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US-12627018-B2 - Rat-race balun and associated method for reducing the footprint of a rat-race balun

US12627018B2US 12627018 B2US12627018 B2US 12627018B2US-12627018-B2

Abstract

A rat-race balun includes a transmission line loop and 4 input-output ports P 1 , P 2 , P 3 , P 4 connected to the transmission line loop, the respective transmission line section between the adjacent ports P 1 and P 4 is of electrical length 2θ 2 , of impedance Z 3 and is a line section loaded by a capacitor of capacitance C2; where θ 2 <135 and the following equalities are satisfied: C ⁢ 2 = - 2 ⁢ tan ⁡ ( θ 2 ) ω ⁢ Z P ⁢ 1 ⁢ P ⁢ 4 ⁢ tan ⁡ ( 2 ⁢ θ 2 ) and ⁢ Z 3 = - Z P ⁢ 1 ⁢ P ⁢ 4 tan ⁡ ( θ 2 ) w being equal to 2πf, with f the operating frequency, and Z P1P4 being the impedance of the unloaded transmission line section of physical length 3λ/4 equivalent to the loaded line section.

Inventors

  • Aymeric CAILLEUX
  • Laure HOGOMMAT-CHABROT

Assignees

  • THALES

Dates

Publication Date
20260512
Application Date
20231228
Priority Date
20221229

Claims (9)

  1. 1 . A rat-race balun, comprising a transmission line loop and 4 input-output ports P 1 , P 2 , P 3 , P 4 connected to said transmission line loop, said balun being designed to receive a first signal on the port P 1 , and to divide said first signal into a second signal that is delivered to the port P 2 and a third signal that is delivered to the port P 4 , said second signal and said third signal being in phase opposition with one another, wherein the ports adjacent to one another from among the ports P 1 , P 2 , P 3 , P 4 are connected by respective sections of the transmission line loop, and at least some of said sections are capacitor-loaded transmission line sections; said balun being wherein: the respective transmission line section between the adjacent ports P 1 and P 4 is of electrical length 2θ 2 , of impedance Z 3 and is a line section loaded by a capacitor of capacitance C 2 ; where θ 2 <135 and the following equalities are satisfied: C ⁢ 2 = - 2 ⁢ tan ⁡ ( θ 2 ) ω ⁢ Z P ⁢ 1 ⁢ P ⁢ 4 ⁢ tan ⁡ ( 2 ⁢ θ 2 ) and ⁢ Z 3 = - Z P ⁢ 1 ⁢ P ⁢ 4 tan ⁡ ( θ 2 ) w being equal to 2πf, with f the operating frequency, and Z P1P4 being the impedance of the unloaded transmission line section of physical length 3λ/4 equivalent to said loaded line section.
  2. 2 . The rat-race balun according to claim 1 , wherein: each of the respective transmission line sections between P 1 and P 2 , between P 2 and P 3 , between P 3 and P 4 is a line section of electrical length 2θ 1 , of impedance Z 1 and loaded by a capacitor of capacitance C and; where θ 1 <45° and the following equalities are satisfied: C = 2 ⁢ tan ⁡ ( θ 1 ) ω ⁢ Z c ⁢ tan ⁡ ( 2 ⁢ θ 1 ) and ⁢ Z 1 = Z c tan ⁡ ( θ 1 ) w being equal to 2πf, with f the operating frequency, and Z c being the impedance of the unloaded transmission line section of physical length λ/4 equivalent to said loaded line section.
  3. 3 . The rat-race balun according to claim 1 , wherein: the balun is kidney-shaped and the ports P 2 , P 4 each comprise at least a first section connected to the transmission line, the first section of the port P 2 being parallel to the first section of the port P 4 .
  4. 4 . The rat-race balun according to claim 3 , wherein the mutually parallel first section of the port P 2 and first section of the port P 4 face one another.
  5. 5 . A method for reducing the footprint of a rat-race balun comprising a transmission line loop and 4 input-output ports P 1 , P 2 , P 3 , P 4 connected to said transmission line loop, said balun being designed to receive a first signal on the port P 1 , and to divide said first signal into a second signal that is delivered to the port P 2 and a third signal that is delivered to the port P 4 , said second signal and said third signal being in phase opposition with one another, wherein the ports adjacent to one another from among the ports P 1 , P 2 , P 3 , P 4 are connected by respective sections of the transmission line loop, and at least some of said sections are capacitor-loaded transmission line sections, said method comprising the following step implemented by an electronic device for determining rat-race balun characteristics: the respective transmission line section between the adjacent ports P 1 and P 4 being of electrical length 2θ 2 , of impedance Z 3 and being a line section loaded by a capacitor of capacitance C 2 , determining the impedance Z 3 and the capacitance C 2 , satisfying θ 2 <135 and the following equalities: C ⁢ 2 = - 2 ⁢ tan ⁡ ( θ 2 ) ω ⁢ Z P ⁢ 1 ⁢ P ⁢ 4 ⁢ tan ⁡ ( 2 ⁢ θ 2 ) and ⁢ Z 3 = - Z P ⁢ 1 ⁢ P ⁢ 4 tan ⁡ ( θ 2 ) w being equal to 2πf, with f the operating frequency, and Z P1P4 being the impedance of the unloaded transmission line section of physical length 3λ/4 equivalent to said loaded line section.
  6. 6 . The method for reducing the footprint of a rat-race balun according to claim 5 , wherein, each of the respective transmission line sections between P 1 and P 2 , between P 2 and P 3 , between P 3 and P 4 being a line section of electrical length 2θ 1 , of impedance Z 1 and loaded by a capacitor of capacitance C, determining the impedance Z 1 and the capacitance C, satisfying θ 1 <45° and the following equalities: C = 2 ⁢ tan ⁡ ( θ 1 ) ω ⁢ Z c ⁢ tan ⁡ ( 2 ⁢ θ 1 ) and ⁢ Z 1 = Z c tan ⁡ ( θ 1 ) w being equal to 2πf, with f the operating frequency, and Z c being the impedance of the unloaded transmission line section of physical length λ/4 equivalent to said loaded line section.
  7. 7 . The method for reducing the footprint of a rat-race balun according to claim 5 , wherein: the balun is kidney-shaped and the ports P 2 , P 4 each comprise at least a first section connected to the transmission line, the first section of the port P 2 being parallel to the first section of the port P 4 .
  8. 8 . The method for reducing the footprint of a rat-race balun according to claim 7 , wherein the mutually parallel first section of the port P 2 and first section of the port P 4 face one another.
  9. 9 . The method for reducing the footprint of a rat-race balun according to claim 5 , wherein the balun comprises an impedance transformer loaded by a capacitor between the port P 1 and the transmission line loop.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to foreign French patent application No. FR 2214619, filed on Dec. 29, 2022, the disclosure of which is incorporated by reference in its entirety. FIELD OF THE INVENTION The invention lies in the field of rat-race baluns. BACKGROUND The term “balun” stems from the words BALanced and UNbalanced. A balun is an electrical circuit used to link 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 produced using wound coaxial cable or a small section of two-wire line wound on a ferrite toroidal core or on a coreless mandrel (balun in air). Such a balun is able to operate over a wide frequency band (2 to 4 octaves). It is also possible to manufacture a balun using a loop of coaxial cable having an electrical length equal to half-wavelength. The balun is then single-frequency: in fact, it works correctly over a narrow frequency band of a few percent. Baluns are produced on printed circuits, with microstrips, striplines for example. A rat-race balun is a loop-shaped component, conventionally in the shape of a ring or a square, comprising four ports numbered 1, 2, 3, 4 such that an incoming signal on port 1 is divided between ports 2 and 4 in phase opposition and an incoming signal on port 3 is divided between ports 2 and 4 in phase, port 3 being isolated. It therefore has the function of dividing a radiofrequency (RF) signal of power P into two RF signals of power P/2 or of combining two RF signals of power P/2 into an RF signal of power P. A rat-race balun may also be used to combine signals: port 3 has delivered to it the difference between two signals injected at the input of the balun, after phase realignment, one at port 2, the other at port 4, and port 1 has delivered to it, after phase realignment, the sum thereof. US 2022/0263212 describes one example of a rat-race balun. There is a need to reduce the footprint of rat-race baluns on the electronic carriers on which they are integrated. SUMMARY OF THE INVENTION 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 P1, P2, P3, P4 connected to said transmission line loop, said balun being designed to receive a first signal on the port P1, and to divide said first signal into a second signal that is delivered to the port P2 and a third signal that is delivered to the port P4, said second signal and said third signal being in phase opposition with one another, wherein the ports adjacent to one another from among the ports P1, P2, P3, P4 are connected by respective sections of the transmission line loop, and at least some of said sections are capacitor-loaded transmission line sections; said balun being characterized in that: the respective transmission line section between the adjacent ports P1 and P4 is of electrical length 2θ2, of impedance Z3 and is a line section loaded by a capacitor of capacitance C2; where θ2<135 and the following equalities are satisfied: C⁢2=-2⁢tan⁡(θ2)ω⁢ZP⁢1⁢P⁢4⁢tan⁡(2⁢θ2)and⁢ Z3=-ZP⁢1⁢P⁢4tan⁡(θ2) w being equal to 2πf, with f the operating frequency, and ZP1P4 being the impedance of the unloaded transmission line section of physical length 3λ/4 equivalent to said loaded line section. Such a balun makes it possible to reduce the footprint of rat-race baluns on the electronic carriers on which they are integrated. In some embodiments, such a balun will furthermore comprise at least one of the following features: each of the respective transmission line sections between P1 and P2, between P2 and P3, between P3 and P4 is a line section of electrical length 2θ1, of impedance Z1 and loaded by a capacitor of capacitance C and; where θ1<45° and the following equalities are satisfied: C =2⁢tan⁡(θ1)ω⁢Zc⁢tan⁡(2⁢θ1)and⁢ Z1=Zctan⁡(θ1)w being equal to 2πf, with f the operating frequency, andZc being the impedance of the unloaded transmission line section of physical length λ/4 equivalent to said loaded line section; the balun is kidney-shaped and the ports P2, P4 each comprise at least a first section connected to the transmission line, the first section of the port P2 being parallel to the first section of the port P4;the mutually parallel first section of the port P2 and first section of the port P4 face one another;the balun comprises an impedance transformer loaded by a capacitor between the port P1 and the transmission line loop. According to another aspect, the invention describes a method for reducing the footprint of 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 designed to receive a first signal on the port P1, and to divide said first signal into a second signal that is delivered to the port P2 and a third signal that is de