FIELD OF THE INVENTION

The present invention relates to high frequency assemblies with at least one dielec tric waveguide fiber, in particular at least one polymer microwave fiber, and the coupling of the at least one fiber to a high-frequency circuit. The invention is par ticularly useful in the context of high speed data transmission devices and data links.

BACKGROUND OF THE INVENTION

In the course of further development of high speed data transmission, dielectric waveguides and in particular polymer microwave fibers (PMFs) are gaining a par ticular interest. A main driver for this trend is, besides the continuous exponential growing demand for cost efficient high data transmission capacity, the improve ment of silicon transistor technologies allowing to build fully integrated transceivers in one single die (MMIC). Such transceivers may operate in frequencies in the mm- wave band and beyond.

In this frequency range, traditional conductor based cables, such as paired lines or coaxial cables, generate high losses due to the increasing conductor losses caused by the skin effect. Cables that are based on waveguides can help to reduce those losses. In the case of pure dielectric-based waveguide cables the attenuation per meter could be reduced to values of about 2...8 dB per meter. Furthermore, the lack of galvanic contacts and significant lower sensitivity to mechanical alignment tolerances increase the attractiveness of such high speed data transmission links. Particular aspects of such high speed data transmission links are addressed in US9373878B2, DE10201 5105657A1 , US2016064795A1 , US9490518B1 , EP3306740A1 , EP3306740A1

SUMMARY OF THE INVENTION

A common underlying assumption in PMF data transmission is that a-PMF-based waveguide cable maintains the polarization of an injected signal over its length. Particularly, in case of fibers respectively cores of non-rotation-symmetric cross section, it is generally assumed that the linear polarization would be maintained by the fiber. In case of rotation-symmetric cables, it is generally assumed that the cir cular polarization would be maintained by the cable. This is the case for ordinary metallic waveguides, where the fundamental mode TE10 is normally used for the data transmission and the electric filed strength vector is always perpendicular to the metallic walls of the waveguide.

However, when characterizing PMFs in a laboratory setup, unexpected effects could be observed. Even if using highly accurate and precise test adapters for the transition from the hollow waveguide ports of a network analyzer to the PMF and accordingly a transition from the fundamental mode TE10 (in the hollow wave guide port) to the fundamental mode HE1 1 (in the PMF) or vice versa, the S-pa- rameters appear to vary in an unpredictable and non-reproducible manner. This variation could not be explained with imperfection such as inaccurate components, tolerances, misalignment and/or parasitic resonators.

The reason for this unexpected and undesired effect is in fact due to the PMF. Al ready small deviations and inhomogeneity that occur during production, material anisotropy (e. g. due to the air bubble distribution in the polymer foam and the molecular orientation in the polymer) result in slight deviations of the electromag- netic wave propagation speed depending on the orientation of the electric field strength vector (E-vector) in the desired and favorable fundamental mode HE1 1 . Similar effects are caused by temperature variations, mechanical stress, twisting and/or bending of the fiber, which will result in the field concentration being dis placed out of the center of the cable. It is noted that the orientation of the E-vector of an electromagnetic wave in the fundamental mode HE1 1 can be expressed as superposition of two electromag netic waves, both having the fundamental mode HE1 1 and having E-vectors (elec tric field strength vectors) that are oriented in perpendicular X- and Y-directions. The variation in the wave propagation speed as described before results in an ini- tially linear polarization (where the E-vector has one linear component only) to be changed into an arbitrary elliptical polarization respectively an unpredictable change in the phase relation between the components of the E-vector in X- and Y- direction. By way of example, it can be found that a twisting of the cable by 10 degrees result in unacceptable ripples and notches of the S-parameter over the de sired frequency band of operation, for example from 1 10 GHz to 140 GHz.

An ordinary rectangular electromagnetic waveguide port (e. g. of a network ana- lyzer or in generally a high-frequency circuit) is designed to receive electromagnetic waves in the fundamental TE10 mode with linear polarization in only one particular orientation, i. e. direction of the E-vector, to allow a good matching with a con nected waveguide. The before-described arbitrary elliptical polarization of the HE1 1 mode when using a PMF for signal transmission will transfer to an similar elliptical polarized TE10 mode signal in the waveguide port, causing a generally bad and varying matching between the PMF and the waveguide port. This results in a significant portion of the energy of the electromagnetic wave to reflected at the interface to the waveguide port. Further, the generally low losses of the PMF itself may ultimately result in multiple reflections. These reflections cause the before-de- scribed effects and the unsatisfying values of the S-parameters as mentioned.

In view of the before-described problems, it is an overall objective of the present invention to improve the state of the art regarding the signal transmission using dielectric waveguide fibers, in particular polymer waveguide fibers and their cou pling to further components. Favorably, some or all of the before-mentioned prob- lems are avoided fully or in part. In an aspect, the overall objective is achieved by a high-frequency assembly respec tively microwave assembly. The high-frequency assembly includes a cable, the ca ble including at least one dielectric waveguide fiber with a first end and an opposed second end. The high-frequency assembly further includes a high-frequency cir- cuit, in particular an electronic high-frequency circuit and an interface unit. The at least one dielectric waveguide fiber is at the first end operatively coupled with the high-frequency circuit via the interface unit.

The interface unit is designed to inject a high-frequency signal into the dielectric waveguide fiber and/or to receive a high-frequency signal from the at least one dielectric waveguide fiber at the first end. The high-frequency signal has a first sig nal component of a first polarization direction and a second signal component of a second polarization direction. The high-frequency assembly is designed to inject the first signal component and the second signal component in a defined manner and/or to split a received high-frequency signal into the first signal component and the second signal component.

An injection of the first signal component and the second signal component in a defined manner means that the amplitudes respectively levels of the first and sec ond signal component and/or the phasing between the first and second signal component is well defined and can be controlled. Both signal components that are injected into or received from the dielectric waveguide fiber may in particular be operated in the fundamental mode HE1 1 . In a further aspect, the overall objective is achieved by a method for transmitting a high-frequency signal via at least one dielectric waveguide fiber of a cable, the die lectric waveguide fiber having a first end and an opposed second end. The method includes injecting a high-frequency signal into the at least one dielectric waveguide fiber and/or to receiving a high-frequency signal from the at least one electro-mag netic waveguide fiber at the first end. The high-frequency signal has a first signal component of a first polarization direction and a second signal component of a sec ond polarization direction. The method includes injecting the first signal component and the second signal component in a defined manner and/or splitting a received high-frequency signal into the first signal component and the second signal com ponent.

The method may in particular be carried out using a high-frequency assembly ac cording to any embodiment in accordance with the present disclosure and may comprise method steps inherent to such embodiments. The high-frequency circuit may in some embodiments include a transmitter, re ceiver, filter, amplifier, attenuator, or any combination thereof. Further in some embodiments, the high-frequency circuit includes one or more microwave semi conductor components. The high-frequency circuit may further include further high-frequency components, in particular waveguide elements, such as metallic waveguide elements, substrate integrated waveguides and/or microstrip lines. The high-frequency circuit may in some embodiments include a phase shifting and/or switching units as electric and/or waveguide devices. The second end of the dielec tric waveguide fiber may be connected to a further high-frequency circuit.

In an embodiment, the at least one dielectric waveguide fiber is a polymeric micro- wave fiber (PMF). This type of embodiment is generally assumed in the following. It is noted that the cable can optionally include two or more dielectric microwave fibers that may each be coupled to a high-frequency circuit via a dedicated interface unit. Instead of a polymer, the at least one dielectric waveguide fiber may be made from other materials of similar characteristics, such as glass or ceramics.

In an embodiment, the first polarization direction and the second polarization di- rection are orthogonal to each other. Such orthogonal directions are in this docu ment also indicated by "X" and Ύ", respectively (for the HE1 1 mode) or "X" and Ύ" (for the TE10 mode).

In an embodiment, the interface unit includes an orthomode transducer or a dual polarization antenna. Orthomode transducers (OMTs) are waveguide components generally known in the art and used for combining orthogonally polarized electro magnetic systems and/or to separating respectively splitting an electromagnetic signal into two orthogonal components. A dual polarization antenna is an antenna arrangement, for example in form of dipole antenna, slot antenna, Vivaldi antenna or patch antenna that is designed to transmit two electromagnetic signal in two orthogonal directions respectively to receive two electromagnetic signals of or thogonal direction. The two electromagnetic signals are guided to respectively from the antenna in two signal lines (e.g. striplines, substrate integrated waveguides, microstrip lines, coaxial lines).

In an embodiment, the high-frequency assembly includes a dielectric lens arranged at the connection of the first end and the interface arrangement. A dielectric lens may in particular be arranged at the first end of the dielectric waveguide fiber and serves as terminal element that terminate the dielectric waveguide fiber.

A Horn antenna provides a transition from the fundamental mode TE10 (in the hol low waveguide port) to the fundamental mode HE1 1 (in the PMF) or vice versa. A horn antenna may in particular be used in combination with an OTM. The horn an- tenna may be arranged between the fiber and the OTM, and radiate into respec tively towards the OTM as receiving element. Similarly, a dielectric lens may be used in combination with a dual polarization antenna. The dielectric lens may be ar ranged between the fiber and the dual polarization antenna and radiate into re spectively towards the dual polarization antenna as receiving element. The dielec- trie lens may be provided integrally with the horn antenna as an antenna compo nent. Alternatively, the dual polarization antenna may be directly arranged adja cent to the fiber end.

In an embodiment, the high-frequency assembly is designed to evaluate a first sig nal level of the first signal component and a second signal level of the second signal component. Further in an embodiment, the high-frequency assembly is configured to feed the first signal component only or the second signal component only into a receiving circuit independence of the first signal level and/or the second signal level signal component. Further in an embodiment, the high-frequency assembly is con figured to switch from feeding the first signal component only into the receiving circuit to feeding the second signal component only into the receiving circuit if the signal level of the first signal component falls beyond a signal level threshold and to from feeding the second signal component only into the receiving circuit to feeding the first signal component only into the receiving circuit if the signal level of the second signal component falls beyond a signal level threshold.

This circuit design is also referred to as Diversity receiver and be the high-frequency circuit or part of the high-frequency circuit. It typically comprises a switching ele ment that switches between the first signal component and the second signal com ponent in dependence of their signal level. It may further comprise a comparison unit that is configured to compare the signal level that is fed into the receiving unit (being it the first or second signal level) with the signal level threshold and control the switching element accordingly. To ensure a stable system behavior and avoid unnecessary switching, the signal level threshold may be adaptive as explained be low in the context of exemplary embodiments.

Since it is highly desired or even crucial to avoid (in the worst case multiple) reflec tions, a termination load is favorably provided that terminates the non-used signal path, i. e. the signal path of the first signal component if the second signal compo nent is fed into the receiving circuit and vice versa. Further in an embodiment, the high-frequency assembly is configured to determine which of the first signal level and the second signal level is larger and feed the first signal component only into a receiving circuit if the first signal level is larger than the second signal level, or to alternatively feed the second signal component only into the receiving circuit if the second signal level is larger than the first signal level. Generally, the signal energy is split between the two signal components, with the distribution between the first and second signal component depending on the ar bitrary polarization. The before-described embodiments where only one of the sig nal components is fed into the receiving circuit can avoid that the received signal level drop below 50% or by bad chance even to zero. Since only part of the full energy of the original electromagnetic signal is utilized, however, this kind of em bodiment is associated with a generally undesired attenuation of up to 3dB. Favor ably for this type of embodiment, the high-frequency assembly, in particular the high-frequency circuit, is designed to do the evaluation of the first signal level and/or of the second signal level of the second signal component as well as the switching in a continuous manner.

In an embodiment, the high-frequency assembly is designed to generate a com bined signal from the received first signal component and the received second sig nal component by superimposing the first signal component and the second signal component with an adjustable phasing such that a combined signal level of the combined signal is maximum. For this type of embodiment, the before-mentioned unfavorable attenuation is avoided since the both the first and second signal com- ponent is utilized. The arbitrary elliptical polarization causes an unknown phase re lation from 0°...360° between the first and second signal component, so a phase shifting unit can hinder that in worst case both signals would be subtracted instead of added. The phase shifting is generally controlled in a favorably continuous man- ner by a receiving circuit.

In an embodiment, the electronics circuit includes a first receiving circuit and a sec ond receiving circuit. The high frequency assembly is configured to feed the first signal component into the first receiving circuit, and to separately feed the second signal component into the second receiving circuit. The high-frequency assembly of this type of embodiment is further configured o superimpose a first output signal of the first receiving circuit and a second output signal of the second receiving cir cuit. For this type of embodiment, the first and second signal components are sep arately demodulated and digital converted by the two receiving circuits and super imposed afterwards in the digital domain In an embodiment, the high-frequency assembly is designed to determine a re ceived signal level that is received at the second end and to control the amplitude and phase relation of the first signal component and the second signal component injected into the at least one dielectric waveguide fiber. The high frequency assem bly of this type of embodiment is favorably designed to control the phase and arm- plitude relation between the first signal component and the second component such that the received signal level is maximum or close to maximum. In the before described embodiments, the problem of an arbitrary and unpredicta ble elliptical polarization at the output side of the dielectric waveguide fiber is ad dressed at the output or receiving side, while the injection of the high-frequency signal at the input side may in principle be arbitrary respectively with any fixed po- larization. For the last-described type of embodiment, in contrast, the waveguide port of a receiving circuit may in principle be designed for any fixed polarization of the electromagnetic wave signal that is injected into the waveguide port. The feed ing of the high-frequency signal at the input side is controlled with respect to the first signal level, the second signal level as well as the phasing between the signal components in a manner that a desired maximum signal level at the output is ob tained. The injection of the high-frequency signal is accordingly controlled in a closed loop and favorably in a continuous manner.

In an embodiment, the high-frequency assembly is configured to transmit and re ceive simultaneously in a polarization duplex operation mode. For this type of em- bodiment, the receiving circuit is configured to evaluate an amplitude and phase relation of a first received signal and a second received signal, thereby determining a received effective polarization vector at the first end. The high-frequency assem bly for this type of embodiment is further configured to calculate an orthogonal polarization vector to this received effective polarization vector and to inject a trans- mit signal into the at least one dielectric waveguide fiber at the first end, the further signal being polarized according to the orthogonal polarization vector. An antenna, such as a horn antenna as mentioned before, favorably receives the received signal with the received effective polarization vector and transmits the transmit signal with the orthogonal polarization vector.

Forthistype of embodiment, the received signal atthefirstend of the fiber (injected at the opposite second end of the fiber) and the transmit signal that is injected at the first end of the fiber (and accordingly received at the opposite second end of the fiber) can travel respectively propagate in opposite directions in the fiber with out interfering. A maximum signal level can in this way be received at both the first and second end of the fiber. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows an embodiment of a high-frequency assembly in a schematic functional view;

Fig. 2 shows a further embodiment of a high-frequency assembly in a sche matic functional view; Fig. 3 shows a still further embodiment of a high-frequency assembly in a schematic functional view;

Fig. 4 shows a still further embodiment of a high-frequency assembly in a schematic functional view. DESCRIPTION OF THE EMBODIMENTS

In the following, reference is first made to Fig. 1 , showing an embodiment of a high-frequency assembly. For the sake of conciseness, this embodiment is ex plained in greatest detail, while the description of the further embodiments is fo- cused on the differences respectively particular aspects of the embodiments.

The high-frequency assembly 1 includes a waveguide cable with at least one poly mer waveguide fiber (PMF) 1 1 as dielectric waveguide fiber.

Thee waveguide cable and accordingly the PMF 1 1 have a first end 1 1 1 and an opposed second end 1 1 2. Here and in the following it is exemplarily assumed that a signal is injected into the PMF 1 1 at the second end 1 1 2 as input respectively injection side and is transmitted respectively conducted in the PMF 1 1 as electro magnetic wave to the first end 1 1 1 as output respectively receiving side. The signal may be injected into the PMF 1 1 by any suitable high-frequency circuit or assembly (not shown). It is to be understood that the first end second end may be reversed. In the PMF 1 1 , the electromagnetic wave propagates with the fundamental mode HE1 1 , having a first signal component that is polarized in a first direction (X) and a second signal component that is polarized in an orthogonal second direction (Y). The two signal components may be understood as two superimposed electromag netic waves in the fundamental HE1 1 mode and the indicated polarization direc- tions X, Y, respectively. The directions X, Y, are traverse to the propagation direc tion of the electromagnetic wave. At the first end 1 1 1 of the PMF 1 1 , a horn antenna 1 2, which may in particular be a circular horn antenna, is arranged. In some embodiments, the PMF has a circular cross section. However, other cross sections such as a rectangular cross sections may also be used. In any case, the PMF 1 1 and the horn antenna are matched ap- propriately.

Via the horn antenna 12, the electromagnetic wave of fundamental mode HE1 1 is transformed into an electromagnetic wave of fundamental mode TE10 at the out put side of the horn antenna 1 2, having two orthogonal signal components of po larization directions X', Y\ As explained in the general description, the signal components in the X- direction and the Y-direction at the first end 1 1 1 and accordingly also the signal components in the X'-direction and the Y' direction of the electromagnetic wave emitted by the horn antenna 1 2 are arbitrary.

The horn antenna 13 radiates its electromagnetic signal into an orthomode trans- ducer 13 as generally known in the art. In the orthomode transducer, the signal is divided respectively split into its orthogonal components in the X'- direction and Y'- direction, respectively. Those signal components are separately fed into associated receiving circuits 141 a, 14b. In the receiving circuits 141 a, 141 b, the signal is de modulated and converted into the digital domain. In a superimposing unit, 142, the output signals of the receiving are superimposed to improve signal to noise ratio before further processed. In the following, reference is additionally made to Fig. 2. In the embodiment of Fig.

2, only a single receiving circuit 141 is present. The superimposition of the signal components is done between the output of the horn antenna 13 and the input of the receiving circuit 141 . For this purpose, a superimposition unit 142' is provided that superimposes the signal components with polarization directions X', Y' of the fundamental mode TE 10 mode signal as emitted by the horn antenna 13. The out put signal of the superimposing unit 142' is fed into the receiving circuit 141 as generally explained before. A phase shifting unit 143 is arranged in one of the two signal branch (in this example in the branch of for the signal component with Y'- polarization), thereby allowing the phasing between the signal components with X'-polarization and Y'-polarization to be adjusted. The phasing is controlled by the receiving circuit 141 such that the output level is always maximum.

In the following, reference is additionally made to Fig. 3. In the embodiment of Fig.

3, only a single receiving circuit 141 with a single input line is present, similar to the embodiment of Fig. 2. In the embodiment of Fig. 3, however, the two signal com ponents with X'- polarization and Y'-polarization are not superimposed. Instead, a switching unit 144 is provided into which the two signal components are fed. Either of them is forwarded to the input of the receiving circuit 141 , in dependence of the state of the switching 144. The switching unit 144 is controlled by the receiving circuit 144 to switch respectively toggle between the first signal component and the second signal component in dependence of a signal level threshold as explained in the general description. In a variant, the signal level threshold may be adaptively increased or decreased in dependence of the number of switching's in a specific time respectively time window.

In the following, reference is additionally made to Fig. 4. The embodiment of Fig. 4 is generally similar to the embodiment of Fig. 2. In contrast to the embodiment of Fig. 2, however, interface unit includes a dual polarization antenna 16 instead of the orthomode transducer 14. At the first end 1 1 1 of the PMF 1 1 respectively at the connection of the PMF 1 1 and the polarization antenna 16, a dielectric lens is 1 5 is arranged. It is noted that the dielectric lens, although it may help to increase the antenna efficiency and reduce RF-leakage, it may be omitted or exchanged by other RF energy focusing elements like tubular parts, directors, mirrors, and/or prisms.

The signal transmission from the dual polarization antenna 143 to the receiver cir cuit 141 is in this example realized by microstrip lines.

REFERENCE SIGNS

I high-frequency assembly

I I dielectric waveguide fiber / cable

I I I first cable end 1 1 2 second cable end

12 horn antenna

13 orthomode transducer

14 high-frequency circuit

141 , 141 a, 141 b receiving circuit 142, 142' superimposing unit

143 phase shifting unit

144 switching unit

1 5 dielectric lens

16 dual polarization antenna O Output signal

X, Y polarization directions (TE1 1 )

X', Y' polarization directions (HE10)