Rat-Race Balun and associated Rat-Race Balun footprint reduction method

Abstract

The invention relates to a Rat-Race Balun, comprising a transmission line loop and 4 input-output ports P1, P2, P3, P4 connected to said transmission line loop, said balun being adapted to receive a first signal on port P1, and to divide said first signal into a second signal delivered on port P2 and a third signal delivered on port P4, said second signal and said third signal being in phase opposition with each other, said balun being characterized in that: the balun has a bean shape and the ports P2, P4 each comprise at least a first section connected to the transmission line, the first section of port P2 being parallel to the first section of port P4. Figure for abstract: Fig. 4

Description

Title of the invention: Rat-Race Balun and associated Rat-Race Balun footprint reduction method Technical field

[0001] The invention lies in the field of Rat-Race type baluns. Prior art

[0002] The term balun comes from the English words BALanced (balanced, balanced) and UNbalanced (unbalanced, unbalanced).

[0003] A balun is an electrical circuit used to make the connection between a symmetrical transmission line (two-wire line or parallel printed lines) and an asymmetrical transmission line (coaxial cable or printed line above a ground plane). A balun is for example made using coiled coaxial cable or a small section of two-wire line wound on a ferrite core or on a coreless mandrel (balun in air). Such a balun can operate over a wide frequency band (2 to 4 octaves). A balun can also be made using a loop of coaxial cable with an electrical length equal to half the wavelength. The balun is then single-frequency, in fact it operates correctly over a narrow frequency band, of a few percent. Baluns are made on printed circuits, with microstrips, striplines for example.

[0004] A Rat-Race type balun is a loop-shaped component, typically ring or square, comprising four ports No. 1, 2, 3, 4 such that a signal entering port 1 is split between ports 2 and 4 in phase opposition and a signal entering port 3 is split between ports 2 and 4 in phase, port 3 being isolated. Its function is therefore to split a radio frequency (RF) signal of power P into two RF signals of power P / 2 or to combine two RF signals of power P / 2 into one RF signal of power P.

[0005] A Rat-Race type balun can also be used to combine signals: at port 3 is delivered the difference between two signals injected at the input of the balun, after re-phasing, one at port 2, the other at port 4 and at port 1 is delivered, after re-phasing, their sum.

[0006] US 2022 / 0263212 describes an example of a Rat-Race type balun.

[0007] There is a need to reduce the size of Rat-Race type baluns on the electronic supports on which they are integrated. Summary of the invention

[0008] To this end, according to a first aspect, the present invention describes a Rat-Race balun, comprising a transmission line loop and 4 input-output ports Pb P2, P3, P4 connected to said transmission line loop, said balun being adapted to receive a first signal on port Pb and to divide said first signal into a second signal delivered on port P2 and a third signal delivered on port P4, said second signal and said third signal being in phase opposition with each other, said balun being characterized in that: the balun has a bean shape and ports P2, P4 each comprise at least a first section connected to the transmission line, the first section of port P2 being parallel to the first section of port P4

[0009] Such a Rat-Race balun takes up little space.

[0010] In embodiments, such a balun will further comprise at least one of the following features: - the first section of port P2 and the first section of port P4 parallel to each other face each other; - the adjacent ports among the ports Pb P2, P3, P4 are connected by respective sections of the transmission line loop, and at least some of said sections are capacitor-charged transmission line sections; - each of the respective transmission line sections between Pi and P2, between P2 and P3, between P3 and P4 is a line section of electrical length 20b of impedance Z / and charged by a capacitor of capacitance C and; where < 45° and the following equalities are verified: U =------4-—- tan ; 2^ )

[0011] and ~ Z. .X'.. ~ ——— * tan (4) w being equal to 2tt / , with f the operating frequency, and Zc being the impedance of the unloaded transmission line section of physical length X / 4 equivalent to said loaded line section;

[0012] - the respective transmission line section between the adjacent ports Pi and P4 is of electrical length 604 comprising three consecutive line subsections each of electrical length S^], of impedance Z, and charged by a capacitor of capacitance C; where < 45° and the following equalities are verified: 2 IC =-----:------ tan s 1 And Z = Zf - w being equal to 2æ / \ with f the operating frequency, and Zc being the impedance of the unloaded transmission line subsection of physical length X / 4 equivalent to said loaded line subsection; - the respective transmission line section between the adjacent ports Pi and P4 is of electrical length 202, of impedance Z3 and is a line section charged by a capacitor of capacitance C2; ​​where 02 < 135 and the following equalities are verified: 2tan(02) “ wZpj^tan ( 2 S, )

[0013] and y ^piP4 ' tan(02)

[0014] w being equal to 2nj\ with f the operating frequency, and ZpiP4 being the impedance of the unloaded transmission line section of physical length 3 / . / 4 equivalent to said loaded line section;

[0015] - the balun comprises an impedance transformer loaded by a capacitor between the Pi port and the transmission line loop.

[0016] According to another aspect, the invention describes a method for reducing the size of a Rat-Race balun comprising a transmission line loop and 4 input-output ports Pb P2, P3, P4 connected to said transmission line loop, said balun being adapted to receive a first signal on the port PH and to divide said first signal into a second signal delivered on the port P2 and a third signal delivered on the port P4, said second signal and said third signal being in phase opposition with each other, comprising the following steps implemented by an electronic device for determining Rat-Race balun characteristics: - determination of a bean shape for the balun; - connection of a first section of each of the ports P2, P4 to the transmission line, the first section of the port P2 being parallel to the first section of the port P4

[0017] In embodiments, such a method will further comprise at least one of the following features:

[0018] - the first section of port P2 and the first section of port P4 parallel to each other face each other;

[0019] - the ports adjacent to each other among the ports Pb P2, P3, P4 are connected by sections respective sections of the transmission line loop, and at least some of said sections are capacitor-charged transmission line sections. Brief description of the drawings

[0020] The invention will be better understood and other characteristics, details and advantages will appear more clearly on reading the following description, given without limitation, and thanks to the appended figures, given by way of example.

[0021] [Fig.l] [Fig.l] schematically represents a push-pull type assembly in one embodiment of the invention;

[0022] [Fig.2] [Fig.2] illustrates the replacement, in a balun functional diagram, of conventional lines by loaded lines;

[0023] [Fig.3] [Fig.3] is a functional diagram of a balun in one embodiment of the invention;

[0024] [Fig.4] [Fig.4] illustrates a balun topology considered in one embodiment of the invention;

[0025] [Fig.5] [Fig.5] represents a conventional 3 / 74 transmission line and an equivalent loaded 3 / 74 line;

[0026] [Fig.6] [Fig.6] represents a loaded 3 / 74 line and three equivalent loaded / 74 lines;

[0027] [Fig.7] [Fig.7] shows a method of reducing balun size in one embodiment of the invention;

[0028] [Fig.8] [Fig.8] shows a top view of a push-pull device circuit board of the type shown in [Fig.l] with a bean-shaped balun.

[0029] Identical references may be used in different figures when they designate identical or comparable elements. Description of the embodiments

[0030] [Fig.l] schematically represents an electronic processing module 1 of the push-pull type in one embodiment of the invention, for example operating at high frequency and integrated, on a printed circuit, in the last stage of a transmission chain of an electronic radiocommunication device.

[0031] The processing module 1 comprises a power transistor (“High Power Amplifier”), called HPA 11. It operates on the L band (or any other frequency band, in narrow band, for example with a width of less than 20 MHz, or even 15 MHz and at powers of up to 1.5 kW peak.

[0032] As is known, power transistors have a low input impedance compared to the standard 50 Q impedance and are regularly composed of two chips (similar to two transistors), in push-pull assembly here, which requires having to divide (split) the input signal and to phase shift them by 180° before supplying them to the transistor input. The fact that the signals supplied to the input of the HPA 11 are in phase opposition makes it possible to reduce their interference due to amplification on two very close chips.

[0033] For this purpose, the processing module 1 comprises upstream of the HPA 11 a balun 10 in one embodiment of the invention.

[0034] The input signal of the processing module 1, typically a train of RF pulses in the L band (in the example considered with power In 47 dBm, and load rate 2%), is provided at the input of the PI port of the balun 10. The power of this input signal is P.

[0035] The two signals at the output of ports P2 and P4, of the same power P / 2 (at + / - 0.2 dB% for example) and in phase opposition with respect to each other, are provided one at the input of one of the two chips of the HPA 11, the other at the input of the other of the two chips of the HPA 11.

[0036] At the output of the HPA 11, the two amplified signals, in phase opposition, are supplied at the input of a balun 12, one on its port P2, the other on the port P4. The balun 12 re-phases these signals with respect to each other and delivers at the output on its port PI, the sum of these two re-phased signals.

[0037] The input impedance of the balun 10 is Zo, which is much higher than each of the input impedances ZE and output Zs of the HPA 11. For example, Zo = 50 Q and ZE, Zs less than 20 or even 10 Q (in particular if LDMOS transistor), for example here 2.5 Q.

[0038] The balun 10, here constructed on a printed circuit board (PCB) with microstrips for example, comprises transmission line sections between each Pb port P2, P3, P4.

[0039] In a first embodiment, each section of transmission line between two adjacent ports, conventionally, has a physical length (in meters) X / 4 outside the section between the adjacent ports Piet P4 (i.e. the section which does not include the ports P2, P3) and which itself has a physical length 3X / 4, X being the wavelength corresponding to the central frequency of the input signal of the processing module 1. The electrical length corresponding to the physical length X / 4 is equal to 90°. As is known, the “electrical length” is a theoretical way of expressing the wavelength without having to mention the environment of the circuit: PCB (printed circuit board)... Concretely this consists of considering that a wavelength X corresponds to 360°. Theoretically, for a specific application, the same wavelength ratio must be kept.The propagation of EM waves depends on the medium, so depending on the substrate X (in m) changes, but not its associated length (always 360°).

[0040] The impedance of the unloaded transmission line of physical length M4 is Zc

[0041] In a second embodiment, each quarter-wave line section considered in the first embodiment is replaced by its equivalent in a transmission line loaded by a capacitor.

[0042] In terms of physical dimensions, these equivalent sections differ, but in terms of behavior (if we study S parameters for example) they are identical, as shown by a narrow band observation.

[0043] This modification is detailed in “Compact Tunable 3 dB Hybrid and Rat-Race Couplers with Harmonies Suppression”, Khair Al Shamaileh, Mohammad Almalkawi, Vijay Devabhaktuni, and Nihad Dib, INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY, VOL.7, NO.6, NOVEMBER 2012, and is illustrated in Figure 2 for the case of a ring-shaped balun: each section of transmission line of length X / 4 (as shown on the left of Figure 2) is thus replaced (as shown on the right of Figure 2) by a section of transmission line of electrical length 20b of impedance Zi and loaded with a capacitor, i.e. by two sections of transmission line each of electrical length and impedance Zi interspersed with a capacitor placed in parallel, of capacitance C, and therefore connected to ground.

[0044] We then have the following equalities:

[0045] Equality 0_l 1

[0046] And equality 0_2:

[0047]

[0048] i ——-

[0049] where w is the frequency pulsation, i.e. û; = 2zr / , with f the operating frequency of the balun, i.e. the central frequency of the signal.

[0050] A reduction in the size of the balun of 52% corresponding in particular to the choice of a value of less than 45° was obtained in an exemplary embodiment.

[0051] The reduction ratio depends on the ^chosen, and also on the PCB (in particular its dielectric permittivity parameter U) considered. There is a reduction as soon as 9] <45°: there is a reduction in the line length, which depends a lot on the PCB used. In addition, as ZI is inversely proportional to tan(0]), that tan(45°) = 1 and that the tan function is increasing on [0;45°] then the impedance of the equivalent lines is higher than that of the original line. In this case there is a reduction in the width of the line, which depends a lot on the PCB used, largely on its thickness.

[0052] The capacitance value of the capacitor as well as the impedance of the sections of loaded lines are deduced from the equations above linking them to the chosen electrical length less than 45°. The impedance being a function of the physical width of the microstrip, the latter are determined as a function of the impedance Zi (Zl here designating the impedance of the characteristic impedance type of the loaded lines, i.e. the impedance that an input line would have if the latter were of infinite length: it does not depend on the length).

[0053] It further follows that the resonant frequency value of the loaded transmission line is adjustable as required by changing the value of C (e.g. using varactor type capacitors).

[0054] In Shamaileh et al., the impedance change was an effect that was experienced by the authors.

[0055] It is proposed here to exploit this change in impedance: the shorter the length of the loaded sections, the higher their impedance. When using a balun 10 operating at low impedance, there is therefore more room for maneuver to reduce the length of the lines before reaching the manufacturability limits associated with the line widths. It is therefore possible to obtain a component with very fine lines, of reduced length, operating at low impedances.

[0056] However, to meet one of the specificities of the HPA mentioned above, a balun 10 operating at low impedances at output P2, P4 is required.

[0057] In a third embodiment of the balun 10, the second embodiment is modified in that the line section 3 / . / 4 between the adjacent ports PB P4 is replaced by its equivalent in line loaded with a single capacitor this time, of capacitance C2, as shown in the functional diagram of figure 3, this line section is then constituted by two sections of transmission line each of impedance Z3 and electrical length #2, interspersed with a parallel capacitor of capacitance C2 also connected to ground.

[0058] This topology is more restrictive than the previous one exposed in the second embodiment, because the impedance of the two sections replacing the line 37. / 4 is then, unlike previously, proportional to their electrical length. 77 and that the tan() function is negative and increasing on this interval. The "-" sign of the equality 0_3 "transforms" the tan() function into an equivalent of the abs(tan) function on this interval. Now abs(tan(^2))^l on [Ï't] mod(jr)-

[0059] This comes from the fact that # G | 1 mO(]( ~ LZ 4 J

[0060] A further reduction in size of the balun 10 can be achieved if the value of #1 is chosen to be less than 45° and if the value of is chosen to be less than 135°, the values ​​of impedance and electrical length being determined using the following equalities 0_3 and 0_4.

[0061] This additional reduction is obtained in particular if 3#i > #2 and if we work with a substrate and impedances which do not generate too large a difference in line width between the impedances ZI and Z3 (i.e. if we work with a substrate, which depending on the impedances ZI and Z3 used, does not generate an increase in the line width which would cause an overall increase in the surface covered by the balun, despite the reduction in the length of the lines); an example of a standard criterion is that the length must be at least greater than 3 times the width.

[0062] Equality 0_3:

[0063] 7 _ 3 tan(Ô2)

[0064] where is the impedance of the equivalent transmission line section between adjacent ports PiP4, of physical length 3 / 74 and unloaded.

[0065] Equality 0_4:

[0066] _ 2tan(g2) C " wZ / 1|Mtan(202)

[0067] This requires making compromises between the impedances of the different sections of the balun lines: to reduce the size of the balun, it is necessary either to reduce the electrical length of its lines, or to increase the impedance of its lines; however, in the case of the 3 / 74 line loaded with a single capacitor, these two parameters are proportional, a compromise is necessary. It is also necessary to take into account the impedance of the X / 4 lines, if it is too different from that of the 3)74 line, the impedance break could lower the performances. The opposite is that if they are too close, then this means that is close to 45° and therefore that the reduction of the X / 4 lines is less important.

[0068] The values ​​of capacitance C and impedance Zi for each section of length 2^1 connecting the adjacent points Pb P2, respectively connecting the adjacent points P2, P3, and connecting the adjacent points P3, P4, remain determined by application of equations 0_l and 0_2 above.

[0069] The shape of a commonly used Rat Race balun is circular or square and is therefore not ideal, particularly for use in a push-pull 10 type processing module on a printed circuit, which has a very long structure.

[0070] In a fourth embodiment, it is therefore proposed to produce the balun 10 by giving it a “bean” shape (in the plane in which the printed circuit extends), as shown in [Fig. 4], instead of a ring shape such as shown in figures 2 and 3. This new topology makes it possible to orient the two ports P2, P4 towards the transistor HPA 11, while having an input port Pi oriented in the opposite direction, via, for example, an impedance transformer.

[0071] In one embodiment, with reference to [Fig.4], the bean balun 10 comprises a perimeter 41 made up of transmission line sections. In the trigonometric direction, the section between the ports P2 and P4 is concave, then the section between P4 and P2 is convex.

[0072] With reference to [Fig.4], each capacitor of loaded line sections is connected on the one hand to the transmission line forming perimeter 41 and on the other hand to the ground by means of one of the vias (represented by small circles in [Fig.4]) in the zone 40 which is located inside the perimeter of the bean balun 10.

[0073] In one embodiment, the bean balun 10 is constructed using circular arcs between the 4 consecutive ports and the lengths of these arcs are set according to the inter-port lengths defined by calculation according to one of the first, second and third embodiments. The combination of this bean shape with the use of loaded lines as described in the second and third embodiments makes it possible to significantly reduce the size of the lines.

[0074] For example, in the case where it is desired to implement the bean shape combined with the second embodiment with 6 capacitors, 31, 32, 33, 34, 35, 36, each of capacitance C: 12 arcs of circles and their respective lengths are defined, with 2 concentric arcs of circles (delimiting a transmission line) between each pair of consecutive ports: the structure is divided into 12 arcs of circle; the angle of some is increased (those adjacent to ports P2, P3 and P4), without changing their length, so as to obtain the desired shape.

[0075] In one embodiment, the sections 52, 54 of the ports P2 and P4 immediately connected to the body of the bean-shaped balun 10 (extending in the plane of the printed circuit) are parallel to each other and extend (in embodiments where their length is non-zero) in a same direction, DE, from the body of the bean-shaped balun 10. In one embodiment, these two parallel sections are identical.

[0076] In one embodiment, a section 51 of port Pi (extending in the plane of the printed circuit) of balun 10 is parallel to sections of ports P2 and P4 and extends in one direction from balun 10 in an opposite direction, DO. In one embodiment, it is replaced by a resistor in parallel

[0077] Thus, as described above and conventionally, in this embodiment also, the input signal is supplied at the input of the bean-shaped balun 10, at the port PI; the signal transmitted in the balun 10 undergoes a power division and a phase opposition and the signals at the output of the pots P2 and P4 have a power equal to

[0078]

[0079]

[0080]

[0081]

[0082]

[0083] half the power of the input signal and are in phase opposition. Port P3 of balun 10 is isolated (connected by a load to ground), in the processing module shown in [Fig.l]. At the output of balun 10, the impedance is for example 12.5 Q, then matching circuits (length different from X / 4) are arranged between the HPA 11 and balun 10 to lower the impedance to ZE if necessary (an impedance transformer in a known manner includes transmission lines with increasing or decreasing diameters to modify the impedance). A balun 10 corresponding to embodiment 2 and / or 3 is particularly suitable for narrowband uses. The embodiments described above may be implemented independently or in combination: for example, in one embodiment of the invention, the bean balun 10 is combined with one of the first, second, and third balun embodiments. Each of the embodiments provides a balun with a reduced footprint. In one embodiment so that the balun can maintain an input impedance of 50 Q, with reference to [Fig. 4], an impedance transformer 42, which, in one embodiment, is also loaded by a capacitor 37, is inserted between the perimeter 41 of the balun 10 and the port Pb to further reduce the size of the processing module 1. Similar to what has been explained in relation to the 2nd embodiment and using the same equalities 0_l and 0_2, a portion X / 4 of the transmission line of the impedance transformer is replaced by a line loaded by a capacitor, which is shorter than the unloaded equivalent. The balun 10 according to the invention is therefore a signal distributor, with or without impedance transformation depending on the case, which is miniaturized and optimized with capacitor-charged transmission lines. The invention advantageously replaces the historical solution associating an impedance transformer A associated with a phase shifter A. The invention is even more interesting for low permittivity substrates (FR-4 or RO4350b, low-cost substrates), where the footprint of the classic solution is even more significant. In terms of comparison with the solution, the size is significantly reduced: for an FR4 HP substrate with a dielectric permittivity constant of 4.34 and a height of 0.245 mm, we observe, with reference to the table below, a reduction of approximately 80%, by combining embodiments 3 and 4 with a loaded transformer. This depends on the minimum width of a line and the power accepted in the lines and in the capacitors.

[0084] [Tables 1] Historical solution Current solution Footprint — 4.34, h = 0.245mm 5 = 40*40= 1600 mm2 £, = 4.34, h = 0.245mm S = 16.5*19.6 = 323 mm 2 Reduction of almost 80% Means Microstrip lines Microstrip lines and 5 to 7 capacitors

[0085] where is the dielectric permittivity associated with the FR4 HP substrate A is the thickness of the substrate, and 5 is the surface area of ​​the component.

[0086] [Fig.8] shows a top view of a printed circuit of a push-pull device 1 in one embodiment of the invention. The balun 10, respectively 12 has a bean shape according to the fourth embodiment (see frame 10_l, respectively 12_1). Frame 10_2, respectively 12_2 indicates where the impedance transformer is located (the load of the transformer is not visible in this figure).

[0087] With reference to [Fig.7], a method of reducing the size of a Rat-Race Balun is now described.

[0088] In one embodiment, in a step 101 of designing such a Rat-Race Balun, for example corresponding to the second embodiment, a space reduction module comprising a memory storing software instructions and a processor, determines, following the execution of the software instructions on the processor, the values ​​of Zi, and C of the balun 10 verifying the equalities 0_l and 0_2 such that <45°.

[0089] For example, the substrate to be used is known, the dimension of the lines as a function of the impedance and the dielectric length is therefore anticipable. The operating impedance is known, is chosen arbitrarily (respecting the condition 9] <45°), according to the values ​​of Zi and C obtained. It is verified that the associated lines are technically feasible, and meet the requirements. Based on this verification, it is decided to keep this 9] or to modify it accordingly. The search is refined at each 0].

[0090] In another embodiment, the clutter reduction module further determines the values ​​of Z3, and C2 verifying the equalities 0_3 and 0_4 such that ^2 <135°.

[0091] The balun is then manufactured taking these characteristics into account.

[0092] In a design step 102, the electrical lengths of the line sections between ports of the balun being defined, the congestion reduction module determines, based on these lengths and the actual impedances of the lines, the data for defining a bean shape for a Rat-Race balun and ports, to obtain a bean balun as described above for example.

[0093] Steps 101, 102 can also be implemented independently of one another.

[0094] Such a method makes it possible to obtain a push-pull assembly comprising the Rat-Race Balun constructed under these conditions, and occupying a reduced footprint.

[0095] The method may be implemented by executing software instructions on a processor as described. Alternatively, it may be implemented by dedicated hardware, typically a digital integrated circuit, either specific (ASIC) or based on programmable logic (e.g. FPGA / Field Programmable Gate Array)

[0096] Justification for obtaining the equalities 0 3 and 0 4:

[0097] In [Fig.5] are represented: - on the left (section a): a classic transmission line (i.e. not loaded by capacitors) of physical length 3 / 74 and electrical length 0q= 270° and - on the right (section b): the equivalent capacitor-loaded transmission line, in the form of only two line sections, each with impedance Zd and electrical length 0d, with a capacitor C in parallel, arranged between the two sections.

[0098] Matrix (1) below provides the ABCD parameters for the conventional transmission line of physical length 3 / 74: ? #(1)

[0099]

[0100] cos(270) jZ?sin(270) LC <!D<! J ~ jZ^‘sin(270) cos(270)

[0101] Then, to have an equivalent, it is necessary to have an equality between (1) and the matrix ABCD of a short-circuited shunt (2) multiplied on both sides by the matrix of a trunk charged in capacitor (3), represented by (4): 101021

[0103]

[0104] M AdBd ] _ F cos^J JZ^in(6L)l # _ jZ^sin^j cos(0ri) j

[0105]

[0106] Mq = MdMcMd # ( 4 )

[0107]

[0108] Equality (4) allows us to establish the following equations:

[0109] _ cos ( 0 d ) 2 - wCZ d sin(3 d )cos( 3 el ) + jZ d 1 sin( 3 cl ) #( 5 - a ) [OHO] Bq = ft d ^3 d )cGs(3 d ) -jœCZ 2 d sm(3 d Ÿ + ^ 2 # < 5 - b )

[0111] Thanks to the correspondence between (1) and (5.a), (6) is determined: wC = ---# (6) Zc / tan(2&tl) '7

[0112] Then by substituting (6) in (5.b), it appears (7) [° 113 ] Z d =—^r#(7) cl tan{& d ) v 7

[0114] Finally, using (6) and (7), the value of the capacitance used in the equivalent loaded line is equal to

[0115] c=_ cuZ7tan( 2©cY) v 7

[0116] As C > O, it follows that:

[0117] tan(0 ( / ) <O andtan(23 d ) >0 #(9zz)

[0118] or

[0119] tan( 3 d ) > 0 and tan( 23 cl) < 0 # (9.b)

[0120] Using conditions (9.a) and (9.b), and taking into account that Zel > O, the only possible values ​​for &d are:

[0121] mod^rr)# ( 10)

[0122] The aim is to reduce the length of the 3 / 74 transmission line by replacing the three loaded X / 4 lines with one loaded 3 / 74 line as shown in [Fig.6], it is necessary to find the condition for:

[0123] ^>63 d3 >26 d # (11)

[0124] To satisfy (11), it is necessary to take into account condition (10). Finally, the loaded line 3 / 74 can have a size reduction for:

[0125] — [ mod(ir) # (12)

[0126] By ADS simulation, it was demonstrated that the miniaturized rat-race couplers exhibit the same performances for three X / 4 lines loaded with capacitors and for one 3 / 74 line loaded with capacitors. - Beyond the miniaturization aspects, these new aspects provide greater flexibility regarding the impedance value.

Claims

Claims

1. Rat-Race Balun (10), comprising a transmission line loop (41) and 4 input-output ports Pb P2, P3, P4 connected to said transmission line loop (41), said balun being adapted to receive a first signal on the port PH and to divide said first signal into a second signal delivered on the port P2 and a third signal delivered on the port P4, said second signal and said third signal being in phase opposition with each other, said balun (30) being characterized in that: - the balun (10) has a bean shape and - the ports P2, P4 each comprise at least a first section (52, 54) connected to the transmission line, the first section (52) of the port P2 being parallel to the first section (54) of the port P4. said balun (10) comprising an impedance transformer (42) loaded by a capacitor (37) between the port Pi and the transmission line loop (41).

2. A Rat-Race Balun (10) according to claim 1, wherein the first section (52) of port P2 and the first section (54) of port P4 parallel to each other face each other.

3. A Rat-Race Balun (10) according to claim 1 or 2, wherein adjacent ones of the PB ports P2, P3, P4 are connected by respective sections of the transmission line loop (41), and at least some of said sections are capacitor-charged transmission line sections (31, 32, 33, 35, 36).

4. Rat-Race Balun (10) according to claim 3, wherein: each of the respective transmission line sections between Pi and P2, between P2 and P3, between P3 and P4 is a line section of electrical length of impedance Z / and charged by a capacitor (36, 35) of capacitance C and; where < 45° and the following equalities are verified: C -------4r_ «Z, tan [ ) and Z. tau S $ i w being equal to , with f the operating frequency, and Zc being the impedance of the unloaded transmission line section of physical length X / 4 equivalent to said loaded line section.

5. A Rat-Race Balun (10) according to claim 3 or 4, wherein: the respective transmission line section between the adjacent ports P i and P4 is of electrical length 60! comprising three consecutive line subsections each of electrical length 20 b of impedance Zj and charged by a capacitor (31, 32, 33) of capacitance C; where < 45° and the following equalities are verified: And w being equal to 2tt / , with f the operating frequency, and Zc being the impedance of the unloaded transmission line subsection of physical length X / 4 equivalent to said loaded line subsection.

6. A Rat-Race Balun (10) according to any one of claims 3 to 4, in which: the respective transmission line section between the adjacent ports P i and P4 is of electrical length 202, of impedance Z3 and is a line section charged by a capacitor of capacitance C2; ​​where 02 < 135° and the following equalities are verified: _ 2tan (02) And y _ ip4 tan(02) w being equal to , with f the operating frequency, and Zp1P4 being the impedance of the unloaded transmission line section of physical length 3 / . / 4 equivalent to said loaded line section.

7. A method for reducing the size of a Rat-Race balun (10) comprising a transmission line loop (41) and 4 input-output ports Pb P2, P3, P4 connected to said transmission line loop, said balun being adapted to receive a first signal on port Pb and to divide said first signal into a second signal delivered on port P2 and a third signal delivered on port P4, said second signal and said third signal being in phase opposition with each other, comprising the following steps implemented by an electronic device for determining Rat-Race balun characteristics: - determining a bean shape for the balun;- connection of a first section (52, 54) of each of the ports P2, P4 to the transmission line, the first section of the port P2 being parallel to the first section of the port P4, said balun (10) comprising an impedance transformer (42) charged by a capacitor (37) between the port Pi and the transmission line loop (41).;

8. A method of reducing the size of a Rat-Race balun (10) according to claim 7, wherein the first section (52) of the P2 port and the first section (54) of the P4 port parallel to each other face each other.

9. A method of reducing the size of a Rat-Race balun (10) according to claim 7 or 8, wherein adjacent ones of the Pb ports P2, P3, P4 are connected by respective sections of the transmission line loop (41), and at least some of said sections are capacitor-charged transmission line sections.

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