The dispersion and dielectric attenuation characteristics of a double-staggered grating waveguide (DSGW) are two crucial features related to the output characteristics of a sheet-beam traveling-wave amplifier and have been previously studied by using theoretical analysis and simulations. In this work, these two characteristics are both experimentally studied. Two ${H}$ -band (220–325 GHz) DSGW circuit prototypes with and without dielectric attenuators made of the BeO-TiO ₂ composite ceramic were machined by using nanocomputer numerical control milling. Experimental studies of the dispersion property were performed successfully where the measurement results were in good agreement with those predicted by simulations, exhibiting a wide passband of 70 GHz (230–300 GHz). The measured transmission coefficient has been decreased from −5 to −55 dB after the introduction of dielectric attenuators, experimentally verifying the feasibility of the adopted methodology. The effects of the variations of dispersion relation and transmission loss on the beam-wave interaction stability were also investigated.

The design, fabrication, and experimental measurement of a broadband and compact TE $^{\Box}_{\text{10}}$ –TE $^{\circ}_{\text{01}}$ (symbols $\Box$ $^{^{^{}}}$ and $\circ $ represent the rectangular and circular waveguides, respectively) mode converter is presented in this article. The proposed mode converter consists of three components, including a TE $^{\Box}_{\text{10}}$ –TE $^{\Box}_{\text{20}}$ mode converter based on a two-way H-T junction power divider, a TE $^{\Box}_{\text{20}}$ –TE $^{+}_{\text{22}}$ mode converter with variable cross-shaped waveguide, and a TE $^{+}_{\text{22}}$ –TE $^{\circ}_{\text{01}}$ mode converter. Two distinct design schemes have been employed for the first part of the TE $^{\Box}_{\text{10}}$ –TE $^{\circ}_{\text{01}}$ mode converter, which are based on two-way $^{^{^{}}}$ H-T junction power dividers with a path difference of odd times half-waveguide wavelength (Scheme 1) and a 180 $^{\circ}$ phase shifter (Scheme 2), respectively. This mode converter is highlighted by the significant advantage of high conversion efficiency over a wide bandwidth with a relatively easy-to-fabricate structure, which is evidenced by the measurement of two identical back-to-back joined mode converters based on Scheme 1. Measurement results matched with simulation ones within reasonable accuracy, which predicted that a 1-dB transmission bandwidth of $\sim$ 56.7 GHz was obtained. Meanwhile, the reflection coefficient S $_{\text{11}}$ was below $-$ 13.2 dB over that bandwidth.

This paper presents a novel magneto-optical isolator based on an ultra-wideband and high efficiency photonic crystals (PCs) waveguide and gyromagnetic ferrites. The three-dimensional numerical simulation finds that the photonic crystals waveguide’s (PCW) transmission efficiency rises with its height and width. The corresponding experiments are performed by using a triangular lattice Al₂O₃ dielectric posts array in 5G millimeter wave band. The measured transmission efficiency is up to 90.78% for the optimal PCs waveguide structure, which has ultra-wide operating bandwidth from 23.45 to 31.25 GHz. The magneto-optical isolator is designed by inserting two rectangular gyromagnetic ferrites into the PCs waveguide. Due to the contrast between the effective permeability of the left and right circular polarization waves passing through the magnetized ferrite sheets, the ferromagnetic resonance absorption of the forward and reverse waves is different. By using finite element method, the isolation is optimized to be 49.49 dB for the isolator and its relative bandwidth reaches 8.85%. The high isolation, broadband, and easy integration indicate that our designed magneto-optical isolator has significant advantage in 5G communication systems.

In this paper, a terahertz circulator based on a magneto photonic crystal slab is envisaged. The triangular lattice photonic crystals with a line defect waveguide were constructed on an Al₂O₃ ceramic slab. Two cylindrical ferrites and two copper-clad plates in the junction of the Y-shaped wave-guide worked as a magneto-optical cavity resonator to approve the nonreciprocal function. In the working frequency range, 0.212–0.238 THz, the isolation of the circulator was better than 20 dB, and the insertion loss was better than 1 dB. The designed circulator based on the magneto photonic crystal slab experienced low loss and a wide bandwidth that satisfied its use in the THz application.

A wideband circulator based on magneto photonic crystals (PCs) is demonstrated in this letter. The 2D PCs are constructed with Al ₂ O ₃ rods embedded in air background. Triangular ferrites are chosen with saturation magnetization Ms = 2100 Gs and magnetic losses AH = 50 Oe; the external magnetic bias is H ₀ = 13500 A/m. The experimental results show the insertion loss less than -0.8 dB and isolation better than -15 dB in a frequency range of 9.4-10.5 GHz, which are well matched to the numerical results. In this letter, a PC circulator working in the whole photonic bandgap of PCs is realized, which can be applied in practical wideband communication systems. Such a PCs circular has potential applications in future integrated photonic crystal systems.