Antenna arrangement

An antenna arrangement has a first signal path connected to a first antenna. A second signal path is connected to a second antenna. A third signal path includes a device that measures the signal strength. Directional couplers couple the first and second signal paths to the third signal path. Filters filter out signal components that are coupled by one antenna into the other antenna.

This application claims priority to German Patent Application 10 2010 048 619.1, which was filed Oct. 15, 2010 and is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an antenna arrangement in which a first and a second signal path are each coupled by means of a directional coupler to a third signal path. The first and second signal paths are each connected to a first and a second antenna, respectively.

BACKGROUND

Appliances for mobile communication should support sending and receiving in different frequency bands. Since an antenna can usually have an optimum radiation characteristic only for one frequency band at the resonant frequency of the antenna, however, communication appliances having a plurality of, but at least two, antennas are customary. In the case of appliances having a plurality of antennas, interactions between the individual antennas are often unavoidable, however. When a first antenna is active, for example, the radiation emitted by the first antenna is coupled into the second antenna again. Such coupling of the two antennas is often undesirable.

In addition, antenna arrangements are known in which a first signal path, which is connected to a first antenna, and a second signal path, which is connected to a second antenna, are coupled by means of directional couplers to a third signal path each.FIG. 1shows such an antenna arrangement, which is known in the prior art.

The first antenna Ant1is used for sending and receiving signals from a high-frequency band. The second antenna Ant2is designed for frequencies from a low-frequency band. In this case, the low-frequency band is defined in that it comprises frequencies which are lower than the frequencies of the high-frequency band. It is possible for the frequency range of the low-frequency band to adjoin the frequency range of the high-frequency band.

The antenna arrangement shown inFIG. 1has a first signal path SP1, a second signal path SP2and a third signal path SP3. The first signal path SP1has a switch S1which can be used to connect the first signal path SP1to further signal paths SPHF1, SPHF2, SPHF3which are connected to a transmission and reception circuit for frequencies from the high-frequency band and which have various filters for high-frequency signals. In addition, the first signal path SP1can be connected by means of this switch S1to a terminating resistor R1. The first signal path SP1is also coupled by means of a dual-band directional coupler DRK to the third signal path SP3. The first signal path SP1is connected to the first antenna Ant1.

A second signal path SP2has a second switch S2which can be used to connect the second signal path SP2to further signal paths SPLF1, SPLF2, SPLF3which are connected to a transmission and reception circuit for frequencies from the low-frequency band and which have various filters for frequency ranges from the low-frequency band. Furthermore, the second signal path SP2can be connected by means of this second switch S2to a terminating resistor R2. The dual-band directional coupler DRK couples the second signal path SP2to the third signal path SP3. The second signal path SP2is connected to the second antenna Ant2.

In the positions of the first switch S1and the second switch S2which are shown inFIG. 1, the first antenna Ant1is connected by means of the first switch S1to the terminating resistor R1and the second antenna Ant2is connected by means of the second switch S2to the further signal path SPLF1, which is connected to a transmission and reception circuit for a particular frequency range from the low-frequency band. Accordingly, the first antenna Ant1is terminated and the second antenna Ant2is active.

The third signal path SP3is coupled by means of the dual-band directional coupler DRK to the first and second signal paths SP1, SP2. The third signal path SP3also has measuring devices ME_forward and ME_reflected. In the switch position of the switches S1, S2which are shown inFIG. 1, a signal from the transmission device for low frequencies is coupled into the second signal path SP2via the signal path SPLF1and the second switch S2. A certain signal component is coupled from the second signal path SP2into the third signal path SP3by means of the dual-band directional coupler DRK. This signal component reaches the measuring device ME_forward. This measurement can be used to determine a gain factor for the antenna arrangement and the transmission device.

In the second signal path SP2, the signal component which has not been deflected into the third signal path SP3by means of the dual-band directional coupler DRK now reaches the second antenna Ant2and is emitted thereby. However, a certain signal component is also reflected by the second antenna Ant2. The reflected signal component now takes the second signal path SP2in the reverse direction and is to some extent coupled into the third signal path SP3by the dual-band directional coupler DRK. In the third signal path SP3, this signal component reaches the measuring device ME_reflected. In this way, a possible mismatch in the second antenna Ant2can be determined.

In a converse switch position for the switches S1, S2, the second signal path SP2is connected to the terminating resistor R2and the first signal path SP1is connected to one of the further signal paths SPHF1, SPHF2or SPHF3. Accordingly, the first antenna Ant1is then active and the second antenna Ant2is terminated.

Again, the dual-band directional coupler DRK prompts part of the inbound signal to be coupled out of the first signal path SP1, to be coupled into the third signal path SP3and thus to reach the measuring device ME_forward, which ascertains the gain factor for the antenna arrangement. In addition, a signal component reflected by the first antenna Ant1is to some extent coupled by means of the dual-band directional coupler DRK into the third signal path SP3, where it reaches the measuring device ME_reflected, which determines the mismatch in the first antenna.

The third signal path SP3also has damping elements DE1, DE2, DE3, DE4, DE5, DE6. These ensure that only a small signal component is coupled into the third signal path SP3from the second or first signal path SP1, SP2. Customary attenuation in this case is in the region of 20 dB.

In the antenna arrangement shown inFIG. 1, it is crucial that the first and second antennas Ant1, Ant2are very well insulated from one another. If the active antenna, in this case the second antenna Ant2, were to couple signals into the passive, terminated antenna, in this case the first antenna Ant1, then these signals would likewise enter the third signal path SP3via the dual-band directional coupler DRK and corrupt the measurements by the measuring devices ME_forward, ME_reflected in the third signal path.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides an antenna arrangement that ensures the same quality of signal isolation when there is little insulation between two antennas.

An embodiment of the invention proposes an antenna arrangement which has a first signal path, which is connected to a first antenna, a second signal path, which is connected to a second antenna, a third signal path, which has means for measuring the signal strength, and directional couplers which couple the first signal path and the second signal path each to the third signal path. In addition, the antenna arrangement according to the invention has filters which filter out signal components which are coupled by one antenna into the other antenna.

The first antenna may be designed for a high-frequency band and the second antenna may be designed for a low-frequency band. In this case, the low-frequency band is defined in that it contains frequencies which are lower than the frequencies in the high-frequency band. The low-frequency band can directly adjoin the high-frequency band.

The first and second signal paths preferably contain switches which can be used to connect the first or the second signal path each to different transmission and reception circuits for different frequency ranges.

The first and second signal paths can each be connected to the third signal path by means of a common dual-band directional coupler.

In a first refinement of the present invention, the first and second signal paths each contain a diplexer. In the first signal path, the diplexer is connected to the first antenna, and, similarly, in the second signal path, the diplexer is connected to the second antenna. One output of each of the two diplexers is in this case connected to a respective terminating resistor. The other output of each of the two diplexers is connected to the dual-band directional coupler. The diplexers have a high-pass filter and a low-pass filter. In addition, the diplexers are connected up such that, in the first signal path, the low-pass filter of the first diplexer is connected to the terminating resistor and the high-pass filter of this diplexer is connected to the dual-band directional coupler. Conversely, in the second signal path, the high-pass filter of the second diplexer is connected to the terminating resistor and the low-pass filter is connected to the dual-band directional coupler. In this case, the first signal path is connected to the high-frequency antenna and the second signal path is connected to the low-frequency band antenna.

The interconnection of the diplexers that is described here allows signals which are coupled by one antenna via the other antenna into the respective other signal path to be filtered out again. In the high-frequency signal path, a wave reflected from the high-frequency antenna is forwarded by the low-pass filter to the terminating resistor. The latter acts as a sump. An inbound wave containing frequencies from the high band passes through the high-pass filter and is not damped in this case.

Conversely, signals can be coupled by the high-frequency antenna into the low-frequency antenna, and these signals are forwarded via the high-pass filter of the diplexer to the terminating resistor. This exemplary embodiment furthermore affords the advantage that the switches do not need to set up a connection to a terminating resistor.

In accordance with a second exemplary embodiment of the present invention, two diplexers are arranged in the third signal path on the input and output sides. In this regard, the third signal path is split into two sub-signal paths, wherein the first sub-signal path is connected by means of a first directional coupler to the first signal path and the second sub-signal path is connected by means of a second directional coupler to a second signal path. The third signal path has two diplexers which each connect the two sub-signal paths to form a main signal path and connect them to the measuring devices.

In an antenna arrangement based on the second exemplary embodiment, a high level of insulation between the two antennas is not necessary since the diplexers can be connected up such that undesirable signals coupled by one antenna into the other antenna can be filtered out again. Since, in accordance with the second exemplary embodiment, the diplexers are now arranged in the third signal path and they are therefore no longer arranged in the first or second signal path, they do not have a damping effect on a wave entering an antenna.

In accordance with a third exemplary embodiment, the third signal path contains a high-pass filter and the second signal path contains a low-pass filter.

The following list of reference symbols may be used in conjunction with the drawings:

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The antenna arrangement shown inFIG. 2is distinguished from the antenna arrangement shown inFIG. 1, which is known in the prior art, by virtue of the first and second signal paths SP1, SP2each containing a diplexer DP1, DP2. Each of these two diplexers DP1, DP2has a high-pass filter HPF1, HPF2and a low-pass filter LPF1, LPF2.

The first signal path SP1is connected to a first antenna Ant1for frequencies from a high-frequency band. The second signal path SP2is connected to a second antenna Ant2for frequencies from a low-frequency band. The diplexer DP1in the first signal path SP1is connected up such that a high-pass filter HPF1is connected to the dual-band directional coupler DRK and the first antenna Ant1. A low-pass filter LPF1is connected to a terminating resistor R1and the first antenna Ant1.

If a signal is now coupled into the first signal path SP1via the first switch S1and the transmission device, this signal is not attenuated in the high-pass filter, since the signal comes from the frequency range of the high band. An inbound wave accordingly reaches the first antenna Ant1undamped. If, by contrast, the second antenna Ant2couples a signal at a frequency from the low-frequency band into the first antenna Ant1, this returning wave is severely damped by the high-frequency filter. Accordingly, such a returning wave does not enter the dual-band directional coupler DRK. The undesirable, coupled-in wave is forwarded via the low-pass filter LPF1to the terminating resistor R1. The latter acts as a wave sump.

The second signal path SP2is set up in a similar manner. In this case too, the diplexer DP2has a high-pass filter HPF2and a low-pass filter LPF2. The high-pass filter HPF2is connected to the second antenna Ant2and to the second terminating resistor R2. The low-pass filter LPF2is connected to the second antenna Ant2and to the dual-band directional coupler DRK. An inbound wave which is coupled into the second signal path SP2by the transmission device for low frequencies is not damped by the low-pass filter LPF2of the second diplexer DP2and accordingly reaches the second antenna Ant2undamped. If, by contrast, a signal emitted by the high-frequency band antenna Ant1is coupled into the second antenna Ant2, this returning wave is severely damped by the high-pass filter HPF2of the second diplexer DP2and does not reach the third signal path SP3. On the contrary, such an outbound wave is forwarded via the high-pass filter HPF2of the second diplexer DP2to the second terminating resistor R2, which acts as a wave sump.

FIG. 3shows a second exemplary embodiment of the present invention. This differs from the antenna arrangement which is known in the prior art, and which is shown inFIG. 1, by virtue of the third signal path SP3being split into two sub-signal paths SP3aand SP3b. The first and second signal paths SP1, SP2are each coupled to one of the sub-signal paths SP3a, SP3bby means of a directional coupler RK1, RK2.

The third signal path SP3also has two diplexers DP1, DP2. The diplexers DP1, DP2are connected up such that they are each connected to one end of one of the sub-signal paths SP3a, SP3band connect up the two sub-signal paths SP3a, SP3bto form a common signal path SP3. The diplexers DP1, DP2each have a high-pass filter HPF1, HPF2and a low-pass filter LPF1, LPF2.

Again, the high-pass and low-pass filters HPF1, HPF2, LPF1, LPF2are connected up such that a wave, the frequency of which corresponds to the resonant frequency of the antenna associated with the relevant signal path, reaches the measuring devices ME_forward, ME_reflected undamped, while a wave which has been coupled into the signal path by the other antenna is severely damped by the relevant filters.

The first signal path SP1also has a first switch S1, which can be used to connect the first signal path SP1to various further signal paths SPHF1, SPHF2, SPHF3which are in turn connected to a transmission and reception device for signals with a frequency range from the high-frequency band. The second signal path SP2also has a second switch S2, which can be used to connect the second signal path SP2to various further signal paths SPLF1, SPLF2, SPLF3which in turn are connected to a transmission and reception device for signals with a frequency range from the low-frequency band.

The switch position of the switches S1and S2which is shown inFIG. 3will now be considered in more detail. The second switch S2connects the second signal path SP2to the further signal path SPLF1, which has a signal with a frequency range from the low-frequency band applied to it. The first switch S1connects the first signal path SP1to the first terminating resistor R1, so that the first antenna Ant1has no signal applied to it.

The signal which is coupled into the second signal path SP2via the second switch S2first of all reaches the directional coupler RK2. A certain signal component is coupled by this directional coupler RK2into the second sub-signal path SP3bof the third signal path SP3. There, the signal arrives at the low-pass filter LPF2of the second diplexer DP2. The signal is not attenuated by this low-pass filter LPF2and enters the third signal path SP3, which is connected to the measuring device ME_forward. This measuring device ME_forward ascertains the signal strength and determines a gain factor therefrom.

The signal component which has not been coupled out of the second signal path SP2by the directional coupler RK2reaches the second antenna Ant2and is emitted thereby. However, a certain signal component is reflected back into the second signal path SP2, possibly on account of a mismatch in the second antenna Ant2. Part of this returning wave is now coupled out by the directional coupler RK2and coupled into the second sub-signal path SP3bof the third signal path SP3. Via the low-pass filter LPF1the first diplexer DP1, this signal component enters the third signal path SP3, which is connected to the measuring device ME_reflected. This measuring device ME_reflected in turn determines the signal strength and ascertains the mismatch in the second antenna Ant2therefrom.

A certain signal component of the signal emitted by the second antenna Ant2is coupled into the first antenna Ant1. The level of this signal component is dependent on the insulation between the two antennas Ant1, Ant2. The antenna arrangements known in the prior art always demand an extremely high level of insulation. The signal component which is coupled into the first antenna Ant1enters the first signal path. In this case, a large signal component is forwarded via the first switch S1to the terminating resistor R1, which acts as a wave sump. However, a small signal component is also coupled by means of the directional coupler RK1into the first sub-signal path SP3aof the third signal path SP3.

Even if the signal strength of this signal component is very low, this signal component would result in a not negligible corruption of the measurements by the measuring devices ME_forward and ME_reflected. However, the signal component in the sub-signal path SP3aarrives at the high-pass filter HPF1of the first diplexer DP1and is filtered out there, so that the measuring devices ME_forward, ME_reflected are not influenced.

Accordingly, the two diplexers DP1, DP2ensure that undesirable signals which are coupled by one antenna into the signal path which is connected to the other antenna are again filtered out and thus cannot corrupt the measurements by the measuring devices ME_forward or ME_reflected. Therefore, for an antenna arrangement as shown inFIG. 3, the requirements in terms of the insulation between the two antennas Ant1, Ant2are significantly lower.

The antenna arrangement shown inFIG. 3affords the advantage over the first exemplary embodiment that the diplexers DP1, DP2are now arranged in the third signal path SP3and that accordingly the signal in the first or in the second signal path SP1, SP2is not attenuated.

FIG. 4shows a third exemplary embodiment of the present invention. This antenna arrangement differs from an antenna arrangement as shown inFIG. 1in that the first signal path SP1contains a high-pass filter HPF and the second signal path SP2contains a low-pass filter LPF.

The way in which this antenna arrangement works essentially corresponds to that of the first exemplary embodiment shown inFIG. 2. Only the diplexer DP1in the first signal path SP1has been replaced by a high-pass filter HPF, and the diplexer DP2in the second signal path SP2has been replaced by a low-pass filter LPF. In addition, the first switch S1in this case can connect the first signal path to a terminating resistor R1, and the second switch S2can connect the second signal path SP2to a second terminating resistor R2.

The high-pass filter HPF in the first signal path SP1prompts signals which are coupled into the first signal path SP1by the second antenna Ant2to be attenuated and not to corrupt a measurement by the measuring devices ME_forward and ME_reflected. The low-pass filter LPF in the second signal path SP2filters out undesirable signals which are emitted by the first antenna Ant1and are coupled into the second antenna Ant2and hence into the second signal path SP2.

Accordingly, the high-pass filter HPF and the low-pass filter LPF ensure that respective undesirable signals which are coupled by one antenna into the signal path connected to the other antenna are filtered out without disturbing the measurements by the measuring devices ME_forward, ME_reflected in the third signal path SP3. For this reason, an antenna arrangement as shown inFIG. 4places much lower demands on the insulation between the two antennas Ant1and Ant2, given the same quality of signal isolation, than would be case with an antenna arrangement as shown inFIG. 1.