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This article was submitted to Radiation Detectors and Imaging, a section of the journal Frontiers in Physics

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The dielectric waveguide in THz and millimeter circuit is widely researched. However, it is rarely researched in a microwave frequency. In this article, a dielectric rod waveguide (DRW) is proposed with low transmission loss in microwave frequency. For the purpose of impedance matching, a transition section composed of the metal-coated dielectric cavity, and a dielectric horn is presented to match the impedance between the coaxial cable and the dielectric rod waveguide. Finally, the dielectric rod waveguide and the transition section have been fabricated for experimental verification. To obtain the propagation constant of the DRW, the thru-line (TL) calibration is used in measurement. The simulation and measurement results show an effective conversion between the coaxial cable and the dielectric rod waveguide.

Waveguide is an important passive component in electronic circuits. Due to the low transmission loss of the dielectric waveguide in millimeter and THz frequency ranges, various dielectric waveguides [

In microwave frequency, the dielectric material has good radiation properties and can be fabricated into dielectric rod waveguide antennas [

The conversion structures between the traditional metal transmission lines and the dielectric waveguides have been widely studied. The dielectric tapering transition sections [

In this article, we present the dielectric rod waveguide with a rectangular cross section in microwave frequency. In order to connect the DRW with the coaxial cable, a transition structure composed of the metal-coated dielectric cavity and dielectric horn is proposed. Simulation and measurement are in good agreement. The results show that the transmission loss of the dielectric rod waveguide is low, and the transition between the coaxial cable and the dielectric rod waveguide is effective from 7.12 to 9.4 GHz. The designed dielectric rod waveguide and the conversion structure are able to apply for further design of dielectric interconnect circuits and novel microwave components.

The structure of the designed dielectric rod waveguide and the conversion section are divided into three parts, as shown in _{
b
} and the length _{
a
} of the coaxial probe position are used to match the impedance between the coaxial cable and the metal-coated dielectric cavity [

_{
a
} = 5.7, _{
b
} = 5.8, _{1} = 13, _{2} = 5, and _{3} = 50 (all in mm). (Dielectric material is blue, and the metal is yellow.)

The electric field distribution at the xoz plane is shown in _{x11} mode [_{10} mode. The TE_{10} mode of the metal-coated dielectric cavity is then converted to the _{x11} mode of the DRW. Thus, the metal-coated dielectric horn provides a smooth transition between the two wave modes.

Electric field distribution at 8 GHz of the designed dielectric rod waveguide and the conversion structure.

In order to verify the properties of the designed dielectric rod waveguide and the conversion structure, two structures with different DRW lengths have been manufactured. The 50 Ω SMA connectors are welded on the top side.

The simulated and measured results of the two structures with different DRW lengths are presented in

In order to obtain the actual propagation parameters, the attenuation constant _{1} and L_{2}) are used to realize the thru and line standards. And the T-matrix under these two cases can be called as TT and TL. These two calibration kits are similar to the thru and line calibration kit in thru-reflect-line (TRL). Based on the symmetry of the error box, it can only use those two calibration kits. The TL calibration is powerful to model the guided wave structures and substrate-integrated circuits and to extract the parameters of the microwave circuits. This method can be easily implemented into commercial software for many types of microwave circuits. The theory derivation will be given as follows, as described in references [

_{
M
}, _{DUT}, and

Schematic diagrams of numerical TL de-embedding procedure and the two standards in TRL.

Because the two error boxes are symmetrical, the relation between ^{−1} denotes the inverse of the matrix A. For a simple expression, we define

Substituting _{2}-_{1}. And the columns of the matrix _{2}-L_{1。}.

The matching network of this design works the error box in the TL calibration, which needs to be removed. After deembedding the error box, the accurate results of the transmission dielectric rod waveguide can be obtained. _{0} is larger than 1 over the whole frequency band, working as the slow wave. So there is no leaky wave, and less radiation wave radiates from the dielectric waveguide. It can serve as a low loss transmission line.

Attenuation constant and normalized propagation constant calculated by the simulation and measurement results. _{0} is the propagation constant in the free space.

In this work, a dielectric rod waveguide in a microwave band has been presented. For an impedance matching purpose, a transition between the coaxial cable and the designed DRW is designed from 7.12 to 9.4 GHz. The metal coated dielectric cavity and a dielectric horn convert the wave mode of the coaxial cable into the Ex11 mode of the dielectric rod waveguide. In order to verify the transmission and transition properties, two dielectric rod waveguides with different transmission line lengths and the same conversion sections are fabricated and tested. The designed dielectric rod waveguide and the conversion section have the potential to advance in developing novel microwave components.

The original contributions presented in the study are included in the article/Supplementary Material; further inquiries can be directed to the corresponding author.

The first author YL simulated the results and TL calibration theory. S-YZ simulated some structures and measured results. S-WW provided the theoretical analysis. J-YL helped with the theoretical analysis.

This work was supported in part by the Shenzhen Science and Technology Programs (Grant/Award Numbers: JCYJ20190808145411289 and JCYJ20180305124543176); Natural Science Foundation of Guangdong Province (Grant/Award Number: 2018A030313481); Shenzhen University Research Start up Project of New Staff (Grant/Award Number: 860-000002110311); and Guangdong Basic and Applied Basic Research Foundation, Grant/Award Number: 2019A1515111166.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

This is short text to acknowledge the contributions of specific colleagues, institutions, or agencies that aided the efforts of the authors.