DIELECTRIC RADIO FREQUENCY (RF) BIDIRECTIONAL COUPLER WITH POWER DIVIDER/COMBINER FUNCTIONALITY

Abstract

An ultra-wideband radio-frequency bidirectional coupler with power divider/combiner functionality (200A, 200B, 300, 400A, 400B, 400C) for signals with frequency reaching up to 300 GHz, a free propagation region substrate (210) with a pair of opposed edges (240A, 240B), a first group of access ports (P-L1-P-LM) established along the at least one edge of said free propagation region substrate (210); and a second group of access ports (P-R1-P-RM) established along the opposite edge of said free propagation region substrate (210), wherein the first and second groups of access ports (P-L1-P-LM), (P-R1-P-RN) comprise dielectric waveguide structures (DW-L1-DW-LM), (DW-R1-DW-RN) providing a high-pass characteristic interconnect operating over a high frequency range starting from a low cut-off frequency f.sub.CL in the microwave range or in the millimeter-wave range.

Claims

1. A wideband and broadband radio-frequency bidirectional coupler with power divider/combiner functionality (200A, 200B, 300, 400A, 400B, 400C) for signals with frequency reaching up to 300 GHz, comprising: a free propagation region substrate (210) with a pair of opposed edges (240A, 240B); a first group of access ports (P-L1-P-LM) established along a first edge (240A) of said pair of opposed edges (240A, 240B); and a second group of access ports (P-R1-P-RM) established along a second edge (240B) of said pair of opposed edges (240A, 240B), wherein the first and second groups of access ports (P-L1-P-LM), (P-R1-P-RN) comprise: dielectric waveguide structures (DW-L1-DW-LM), (DW-R1-DW-RN) providing a high-pass filter transfer function operating over a high frequency range starting from a low cut-off frequency fez in the microwave range or in the millimeter-wave range.

2. The ultra-wideband radiofrequency bidirectional coupler (200A, 200B, 300, 400A, 400B, 400C) according to claim 1, wherein the first edge (240A) of said pair of opposed edges is shaped as an arc of a circle with radius r1 whose center OA is located closer to the second edge (240B).

3. The ultra-wideband radiofrequency bidirectional coupler (200A, 200B, 300, 400A, 400B, 400C) according to claim 2, wherein the second edge (240B) of said pair of opposed edges is shaped as an arc of a second circle with radius r2 whose center OB is located closer to the first edge (240A).

4. The ultra-wideband radiofrequency bidirectional coupler (200A, 200B, 300, 400A, 400B, 400C) according to claim 3, wherein r1=r2.

5. The ultra-wideband radiofrequency bidirectional coupler (200A, 200B, 300, 400A, 400B, 400C) according to claim 1, further comprises a plurality of arms, wherein the plurality of arms allocates the first group of access ports (P-L1-P-LM) and the second group of access ports (P-R1-P-RN).

6. The ultra-wideband radiofrequency bidirectional coupler (300) according to claim 1, wherein the dielectric waveguide structures (DW-L1-DW-LM), (DW-R1-DW-RN) are established on top of the free propagation region substrate (310).

7. The ultra-wideband radiofrequency bidirectional coupler (400A, 400B) according to claim 1, wherein the dielectric waveguide structures (DW-L1-DW-LM), (DW-R1-DW-RN) are embedded in the free propagation region substrate (310).

8. The ultra-wideband radiofrequency bidirectional coupler (200B, 300) according to claim 1, wherein the dielectric waveguide structures (DW-L1-DW-LM), (DW-R1-DW-RN) comprise tapered ends with a defined tapering profile, and wherein the first and second group of access ports (P-L1-P-LM), (P-R1-P-RN) further comprise tapered slot antennas (TSA-L1-TSA-LM), (TSA-R1-TSA-RN) providing a band-pass filter transfer function, operating over a low frequency range up to a high cut-off frequency f.sub.CH in the millimeter wave range, wherein the tapered slot antennas (TSA-L1-TSA-LM), (TSA-R1-TSA-RN) comprise a TSA tapering profile (300a, 300b, 300c), wherein the first tapered end of the dielectric waveguide structures (DW-L1-DW-LM), (DW-R1-DW-RN) lies between the tapered slot antennas (TSA-L1-TSA-LM), (TSA-R1-TSA-RN), wherein the TSA tapering profile (300a, 300b, 300c) matches the DW tapering profile.

9. The ultra-wideband radiofrequency bidirectional coupler (200B) according to claim 8, wherein the TSA tapering profile (300a) and the DW tapering profile are linear tapered.

10. The ultra-wideband radiofrequency bidirectional coupler (200B) according to claim 8, wherein the TSA tapering profile (300b) and the DW tapering profile are exponential tapered.

11. The ultra-wideband radiofrequency bidirectional coupler (200B) according to claim 8, wherein the TSA tapering profile (300c) and the DW tapering profile are FERMI tapered.

12. The ultra-wideband bidirectional coupler (700) according to claim 1 that further comprises: a low-frequency directional coupler (750) with operating frequency range starting at DC or from a low-frequency in the kilohertz range and reaching up to a low cut-off frequency f.sub.DCH in the millimeter wave range, wherein f.sub.DCH>a low cut-off frequency of dielectric waveguide structures, f.sub.CL; a plurality of transmission lines (720) and waveguide transitions that connect the low-frequency directional coupler (750) and the tapered slot antennas (TSA-L1-TSA-LM), (TSA-R1-TSA-RN) for a combined operating frequency range up to f.sub.CH.

13. The ultra-wideband bidirectional coupler (300) according to claim 16, comprising: Two first access ports (P-L1-P-L3) along the at least one edge of said free propagation region substrate (310) comprising dielectric waveguide structures (DW-L1-DW-L3) having tapered ends, Two second access ports (P-R4-P-R2) along the opposite edge of said free propagation region substrate (310) comprising dielectric waveguide structures (DW-R4-DW-R2) having tapered ends, wherein a tapered end of the dielectric waveguide structure (DW-L1) points toward a tapered end of the dielectric waveguide structure (DW-R2), wherein a tapered end of the dielectric waveguide structure (DW-R4) points towards a tapered end of the dielectric waveguide structure (DW-L1), and wherein a tapered end of the dielectric waveguide structure (DW-L3) points towards a tapered end of the dielectric waveguide structure (DW-R2).

14. The ultra-wideband bidirectional coupler (300) according to claim 13, wherein the dielectric waveguide structures (DW-L1-DW-L3), (DW-R2-DW-R4) comprise a DW tapering profile, and further comprises tapered slot antennas (TSA-L1-TSA-L3), (TSA-R2-TSA-R4) providing a low-pass characteristic interconnect, operating over a low frequency range up to a high cut-off frequency f.sub.CH in the millimeter wave range, wherein the tapered slot antennas (TSA-L1-TSA-L3), (TSA-R2-TSA-R4) comprise a TSA tapering profile (300a, 300b, 300c) around a first tapered end of the dielectric waveguide structures (DW-L1-DW-L3), (DW-R2-DW-R4) wherein the TSA tapering profile (300a, 300b, 300c) matches the DW tapering profile.

15. The ultra-wideband radiofrequency bidirectional coupler (400A, 400C) according to claim 1, wherein the dielectric waveguide structures (DW-L1-DW-LM), (DW-R1-DW-RN) comprise at least one truncated end.

16. The ultra-wideband bidirectional coupler (200A, 200B, 300, 400A, 400B, 400C) according to claim 1, wherein the free propagation region substrate (310) has a different permittivity than the dielectric waveguide structures (DW-L1-DW-LM), (DW-R1-DW-RN).

17. The ultra-wideband bidirectional coupler (200A, 200B, 300, 400A, 400B, 400C) according to claim 1, wherein the free propagation region substrate (310) comprises absorbers.

18. The ultra-wideband bidirectional coupler (400C) according to claim 1, wherein the free propagation region substrate (310) comprises dielectric material.

19. The ultra-wideband bidirectional coupler (200A, 200B, 300, 400A, 400B, 400C) according to claim 1, wherein the arc of the circle for the first group of access ports (P-L1-P-LM) is equal to the radius r2 of the arc of the second circle; and wherein the centers (OA, OB) of the two circles and are radially aligned.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] For a better understanding the above explanation and for the sole purpose of providing an example, some non-limiting drawings are included that schematically depict a practical embodiment.

[0026] FIG. 1 shows a directional coupler as is commonly understood by experts in the field of radio-frequency engineering.

[0027] FIG. 2A shows an ultra-wideband bidirectional coupler according to the present invention.

[0028] FIG. 2B shows the ultra-wideband bidirectional coupler of FIG. 2A further comprising tapered slot antennas to launch radio-frequency signals into the dielectric waveguides according to the present invention.

[0029] FIG. 3 shows a particular example of an ultra-wideband bidirectional coupler according to the present invention having four access ports.

[0030] FIG. 4A shows a 3D view of the particular example of an ultra-wideband bidirectional coupler shown in FIG. 3, where the dielectric waveguide access structures are located on top of the free propagation region substrate.

[0031] FIGS. 4B to 4D show 3D views of examples of an ultra-wideband bidirectional coupler according to the present invention where the dielectric waveguide access structures are embedded in the free propagation region substrate.

[0032] FIGS. 5A to 5H show the E-field amplitude distributions at different frequencies in the range from 20 GHz to 300 GHz of the particular example of the ultra-wideband bidirectional coupler shown in FIG. 3 according to the present invention.

[0033] FIG. 6 shows the simulated S parameter amplitude of the particular example of the ultra-wideband bidirectional coupler shown in FIG. 3 according to the present invention.

[0034] FIG. 7 shows another example of an ultra-wideband bidirectional coupler according to the present invention with extension of the operating frequency range towards lower frequencies.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0035] FIG. 2A shows a proposed dielectric structure as bidirectional coupler with power divider/combiner functionality (200A) according to the present invention. The proposed structure (200A) comprises a first group of M input access ports in the left in the figure from (P-L1) to (P-LM), which are coupled to the second group of N output access ports on the right in the figure from (P-R1) to (P-RN) via a free propagation region substrate (210). The left edge (240A) of the free propagation region, along which the access ports (P-L1) to (P-LM) are laid along, is shaped by the arc of a circle with a radius r1 whose centre OA is closer to the opposite edge (240B) of the free propagation region substrate (210). The edge (240B) of the free space propagation region, along which the output access ports (P-R1) to (P-RN) are laid along, is shaped by the arc of a circle with a radius r2 whose centre OB is closer to the opposite edge (240A) of the free space propagation region.

[0036] In a preferred implementation, the arc of the circle for input and output waveguides can have the same radius (r1=r2=r), and the centres, OA and OB, are laid in one of the port axes.

[0037] The access ports (PL1-PLM), (PR1-PRM) comprise dielectric waveguide structures, in the left in the figure from (DW-L1) to (DW-LM), and in the right in the figure from (DW-R1) to (DW-RN), all comprising tapered ends for this particular example. Advantageously, the dielectric waveguide structures couple the electromagnetic energy propagating through them into the free propagation region substrate (210), reducing the insertion losses between ports which are now proportional to the distance between the input and output ports instead of being proportional to the square spacing of the DW structures by a distance d between them which is not constrained by the far-field criterion, wherein:

[00001]$d>>2D^2/?$

where D is the largest waveguide structure dimension and A is the signal wavelength. However, DW structures emit in a specific region that shifts along its axis for varying signal frequency. Since the phase centre is close to the DW tip at high frequencies, any distance between two radiation zones fits the far-field criterion.

[0038] The separation between the access ports (PL1-PLM), (PR1-PRM) is advantageously reduced by the confinement of the electromagnetic energy within the dielectric waveguide, enabling a compact configuration without introducing crosstalk between adjacent access ports.

[0039] FIG. 2B shows a preferred implementation for another structure (200B). The structure (200B) comprises a plurality of arms that allocate the first group of access ports (PL1-PLM) and the second group of access ports (PR1-PRM). The structure (200B) includes launching structures for the radio-frequency signal in the dielectric waveguide DW, which advantageously excite only the fundamental mode of the dielectric waveguide DW for every frequency of the operating frequency range. The launching structure comprises a tapered end of the dielectric waveguide structure and a tapered slot antenna, both having the same tapering profile. In the figure, the launching structure is shown for all access ports, with tapered slot antennas on the left (TSA-L1 to TSA-LM) and on the right (TSA-R1 to TSA-RN) around the tapered end of the dielectric waveguide structures (DWL1-DWLM), (DWR1-DWRN) having a matching linear tapering profile between the tapered slot antennas and the dielectric waveguide structures.

[0040] The dielectric waveguide structures (DWL1-DWLM), (DWR1-DWRN) have a high-pass filter characteristic, enabling the electrical interconnection of radio-frequency signals with frequencies above a low cut-off frequency (f.sub.CL). The dielectric waveguide structures (DWL1-DWLM), (DWR1-DWRN) can be designed to have a low cut-off frequency (f.sub.CL) in the microwave range (i.e. between 3 GHz to 30 GHZ) or in the millimeter-wave range (i.e. between 30 GHz to 300 GHZ), e.g. at an operating frequency of 60 GHz covering a broad frequency range that extends into the Terahertz wave range (i.e. between 300 to 3000 GHZ) and beyond. Preferably, the ultra-wideband bidirectional coupler has a low cut-off frequency (f.sub.CL) of 65 GHz that can be tuned by modifying the structure dimensions.

[0041] The tapered slot antennas (TSA-L1-TSA-LM), (TSA-R1-TSA-RN) have a low-pass filter characteristic, enabling the electrical interconnection of signals from low frequencies up to a high cut-off frequency (f.sub.CH) in the millimeter-wave range. The tapered slot antenna can be designed as a transmission line with contact tips at its extreme with which establish electrical contact with the access port of the device and can be designed to operate over a range that starts at 0 Hz and extends up into the millimeter-wave range (i.e., between 30 GHz to 300 GHz, e.g., at an operating frequency of 100 GHZ).

[0042] As shown in the figure, the tapered slot antennas (TSA-L1-TSA-LM), (TSA-R1-TSA-RN) comprise a tapering profile around a first tapered end of the dielectric waveguide structures (DWL1-DWLM), (DWR1-DWRN). Preferably, the TSA tapering profile and the DW tapering is linear tapered. In other examples, different tapering profiles can be implemented, as e.g. fermi or exponential tapering.

[0043] In a preferred embodiment for wideband operation, the tapered slot antennas operate over a frequency range that starts at low frequency and extends above the low cut-off frequency of the dielectric waveguide structure (f.sub.CH>f.sub.CL, e.g., above the 60 GHZ of previous example). Preferably, the ultra-wideband bidirectional coupler has a higher cut-off frequency (f.sub.CH) of, at least, 300 GHZ. The cut-off frequency can be increased e.g. by reducing the thickness of the components of the ultra-wideband bidirectional coupler and/or by using materials with different electrical permittivity.

[0044] FIG. 3 shows another bidirectional coupler new bidirectional coupler with power divider/combiner functionality (300) according to the invention. The ultra-wideband bidirectional coupler (300) has four access ports, i.e. two input ports (P-L1 and P-L3) and two output ports (P-R4 and P-R2). The signal enters to the directional coupler through an input port (P-L1), coupling a defined amount of electromagnetic power to an output transmission port (P-R2) and another amount to a second output, known as coupled port (P-R4). There is a second input port, (P-L3), known as the isolated port.

[0045] The access ports of the ultra-wideband bidirectional coupler (300) comprise dielectric waveguide structures with tapered ends, dielectric waveguide structure (DW-L1) in the input port (P-L1), dielectric waveguide structure (DW-R2) in the transmission port (P-R2), dielectric waveguide structure (DW-R4) in the coupled port (P-R4) and dielectric waveguide structure (DW-L3) in the isolated port (P-R1). The dielectric waveguides structures provide a high-pass filter transfer function operating over a high frequency range starting from a low cut-off frequency (f.sub.CL) in the microwave range or in the millimeter-wave range.

[0046] Optionally, the access ports (P-L1), (P-R2), (P-L3) and (P-R4) can include launching structures to inject the signals into their corresponding dielectric waveguides. The launching structures comprise a tapered slot antennas and tapered ends of the dielectric waveguide, the tapers of both structures comprise the same tapering profile. The tapered slot antennas (TSA-L1), (TSA-R2), (TSA-L3) and (TSA-R4) provide a low-pass characteristic, operating over a low frequency range up to a high cut-off frequency (f.sub.CH) in the millimeter wave range. The tapered slot antennas comprise a matching pattern defining a tapered coupler, preferably a linear tapering profile around the tapered end of the dielectric waveguide at the access port which together with the corresponding tapered end of the dielectric waveguide achieves an ultra-wideband excitation of the directional coupler in a single-mode regime.

[0047] A characteristic of this structure is that allows to control the amount of power coupled from one input port to an output port from the relative angle of their respective locations at the opposite edges of the free propagation region. In FIG. 3 for the ultra-wideband bidirectional coupler (300), the input port (P-L1) electromagnetic energy is divided between the output ports, (P-R2) and (P-R4).

[0048] The maximum power coupling occurs when the dielectric waveguides of an input port and an output port are located along the same axis, as shown in FIG. 3 for the Input Port (P-L1) and the Transmission Port (P-R2) of the ultra-wideband bidirectional coupler (300). In this situation, the transmitted signal level between ports (P-L1) and (P-R2) is controlled by the (DW-L1) antenna tapering angle e and the distance between the tips of the (DW-L1, DW-R2) antenna tips, d. Both, smaller e and d lead to larger transmitted signal level.

[0049] In the example of FIG. 3, to achieve an ultra-wideband operating frequency range, the structures (DW-R2) and (DW-R4) may point to the phase centre of the structure (DW-L1). By reciprocity, the DW structures (DW-L1) and (DW-L3) may point to the phase centre of the DW structure (DW-R2). Since the phase centre of this structure varies with frequency along the antenna axis, a trade-off can be established to select the frequency for which the phase front is pointed, which sets the upper frequency limit to the bandwidth of the structure.

[0050] As shown in FIG. 3, for this example, the DW structure (DW-L1) points toward the DW structure (DW-R2). The DW structure (DW-R4) points toward the structure (DW-L1) phase centre at 260 GHz. The length c determines the distance between the phase centre and the tip of the DW structure (DW-L1). In this particular example, the DW structure (DW-L3) points towards the DW structure (DW-R2) phase centre at 260 GHz.

[0051] The coupling level between an input port and an output port when these are not in the same axis is controlled by the relative angle between their positions, as shown in FIG. 3 for the input port (P-L1) and the transmission port (P-R4) of the ultra-wideband bidirectional coupler (300). For this example, the angle a controls the coupling ratio between the input port (P-L1) and the transmission port (P-R4). By reciprocity, the angle b controls the coupling ratio between the output port (P-R2) and the isolation port (P-L3). In the figure, both angles are equal, but a and b can be designed independently to achieve different coupling ratios between ports (P-L3) and (P-R2) with respect to (P-L1) and (P-R4). The coupling ratios are reduced when the angle increases.

[0052] In this particular embodiment, the tapered slot antenna (TSA-L3) tapering profile (300a) and the DW tapering is linear tapered, as shown in the zoom of FIG. 3. However, other tapering profiles can be implemented, as e.g. wherein the tapered slot antenna (TSA-L3) tapering profile (300b) and the DW tapering profile are exponential tapered, or wherein the (TSA-L3) tapering profile (300c) and the DW tapering profile are FERMI tapered.

[0053] Other examples with different trade-offs are possible, that allows to boost the device specifications in a sub-band of interest or to increase the bandwidth. For avoiding reflections in the dielectric material, absorbers can be placed in the end of the free propagation region (310).

[0054] FIG. 4A shows a 3D view of ultra-wideband bidirectional coupler (300) when the dielectric waveguides and the free propagation region, which can be realized with materials of equal or different permittivity, are stacked, i.e. the free propagation region (310), the four DW structures (DW-L1, DW-R2, DW-L3, DW-R4) and the tapered slot antennas (TSA-L1, TSA-R2, TSA-L3, TSA-R4).

[0055] In another example, an alternative single-layer embodiment is obtained when the DW structures (DW-L1, DW-R2, DW-L3, DW-R4) are embedded within the free propagation region (310) to obtain a more compact system. The embedding implies any fabrication method that achieves to create differences in the permittivity within the free propagation region to define a dielectric waveguide structure, i.e. for example, either by etching porosities for reducing the permittivity around the DW structures or by assembling parts of different permittivity. In this respect, FIG. 4B shows a 3D view of ultra-wideband bidirectional coupler (400A), wherein the DW structures (DW-L1, DW-R2, DW-L3, DW-R4) are embedded in the free propagation region (310) and wherein the DW structures (DW-L1, DW-R2, DW-L3, DW-R4) are truncated.

[0056] FIG. 4C shows a 3D view of ultra-wideband bidirectional coupler (400B), wherein the DW structures (DW-L1, DW-R2, DW-L3, DW-R4) are embedded in the free propagation region (310) and include the launching structure tapered slot antennas (TSA-L1, TSA-R2, TSA-L3, TSA-R4) at the access ports, wherein the tapered slot antennas are established on the dielectric material of the free propagation region.

[0057] FIG. 4D shows a 3D view of ultra-wideband bidirectional coupler (400C), wherein the free propagation region (310) comprises the same dielectric material as the DW structures and wherein the DW structures have a truncated end.

[0058] The operating characteristics of the of ultra-wideband bidirectional coupler (300) of FIGS. 3 and 4A have been characterized through full-wave simulations. The obtained E-field amplitude distributions at different frequencies in the range from 20 GHz to 300 GHz are shown in FIGS. 5A to 5H. As it can be appreciated through these figures, most of the power of an incoming signal at a first port (P-L1) travels through the structure to a second port (P-R2) in a single-mode regime. A small fraction of the incoming power is diverted towards port (P-R4). As shown in the figures, a smaller amount of power of the signal arrives to port (P-L3). Due to the single-mode regime, the phase between ports can be univocally defined, which allows its use for instrumentation purposes as shown in FIG. 1.

[0059] FIG. 6 shows the simulated S parameter amplitude (in dB): S11 (601) (incoming port matching), S21 (602) (transmission between port (P-L1) and (P-R2)), S13 (603) (coupling between the incident port P-L1 and the isolated port P-L3), and S14 (604) (coupling to the coupled port (P-R4)).

[0060] The transmission between ports (P-L1, P-R2), i.e. S21 (602) stays flat from 65 GHz to at least 300 GHz. The insertion losses are, approximately 4 dB. The coupling (602) between ports (P-L1, P-R4), i.e. S14 (604) is not constant with frequency, leading to a higher coupler directivity at higher frequencies. Due to the smoothness of the curves, this effect can be easily compensated through a path calibration. The S11 (601) amplitude port matching is lower than-15 dB for the whole band, and lower than ?20 dB for frequencies greater than 80 Ghz. The isolation between ports (P-L1, P-L3), i.e. S13 (603) is greater than 25 dB in the whole band.

[0061] The ultra-wideband coupler (300) works as a bidirectional coupler. When port (P2) works as the source of incident signal, port (P-L1) works as the transmission port and port (P-L3) works as the coupled port, while port (P-R4) works as the isolated port. The matching, transmission, coupling and isolation parameters can be the same as in FIG. 6, e.g. S22-S11 (601), S12=S21 (602), S32=S41 (604), and S42=S31 (603).

[0062] If a transmitter device is connected to port (P-L1) and two receivers to ports (P-L3, P-R4), wherein (P-L4) is optional, port (P-R2) becomes a bi-directional (input and output) port. In a realistic scenario, port (P-R2) would be connected to an antenna, a waveguide or a connector. In a communication application, an antenna may be placed on port (P-R2). In instrumentation applications, port (P-R2) would be connected to the DUT (device under test). The signal received in port (P-L3) would be proportional to the DUT incident signal and the signal received in port (P-R4) would be proportional to the signal incident in the DUT.

[0063] FIG. 7 shows a coupler (700) that works with a DC extension, which is a solution to extend the operating frequency range of the bidirectional coupler (300) structure in the low frequency range, towards DC. The coupler (700) comprises the bidirectional coupler (300) and further comprises a low-frequency directional coupler (750). The low-frequency directional coupler (450) works for frequencies up to f.sub.0=65 GHz. The low-frequency directional coupler (450) comprises ports (P-L1, P-R2, P-L3, P-R4) that are connected to the transmission structures (TSA-L1, TSA-R2, TSA-L3, TSA-R4) ends through metal wires that conforms bifilar lines (720) that can be used for exciting the DW's fundamental mode for all the frequencies above f.sub.0 and suitable for the integration of the low-frequency directional coupler (700).

[0064] For frequencies above f.sub.0, the signals are efficiently coupled to the DW structures (DW-L1, DW-R2, DW-L3, DW-R4) from the ports through the structures (TSA-L1, TSA-R2, TSA-L3, and TSA-R4), as illustrated in FIGS. 5 and 6. For frequencies below f.sub.0, the signal propagates from the ports through a structures TSA though the bifilar lines (720) without being coupled to the DW structures. One of several transitions can be incorporated from the bifilar line (720) to the low-frequency directional coupler ports (P-L1, P-R2, P-L3, and P-R4). For illustrative purposes, FIG. 7 shows a low-frequency directional coupler (700) with CPW ports and the transitions between the bifilar lines (720), the CPS and the CPW waveguides.

[0065] The transitions and the low-frequency directional coupler (750) are placed in a substrate (710) that can be placed far enough over (or under) the dielectric coupler (300). Since the waves propagates in the 2D plane (in the free propagation region (210)), there is no radiation in the normal direction a compact configuration can be achieved. The distance between both couplers (300, 750) must be big-enough for avoiding near-field coupling between them.