Using Parallel-Plate Dielectric Waveguides in Terahertz Technology

Key Takeaways

• The spatial confinement of parallel-plate waveguides is poor, but parallel-plate dielectric waveguides are an efficient alternative to them.

• The fundamental mode, which can propagate down to DC, is the most important property of a parallel-plate dielectric waveguide. 

• The fundamental mode of propagation in an ideal parallel-plate dielectric waveguide is TE10 mode. This mode supports the electric field distribution across the parallel plates.

In fields such as spectroscopy, terahertz technology is extensively used. In such terahertz applications, parallel-plate dielectric waveguides are often used as the guiding medium.

In fields such as spectroscopy, imaging, security, and biotechnology, terahertz technology is extensively used. In terahertz applications, a parallel-plate dielectric waveguide is used as the new guiding medium. Parallel-plate dielectric waveguides are an efficient alternative to parallel-plate waveguides, as parallel-plate waveguides have poor spatial confinement and parallel-plate dielectric waveguides are effective at minimizing parallel-plate mode excitation problems.

Let’s take a closer look at parallel-plate dielectric waveguides and why they are the best choice for terahertz applications. 

Finding Efficient Waveguides for Terahertz Technology

In spectroscopy, sensors, radars, and imaging, electromagnetic waves ranging from 0.1THz to 3THz are most commonly used. Terahertz applications have difficulty transmitting signals using guided wave structures. The lack of efficient waveguides is one of the major research challenges in the application of terahertz technology. The research solutions devised for guiding structures include metal film dielectric waveguides, parallel-plate waveguides, and H-guides. 

Parallel-Plate Waveguides Offer a Solution

Parallel-plate waveguides offer dispersionless propagation and give an above-average performance in terahertz structures or circuits. However, in a parallel-plate waveguide, the radiation loss is high due to electric field distribution covering the entire cross-section. The structure of H-guide-a hybrid waveguides offers low conduction loss for wave modes where the electric field is parallel to the plates. In its semi-open structure, the radiation loss makes an H-guide unsuitable for terahertz applications. Considering all the drawbacks, parallel-plate dielectric waveguides are effective low-loss transmission structures for terahertz applications.

The Advantages of Parallel-Plate Dielectric Waveguides

Parallel-Plate Dielectric Waveguides vs. Parallel-Plate Waveguides

The strong energy concentration and weak radiation field exhibited by parallel-plate dielectric waveguides provide better results in terahertz applications than parallel-plate waveguides. The metal plates provide isolation in parallel-plate dielectric waveguides, which is a requirement in multilayer microwave integrated circuits. 

Parallel-Plate Dielectric Waveguides vs. H-Guides and Non-Radiative Dielectric Guides

The simple excitation, such as a coaxial feed and the absence of cut-off frequency, makes parallel-plate dielectric waveguides superior to H-guides and non-radiative dielectric (NRD) guides. The cut-off frequency and the multi-mode excitation problems associated with H-guides and NRD guides offset their use in terahertz applications. The fundamental mode, which can propagate down to DC, is the most important property of parallel-plate dielectric waveguides, which makes them more suitable than H-guides and NRD guides.

The Geometry of Parallel-Plate Dielectric Waveguides

Parallel-plate dielectric waveguides consist of parallel plates that are perfectly conducting. There are three rectangular dielectric materials placed between the parallel plates. Some of the dielectric materials and their permittivity values are given in the table below.

Materials used in parallel-plate dielectric waveguides

For mode guidance, the dielectric constant or permittivity follows the condition:

In symmetric parallel-plate dielectric waveguides, the dielectric constants 2and 3are equal. 

The Fundamental Mode of Parallel-Plate Dielectric Waveguides

The fundamental mode of propagation in an ideal parallel-plate dielectric waveguide is TE10 mode. This mode is also called LSE10 mode. This fundamental mode supports the electric field distribution across the parallel plates. Even though TE10 mode is a non-TEM mode, the field distribution in the central region is more like a quasi-TEM transmission line. This feature permits the excitation of parallel-plate dielectric waveguides without using complex transition geometries.

In parallel-plate dielectric waveguides, electromagnetic power is confined within dielectric strips. There is no leakage or radiation of the electromagnetic power into the parallel plates in parallel-plate dielectric waveguides compared to parallel-plate waveguides. Therefore,  we can say that parallel-plate dielectric waveguide propagation mode is a non-radiating mode. Fields are bounded to the central guiding region and this prevents leakage problems in parallel-plate dielectric waveguides. The elimination of the cut-off state in fundamental mode establishes the use of thinner parallel-plate dielectric waveguides, which is why they are the most desirable dielectric waveguiding structure in terahertz applications.

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