Branch Waveguide Coupler Research Articles

Branch Waveguide Couplers with a frequency of 510 GHz for Terahertz Transmit/Receive Isolation Applications.

To address the requirement of functioning as a transmit/receive isolation device in terahertz transceiver systems, in this paper, we present two high-isolation multi-branch waveguide directional couplers operating at a center frequency of 510 GHz. One is a high-performance five-branch directional coupler, and the other is a new type of three-branch waveguide coupler with lower processing difficulty. Both couplers were fabricated using low-cost CNC milling technologies. The performance of these couplers was verified through measurement results, demonstrating high isolation at the center frequency.

A Novel Ultrawideband Branch Waveguide Coupler With Low Amplitude Imbalance

In this article, we present a novel ultrawideband branch waveguide coupler (BWC) with low amplitude imbalance. This novel design is based on a new structure of branch waveguide obtained by symmetrically increasing the waveguide width. The coupling degree can be independently controlled by the height and width of the new branch waveguide, which significantly increases the design flexibility. In addition, this structure can produce a transmission zero (TZ), and a concept to improve the fractional bandwidth of the BWC with out-of-band TZ is proposed. Based on the analysis, the design guidelines for the novel BWC are provided. For a given center frequency, an n-branch novel BWC can be easily designed. Moreover, because of the larger branch waveguide height, this novel design has greatly eased the machining difficulty. Finally, to verify the design concept, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band eight-branch prototype is processed and measured. In full <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band, the amplitude imbalance is less than 0.52 dB, the phase imbalance is less than 2.5°, the return loss (RL) is greater than 21.4 dB, and the isolation is greater than 20.5 dB. The simulation and experimental results are in good agreement.

Mode Analyzing Method for Fast Design of Branch Waveguide Coupler

An accurate and efficient method for analyzing the coupling ratio of symmetrical four-port branch waveguide coupler is presented. The method is based on the mode-matching method (MMM) and the odd and even mode analysis, considering the interactions between the fundamental and higher order modes in junctions and discontinuities. It is found that the coupling ratio of the waveguide coupler is depended on the sum of all the branch line height if the center frequency is determined, which is valid for any coupling ratio and any number of shunt branches (≥3) waveguide coupler. Compared to the traditional design method that is complex and only valid under some restrictions, the proposed method has the characteristics of accuracy and universality, and has a simple and intuitive expression. The theoretical work is verified in an experiment by characterizing four fabricated waveguide couplers with a different number of shunt branches.

Design and Millimeter-Wave Measurement of a Wideband Power Coupling Structure for Sheet Electron Beam Devices

Two power coupling structures based on a Y-type branch waveguide (YTBW) coupler for sheet electron beam devices are presented in this paper. The YTBW coupler is a good choice for the power coupling due to its broad bandwidth property and compact configuration. However, according to the previous studies, it is difficult for a YTBW coupler to obtain good isolation, small port reflection and, meanwhile, high transmission in a broad frequency band. To address this issue, the following two approaches were proposed: 1) introducing multiple branch slots between branch waveguide 1 and branch waveguide 3 of the YTBW coupler to cancel out the electromagnetic (EM) wave propagating toward the isolation port and 2) enlarging branch waveguide 1 at the junction of the three branch waveguides to achieve a port impedance matching and guide the EM wave to propagate to the port connecting with the slow-wave structure. The measured results demonstrated that the bandwidth of port reflection lower than -12.5 dB, isolation coefficient smaller than -12.0 dB, and meanwhile, the transmission higher than -1.0 dB, was 13.5 GHz (50.0-63.5 GHz), corresponding to a fractional bandwidth of 23.8%.

Theoretical analysis and design optimization of wideband input/output branch waveguide couplers for a sheet beam traveling wave tube

The branch waveguide coupler (BWC) with an intrinsically excellent microwave property in an extremely wide frequency range was proposed to build the input/output (I/O) structure for the sheet beam traveling wave tube. The odd and even mode theory is utilized to analyze the BWC. Based on the theory, a code is written to calculate its microwave performance parameters. The numerical calculation has a good agreement with the computation simulation. To improve the efficiency of developing the BWC, a novel design optimization approach based on the MATLAB optimization tool is proposed. A BWC with nine branch waveguides is optimized using multi-objective genetic algorithm. In addition to the excellent microwave property, a compact configuration is achieved. It is predicted that the I/O structure possesses a very good performance with coupling above −0.3 dB, port reflectivity under −19 dB, and isolation less than −15 dB in a broad frequency range of 37.4–51.0 GHz, corresponding to a bandwidth of 13.6 GHz (30.7%).

Design and microwave test of an ultrawideband input/output structure for sheet beam travelling wave tubes.

Broadband operation is of great importance for the applications of travelling wave tubes such as high-data communication and wideband radar. An input/output (I/O) structure operating with broadband property plays a significant role to achieve these applications. In this paper, a Y-type branch waveguide (YTBW) coupler and its improvements are proposed and utilized to construct an extremely wideband I/O structure to ensure the broadband operation for sheet beam travelling wave tubes (SB-TWTs). Cascaded reflection resonators are utilized to improve the isolation characteristic and transmission efficiency. Furthermore, to minimize the reflectivity of the port connected with the RF circuit, wave-absorbing material (WAM) is loaded in the resonator. Simulation results for the YTBW loaded with WAM predict an excellent performance with a 50.2% relative bandwidth for port reflectivity under -15 dB, transmission up to -1.5 dB, and meanwhile isolation under -20 dB. In addition, the coupler has a relatively compact configuration and the beam tunnel can be widened, which is beneficial for the propagation of the electrons. A Q-band YTBW loaded with two reflection resonators is fabricated and microwave tested. Vector network analyzer (VNA) measured results have an excellent agreement with our simulation, which verify our theoretical analysis and simulation calculation.

Time dependence of directive channelling in photonic crystal based multiport devices

Time dependence of directive routing of an optical wave in an add-drop multiplexer is theoretically studied using finite difference time domain (FDTD) methods. The device under investigation is a double branch waveguide coupler patterned in a two-dimensional photonic crystal. The latter is constituted by a two-dimensional array of air holes deeply etched in the growth direction of a InP-based semiconductor heterostructure which ensures the lateral confinement of light. Sub-picosecond transfer times and picosecond switching times between coupled channels are demonstrated around 1.55 μm and various operating modes (dropping, three-color operation) are detailed.

The Multiple Branch Waveguide Coupler

A multiple branch directional coupler is discussed for rectangular waveguide applications for series junctions. A design method is developed which is valid for any coupling ratio and any number of branch lines with perfect match and directivity. The frequency response of this type coupler is calculated with the aid of a digital computer.