SATELLITE BROADCASTING RECEIVER

Abstract: A compact satellite broadcasting receiver is described comprising circular waveguide, a strip-line-shaped probe pro­ jected into the circular waveguide. a reflecting element pro­ vided backward from the probe in the circular waveguide and a microwave circuit having a strip line provided around the circu­ lar waveguide and connected with the probe. Furthermore, a satellite broadcasting receiver capable of simultaneously re­ ceiving two kind of microwaves polarized perpendicular to each other is realized by jointing two compact satellite broad­ casting receivers as mentioned avobe with a relative arrange­ ment of the strip-line-shaped probes placed at right angles.

Description: The present invention relates to a satellite broadcasting receiver, particularly to an antenna arrangement comprising a frequency down converter for converting an electromagnetic wave received by a parabolic antenna to a signal having a lower frequency. A satellite broadcasting receiver is used for receiving an electromagnetic wave transmitted by a satellite positioned on a stationary orbit in the sky, and generally comprises a parabolic antenna, a waveguide situated at a focus of the parabolic antenna, a frequency down converter having a strip line circuit, a mode converter provided between the waveguide and the strip line circuit of the frequency down converter for converting a waveguide mode (TE₀₁ mode) to a strip line mode (TEM mode). An output of the frequency converter is applied to a domestic television receiver through an FM-AM converter or a demodulator. In a conventional satellite broadcasting receiver (see US-A- 3832 717), the electromagnetic wave is guided to the outside of the parabolic antenna through the waveguide where the mode converter and the frequency down converter are provided, or the waveguide, the mode converter and the frequency down converter are unified in one body and provided at the focus of the parabolic antenna. However, in this conventional receiver, the mode conversion is processed sequentially from the waveguide mode to the strip line mode through the coaxial cable mode, cause a defect owing to the complexity of the configuration. Alternatively, a mode converter for directly converting the rectangular waveguide mode to the strip line mode is employed. However, where the mode converter of this kind is employed, two kinds of differently polarized waves cannot be received without rotating the whole antenna. Moreover, when the receiver is arranged for simultaneously receiving these two kinds of differently polarized waves, these two kinds of polarized wave each has to be derived from different positions of the waveguide provided at the focus of the parabolic antenna, so creating a further defect by reducing the effective area of the parabolic antenna. US-A-4208 660 discloses an arrangement comprising a dielectric sheet carrying two probes. On the front and the back surface of said dielectric sheet is attached a first dielectric substrate and a second dielectric substrate respectively. Said first dielectric substrate is covered with an electrically conductive sheet comprising three concentric circular apertures. Said second substrate is backed by a wave guide structure whose bottom functions as a reflecting element in the circular wave guide downstream of said probes, which are connected via feed lines to terminating structure and a coaxial connector respectively An object of the present invention is to provide a satellite broadcasting receiver in which an electromagnetic signal received by a parabolic antenna can be converted extremely simply to strip line mode and further a frequency down converter circuit can be arranged around a waveguide. Another object of the present invention is to provide a satellite broadcasting receiver in which two kinds of differently polarized waves can be received without reducing the effective area of a parabolic antenna by serially arranging two frequency down converter circuits in the direction of an axis of a waveguide provided at the focus of a parabolic antenna. Still another object of the present invention is to provide a mode converter for effecting the mode conversion between a circular waveguide mode and a strip line mode which is capable of realizing a remarkably small-sized satellite broadcasting receiver. The above objects are achieved by a satellite broadcasting receiver comprising the features of claim 1. For the better understanding of the invention, reference is made to the accompanying drawings, in which: Fig. 1 is a diagram showing an outline of a satellite broadcasting receiver; Fig. 2 is a perspective view showing a mode converter for effecting the mode conversion between a rectangular waveguide mode and a coaxial mode; Fig. 3 is a perspective view showing an example of a conventional satellite broadcasting receiver comprising a circular waveguide at a parabolic antenna focus, a mode converter for effecting the mode conversion between a rectangular waveguide mode and a coaxial mode and a frequency down converter containing a strip line; Fig. 4(a) is a perspective view showing an outline of a conventional mode converter for effecting the mode conversion between a rectangular waveguide mode and a strip line mode; Fig. 4(b) is a perspective view showing an outline of a conventional mode converter for effecting the mode conversion between a circular waveguide mode and a strip line mode; Fig. 5(a) is a side view showing an outline of an embodiment of the present invention; Fig. 5(b) is a side view showing an outline of another embodiment of the present invention in which two kinds of waves polarized perpendicular to each other can be simultaneously received; Fig. 6 is a perspective view showing a mode converter for effecting the mode conversion between a circular waveguide mode and a strip line mode according to the present invention; Figs. 7(a), 7(b) and 7(c) are a front view, a side view and a plan of the mode converter as shown in Fig. 6,respectively; Figs. 8(a) and 8(b) are a side cross-section and an elevation showing a three-dimensional structure of a frequency converter employing the mode converter as shown in Fig. 6, respectively; Fig. 9 is a cross-section showing a dummy mounted at an end of the frequency converter as shown in Figs. 8(a) and 8(b); Fig. 10 is a diagram showing an outline of an arrangement of a printed base plate and circuit elements forming the converter circuit containing the probe as shown in Figs. 8(a) and 8(b); Fig. 11 is a plan showing a series connection of two converters provided for simultaneously receiving two kinds of waves polarized perpendicular to each other; Fig. 12 is a cross-section showing an arrangement of a mode converter provided between a circular waveguide and a strip line for simultaneously receiving two kinds of waves polarized perpendicular to each other; Fig. 13 is a diagram showing characteristic curves of performances of the mode converter provided between the circular waveguide and the strip line as shown in Fig. 6; Fig. 14 is a perspective view showing another example of the mode converter provided between the circular waveguide and the strip line, which can be employed in an embodiment of the present invention; Fig. 15(a) is a diagram showing a reflecting element used for the mode converter as shown in Fig. 14; Fig. 15(b) is a circuit diagram showing an equivalent circuit in an X direction of the reflecting element as shown in Fig. 15(a); Fig. 15(c) is a circuit diagram showing an equivalent circuit in a Y direction of the reflecting element as shown in Fig. 15(a); Fig. 16 is a perspective view showing an arrangement provided for simultaneously receiving two kinds of waves polarized perpendicular to each other; and Figs. 17(a) and 17(b) are perspective views showing another arrangement of the strip line inserted into the circular waveguide in the mode converter as shown in Figs. 6 and 14. Firstly, for the better understanding of the invention also, an outline of a satellite broadcasting receiver and conventional techniques employed therefor will be explained. Fig. 1 shows an outline of a satellite broadcasting receiver in which a waveguide accompanying a frequency down converter is provided at the focus of a parabolic antenna. In Fig. 1, a horn 2 receives a microwave caught by a parabolic antenna 1. The microwave received by the horn 2 is supplied to a frequency down converter 3 coupled with a waveguide, which is connected with the horn 2, and converted into a lower frequency signal therein. The output of the frequency down converter 3 is applied to a demodulator or an FM-AM converter 5 provided apart therefrom through a coaxial cable 4. Moreover, a DC current is supplied from the demodulator 5 to the frequency down converter 3 through the coaxial cable 4 also. In the frequency down converter 3 as shown in Fig. 1, a mode conversion is effected for transmitting the microwave supplied through the waveguide to a frequency down converter circuit containing a strip line. This mode conversion is carried out from the waveguide mode to the strip line mode through the coaxial mode, or direct from the waveguide mode to the strip line mode. Fig. 2 shows an conventional mode converter for carrying out the mode conversion from the waveguide mode to the coaxial mode equal to the strip line mode. In this mode converter, a coaxial cable 7 is connected to a lower wall of a rectangular waveguide 6, in which a coupling probe 8 extended from an inner conductor of the coaxial cable 7 is provided. In this mode converter, an adjusting stub 9 extended from an upper wall of the waveguide 6 thereinto is provided also as occasion demands. Fig. 3 shows an example of a frequency down converter which is unified with a waveguide provided close to a focus of a parabolic antenna. In this converter, a microwave caught by the parabolic antenna is first received by a circular horn 10, and then supplied to a rectangular waveguide 12 through a mode converter 11 between a circular waveguide connected with the circular horn 10 and the rectangular waveguide 12. In this rectangular waveguide 12, the waveguide mode is converted into the coaxial mode through the mode converter as shown in Fig. 2. Thereafter, the microwave is applied to a frequency down converter 14 containing a strip line through a coaxial cable 13. On the other hand, for carrying out the mode conversion direct from the waveguide mode to the strip line mode, mode converters as shown in Figs. 4(a) and 4(b) are usually employed. However, in a situation where the above mentioned conventional mode conversions are applied for the satellite broadcasting receiver used to receive two kinds of waves polarized perpendicular to each other, the aforesaid defects are produced. That is, it is difficult to receive those two kinds of waves polarized perpendicular to each other through the converter as shown in Fig. 4(a) without rotation of the whole antenna, while in Fig. 4(b), the area of the frequency converter circuit and the mode converter takes a up large space around the waveguide and, as a result, the effective area of the parabolic antenna is reduced. Fig. 5(a) schematically shows an outline of a embodiment of the present invention. In Fig 5(a), a circuit horn 15 for receiving a microwave is provided at the focus of the parabolic antenna 1 and a frequency down converter circuit 16 is arranged around a waveguide extended from the circular horn 15, so as to prevent the reduction of the effective area of the parabolic antenna 1. In this figure, the output of the converter circuit is transmitted to a demodulator 5 through a coaxial cable 4. Fig. 5(b) shows another embodiment of the present invention, in which two kinds of waves polarized perpendicular to each other are received simultaneously. In this embodiment, only another converter circuit 17 arranged around the circular waveguide is added to that shown in Fig. 5(a), so that those two kinds of waves polarized perpendicular to each other can be simultaneously received without reducing the effective area of the parabolic antenna 1. In Fig. 5(b), furthermore, the output derived from the converter circuit 17 is transmitted to another demodulator 5' through another coaxial cable 4'. Next, the mode converter connected between the circular waveguide and the strip line, which is employed for the embodiments as shown in Figs. 5(a) and 5(b) and in which the frequency down converter circuit or other circuits can be easily and effectively arranged around the circular waveguide, will be explained by referring to Fig. 6. In Fig. 6, a strip line 19 is projected into a circular waveguide 18, which is connected to the horn 15 shown in Fig. 5(a), so as to function as a probe. This strip line 19 is formed or mounted on a circuit board 20, which is arranged around the circular waveguide 18 and on which the frequency down converter circuit corresponding to the block 16 as shown in Fig. 5(a) is assembled, and coupled with the wave polarized in the vertical direction in Fig. 6, that is, the V-wave among the waves guided through the circular waveguide 18. In addition thereto, a metal plate 21 functioning as a reflecting element against the V-wave is provided backward from the probe 19. The output of the frequency down converter circuit 16 mounted on the circuit board 20 is transmitted to the demodulator 5 through the coaxial cable 4 as shown in Fig. 5(a). Figs. 7(a), 7(b) and 7(c) show the configuration of the mode converter respectively in the directions A, B and C as shown in Fig. 6. In the mode converter as shown in Fig. 6, a length of the probe 19 is selected to about one fourth of the wavelength, that is, 1/4 λ in response to the frequency of the desired microwave, and a distance from the probe 19 to the plate 21 is selected also to about 1/4λ. Further, 2 length of the plate 21 functioning as the reflecting element is selected to about 1/2 λ. Further, it is preferable to form a matching section 22 between the probe 19 and the strip line (input of the frequency down converter circuit) as shown in Fig. 7(a). Referring to Fig. 7(b), the incoming V-wave is absorbed by the probe 19 and further reflected by the plate 21 so as to be more effectively absorbed by the probe 19. On the other hand, the other wave polarized perpendicular to the V-wave, that is the H-wave, is not absorbed by the probe 19 and passed backwards, because it perpendicularly crosses the probe 19 and the plate 21. Figs. 8(a) and 8(b) show the concrete structure of a frequency down converter according to the present invention which includes the mode converter as shown in Fig. 6. That is, Figs. 8(a) and 8(b) are a side cross-section and an elevation thereof respectively. The circular horn 15 positioned at the focus of the parabolic antenna 1 (Fig. 5(a)) is connected with a circular waveguide 25 through a flange 23. The circular waveguide 25 is protruded through a center of a converter body 24. A probe 27 mounted on a circuit board 26 is projected into the circular waveguide 25. In this circular waveguide 25, a metal plate 28 functioning as a reflecting element is provided backward from the probe 27. In the case that a single polarization wave is received, a dummy 30 as shown in Fig. 9 is fitted on a flange 29 provided at the other end of the circular waveguide 25. This dummy 30 is formed by a wave-absorber 30a mounted on the termination of the dummy 30 thereof. Fig. 10 shows an outline of an example of a converter circuit arranged on the board 26. In Fig. 10, the microwave absorbed by the probe 27 is frequency-down converted and derived from an output terminal 37 via a low noise amplifier 31, a bandpass filter 32, a mixer 33 and an IF amplifier 34 successively. On the circuit board 26, a bias circuit 35 for the low noise amplifier 31 and a local oscillator 36 are further arranged. In the satellite broadcasting receiver according to the present invention, any one of two kinds of waves polarized to each other can be easily received just by rotating by 90 degrees the arrangement of the frequency down converter coupled with the circular waveguide provided close to the focus of the parabolic antenna. Moreover, in the situation where another frequency down converter is fitted on the flange 29 shown in Fig. 8(a) with angle difference of 90 degrees, two kinds of waves polarized perpendicular to each other can be simultaneously received. Fig. 11 shows an example in which two frequency down converters are coupled with a circular horn 31 in series to each other as mentioned above, while Fig. 12 shows the manner by which respective probes of those two frequency down converters are coupled with the V-wave and the H-wave, respectively. Regarding the above-mentioned embodiments, though only the converter circuit is arranged on the circuit board on which the probe is mounted, it is of course possible to further provide a demodulator circuit or other circuits on the same board. Fig. 13 shows various characteristics of the mode converter between the circular waveguide and the strip line as shown in Fig. 6. In Fig. 13, the curve ω₁ indicates matching loss of the probe with regard to the parallel polarized wave, that is, the V-wave absorbed into the probe 19 in parallel as shown in Fig. 6. The curve ω ₂ indicates the insertion loss of the probe with regard to the perpendicularly polarized wave, that is, the H-wave perpendicular to the V-wave and, in other word, the loss of the H-wave while passing through the mode converter as shown in Fig. 6. The curve ω₃ indicates the identification factor for the cross polarization, that is, the ratio of the amount absorbed into the probe 19 between the V-wave and the H-wave as shown in Fig. 6. As indicated by the curves shown in Fig. 13, in the mode converter as shown in Fig. 6, the parallel polarized wave can be converted from the waveguide mode to the strip line mode with extremely little loss, while the perpendicularly polarized wave can be passed with extremely little loss. This mode converter has excellent features as mentioned above, together with the high identification factor for the cross polarization waves. The above exemplified mode converter for effecting the mode conversion from the waveguide mode to the strip line mode according to the present invention is provided with the waveguide in which the probe is inserted and the metal plate functioning as the reflecting element is arranged backward from the probe in parallel therewith. However, it is possible to employ a resonating window (an iris filter) as the reflecting element in place of the above mentioned metal plate. Fig. 14 shows an example of the mode converter employing the iris filter 47, and except for the iris filter 47 it is arranged exactly the same as that shown in Fig. 6. In the mode converter as shown in Fig. 14 also, the V-wave is coupled to the probe 19, while the H-wave is passed through the iris filter 47. Next, by referring to Figs. 15(a), 15(b) and 15(c), the above mentioned iris filter 47 will be explained. Concerning the slit in the iris filter as shown in Fig. 15(a), the equivalent circuit thereof for the wave polarized in parallel with the short axis thereof, that is in the Y direction, is formed as shown in Fig. 15(b). When the length L of the long axis of the slit is selected to about 1/2 λ of the intended microwave, the resonant frequency of the iris filter can be matched to the frequency of the intended microwave, so that the wave polarized in the Y direction can be passed through this iris filter. In contrast therewith, the equivalent circuit thereof, for the wave polarized in the X direction shown in Fig. 15(a) is formed as shown in Fig. 15(c), so that the iris filter is operated as a reactance having a large susceptance, and, as a result, the wave polarized in the X direction is reflected by the iris filter. Accordingly, it cannot pass through the iris filter. Consequently, in the mode converter as shown in Fig. 14, the injected V-wave is absorbed by the probe 19 and further reflected by the iris filter 47, so as to be more effectively absorbed by the probe 19, while the injected H-wave is not absorbed by the probe 19 because it crosses perpendicular thereto and is then passed through the iris filter 47. As mentioned above, an effective satellite broadcasting receiver can be obtained also by employing the mode converter containing the iris filter. Furthermore, a satellite broadcasting receiver is possible which can simultaneously receive two kinds of waves polarized perpendicular to each other by jointing two mode converters in series to each other, so as to form two stages with the angle difference of 90 degrees for the arrangement. Fig. 16 shows an outline of the arrangement of two circuit boards and two mode converters connected in series to each other. In the above mentioned examples of the mode converter according to the present invention, the direction of the insertion of the probe into the circular waveguide is selected so that the plane of the strip line (probe) crosses the axis of the circular waveguide. However, as shown in Figs. 17(a) and 17(b), it is possible to insert the probe so that the plane of the strip line is parallel with the axial direction of the circular waveguide. Furthermore, according to the present invention, the regular square waveguide can be employed as the waveguide through which two kinds of waves polarized perpendicular to each other can be guided.

Claims: A satellite broadcasting microwave receiver for use with a parabolic reflector comprising a circular waveguide (18, 25) for receiving an electromagnetic microwave signal, a probe (19, 27) having the shape of a strip line and projecting into said circular waveguide, the plane of said strip line of said probe (19,27) extending in a direction crossing the axis of said circular waveguide (18, 25); a reflecting element (21, 47; 28) provided in said circular waveguide downstream of said probe (19, 27) and a microwave circuit for processing a received microwave signal having a strip line connected to said probe (19, 27) and being disposed on a printed circuit board (20, 26) characterised in that the board has an aperture therein through which said circular waveguide (18, 25) passes; and said microwave circuit includes a low noise amplifier (31) for amplifying said received microwave signal, a band pass filter (32) an oscillator (36) for generating a local frequency signal, a mixer (33) for mixing the amplified microwave signal from said first amplifier (31) and the local frequency signal from said oscillator (36) to produce an intermediate frequency signal and a second amplifier (34) for amplifying said intermediate frequency signal. A satellite broadcasting microwave receiver as claimed in claim 1, further comprising another probe having the shape of a strip line and projecting into said circular waveguide at a location downstream of said reflecting element and displaced by an angle of 90° relative to said probe the plane of said strip line of said probe extending in a direction crossing the axis of said circular waveguide; and another microwave circuit for processing another received microwave signal having a strip line connected to said another probe and being disposed on a printed circuit board characterised in that the board has an aperture therein through which said circular waveguide passes (Fig. 16); and said another microwave circuit includes a first amplifier (31) for amplifying said another received microwave signal, a band pass filter (32) an oscillator (36) for generating a local frequency signal, a mixer (33) for mixing the amplified another microwave signal from said first amplifier (31) and the local frequency signal from said oscillator (36) to produce another intermediate frequency signal, and a second amplifier (35) for amplifying said another intermediate frequency signal. The satellite broadcasting receiver as claimed in claim 1 or 2, wherein said reflecting element is formed of a metal plate (21,28) provided in said circular waveguide (18,25) in parallel with the projectional direction of said probe (19,27) and the axial direction of said circular waveguide. The satellite broadcasting receiver as claimed in claim 1 or 2, wherein said reflecting element is formed of an iris filter (47) having a slit, a longitudinal direction of which is parallel with the projectional direction of said probe (19).

Inventors: AOKI, EIJI, WATANABE, HIROSHI
Applicants: NEC CORPORATION
Application year: 1982
Main classification: H01P1
IPC codes: H01Q1, H01P1, H01Q13