Waveguide Bandwidth Research Articles

Design and characterization of mesoscopic dielectric cuboid antenna for operation in WR-3.4 waveguide bandwidth (220–330 GHz)

We designed a mesoscopic dielectric cuboid antenna connected to a flangeless WR-3.4 open-ended waveguide, and the antenna characteristics at 300 GHz were examined through simulations and experiments. Simulations confirmed that the flangeless design eliminated the flange-induced ripples in the radiation pattern, whose shape varied with frequency, and that the antenna operated in the full bandwidth of the WR-3.4 waveguide (220–330 GHz). Prototypes were then fabricated based on the simulation findings. A prototype with an antenna aperture area of 1.5 mm times 1.5 mm and an antenna length of 2.35 mm exhibited an antenna gain of 17.2 dBi at 300 GHz and a voltage standing wave ratio of less than 1.5 throughout the WR-3.4 waveguide bandwidth. The level of the side lobes at about pm 30 degrees in the E-plane pattern was approximately -10 dB that of the main lobe. Therefore, the proposed antenna, connected to a flangeless waveguide, is a promising antenna for use in future short-range high-speed terahertz wireless applications such as kiosk downloads and board-to-board communication.

Optical printed circuit boards with multimode polymer waveguides and pluggable connectors for high-speed optical interconnects.

We demonstrate the development of optical printed circuit boards (OPCBs) containing multimode polymer waveguides and pluggable optical connectors. The basic optical characteristics of the PCB-embedded waveguides, waveguide connectors, and high-speed performance were comprehensively evaluated. The fabricated OPCB comprises eight electrical layers and one optical layer. Waveguides are terminated at both ends with MT/MPO connectors. The optical channels comprising 10 cm-long waveguides embedded in OPCBs with two connectors show an average insertion loss of 6.42 dB. The resulting coupling loss is 0.77 dB per interface, which is very low and to our knowledge is among the lowest reported to date for waveguides embedded in rigid PCBs. 30 Gbps per channel NRZ data transmission was demonstrated with a measured waveguide bandwidth of 23 GHz × m, which gives a possible data traffic of 720 Gb/s for such 24-channel parallel optical link. Our efforts lay the foundation for the further development of OPCBs with higher performance.

Method to Change the Through-Hole Structure to Broaden Grounded Coplanar Waveguide Bandwidth.

A grounded coplanar waveguide (GCPW), as a millimeter wave special transmission line, can be used to calibrate broadband oscilloscope probes. A method to change the through-hole structure to widen the GCPW is investigated in this paper. The effect of the through-hole array on the band-width of the GCPW is investigated and verified using COMSOL Multiphysics simulation software. Finally, the S-parameters of the fabricated GCPWs are measured by a vector network analyzer, and the results show that they have an insertion loss > -3 dB and return loss < -10 dB in the frequency range of DC to 60 GHz, which satisfies the design requirements.

High-speed performance evaluation of ultra-flexible polymer waveguides supporting meter-scale optical interconnects.

We demonstrate bandwidth measurement and high-speed data transmission of meter-scale connectorized ultra-flexible multimode waveguide links with a maximum length of 180 cm. The pulses propagating through the waveguides broadened linearly with the increase of the length from 20 cm to 240 cm and the estimated mode delay from the pulse broadening was 0.093 ps/cm. The corresponding waveguide bandwidth decreased inversely with the increase of waveguide length, leading to a bandwidth-length product of 42 GHz·m. Degradation in bandwidth due to the introduction of bending or twisting was small when the samples were bent with a bending radius as small as 1 mm for 3 turns or twisted for 4 full turns, respectively. Error-free transmission of 30 Gb/s non-return-to-zero (NRZ) signal was achieved with a record link length up to 140 cm to the best of our knowledge. Our results show that the demonstrated flexible waveguides have both excellent optical and mechanical properties and are ideal for high-speed optical interconnects application especially those have a strict requirement on flexibility.

Compact Full Ka-Band Waveguide Directional Coupler Based on Rectangular Aperture Array with Stairs.

This article presents a compact 3 dB waveguide directional coupler with full waveguide bandwidth. It consists of a pair of rectangular waveguides with stairs structures in the coupling region. The waveguides are placed parallel to each other along their broad wall, which has a rectangular aperture array. The compact size, broad bandwidth, good in-band coupling flatness, and good return loss are achieved by using the proposed structure. For verification purposes, a prototype of the proposed coupler was designed, manufactured, and measured. The experimental results show that over the full waveguide bandwidth a return loss of input port better than 17.46 dB, coupling strength varying between −2.74 dB and −3.80 dB, power-split unbalance within 0.76 dB, and an isolation better than 20.82 dB were obtained. The length of the coupling region was only 15.82 mm.

Compact W-Band “Swan Neck” Turnstile Junction Orthomode Transducer Implemented by 3-D Printing

A turnstile junction orthomode transducer (OMT) provides polarization separation/combining on a full waveguide bandwidth; however, it bears a complex connecting structure, which accordingly leads to a bulky volume. We present a compact W-band (75-110 GHz) OMT using a “swan neck” twist for the connection between a turnstile junction and an E-plane Y-junction, for minimizing the overall OMT structure. The core volume for the proposed OMT is 9× less than the previously reported stacked-layer OMT. The compact W-band OMT was built by digital light processing (DLP) 3-D printing technology and was postmetallized by silver electroless plating. The return loss of the vertical-polarized port (V-port) and the horizontal-polarized port (H-port) is characterized, as averagely 17 and 15 dB, respectively. The measured average insertion loss from H- and V-ports to the common port is 0.5 and 0.6 dB. The measured isolation between V- and H-ports is averagely 28 dB. Furthermore, the turnstile junction asymmetry along the central axis was revealed in computed tomography (CT) scanned images. The simulation shows a negative effect of the asymmetric structure on the OMT isolation. In addition, the dual-polarized (dual-pol) antenna combining such OMT and a corrugated horn was realized in a compact size. The cross-polarization level of the OMT, characterized in a far-field test of this dual-pol antenna, is averagely -18 dB at the W-band.

Direct Chip-to-Waveguide Transition Realized With Wire Bonding for 140–220 GHz G-Band

This work presents a method to realize a direct chip-to-waveguide transition by means of commercial wire-bonding tools. A straight E-field probe is formed by a freely suspended bondwire and mounted to a standard RF pad on-chip. In contrast to conventional approaches, no additional dedicated substrate or large integrated radiating structure are necessary. A preliminary analysis is performed to illustrate the basic feasibility and a WR-05 prototype module, with dedicated test chip, is designed and optimized for a frequency range of 140–220 GHz (G-Band). The measured return loss of a back-to-back configuration is above 10 dB, while the deembedded absolute loss of a single transition is between 0.4 and 1 dB, both within the complete waveguide bandwidth of 80 GHz. The demonstrated performance is very well suited to ultrawideband communication systems or general-purpose mm-wave components.

A Compact Machinable 90° Waveguide Twist for Broadband Applications

We present a novel machinable 90° waveguide twist design suitable for broadband applications from microwave to terahertz frequency. The design achieves compactness and ease of fabrication by utilizing a series of quarter-wave transformer steps machined in split blocks. Three WR3.4 (220-330 GHz) prototypes with standard UG-387 flanges were fabricated and measured. The prototypes outperform two commercial waveguide twists in both return loss and insertion loss. The simulation and measurement results show that this design achieves a performance of -25 dB return loss for full waveguide bandwidth. Tolerance studies confirm that this design could be scaled up to terahertz frequency with modern computer numerical control (CNC) fabrication technology. In integrated waveguide systems, the waveguide twist design presented in this article can reduce losses at millimeter wave frequencies and achieve valuable weight savings in aerospace and other applications.

Compact full Ka‐band waveguide directional coupler based on large aperture array

A compact full Ka-band waveguide directional coupler based on novel aperture array is presented. The broadband, good in-band coupling flatness and excellent return loss are achieved by using the proposed novel aperture array in the common broad wall of two paralleled waveguides. For verification purpose, a prototype of the proposed directional coupler has been designed, fabricated and measured. The experimental results show that the return loss and isolation of the proposed coupler are better than 28 and 30 dB, respectively, and coupling strength varies from −20.35 to −19.23 dB over the full waveguide bandwidth. The length of the coupling region is only 8.5 mm.

Compact 3‐dB waveguide hybrid with full bandwidth

A compact waveguide 3-dB hybrid with full bandwidth is proposed in this Letter. The tight coupling and full bandwidth of Ka-band (from 26.3 to 40 GHz) are achieved by introducing multi-sections of waveguide with different width and depth, together with loaded posts on the bottom of some waveguide sections. The whole structure is symmetric both longitudinally and transversely (patent pending). The measured results show that return loss and isolation of the hybrid better than 25 dB and 26 dB, respectively, phase difference of the two output terminals within 90° ± 3° and the power-split unbalance within 3.1 dB ± 0.5 dB are achieved over the full Ka-band waveguide bandwidth.

40 Gb/s Data Transmission Over a 1-m-Long Multimode Polymer Spiral Waveguide for Board-Level Optical Interconnects

Optical interconnects have attracted considerable attention for use in short-reach communication links within high-performance electronic systems, such as data centers, supercomputers, and data storage systems. Multimode polymer waveguides, in particular, constitute an attractive technology for use in board-level interconnects as they can be cost-effectively integrated onto standard PCBs and allow system assembly with relaxed alignment tolerances. However, their highly multimoded nature raises important concerns about their bandwidth limitations and their potential to support very high on-board data rates. In this paper, we report record error-free (BER <; 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> ) 40 Gb/s data transmission over a 1-m-long multimode polymer spiral waveguide and present thorough studies on the waveguide bandwidth performance. The frequency response of the waveguide is investigated under a wide range of launch conditions and in the presence of input spatial offsets, which are expected to be highly-likely in real-world systems. A robust bandwidth performance is observed with a bandwidth-length product of at least 35 GHz×m for all launch conditions studied. The reported results clearly demonstrate the potential of this technology for use in board-level interconnects, and indicate that data rates of at least 40 Gb/s are feasible over waveguide lengths of 1 m.

A Compact 3 dB ${\rm E}$-Plane Waveguide Directional Coupler With Full Bandwidth

A compact 3 dB E-Plane waveguide directional coupler (patent pending) with full bandwidth is proposed in this letter. It consists of a pair of rectangular waveguides placed parallel to each other along their broad side. The tight coupling and wide bandwidth are achieved by using reduced height waveguide and large aperture in the common broad wall of the two parallel waveguides. For verification purpose, a prototype has been manufactured and measured. The measured results show that return loss and isolation of the coupler better than 25 and 26 dB, respectively, and the power-split unbalance within 0.6 dB are achieved over the full waveguide bandwidth.

A Cross-Guide Waveguide Directional Coupler With High Directivity and Broad Bandwidth

A cross-guide waveguide directional coupler (patent pending) with high directivity and broad bandwidth is proposed in this letter. It consists of two rectangular waveguides (called main waveguide and branch waveguide) crossing at a certain angle and sharing a common broad wall. High directivity is achieved by adding metal inserts in the branch waveguide in the coupling region near the crossed round-ended slots. For verification purpose, a sample coupler has been designed, manufactured and measured. The measured results show that the sample coupler has a directivity greater than 28 dB over the full waveguide bandwidth.

Design of a novel wideband single-mode waveguide in a photonic crystal slab structure

We propose a novel photonic crystal slab waveguide that provides a single-mode band with large bandwidth. The proposed waveguide is obtained by introducing a line defect in a triangular lattice of air holes in a dielectric slab. This line defect consists of holes which are not located in the original lattice points. The plane wave expansion (PWE) method is used to extract the band diagram of guiding modes and based on the results, photonic crystal holes in the defect row and its adjacent rows are modified to maximize the waveguide bandwidth. We show that using the proposed structure, a single-mode bandwidth of 17% can be achieved.

Planar photonic crystal structure with inherently single-mode waveguides.

A planar photonic crystal that allows inherently gap-guided single-mode waveguides is proposed and discussed. This novel structure consists of a two-dimensional lattice of silicon rods embedded on a thin silica slab sandwiched between two silica claddings whose refractive indices are slightly lower than the index of the silica core. The physical parameters of the structure, i.e., rod radius and core thickness, are optimized to maximize the bandgap width for odd modes. Lossless guided modes inside the bandgap and below the claddings' light cone are obtained by reducing the radius of a row of rods. The waveguide bandwidth can be increased by inserting a thin silicon dielectric waveguide instead of the row of rods. The proposed approach may overcome many of the common drawbacks in conventional holes-on-dielectric planar photonic crystal waveguides.

Scattering by inductive post in uniformly curved rectangular waveguide

A rigorous solution to the problem of wave scattering by a single inductive post in a continuously curved rectangular waveguide is presented. The position of the post and its radius are arbitrary. The waveguide curvature can be varied over wide limits. An efficient mathematical model of the unit is based on the domain-product technique. The theory developed is applied to the normalised reactances of the discontinuity and the induced surface current. The results obtained lend support to the validity of the known approximate solution for a thin post as far as this approximation goes. It is found that data for a centrally placed post deviate slightly from those for a straight guide in a broad interval of curvature variation. The off-centre shift affects the characteristics appreciably. Over full waveguide bandwidth, the paper provides the data that are essential in the design of devices containing uniform bends, such as bandpass filters or transmission resonators.

Improved design for multistate reflectometer (with two power detectors) for measuring reflection coefficients of microwave devices

The optimum-performance criteria originally developed for use with six-port reflectometers may, under certain circumstances, be extended to the design of the multistate reflectometer (which utilizes two power detectors to measure the reflection coefficients of microwave components). Test results-from simulations as well as experiments-have confirmed that the novel WR90 multistate instrument proposed in the present paper is able to yield near-optimum performance over the entire waveguide bandwidth.

Analysis and design of full-band matched waveguide bends

Compact waveguide bends with low return loss over the full waveguide band width are realized by placing properly selected discontinuities inside the curve. The component is designed by using an extremely efficient computer code which employs the local modes approach to analyze curved sections, while discontinuities are rigorously accounted for by considering their multimode equivalent circuit. A simple technique to select the appropriate matching elements is described and examples of full-band matched bends are provided.

Symmetrical five-port waveguide junction with -20 dB residual mismatch over waveguide bandwidth

Current designs for the symmetrical five-port waveguide junction have residual mismatches that rise to -14 dB over parts of the waveguide bandwidth. The present paper describes the use of a computer model to search for a new design (based on a combination of metallic post, dielectric sleeve and five inductive diaphragms) which yields a residual mismatch that does not exceed -20 dB over the entire waveguide bandwidth. Experimental tests on a WG 16 prototype confirm the results predicted by the computer model. >

Improvements in design of six-port reflectometer comprising symmetrical five-port waveguide junction and directional coupler

A six-port reflectometer that comprises a symmetrical five-port waveguide junction and a directional coupler is discussed. Computer models of the waveguide junction by itself and as part of a six-port setup are used to improve the design of the reflectometer. Two types of improvements were effected: the waveguide junction structure was redesigned to improve its overall residual mismatch; and the interconnections among the constituent components were rearranged to alter the way the reflected waves from the various components combine in the power-detection arms. The combination of these two schemes yielded a six-port reflectometer that has a well-spaced q/sub k/ distribution over the entire waveguide bandwidth. >