Antenna for transceiver devices or the like

Abstract: In an antenna for transceiver devices or the like, in order to eliminate the presence of separate modulators and demodulators and the associated circuits, according to the invention a detector/mixer diode (6) is associated with the radiating antenna structure (1), so as to form a single device which is alternately able to receive a modulated carrier wave and demodulate from the said wave the modulation signals received as well as modulate, with local modulation signals, a carrier wave, reflecting it for example back to the emitting source. The modulation signals received and the local modulation signals transmitted are respectively detected and supplied to the radiating structure (1) at a point (P) of the said structure, where the electric field of the carrier wave is equal to zero. The point of insertion (I) of the detector/mixer diode (6) in the radiating structure (1) is determined so as to obtain optimum matching between the impedance of the radiating structure (1) at the insertion point (I) and of the detector/mixer diode (6), during reception and transmission.

Description: The invention relates to an antenna for transceiver devices or the like, having a radiating structure which is provided in combination with a single detector/mixer diode; - the radiating structure being formed by a waveguide with a so-called microstrip structure having a resonating/radiating conductor formed by a conductor plate of quadrilateral, preferably rectangular, shape which coincides with the middle zone of an earth conductor plate, a so-called earth plane, from which it is separated by a layer of dielectric material, preferably by a plate of solid dielectric material; the detector/mixer diode connecting said resonating/radiating conductor with the earth conductor; the resonating/radiating conductor being connected at a predetermined point to an input/output conductor for the received signals and the transmitted signals. Document GB-A-2 223 130 (see Fig.3) discloses an antenna of the above mentioned kind, being formed by a patch antenna connected to a local oscillator. The patch and the earth plate of the antenna are connected toghether by a mixer diode. The point of connection of the mixer diode to the patch is located off-centre of a patch diagonal, in one corner. The radiative signals received by the antenna and the local oscillator signals fed to it excite resonances with non zero amplitudes at the mixer connection point. The radiative and the local oscillator signals are therefore combined on the antenna patch for subsequent mixing. The mixer diode developes intermediate frequency signals which are extracted from the antenna patch through a coaxial lead having an internal conductor and an outer shield. The internal conductor is bonded to the centre of the antenna patch, while the shield is connected to the earth plane of the antenna. The intermediate frequency signal must then be further processed for extracting the information signals carried by the received waves. Document EP-A-0 412 884 relates to a system for data transmission between an active central station ad at least one passive local station. The passive local station are able to receive and demodulate a modulated carrier wave transmitted from the central station and to locally modulate and to reflect back an unmodulated carrier wave transmitted to it by the central station using the same antenna for alternatively transmitting and receiving. Also this antenna shows a microstrip radiating structure. For extracting the received information signals and charging the information signals to be transmitted the antenna must be provided in combination with modulators and demodulators units. Document DE-A-40 17 625 discloses a microwave transponder having an antenna which is formed by two microstripe-conductors being complanar and longitudinally aligned and which are spaced apart one of the other with their facing ends. This two facing ends of the two conductors are connected together by a diode. By commuting the diode in an on and off state of conduction the antenna radiating structure is alternatively able to getting in resonance or not with the carrier wave. This allows to perform modulation and demodulation of the carrier wave without providing modulation or demodualtion units. In order to adjust and dimensionate the antenna in the way as to obtain maximum efficency, the microstrip-conductors' length, their distance and the position of the diode can be suitably adjusted. In the transceiver devices, extraction, from the modulated carrier wave received, of the modulation signals containing logic information, and superimposition, on the carrier wave transmitted, of the logic information contained in local modulation signals are generally performed by means of demodulators and modulators. Modulators and demodulators are also used in so-called "transponders", i.e. receiving/reflecting devices which, instead of generating their own transmission carrier wave, use for transmission the carrier wave, preferably unmodulated, which they receive from a remote transmitting station and which is modulated by them and then reflected back. These devices possess the advantage that they do not require local oscillators and the corresponding power circuits for generation of the carrier wave. On account of their small dimensions, they are used extensively in telecommunications and in control and remote identification systems where they are combined with local control devices or with the identification units. The frequency ranges used may be of any kind and in particular are within the microwave range. Owing to the growing automation and robotisation of industrial processes and plants of all kinds, there is a tendancy towards' increasingly widespread use of such systems. This has given rise to the need to improve the transceiver/reflecting devices and reduce their costs and dimensions as far as possible, with the development of special technologies in the microwave range. The object of the invention, therefore, is to provide an antenna for transceiver devices or the like, in particular for receiving/reflecting devices, which results in a simple, inexpensive and extremely compact design of such devices, all of which without adversely affecting, but on the contrary actually improving their operation and performance. The invention achieves the above objects with an antenna for transceiver devices or the like, as claimed in Claim 1. The antenna is able to receive a carrier wave, preferably unmodulated, and modulate the said wave with local modulation signals, reflecting it back. Demodulation of the signals received and modulation with the local transmission signals is therefore performed without having to use separate demodulators and modulators, together with the corresponding filters, local oscillators and the usual circuitry associated with them. In addition to the reduction in the number of components and the extremely simple design, a considerable reduction in the dimensions is also achieved. The point chosen for detection and supplying of the modulation signals received and transmitted ensures that the carrier is confined entirely in the resonating/radiating conductor, and the point of insertion chosen for the detector/mixer diode on the resonating/radiating conductor forms the optimum connection between diode and conductor. This results in optimisation of both the level of the demodulated signals received and the efficiency of reflection of the locally modulated carrier. The invention also relates to other features which further improve the abovementioned antenna and which are described in the subclaims. The characteristic details of the invention and the advantages resulting thereform will emerge more clearly from the description of a preferred embodiment, illustrated by way of a non-limiting example in the accompanying drawings, in which: Figure 1 shows a perspective view of the side of the antenna constructed in microstrip technology, where the so-called patch is located; Figure 2 shows a cross-section through the antenna of Figure 1 in the area of the detector/mixer diode and along the line II-II of Figure 3. Figure 3 shows a plan view of the side of the antenna according to the preceding figures, where the so-called reference earth plane is located. In the example shown in the Figures, the antenna according to the invention is constructed in so-called microstrip technology, already used for the construction of waveguides for propagating signals in the microwave briefly "antenna" below, consists of two conductors separated by a solid dielectric element. The said structure comprises a rectangular plate 2 of dielectric material, on each face of which a thin conducting plate 3, 4 is fixed. One of the two conducting plates 4, called an "earth plane", covers the entire surface of the dielectric plate 2. The other conducting plate 3, the so-called "patch", is arranged in the centre of the opposite face of the dielectric plate 2 and has a rectangular shape with dimensions significantly smaller than those of the earth plane 4. The so-called patch 3 forms the resonating/radiating conductor, while the earth plane 4 performs the function of an artificial earth. From a supply and detection point P of the patch 3, namely in this case the central point of one of its shortest sides 103, there extends an input/output conductor 5 to which the remainder of the circuit of a transceiver device (not shown), for example a transponder, is connected. A diode 6 connects the patch 3 to the earth plane 4. The point of connection of the diode 6 to the patch 3, the so-called insertion point I, coincides with the median axis M parallel to the shortest side 103 of the patch 3, while it is arranged at a given distance D from one of the longitudinal sides 203 of the patch 3 perpendicular to the said median axis M. The diode 6 is arranged in the direction of conduction from the patch 3 to the earth plane 4 (Figure 2) and is fixed to the antenna 1 on the side where the earth plane 4 is located. In particular (Figure 2), in the region of the insertion point I, the earth plane 4 has a through-aperture 104, inside which an extension 7 of the patch 3 forming a connection to the detector/mixer diode 6 is accommodated so as to be electrically insulated from the earth plane 4 itself. The connection extension 7, on the side where the earth plane 4 is located, is connected electrically to the patch 3 by means of a tubular conducting bush 8 which passes from one side to the other of the dielectric plate 2 through a hole 102 coinciding with the insertion point I itself. The insertion point I of the detector/mixer diode 6 is determined so as to obtain the optimum impedance matching of the antenna 1 with the detector/mixer diode 6. Determination of the insertion point I is not easy, since the detector/mixer diode 6 acts alternately as a loading device for the antenna 1 and generator, during reception and transmission. Matching of the impedance of the antenna 1 at the insertion point I with the impedance of the detector/mixer diode 6 must be performed taking this into account, in order to optimise simultaneously the efficiency during reception and that during transmission/reflection. For this purpose, the insertion point I may be determined experimentally or theoretically. In the latter case, the insertion point I is calculated to a good and adequate degree of approximation, as is the point of the patch 3, the input impedance of which assumes a predetermined value matching the impedance of the detector/mixer diode 6, in particular for example of the order of magnitude of the impedance of the detector/mixer diode 6 or approximately identical to the impedance of the same at the resonant frequency w 10 of the radiating antenna structure (1). Obviously the radiating structure (1) is constructed such that the resonant frequency w 10 coincides substantially with the frequency of the carrier wave. With reference to the present example in which the insertion point I is arranged on the median axis M of the patch 3 parallel to the side 103 on which the detection and supply point P is provided, the distance D of the insertion point I from one of the sides 203 of the patch 3 transverse relative to the said median axis M is defined by the relation with the input ipedance Z in of the radiating structure 1 at the insertion point I at the resonant frequency w 10 : Z in = Z in (L, W, D, h, K o , Z o ,ετ, Q T , W 10 ) where: L: length of the side 203 of the patch 3 W: length of the side 103 of the patch 3 D: distance of the insertion point I from the side 203 of the patch 3 h: distance of the patch 3 from the earth plane 4 K o : 2π/λ o with λ o : wavelength in air Z o : characteristic impedance of vacuum ετ : dielectric constant Q T : merit factor of the antenna (calculable) w 10 : resonant frequency. The point P for detecting and supplying the demodulated signals received and the local modulation signals is determined so as to coincide with the point of the patch 3-where the electric field generated by the carrier wave is equal to zero. During reception of a modulated carrier wave, the diode 6 acts as detector, extracting from the modulated carrier the modulation signals and hence the information transmitted therein. Owing to the particular arrangement of the insertion point I, the level of the demodulated signals is optimised. As a result of the positioning of the detection and supply point P, automatic filtering of all the components of the carrier wave confined in the patch 3 can be achieved. Only the baseband signals relating to the information transmitted are output from the patch 3, thus avoiding the need for both a conventional envelope demodulator and the filters associated therewith. During reflection, the diode 6 acts as a modulator of the carrier wave which during this phase is transmitted preferably unmodulated and which is confined in the patch 3. The local modulation signals are sent to the antenna 1 at the detection and supply point P. Modulation can be performed without the use of local oscillators and the usual additional circuits associated therewith. The arrangement of the point P for detecting and supplying the modulated signals received and transmitted, and of the insertion point I of the diode 6 prevent diffusion of the carrier wave beyond the detection and supply point P towards the internal circuits and thus result in optimum efficiency of reflection of the carrier wave itself, modulated with the local modulation signals. The efficiency of the antenna according to the invention both during reception and transmission/reflection is also influenced by additional parameters which depend in each case on the operating conditions, such as type of modulation, structure of the analog or digital signals, wavelength of the carrier and frequency of the modulation signals, and type of polarisation. All of this influences the dimensions of the antenna, the choice of diode, the polarisation current of the diode, where present, and the orientation of the antenna and/or the diode itself. In the case, for example, of a system with at least one transmitting/receiving station and a transponder, in which a carrier wave of between 5.72 and 5.8 GHz is used to send information to the transponder, it is appropriate to modulate the amplitude of the carrier, whereas, in order to send data from the transponder to the station, the carrier is frequency-modulated. When the data received and transmitted are of the digital type it is preferable to use ASK amplitude modulation during reception and frequency modulation of the carrier during transmission/reflection, as in the case where the carrier is mixed with a medium frequency signal obtained from frequency modulation, for example FEK modulation. By varying the polarisation current of the detector/mixer diode 6, it is possible to modify and correct the waveform and the amplitude of the modulating signals, in particular during reception. In this case, the dimensions of the antenna, in particular the patch 3, are extremely small, namely of the order of ten millimentres or so for the side 103 and 203, while the distance D of the insertion point from the side 203 of the patch 3 is a few millimetres. Further-more, in view of the extremely small dimensions of the patch 3, the tolerances for determining the insertion point I are relatively large, the extension of the pins 106 of the detector/mixer diode 6 not being insignificant compared to the surface area of the patch 3. In this case, for most of the commercially available diodes 6 with characteristics suitable for the purpose, it has been shown that the impedance matching between radiating antenna structure 1 and diode 6 is almost always ensured, within the context of the operational requirements of the antenna, when the impedance of the radiating structure 1, or the patch 3, at the insertion point is between 10 and 100 ohms, in particular from 40 to 50 ohms. With special plane polarisation of the carrier wave, the efficiency of the antenna both during reception and reflection is optimum when, as shown in Figure 3, the diode 6 is oriented with the axis C which joins the two pins 106, parallel to the side 203 of the patch 3, the said side 203 of the patch 3 and the said axis C being oriented at an angle of 90° with respect to the plane containing the electric field of the carrier wave. Obviously, the invention is not limited to the embodiments described and illustrated herein, but may also be substantially varied and modified, in particular from a constructional point of view. The antenna/diode structure of the present invention may be used with any type of radiating antenna structure for any type of use, all of which without departing from the underlying principle described above and claimed below.

Claims: Antenna for transceivers devices or the like, having a radiating structure (1) which is provided in combination with a single detector/mixer diode (6), the radiating structure (1) being formed by a waveguide with a so-called microstrip structure (1) having a resonating/radiating conductor (3) formed by a conductor plate of quadrilateral, preferably rectangular, shape which coincides with the middle zone of an earth conductor plate (4), a so-called earth plane, from which it is separated by a layer of dielectric material (2), preferably by a plate of solid dielectric material; the detector/mixer diode (6) connecting said resonating/radiating conductor (3) with the earth conductor (4); the resonating/radiating conductor (3) being connected at a predetermined point (P) to an input/output conductor (5) for the received signals and the transmitted signals, characterized in that the detector/mixer diode (6) is connected to the resonating/radiating conductor (3) and to the earth conductor (4), being oriented in the direction of conduction from the resonating/radiating conductor (3) to the earth conductor (4); the detector/mixer diode (6) being connected to the resonating/radiating conductor (3) at such a point (I) of the said conductor (3) (insertion point) as to obtain optimum impedance matching between the characteristic impedance of the radiating structure (1), or of the resonating/radiating conductor (3), with reference to the said insertion point (I), and the impedance of the detector/mixer diode (6); the detector/mixer diode (6) being arranged on one side of the antenna structure (1) outside said structure (1) and having a predetermined orientation with respect to the antenna structure, depending on the fact whether the carrier wave is polarised and on the predetermined direction of polarisation of the carrier wave; the conductor (5) for detecting and supplying respectively the received signals and the transmitted signals being connected at a point (P) of the resonating/radiating conductor (3) at which the electric field of the carrier wave is equal to zero; so as to form an integrated device for receiving modulated carrier waves and demodulating at the same time from said modulated carrier wave the modulation signals received and for modulating with locally generated modulation signals a locally generated carrier wave and transmitting said modulated carrier wave or modulate with said locally generated modulation signals an unmodulated carrier wave received and reflecting it back, the demodulated modulation signals received and the modulation signals transmitted being respectively directly detected at and directly supplied to the point (P) of the resonating/radiating conductor (3) without processing the signals in further modulation or demodulation units. Antenna according to Claim 1, characterized in that the resonating/radiating conductor (3) has a resonant frequency corresponding to the frequency of the carrier wave used, the insertion point (I) of the detector mixer diode (6) on the said resonating/radiating conductor (3) coinciding with the point of the resonating/radiating conductor (3) where the charateristic impedance is of the order of magnitude of or substantially identical to the impedance of the detector/mixer diode (6) at the resonant frequency w 10 corresponding to the frequency of the carrier wave. Antenna according to one or more of the preceding claims, characterised in that the detector/mixer diode (6) may have applied to it a polarisation current which constitutes a parameter for adjusting and correcting the waveform and amplitude, in particular of the modulation signals received. Antenna according to one or more of the preceding claims, characterised in that the point (P) for detecting and supplying the modulating signals, during reception and transmission, coincides with the middle point of one of the lateral edges (103) of the resonating/radiating conductor (3). Antenna according to Claim 4, characterised in that the insertion point (I) of the detector/mixer diode (6) is provided so as to coincide with the median axis (M) parallel to the side (103) of the resonating/radiating conductor (3) on which the detection and supply point (9) is provided, and at a predetermined distance (D) from one of the sides (203) of the resonating/radiating conductor transverse relative to the said median axis (M), which distance is determined experimentally and/or theoretically so as to ensure optimum impedance matching of the resonating/radiating conductor (3) at the insertion point (I) with the impedance of the detector/mixer diode (6) at the carrier wave frequency. Antenna according to Claim 5, characterised in that the distance (D) of the insertion point (I) on the median axis (M), from the side of the resonating/radiating conductor (3) is determined by the relation with the input impedance Z in of the resonating/radiating conductor (3) at the insertion point (I) at the said carrier wave frequency w 10 , defined by the following equation: Z in = Z in (L, W, D, h, K o , Z o , ετ, Q T , W 10 ) where: L, W: dimensions of the sides (103, 203) of the resonating/radiating conductor (3) D : distance of the insertion point (I) from the side (203) of the resonating/radiating conductor (3) transverse relative to the median axis (M) h : thickness of the dielectric element (2) K o : 2π/λ o with λ o : wavelength in air Z o : characteristic impedance of vacuum ετ: dielectric constant Q T : merit factor of the antenna (calculable) w 10 : resonant frequency, while the input impedance Z in corresponds to an empirical or experimental value aimed at optimising the impedance matching between detector/mixer diode (6) and resonating/radiating conductor (3), during reception and transmission/reflection, in particular of the order of magnitude of or even identical to the impedance of the detector/mixer diode (6). Antenna according to one or more of Claims 4 to 6, characterised in that the detector/mixer diode (6) is connected to the radiating antenna structure (1), on the side where the earth conductor plate (4) is located, an extension (7) being provided on the said side for connecting the resonating/radiating conductor (3) to the detector/mixer diode (6) which coincides with the zone of the insertion point (I) and is insulated electrically from the earth conductor plate (4), while the said connection extension (7) is connected electrically to the opposite resonating/radiating conductor (3) by means of a tubular conducting bush (8) coaxial with the insertion point (I) and passing through from one side to the other of the dielectric plate (2). Antenna according to one or more of the preceding claims, characterised in that, in the case of polarised carrier waves, the detector/mixer diode (6) is oriented, with the axis (C) connecting the two pins (106), in a predetermined manner with respect to the sides of the resonating/radiating conductor (3) and, in particular, in the case of plane polarised waves, the said axis (C) is oriented parallel to the side (203) of the resonating/radiating conductor (3) which is transverse relative to the median axis (M) coinciding with the insertion point (I), the said side (203) being oriented at angle of 90° with respect to the plane of polarisation of the electric field of the carrier wave. Antenna according to one or more of the preceding claims, characterised in that the detector/mixer diode (6) constitutes a demodulator preferably of amplitude-modulated carrier waves received and a frequency modulator of the carrier waves transmitted/reflected, preferably a mixer of the carrier wave transmitted/reflected with a frequency-modulated medium frequency signal. Antenna according to one or more of the preceding claims, characterised in that in the range of microwaves, in particular of the order of magnitude of 1A to 20 GHz, preferably 5 to 10 GHz, the distance (D) of the insertion point (I) is determined in correspondance with a matched input impedance Z in of the resonating/radiating conductor (3) at the insertion point (I) from 10 to 100 ohms, in particular from 40 to 50 ohms. Antenna according to Claim 10, characterised in that, for a carrier wave at 5.76 GHz, the dimensions of the resonating/radiating conductor (3) are of the order of ten millimetres or so for the sides (203) oriented transversely relative to the median axis (M) and for the sides (103) parallel to the said median axis (M), whereas the distance (D) of the insertion point (I) from one of the said transverse sides is of the order of a few millimetres.

Inventors: FRATTONI ALESSANDRO, ODDO MARIO, ZANCHET SILVIO, FRATTONI, ALESSANDRO, ODDO, MARIO, ZANCHET, SILVIO
Applicants: MARCONI SPA, MARCONI S.P.A.
Application year: 1992
Main classification: H01Q1
IPC codes: G01S13, H01Q1