US2742612A - Mode transformer - Google Patents

Description

April 17, 1956 s. B. COHN MODE TRANSFORMER Filed Oct. 24, 1950 ATTORNEY 2,742,612 MODE TRANSFORMER Seymour B. Cohn, Flushing, N. Y., assignor to Sperry Rand Corporation, a corporation of Delaware Application October 24, 1950, Serial No. 191,849

' 11 Claims. Cl. 333-21 The present invention relates generally to ultrahigh frequency apparatus, and in particular to a mode transformer for transforming a TE11) mode in a rectangular waveguide to a circularly polarized TE11 mode in an axially aligned circular waveguide.

In many types of ultra-high frequency equipment it is desirable to couple a rectangular waveguide to a circular waveguide. In such coupling it is frequently desired that the mode of transmission in the rectangular guide be TE and the mode in the circular guide be the TE11 mode.

Copending application S. N. 234,l24,filed June 28, 1951, describes such a structure wherein the axis of the rectangular guide is at right angles to the circular waveguide.

United States Patent waveguide section 10, is oriented with its axis parallel i dipole 20. As a result, energy is transmitted along co-' axial line section and is radiated into circular waveguide by dipole 25. Because of the orientation of dipole The present invention describes a structure wherein'the same electrical result obtains, but the, rectangular wave guide and the circular guide are in axial alignment.

It is, therefore, an-object of the present invention -to provide a mode transformer for coupling a rectangular two waveguide to a circular waveguide in which'the guides are in axial alignment.

It is a further object of the present invention to provide a mode transformer for coupling the TE11) mode in a rectangular waveguide to a circularly polarized wave of the TE1 mode in a circular waveguide.

It is still a further object of the present invention to* provide an axially aligned mode transformer which operates overa relatively broad'rangeof frequencies.

These and other objects will become more apparent and a better understanding of the invention will result from a consideration of the drawings in which:

Fig. l is a perspective view partially in section of one embodiment of the present invention, i

Fig. 2 is a diagrammatic sketch of the device shown in Fig. l useful in explaining its operation,

.Fig. 3 is a section view of a modification of th e device shown in Fig. 1, and I 7 Figs. 4-6 are perspective views partially ins ection of further embodiments of the present invention.

Referring now more particularly to Fig. 1, there, is

shown a section of rectangular waveguide 110. having a width a and a height b.- Rectangular waveguide section 10 abuts end plate 11 of circular waveguide section 12,

and is permanently joinedthereto, the two waveguide sections being axially aligned.

Acoaxial line section 15 is supported at the junction of rectangular waveguide section 10 and circular waveguide; section 12,and is oriented along the common axis 16 of the two waveguide sections. This coaxial section 15 may be supported in a numberof ways, for example, by a;

dielectric support 17. One end of coaxial line section terminates within rectangular waveguide section'10 and the other end terminates'within circular waveguide section 12.

Mounted at each end of coaxial line section is a pickup 1 unit. In Fig. 1, these pickup units are shown as dipoles,

although any other similar energy pickup unit may be utilized. Dipole 20, which is mounted at that end of coaxial line section 15 which terminates in rectangular to the shorter dimension of the waveguide cross section.

That is, dipole 20 is so positioned to be excited by the electric vector of the dominant mode TEm in the rectangular waveguide section 10.

Dipole 25, which is mounted at that end of coaxial line section 15 which terminates within circular waveguide section 12, is oriented at right angles to dipole 20. That is, the axis of dipole 2-5 lies along a diameter of circular waveguide section 12 which is parallel to the large dimension' of the 'ci'oss section of rectangular waveguide s'ec-. 'tion 10.

I In operation, energy is transmitted along rectangular waveguide section 10 in the TE10 mode. The electric vector, shown diagrammatically as E1 in Fig. 1, excites 25, the radiated energy has its electric vector at right angles to E1 as is indicated by vector E3.

Since rectangular waveguide section 10 is directly coupled to circular waveguide section 12 energy will also be coupled directly thereto. The electric vector of this directly coupled'energy will, of course, be parallel to the electric vector E1. This is represented by vector E2.

It is immediately seen that the physical orientation of the two electric vectors of the energycoupled from rec tangular waveguide section 10 to circular waveguide se'c-" tion 12 is one of right angles; that is, they are physically apart in space.-

By adjusting the length L of the coaxial line section properly, the electrical orientation of vectors E2 and E3 can be made to be 90 apart in phase. Thus it is seen thatthere are established in the circular waveguide section 12 two waves of the TE11 mode that are spaced 90 apart electrically and physically, so that the resultant is a circularly polarized wave of the TE11 mode. I

Fig. 2 illustrates this effect in somewhat greater detail. The energy passing through the rectangular waveguide section 10 is in the'TE1o mode. This energy excites pickup unit 20. In addition, it travels a distance l1 farther inwaveguide section 10. In so doing, shift, 1,-which is equal to 2 1rl M1 where kgi is the wavelength within guide 10. I

it sulfers a phase The energy'induced in coaxial line section 15 travels in. Y a TEM mode andsufiers a phase shift, 3, which is equal where K3 is the dielectric constant .of the coaxial line} section 15 and A is the freespace Wavelength of the energy.

The energy which is directly coupled into the circular Therefore, all that is necessary in order to insure E2 and E3 of being in time quadrature is that the following relationship" obtain where n=zero or any integer, and 4:4 is a phase shift approximately independent of l; and Z2 which lumps to- Patented A r. 17,1956;

This energy is in the TE11 mode and suffers gether the individual phase shifts at the dipoles and at the junction of waveguides and 12.

"Sin'' xgl'and'xg'' vary because of the different guide section and their resulting mode differences, it is possible to maintain the overall length of coaxial line section cfonstant and vary the ratio 11/12 and thus adjust the deviceto operate over a range a frequencies. Such a siructure is shown in Fig. 3. In this figure, coaxial line section 15 is supported on a dielectric slide 30 which passes through a wall of rectangular waveguide section By adjusting the longitudinal position of slide 3t), the ratio of Il iIO 12 may be varied. This changes 51, and 1155, so that the desired 90 phase shift occurs at a selected operating frequency.

As stated above, the invention is not intended to be limited to the use of dipoles as pickup units, but other forms such as loops and probes may be used with equal facility. The only requirement in the type used is that the pickup unit inserted in the rectangular guide be excited by the regular TEio mode, and that the pickup unit in the circular guide excite a TEll mode having a plane of polarization which is at right angles to the electric vector of the TEio mode.

In addition, the invention is in no way limited to coaxial line for coupling. Instead a two wire transmission line may also be utilized.

It should further be pointed out that, although the operation of the device is described as transforming energy from the 'IEm mode in the rectangular guide to a circularly polarized wave of the T1511 mode in the circular guide, the structure will also operate in the reverse direction. In Fig. l, dipole 25 will be excited by the horizontal component of an incident circularly polarized wave, which will enable dipole to excite a T510 mode in rectangular guide 10.

In some cases, it may be necessary to minimize phase shifts due to the discontinuity of the two wave guide sections. Another embodiment of the present invention is shown in Fig. 4. In this embodiment rectangular guide section couples to an intermediate rectangular guide section 40 which in turn couples to circular guide section 12. By using such an intermediate guide section 40, the effect of the discontinuities may be reduced. Knob 41 is utilized to adjust the position of coaxial wave guide section 15, longitudinally as before.

In order to further reduce the discontinuities, a taper section could be applied between rectangular'wave guide section 10 and rectangular wave guide section 40. This embodiment is illustrated in Fig. 5, with taper section 50 inserted.

Fig. 6 shows a further modification in which a flared section 60 is inserted between rectangular wave guide section 10 and circular wave guide section 12. As before, coaxial line section 15 is inserted therein and may be longitudinally positioned by knob 61.

It is thus seen that the present invention provides a mode transformer for coupling a rectangular wave guide to a circular wave guide, the two guides being in axial alignment. The invention further provides a structure for coupling the T1510 in the rectangular guide to a circular polarized wave of the T1511 mode in a circular wave guide. Still further, the present invention provides an axially aligned mode transformer which is capable of operating efficiently over a range or operating frequencies.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An electromagnetic wave energy mode transformer comprising a section of rectangular waveguide, a section of circular waveguide, said waveguide sections having wave energy propagation axes in substantial alignment, means for coupling wave energy directly between said wave uide sections, a section of"coaxial transmission line extending through saidfmeans and having one end portion thereof extending within said rectangular waveguide section and having the other end portion thereof extending within said circular waveguide section, and wave energy pick-ups terminating the ends of said coaxial line section and oriented to couple said coaxial line section to said circular Waveguide section with a fundamental trans verse electric wave energy mode having its electric field vector in quadrature relative to the electric field vector of the wave energy field in said waveguide section, whereby the wave energy phase transitions provided by said coupled waveguide sections, said means, and said coaxial line section cooperate with said oriented pick-ups to maintain a wave energy mode transformation between a transverse electric wave energy mode in said rectangular section and a circular-polarizedfundamental transverse electric wave energy mode in said circular waveguide section.

2. An electromagnetic wave energy mode transformer comprising a continuous length of hollow wave guide having a central longitudinal axis of propagation, a first portion of said wave guide being rectangular in crosssection and a second portion of said wave guide having a circular cross-section, a transmission line positioned within said wave guide along said axis of propagation, means for supporting said line, and energy pick-up and radiating'means terminating each end of the transmission line, the ends of the transmission line terminating respectively in the rectangular and circular portions of the wave guide' .3. An electromagnetic wave energy mode transformer as described in claim 2 wherein said transmission line is a coaxial line section.

4. An electromagnetic wave energy mode transformer as described 'in claim 3' wherein said energy pick-up and radiating means is a dipole element, the dipoles at each end of the coaxial line section being oriented at substantially with respect to each other.

5. Apparatus as defined in claim 4 wherein the means for supporting the coaxial line is adjustable longitudinally of the 'wave guide.

6. Apparatus as defined in claim 2 wherein said wave guide includes a portion of wave guide intermediate said circular and rectangular portions.

7. Apparatus asdefinedin claim 6 wherein said intermediate portion is rectangular and substantially larger in cross-sectional dimensions than the first-mentioned rectangular portion but no't'larger in any cross-sectionaldirh'ension than the diameter of said circular portion.

8. Apparatus as dfefined in claim 7 wherein a tapered line section joins said'interrnediate portion and said firstmentioned rectangular portion of the wave guide.

9. Apparatus a's'defined in claim 6 wherein said intermediate portionis a rectangular-to-circular wave guide transition section.

' 10. An electromagnetic wave energy mode transformer comprising a continuous length of hollow wave guide hav ing a central longitudinal axis of propagation, a length of transmission line positioned within the wave guide along said axis, and energy pickup and radiating'meansterminating each end "ofthe transmission line whereby a portion of the energy transmitted along the wave guide is carried by the transmission line, the length of the transmission line being such as to effect a quadrature phase difference between the portion of energy propagated directly by the wave guide and the portion of energy propagated by the transmission line, the pickup and radiating means at one end of the transmission line being oriented at ninety degrees relative to the pickup and radiating means at the other end of the transmission line whereby the plane of the E-vectoi of the'energy radiated at one end of the transmission'line is rotated ninety degrees with respect to the energy picked up at the other end of the transmission line.

11. An electromagnetic wave energy mode transformer comprising a continuous length of hollow wave guide having a central longitudinal axis of propagation, a first portion of the wave guide being rectangular in cross-section and a second portion of the wave guide being circular in cross-section, a length of transmission line having the ends thereof positioned respectively in the rectangular and circular portions of the wave guide, and energy pickup and radiating means terminating each end of the transmission line whereby a portion of the energy transmitted along the wave guide is carried by the transmission line, the length of the transmission line being such as, to effect a quadrature phase difierence between the portion of energy propagated directly by the wave guide and the portion of energy propagated by the transmission line, the energy pickup and radiating means at one end of the transmission line being oriented at 90 degrees relative to the energy pickup and radiating means at the other end of the transmission line whereby the plane of the E-vector of the energy radiated at one end of the transmission line is rotated 90 degrees with respect to the energy picked up at the other end of the transmission line.

References Cited in the file of this patent UNITED STATES PATENTS 2,106,769 Southworth Feb. 1, 1938 2,129,669 Bowen Sept. 13, 1938 2,232,179 King Feb. 18, 1941 2,281,550 Barrow May 5, 1942 2,412,320 Carter Dec. 10, 1946 2,425,345 Ring Aug. 12, 1947 2,441,598 Robertson May 18, 1948 2,443,612 Fox June 22, 1948 2,501,335 Hunter Mar. 21, 1950 2,545,472

Kline Mar. 20, 1951

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