Frequency-tunable and slot-fed planar antenna, and satellite-based positioning receiver comprising such an antenna

Abstract

A Frequency-tunable and slot-fed planar antenna is proposed. The antenna includes resonant patch, a first dielectric layer, a ground plane having a first slot for each linear polarization, a second dielectric layer and a transmission line having, for each first slot, an end strand extending beneath the first slot. The antenna is frequency tunable for each linear polarization through at least one variable capacitance element. The matching of the antenna varies, for each linear polarization, as a function of a bias voltage applied to the variable capacitance element(s). The antenna includes, for each linear polarization, at least one second slot extending along the first slot. The end strand of the transmission line extends between the first slot and second slots. The at least one second slot creates an additional resonance.

Claims

1. A frequency-tunable and slot-fed planar antenna comprising: a structure in which there are successively superimposed a resonant patch, a first dielectric layer, a ground plane comprising a first slot for each linear polarization, a second dielectric layer and a transmission line comprising, for each first slot, an end strand extending beneath said first slot, said antenna being frequency tunable for each linear polarization through at least one variable capacitance element connected between a radiating side of the resonant patch and the ground plane, wherein matching of said antenna varies for each linear polarization as a function of a bias voltage applied to said at least one variable capacitance element, for each linear polarization, at least one second slot extending along the first slot and having at least one dimension different from the first slot, said end strand of the transmission line extending beneath said first slot and said at least one second slot, said first slot creating a first resonance and said at least one second slot creating an additional resonance, and a frequency tunability resulting, for each linear polarization, from said first resonance for at least one first value of the bias voltage, and from said additional resonance for at least one second value of the bias voltage, for a first value of the bias voltage, the antenna covers a first sub-band resulting from the first resonance created by the first slot and, for a plurality of second successive values of the bias voltage, the antenna covers a plurality of second successive sub-bands distinct from the first sub-band, and each resulting from the additional resonance created by said at least one second slot, the first sub-band is around 2.5 GHz and the plurality of successive second sub-bands form a band ranging from 1.1 GHz to 1.6 GHz, the first value is 0V and the plurality of second successive values are between 1.5V to 3V.

2. The frequency-tunable and slot-fed planar antenna according to claim 1, wherein, for each linear polarization, said at least one second slot and said first slot are of the same shape.

3. The frequency-tunable and slot-fed planar antenna according to claim 2, wherein, for each linear polarization, said at least one second slot and said first slot possess parallel longitudinal axes.

4. The frequency-tunable and slot-fed planar antenna according to claim 1, wherein the resonant patch is square shaped with a side length l.sub.p equal to 55 mm 1 mm, and, for each linear polarization: said first slot is rectangular with a length l.sub.3 equal to a 40 mm 1 mm and a width w.sub.3 equal to 1 mm 0.1 mm; and said at least one second slot is rectangular, with a length l.sub.2 equal to 30 mm 1 mm and a width w.sub.2 equal to 2 mm 0.1 mm.

5. The frequency-tunable and slot-fed planar antenna according to claim 1, wherein the antenna works according to a single linear polarization.

6. The frequency-tunable and slot-fed planar antenna according to claim 1, wherein the antenna works according to first and second orthogonal linear polarizations, the combination of which gives a circular polarization, and the first slot and said at least one second slot for the first linear polarization are orthogonal respectively to the first slot and said at least one second slot for the second linear polarization.

7. A satellite positioning receiver enabling reception and processing of signals coming from different satellite positioning systems, comprising: a frequency-tunable, over at least two frequency bands, and slot-fed planar antenna comprising: a structure in which there are successively superimposed a resonant patch, a first dielectric layer, a ground plane comprising a first slot for each linear polarization, a second dielectric layer and a transmission line comprising, for each first slot, an end strand extending beneath said first slot, said antenna being frequency tunable for each linear polarization through at least one variable capacitance element connected between a radiating side of the resonant patch and the ground plane, wherein matching of said antenna varies for each linear polarization as a function of a bias voltage applied to said at least one variable capacitance element, for each linear polarization, at least one second slot extending along the first slot and having at least one dimension different from the first slot, said end strand of the transmission line extending beneath said first slot and said at least one second slot, said first slot creating a first resonance and said at least one second slot creating an additional resonance, and a frequency tunability resulting, for each linear polarization, from said first resonance for at least one first value of the bias voltage, and from said additional resonance for at least one second value of the bias voltage, for a first value of the bias voltage, the antenna covers a first sub-band resulting from the first resonance created by the first slot and, for a plurality of second successive values of the bias voltage, the antenna covers a plurality of second successive sub-bands distinct from the first sub-band, and each resulting from the additional resonance created by said at least one second slot, the first sub-band is around 2.5 GHz and the plurality of successive second sub-bands form a band ranging from 1.1 GHz to 1.6 GHz, the first value is 0V and the plurality of second successive values are between 1.5V to 3V.

Description

5. LIST OF FIGURES

(1) Other features and advantages of the invention shall appear from the following description given by way of an indicative and non-exhaustive example, and from the appended drawings of which:

(2) FIGS. 1A, 1B, 2A and 2B, already described with reference to the prior art, illustrate the structure and performance of an example of a slot-fed and frequency-tunable antenna according to the prior art;

(3) FIGS. 3A and 3B are top views respectively presenting the structure and dimensions of an antenna according to a first particular embodiment of the invention, working according to a single linear polarization;

(4) FIGS. 4A and 4B are views in section presenting respectively the structure and the dimensions of an antenna according to said first particular embodiment of the invention, working according to a single linear polarization;

(5) FIG. 5 is a top view presenting the structure of an antenna according to a second particular embodiment of the invention, working according to a circular polarization;

(6) FIG. 6 illustrates the performance characteristics of a slot-fed and frequency-tunable planar antenna in one particular implementation of said third particular embodiment of the invention;

(7) FIG. 7 illustrates various possible shapes for the slots of the antenna according to the invention;

(8) FIG. 8 illustrates various possible shapes for the resonant patch of the antennas according to the invention; and

(9) FIGS. 9 to 13 present the structure of an antenna according to a third particular embodiment of the invention, working according to a circular polarization.

6. DETAILED DESCRIPTION

(10) In all the figures of the present document, the identical elements are designated by a same numerical reference.

(11) Referring now to FIGS. 3A, 3B, 4A and 4B, we present an antenna 30 according to a first particular embodiment of the invention, working according to a single linear polarization.

(12) Purely for the sake of simplification, the top views (FIGS. 3A and 3B) and the views in section (4A and 4B) are partial views. These figures do not show the variable capacitance elements (for example varicap diodes) which make the antenna 30 tunable over a wide band of frequencies. As in the prior art technique illustrated in FIG. 1A, the antenna 30 comprises for example, a variable capacitance element (varicap diode) connected between each radiating side of the resonant patch and the ground plane.

(13) The antenna 30 possesses a structure in which the following are super-imposed in succession: a resonant patch 31; a first dielectric layer 32 (for example air or a dielectric substrate); a ground plane 33, comprising first and second slots 34A, 34B (working according to a single linear polarization in this example); a second dialectic layer 35 (for example air or a dielectric substrate); and a transmission line 36 comprising an end strand extending beneath the two slots 34a, 35b.

(14) In this example, the resonant patch 31 is square shaped. However, it is possible to use different shapes of patches and especially but not exclusively the shapes illustrated in FIG. 8 ((a) square shape (b) rectangular (c) dipole (d) circular (e) elliptical (f) triangular (g) disk sector (h) circular ring (i) ring sector).

(15) The second slot 3b extends along the first slot 34a. These slots differ in at least one dimension. In this example, the two slots 34a, 34b have the same shape, namely rectangular, and have parallel longitudinal axes. It is however possible to use other shapes of slot and especially but not exclusively the shapes illustrated in FIG. 7 ((a) (H) dog bone (c) bowtie (d) hourglass).

(16) As indicated in FIGS. 3B and 4B, the antenna is defined by the following dimensions: for the square-shaped resonant patch 31, the length l.sub.p of the sides; for the first dielectric layer 32, thickness h.sub.2 and permittivity for the first layer of dielectric 32, thickness h.sub.2 and permittivity and .sub.r2; for the square-shaped ground plane 33, the length l.sub.0 of the sides; for the first rectangular slot 34a the length l.sub.3 and the width w.sub.3, as well as the abscissa value x.sub.3 (corresponding to the point obtained by orthogonal projection along the longitudinal axis of the first slot) in a referential system centered on the lower left-hand corner of the ground plane 33; for the second rectangular slot 34b the length l.sub.2 and the width w.sub.2, as well as the abscissa value x.sub.2 (corresponding to the point obtained by orthogonal projection along the longitudinal axis of the second slot) in the above-mentioned reference mark; for the second dielectric layer 35, thickness h.sub.1 and permittivity .sub.r1; for the transmission line 36, the length l.sub.1, the width w.sub.1, the ordinate value y.sub.1 in the above-mentioned referential system.

(17) In one particular embodiment, the antenna 30 possesses the following dimensions:

(18) TABLE-US-00001 l.sub.0 = 105 m**m l.sub.p = 55 mm h.sub.1 = 0.8 mm h.sub.2 = 6 mm 1 mm 1 mm 0.01 mm 0.5 mm l.sub.2 = 30 mm w.sub.2 = 2 mm l.sub.3 = 40 mm w.sub.3 = 1 mm 1 mm 0.1 mm 1 mm 0.1 mm w.sub.1 = 2 mm x.sub.2 = 34.5 mm x.sub.3 = 26 mm l.sub.1 = 60 mm 0.5 mm 0.5 mm 0.5 mm 1 mm y.sub.1 = 52.5 mm 1 mm

(19) Referring now to FIG. 5, we present an antenna 50 according to a second particular embodiment of the invention, working according to a circular polarization, resulting from the combination of two orthogonal linear polarizations.

(20) The antenna 50 comprises all the elements of the antenna 30 of FIGS. 3A, 3B, 4A and 4B (the transmission line 36 and the slots 34a, 34b being used for one of the two orthogonal linear polarizations).

(21) The antenna 50 furthermore comprises another transmission line 56 and two other slots 54a, 54b (orthogonal to the slots 34a, 34b) which are used for the other of the two orthogonal linear polarizations.

(22) Referring now to FIGS. 9 to 13, we present an antenna 90 according to a third particular embodiment of the invention, working according to a circular polarization.

(23) As illustrated in FIGS. 9 and 10 (a three-quarter view and a view in section respectively), the antenna 90 has a structure in which the following are superimposed respectively: a first dialectic substrate 91 (for example NELTEC NX9300) on the lower face of which there is printed a resonant patch 92 (cf. FIG. 11), a second dielectric substrate 93 (for example NELTEC NX9300) on the upper face of which there is printed a ground plane 94 comprising two pairs of slots (95a, 95b) and (96a, 96b) (cf. FIG. 12) and on the lower face of which there is printed a transmission line 97 (cf FIG. 13); a metal plate 98 forming a reflector plane (second ground plane).

(24) The antenna 90 comprises a layer of air 99 (forming a dielectric layer) between the resonant patch 92 and the ground plane 94. To this end, the first and second dielectric substrates 91, 93 are separated by first metal spacers 100 (for example of 6 mm height).

(25) The second dielectric substrate 93 and the metal plate 98 are separated by second metal spacers 101.

(26) As illustrated in FIG. 11 (which is a view of the lower face of the first dielectric substrate 91), the antennas also comprise varicap diodes 102 (or any other variable capacitance element) each connected between a radiating side of the resonant patch 92 (in the middle of each ridge of the resonant patch 92) and the ground plane 93 (via the first metal spacers 100). The varicap diodes are powered by means of the resonant patch 92.

(27) As illustrated in FIG. 12 (which is a view of the upper face of the second dielectric substrate 93), the two slots 95a, 95b have the same shape, namely a rectangular shape, and possess parallel longitudinal axes. Similarly, the two slots 96a, 96b have the same shape, namely a rectangular shape, and possess parallel longitudinal axes. The slots 95a, 95b are orthogonal to the slots 96a, 96b.

(28) As illustrated in FIG. 13 (which is a view of the lower face of the second dielectric substrate 93), the transmission line 97 comprises a first end strand 97a extending beneath the pair of slots (95a, 95b) and a second end strand 97b extending beneath the pair of slots (96a, 96b). The antenna comprises a coupler 105 to combine the two orthogonal polarizations (in phase quadrature). The bias voltage of the varicap diodes 102 is for example sent by a port 103 and by the transmission line 97 (used also for the RF signals received by the antenna; in one variant, the bias voltage arrives on a separate port and is transmitted by a separate line). Then, it is conveyed to the resonant patch 92 via a polarization circuit 104 (DC block) so as not to disturb the HF signals. The first metal spacers 100 provide for a link between the ground of the diodes and the ground of the slots.

(29) In one particular embodiment, the antenna 90 possesses the following dimensions (repeating the notations Oven further above for the antenna 30):

(30) TABLE-US-00002 l.sub.0 = 105 mm l.sub.p = 55 mm h.sub.1 = 0.8 mm h.sub.2 = 6 mm 1 mm 1 mm 0.01 mm 0.5 mm l.sub.2 = 30 mm w.sub.2 = 2 mm l.sub.3 = 40 mm w.sub.3 = 1 mm 1 mm 0.1 mm 1 mm 0.1 mm w.sub.1 = 2 mm x.sub.2 = 34.5 mm x.sub.3 = 26 mm l.sub.1 = 30 mm 0.5 mm 0.5 mm 0.5 mm 1 mm

(31) FIG. 6 illustrates the performance characteristics of the slot-fed and frequency-tunable planar antenna in a particular implementation of the third particular embodiment of the invention (that of FIGS. 9 to 13).

(32) FIG. 6 presents five curves illustrating the variation of the reflection coefficient S.sub.11 as a function of the frequency for different values of the bias voltage of the varicap diodes. Each curve corresponds to a distinct resonance and is obtained for one of the values of the bias voltage (1V, 1.7V, 2V, 3V and 0V). The matching of the antenna varies according to the bias voltages of the diode. The frequency of operation of the antenna varies between 1.1 GHz (for a bias voltage of 1.5V) and 2.5 GHz (for a bias voltage of 0V).

(33) This antenna is therefore tunable over a wide band of frequencies (the GNSS band) with a low bias voltage, varying from 0V to 3V, which is compatible with the voltages available on portable devices. The consumption is extremely low since it relates for example to reverse-polarized varicap diodes.

(34) The antennas are adapted to the reception of the signals from the different GNSS constellations in a band ranging from 1164 MHz to 2506 MHz (more than one octave), with a circular polarization and a directional radiation pattern. The solution therefore enables a use of a single antenna for the entire GNSS band which brings together all the satellite navigation systems, even the 2.5 GHz system and does so selectively.

(35) The invention proposes a bandwidth of about 50 MHz (narrow band) tunable on a wider range of frequencies. The invention is therefore distinguished from rival approaches by: a coverage of the entire band dedicated to GNSS, even the 2.5 GHz band (IRNSS signals); very low consumption with a bias voltage that does not exceed 3V; selection of reception from a constellation by filtering out the other bands of the other constellations efficiently and naturally.

(36) The dimensions of the two slots of a same pair (95a, 95b) or (96a, 96b) optimize the resonance frequency of the antenna according to the bias voltage. The originality here is the use of (at least) two slots to create two resonance values in the GNSS frequency band. These two resonance values cover all the frequency bands used for satellite localization applications.

(37) Thus, in the example of FIG. 6, the antenna operates on the principle of covering a band around a 2.5 GHz with a bias voltage of 0V, and then a band of 1.1 GHz to 1.6 GHz with a bias voltage that varies between 1.5V and 3V. Operation in the 2.5 GHz band is provided by the slots 95b, 96b. The slots 95a, 96a provide for operation in the 1.1 to 1.6 GHz band.

(38) In the GNSS frequency band (including the frequencies around 2.5 GHz), the antenna enables the selection of a sub-band (i.e. the reception band of a constellation) by efficiently and naturally filtering out the other sub-bands (i.e. the reception bands of the other constellations). In this way, the antenna plays the role of a natural filter for the unused frequency bands.

(39) The present invention also relates to a satellite navigation receiver (GNSS receiver) enabling the reception and processing of the signals coming from the different satellite positioning systems and comprising or cooperating with an antenna according to this technique described and illustrated here above with different embodiments.

(40) It is clear that many other embodiments of the invention can be envisaged. It is possible especially to envisage frequency bands other than the GNSS band, such as for example: the GSM 900 band (the GSM 900 band uses the 880-915 MHz band for sending voice and data from a cell phone and the 925-960 MHz band for receiving information coming from the network); the mobile telephony band (LTE+GSM+UMTS) which covers the 1.71-2.17 GHz band; the locating or transfer of data by WIFI at 2.4 GHz; the LTE band (4G) which covers the 2.5-2.7 GHz band for high bit-rate mobile telephony; discreet antennas for vehicles in the UHF band (the ultra-high frequency band (UHF) band is the band of the radio-electric spectrum ranging from 300 MHz to 3,000 MHz).

(41) An exemplary embodiment of the present disclosure aims at overcoming the different drawbacks of the prior art.

(42) An exemplary embodiment provides a slot-fed planar antenna that is frequency tunable on a wide band of frequencies while at the same time, requiring bias voltage that is lower than in present-day solutions, preferably below 3V.

(43) An exemplary embodiment provides an antenna of this kind that covers the entire GNSS frequency band (including the frequencies around 2.5 GHz) with a small bias voltage compatible with the voltages available on portable devices.

(44) An exemplary embodiment provides an antenna of this kind which, in the GNSS frequency band, enables the selection of the reception band of one constellation by efficiently and naturally filtering the reception bands of the other constellations.

(45) An exemplary embodiment provides an antenna of this kind that costs little and is compact.

(46) Although the present disclosure has been described with reference to one or more examples, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the disclosure and/or the appended claims.