STEERABLE ANTENNA AND METHOD FOR HEATING AND/OR TEMPERING OF A STEERABLE ANTENNA

Abstract

A steerable antenna having a plurality of radiating elements and a plurality of modifier elements configured for shifting phase and/or adjusting amplitude of a signal to be emitted by the radiating elements is disclosed. Each of the radiating elements is coupled to one of the modifier elements, wherein the modifier elements each comprise a liquid crystalline medium and wherein the modifier elements are configured such that the adjustment of the phase and/or amplitude is dependent on a state of the liquid crystalline medium. The steerable antenna further comprises a signal generator connected to the modifier elements and configured for generating a signal suited for dielectric heating of the liquid crystalline media of the modifier elements. Further aspects relate to a method for heating and/or controlling the temperature of the liquid crystalline medium of such a steerable antenna.

Claims

1. Steerable antenna (10) comprising a plurality of radiating elements (12) and a plurality of modifier elements (14) configured for shifting phase and/or adjusting amplitude of a signal to be emitted by the radiating elements (12), wherein one or more of the radiating elements (12) is coupled to one or more of the modifier elements (14), wherein the modifier elements (14) each comprise a liquid crystalline medium and wherein the modifier elements (14) are configured such that the adjustment of the phase and/or amplitude is dependent on a state of the liquid crystalline medium, characterized in that the steerable antenna (10) further comprises a signal generator (20) connected to the modifier elements (14) and configured for generating a signal suited for dielectric heating of the liquid crystalline media of the modifier elements (14).

2. Steerable antenna (10) according to claim 1, wherein the radiating elements (12) are arranged in form of a grid or in form of concentric rings.

3. Steerable antenna (10) according to claim 1, wherein the modifier elements (14) are configured as phase shifters.

4. Steerable antenna (10) according to claim 3, wherein the antenna additionally comprises modifier elements (14) configured as variable attenuators.

5. Steerable antenna (10) according to claim 3, wherein the phase shifters have a waveguide (30).

6. Steerable antenna (10) according to claim 5, wherein the waveguide (30) is configured as microstrip line or coplanar waveguide arranged adjacent to a liquid crystal layer or as hollow waveguide at least partially filled with liquid crystalline medium.

7. Steerable antenna (10) according to claim 1, wherein the steerable antenna (10) further comprises a common waveguide with a plurality of slots, wherein the modifier elements (14) are arranged between the common waveguide and the slots.

8. Steerable antenna (10) according to claim 1, wherein each of the modifier elements (14) has at least two electrodes, wherein a first electrode is configured for applying an electric field for adjusting the orientation state of the liquid crystalline medium and a second electrode is connected to the signal generator (20) and configured to apply an electric field for dielectric heating of the liquid crystalline medium.

9. Steerable antenna (10) according to claim 1, wherein each of the modifier elements (14) has at least one electrode (144), which is configured for applying both an electric field for adjusting the orientation state of the liquid crystalline medium and is further connected to the signal generator (20) and configured to apply an electric field for dielectric heating of the liquid crystalline medium.

10. Steerable antenna (10) according to claim 1, wherein the steerable antenna (10) further comprises a temperature sensor (40) configured to measure a temperature of the liquid crystalline medium of the modifier elements (14).

11. Steerable antenna (10) according to claim 1, wherein a control unit (50) is provided which is configured to adjust the frequency of the signal suited for dielectric heating in dependence of the temperature of the liquid crystalline medium of the modifier elements (14).

12. Method of heating and/or tempering of a steerable antenna (10) comprising a plurality of radiating elements (12) and a plurality of modifier elements (14) configured for shifting phase and/or adjusting amplitude of an antenna signal to be emitted by the radiating elements (12), wherein one or more of the radiating elements (12) is coupled to one or more of the modifier elements (14), wherein the modifier elements (14) each comprise a liquid crystalline medium and wherein the modifier elements (14) are configured such that the adjustment of the phase and/or amplitude is dependent on a state of the liquid crystalline medium, characterized in that an alternating electric field having a frequency suited for dielectric heating of the liquid crystalline medium is applied to the liquid crystalline medium of the modifier elements (14).

13. The method of claim 12, wherein a temperature of the liquid crystalline medium is measured and the frequency of the alternating electric field is adjusted in dependence of the measured temperature.

14. The method of claim 13, wherein the frequency is determined from the measured temperature by means of a look up table.

15. The method of claim 12, wherein the frequency of the alternating electric field is adjusted in dependence of the power input of the dielectric heating of the antenna (10).

16. The method of claim 15, wherein the frequency is determined by i) sweeping said frequency through a predetermined frequency range while monitoring the power input of the antenna (10), ii) determining the frequency from where the power input has a maximum.

17. The method of claim 16, the method further comprising the steps of i) measuring the power input of the dielectric heating of the antenna, ii) determining whether or not a change has occurred in said power input, and if so, iii) varying the frequency of the heating signal in response to said change so that the change of the power input with the frequency is adjusted to maintain a predetermined value.

18. The method of claim 13, wherein the temperature is measured via a temperature sensor (40) arranged within the liquid crystalline medium or in proximity of the liquid crystalline medium.

19. The method of claim 13, wherein the temperature is determined via measuring the capacitance of the liquid crystalline medium.

20. The method of claim 19, wherein a look up table is used for determining temperature from the measured capacitance.

21. The method of claim 12, wherein heating of the liquid crystalline medium is performed for temperatures of the liquid crystalline medium at or below 40° C., preferably in the range of from -40° C. to 40° C.

22. The method of claim 12, wherein temperature control is performed and the temperature of the liquid crystalline medium is controlled to a predetermined temperature set-point.

23. The method of claim 12, wherein the steerable antenna (10) further comprises a signal generator (20) connected to the modifier elements (14) and configured for generating a signal suited for dielectric heating of the liquid crystaline media of the modifier elements (14).

24. The method of claim 12, wherein heating of the liquid crystalline medium is performed for temperatures of the liquid crystalline medium in the range of from -40° C. to 40° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0112] The drawings show:

[0113] FIG. 1 A schematic block diagram of a steerable antenna having four radiating elements,

[0114] FIG. 2 a schematic diagram of a modifier element configured as phase shifter,

[0115] FIG. 3 temperature and frequency dependence of the real part of the permittivity for an exemplary liquid crystalline medium, and

[0116] FIG. 4a temperature and frequency dependence of the loss tangent perpendicular to the director of the liquid crystal, for the exemplary liquid crystalline medium.

[0117] FIG. 4b temperature and frequency dependence of the loss tangent parallel to the director of the liquid crystal, for the exemplary liquid crystalline medium.

[0118] The figures are only a schematic, non-limiting representation of the invention.

[0119] In FIG. 1, a schematic block diagram of a steerable antenna 10 having four radiating elements 12 is shown. The steerable antenna 10 has an antenna signal input 16 for supplying an antenna signal which is to be emitted by the steerable antenna 10. Further, the steerable antenna 10 comprises a control unit 50.

[0120] The steerable antenna 10 of FIG. 1 is configured as a phased array antenna, wherein each of the radiating elements 12 is connected via a modifier element 14 configured as phase shifter and a distribution network 18 to the antenna signal input 16. The radiating elements 12 are in the example of FIG. 1 arranged in a two by two array.

[0121] An antenna signal which is fed to the antenna signal input 16 is distributed by the distribution network 18 to the phase shifters which are connected to the radiating elements 12. If all phase shifters are configured to produce an in-phase output, the phase front of the radiated signal is aligned parallel to an antenna surface, therefore directing an antenna beam perpendicular to the antenna surface. When introducing a specific incremental phase shift, the phase front of the radiated fields is tilted and therefore the antenna beam is also tilted towards the desired direction.

[0122] The modifier elements 14 which are configured as phase shifters each comprise a liquid crystalline medium and the phase shift is dependent on a state of the liquid crystalline medium. The state of the liquid crystalline medium is controlled by means of an electric field, which is applied using electrodes arranged in the modifier element 14. The electric field is dependent on a control signal which is applied to said electrodes.

[0123] In the example embodiment shown in FIG. 1, the control unit 50 may be used to control the phase shifts required for steering the antenna beam. The control unit 50 is connected to a control signal generator 22 which is connected to each of the modifier elements 14 which are configured as phase shifters.

[0124] As the physical properties of the liquid crystalline medium are temperature dependent, it is necessary to ensure that at least the liquid crystalline medium of the modifier elements 14 of the steerable antenna 10 has a temperature within an operating temperature range. This is of particular importance for low temperature environments with a temperature below 0° C. In order to heat the liquid crystalline layer of the modifier elements 14, the steerable antenna 10 further comprises a heating signal generator 20 which is also connected to the modifier elements 14. The heating signal generator 20 is configured to provide a heating signal which is suitable for generating an electric field for dielectric heating of the liquid crystalline layer. Accordingly, the modifier elements 14 comprise electrodes which may be used to generate an electric field within the liquid crystalline medium when the heating signal is applied to said electrodes.

[0125] In the embodiment shown in FIG. 1, the heating signal generator 20 and the control signal generator 22 are configured as a common signal generator which generates a combined signal. The combined signal is then applied to a pair of electrodes arranged next to the liquid crystalline medium in each of the modifier elements 14.

[0126] In the embodiment shown in FIG. 1, the control unit 50 is further configured to control the temperature of the liquid crystalline medium of the modifier elements 14. Accordingly, the control unit 50 is connected to the heating signal generator 20 and is also connected to a temperature sensor 40 arranged in proximity to the liquid crystalline medium in one of the modifier elements 14. In another embodiment it is possible to arrange temperature sensors 40 for each of the modifier elements 14.

[0127] The control unit 50 may, for example, comprise a temperature controller such as a proportional-integral-derivative (PID) controller, for controlling the temperature of the liquid crystalline medium of the modifier elements 14 to a desired temperature setpoint using the feedback provided by the temperature sensor 40.

[0128] In order to select the optimal frequency for the heating signal, the control unit 50 may comprise a memory unit having a stored look up table. The entries of the look up table provide the correct frequency to be used for dielectric heating for the respective temperature of the liquid crystalline medium.

[0129] FIG. 2 shows a modifier element 14 configured as phase shifter in a schematic diagram.

[0130] The phase shifter comprises a microstrip line configured as a coplanar waveguide 30. The coplanar waveguide 30 comprises a signal line 142 arranged on a first substrate 141 which is connected to the distribution network 18 and a respective one of the radiating elements 12, see FIG. 1.

[0131] The signal line 142 is arranged on the first substrate 141 together with a pair of ground lines 146 arranged on either side of the signal line 142. For forming of a cavity for enclosing the liquid crystalline medium in form of a liquid crystal layer 143, a second substrate 145 is arranged facing the side of the first substrate 141 carrying the signal line 142. The gap width and thus the thickness of the liquid crystal layer 143 is typically less than 10 .Math.m .

[0132] In the embodiment shown in FIG. 2, a top electrode 144 is arranged on the surface of the second substrate 145 facing towards the liquid crystal layer 143. For application of an electric field for controlling the state of the liquid crystalline medium of the liquid crystal layer 143, the signal line 142 may be used as first electrode. The top electrode 144 and/or the ground lines 146 may be used as second electrode for applying the electric field for controlling the state of the liquid crystalline medium as well as for applying the electric field for heating of the liquid crystalline medium.

[0133] The media N1 and N2 have the following compositions and physical properties

TABLE-US-00001 Example N1 [00057] 6% [00058] 12% [00059] 23% [00060] 25% [00061] 14% [00062] 10% [00063] 10%

TABLE-US-00002 Clearing Temperature [°C]: 157 Δε [1 kHz, 20° C.]: 13.5 ε.sub.ll [1 kHz, 20° C.]: 17.2 ε.sub.⊥ [1 kHz, 20° C.]: 3.7 K.sub.1 [pN, 20° C.]: 15.4 K.sub.3 [pN, 20° C.]: 26.0 V.sub.0 [V, 20° C.]: 1.12 τ [20° C., 19 GHz]: 0.33 ε.sub.r,|| [20° C., 19 GHz]: 3.62 ε.sub.r,⊥ [20° C., 19 GHz]: 2.42 tan δ.sub.ε .sub.r,|| [20° C., 19 GHz]: 0.0053 tan δ.sub.ε .sub.r,⊥ [20° C., 19 GHz]: 0.0086

TABLE-US-00003 Example N2 [00064] 10% [00065] 8% [00066] 18% [00067] 7% [00068] 9% [00069] 6% [00070] 22% [00071] 20%

TABLE-US-00004 Clearing Temperature [°C]: 157 Δε [1 kHz, 20° C.]: 13.5 ε.sub.|| [1 kHz, 20° C.]: 17.2 ε⊥ [1 kHz, 20° C.]: 3.7 K.sub.1 [pN, 20° C.]: 15.4 K.sub.3 [pN, 20° C.]: 26.0 V.sub.0 [V, 20° C.]: 1.12

[0134] FIG. 3 shows the real part of the permittivity ε′ vs. temperature for an example liquid crystalline medium N1 for different frequencies ranging from 100 Hz to 100 kHz.

[0135] The first curves 201 depict the permittivity parallel to the molecular axis. The second curve 202 shows the permittivity perpendicular to the molecular axis for a frequency of 100 Hz. Only the second curve 202 for 100 Hz is shown as an example as the curves for the further frequencies up to 100 kHz differ only slightly. The third curves 203 show the difference Δε between the permittivity parallel and perpendicular to the molecular axis.

[0136] As can be seen from the diagram of FIG. 3, a maximum of the permittivity shifts with temperature.

[0137] FIG. 4a shows the temperature and frequency dependence of the loss tangent perpendicular to the director for the liquid crystal mixture of example N2. For example, at 0° C. it is advantageous to apply a heating signal of 1 Hz for vertical orientation of the liquid crystal because the highest value of the loss tangent is observed here (tan δ = 3.61). Upon heating to 20° C. the maximum shifts to 1.58 Hz (tan δ = 5.67).

[0138] FIG. 4b shows the temperature and frequency dependence of the loss tangent parallel to the director for the liquid crystal medium N2. For example, at -30° C. the highest value of the loss tangent for parallel orientation is observed at a frequency of 631 Hz (tan δ = 0.685) which is the optimum frequency for dielectric heating in this case. Upon heating to e.g. -10° C., the optimum frequency, i.e. the maximum loss shifts to 10 kHz (tan δ = 0.717).

LIST OF REFERENCE NUMERALS

[0139] 10 steerable antenna [0140] 12 radiating element [0141] 14 modifier element [0142] 16 antenna signal input [0143] 18 distribution network [0144] 20 heating signal generator [0145] 22 control signal generator [0146] 30 (coplanar) waveguide [0147] 40 temperature sensor [0148] 50 control unit [0149] 141 first substrate [0150] 142 signal line [0151] 143 liquid crystal layer [0152] 144 top electrode [0153] 145 second substrate [0154] 146 ground line [0155] 201 first curves [0156] 202 second curves [0157] 203 third curves