Abstract:
The invention relates to a device for transmission and/or reception of signals. It comprises a first waveguide ( 9 ) for the reception/transmission of signals and a second waveguide ( 23 ) for the transmission of a signal originating from an oscillator of the reception board, for example, to the transmission board. Particular application to the field of broadcasting signals exchanged between a station and a dwelling, in the scope of the MMDS, LMDS or MVDS, or between a satellite and a dwelling, in the scope of a satellite telecommunications system.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for transmission and/or reception of signals. 
     BACKGROUND OF THE INVENTION 
     Telecommunication services of the wire-free interactive type are developing rapidly. These services relate to telephony, facsimile transmission, television, in particular digital television, the so-called “multimedia” sector and the internet network. The equipment for these mass-market services has to be made available at a reasonable cost. This is so, in particular, as regards the user&#39;s receiver/transmitter which has to communicate with a server, most often via a telecommunication satellite, or in the scope of an MMDS (multi-point multi-channel distribution system), LMDS (local multi-point distribution system) or MVDS (multi-point video distribution system). These communication methods generally use the microwave range. For example, in the scope of the MMDS, frequency bands of the order of 40 GHz are used. 
     For these frequency ranges, a waveguide receiver and a wavelength transmitter can be used, the two waveguides being separate. 
     FIG. 1 represents a diagram of a device  1  for the transmission/reception of signals, in general located outside a dwelling (not shown). This device  1  comprises, on the one hand, a reception antenna  2 , connected by a reception path  3  to a unit  4  for conversion to intermediate frequency and, on the other hand, a transmission antenna  5 , connected by a transmission path  6  to a unit  7  for frequency conversion to a higher frequency. The two units  4 ,  7  are connected by a coaxial cable  80  to a set inside the dwelling. Each unit  4 ,  7  respectively comprises a mixer  4   1 ,  7   1  connected to a local oscillator  4   2 ,  7   2 . The transmission antenna makes it possible to employ a return path to the transmitter. 
     The device which has just been described has the disadvantage of requiring, in particular, two local oscillators in the conversion units  4 ,  7  of the outside set, one for reception and the other for transmission. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to avoid the drawbacks of the prior art cited. 
     It relates to a device for transmission and/or reception of signals, comprising: 
     a first waveguide for the operation in a first frequency band and the operation in a second frequency band, 
     a first frequency conversion circuit and a second frequency conversion circuit coupled with the first waveguide for the frequency conversion respectively of a first signal and of a second signal, 
     a local oscillator connected to one of the two circuits, characterized in that said device comprises further: 
     a second waveguide for the transmission of a signal of the local oscillator to the other of the two circuits for its use in the frequency conversion for the second circuit. 
     In this way, the invention avoids at least the duplication of certain components, in the case in point the local oscillator. The production cost is thus reduced by this. Furthermore, the microstrip links connecting the local oscillator to the circuit opposite would generate injection losses, causing degradation of the signal conveyed along these lines, whereas guided propagation of the signals minimizes these losses over the length of the waveguide, further economizing on the use of an amplifier. 
     If a single polarization is transmitted, the said first guide may be of parallelepipedal shape. According to a variant of the invention, the guide is cylindrical. 
     In order to maximize the energy delivered at the junctions between the second waveguide and the microstrip lines, the said second guide is closed at its ends by a quarter-wave cavity of length equal to one quarter of the guided wavelength of the transmitted signal. These quarter-wave cavities function as open circuits in the planes of the transmission and reception circuits for the waves to be delivered. 
     According to one embodiment, said first and second waveguides are interdependent with a same support. 
     According to one embodiment, said the first and second circuits are arranged on a first and a second microstrip circuit boards. 
     According to one embodiment, said coupling of the local oscillator connected to the one of the two circuits with the second waveguide and the coupling of this second waveguide with the other of the two circuits are realized by means of probes. 
     According to one embodiment, one of the frequency bands is used for the transmission of signals, and the second frequency band is used for the reception of signals. 
     According to one embodiment, the microstrip circuit boards cut the first waveguide in cross sections of said first guide. 
     According to one embodiment, the circuit board used for transmission is arranged upstream of the said circuit board used for reception in the signal reception direction of the device. 
     According to one embodiment, the circuit board used for transmission is arranged upstream of the said circuit board used for reception in the signal reception direction of the device. 
     According to one embodiment, the first waveguide comprises filtering means of type comprising a filter with iris cavity, a filter with screw cavity or a filter comprising at least two resonant cavities connected transversely to the body of the guide by coupling with irises, said filtering means being arranged in such a way that the waves transmitted by the first probe are attenuated enough on the second probe side in order not to interfere with the waves received at this second probe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the present invention will become apparent from the description of the illustrative embodiments which follow and which are taken by way of non-limiting examples, with reference to the appended figures, in which: 
     FIG. 1, already described, represents a diagram of a transmission/reception device, 
     FIG. 2 represents a simplified exploded view of an embodiment according to the invention, 
     FIG. 3 represents a cross section of the embodiment in FIG. 2, 
     FIG. 4 more particularly represents a unit for conversion to intermediate frequency which is arranged on the reception circuit, and a unit for conversion to higher frequency which is arranged on the transmission circuit, 
     FIGS. 5. a,    5 . b,    5 . c,    5 . d  and  5 . e  schematically represent views of five embodiments of filtering means according to the invention, 
     FIG. 6 represents a device for transmission/reception of signals comprising a frequency drift compensator according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     To simplify the description, the same references will be used in the various figures to denote those elements which fulfill identical functions. 
     FIG. 2 represents an embodiment of a device  8  according to the invention, whereas FIG. 3 represents a cross section of the device  8  in FIG.  2 . The device comprises a cylindrical cap  9  whose open end is arranged at the focus  10  of a parabola (not shown). The open end of the cap  9  extends in a frustoconical part or horn  11  which has discontinuities or grooves allowing good reception/transmission of the signals, which discontinuities are known per se and have not been represented. The cap  9  of the guide is separated into three parts  9   1 ,  9   2  and  9   3 . Part  9   1  is connected to the horn  11 , part  9   2  is the central part of the cylindrical cap  9 , and part  9   3  is the end part of the guide  9 , comprising a resonant cavity. Between the first and the second guide parts  9   1  and  9   2 , a microstrip circuit board  13  for transmitting the signals to be transmitted is arranged transversely with respect to a principal axis  12  of the guide  9 , and between the second and third guide parts  9   2  and  9   3 , a microstrip circuit board  14  for receiving the said signals is arranged transversely with respect to the axis  12 . These two boards  13  and  14 , each forming a substrate, consist of a material which has a given dielectric permitivity and is known per se. The said boards  13  and  14  have respective upper surfaces  13   1 ,  14   1  turned towards the space where the energy is to be regulated or picked up, and lower surfaces  13   2 ,  14   2  corresponding to the other face of the substrate. The lower surfaces  13   1 ,  14   1  are metallized, forming an earth plane, and are in contact with the conductive walls of the guide  9 . The boards  13  and  14  are respectively supplied by a probe  15  and  16 , which are respectively etched on the lower surfaces  13   2 ,  14   2  of the boards  13  and  14  and which penetrate inside the perimeter of the guide  9  through openings, without touching the wall of the guide  9 . 
     In a variant of the invention (not shown) to permit the reception and transmission of orthogonally polarized waves, two probes are etched on each of the said substrates and are arranged at right angles to one another. 
     The guide part  9   3  closing the guide  9  is a quarter-wave λ GR /4 guide section which forms a resonant cavity and operates as an open circuit in the plane of the substrate  14  for the received waves, λ GR  representing the guided wavelength of the received wave. In contrast, the guide part  9   2  is an electromagnetic filter making it possible to isolate the probe  16  from the energy leaks due to the waves broadcast by the probe  15 . Various embodiments of this filter  9   2  are described in FIGS. 5 a  to  5   e.    
     These two probes  15  and  16  are connected, on the boards  13  and  14  by microstrip lines  17 ,  18  whose technology is known per se, respectively to a unit for conversion to high frequency, referred to as the transmission unit  19 , and a unit for conversion to intermediate frequency, or reception unit  20 . The transmission  19  and reception  20  units, which are represented in detail in FIG. 4, are connected by means of a coaxial cable  200  represented in FIG. 4 to an indoor set located inside a dwelling (not shown) represented in FIG.  6 . The units  19 ,  20  are also respectively connected to probes  21 ,  22  which penetrate inside the perimeter of rectangular openings in the substrates  13 ,  14 . The two boards  13 ,  14  delimit, on either side of the probe and the rectangular opening which correspond to them, three parts  23   1 ,  23   2  and  23   3  of a cap  23  which has a rectangular cross section and forms a waveguide of parallelepipedal shape. In order to maximize the energy delivered at the junctions between the cap  23   2  guiding the transmitted waves and the microstrip probes of the transmission  13  and reception  14  boards, the cap  23   2  is closed at its ends by the parts  23   1  and  23   3  which each form a quarter-wave (λ LO /4) cavity of length equal to one quarter of the guided wavelength (λ LO ) corresponding to a signal S OL  of frequency F LO  generated by a local oscillator  24 , the role of which will be explained below, These parts  23   1  and  23   3  respectively function as open circuits in the planes of the substrates  13  and  14  for the waves transmitted at the frequency of the said local oscillator  24 . 
     In FIG. 4, the probe  16  is connected to a low-noise amplifier  25  which receives signals in the [41.5 GHz; 42.45 GHz] band and whose output is connected to a first input of a mixer  26 . A second input of this mixer  26  is driven by the oscillator  24  of frequency 20.2625 GHz via an amplifier  27  which amplifies a band centred on the frequency of the oscillator  24 . The output of the subharmonic mixer  26  of harmonic N=2 delivers signals which are amplified by an intermediate-frequency amplifier  28 . The output of this intermediate-frequency amplifier  28  then delivers signals in a [975 MHz-1925 MHz] band. 
     Similarly, the probe  15  is connected to a power amplifier  29  whose input is connected to the output of a subharmonic mixer  30  of harmonic N=2. A first input of this mixer  30  is driven by a signal delivered by an amplifier  31 , and a second input is connected to the output of an amplifier  32  whose input is connected to the output of a bandpass filter  33  whose pass band is [0; 25 MHz]. The input of the amplifier  31  is connected to the probe  21 . In the same way, the probe  22  is connected to a second output of the oscillator  24 . The signal generated by the local oscillator  24  is then transmitted by the probe  22  into the waveguide  23  and picked up at the probe  21  to be recovered in the high-frequency conversion unit  19 . 
     FIG. 5 a  represents a bandpass filter  34  using several resonant cavities coupled inductively by irises  35 . The distance between two consecutive irises  35  in the length direction of the guide  9  is chosen so that the reflections between the two irises cancel each other out at the resonant frequency of the cavity. This distance is of the order of λ GR /2, λ GR  being the guided wavelength of the frequencies received by the probe  16 . The bandpass filter  34  produced in this way, furthermore having a quarter-wave λ GT /4 guide section at its input, λ GT  being the wavelength of the frequencies broadcast by the probe  15 , can be considered as an open circuit for the energy radiated by the probe  15  in the plane of the substrate  13 , and does not filter for the received-frequency band. It has been deemed expedient to introduce several successive cavities separated by irises  35 , this making it possible to improve the frequency response of the filter  34 , allowing sharper cutoff. By way of explanation, as the number of irises  35  increases, the frequency response of the filter  34  becomes steeper. In view of the compromise between the performance which is obtained by increasing the number or irises  35  and the complexity which may result from this, it is preferable to use a filter  34  containing fewer than  10  irises  35 . It should be noted that the distance I separating the last iris and the board  14  is arbitrary, this also being true for the filters below. 
     FIG. 5 b  is a longitudinal section of a variant of the bandpass filter  34  in the view A—A. 
     FIG. 5 c  represents a bandpass filter  36  produced using a succession of screws  37 . In order to allow fine adjustment of the resonant frequency of each cavity to be made, these screws  37 , which have variable insertion and behave as capacitive susceptances, are placed so as to make it possible to optimize the setting of the filter  36 . 
     FIG. 5 d  represents a notch filter  38 . This filter  38  is produced by using resonant cavities  39  which are connected transversely to the body of the guide  9   2  by coupling with irises  40 . The distance between these cavities is of the order of one quarter of the guided wavelength of the waves broadcast by the probes  15 . 
     FIG. 5 e  represents a bandpass filter  41  called a finline. These filters  41  are easy to produce by inserting a metallized substrate  42 , which has windows  43 , in the E plane of the waveguide  9 . A metal plate having identical geometry to the said substrate  42  may also be used. 
     In the embodiment in FIG. 2, for a device  8  for transmission/reception of signals in the band around 40 GHz, the diameter of the cross section of the guide  9  is 4.8 mm. In order to make it possible to convey a signal around 20 GHz, corresponding to the frequency of the local oscillator  24  shared between the transmission  13  and reception  14  circuits, the short dimension of the rectangular guide  23  is 4.3 mm whereas its long dimension is 10.7 mm. The length between the transmission  13  and reception  14  circuits is 8 cm. 
     These numerical values do not of course imply any limitation. 
     FIG. 6 represents a device  50  for transmission/reception of signals comprising a frequency drift compensator according to the invention. This device  50  is contained in the interior set  51  located inside the dwelling. This device  50  is capable of detecting the frequency drift which the oscillator  24  suffers on the reception path, and makes it possible to offset the return channel so as to centre it on the return channel. 
     In FIG. 6, the input/output of the said interior set  51  is connected to a reception path  52  whose general role is, amongst other things, to carry out the conversions to low frequency and to decode the encrypted video signals which originates from the exterior set and are sent to the coaxial cable  200 , in the same way as a conventional interior set. The decoded signals available at the output of this interior set  51  are then sent to one of its outputs, at which an assembly  152  is connected. The input of the assembly  152  is connected to a television receiver  53  and a remote control  54  with the role of an active interface makes it possible to send instructions generated by the user to a modulator  55 . 
     The input of the reception path  52  is connected to a reception frequency tuner comprising a frequency converter circuit  56  (referred to below as “converter”) which is known per se. The converter  56  comprises a mixer  57 , a first input of which receives the signal originating from the input of the reception path  52  and a second input of which is driven by a local oscillator  58  controlled by a phase-locked loop circuit  59 , referred to below as PLL. The output of a mixer  57 , which is the output of the converter  56 , is connected to an input of a bandpass filter  60  whose passband is substantially centred on the nominal value of the reception band of a demodulator/decoder  61 . The output of the demodulator/decoder  61  produces a television signal S RF  which is sent to the television receiver  53 . 
     The interactive interface  54  delivers packets on a return path  62  of the interior set  51  through the modulator  55  which performs modulation of the QPSK type. The output of the modulator  55  is connected to an input of a bandpass filter  63  centred on the transmission frequency of the interface  54 . The output of the filter  63  is connected to a transmission frequency tuner of the device, consisting of a frequency converter circuit  64 . The converter  64  comprises a mixer  65 , one input of which receives the signal originating from the filter  63  and a second input of which is driven by a local oscillator  66  controlled by a PLL circuit  67 . The output of the converter circuit  64 , which is the output of the mixer  65 , has the role of sending the transmitted signals via the coaxial cable  200  to the device  8  of the exterior set. The local oscillator  66  delivers a sinewave signal at the desired frequency or transmission channel. 
     The device  50  was the subject of a patent application filed in the name of the Applicant Company on Oct. 31, 1997, having the number 9713708. It comprises a compensator comprising a digital module for automatic frequency correction, consisting of a microcontroller  68  in the embodiment represented. The microcontroller  68  is capable of recording the total frequency drift δF 10  introduced on the reception path  52  and of offsetting the spectrum of the transmission signal by a value (−δF 10 ) so as to match the frequency of the carrier of the said signal to the nominal frequency of the carrier of the transmission channel. This microcontroller  68  receives and transmits digital signals with the PLL circuit  59  downlinked via a first control/drive bus  69 , receives digital signals from the demodulator/decoder unit  61  via a second control/drive bus  70 , transmits digital signals intended for the PLL circuit  67  uplinked there via a third control/drive bus  71  and for the modulator/encoder  55  via a fourth control/drive bus  72 , as shown by FIG.  6 . 
     In the embodiment described in FIG. 6, the microcontroller  68  comprises a memory  73  which can record two digital values used for controlling the carrier of the signal transmitted on the transmission path in relation to the nominal frequency of the carrier of the uplink channel. The way in which the interior set  51  and, in particular, the frequency drift compensation module operate will not be described in the present application, and can be found in the aforementioned patent application No. 9713708 in the name of the Applicant Company dated Oct. 31, 1997. 
     The device  8  according to the invention operates as follows. 
     The electromagnetic waves arriving on the reflector (not shown) of the transmission/reception system according to the invention are focused on its focus  10  to be guided along the guide  9 . These waves pass through the filter  9   2 , which may be a bandpass filter allowing only the reception frequency band through, a notch filter cutting off the transmission frequency band or a high pass filter, or a low pass filter, respectively, in the case when the transmission band is chosen, in the frequency plane, so that the transmission frequencies are lower, or higher, respectively, than the reception frequencies. The said waves are then received and picked up by the probe  16  which delivers to the conversion unit  20  a reception signal which, after conversion to intermediate frequencies, is intended to be sent to the interior unit  51  of the dwelling. This signal is then processed in the device  50  to be utilized in the receiver  53 . 
     Simultaneously, a return signal which originates from the device  50  and is frequency-rectified using the method explained in French Patent Application No. 9713708, passes through the unit  19  for conversion to high frequency, which supplies the probe  15  with the waves to be broadcast to the horn  11 . The energy radiated by this probe  15  at the filter  9   2  side is attenuated by the filter so that the leaks of the transmitted waves are small enough not to cause interference for the reception board  14 . By way of example, interference will be considered to be negligible if the waves broadcast by the probe  15  are attenuated by 70 dB below their initial level during transmission on the reception board  14   2  side. 
     During the conversion of the signal received by the unit  20 , the oscillator  24  contained in the unit  20  generates an oscillation signal S OL  of frequency F LO  allowing the said signals to be transposed into the intermediate band. The same oscillator  24  generates a second signal S OL  with the same frequency F LO  which is supplied to the probe  22 . The latter transmits, via the waveguide  23   2 , the said signal which is picked up at the probe  21 . The probe  21  has the task of delivering it to the input of the amplifier  31  for transposing the transmission signals in the uplink path to high frequency. 
     The guided propagation of the oscillatory signal S OL  generated by the oscillator  24  makes it possible to use a single common local oscillator  24  for the transmission and reception paths. 
     Various other configurations may clearly be envisaged in the established frequency plane, for example: 
     a reception band [40.55 GHz; 41.5 GHz] and a transmission band [42.45 GHz; 42.5 GHz], 
     a reception band [41.5 GHz; 42.45 GHz] and a transmission band [40.5 GHz; 40.55 GHz]. 
     At these high reception/transmission frequencies, current filters  9   2  need to be provided with a frequency space of about one gigahertz between the reception band and the transmission band. The various frequency plane configurations, as well as others which have not been mentioned, need to satisfy this condition. 
     It is remarkable that the two waveguides are interdependent to a same support  100  which makes the device according to the invention be small and compact structure. 
     Of course, the invention is not limited to the embodiments as described. Thus, the guides  9  and  23  may be of any shape allowing good reception/transmission of the electromagnetic waves. By way of example, they may be rectangular if one polarization is favoured over another. The horn  11  may furthermore be of any kind, for example a grooved horn. 
     It is also possible to use guided propagation means for sending a signal other than an oscillatory signal. 
     It is also well possible to use the two circuit boards for the reception only or for the emission only of signals.