A compact filtering dipole antenna that requires no extra circuits is investigated. It consists of two folded arms and one additional extended arm, which are all printed on a single layer substrate. Two independently tunable radiation nulls are produced near the edges of the passband, giving filtering responses without the need of any filtering circuits. It has omnidirectional radiation patterns. Its measured -10-dB impedance bandwidth and average realized gain are 15.5% and of 2.0 dBi, respectively. It has a high selectivity with a suppression level of over 20 dB across the stopband. This basic design is extended to an electrically small filtering dipole antenna by using meander-line structures. Without greatly sacrificing the filtering effects, the antenna dimension can be reduced from about half wavelength (0.5λ0) to 0.3λ0. To verify the idea, a prototype was fabricated and tested, with reasonable agreement between the measured and simulated results. The antenna is electrically small (ka = 0.96) with a bandwidth of 10.8%. Its out-of-band suppression level is over 15.5 dB across the stopband with a high frequency selectivity.

In this article, a ridged substrate integrated coaxial line (RSICL) is proposed, which has a compact size, wide bandwidth, and excellent shielding. The RSICL has two ridges set on both sides of its outer conductor, which introduce additional capacitance and enhance shielding performance. Compared with the SICL, the width of the RSICL can be reduced significantly for 50- Ω characteristic impedance. Hence, the monomode bandwidth of the RSICL is larger than that of the SICL. Closed-form formulas based on the conformal mapping method are derived for fast calculation of the characteristic impedance of the RSICL. Compared with full-wave simulation, the proposed formula has an error of less than 1%. An RSICL with grounded coplanar waveguide (GCPW) transitions is designed and fabricated under print circuit board (PCB) technology. The measurement results show the RSICL with the transitions has a bandwidth from dc to 40 GHz, insertion loss less than 1.9 dB, return loss larger than 10.5 dB, and a data rate of 32 Gb/s with a good eye diagram and low bit error rate (BER). The measured attenuation of the RSICL is 0.021 dB/mm at 40 GHz. Full-wave simulation results show that the width of the RSICL is 6% smaller than that of the SICL, the monomode bandwidth is 6.7% wider, and the energy leakage of the RSICL is only 1/120 of the SICL.

This article proposes a hollow rectangular dielectric waveguide (HRDW) for sub-terahertz (sub-THz) applications. Comprising three layers of dielectric material, the HRDW features a hollow structure achieved by cutting a slot in the middle layer. In addition, the propagation constant of the HRDW is analyzed based on the effective dielectric constant (EDC) method. The HRDW and rectangular metallic waveguide transitions are designed, optimized, and fabricated by the printed circuit board (PCB) process and computer numerical control (CNC) machining, respectively. The HRDW supports monomode operation in the range of 90–294-GHz frequency. The measurement results show that the average attenuation constant of the HRDW is 0.028 dB/mm in the range of 220–294-GHz frequency. With its low-loss and high-bandwidth properties, the HRDW provides an innovative solution for sub-THz interconnects.

The ridged substrate integrated coaxial line (RSICL) supports transverse electromagnetic (TEM) wave with small size, broadband, and good shielding performance. This article presents a two-material RSICL, which has two different dielectric materials filled in its substrate layers. Compared with the conventional RSICL with only one dielectric material, the two-material RSICL shows a higher cutoff frequency of the first higher order mode. Hence, the monomode bandwidth of the two-material RSICL can be improved accordingly. Based on the printed circuit board (PCB) process, the two-material RSICL with feeding structures is designed and fabricated. In the experiment, the first two-order modes of the two-material RSICL are excited with two types of transitions. The measured monomode bandwidth of the two-material RSICL is from dc to 44 GHz, which is 14.9% wider than that of the one-material RSICL.

This article proposes a microstrip-to-microstrip (MS-to-MS) vertical transition with pixel structures and then proposes a knowledge-assisted proximal policy optimization (PPO), which is a reinforcement learning (RL) for the design of this transition. The transition requires fully connected structures and a novel mechanism to generate the pixel structures with fully connected shape is proposed and incorporated into PPO. The proposed method is compared with the particle swarm optimization (PSO) and the genetic algorithm (GA) and demonstrates benefits in improving design efficiency. The designed MS-to-MS transition is fabricated using the PCB process. Measurement results indicate that the designed MS-to-MS vertical transition operates in the band from 3.4 to 14.8 GHz with low insertion loss.

In this article, a mode composite ridged substrate integrated coaxial line (MCRSICL) is proposed for concurrent multichannel operation. The TEM and TE₁₀ modes of the MCRSICL are excited simultaneously with high isolation. Consequently, the operation frequency band of the ridged substrate integrated coaxial line (RSICL) is expanded without necessitating additional physical space. The transmission performance and design principle of the MCRSICL are studied. Based on the low-temperature co-fired ceramic (LTCC) technology, an MCRSICL prototype is designed and fabricated to enable parallel TEM and TE₁₀ operations. The measurement results show that the TEM and TE₁₀ channels operate from dc to 40 and from 18 to 40 GHz, respectively, and the crosstalk between the two channels is below -35 dB. Besides, a multichannel high-speed signal transmission system is designed based on the MCRSICL prototype for high-speed interconnect applications, and the measured output signals exhibit good eye diagrams with 25-and 10-Gb/s pseudorandom binary sequence (PRBS) input signals. Subsequently, a dual-band bandpass filter (BPF) is proposed based on the MCRSICL, whose two channels operate at 5.7 and 29 GHz in a large frequency ratio of 5.1. In addition, a reconfigurable RF front end is designed using the MCRSICL BPF operating in both the sub-6G and Ka bands for an integrated communication and navigation system. The innovative MCRSICL establishes a novel platform for multichannel interconnect and component, characterized by compact dimension, simple transition, versatile design flexibility, and weak coupling between channels.