The present invention relates to a four-channel rotary joint for changing direction of microwave propagation in waveguides with reduced energy-loss.

The invention relates more particularly to a rotary joint suitable for changing direction of the dominant mode propagation of microwaves of a wide frequency range in C-and Ku-brands i.e. 6.435+ 1.176 and 14.250 ± 0.500

GHz, in two transversely cut-sections each of four rectangular waveguides of which one cut-section of each waveguide is rotatable with respect to the other half section thereof in a single bearing over ari angle of + 150°, for changing the propagation direction of microwaves transmitted through the waveguides and controlling the polarization, phase and amplitude of microwaves supplied to the feed system of antennas at the Radar and satellite Earth stations.

In WO 2005/051604 Al, a method and assembly device for producing a rotary joint between a drive element and a flange is described. A bolt of the drive element is driven into a nut of the flange until the bolt is drawn into a bore in the flange.

In US 4,800,389, a rotary joint formed by a commutator having conductive brushes and rings for connecting the antenna system with the processing circuitry of a Radar apparatus is described for avoiding the loss of signal energy encountered in the conventional rotary joints for providing microwave coupling between the antenna and circulator of a RADAR apparatus.

In KR 2005 0113 769, a rotary joint for feeding microwave signals into the antenna system has been disclosed.

The conventional rotary joints used for changing the direction of microwave propagation between two waveguides by rotating one waveguide with respect to the other waveguide as required for polarization rotation, antenna feeding and controlling azimuth and elevation motion at Radar and satellite Earth stations, have generally the drawbacks of excessive loss of signal energy at the joints, variation of the energy loss with rotation of the waveguides and

generation of spurious wave modes in the signals propagated through the waveguides.

In addition, the conventional rotary joints are suitable for joining only coaxial lines and circular waveguides, and are not suitable for joining rectangular waveguides, which (are most commonly used). Moreover, the conventional rotary joints for multiple channels of co-axial lines and circular waveguides are of relatively complex design and unless precisely constructed it is found to be difficult to avoid appreciable loss of energy and amplitude/phase modulations of the signals at the conventional rotary joints.

The object of the present invention is to provide a four-channel rotary joint of relatively simple and compact design, and suitable for joining commonly-used rectangular waveguides using only a single bearing for rotating the waveguides of all the four channels.

The other object is to provide a four-channel rotary joint in which the loss of signal energy is reduced appreciably along with reduction in the integrated return loss of energy.

Another object is to provide a four-channel rotary joint which is capable of propagating increased energy over a wide frequency band.

Yet another object is to provide a four-channel rotary joint which ensures a high level of isolation between different channels.

A further object is to provide a four-channel rotatory joint in which no RF (radio frequency) choke with joint is required to be incorporated for reducing leakage of microwave signals.

The invented rotary joint comprises four rectangular waveguides of which two rectangular waveguides are used for propagating microwaves in the C-band i.e..

6.435 + 1.170 GHz frequency and two rectangular waveguides are used for propagating microwaves in the Ku-band i.e. 14.250 + 0.500 GHz frequency.

The microwaves of dominant wave mode TElO only are allowed to propagate through the waveguides. The four rectangular waveguides are each cut transversely into two sections at the cross section thereof where the current density in the wall of wave guides is zero, eliminating thereby the leakage of signal energy, and the need for using a RF (radio frequency) choke for preventing leakage of signal energy at the rotary joint.

One cut section each of the four rectangular waveguides is mounted co- centrically on a stationary cover plate which is attached parallelly and co- axially to one half transverse-section of a broad wall, having a spindle projecting outwardly and perpendicularly to the surface and at the centre thereof.

Each of the other cut-sections of the four rectangular waveguides are mounted co-centrically on a rotatable cover plate which is attached parallelly and co- axially to the other half transverse-section of the broad wall having a single bearing fitted at the centre thereof and co-operatingly engaged with the spindle projecting from the centre of the half transverse-section of the broad wall attached to the said stationary cover plate.

Each cut-section of the four waveguides is provided with a 90°- bend and a matching septum for feeding into and delivering the microwave signals from the waveguide sections.

A single bearing and a single spindle engaged co-operatingly therein have been used to join rotatably the cut-section-pairs of all the four waveguides.

Thus the present invention provides a four-channel rotary joint for changing direction of microwave propagation in waveguides with reduced energy-loss, characterised in that the rotary joint comprises four E-plane rectangular-cross section waveguides each cut transversely into two sections at the cross section thereof where the current density in the wall is zero, two cover plates of which one is stationary and the other is rotatable and one broad wall divided

transversely into two half sections of which one half section haying a spindle at the centre thereof is attached parallelly and co-axially to the stationary cover plate holding one cut-section each of the four waveguides mounted co- centrically thereon, and the other half section having a single bearing at the centre thereof is attached parallelly and co-axially to the rotatable cover plate holding the other cut-section each of the four waveguides mounted co- centrically thereon, the said spindle and bearing being engaged co-operatingly with each other.

The invention is described in details in an unrestricted manner with reference to a particular embodiment thereof illustrated in the accompanying drawings, in which -

Figure 1 is a perspective view of the main components shown separated from one another;

Figure 2 is a view of the cross section through the axis of rotation of the joint;

Figure 3 is a perspective view (partially in section) of the stationary cover plate with the cut-section each of the four rectangular waveguides disposed thereon;

Figure 4 shows: (a) perspective view, (b) plan, (c) side elevation of the matching septum used one each in the cut-sections of waveguides;

Figure 5 shows: (a) half section of the stationary cover plate and (b) half section of broad wall connected to the stationery cover plate.

Referring to Figs 1 to 5, the half-section (14) of the broad wall attached parallelly and co-axially to the stationary cover plate (5) is provided with a spindle (16) projecting outwardly and perpendicularly at the centre of the surface thereof. The other half-section (15) of broad wall attached similarly to . the rotatable cover plate (7) is provided with a bearing (8) at the centre thereof. The waveguides (1, 2, 3, 4) are each cut transversely into two sections at the cross section thereof wherein the current density in the wall of the waveguides

is zero, preventing thereby leakage of signal energy at the junction of the pair of cut-sections of each waveguide.

One cut-section of each of the four waveguides is mounted co-centrically on the surface of the stationary cover plate (5), which is not attached to the broad wall section (14). The other cut-section of each of the four waveguides is mounted co-centrically on the surface of the rotatable cover plate (7), which is not attached parallelly and co-axially to the other broad wall section (15). The single bearing (8) fitted at the centre of broad wall section (15) is engaged co- operatingly with the spindle (16) fitted at the centre of the broad wall section (14).

The waveguides (1 and 2) are adapted to propagate the dominant mode TElO of microwaves in the C-band i.e. 6.435 j^_1.170 GHz frequency. The waveguides (3 and 4) are adapted to propagate the dominant mode TE 10 of microwaves in the Ku-band i.e. 14.250 + 0.500 GHz frequency.

The cover plate (7) is rotatable over an angle of + 150° with respect to the cover plate (5).

The ball bearing (8) is provided with a cover ring (9), a cover plate (10) and a self-aligning mechanism (13).

Each cut-section of the four waveguides (1, 2, 3, 4) is provided with a 90° ^" bend (not shown) for feeding into/delivering out the microwaves propagated through the waveguides.

Four E-plane rings (not shown) of different diameters are provided, one with each E-plane rectangular waveguide.

Each cut-section of the waveguides is provided also with a matching septum (6) comprising a shorting section (S) of rectangular cross section and a tapered section (T) having a slope of 45° with respect to the bottom surface thereof.

The invented rotary joint is adapted to operate without any RF (radio frequency) choke because of cutting of waveguides (1, 2, 3, 4) at the cross section thereof where the current density in the wall is zero.

The typical operational and constructional features of the invented four-channel rotary joint are presented in Table I.

The cut-sections of the waveguides are fabricated from Aluminium sheets using Computer Numerical Control lathe machine within the tolerance limits of + 0.020 mm in dimensions.

From Table 1 it is noted :-

the waveguides used are all rectangular in cross-section and operable in C- band at 6.435 ± 1.170 GHz and in the Ku band at 14.250 ± 0.500 GHz frequencies with an integrated return loss of energy of -20 db over the bands;

the bearing (8) is of diameter 30.0 mm ;

the outermost diameter of the rotary joint is 265.0 mm;

the depth of the rotary joint is 65.0 mm;

the peak power handling capacity of the rotary joint is 0.25 M watt;

the angle of rotation of the rotatable cover plate (7) is + 150° with respect to stationary cover plate (5);

the rotary joint is operable in the temperature range of -40° to -Jf 7O ⁰ C; and

the stress bearing capacity of the rotary joint is 1.5 Kg/mm ^" .

The invented four-channel rotary joint has a number of advantageous features over the existing rotary joints used in Radar/Satellite earth station antenna systems, such as, (i) relatively simple and compact design and construction, (ii) broad band performance, (iii) adaptable for operation at any desired microwave frequency range, (iv) applicability to rectangular waveguides, (v) low propagation loss of signal energy at all angles of rotation, (vi) operable by a single bearing for all the four channels, (vii) no RF choke is required to be used with joints, for preventing leakage of microwaves, (viii) optimum impedance matching at the delivery of signal, output with consequent reduced return loss of energy of —20 db, and (ix) a high level of isolation between different channels, (x) the energy loss of signals propagated is less than 0.2 db and (xi) the dimensions of the joint are relatively small.

TABLE-I : Operational and Constructional Features of the Invented

Rotary Joint