Title of Invention	A WAVEGUIDE ROTARY JOINT
Abstract	A waveguide rotary joint for uninterrupted transmission of electromagnetic energy during rotation of one of the wave guide sections of the rotary joint. The wave guide rotary joint comprises a rotatable circular wave guide section in close electrical contact with a symmetrical and matching stationary circular wave guide section to form a choke joint, opposite to the ends of choke joint of rotatable circular wave guide section. The stationary circular wave guide section is provided with a shorting section and a rectangular wave guide section with a door-knob transition element.

Title of Invention

A WAVEGUIDE ROTARY JOINT

Abstract

A waveguide rotary joint for uninterrupted transmission of electromagnetic energy during rotation of one of the wave guide sections of the rotary joint. The wave guide rotary joint comprises a rotatable circular wave guide section in close electrical contact with a symmetrical and matching stationary circular wave guide section to form a choke joint, opposite to the ends of choke joint of rotatable circular wave guide section. The stationary circular wave guide section is provided with a shorting section and a rectangular wave guide section with a door-knob transition element.

Full Text	The invention relates to a waveguide rotary joint capable of uninterrupted transmission electromagnetic energy while rotation of a waveguide section at the joint. Such waveguide rotary joints are extremely usefiil in radar rotating antennas at higher frequency bands where the use of coaxial rotary joint is not feasible. In the wave guide rotary joint according to the invention, symmetrical TMoi mode is executed by converting the dominant TEi0 mode in the rectangular waveguide to a circular waveguide through a coaxial probe fed from the back side of the circular wave guide. A door-knob transition is provided near to the probe length to enhance the bandwidth performance. The waveguide rotary joint according to the invention when used for Ku band transmission offers minimum insertion loss of the order of 0.4 dB with good return loss requirement. Waveguide rotary joints according to the invention provide continuous rotation in either direction about an axis without deteriorating the electrical performance of the system. This requires field configurations of the propagating modes in round waveguides which have circular symmetry about the axis of rotation. This symmetricity of fields ensures the invariance of the amplitude and phase of the desired modes at the output stationary ports of the rotary joint corresponding to the input rotating ports. In practice, the TEM coaxial dominant mode, or TM0i or TEoi symmetrical mode in circular waveguide is used in waveguide rotary joint according to the invention. A circular waveguide rotary joint using a circularly polarised TEn mode is also possible to develop. Development of rotary joint with coaxial TEM mode is not feasible at Ku band because of the reason that cross-sectional dimension for the excitation of the desired dominant TEM mode in coaxial waveguide will be too small to incorporate a choke joint and also the power handling capability will be very small. The bigger cross-sectional dimension will allow the asymmetrical higher order modes to propagate. In the TMoi mode exciter, asymmetrical TEU mode is of lowest order and if present in the circular waveguide of a rotary joint will cause the joint impedance and the output phase to vary as a function of angular rotation. Hence asymmetrical modes like TEn mode which is excited must be almost completely suppressed. Using computer aided design (CAD) ensures that power in the TEn mode is less than 0.5%. The fixed and rotating part of the rotary joint is separated by a single guide wavelength (Xg). Probe dimensions are computed by calculating the impedance offered by the circular waveguide when TMoi mode is propagating. This impedance is later transformed by putting the door knob at the interface of rectangular and circular waveguide to enhance the bandwidth. The impedance and the probe length as well as diameter are designed by CAD. Short is provided in the rectangular waveguide at a distance of quarter wavelength of the wave guide and fine tuning was carried out at that location to arrive at final position. The lowest order symmetrical mode in a circular waveguide is TMoi mode and the excitation of TMoi mode consists of a coaxial radiating rod in the center of the cylinder, protruding through a hole in the bottom. This method is selected because this coaxial rod can produce only radial and longitudinal parallel to the axis of the circular waveguide electric field components and hence transverse magnetic field components. Therefore, it cannot generate any asymmetric mode like TEn mode. This configuration acts like TEn mode filter. This conventional method of exciting TM 0i mode, however, shows excessively narrow impedance bandwidth. This problem can be overcome by developing door knob transition right at the interface of the rectangular waveguide without effecting the insertion loss requirement. Generally there must be less than 0.5% of the power in TEn mode as compared to TM0i mode. The return loss and insertion loss was measured when rotating part is clamped with the fixed part. After getting the required performance the rotating part is rotated by 10 degrees and again it was measured to ascertain that the changes are well within the acceptable limit. Thus the invention provides a waveguide rotary joint for uninterrupted transmission of electromagnetic energy during rotation of one of the wave guide sections of the rotary joint, the said wave guide rotary joint comprising a rotatable circular wave guide section in close electrical contact with a symmetrical and matching stationary circular wave guide section to form a choke joint, opposite to the ends of said choke joint of said rotatable circular wave guide section and the stationary circular wave guide section being provided with a shorting section and a rectangular wave guide section with a door-knob transition element. With reference to the accompanying drawings : Figure 1 shows an isometric view of the waveguide rotary joint according to the invention. Figure 2 shows a exploded view of the waveguide rotary joint shown in figure 1. Figure 3 shows a sectional view of the rotary joint shown in figure 1. The waveguide rotary joint according to the invention comprises a rotatable circular waveguide section (1) and a matching symmetrical stationary circular wave guide section (2) in close electrical contact to form a choke joint (6). Opposite ends of the choke joint (6) of the said stationary waveguide secction (2) and the said rotatable waveguide section (1), shorting sections (3) are provided. Rectangular wave guide sections (4) are connected to each of the said shorting sections (3) and door-knob transition elements (5) provided in the rectangular wave guide sections (4) for allowing the electromagnetic energy to freely pass from the circular wave guide sections (1,2) to the rectangular waveguide sections (4). The waveguide rotary joint according to the invention ensures complete electrical continuity between the stationary and rotating parts of a system over the entire 360 degrees of rotation. It provides a very reliable rotary choke joint and can be made with negligible leakage of electromagnetic energy at the joint by precise manufacture of components. The return loss of the order of -20 dB at the input and output ports and the insertion loss of better than 0.4 dB are achieved with the waveguide rotary joint according to the invention. A typical TMoi mode exciter made according to the invention has the following specification: WE CLAIM: 1. A waveguide rotary joint for uninterrupted transmission of electromagnetic energy during rotation of one of the wave guide sections of the rotary joint, the said wave guide rotary joint comprising a rotatable circular wave guide section (1) in close electrical contact with a symmetrical and matching stationary circular wave guide section (2) to form a choke joint (6), opposite to the ends of said choke joint (6) of said rotatable circular wave guide section (1) and the stationary circular wave guide section (2) being provided with a shorting section (3) and a rectangular wave guide section (4) with a door-knob transition element (5). 2. The waveguide rotary joint as claimed in claim 1, wherein the ends joining the rotary circular wave guide section (1) and the stationary circular wave guide section (2) have precise dimension for perfect matching to reduce loss of electromagnetic energy. 3. A waveguide rotary joint, substantially as hereinabove described and illustrated with reference to the accompanying drawings.

Full Text

The invention relates to a waveguide rotary joint capable of uninterrupted transmission electromagnetic energy while rotation of a waveguide section at the joint. Such waveguide rotary joints are extremely usefiil in radar rotating antennas at higher frequency bands where the use of coaxial rotary joint is not feasible.
In the wave guide rotary joint according to the invention, symmetrical TMoi mode is executed by converting the dominant TEi0 mode in the rectangular waveguide to a circular waveguide through a coaxial probe fed from the back side of the circular wave guide. A door-knob transition is provided near to the probe length to enhance the bandwidth performance. The waveguide rotary joint according to the invention when used for Ku band transmission offers minimum insertion loss of the order of 0.4 dB with good return loss requirement.
Waveguide rotary joints according to the invention provide continuous rotation in either direction about an axis without deteriorating the electrical performance of the system. This requires field configurations of the propagating modes in round waveguides which have circular symmetry about the axis of rotation. This symmetricity of fields ensures the invariance of the amplitude and phase of the desired modes at the output stationary ports of the rotary joint corresponding to the input rotating ports. In practice, the TEM coaxial dominant mode, or TM0i or TEoi symmetrical mode in circular waveguide is used in waveguide rotary joint according to the invention. A circular waveguide rotary joint using a circularly polarised TEn mode is also possible to develop. Development of rotary joint with

coaxial TEM mode is not feasible at Ku band because of the reason that cross-sectional dimension for the excitation of the desired dominant TEM mode in coaxial waveguide will be too small to incorporate a choke joint and also the power handling capability will be very small. The bigger cross-sectional dimension will allow the asymmetrical higher order modes to propagate. In the TMoi mode exciter, asymmetrical TEU mode is of lowest order and if present in the circular waveguide of a rotary joint will cause the joint impedance and the output phase to vary as a function of angular rotation. Hence asymmetrical modes like TEn mode which is excited must be almost completely suppressed. Using computer aided design (CAD) ensures that power in the TEn mode is less than 0.5%. The fixed and rotating part of the rotary joint is separated by a single guide wavelength (Xg). Probe dimensions are computed by calculating the impedance offered by the circular waveguide when TMoi mode is propagating. This impedance is later transformed by putting the door knob at the interface of rectangular and circular waveguide to enhance the bandwidth. The impedance and the probe length as well as diameter are designed by CAD. Short is provided in the rectangular waveguide at a distance of quarter wavelength of the wave guide and fine tuning was carried out at that location to arrive at final position.
The lowest order symmetrical mode in a circular waveguide is TMoi mode and the excitation of TMoi mode consists of a coaxial radiating rod in the center of the cylinder, protruding through a hole in the bottom. This method is selected because this coaxial rod can produce only radial and longitudinal parallel to the axis of the circular waveguide electric field components and hence transverse magnetic field components. Therefore, it

cannot generate any asymmetric mode like TEn mode. This configuration acts like TEn mode filter. This conventional method of exciting TM 0i mode, however, shows excessively narrow impedance bandwidth. This problem can be overcome by developing door knob transition right at the interface of the rectangular waveguide without effecting the insertion loss requirement. Generally there must be less than 0.5% of the power in TEn mode as compared to TM0i mode. The return loss and insertion loss was measured when rotating part is clamped with the fixed part. After getting the required performance the rotating part is rotated by 10 degrees and again it was measured to ascertain that the changes are well within the acceptable limit.
Thus the invention provides a waveguide rotary joint for uninterrupted transmission of electromagnetic energy during rotation of one of the wave guide sections of the rotary joint, the said wave guide rotary joint comprising a rotatable circular wave guide section in close electrical contact with a symmetrical and matching stationary circular wave guide section to form a choke joint, opposite to the ends of said choke joint of said rotatable circular wave guide section and the stationary circular wave guide section being provided with a shorting section and a rectangular wave guide section with a door-knob transition element.
With reference to the accompanying drawings :
Figure 1 shows an isometric view of the waveguide rotary joint according to the invention.

Figure 2 shows a exploded view of the waveguide rotary joint shown in figure 1.
Figure 3 shows a sectional view of the rotary joint shown in figure 1.
The waveguide rotary joint according to the invention comprises a rotatable circular waveguide section (1) and a matching symmetrical stationary circular wave guide section (2) in close electrical contact to form a choke joint (6). Opposite ends of the choke joint (6) of the said stationary waveguide secction (2) and the said rotatable waveguide section (1), shorting sections (3) are provided. Rectangular wave guide sections (4) are connected to each of the said shorting sections (3) and door-knob transition elements (5) provided in the rectangular wave guide sections (4) for allowing the electromagnetic energy to freely pass from the circular wave guide sections (1,2) to the rectangular waveguide sections (4).
The waveguide rotary joint according to the invention ensures complete electrical continuity between the stationary and rotating parts of a system over the entire 360 degrees of rotation. It provides a very reliable rotary choke joint and can be made with negligible leakage of electromagnetic energy at the joint by precise manufacture of components. The return loss of the order of -20 dB at the input and output ports and the insertion loss of better than 0.4 dB are achieved with the waveguide rotary joint according to the invention.
A typical TMoi mode exciter made according to the invention has the following specification:

WE CLAIM:
1. A waveguide rotary joint for uninterrupted transmission of electromagnetic energy during rotation of one of the wave guide sections of the rotary joint, the said wave guide rotary joint comprising a rotatable circular wave guide section (1) in close electrical contact with a symmetrical and matching stationary circular wave guide section (2) to form a choke joint (6), opposite to the ends of said choke joint (6) of said rotatable circular wave guide section (1) and the stationary circular wave guide section (2) being provided with a shorting section (3) and a rectangular wave guide section (4) with a door-knob transition element (5).
2. The waveguide rotary joint as claimed in claim 1, wherein the ends
joining the rotary circular wave guide section (1) and the stationary
circular wave guide section (2) have precise dimension for perfect
matching to reduce loss of electromagnetic energy.
3. A waveguide rotary joint, substantially as hereinabove described
and illustrated with reference to the accompanying drawings.

Documents:

0310-mas-2001 others.pdf

0310-mas-2001 abstract.jpg

310-mas-2001- abstract.pdf

310-mas-2001- claims duplicate.pdf

310-mas-2001- claims original.pdf

310-mas-2001- correspondence others.pdf

310-mas-2001- correspondence po.pdf

310-mas-2001- description complete duplicate.pdf

310-mas-2001- description complete original.pdf

310-mas-2001- drawings.pdf

abs-310-mas-2001.jpg

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Patent Number

207455

Indian Patent Application Number

310/MAS/2001

PG Journal Number

44/2007

Publication Date

02-Nov-2007

Grant Date

13-Jun-2007

Date of Filing

10-Apr-2001

Name of Patentee

M/S. INDIAN SPACE RESEARCH ORGANISATION

Applicant Address

ISRO HEADQUARTERS,DEPARTMENT OF SPACE,ANTARIKSH BHAVAN,NEW BEL ROAD,BANGLORE 560 094

Inventors:

#	Inventor's Name	Inventor's Address
1	DR.SHASHI BHUSHAN SHARMA (ETC)	SCI/ENGR G,SENSORS ANTENNA & FEED GROUP(SAFG),SAC,INDIAN SPACE RESEARCH ORGANISATION,ISRO HEADQUARTERS,DEPARTMENT OF SPACE,ANTARIKSH BHAVAN,NEW BEL ROAD,BANGLORE 560 094
2	MR.KRISHNACHARYA DAMODARPRASAD ACHARYA	SCI/ENGR SF,SAFG,SAC,ISRO HEADQUARTERS,DEPARTMENT OF SPACE,ANTARIKSH BHAVAN,NEW BEL ROAD,BANGLORE 560 094

PCT International Classification Number

H01P001/06

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA