Groove Gap Research Articles

Design of evanescent mode band-pass filters based on groove gap waveguide technology

This paper proposes for the first time a design method of Chebyshev band-pass filters based on groove gap waveguide (GGW) technology and evanescent mode. The evanescent mode GGW section has been implemented by decreasing the width of the groove area by means of two additional rows of metallic pins, and the filter structure has been obtained by inserting resonators of metallic pins along the central part of this narrower GGW section according to a coupling matrix synthesis method. The proposed method has allowed reducing the analysis number of this band-pass filter during the design process and the computation cost with the electromagnetic (EM) simulator, solving the discretization problem of the different lengths of the evanescent mode section. This design technique has been applied to a fourth-order Chebyshev band-pass GGW filter. The design has been performed in the recommended band of the WR75 standard (10 GHz – 15 GHz). The design specifications have been a central frequency f0=12 GHz, a fractional bandwidth FBW = 2.5 % and return loss RL = 20 dB. Measurement and electromagnetic (EM) simulation results have shown a good agreement. Return and insertion losses in the pass-band region of the measured prototype have been, respectively, RL = 20 dB and IL = 0.3 dB, while maximum attenuation in the stop-band regions reached ASB = 83 dB. A comparison has been performed between the measured prototype and other GGW band-pass filters. The proposed GGW band-pass filter has been shown to have reduced size and high-performance characteristics. Future emerging communications systems could benefit from this evanescent mode GGW Chebyshev band-pass filter.

A Fixed-Frequency Beam-Scanning Leaky-Wave Antenna Using Phase and Amplitude Control for Millimeter-Wave Applications

A new type of fixed-frequency beam-scanning leaky-wave antenna (LWA) in Ka millimeter-waveband is developed in this article, based on dual control of phase and amplitude. The antenna consists of a groove gap waveguide (GGW) and 80 perturbation units. Each unit contains one patch and a pair of H-shaped slots. By controlling the state of a slot with p-i-n diodes, the phase of the radiated field from each unit can be switched between two opposite phases, called “1” state and “−1” state, while the magnitude of the radiated field remains unchanged. In addition, the radiation strength of each unit can be also turned off to provide amplitude control. The main principle for beam scanning is based on the phase compensation to the perturbation units on the surface of the LWA, combined with 1-bit amplitude control to achieve lower sidelobe levels, so the principle is different from that of the existing fixed-frequency beam-scanning LWAs. The entire antenna structure relies on GGW transmission to reduce dielectric loss in millimeter-waveband, and shows good characteristics of scanning angle and realized gain. In the measurement, a high peak gain of 16.8 dBi and a large beam-scanning range over 110° are achieved.

A Quad-Polarization Reconfigurable Fixed-Frequency Beam-Scanning Leaky-Wave Antenna Based on the Holographic Method for Millimeter-Wave Application

A quad-polarization reconfigurable fixed-frequency beam-scanning leaky-wave antenna (LWA) operating at millimeter-wave Ka-band is presented in this article. A low-loss groove gap waveguide (GGW) structure is employed for low-loss transmission and feeding, above which there locates a metal-covered superstrate. Two rows of inclined slots etched on the metal cover in a staggered arrangement operate as the radiated sources. A modified holographic method is presented, and the hologram can be manipulated by switching the states between “ON” and “OFF” of the p-i-n diodes, and hence the fixed-frequency beam-scanning property with polarization agility of four different polarization states can be realized, including horizontal polarization (HP), vertical polarization (VP), left-handed circular polarization (LHCP), and right-handed circular polarization (RHCP). Besides, measured results of the fabricated antenna are given to verify its performance. The measured peak gains at 30 GHz reach 11.3 dBi in the HP state, 13.0 dBi in the VP state, 11.5 dBic in the LHCP state, and 11.8 dBic in the RHCP state, respectively, with a beam-scanning range of 100° (from −50° to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{50}^{\circ }$ </tex-math></inline-formula> ), showing good agreement with the simulated results.

Robust Design of 3D-Printed W-Band Bandpass Filters Using Gap Waveguide Technology

In this paper, a W-band 3D-printed bandpass filter is proposed. The use of higher-order TE10n modes in groove gap waveguide (GGW) technology is evaluated in order to alleviate the manufacturing requirements. In addition to the use of higher-order modes, the coupling between them is analyzed in detail to improve the overall fabrication robustness of the component. This allows the implementation of narrow-band filters operating at millimeter-wave frequency bands (or above), which usually demand complex manufacturing techniques to provide the high accuracy required for this kind of devices. In order to show the applicability of the proposed method, a narrow-band 5th-order Chebyshev bandpass filter centered at 94 GHz, which can be easily fabricated by state-of-the-art stereolithographic (SLA) 3D-printing techniques followed by silver coating, is shown. Excellent measured performance has been obtained.

An H-Plane Groove Gap Waveguide Magic-T for X-Band Applications

An X-band H-plane groove gap waveguide magic-T is presented as a combination of an H-plane and an E-plane T-junction. Two architectures can be derived by orientating the sum and difference ports to the same or opposite directions, respectively. Slot coupling allows the reduction of the device dimensions along the E-plane, and such a low profile can be attractive in all groove gap waveguide applications where compactness is required. A proof-of-concept prototype is fabricated with standard low-cost CNC milling machine manufacturing techniques. Good agreement between simulations and measurements is observed.

Development of a compact transverse slot array antenna using corrugation in groove gap waveguide technology

SummaryWe present the proof of concept of a compact slot array antenna with proper side lobe level in groove gap waveguide (GGW) technology. Four transverse slots are etched at the GGW broad wall along with the nulls of standing TE10 wave existing inside the shorted GGW. To decrease the sidelobes and antenna size, corrugations are applied through the wave path inside the GGW. Proper use of corrugations can reduce the wavelength inside the GGW leading to reduction of the distance between adjacent transverse slots, which can help to suppress the grating lobe problem and consequently enhance the radiation efficiency, which is a challenge in transvers slot array antennas. The designed antenna is optimized to achieve maximum gain, lowest grating lobe level, and return loss at 15 GHz using HFSS simulator. The achieved gain is about 13 dBi, and the SLL is better than 15 dB. To confirm the simulation results, the designed antenna was fabricated and tested. Both simulation and measurement results confirm that the grating lobes are well suppressed at the antenna operating frequency.

Contactless Air-Filled Mode Selective Transmission Line

An air-filled mode selective transmission line (AF-MSTL) consisting of an opened groove gap waveguide (GWG) and an inverted coplanar waveguide (CPW) is proposed in this letter. By using the electromagnetic band gap (EBG) structure, the electrical contacts of AF-MSTL are not required during the assembly process. To verify the design, the AF-MSTL prototype, connected to two designed grounded-CPW (GCPW) to AF-MSTL transitions to build a back-to-back structure, has been fabricated and measured. A measured insertion loss of 0.2857 dB/mm at 110 GHz is achieved, which is lower than the dielectric filled (DF) MSTL of 0.5012 dB/mm at 110 GHz.

Broadband Contactless 90° Waveguide Transition With a U-Shaped Choke Groove

This letter presents a broadband 90° bent waveguide transition that is suitable for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$H$ </tex-math></inline-formula> -plane split-blocks technique. In this transition, imperfect metal connections will not cause unacceptable transmission loss by employing a novel U-shaped choke groove and a groove gap waveguide. Such contactless waveguide transitions are advantageous as they allow for easy interconnection and packaging of millimeter-wave and terahertz circuitry. A 90° bent waveguide operating over the WR-4.3 waveguide frequency band (170–260 GHz) is designed, and the transition with a different air gap between the top and bottom parts is measured. The measured results show that the transmission losses are about 0.2 dB with good consistency.

Terahertz groove gap waveguide leaky wave antenna

AbstractA groove gap waveguide (GGW) leaky wave antenna with a wide scan angle in the terahertz (THz) band (430–560 GHz) is presented in this study. The unnecessary tight contact between the top plate and pins of the GGW makes it easy for the fine fabrication and assembly of this THz antenna. Scanning of pointing directions with frequency, together with the low side‐lobe level (SLL), is designed for the pins' heights and intervals as well as the groove cavity width. Measurement results of S11 parameters remain about −20 dB, besides, the antenna scan angle range is 15o within 430–560 GHz, and the gains are also above 15 dB within that working frequency bands.

W-Band Binary Phase-Controlled Multibeam Antenna Array Based on Gap Waveguide Magic-Tee

In this article, a compact 94 GHz multibeam antenna array based on the binary phase-controlled concept is proposed. The feeding network is composed of four unconnected layers, and the ridge or groove gap waveguides are adopted as the guided wave structures. A key planar gap waveguide Magic-Tee is designed to obtain 0° and 180° phase states and then integrates with an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\,\times \,8$ </tex-math></inline-formula> slot antenna array to achieve multibeam operation for the first time. Compared with the traditional phased array and passive beamforming networks (BFNs), the feeding design is simple in construction, consisting of only Magic-Tees and cascaded power dividers without any phase shifters. Benefiting from the gap waveguide technology, the antenna array does not require electrical contact among the metal layers, so it is simple and low cost to manufacture. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times8$ </tex-math></inline-formula> slot antenna array can easily switch among one-beam and three different dual-beam states that point to ±7°, ±17°, and ±38°. The measurement results of 6.6% bandwidth from 91.7 to 98 GHz for both reflection coefficients <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt; -10$ </tex-math></inline-formula> dB and isolations >25 dB are achieved. The proposed multibeam antenna array would be an attractive candidate for millimeter-wave multiuser communication where it requires multiple beams simultaneously.

Ultra-Wideband Full-Metal Planar Array Antenna With a Combination of Ridge Gap Waveguide and E-Plane Groove Gap Waveguide

An ultrawideband (UWB) full-metal planar array antenna based on a combination of ridge gap waveguide (RGW) and E-plane groove gap waveguide (E-GGW) is presented for millimeter-wave (mmWave) applications. First, the radiation element of a double-step double-ridged slot structure is proposed and designed. By removing the vertical walls of the cavity in the H-plane, the impedance matching characteristics presents a UWB bandwidth of 53%. Second, a UWB double-layer feeding network is achieved by combining RGWs and double-side-pin E-GGWs for the radiation elements. Finally, an 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 8 full-metal planar array antenna with the presented elements and network is designed, prototyped, and measured. The measured results agree well with the simulated results. The proposed antenna provides an impedance matching bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert \text{S}_{11}\vert &lt; -10$ </tex-math></inline-formula> dB) of 46.8% from 18.8 to 30.3 GHz. The maximum gain is 27.7 dBi at 27 GHz and a stable gain of 26 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm ~1.7$ </tex-math></inline-formula> dBi is obtained over the operation band.

Research on Filling Strategy of Pipeline Multi-Layer Welding for Compound Narrow Gap Groove.

With the increase in transmission pressure and pipe diameter of long-distance oil and gas pipelines, automatic welding of the pipeline has become the mainstream welding method. The multi-layer and multi-pass welding path planning of large-diameter pipelines with typical narrow gap grooves are studied, and a welding strategy for pipeline external welding robot is proposed. By analyzing the shape of the weld bead section of the narrow gap groove and comparing the advantages and disadvantages of the equal-height method and the equal-area method, the mathematical model of the filling layer is established. Through the test and analysis in the workshop, the predicted lifting value meets the actual welding requirements. The microstructure of the weld was analyzed by SEM. The main structure of the weld was fine acicular ferrite, which could improve the mechanical properties of the welded joint. After multi-layer filling, the filling layer is flush with the edge of the groove. The establishment of this model lays a foundation for the formulation of welding process parameters for large-diameter pipes and the off-line programming of welding procedures.

A Broadband Low-Profile Monopulse Comparator for Dual-Circularly Polarized Feeder

This article proposes a scheme to design a broadband low-profile monopulse comparator for the dual-circularly polarized feeder. For obtaining a compact and easily integrated structure, a monopulse comparator with a ring-shaped symmetrical planner topology is proposed by using the 3 dB coupler and the phase shifter based on the groove gap waveguide (GGW). Then, in order to achieve the equal-amplitude distribution in a broad bandwidth, the asymmetrical coupling structure and the novel dispersion-matched transition are proposed to improve the directivity of a 3 dB coupler. Moreover, a ridge waveguide with periodic grooves featuring stable dispersion change is adopted to design the phase shifter, which contributes to obtain an accurate phase control in the broad frequency band. To validate experimentally the broadband performance, a dual-circularly polarized four-horn feeder with two identical monopulse comparators is designed and fabricated. The results show that the symmetrical radiation patterns with 32 dB null-depth can be obtained from 27 to 31 GHz. The monopulse comparator characterizes broad bandwidth, low loss, and a compact size, which provides a monopulse comparator with accurate amplitude/phase control for the research of the monopulse antenna.

A Shared-Aperture Dual-Band High-Efficiency Antenna Based on Groove Gap Waveguide

A shared-aperture dual-band antenna at 2.4 GHz Wi-Fi and Ku-bands is proposed in this letter. The antenna in the high-frequency band is featured by a slotted cavity configuration based on the gap waveguide technology. The slotted antenna consists of 3 × 3 slots incorporated into the top metal of the cavity. The periodic structure is loaded into the proposed antenna, which reduces the resonant frequency of the cavity. The top metal of the cavity is enlarged and four shorted screws are loaded, which achieve four half-mode cavities operated in the Wi-Fi band. Two antennas (slotted cavity antenna and dual-band antenna) are designed, fabricated, and tested. Measured results show that a −10 dB impedance bandwidth of 18.3% (13.15–15.8 GHz), a 3 dB gain bandwidth of 17.7% (13.1–15.65 GHz), and a peak gain of 14.8 dBi are realized for the cavity antenna. The impedance bandwidth of the proposed dual-band antenna covers 2.4–2.5 and 13.4–16.2 GHz. A 2 dB gain bandwidth of 16.4% (13.4–15.8 GHz) is realized. Owing to an all-metal structure that exhibits no dielectric loss, the radiation efficiency of the antenna is better than −1 dB in the whole working band. The proposed antenna shows the characteristics of high gain, high efficiency, and low cost, which is suitable for simultaneous satellite communication and Internet of Things applications.

Fully Metallic Glide-Symmetric Leaky-Wave Antenna at Kₐ-Band With Lens-Augmented Scanning

A fully metallic leaky-wave antenna (LWA) with enhanced scanning rate is presented. The leaky waveguide is implemented in groove gap waveguide technology and is periodically loaded to produce backward radiation. Furthermore, glide-symmetric pins are placed inside the leaky waveguide to increase the dispersion. A parallel-plate waveguide metasurface prism lens is used to disperse the backward radiation and increase the scanning rate of the LWA. The designed antenna can steer the radiation from −26° to 26° from 27 to 35 GHz, and an average total efficiency of 74% is achieved. A prototype of the designed antenna is manufactured, and measurements corroborate the simulated results. The proposed concept is applicable to other frequency-scanning antennas and can be used to increase the scanning rate in radar and imaging systems.

X-Band In-Line Coaxial-to-Groove Gap Waveguide Transition

A coaxial-to-groove gap waveguide transition is proposed for the first time, addressing the lack of similar designs in the state-of-the-art literature. An in-line configuration is adopted in case of stringent space requirements in groove gap waveguide systems. This device has no dielectric and makes use of a waveguide multi-step ridged section connected to the inner conductor of a coaxial line. Three versions are presented, covering progressively wider bandwidths depending on the number of employed steps. The three configurations achieve 20-dB return loss fractional bandwidths of 2.63%, 16.79%, and 38.08%, and 30-dB return loss fractional bandwidths of 0.84%, 10.63%, and 33.49%, with a simulated insertion loss always better than 0.05 dB when a realistic metal conductivity of 2 × 10 7 S/m is assumed. A tolerance analysis on the most critical geometrical parameters is provided to assess the mechanical feasibility, preserving a remarkable performance at X band.

Peak Power Handling Capability in Groove Gap Waveguide Filters Based on Horizontally Polarized Resonators and Enhancement Solutions

This letter studies the peak power handling capability (PPHC) in groove gap waveguide filters based on horizontally polarized resonators. Moreover, a modification of the resonant cavity is proposed, where the central pins of the original structure are replaced by a rounded metal block. As a result of this change, the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> -like mode can still be excited, but the maximum electric field strength is shifted to the center of the cavity, which leads to a higher PPHC. The main advantages of the original structure are maintained, and greater robustness in the manufacturing process is achieved. Next, some guidelines for the design of the coupling windows and the dimensions of the blocks are shown to minimize the electric field strength and, consequently, maximize the PPHC. Finally, two third-order bandpass filters (with pins and with blocks) centered at 16 GHz have been manufactured and tested in a measurement campaign, where a PPHC enhancement of 8.7 dB at high pressures is achieved for the novel solution presented in this work.

Wideband mm-wave high-gain multibeam antenna array fed by 4 × 4 groove gap waveguide butler matrix with modified crossover

This paper presents a wideband millimeter wave (mm-Wave) high-gain multibeam antenna array fed by Butler Matrix (BM) based on groove gap waveguide (GGW) technology. First, the components of 4 × 4 GGW BM have been designed and analyzed, especially the proposed modified crossover, which greatly improves the performance of BM as feeding network. Then a 2 × 2-element subarray with three layers has been proposed, combined with the 4 × 4 GGW BM to form a 1 × 4 broadside antenna array. Finally, the prototype of high-gain wideband four-beam antenna array has been manufactured and measured. The measured results verify the superior performance of the multibeam antenna array between 26.3-29.7 GHz. The return loss (RL) can reach 15 dB and isolation between ports is also less than 15 dB, and the measured maximum gain of radiation patterns and the maximum radiation efficiency can also reach 19.05 dBi and 86.8%, respectively. The measured results have a good agreement with the simulated results.

A TE₀₁-Mode Groove-Gap-Waveguide-Based Wideband Fixed-Frequency Beam-Scanning Leaky-Wave Antenna for Millimeter-Wave Applications

A wideband fixed-frequency beam-scanning leaky-wave antenna (LWA) operating at the millimeter-waveband is presented in this article. A groove gap waveguide (GGW) supporting base is introduced as a transmission structure of the antenna with a TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> -mode excitation, and two rows of longitudinal slots etched on top of the superstrate act as the radiating structures. Two rows of PIN diodes are soldered below the longitudinal slots, so that the long slots can be cut into a group of short slots. By controlling the PIN diodes, the working states of the slots can be switched between “ON” and “OFF.” Then, by selecting proper activation states, the fixed-frequency beam scanning can be obtained. In addition, the developed antenna is verified in practical fabrication and experiment. The experimental results have good agreements with that in simulations. The measured peak gain reaches at 16.8 dBi, and the beam-scanning range more than 70° from 23 to 29 GHz is realized.

Novel Band Gap Waveguide for Low-Loss and Dual Band Applications

In this article, the band gap waveguide (BGW) is proposed and studied. The BGW is formed by a groove gap waveguide (GGW) and a rectangular waveguide, and the former is totally integrated inside the latter. The units of the GGW form a stopband to confine the electromagnetic (EM) wave inside the groove of GGW and propagate the quasi-TE₁₀ mode at high frequencies. When operating at low frequencies, the units cannot block EM waves, and the latter can pass through them and propagate in the entire rectangular waveguide region as a TE₁₀-like mode. Besides, the characteristics, propagation modes, and designing methods of the BGW are illustrated and analyzed. Two transition structures corresponding to high- and low-frequency operations are then designed to verify the transmission performance of the BGW, as well as its integration capability with other passive components. A back-to-back transition prototype has been fabricated to evaluate its performance. The measured results are in great agreement with the simulated results. According to the experimental results, good impedance matchings and low insertion losses are achieved from 6.8 to 8.05 GHz for low frequency and from 71 to 86 GHz for high frequency, respectively.