Composite right/left handed (CRLH) couplers

• US 7,508,283 B2
• Filed: 03/28/2005
• Issued: 03/24/2009
• Est. Priority Date: 03/26/2004
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Lin, I-Hsiang, Caloz, Christophe, Itoh, Tatsuo, Okabe, Hiroshi
• Primary Examiner(s): TAKAOKA, DEAN O
• Application Number:
  US11/092,141
• Publication Number:
  US 20050253667A1
• Time in Patent Office: 1,457 Days
• Field of Search: 333/109, 333/112, 333/117, 333/118
• US Class Current: 333/118
• CPC Class Codes: H01P 5/227 90° branch line couplers

Abstract

High-frequency couplers and coupling techniques are described utilizing artificial composite right/left-handed transmission line (CRLH-TL). Three specific forms of couplers are described; (1) a coupled-line backward coupler is described with arbitrary tight/loose coupling and broad bandwidth; (2) a compact enhanced-bandwidth hybrid ring coupler is described with increased bandwidth and decreased size; and (3) a dual-band branch-line coupler that is not limited to a harmonic relation between the bands. These variations are preferably implemented in a microstrip fabrication process and may use lumped-element components. The couplers and coupling techniques are directed at increasing the utility while decreasing the size of high-frequency couplers, and are suitable for use with separate coupler or couplers integrated within integrated devices.

Claims

1. A coupler apparatus for generating separate signal channels from a radio-frequency input, comprising:

an input line configured for receiving a high-frequency input signal;

a transmission line connecting said input line to an output line and to at least one separate signal channel; and

means for creating a left-handed anti-parallel relationship between phase and group velocities below a transition frequency, ω

₀, and a right-handed parallel relationship between phase and group velocities above transition frequency ω

₀, within at least a portion of said transmission line, to generate backward wave coupling.

2. A coupler as recited in claim 1, wherein said coupler is configured for operation at high-frequency, with transition frequency ω

₀ at or above approximately 100 MHz.

3. A coupler as recited in claim 1, wherein said coupler comprises unit cells having an electrical length less than π

/2.

4. A coupler as recited in claim 1, wherein said means comprises an artificial composite right/left-handed (CRLH) transmission line (TL).

5. A coupler as recited in claim 1, wherein said coupler comprises a coupled-line backward coupler with two parallel transmission lines (TLs).

6. A coupler as recited in claim 5:

wherein said backward coupler is configured with a gap ratio s/h which can be increased up to a ratio s/h of approximately 1/4; and

wherein s is the pap between the two parallel transmission lines, and h is the thickness of a substrate retaining the transmission lines.

7. A coupler as recited in claim 1, wherein said coupler comprises a hybrid ring coupler with at least one portion of the ring implemented with LH-TLs providing a negative phase rotation.

8. A coupler as recited in claim 7, wherein said negative phase rotation comprises a -90°

phase rotation to replace an RH-TL section with a 270°

phase shift.

9. A coupler as recited in claim 1:

wherein said coupler comprises a branch-line coupler with microstrip line interconnecting said inputs with more than one output; and

wherein at least one said microstrip line includes an LH-TL portion.

10. A coupler as recited in claim 9, wherein said LH-TL portion comprises discrete capacitors and inductors.

17. A coupler apparatus as recited in claim 1:

wherein said left-handed anti-parallel relationship and said right-handed parallel relationships comprise contributions within a combined composite right/left handed (CRLH) transmission line (TL) section; and

wherein said left-handed contribution of said CRLH is derived from lumped series capacitor and shunt inductor elements; and

wherein said right-handed contribution of said CRLH is derived from either lumped or distributed shunt capacitor and series inductor elements.

18. A coupler apparatus as recited in claim 17, wherein said right-handed contribution of said CRLH comprises microstrip line.

19. A coupler apparatus as recited in claim 17, wherein shunt capacitor and series inductor values of said right-handed contribution of said CRLH are determined in response to solving a set of equations for first and second center frequencies.

20. A coupler apparatus as recited in claim 1, wherein combining the anti-parallel relationship and parallel relationship allows achieving any desired pair of center frequencies.

24. A coupler as recited in claim 4:

wherein said CRLH TL comprises a unit cell;

wherein said unit cell comprises a series combination of a right-handed inductor and a left-handed capacitor; and

wherein said series combination of said right-handed inductor and said left-handed capacitor is coupled to a paralleled combination of a right-handed shunt capacitor and a left-handed shunt inductor.

25. A coupler as recited in claim 4:

wherein said CRLH TL comprises a right-handed (RH) TL section and a left-handed (LH) TL section; and

wherein the LH TL section is configured with alternating series capacitors of value C and shunt inductors of value L, and is coupled to the RH TL section with a capacitor of value 20.

26. A coupler as recited in claim 4, wherein said CRLH TL comprises alternating left-handed (LH) capacitors and right-handed (RH) TL sections coupled in series, and LH inductors shunting said RH TL sections, respectively.

11. A backward-coupler apparatus for generating separate signal channels from a radio-frequency (RF) input, comprising:

an input line configured for receiving a high-frequency RF input signal;

a first composite right/left-handed (CRLH) transmission line (TL) connecting said input line to an output line; and

a second CRLH-TL terminating in a coupled output and an isolated output, said second CRLH-TL positioned parallel to and in sufficient proximity with said first composite right/left-handed transmission line to generate a backward wave;

wherein capacitance and inductance contributions of the left-hand (LH) portion and the right-handed (RH) portions of said CRLH are chosen so that the phase response of each said TL is dominated by the LH contribution of the CRLH at below a center frequency, while the phase response is dominated by the RH contribution of the CRLH at above a center frequency.

12. A backward-coupler as recited in claim 11, wherein said backward-coupler is configured to a −

3 dB bandwidth on the order of 35%.

13. A backward-coupler as recited in claim 11, wherein an LH-TL contribution of said CRLH-TL comprises a combination of series capacitors with shunt-shorted inductors.

14. A backward-coupler as recited in claim 13, wherein said combination comprises capacitors of value 2 C in series with inductors of value L.

15. A backward-coupler as recited in claim 13, wherein said combination comprises interdigital capacitors on either side of shunt-shorted stub inductors.

16. A backward-coupler as recited in claim 11, wherein said second CRLH-TL is sufficiently proximal said first CRLH-TL so that the gap s between said first and second CRLH-TL, each of height h, can be increased up to a ratio s/h of approximately 1/4 without loss of backward wave.

21. A backward-coupler apparatus as recited in claim 11:

wherein said LH contribution of said CRLH is derived from lumped series capacitor and shunt inductor elements; and

wherein said RH contribution of said CRLH is derived from either lumped-distributed or microstrip line shunt capacitor and series inductor elements.

22. A backward-coupler apparatus as recited in claim 21, wherein capacitor and inductor values of said right-handed contribution of said CRLH are determined in response to solving a set of equations for first and second center frequencies.

23. A backward-coupler apparatus as recited in claim 11, wherein combining the anti-parallel relationship and parallel relationship allows reaching any desired pair of frequencies.