wide or b dimension of the wave guide 10 acts as an inductive iris. With both inductive and capacitive reactance introduced at the misaligned interface between the wave guides 10 and 11, the magnitude and nature of the resultant or predominant reactance is determined by the skew angle 6'.

The impedance contributed by the discontinuity between the wave guides 10 and 11 ranges from zero when the angle 0 is zero to infinity when the angle 0 equals 90 and the b dimension of the wave guide 10 is reduced below the cutoff value. When 0 is zero and the impedance contribution of the interface is zero, the resultant impedance of the transition is the characteristic impedance of the wave guides 10 and 11.

Fig. 2 shows an embodiment of the invention comprising a first wave guide 17 in two sections having a second wave guide 16 interposed collinearly between said sections and longitudinally coupled thereto. The second wave guide 16 is rotatable about the common longitudinal axis of the guides 16 and 17, permitting two misalignment boundaries as illustrated in Fig. 1 to be simultaneously introduced at the regions where these guides 16 and 17 are joined.

To prevent the loss of energy at the discontinuous interfaces between the fixed and rotatable guides and to make the impedance change offered by the apparatus a purely reactive one, conventional circular choke joints 15, held rotatably in proper alignment by clamps 18, are usedto connect the two guides at said interfaces.

The impedance changing effect of turning the rotatable section of wave guide 16 is similar in principle to that described hereinabove in connection with the apparatus of Fig. 1, but is greater in magnitude because of the two sets of misaligned interfaces. The impedance transition structure of Fig. 2 can also be considered as a high frequency transformer with voltage step-down properties.

Control of the impedance characteristics of the wave guide device of Fig. 2 is gained not only by adjustment of the tilt angle 6 but also in the original. design of the unit. The length 19 of the rotatable section 16 determines the phase at which energy being reflected back from the two boundaries recombines and thus controls the quantity of mismatch energy reflected back to the source. For a matched discontinuity, length 19 is made an even number of quarter wave lengths of energy in the guide The position of the wave guide tilting section 16 in the main transmission line 17 is another factor to be chosen and determines the nature and value of reactance reflected back to any point in the main wave guide 17.

Figs. 3 and 4 illustrate wave guide structures specifically designed for the purpose of inserting a variable impedance at a given point in a transmission line. In Fig. 3, awave guide 20 is connected to the broad side of main wave 21 to form a series connected stub. Collinear with wave guide stub 20 and longitudinally coupled thereto is a rotatable wave guide 22 having a shorted termination 23. The shorted section 22 is rotatable about the common longitudinal axis of the stub guide and the shorted termination 22, and is rotatably coupled to the stub guide 20 by a choke joint 15, similarly to the wave guides 16 and 17 of Fig. 2. In Fig. 4, a main Wave guide 24 has a parallel connected stub wave guide 26 joined to its narrow side. Again, a rotatable wave guide section 25 having a shorted termination 23 is longitudinally coupled to stub wave guide 26 by means of choke joint 15.

The impedance of series and parallel stubs 2t and 26 looking in from the main wave guides 21 and 2 is controlled by the rotatable terminations 22 as follows. As is well known in the art, the zero termination impedance of the rotational wave guides 22 appears at the coupling 15 with a value of impedance determined by the electrical length 25 of the rotatable guide sections 22. At the couplings 15, which are at the interfaces between the fixed and rotational guide sections, a reactance which can be controlled by the skew or misalignment angle between the guides is added to the reflection termination impedance. down the remaining stub section 20 or 26, being transformed to a value determined by the electrical length 27 of these sections. The overall stub impedance can be placed either in series or in parallel with the main wave guide 21 or 24, as is shown in Figs. 3 and 4 respectively.

As can be readily appreciated by those skilled in the art, the variable impedance wave guide apparatus of this invention is not restricted to rectangular guides but can be adapted to use with any type of guide having other than circular cross-section.

The invention described in the foregoing specification need not be limited to the details shown, which are considered to be illustrative of one form the invention may take.

What I desire to secure by Letters Patent and claim is:

1. In combination, a first wave guide of other than circular cross-section and a second wave guide dimensionally similar to the first, said first and second wave guides being disposed along a common longitudinal axis with cofacing ends in sufficient proximity to provide an aperture area therebetween effectively common to the apertures of said cofacing ends, said second wave guide being rotatable about its longitudinal axis, the impedance offered by said first and second wave guides in combination to electromagnetic fields travelling therethrough being determined by the angle through which said second wave guide is rotated relative to said first wave guide.

2. In combination, first, second, and third elongated rectangular wave guides having a common longitudinal axis and cofacing ends adjacent and electrically coupled through rotatable choke joints, the cofacing ends of said wave guides being in sufiicient proximity to provide apertures therebetween effectively common to the apertures of the cofacing ends of said wave guides, said first and third wave guides being fixed and said second wave guide being disposed therebetween and rotatable about said axis with respect thereto, and means associated with each of said choke joints for maintaining said wave guides in coaxial alignment.

3. In combination, two wave guides dimensionally similar and of other than circular cross section adjacently positioned along a common longitudinal axis and having cofacing ends defining apertures lying in planes transverse The resulting impedance is then reflected to said longitudinal axis, the cofacing ends of said guides being in suflicient proximity with respect to each other to define an aperture therebetween effectively common to the apertures of said cofacing ends and in a plane transverse to said common longitudinal axis, one of said wave guides being rotatable about said longitudinal axis with respect to the other of said wave guides, the magnitude and configuration of said common aperture area being functions of the angular position of said rotatable with respect to the other of said wave guides, whereby the impedance oifered by said wave guides in combination to electromagnetic fields travelling therethrough is determined by the angular displacement of said rotatable wave guide with respect to the other of said wave guides.

4. Apparatus as defined in claim 3 and a rotatable choke joint electrically coupling said cofacing ends.

5. Apparatus as defined in claim 3 wherein said wave guides have rectangular cross sections.

6. Apparatus as defined in claim 3 wherein said wave guides have rectangular cross sections, and a rotatable choke joint electrically coupling said cofacing ends.

7. In combination, first, second and third elongated rectangular wave guides disposed coaxially adjacent along a common-longitudinal axis, the cofacing ends of said wave guides being positioned in sufiicient proximity to provide apertures between said first and second guides and between said second and third guides efiectively common to the apertures of the respective cofacing ends of said guides and transversely of said longitudinal axis, said first and third wave guides being fixed in position and said second wave guide being disposed therebetween and rotatable about said axis with respect thereto, and a rotatable choke joint surrounding each pair of cofacing ends and electrically coupling said wave guides together, the magnitude and configuration of the common aperture area at each pair of said cofacing ends being functions of the angular displacement of said second wave guide with respect to said fixed wave guides.

8. In combination, first and second rectangular wave guides having the same cross section throughout their lengths and disposed coaxially adjacent along a common longitudinal axis, the cofacing ends of said first and second wave guides being positioned in sufficient proximity to define an aperture therebetween effectively common to the apertures defined by said cofacing ends and in a plane transverse to said longitudinal axis, said first wave guide being rotatable about said longitudinal axis with respect to said second wave guide and shorted at its end opposite said cofacing end, and a third rectangular wave guide having the same cross section as said first and second wave guides, said second wave guide being connected at its end opposite its cofacing end to a wall of said third wave guide to form a stub.

9. Apparatus as defined in claim 8 and a rotatable choke joint surrounding said first and second wave guides at their cofacing ends.

References Cited in the file of this patent UNITED STATES PATENTS 2,257,783 Bowen Oct. 7, 1941 2,419,613 Webber Apr. 29, 1947 2,521,818 Aron et al. Sept. 12, 1950 2,529,381 Frear Nov. 7, 1950

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