Compact Uniform Folded Section Rat-Race Couplers with Harmonic Suppression

Abstract

In this paper, two 50Ω terminated rat-race hybrid couplers based on uniform folded structures are proposed for equal division of power. The proposed designs are of simple in geometry and have an area of only one-fourth of the conventional coupler. The first technique is two-fold double section topology operating at 1.77 GHz designed with the conventional impedance ratio of √2 between port and transmission line which exhibits good in-band characteristics and requires a minimum track width of 0.8 mm. The second technique is stub-loaded double section topology where the novelty lies in deploying impedance matched stubs which avoids high impedance lines by maintaining an impedance ratio less than 2 between port and transmission line. In addition to good passband characteristics, it also suppresses higher harmonics up to 6.3f₀ and requires a minimum track width of 0.41 mm which makes it easy for realization. The bottom line of both designs is to achieve extreme structural simplicity without using high impedance transmission lines of more than 100Ω, narrow tracks less than 0.4 mm, lumped elements, and via holes. The prototype of the proposed coupler is fabricated and the simulated results are validated using measurements.

KEYWORDS:

• Harmonic suppression
• Impedance matching
• Miniaturization
• Rat-race hybrid couplers
• Stub-loaded double section
• Two-fold double section

ACKNOWLEDGEMENTS

The authors thank the SSN Trust, AICTE and DST funded RF Measurement Facility at Sri Sivasubramaniya Nadar College of Engineering, Chennai, India for the measurements.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

V. Chandra Prasad

V Chandra Prasad received the BE degree in electronics and communication engineering, and the ME degree from Anna University, Chennai, India. His research interest includes antenna and microwave filter design.

Ramprabhu Sivasamy

Ramprabhu Sivasamy received the BE degree in electronics and communication engineering, ME and PhD degrees from Anna University, Chennai, India. His research interest includes antenna, filter design and frequency selective surfaces. Email: [email protected]