ENCAPSULABLE ANTENNA UNIT

Abstract

An antenna unit for transmitting and receiving high frequency signals includes a substrate that is optionally encapsulable with a potting compound having a defined dielectric value. Arranged on the substrate are two planar antennas each tuned for the high frequency signal. The planar antennas are designed such that the values of the real parts of the impedances of the planar antennas differ by the square root of the dielectric value of the potting compound. By providing two antennas, wherein one thereof is impedance-matched to a possible potting compound encapsulation, the antenna unit is able to function independently of a possible potting compound encapsulation. Electronic modules which comprise the antenna unit for wireless communication can be implemented according to the platform principle in devices that require a potting compound encapsulation and also in devices that are not encapsulated.

Claims

1-14. (canceled)

15. An antenna unit for transmitting and receiving high frequency signals having a defined frequency, comprising: a substrate encapsulable with a potting compound having a defined dielectric value; a signal gate via which the high frequency signal can be coupled in and out; a first planar antenna connected to the signal gate and tuned to the frequency of the high frequency signal; a second planar antenna connected to the signal gate and tuned to the frequency of the high frequency signal; wherein the signal gate, the first planar antenna, and the second planar antenna are arranged on the substrate, and wherein the planar antennas are so designed that a real part of an impedance of the first planar antenna differs from a real part of an impedance of the second planar antenna by a defined factor corresponding to a square root of the dielectric value of the potting compound.

16. The antenna unit as claimed in claim 15, further comprising: a signal splitter arranged between the signal gate and the planar antennas and designed to supply the high frequency signal to the first planar antenna at a wavelength corresponding to the frequency of the high frequency signal at the dielectric value of the potting compound.

17. The antenna unit as claimed in claim 16, wherein the signal splitter is designed to supply the high frequency signal to the second planar antenna at that wavelength corresponding to the frequency of the high frequency signal at the dielectric value of air or vacuum.

18. The antenna unit as claimed in claim 17, wherein the signal splitter includes: a first signal path arranged between the signal gate and the first planar antenna and having a defined first path length corresponding to half the wavelength or to a whole numbered multiple of half the wavelength of the frequency of the high frequency signal at the dielectric value of the potting compound; and a second signal path arranged in parallel with the first signal path between the signal gate and the second planar antenna and having a defined second path length corresponding to half the wavelength or to a whole numbered multiple of half the wavelength of the frequency of the high frequency signal at the dielectric value of air or vacuum.

19. The antenna unit as claimed in claim 18, wherein the signal splitter includes a defined resistance arranged between the first planar antenna and the second planar antenna, wherein the magnitude of the resistance corresponds to an input resistance of the antenna unit at the signal gate.

20. The antenna unit as claimed in claim 18, wherein the first signal path and the second signal path each include at least one defined reflection site for the high frequency signals.

21. The antenna unit as claimed in claim 18, wherein the first signal path includes two reflection sites, and wherein a first path length between the two reflection sites in the first signal path corresponds to half the wavelength or to a whole numbered multiple of half the wavelength of the frequency of the high frequency signal at the dielectric value of the potting compound, and wherein the second signal path includes two reflection sites, and wherein a second path length between the two reflection sites in the second signal path corresponds to half the wavelength or to a whole numbered multiple of half the wavelength of the frequency of the high frequency signal at the dielectric value of air or vacuum.

22. The antenna unit as claimed in claim 20, wherein the at least one reflection site is embodied as a right angled extension or as a gap.

23. The antenna unit as claimed in claim 15, wherein the first planar antenna and/or the second planar antenna is/are designed as a patch antenna or as patch antennas.

24. The antenna unit as claimed in claim 15, wherein the planar antennas are designed as linear antennas, wherein the first planar antenna is dimensioned with a length corresponding to half the wavelength or to a whole numbered multiple of half the wavelength of the frequency of the high frequency signal at the dielectric value of the potting compound, and wherein the second planar antenna is dimensioned with a length corresponding to half the wavelength or to a whole numbered multiple of half the wavelength of the frequency of the high frequency signal at the dielectric value of air or vacuum.

25. The antenna unit as claimed in claim 24, wherein an extension or extensions of the first planar antenna and/or the second planar antenna are/is connected via a right angled extension with a ground connection, wherein the right angled extension of the first planar antenna is dimensioned with a length corresponding to half the wavelength or to a whole numbered multiple of half the wavelength of the frequency of the high frequency signal at the dielectric value of the potting compound, and/or wherein the right angled extension of the second planar antenna is dimensioned with a length corresponding to half the wavelength or to a whole numbered multiple of half the wavelength of the frequency of the high frequency signal at the dielectric value of air or vacuum.

26. The antenna unit as claimed in claim 15, wherein the substrate is embodied as a circuit board, and wherein the signal gate, the planar antennas, and/or signal splitter are implemented as a conductive trace structure.

27. The antenna unit as claimed in claim 15, wherein the planar antennas are adapted such that the high frequency signal has a frequency in the range between 300 MHz and 6 GHz.

28. A process automation field device, comprising: an antenna unit for transmitting and receiving high frequency signals having a defined frequency, including: a substrate encapsulable with a potting compound having a defined dielectric value; a signal gate via which the high frequency signal can be coupled in and out; a first planar antenna connected to the signal gate and tuned to the frequency of the high frequency signal; a second planar antenna connected to the signal gate and tuned to the frequency of the high frequency signal; wherein the signal gate, the first planar antenna, and the second planar antenna are arranged on the substrate, and wherein the planar antennas are so designed that a real part of an impedance of the first planar antenna differs from a real part of an impedance of the second planar antenna by a defined factor corresponding to a square root of the dielectric value of the potting compound.

Description

[0026] The invention will now be explained in greater detail based on the appended drawing, the figures of which show as follows:

[0027] FIG. 1 an equivalent circuit diagram of the antenna unit of the invention, and

[0028] FIG. 2 a plan view of a possible embodiment of the antenna unit.

[0029] For providing a general understanding of the invention, FIG. 1 shows an equivalent circuit diagram of the antenna unit 1. As is shown, antenna unit 1 includes as essential electrical components two planar antennas 13, 14, which in the case of the shown embodiment are connected via a signal splitter 15 with a signal gate 12. For transmitting and for receiving high frequency signals SHE, which are formed, for example, according to the Bluetooth standard, a correspondingly designed signal production unit/ signal evaluation unit (not shown), is connected to the signal gate 12.

[0030] The two planar antennas 13, 14 are adapted to operate at the frequency f of the high frequency signal SHE, thus, in the case of Bluetooth communication, at a frequency between 2 GHz and 3 GHz. Depending on the type of planar antennas 13, 14, for example, linear antennas or patch antennas, the impedance depends on the particular geometric dimensions of the planar antennas 13, 14. According to the invention, the planar antennas 13, 14 are, moreover, however, so designed that the real part of the impedance of the first planar antenna 13 differs by a defined factor √DK.sub.pc from the real part of the impedance of the second planar antenna 14. In such case, the factor √DK.sub.pc corresponds according to the invention to the square root of the dielectric value DK.sub.pc of the chosen potting compound. In such case, the dielectric value of a thermoplastic or thermosetting potting compound lies, as a rule, in a range between 2 F*m.sup.−1 and 3 F*m.sup.−1, in rare cases also up to 15 F*m.sup.−1.

[0031] Thus, the two planar antennas 13, 14 are, indeed, designed for the frequency f of the high frequency signal S.sub.HF. The propagation velocity c.sub.pc, c.sub.0 of the high frequency signal S.sub.HF in the planar antennas 13, 14 depends, however, on the medium that surrounds the planar antennas 13, 14 in the radiation direction, thus, within the scope of the invention either a potting compound or air, or vacuum. Accordingly, there results in the planar antennas 13, 14, in spite of equal frequency f of the high frequency signal S.sub.HF, depending on whether a potting compound covers the antenna unit 1 or not, a wavelength λ.sub.pc,0 dependent on the potting compound, based on the formula

c.sub.pc,0=λ.sub.pc,0*f.

[0032] Due to the impedance difference of the invention between the planar antennas 13, 14, in the case of present potting compound, the high frequency signal S.sub.HF is accordingly transmitted predominantly by that planar antenna 13, 14, which has, with reference to the real part, the higher impedance, i.e. is best matched to the output-impedance of the unit connected to the signal gate. In the case of potting compound free design of the antenna unit 1, i.e. of the module, the behavior is accordingly in an exactly opposite manner: In such case, the high frequency signal S.sub.HF is transmitted predominantly by that planar antenna 13, 14, which has the lower impedance in the real part. In this way, the high frequency signal S.sub.HF is thus transmitted, and received, depending on the possibly present potting compound, virtually selectively by that of the planar antennas 13, 14, whose impedance is better matched to the particular situation.

[0033] This selective transmitting and/or receiving of the high frequency signal S.sub.HF according to the invention via predominantly one of the two planar antennas 13, 14 is, in the case of the embodiment of the antenna unit 1 shown in FIGS. 1 and 2, further supported by the signal splitter 15. For this, the signal splitter 15 connects the signal gate 12 either with the first planar antenna 13 or with the second planar antenna 14, depending on whether the antenna unit 1 is encapsulated with a potting compound or not. In such case, the signal splitter 15 switches analogously to the planar antennas 13, 14, upon present potting compound, through that planar antenna 13, 14, which, with reference to the real part, has the higher impedance. In the case of potting compound not present, the signal splitter 15 switches correspondingly through the low ohm planar antenna 13, 14.

[0034] A possible embodiment of the signal splitter 15 is shown in FIG. 2: It includes a first signal path 151, which is arranged between the signal gate 12 and the first planar antenna 13, as well as a second signal path 152, which is arranged between the signal gate 12 and the second planar antenna 14.

[0035] In such case, the two signal paths 151, 152 have in defined subregions different path lengths L.sub.151, L.sub.152. The path length L.sub.151 in the subregion of the first signal path 151 is dimensioned corresponding to half the wavelength λ.sub.pc of the frequency f of the high frequency signal S.sub.HF at the dielectric value DK.sub.pc of the potting compound, or in practice due to the short wavelength in the mm range to a whole numbered multiple thereof. Analogously thereto, the path length L.sub.152 in the corresponding subregion of the second signal path 152 is dimensioned corresponding to half the wavelength λ.sub.0 of the frequency f of the high frequency signal S.sub.HF at the dielectric value DK.sub.0 of air or vacuum, or, again, to a whole numbered multiple thereof. Because of this dimensioning of the path lengths L.sub.151, L.sub.152, the high frequency signal S.sub.HF is led either predominantly via the first signal path 151 or the second signal path 152, depending on whether the antenna unit 1 is encapsulated with a potting compound or not.

[0036] The subregions, in which the signal paths 151, 152 are dimensioned with the above described path lengths L.sub.151, L.sub.152, are bounded in the case variant of the signal splitter 15 shown in FIG. 2 by, in each case, two reflection sites 16, 153. In such case, the reflection site 16 is embodied as a gap 16 toward the signal gate 12. The second reflection site 153, is embodied, in each case, in the form of a right angle 153 in the signal path. The implementing of the signal splitter 15 with reflection sites 16, 153 offers the advantage that the selectivity between the planar antennas 13, 14 is further improved. In contrast with FIG. 2, the signal paths 151, 152 can also be implemented without reflection sites. In such case, the path lengths L.sub.151, L1.sub.52 of the total signal paths 151, 152 are to be dimensioned corresponding to half the wavelength λ.sub.pc,0 of the frequency f of the high frequency signal S.sub.HF at the dielectric value DK.sub.pc,0 of the potting compound, or air/vacuum, as the case may be, or, again, to a whole numbered multiple thereof.

[0037] In the case of the embodiment shown in FIG. 2, the planar antennas 13, 14 are designed as linear antennas, wherein the value of the real part of the impedance of the first planar antenna 13 differs from the value of the real part of the impedance of the second planar antenna 14 by the square root of the dielectric value DK.sub.pc of the potting compound. For this, the first linear antenna 13 is dimensioned with a length Lia corresponding to half the wavelength λ.sub.pc of the frequency f of the high frequency signal (S.sub.HF) at the dielectric value (DK.sub.pc) of the potting compound, or to a whole numbered multiple thereof. Analogously thereto, the second linear antenna 14 is dimensioned with a length L.sub.14 corresponding to half the wavelength λ.sub.0 of the frequency f of the high frequency signal S.sub.HF at the dielectric value DK.sub.0 of air or vacuum, or, again, to a whole numbered multiple thereof.

[0038] The selective transmitting/receiving of the high frequency signal S.sub.HF as a function of the possible potting compound is thus achieved according to the invention because of the different lengths of the linear antennas 13, 14,. In contrast with the shown embodiment, the planar antennas 13, 14 can also be designed as block shaped patch antennas. In such case, the edge lengths of the patch antennas are dimensioned analogously to the lengths L.sub.13, L.sub.14 of the linear antennas 13, 14 described in connection with FIG. 2.

[0039] As is shown in FIG. 2, the first linear antenna 13 and the second linear antenna 14 are connected in this embodiment of the antenna unit 1 via a right angled extension 131, 141 with a ground connection. Analogously to the linear antennas 13, 14, also the right angled extension 131 of the first planar antenna 13 is dimensioned with a length corresponding to half the wavelength λ.sub.pc of the frequency f of the high frequency signal S.sub.HF at the dielectric value DK.sub.pc of the potting compound, or to a whole numbered multiple thereof; and the right angled extension 141 of the second planar antenna 14 is dimensioned with a length corresponding to half the wavelength λ.sub.0 of the frequency f of the high frequency signal S.sub.HF at the dielectric value DK.sub.0 of air or vacuum, or to a whole numbered multiple thereof. Because of this type of grounding of the linear antennas 13, 14, it is possible to dimension the linear antennas 13, 14, as a whole, compactly, without having to sacrifice transmitting/receiving efficiency.

[0040] The substrate 11 shown in FIG. 2, on which the planar antennas 13, 14, the signal splitter and the signal gate 12 of the antenna unit 1 are arranged, can be, for example, a circuit board 11. In such case, there can be arranged on such circuit board 11 besides the antenna unit 1 also other electronic components of the relevant electronics module. Accordingly, the signal splitter 15 and the planar antennas 13, 14 can be embodied, for example, as copper- or gold-based, conductive traces. The signal gate 12 and the ground connections of the extensions 131, 141 can, such as shown in FIG. 2, be implemented as electrical vias through the circuit board 11. Because of the planar design of the components 12, 13, 14, 15, the antenna unit 1 can, thus, depending on application, be encapsulated on the surface of the circuit board 11 by an appropriately thin, (continuous) potting compound.

LIST OF REFERENCE CHARACTERS

[0041] 1 antenna unit

[0042] 11 substrate

[0043] 12 signal gate

[0044] 13 first planar antenna

[0045] 14 second planar antenna

[0046] 15 signal splitter

[0047] 16 gap

[0048] 131 right angled extension

[0049] 141 right angled extension

[0050] 151 first signal path of the signal splitter

[0051] 152 second signal path of the signal splitter

[0052] 153 angled section in the signal path

[0053] c.sub.pc,0 propagation velocity of the high frequency signal

[0054] DK.sub.pc dielectric value of the potting compound

[0055] DK.sub.0 dielectric value of air/vacuum

[0056] f frequency of the high frequency signal

[0057] L.sub.13,14 lengths of the planar antennas

[0058] L.sub.151,152 path lengths of the signal paths of the signal splitter

[0059] S.sub.HF high frequency signal

[0060] λ.sub.pc wavelength of the high frequency signal in the potting compound

[0061] λ.sub.0 wavelength of the high frequency signal in air/vacuum