Design and Fabrication of Wideband Millimeter-Wave Directional Couplers With Different Coupling Factors Based on Gap Waveguide Technology

Davoud Zarifi,Ashraf Uz Zaman,Ali Farahbakhsh

doi:10.1109/access.2019.2926233

Abstract

A class of wideband directional couplers suitable for achieving different coupling levels are proposed in this paper. The proposed couplers have been implemented using the double-layer groove gap waveguide at the millimeter-wave frequency range. They are composed of two parallel groove gap waveguide parts placed on top of each other in such a way that the coupling between the two waveguide sections can be achieved via the coupling structures placed in the common wall. Usually, the coupling layer consists of two rows of holes and depending on the number of holes the coupling levels can be controlled. The manifest and applicable property of the proposed directional coupler is that the coupling level can be simply changed using the different coupling layers without changing the top and bottom groove waveguides and transitions. As another significant advantage of the proposed coupler, there is no requirement of good electrical contact among different metallic parts of the structure, which considerably simplifies the manufacturing processes and mechanical assembly at millimeter-waves applications. For verification purpose, three sample couplers with coupling levels of 10, 20, and 30 dB have been designed, fabricated, and measured. To make the device accessible and measurable using the standard rectangular waveguides, two types of transitions from the groove gap waveguide to standard WR-15 are designed. The simulation and experimental results are in good agreement and show that the proposed couplers have large bandwidth for return loss level of 20 dB, coupling level of 10±1, 20±1, and 30±1 dB, and isolation level of 30, 35, and 40 dB over the desired frequency band of 50-70 GHz. The proposed directional couplers can be used as good candidates at millimeter-wave frequencies for probing and the design of compact integrated microwave circuits and systems, such as antenna array feeding networks.

Highlights

Directional couplers are passive four-port devices which have different applications such as signal quality and power level, measuring reflections, mixing signals and for isolation of signal sources in microwave and millimeter-wave systems
This paper presents the investigation and development of innovative groove gap waveguide directional couplers design centered at the 60 GHz for potential generation communication systems and V-band applications
VOLUME 7, 2019 level of directional couplers can be changed using the different coupling layers without changing in groove waveguide sections and transitions and there is no requirement of good electrical contact among different metallic parts of the structure even though the waveguide sections has been splitted in the H-plane

Summary

INTRODUCTION

Directional couplers are passive four-port devices which have different applications such as signal quality and power level, measuring reflections, mixing signals and for isolation of signal sources in microwave and millimeter-wave systems. Many early proposed directional couplers, including Bethe-hole coupler [1], multi-hole coupler [2], and Schwinger coupler [3], were invented and characterized in the 1940s These components can be implemented in the context of different transmission line structures such as waveguides [4]–[6], microstrips [7], [8], substrate integrated waveguide (SIWs) [9]–[11]. D. Zarifi et al.: Design and Fabrication of Wideband Millimeter-Wave Directional Couplers With Different Coupling Factors major advantages over their waveguide counterpart, namely, compactness, planarity, low fabrication cost, and integrability with active microwave components and circuits.

GROOVE GAP WAVEGUIDE

DESIGN OF TRANSITION

FABRICATION AND MEASUREMENT

CONCLUSIONS