Over the air measurement module

An over the aft measurement module comprises an antenna, adapted to receive a first measuring signal from a device under test or adapted to transmit a second measuring signal to the device under test. Furthermore, the over the air measurement module comprises a mixer, directly connected to said antenna, adapted to reduce or increase a frequency of the received first measuring signal, resulting in a frequency reduced or increased first measuring signal, or adapted to increase or reduce a frequency of a frequency reduced or increased second measuring signal, resulting in the second measuring signal. In addition to this, the over the air measurement module comprises a first connector, connected to said mixer, adapted to input a local oscillator signal into the mixer for frequency conversion.

PRIORITY

This application is a Continuation-In-Part of U.S. application Ser. No. 15/175,197, filed on Jun. 7, 2016 and claims priority of European patent application EP 16 153 360.9 filed on Jan. 29, 2016, which are incorporated by reference herewith.

FIELD OF THE INVENTION

The invention relates to an over the air measurement module for measuring high frequency signals, especially communication signals over the air.

BACKGROUND OF THE INVENTION

During recent years, radio frequencies employed for performing communication tasks have continually risen. Especially with frequencies exceeding many GHz, new problems regarding the measurement of respective signals arise. By connecting the signal source to a measuring device using a cable connection, the behavior of the device under test is influenced.

For example the document US 2015/0035707 A1 shows a slot line antenna on a printed circuit board. The antenna shown there is capable of receiving high frequency signals.

There arises the need of providing measuring means for measuring high frequency signals with a high accuracy and a small size and hardware effort.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, an over the air measurement module is provided. The over the air measurement module comprises an antenna, which is adapted to receive a first measuring signal from a device under test or adapted to transmit a second measuring signal to the device under test. Moreover, the over the air measurement module comprises a mixer which is directly connected to said antenna and is adapted to reduce or increase a frequency of the received first measuring signal, resulting in a frequency reduced or increased first measuring signal, or is adapted to increase or reduce a frequency of a frequency reduced or increased second measuring signal, resulting in the second measuring signal. Furthermore, the over the air measurement module comprises a first connector, connected to said mixer, which is adapted to input a local oscillator signal into the mixer for frequency conversion.

According to a preferred implementation form of the first aspect, the over the air measurement module further comprises a second connector, connected to the mixer, adapted to output the frequency reduced or increased first measuring signal or a corresponding intermediate frequency signal. It is thereby possible, on the one hand, to acquire a measuring signal of an extremely high frequency without altering it and to provide a lower frequency measuring signal to further measuring devices, and on the other hand, to provide a measuring signal of extremely high frequency to the device under test in a controlled manner without influencing the measuring results.

According to a preferred implementation form of the first aspect, the mixer is based on monolithic microwave integrated circuit technology, or the mixer is a harmonic mixer or a mixer comprising a multiplier for the local oscillator signal.

According to a preferred implementation form of the first aspect, a frequency of the local oscillator signal is divided by a factor before inputting the local oscillator signal into the mixer.

According to a preferred implementation form of the first aspect, the over the air measurement module is mounted within a shielded box. It is thereby possible to avoid interference, and thus to guarantee highly accurate measurements.

According to a preferred implementation form of the first aspect, at least one of a frequency of the local oscillator signal and a frequency of the intermediate frequency signal is within a frequency range from 1 GHz to 10 GHz.

According to a preferred implementation form of the first aspect, the over the air measurement module further comprises a power sensor, adapted to measure at least one of the power of the frequency reduced or increased first measuring signal or the power of the second measuring signal.

According to a preferred implementation form of the first aspect, the antenna is a planar antenna. A main radiation direction of the antenna is in the plane of the planar antenna. It is thereby possible to achieve a very low size of the over the air measurement module.

According to a further preferred development of this implementation form, at least some surfaces, advantageously all surfaces of the measuring module facing in the main radiation direction of the antenna are adapted to absorb electromagnetic radiation and do not reflect electromagnetic radiation. Thereby, reflections towards the device under test are prevented. This increases the measuring accuracy.

According to a further preferred implementation form, at least some surfaces, advantageously all surfaces of the measuring device facing in the main radiation direction of the antenna are coated with a paint absorbing electromagnetic radiation and/or covered with absorber material absorbing electromagnetic radiation and/or fabricated from absorber material absorbing electromagnetic radiation. It is thereby possible to further reduce reflections towards the device under test thereby increasing the measuring accuracy.

According to a further preferred implementation form of the first aspect, the over the air measurement module is tapered towards the main radiation direction of the antenna. First of all, this measure also reduces reflections towards the device under test, thereby increasing measuring accuracy. Also, this measure allows for an especially small foot print of the over the air measurement module. This increases the flexibility of use.

According to a further preferred implementation form of the first aspect, at least one of the first connector or the second connector is a coaxial connector allowing to output the intermediate frequency signal to external units or to input a user-defined external local oscillator signal.

According to a further preferred implementation form of the first aspect, a relative power loss for mixing is less than 10 percent, preferably less than 5 percent, most preferably less than 1 percent. In other words, the relative power loss for mixing means the power loss occurring within the mixer due to non-ideal components of the mixer.

According to a further preferred implementation form of the first aspect, the over the air measurement module comprises a substrate, advantageously a printed circuit board. The antenna and the analog signal processor are arranged on the substrate. The antenna is planar with the substrate. The main radiation direction of the antenna is towards an edge of the substrate. It is thereby possible to achieve an extremely small size and low footprint of the over the air measurement module.

According to a further preferred implementation form of the first aspect, the mixer is ring mixer or the mixer comprises at least four diodes.

According to a further preferred implementation form of the first aspect, the antenna is a tapered slot line antenna, advantageously a Vivaldi antenna. It is thereby possible, to achieve satisfactory high frequency characteristics, while achieving a very small size of the antenna.

According to a further preferred development form of the previous implementation form, the substrate comprises an opening between conductors of the tapered slot line antenna. Additionally or alternatively, a substrate bridge connects opposite parts of the tapered slot line antenna in an area of an antenna aperture. A very stable construction of the antenna with beneficial radio frequency characteristics is thereby achieved.

According to a second aspect of the invention, a measuring system comprising a previously described over the air measurement module is provided. The measuring system comprises a measuring device. The measuring device is adapted to receive and measure the frequency reduced first measuring signal from the over the air measurement module. Alternatively or additionally, the measuring device is adapted to provide the frequency reduced second measuring signal to the over the air measurement module. A very flexible and accurate measurement is thereby possible.

DETAILED DESCRIPTION OF THE DRAWINGS

First we demonstrate the general construction and function of an over the air measurement module alongFIG. 1,FIG. 2, andFIG. 3. AlongFIG. 4andFIG. 5further details of another implementation form are described. Finally, according toFIG. 6andFIG. 7, an exemplary embodiment of a mixer and an exemplary embodiment of a monolithic microwave integrated circuit frequency divider, each employed for the over the air measurement module, are described. Similar entities and reference numbers in different figures have been partially omitted.

InFIG. 1, a first embodiment of the over the air measurement module1according to the first aspect of the invention is shown. The over the air measurement module1comprises a housing15which contains a substrate18, advantageously a printed circuit board. On the substrate18, two antenna elements16,17forming a tapered slot line antenna19, are arranged. The antenna19is connected to a mixer14which is also arranged on the substrate18. The mixer14moreover is connected to an analog signal processor35connected to a first connector31and a second connector33. Additionally or alternatively, the mixer14is directly connected to said first connector31and said second connector33via connections38and39.

Connectable to the first connector31is a local oscillator32, which is not part of the over the air measurement module1, for providing a local oscillator signal for the mixer14. Additionally, the frequency of the local oscillator signal may be divided by a factor with the aid of a frequency divider before directly or indirectly inputting the local oscillator signal into the mixer14. Analogously, connectable to the second connector33is a measuring device2, which is likewise not part of the over the air measurement module1. Preferably, at least one of the first connector31and the second connector33is a coaxial connector. Furthermore, the antenna19has a main radiation direction towards the right edge of the substrate18, indicated by an arrow in the figures. A device under test3is suitably arranged in this direction.

In order to minimize reflections from the over the air measurement module1, the housing15is tapered towards the main radiation direction of the antenna19. This tapering reduces the effective surface area, which can produce reflections. In order to further reduce such reflections, the housing15can be fabricated from an electromagnetic radiation absorbing material. It can also be covered with such a material or can be coated with an absorptive paint. The housing15furthermore comprises a back plate11, which is covered with absorptive material12in order to further reduce reflections.

The over the air measurement module1is suitable for two types of measurements. In a first type of measurement, a first measuring signal emitted from the device under test3is received by the antenna19and handed to the mixer14. The mixer14typically reduces, or alternatively increases, the frequency of the first measuring signal resulting in a frequency reduced, respectively increased, first measuring signal. This is done by down-converting, respectively up-converting, the first measuring signal with the aid of the mixer14. In this context, if the frequency reduced, respectively increased, first measuring signal is not directly passed to the connectors31and33, respectively the signal is passed through the analog signal processor35, it should be mentioned that the analog signal processor35may comprise one or more filters for filtering the frequency reduced, respectively increased, first measuring signal, a power sensor, which can be used for directly measuring a power of the frequency reduced, respectively increased, first measuring signal, an amplifier for amplifying the first frequency reduced, respectively increased, measuring signal, and a radio frequency switch for switching between the previously described measuring option and the measuring option described in the following.

The processed frequency reduced, respectively increased, measuring signal is then handed on to the second connector33, which passes on the signal to for example an external measuring device2for further processing the frequency reduced, respectively increased, measuring signal.

Alternatively, the over the air measurement module can be used for another type of measurement. In this case, the second connector33receives a typically frequency reduced, alternatively a frequency increased, second measuring signal from the measuring device2. It is handed on to the mixer14. The mixer14increases, respectively reduces, the frequency of the frequency reduced, respectively increased, second measuring signal resulting in a second measuring signal. This is done by mixing the frequency reduced, respectively increased, second measuring signal with the local oscillator signal provided at the first connector31with the aid of the mixer14.

The second measuring signal is then transmitted by the antenna19to the device under test3. By analogy with the explanations mentioned above, the analog signal processor35may comprise additional components. The analog signal processor35can comprise a filter, for filtering the second measuring signal and/or the second frequency reduced, respectively increased, measuring signal. Also, the analog signal processor35can comprise an amplifier for amplifying the second measuring signal and/or the second frequency reduced, respectively increased, measuring signal. Moreover, the analog signal processor35can comprise a radio frequency switch, adapted to switch between different operating modes of the over the air measurement module1.

With respect to each type of operation, the second connector33is adapted to output the frequency reduced, respectively increased, signal or a corresponding intermediate frequency signal.

Also here, the measurement system30according to the second aspect of the invention is depicted. The measuring system30comprises the over the air measurement module1and the measuring device2. The measuring device2is adapted to receive and measure the frequency reduced, respectively increased, first measuring signal and/or to provide the frequency reduced, respectively increased, second measuring signal to be transmitted to the device under test3as second measuring signal. In addition to this, the system30comprises a local oscillator32adapted to provide a local oscillator signal for the mixer14for the respective frequency conversion.

InFIG. 2the over the air measurement module ofFIG. 1is shown in a cut view from the side. Here it can be seen that the analog signal processor14and the first connector31and the second connector33are arranged on the substrate18. Moreover, the tapering of the housing15and the arrangement of the absorbers12can be seen.

Now, with respect toFIG. 3, an exemplary embodiment of a schematic circuit board80of the over the air measurement module1is shown. As already mentioned above, on the substrate18, the two antenna elements16,17forming a tapered slot line antenna19, are arranged. In order to ensure a highly accurate signal transition between the antenna19and the mixer14, bridging elements36and37are used. In this manner, an optimal transition between signals of a slotline and signals of a coplanar waveguide is guaranteed.

Furthermore, the mixer14is connected to the analog signal processor35which is connected to the first connector31, which is adapted to input a local oscillator signal of the local oscillator32directly into the mixer14with the aid of connection38or indirectly into the mixer14via the analog signal processor35. In addition to this, the analog signal processor35is connected to the second connector33, which is adapted to output the frequency reduced, respectively increased, measuring signal or a corresponding intermediate frequency signal to the measuring device2. Additionally or alternatively, the second connector33may be directly connected to the mixer14in order to output the frequency reduced, respectively increased, measuring signal or a corresponding intermediate frequency signal to the measuring device2without the aid of the analog signal processor35.

InFIG. 4a second embodiment of the over the air measurement module1is shown. Here, a three-dimensional view of the over the air measurement module1is depicted. The housing15comprises a first part15aand a second part15b. The two housing parts surround the substrate18and hold the substrate18between themselves. The substrate18comprises an opening27between the antenna elements16and17. This opening27further reduces the influence of the substrate material on the received or transmitted signal. For reasons of stability, the embodiment shown here comprises a substrate bridge28connecting opposite parts of the tapered slot line antenna in the area of the antenna aperture.

Moreover, the over the air measurement module1comprises an absorber20, which is arranged surrounding the substrate18at the narrow end of the tapered slot line antenna19. The absorber20prevents reflections towards the device under test2.

Moreover, in this embodiment, the geometric shape of the over the air measurement module1is evident. Especially, it is evident here, that the over the air measurement module1is tapered towards the main radiation direction of the antenna19. Moreover, it is evident that all surfaces of the over the air measurement module1facing the main radiation direction of the antenna19are angled away from a normal of the main radiation direction of the antenna19. This leads to an especially low reflectivity for signals emitted by the device under test2. Here, only the very small surfaces23,24point towards the device under test. All other surfaces21,22,25,26are angled away from the device under test.

Especially, at least 50%, preferably at least 80%, most preferably all surfaces of the over the air measurement module facing the main radiation direction of the antenna are therefore angled away from a normal of the main radiation direction of the antenna by at least 30°, preferably by at least 45°, most preferably by at least 60°.

In order to further reduce the effect of the substrate18on the received or transmitted signal, the relative permittivity εris low. Especially, it is lower than 4, preferably εr<2, most preferably εr<1.5. For the same reason, the relative permeability μris low. Advantageously it is below 3, preferably μr<2, most preferably μr<1.5.

InFIG. 5a cut open view of the embodiment ofFIG. 4is shown. Here it is evident that the housing15comprises an opening29, which encloses the substrate18. Arranged on the substrate18is the mixer14, which is connected to the antenna element16,17of the antenna19. As explained earlier, the mixer14down-converts, respectively up-converts, signals received by the antenna19and signals to be transmitted by the antenna19. In addition to this, as explained above, signals may be further processed with the aid of an analog signal processor which is not explicitly depicted inFIG. 4andFIG. 5.

Evident fromFIG. 5is that the absorber20surrounds the substrate18on both sides in order to reduce the reflections towards the device under test.

Instead of forming the antenna19as depicted here, it is also possible to use two tapered slot line antennas on substrates, which are arranged orthogonally. In this case, a dual linear polarization measurement can be provided. The signals of these two antennas can be handled separately or can be combined.

Also advantageously, a power sensor can be integrated into the analog signal processor. A power measurement of signals received from the device under test can then be performed there. The power measurement in this case would be performed under a frequency reduced first measuring signal. In this case, a load resistor of the power sensor of the antenna has a higher value than 50 Ohm.

As a power sensor, a diode sensor produced in slot line technology can be used.

In addition, a rectification and/or a bandwidth limitation and/or an analog-digital-conversion can also be integrated into the analog signal processor. Furthermore, in addition to the mixer14, the analog signal processor can moreover be adapted to provide an intermediate frequency signal or a baseband signal to the second connector33.

Advantageously, the over the air measurement module1is adapted to perform a wireless measurement. This means that at least one of the connectors31and33can be implemented as a wireless interface for wirelessly transmitting the local oscillator signal provided by the local oscillator32, respectively the measuring results to the measuring device2.

Especially, it is possible to split the measuring system30into an antenna module and a detector module. The antenna module would then comprise all aspects presently contained in the over the air measurement module, while the detector module would comprise at least a detector for determining certain aspects of the measured signal, for example the power of the signal. Moreover, a sensor/processing module could be separately constructed. In this case, the over the air measurement module1could be split into an antenna module only comprising the antenna19in combination with the mixer14and a processing module comprising the analog signal processor35. Alternatively, the over the air measurement module1could be split into an antenna module only comprising the antenna19and a processing module comprising the analog signal processor35in combination with the mixer14. The antenna module, processing module and detector module can be integrated into a single module or housing. Also they can be separately constructed. Especially, an integration of the detector module and the antenna module is possible.

In order to connect the different modules, especially the sensor module, the antenna module, the detector module and the processing module, electrical conductors, for example coplanar transmission lines can be used. Also the use of optical transmission lines is possible.

In order to minimize noise, a chopper can be integrated into the detector module. By repeatedly reversing the polarity of the measured signal, the influence of noise can be mitigated. Especially, the influence of accidently coupling noise signals can be reduced.

Advantageously, the detector can be formed based on a coplanar transmission line. This allows for an easy transmission of the detected power to further components.

Advantageously, the antenna signals, especially if the antenna is a slot line antenna, can be converted to a signal on a coplanar transmission line so that they can be more easily handled on the circuit board and supplied to the further components.

The change of the transmission typology from slot line to coplanar can be performed either between the antenna and the analog signal processor or between the analog signal processor and the connector.

The mixer60comprises four diodes61,62,63, and64. Said mixer60further provides four ports for a local oscillator (LO) signal, internal termination, an intermediate frequency (IF) signal, and a radio frequency (RF) signal.

Finally, with respect toFIG. 7, which originates from page626of above-mentioned “Ulrich L. Rohde: Microwave and Wireless Synthesizers—Theory and Design, 1997”, a frequency divider70based on monolithic microwave integrated circuit MMIC technology is shown. Said frequency divider70can be used for dividing the frequency of the local oscillator signal by a factor as already mentioned with respect toFIG. 1above.

The frequency divider70comprises an input port71and an output port72. Furthermore, the frequency divider comprises a plurality of striplines73ato73h, wherein at least two73gand73hof them are capacitively and/or inductively coupled. In addition to this, the frequency divider70comprises at least one coupled resonator74, preferably based on a finger structure, at least one resistor76, at least one amplifier77, and at least two diodes75aand75b.

The invention is not limited to the examples and especially not to a specific measurement direction. Also the measured signals are not limited to a specific communications task. The characteristics of the exemplary embodiments can be used and can be combined in any advantageous combination.