FIELD OF THE INVENTION
[0001] The present invention relates to the field of microwave circuits and apparatuses
and more precisely to a microstrip to waveguide transition for millimetric waves embodied
in a multilayer printed circuit board. We remind that "microwaves" is a generic term
to indicate several frequency ranges for the air propagation from about 1 GHz up to
roughly 3 THz, millimetric waves correspond to the EHF range from 30 to 300 GHz (λ
= 10 to 1 mm). The embodiment of the present invention is particularly suitable to
the EHF range but there are not limitations to the application in other frequency
ranges, for example the SHF one from 3 to 30 GHz (λ = 10 to 1 cm). The invention is
referred both to a method for manufacturing the transition and the transition itself.
[0002] Nowadays the manufacturers of microwave transceivers are pressed by an increasing
demand of apparatuses operating in the range of millimetric waves, e.g. for applications
in: high/medium/low capacity radio links, point-to-multipoint networks, satellite
communications, etc. Having recourse to mass manufacturing techniques oriented to
achieve cost-effective products like the traditional Printed Circuit Boards (PCB)
are problematic in this frequency range, due to the increased dielectric losses of
the substrates and the inadequacy of the known designs to interface planar circuits
with mechanical waveguides.
BACKGROUND ART
[0003] Microstrip to waveguide transitions embodied with high-loss dielectric substrates
for PCB manufacturing are known in the art. The Applicant of the present invention
filed on 30-5-2002 an European patent application indicated as
Ref.[1] in the
REFERENCES listed at the end of the description. According to
Ref.[1] the operating frequency range of the transition was extending until to 35 GHz on
fibre reinforced glass (FR4) substrates. The multilayer board made use of a thick
copper layer as second layer of the build-up wafer structure to provide mechanical
stiffness to the FR4 substrate for the connection of a rectangular waveguide on the
bottom face. The copper layer was milled to lay bare the dielectric window of a slot
transition and obtain in the meanwhile a sort of flange around it for mounting the
waveguide. Disregarding the transition for the moment, the idea of making use of high-loss
substrates to obtain reliable and low-cost microwave circuits suitable to the automatic
or semiautomatic assembly techniques, already widely used in the manufacturing of
the PCBs, had been inherited from a preceding European patent application filed by
the same Applicant on 26/07/2001 and presently indicated as
Ref.[2]. This second application was describing a chip-on-board (COB) technology which allowed
to integrate on the substrate many parts of the transceiver, in particular it was
possible to accommodate on the substrate both the surface mounting components and
those in-chip (either discrete or MMIC) with the relevant polarisation circuitry,
so as the conventional waveguide transition that constituted the radio interface of
the transceiver. The frequency of 80 GHz was the theoretical limit depending on the
minimum width Wm of the microstrip and the thickness h of the FR4 layer allowed by
the technology. Having considered Wm = 200 µm the width of the microstrip, and λ/Wm
= 10 as a good design parameter, then in order to obtain 50 Ω value for the characteristic
impedance of the microstrip the thickness of the FR4 layer was h = 100 µm. The optimistic
value of 80 GHz had been calculated for the only wave propagation along the microstrip
without taking into due consideration the effects of microstrip to waveguide transitions.
Because the invention that will be disclosed is referred to an alternative embodiment
to the transition of
Ref.[1] capable to really operate up to 80 GHz, some details of the embodiment at
Ref.[1] are needed in order to appreciate the improvements.
Figures 1a, 1b, 2a, 2b, and
3 disclose those details.
[0004] Fig.1a shows a metallic layout laid down on the upper face of a dielectric FR4 substrate
belonging to a multilayer structure. The layout includes a microstrip which extends
along the longitudinal symmetry axis of the substrate and terminates with a metal
patch. The microstrip and the remaining circuitry (not visible for simplicity) are
encircled by a shielding metallic layout delimiting a rectangular unmetallized window,
corresponding to a dielectric window, entered by the patched microstrip. The perimetrical
metallization of the dielectric window is shaped as a rectangular frame with four
unmetallized circle at the four corners in correspondence of threaded holes through
the multilayer structure.
Fig.1b shows a thick copper layer glued to the bottom face of the dielectric substrate to
form a metal core giving stiffness to the multilayer structure and constituting a
ground plane for the upper microstrip. The metal core is milled and completely removed
to lay bare the dielectric substrate in correspondence of the dielectric window, so
that the patch is visible from the rear due to the semitransparency of the FR4 layer.
Fig.2a is a cross-section along the axis A-A of
fig.1a. The figure shows the structure of the multilayer including three dielectric substrates,
and the metal core. The upper and the lower dielectric substrates are metallized wile
the interposed one is used as insulator. The end of a rectangular waveguide joins
the rectangular window milled in the metal core in correspondence of the dielectric
window of the upper substrate, so that the opening in the metal core is a continuation
of the waveguide to the dielectric window of the substrate. A metallic lid placed
upon the frame of the upper face is fixed to the multilayer structure by means of
four screws at the corner of the frame penetrating into the upper dielectric substrate,
the metal core (flange) and the walls of the rectangular waveguide. The metallic lid
is a hollow body with a rectangular recess faced to the unmetallized window. In operation,
the patched end of the microstrip which comes into the dielectric window acts as an
electromagnetic probe for radiating into the closed space around it. The dimensions
of the patch are calculate so as to transfer the energy from the feeding microstrip
to the waveguide efficiently. The screwed metallic lid is used as a reflector to prevent
propagation from the patch in the opposite direction to the waveguide. To this aim
the recess of metallic lid acts as a back short for the signal. From the above considerations
it can be conclude that the probe and the dielectric window in communication with
the waveguide constitute a microstrip to waveguide transition that transforms the
"quasi-TEM" propagation mode of the microstrip into the TE
10 mode of the rectangular waveguide. The electromagnetic properties of the transitions
are reciprocal, so that the same structure used by the RF transmitter for conveying
inside the waveguide a transmission signal from the microstrip is also used by the
receiver for conveying a RF reception signal from the waveguide to the microstrip.
[0005] Fig.2b shows a series of metallized through holes (via-holes visible in
Fig.2a) regularly spaced along the frame. These via-holes around the transition zone have
been introduced successively the filing of
Ref.[1] to the aim of improving the performances of the transition at the higher frequencies
(35.5 GHz) of the operating range. This statement is possible because the transition
at
Ref.[1] and the transition of the present invention are both developed in the laboratories
of the same Applicant. The via-holes supply to the lack of continuity of the waveguide
through the thickness of the dielectric substrate around the zone of the transition.
Thanks to via-holes, the energy is bound inside the parallelepipedal part of the dielectric
substrate adjacent to the air cavity of the waveguide, otherwise the propagation through
the dielectric substrate outside the zone of the transition would constitute a cause
of losses. Furthermore, the via-holes supply the upper lid with ground contacts distributed
around the transition, improving the poor contact provided by the screws at the four
corners of the frame.
Fig.3 is a photography of the layout of the transceiver which depicts the real arrangement
of via-holes; as it can be noticed, several rows of metallized holes are needed to
a satisfactory operation in the SHF range (not in the EHF).
[0006] Despite of the manufacturing simplicity of the transition illustrated in the above
figures, any attempts to arrange it to the be used in the EHF range has been concluded
with a failure due to unacceptable power loss and distortion introduced by the transition.
From the analysis of the main causes of these failures it results that at the millimetric
waves:
- 1. Via-holes are not more able to bound the electromagnetic field into the encircled
parallelepipedal part of the dielectric substrate. The drawback is due to the fact
that diameters and reciprocal distances of the holes are comparable with the used
wavelength and can not be further reduced cause unavoidable technological limitations
of the via-hole process.
- 2. The thickness of the dielectric substrate is no more completely negligible in comparison
with the wavelength of the signal, as a consequence via-holes don't connect to the
ground the upper lid efficiently. As a consequence the lid couldn't be considered
as a continuation of the waveguide opportunely terminated at the top, and a mismatch
between the two sides of the patch may generates unwanted reflections and of spurious
resonating modes.
- 3. Losses inside the dielectric part of the transition is excessive due to the poor
performances of the semi-valuable substrate.
[0007] The european patent application indicated in
Ref.[5] discloses a high-frequency package comprising a dielectric substrate, a high-frequency
element that operates in a high-frequency region and is mounted in a cavity formed
on said dielectric substrate, and a microstrip line formed on the surface or in an
inner portion of said dielectric substrate and electrically connected to said high-frequency
element, wherein a signal transmission passage of a waveguide is connected to a linear
conducting passage or to a ground layer constituting the microstrip line. In the junction
portion of the waveguide, for example, an end of the linear conducting passage is
electromagnetically opened, so that the end portion works as a monopole antenna inside
the waveguide that is connected.
[0008] The aforementioned high-frequency package has been designed to operate at millimetric
waves using costly and rigid substrate materials having a low dielectric constant
and small losses (e.g. alumina). Moreover, the complicated structure makes the sealing
of the multilayer to the waveguide and the application of an upper closing lid both
difficult to obtain. Another difficult arises in correctly terminating the irradiating
microstrip inside the waveguide.
OBJECT OF THE INVENTION
[0009] The main object of the present invention is that to overcome the drawbacks of the
known art and indicate a microstrip to waveguide transition obtainable on PCBs arranged
for operating at the microwaves with good performances in the nearest EHF range (up
to 80 GHz)
SUMMARY AND ADVANTAGES OF THE INVENTION
[0010] The invention achieves said object by providing a method to manufacture a microstrip
to waveguide transition, as disclosed in the method claims.
[0011] Other object of the invention is a microstrip to waveguide transition obtained according
to the method, as disclosed in the device claims.
[0012] According to the invention, the transition disclosed at
Ref.[1] is now completely redesigned in order to remove almost completely the former dielectric
diaphragm from the space of the transition. Prevalently air fills up the propagation
space of the electromagnetic waves in the new transition; with that the drawback highlighted
at point 3 is overcome. Another fundamental difference from the prior art is that
the waveguide now penetrates the dielectric substrate to connect the metallic lid,
without breaking the continuity of the metallic walls, except for the two grooves
whose effect is completely marginal. In other words, the frame of via-holes is completely
unnecessary to confine the electromagnetic field, and also the drawbacks highlighted
at points 1 and 2 are overcome.
[0013] Advantageously, the waveguide part of the transition and the other mechanic part
of the transceiver can be obtained by means of numerical control manufacturing techniques
starting from a rough metal block. Microstrip to waveguide transitions for rectangular
waveguides according to the present invention are the easiest to obtain, but the same
approach is applicable to obtain transitions for circular or elliptic waveguides.
[0014] Being all causes of losses and misoperation imputable to the only transition removed,
the upper frequency limit due to the microstrip on PCBs technique, for example 80
GHz, is now fully exploitable from the transceiver.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The features of the present invention which are considered to be novel are set forth
with particularity in the appended claims. The invention and its advantages may be
understood with reference to the following detailed description of an embodiment thereof
taken in conjunction with the accompanying drawings given for purely non-limiting
explanatory purposes and wherein:
- figures 1a to 3, already described, show a microstrip to waveguide transition according to the prior
art mentioned at Ref.[1];
- figures 4a to 4d show some manufacturing steps of the multilayer and the waveguide according to the
method of the invention;
- figures 5a to 5d show a top view, a longitudinal, and transversal cross section views of the transition
according to the invention;
- figures 6a and 6b show a perspective simulation model and relevant parameters of the transition according
to the invention;
- figures 7 and 8 show the S11 and S21 parameters of the simulated model;
- fig. 9a shows a top view of two transition back-to-back used for measures;
- fig. 9b shows a photography of the back-to-back transition of fig.9a;
- figures 10. and 11 show the S11 and S21 parameters really measured at the ends of the back-to-back arrangement of fig.9a;
- fig. 12 shows a top view of a microstrip to circular waveguide transition, without the upper
lid.
DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION
[0016] As a description rule, in the several figures of the drawings like referenced numerals
identify like elements. Besides, the various elements represented in the figures are
not a scaled reproduction of the original ones. With reference to
fig.4a we see a partial upper face of a dielectric substrate 1 belonging to a known multilayer
structure presently used to obtain the circuitry of a transceiver operating nearby
60 GHz (EHF range) employing traditional PCB techniques. The multilayer structure
is a simpler version of the one disclosed at
Ref.[1] limited to include a thin dielectric substrate 1, characterized by high dielectric
losses in comparison with alumina or Gallium Arsenide substrates traditionally used
for EHF applications, made adherent to a thick copper plate giving the needed stiffness
to the planar structure. A microstrip to waveguide transition, and vice versa, used
to connect both the transmitter and the receiver amplifiers to the same antenna by
means of a duplexer, is the only part of the transceiver the present invention is
concerned with. The substrate 1 gives support to a metallic layout including among
other things a microstrip 2 placed along the axis of longitudinal symmetry of the
figure. The microstrip 2 terminates with a small patch 3 nearby the centre of a stripe
4 placed between two symmetric rectangular windows 5 and 6 obtained from the removal
of the multilayer by milling (or drilling and sawing) according to the known techniques.
The area of the two windows 5 and 6 prevails with respect to the area of the central
stripe 4 so that the space of the transition is filled prevalently with air. A metallization
7 encircles, as a frame, the two symmetric windows 5 and 6 and the central stripe
4, leaving a short passage free for the microstrip 2, but having a finger 7a covering
the stripe 4 for a short tract opposite to the patch 3. Several metallized thorough
holes 8 are regularly spaced along the perimeter of the frame 7. The only purpose
of these holes is that of avoiding possible detachments of the upper dielectric layer
from the metal core (plate) as a consequence of the milling operation for opening
the windows 5 and 6, because of the not perfect physical compatibility at the interface
between the two layers.
[0017] In
fig.4b a partial top view of the mechanical part 9 of the transceiver is depicted.
The mechanic is manufactured in a way to include the end of a rectangular waveguide
10. The internal cavity 11 of the metallic waveguide10 is filled up with air. Two
rectangular grooves 12 and 13 are milled for all the thickness of the two longer walls
at the extremity of the waveguide 10, along the symmetry axis. Four threaded holes
14 are visible at the four corners of the mechanical part 9. The dimensions of the
two windows 5 and 6 and the width of the stripe 4 are set to accommodate at the same
time the stripe 4 into the grooves 12 and 13 at the edge of the waveguide 10 and the
edge of the waveguide 10 inside the windows 5 and 6, as far as the depth of the grooves
12 and 13 allows it. With reference to
figures 4c and
4d, before this accommodation takes place part of the metal core must be removed from
the stripe 4.
Fig.4c and
fig.4d show the metal core before and after removal, respectively. An indication of the
real placement of the internal cross-section 11 of the waveguide 10 is added with
dashed line in
fig.4d. It can be appreciated that the stripe 4 is free from metal in correspondence of the
cavity of the microwave 10, so that the tract of the patched microstrip 2, 3 penetrating
the cavity 11 is free to radiate as a probe inside the waveguide 10.
[0018] Fig.5a shows a top view of the assembly constituted by the multilayer of
fig.4a superimposed to the mechanic of
fig.4b so as they can interpenetrate. Two axes A-A and B-B are indicated in the figure as
reference planes for the cross-sections reported in the successive figure.
Fig.5b shows the cross-section along the longitudinal symmetry axis A-A of fig.5a. With
reference to
fig.5b, the edge of the waveguide 10 emerges from the openings 5 and 6 and a metallic lid
16 is leant on it. The lid 16 is fastened to the waveguide 10 by means of screws 17
penetrating the four threaded holes 14 (fig.4b). The lid 16 includes a central hollow
18 shaped as a very short tract of waveguide 10 closed at the end. By comparison with
the prior art of
fig.2a, the lid 16 is now connected to the waveguide without any interposed dielectric layer,
so that the metallic continuity of the walls of the waveguide 10 is never interrupted
across the transition until the lid is reached. In this way the back currents reflected
from the lid reach the ground directly and, as a consequence, via-holes around the
transition as in
fig.2b are unneeded for the reasons stated before. Grooves 12 and 13 have different depths,
the first one (12) is deeper than second one (13) to also include the copper finger
15a (fig.4d). The highlighted dissymmetry on the two depths is a consequence of the
dissymmetric layout on the stripe 4, which bears a microstrip on the left part wile
the right part is bare. More precisely, the microstrip 2 stops to be a as such only
at the end of the groove 12, whose depth is calculated accordingly. Moreover the depth
of both the grooves 12 and 13 shall be calculated to assure a certain free space between
the end of the waveguide 10 and the microstrip 2, and considering that a certain tolerance
on the width of the grooves 12 and 13 is foreseen for the insertion of the stripe
4 without problems, as visible in fig.5a, the substrate 1 has to be fixed to the mechanic
1. Two holes 19, visible in
fig.5a, are part of a number of them drilled in the multilayer and the mechanic 9 to align
the planar circuit with respect to the waveguide 10 and fasten them to the mechanic.
Figures 5c and
5d show the cross-sections along the transversal symmetry axis B-B and C-C of fig.5a,
respectively. The observation of these figures further clarifies the arguments already
developed in the description of the preceding ones and not additional description
is needed.
[0019] In the operation, the transition has been designed to operate in the range of 55-60
GHz in accordance with the market request for the transceiver apparatuses. The mechanic
is worked by a numerical control machine so as to obtain a WR15 (1.88 x 3.76 mm) waveguide.
The planar circuitry is obtained starting form a multilayer including a dielectric
substrate 0.1 mm thick glued to a copper metal plate (core) 2 mm thick is used. The
selected dielectric substrate is known with its commercial name Roger
™ 4350, having losses measured by a tanδ = 0.037 at 10 GHz, as declared by the manufacturer;
this value clearly increases in the operating frequency range of the transition. Roger™
is similar to FR4 or "vetronite"™ used to manufacture the transition cited at
Ref.[1], to say, a material made of glass fibres impregnated with epoxy resin having tanδ
from 0,025 to 0,05. These values of tanδ are typical for PCBs but not immediately
for microwave circuits where alumina imposes with a tan δ = 0,0001. The electromagnetic
coupling between the microstrip 2 and the waveguide 10 is obtained by means of a probe
laying on the E-plane of the rectangular waveguide 10 and terminating with the small
patch 3. This probe has been obtained as continuation of the microstrip 2 inside the
cavity 11 of the waveguide 10 after having removed the ground plane below. The edge
of the waveguide 10 emerges from the multilayer in the zone of the transition, as
far as the depth of grooves 12 and 13 allows it, and joins the edge of the lid 16.
The top wall of lid 16 acts as a short circuit reflecting back the signal toward the
patch 3. The latter has to see an open circuit on its plane for the reflected signal
in order to keep it matched to the waveguide 10. The required impedance transformation
is obtained by milling the length of tract 18 in a way that the distance of the plane
of the patch 3 from the short circuit plane internal to lid 16 is about λ/4. To complete
the analysis of the transition, the effect of two slots delimited by lid 16 and either
grooves 12 or 13 must be considered. There are not problems with these slots because
their transversal dimensions are such they behave as two under-cut waveguides in the
55-60 GHz frequency range. Besides, the slots are longer than few λ and the effect
of non-propagating modes is negligible, so that the electromagnetic field is completely
confined in the volume of the transition, diversely from the via-holes of the prior
art.
[0020] A first design of the 55-60 GHz transition has been performed roughly calculating
the dimensions of its relevant parts with the help of two canonical books cited at
Ref.[3] and
Ref.[4]. The design has been refined successively by several simulation sessions performed
by means of the electromagnetic simulator 3D Agilent™ HFSS operating on the model
shown in
fig.6a. The goal is that to optimize the probe dimensions, inclusive of patch 3, for operating
in the desired band maintaining the bandwidth and matching conditions as far as possible
unaffected by mechanical and assembly tolerances. With reference to
fig.6a, we see the model including the dielectric stripe 4 leant on the edge of the waveguide
10 transversally to its rectangular cavity 11. This model also includes the slot comprised
between groove 12 and lid 16, containing the relevant tract of microstrip 2. The terminal
part of the probe with the patch 3 is modelled inside the cavity 11 and represented
with greater details in
fig.6b. With reference to
fig.6b, we see the microstrip 2 and patch 3 shaped as a
T. The base of the rectangular patch 3 perpendicular to the microstrip 2 has a length
c greater than the height
b, but this is not a general rule. Labels
w and
h indicate respectively the longer and the shorter dimensions of the rectangular cavity
11, while label
a indicates the length of the microstrip 2 (without copper below) inside the cavity
11 from the internal sidewall 12 to the base of the patch 3; i.e.: the length of the
line which carries the signal to the patch 3. The simulation is carried out considering
a WR15 (1.88 x 3.76 mm) waveguide; with that:
h = 0.5w. The simulation results have confirmed that the central frequency of the transition
depends on the ratio (a+b)/w, while the adaptation level at the input and the output
ports depends on the ratio c/b inside the considered bandwidth. Generally speaking,
the greater the ratio (a+b)/w (i.e. the patch nearer to the centre of the cavity)
the lower is the central frequency fo of the transition. Besides, once w (3.76 mm)
is selected in accordance with standard design rules for rectangular waveguides operating
in the proximity of the desired central frequency fo (58 GHz), and (a+b)/w is set
to obtain the exact fo, then b (and hence a) and c are optimized in the desired frequency
band independently of the exact fo previously set. For the operating band of 55-60
GHz, the values of (a+b)/w = 0,18 and c/b = 2.22 are found to be optimal. The results
of simulations are reported in
figures 7 and
8 which concern the scattering parameters
S11 and
S21 versus frequency, respectively. With reference to
fig.7, we see that the reflection coefficient
S11 never falls below 20 dB in the considered band, while in
fig.8 the maximum insertion loss
S21 is about 0.1 dB.
[0021] In order to check the soundness of simulations and the actual performances of the
transition, a prototype with two transitions connected back-to-back by a central microstrip
has been realized, as the one depicted in
fig.9a photographed in
fig.9b. The left part of
fig.9a is a mirror image of the transition of
fig.5a. The adaptation at one input port of the double structure is measured after having
closed the other port on a matched load, therefore the measure concerns the whole
matching of the two transitions. The measured scattering parameters
S11 and
S21 versus frequency are reported in
figures 10 and
11, respectively. With reference to
fig.10, we see that the reflection coefficient
S11 is never worse than 10 dB in the considered band. The insertion loss parameter
S21 reported in
fig.11is strongly influenced by the central microstrip which interconnect the two transitions.
In fact, the 20 mm length (about 7λ) of the microstrip causes losses of about 1.5
dB, as a consequence each transition contributes to the measure with about 1.25 dB.
[0022] Fig.12 shows a top view of a microstrip to circular waveguide transition, without the upper
lid, the embodiment of which is directly achievable from the preceding description
of the microstrip to rectangular waveguide transition. The same applies for a microstrip
to elliptic waveguide transition (not represented in the figure).
REFERENCES
1. Method to manufacture a microstrip to waveguide transition, wherein the transition
comprises:
- a multilayer structure comprising at least a dielectric substrate (1) of the type
usable in the technology of printed circuits boards;
- the multilayer substrate is provided on a rigid metal plate (15);
- a metallic layout (2, 3, 7) is supported by the dielectric substrate (1);
- wherein the metallic layout (2, 3, 7) includes: a microstrip (2) terminating with
a patch (3) acting as a probe for coupling the microstrip (2) to a waveguide (10)
through the dielectric substrate (1); and two windows (5, 6) symmetric to a longitudinal
axis of the metallic layout (2, 3, 7), separated to each other by a central strip
(4) bearing the probe;
the method includes the steps of:
- removing the multilayer (1), the rigid metal plate (15) and the metallic layout
(2, 3, 7) in correspondence to the two windows (5, 6);
- removing the rigid metal plate placed below the strip (4) at least in the region
between the windows; milling two rectangular grooves (12, 13) of given depth for all
the thickness of two opposite walls at the extremity of the waveguide (10) along the
symmetry axis;
- the dimensions of the two windows (5,6) and the width of the strip (4) are set to
accommodate at the same time the strip (4) into the grooves (12,13) at an edge of
the waveguide (10) and said edge of the waveguide (10) inside the windows (5,6), as
far as the depth of the grooves (12,13) allows it;
- fastening a metallic lid (16) to the edge of the waveguide (10) emerging from the
two sides (5, 6) of the strip (4) for reflecting back to the waveguide (10) the power
radiated by the probe (3) in the opposite direction.
2. The method of claim 1, characterized in that the whole area of the two windows (5, 6) at the two side of the stripe (4) prevails
with respect to the area of the central stripe (4), so that the space of the transition
is filled up prevalently with air.
3. The method of claim 1 or 2, characterized in that includes the step of aligning the metallic layout (2, 3, 7) with respect to the waveguide
(10) and fastening the multilayer to a metallic support body (9) which has been worked
to obtain the waveguide (10).
4. The method of any claim from 1 to 3, characterized in that includes the step of removing the rigid metal plate (15) from said stripe (4) at
least in correspondence of the cavity (11) of the waveguide (1 0) crossed by the stripe
(4).
5. The method of claim 4, characterized in that includes the step of milling in the body of said lid (16) a central hollow (18) shaped
as a short tract of said waveguide (10) with a depth of about λ/4.
6. The method of any claim from 1 to 5, characterized in that before opening said windows (5, 6) in the multilayer (1,15), a drilling and a metallizing
step are performed to encircle said windows (5,6) and the stripe (4) with metallized
through holes (7,8) to avoid possible detachments between the dielectric layer (1)
and the rigid metal plate (15).
7. The method of any preceding claim, characterized in that said windows (5, 6) opened in the multilayer (1, 15) have rectangular shape.
8. The method of any claim from 1 to 7, characterized in that includes the step of setting the central frequency of the transition by fixing a
corresponding value of the ratio (a+b)/w, were: w is the longer cavity dimension of a rectangular waveguide whose shorter dimension
holds known ratio with w, a is the length of the line which carries the signal to the patch (3), and b is the
base of the patch (3) shaped as a rectangle perpendicular to the microstrip (2).
9. The method of claim 8, characterized in that includes the step of optimizing the adaptation at the input and the output ports
inside the desired frequency band by fixing the ratio c/b, where c is the height of the rectangular patch inside the considered bandwidth; wherein the
desired frequency band spans 55 to 60 GHz; wherein a dielectric layer (1) with relative
dielectric constant εr of approximately 3.54 is used and wherein the thickness is about 100 µm, the value
of (a+b)/w is about 0,18 and the value of c/b is about 2.22.
10. Microwave to waveguide transition manufactured with the method according to any of
the claims 1 to 9.
11. The transition of claim 10, characterized in that the two opposite grooves (12, 13) have different depths and the deeper one includes
the microstrip (2) inclusive of the rigid metal plate (1 5).
12. The transition of claim 11, characterized in that the two opposite grooves (12,13) have transversal dimensions such they behave as
two under-cut waveguides in the desired frequency range of the transition able to
confine the electromagnetic field in the volume of the transition.
13. The transition of any claim from 10 to 12, characterized in that said waveguide (10) is rectangular.
14. The transition of any claim from 10 to 12, characterized in that said waveguide (10) is circular.
15. The transition of any claim from 10 to 12, characterized in that said waveguide (10) is elliptic.
16. The transition of any claim from 10 to 15, characterized in that includes a crown of metallized through holes (7, 8) which contains the edge of the
waveguide (10) at the two sides of the stripe (4) to avoid possible detachments between
the dielectric layer (1) and the rigid metal plate (15).
1. Verfahren zum Herstellen eines Mikrostreifenleiter-Hohlleiter-Übergangs, wobei der
Übergang Folgendes umfasst:
- eine Mehrschichtstruktur, die mindestens ein dielektrisches Substrat (1) von dem
Typ umfasst, der in der Technologie der gedruckten Leiterplatten verwendet werden
kann;
- wobei das Mehrschichtsubstrat auf einer starren Metallplatte (15) bereitgestellt
wird;
- ein metallisches Layout (2, 3, 7) von dem dielektrischen Substrat (1) gestützt wird;
- wobei das metallische Layout (2, 3, 7) Folgendes enthält: einen Mikrostreifenleiter
(2), der mit einem Patch (3) endet, das als eine Sonde dient zum Koppeln des Mikrostreifenleiters
(2) an einen Hohlleiter (10) durch das dielektrische Substrat (1); und zwei Fenster
(5, 6), die symmetrisch zu einer Längsachse des metallischen Layouts (2, 3, 7) sind,
voneinander durch einen die Sonde tragenden zentralen Streifen (4) getrennt;
wobei das Verfahren die folgenden Schritte beinhaltet:
- Entfernen der Mehrfachschicht (1), der starren Metallplatte (15) und des metallischen
Layouts (2, 3, 7) entsprechend den beiden Fenstern (5, 6);
- Entfernen der unter dem Streifen (4) platzierten starren Metallplatte mindestens
in dem Gebiet zwischen den Fenstern; Fräsen von zwei rechteckigen Nuten (12, 13) mit
gegebener Tiefe für die ganze Dicke von zwei gegenüberliegenden Wänden an dem Endpunkt
des Hohlleiters (10) entlang der Symmetrieachse;
- die Abmessungen der beiden Fenster (5, 6) und die Breite des Streifens (4) sind
derart eingestellt, dass gleichzeitig der Streifen (4) in die Nuten (12, 13) an einer
Kante des Hohlleiters (10) aufgenommen wird und die Kante des Hohlleiters (10) innerhalb
der Fenster (5, 6) soweit wie die Tiefe der Nuten (12, 13) dies gestattet;
- Befestigen eines metallischen Deckels (16) an der Kante des Hohlleiters (10), aus
den beiden Seiten (5, 6) des Streifens (4) auftauchend, um die von der Sonde (3) in
der entgegengesetzten Richtung abgestrahlte Leistung zurück zum Hohlleiter (10) zu
reflektieren.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass der ganze Bereich der beiden Fenster (5, 6) auf den beiden Seiten des Streifens (4)
bezüglich des Bereichs des zentralen Streifens (4) überwiegt, so dass der Raum des
Übergangs überwiegend mit Luft gefüllt ist.
3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass es den Schritt des Ausrichtens des metallischen Layouts (2, 3, 7) bezüglich des Hohlleiters
(10) und des Befestigens der Mehrfachschicht an einen metallischen Trägerkörper (9),
der bearbeitet worden ist, um den Hohlleiter (10) zu erhalten, beinhaltet.
4. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, dass es den Schritt des Entfernens der starren Metallplatte (15) von dem Streifen (4)
mindestens entsprechend dem Hohlraum (11) des Hohlleiters (10), der von dem Streifen
(4) gekreuzt wird, beinhaltet.
5. Verfahren nach Anspruch 4, dadurch gekennzeichnet, dass es den Schritt beinhaltet, in dem Körper des Deckels (16) eine zentrale Aushöhlung
(18) zu fräsen, die als ein kurzer Teil des Hohlleiters (10) mit einer Tiefe von etwa
λ/4 geformt ist.
6. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass vor dem Öffnen der Fenster (5, 6) in der Mehrfachschicht (1, 15) ein Bohr- und ein
Metallisierungsschritt durchgeführt werden, um die Fenster (5, 6) und den Streifen
(4) mit metallisierten Durchgangslöchern (7, 8) zu umgeben, um mögliche Ablösungen
zwischen der dielektrischen Schicht (1) und der starren Metallplatte (15) zu vermeiden.
7. Verfahren nach einem der vorhergehenden Ansprüche, dadurch gekennzeichnet, dass die in der Mehrfachschicht (1, 15) geöffneten Fenster (5, 6) eine rechteckige Gestalt
aufweisen.
8. Verfahren nach einem der Ansprüche 1 bis 7, dadurch gekennzeichnet, dass es den Schritt des Einstellens der Mittenfrequenz des Übergangs durch Fixieren eines
entsprechenden Werts des Verhältnisses (a+b)/w beinhaltet,
wobei w die längere Hohlraumabmessung eines rechteckigen Hohlleiters ist, dessen kürzere
Abmessung das bekannte Verhältnis mit w enthält, a die Länge der Leitung ist, die das Signal zu dem Patch (3) trägt, und b die Basis des Patch (3) ist, als ein Rechteck senkrecht zum Mikrostreifenleiter (2)
ausgebildet.
9. Verfahren nach Anspruch 8, dadurch gekennzeichnet, dass es den Schritt des Optimierens der Adaptation der Eingangs- und Ausgangsports innerhalb
des gewünschten Frequenzbandes durch Fixieren des Verhältnisses c/b beinhaltet, wobei
c die Höhe des rechteckigen Patch innerhalb der betrachteten Bandbreite ist; wobei
das gewünschte Frequenzband 55 bis 60 GHz überspannt; wobei eine dielektrische Schicht
(1) mit einer relativen Dielektrizitätskonstante εr von etwa 3,54 verwendet wird und wobei die Dicke etwa 100 µm beträgt, der Wert (a+b)/w
etwa 0,18 beträgt und der Wert von c/b etwa 2,22 beträgt.
10. Mit dem Verfahren nach einem der Ansprüche 1 bis 9 hergestellter Mikrowellen-zu-Hohlleiter-Übergang.
11. Übergang nach Anspruch 10, dadurch gekennzeichnet, dass die beiden gegenüberliegenden Nuten (12, 13) unterschiedliche Tiefen aufweisen und
die tiefere den Mikrostreifenhohlleiter (2) einschließlich der starren Metallplatte
(15) enthält.
12. Übergang nach Anspruch 11, dadurch gekennzeichnet, dass die beiden gegenüberliegenden Nuten (12, 13) Querabmessungen derart aufweisen, dass
sie sich als zwei hinterschnittene Hohlleiter in dem gewünschten Frequenzbereich des
Übergangs verhalten, die in der Lage sind, das elektromagnetische Feld in dem Volumen
des Übergangs zu begrenzen.
13. Übergang nach einem der Ansprüche 10 bis 12, dadurch gekennzeichnet, dass der Hohlleiter (10) rechteckig ist.
14. Übergang nach einem der Ansprüche 10 bis 12, dadurch gekennzeichnet, dass der Hohlleiter (10) kreisförmig ist.
15. Übergang nach einem der Ansprüche 10 bis 12, dadurch gekennzeichnet, dass der Hohlleiter (10) elliptisch ist.
16. Übergang nach einem der Ansprüche 10 bis 15, dadurch gekennzeichnet, dass er eine Krone aus metallisierten Durchgangslöchern (7, 8) enthält, die die Kante
des Hohlleiters (10) an den beiden Seiten des Streifens (4) enthält, um mögliche Ablösungen
zwischen der dielektrischen Schicht (1) und der starren Metallplatte (15) zu vermeiden.
1. Procédé de fabrication d'une transition de microruban à guide d'ondes, dans lequel
la transition comprend :
- une structure multicouche comprenant au moins un substrat diélectrique (1) du type
utilisable dans la technologie des cartes de circuits imprimés ;
- le substrat multicouche est prévu sur une plaque de métal rigide (15) ;
- une topologie métallique (2, 3, 7) est supportée par le substrat diélectrique (1)
;
- dans lequel la topologie métallique (2, 3, 7) inclut : un microruban (2) se terminant
avec une fiche (3) agissant comme une sonde pour coupler le microruban (2) à un guide
d'ondes (10) par l'intermédiaire du substrat diélectrique (1) ; et
- deux fenêtres (5, 6) symétriques par rapport à un axe longitudinal de la topologie
métallique (2, 3, 7), séparées l'une de l'autre par une bande (4) centrale portant
la sonde ;
le procédé inclut les étapes de :
- suppression de la multicouche (1), de la plaque de métal rigide (15) et de la topologie
métallique (2, 3, 7) en correspondance aux deux fenêtres (5, 6) ;
- suppression de la plaque de métal rigide placée en-dessous de la bande (4) au moins
dans la région entre les fenêtres ; fraisage de deux rainures (12, 13) rectangulaires
de profondeur donnée pour la totalité de l'épaisseur de deux parois opposées à l'extrémité
du guide d'ondes (10) le long de l'axe de symétrie ;
- les dimensions des deux fenêtres (5, 6) et la largeur de la bande (4) sont fixées
de façon à recevoir en même temps la bande (4) dans les rainures (12, 13) au niveau
d'un bord du guide d'ondes (10) et ledit bord du guide d'ondes (10) à l'intérieur
des fenêtres (5, 6), tant que la profondeur des rainures (12, 13) le permet ;
- fixation d'un couvercle métallique (16) sur le bord du guide d'ondes (10) émergeant
des deux côtés (5, 6) de la bande (4) pour réfléchir en retour vers le guide d'ondes
(10) l'énergie rayonnée par la sonde (3) dans la direction opposée.
2. Procédé selon la revendication 1, caractérisé en ce que la totalité de la superficie des deux fenêtres (5, 6) au niveau des deux côtés de
la bande (4) prévaut par rapport à la superficie de la bande (4) centrale, de sorte
que l'espace de la transition est rempli de façon prévalente avec de l'air.
3. Procédé selon la revendication 1 ou 2, caractérisé en ce qu'il inclut l'étape d'alignement de la topologie métallique (2, 3, 7) par rapport au
guide d'ondes (10) et de fixation de la multicouche à un corps de support métallique
(9) qui a été travaillé pour obtenir le guide d'ondes (10).
4. Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce qu'il inclut l'étape de suppression de la plaque de métal rigide (15) de ladite bande
(4) au moins en correspondance de la cavité (11) du guide d'ondes (10) traversée par
la bande (4).
5. Procédé selon la revendication 4, caractérisé en ce qu'il inclut l'étape de fraisage dans le corps dudit couvercle (16) d'un creux (18) central
formé comme une courte zone dudit guide d'ondes (10) avec une profondeur d'environ
λ/4.
6. Procédé selon l'une quelconque des revendications 1 à 5, caractérisé en ce qu'avant l'ouverture desdites fenêtres (5, 6) dans la multicouche (1, 15), une étape
de perçage et de métallisation est mise en oeuvre pour encercler lesdites fenêtres
(5, 6) et la bande (4) avec des trous traversants (7, 8) métallisés pour éviter des
détachements possibles entre la couche diélectrique (1) et la plaque de métal rigide
(15).
7. Procédé selon l'une quelconque des revendications précédentes, caractérisé en ce que lesdites fenêtres (5, 6) ouvertes dans la multicouche (1, 15) ont une forme rectangulaire.
8. Procédé selon l'une quelconque des revendications 1 à 7, caractérisé en ce qu'il inclut l'étape de réglage de la fréquence centrale de la transition par fixation
d'une valeur correspondante du rapport (a+b)/w, où : w est la dimension de cavité la plus longue d'un guide d'ondes rectangulaire dont la
dimension la plus courte a un rapport connu avec w, a est la longueur de la ligne qui transporte le signal jusqu'à la fiche (3), et b est la base de la fiche (3) formée comme un rectangle perpendiculaire au microruban
(2).
9. Procédé selon la revendication 8, caractérisé en ce qu'il inclut l'étape d'optimisation de l'adaptation aux ports d'entrée et de sortie à
l'intérieur de la bande de fréquences désirée par fixation du rapport c/b, où c est la hauteur de la fiche rectangulaire à l'intérieur de la largeur de bande considérée
; dans lequel la bande de fréquences désirée s'étend de 55 à 60 GHz ; dans lequel
une couche diélectrique (1) avec une constante diélectrique relative εr d'approximativement 3,54 est utilisée et dans lequel l'épaisseur est environ 100
µm, la valeur de (a+b)/w est environ 0,18 et la valeur de c/b est environ 2,22.
10. Transition de micro-onde à guide d'ondes fabriquée avec le procédé selon l'une quelconque
des revendications 1 à 9.
11. Transition selon la revendication 10, caractérisée en ce que les deux rainures (12, 13) opposées ont des profondeurs différentes et la plus profonde
inclut le microruban (2) incluant la plaque de métal rigide (15).
12. Transition selon la revendication 11, caractérisée en ce que les deux rainures (12, 13) opposées ont des dimensions transversales telles qu'elles
se comportent comme deux guides d'ondes sous-jacents dans la plage de fréquences désirée
de la transition apte à confiner le champ électromagnétique dans le volume de la transition.
13. Transition selon l'une quelconque des revendications 10 à 12, caractérisée en ce que ledit guide d'ondes (10) est rectangulaire.
14. Transition selon l'une quelconque des revendications 10 à 12, caractérisée en ce que ledit guide d'ondes (10) est circulaire.
15. Transition selon l'une quelconque des revendications 10 à 12, caractérisée en ce que ledit guide d'ondes (10) est elliptique.
16. Transition selon l'une quelconque des revendications 10 à 15, caractérisée en ce qu'elle inclut une couronne de trous traversants (7, 8) métallisés qui contient le bord
du guide d'ondes (10) au niveau des deux côtés de la bande (4) pour éviter des détachements
possibles entre la couche diélectrique (1) et la plaque de métal rigide (15).