Gap Waveguide Research Articles

Accurate Characterization and Design Guidelines of Glide-Symmetric Holey EBG

The dispersion characteristics of a glide-symmetric holey periodic surface are investigated, with special emphasis on a detailed study of its stopbands. The unit cell is modeled as a multiport network associated with multiple modes at each of the lattice boundaries. Enforcing the periodic conditions, the real and imaginary parts of the wavenumbers of the Floquet modes are calculated through an eigenproblem posed in terms of the generalized multimodal transfer matrix, which is computed from the scattering parameters obtained with a full-wave simulator. This procedure allows us to take into account the higher order modal couplings between adjacent unit cells that are crucial for accurate dispersion analysis. The resulting simulation-assisted approach provides both a convenient computational tool and a very fruitful physical insight that reveals the existence of complex modes, the convergence of opposite-parity modes, and the anisotropy in both passband and stopband. This approach enables a precise calculation of the attenuation constant, which is not possible with conventional techniques as the eigenmode solvers of commercial software. Based on this approach, an extensive parametric study is carried out, rigorously establishing a set of critical criteria for the use of such a periodic surface as an electromagnetic bandgap structure in gap waveguide technology. Moreover, the analysis of the directional properties of the structure is applied to further suppress the leakage.

Analysis of the Propagation Constant of a Ridge Gap Waveguide and Its Application of Dual-Band Unequal Couplers

In this article, an analysis of the propagation constant and the characteristic impedance of a ridge gap waveguide (RGW) is proposed, which includes the comparison of the phase variation between three kinds of guiding structures, the approximation for the propagation constant of RGW, and the variation of characteristic impedances and phase characteristics. According to the analysis, the RGW technology, rather than the traditional microstrip transmission line, is utilized to implement two dual-band unequal couplers operating at two frequency bands. Furthermore, a coupler is fabricated and measured, exhibiting a dual-band operation with a power-dividing ratio of 2 dB and a quadrature phase difference with the same sign between two output ports.

A Wideband High-Power Ridge Gap Waveguide Power Divider for High-Power Division Sub-Systems Applications

ABSTRACT In this paper, a wideband high-power ridge gap waveguide (RGW) T junction power divider within the frequency band from 10 to 13.5 GHz is introduced. In this configuration, the air has the ridge gap to have maximum power handling capability. An excitation transition, from coaxial cable to the ridge gap waveguide, is introduced. The ridge gap waveguide power divider was fabricated using aluminum sheets to gain the advantage of low cost. The power divider has a wider bandwidth (30%) than the recent most successful RGW power divider along with the high handling power capability (more than 20 K Watts). The power divider design was validated using circuit and 3D full wave electromagnetic simulations and confirmed using experimental measurements with all agreements between results. It has been proved that the power divider attenuation has good matching (15 dB return loss) and equal 3 dB power division with less than 0.05 dB insertion loss. The power divider can be used as a feeder for many high-power application components.

Broadband Transition from Rectangular Waveguide to Groove Gap Waveguide for mm-Wave Contactless Connections

In this paper, the authors present a broadband transition from the standard WR-10 rectangular waveguide (RW) to a groove gap waveguide (GGW) in the W-band. The transition structure is based on electromagnetic band gap (EBG) technology where two EBG units are used, which are responsible for the transition and forming the transmission line. Metal pins in the E-plane together with the back surface of the transmission line create a forbidden band, which prevents power leakage between the connecting parts. Small air gaps will not harm the transition performance according to the simulation, which means it has a better tolerance of manufacturing and assembly errors and, thus, has advantages for mm-wave contactless connections. A back-to-back transition prototype was designed, fabricated and measured. The length of the GGW is 39.6 mm. The measured |S11| is better than −13 dB and the measured |S21| is better than −0.6 dB over 76.4–109.1 GHz, covering a bandwidth of 35.3%.

Wideband 4 × 4 Butler Matrix in the Printed Ridge Gap Waveguide Technology for Millimeter-Wave Applications

A wideband printed ridge gap waveguide $4\times 4$ Butler matrix at 30 GHz is presented. The printed ridge gap technology is used as it has very low losses and supports the propagation of quasi-TEM mode. Each component of the Butler matrix has been designed and analyzed where a superior performance is achieved in terms of bandwidth and size. The designed components are combined to form the Butler matrix. The Butler matrix has a wideband performance where the return loss and isolation levels are higher than 10 dB in the frequency range from 26.9 to 33.3 GHz, the output amplitude imbalance is ±1.6 dB, and the phase error is ±10°. The measured radiation patterns are in a good agreement with the simulated ones, beam directions are at ±13° and ±36° at the center frequency. The gain is ranging from 10.2 to 11.35 dBi for excitation from port 1 and ranging from 8.4 to 10.2 dBi for excitation from port 2.

A Dual-Polarized Magneto-Electric Dipole Antenna Based on Printed Ridge Gap Waveguide Technology

In this communication, a dual-polarized magneto-electric (ME) dipole antenna is implemented in the printed ridge gap waveguide (PRGW) technology. The antenna is composed of a cross-shaped ME-dipole backed by an artificial magnetic conductor (AMC) sidewall cavity. This cavity is fed by two orthogonal PRGWs implemented in two separate layers to achieve a dual-polarization with −28 dB isolation level at the center operating frequency (30 GHz). The proposed antenna achieves a 23.4% relative impedance bandwidth at 30 GHz with isolation better than 20 dB over the whole operating frequency band. In addition, a gain enhancement technique is used to increase the gain to 10 dB over the operating bandwidth. A prototype is fabricated and there is a good agreement between simulated and measured results.

True-Time-Delay Mechanical Phase Shifter in Gap Waveguide Technology for Slotted Waveguide Arrays in Ka-Band

This article proposes a novel all-metal mechanical phase shifter in gap waveguide technology. The phase shifter is aimed at providing beam-scanning capabilities to conventional slot array antennas along the elevation plane. To validate experimentally the beam-steering functionality, a 4×8 slot-array antenna has been designed and fabricated, along with the phase-shifting mechanism. The whole antenna consists of two pieces: a lower rotatable block, which changes the length of concentric groove gap waveguides, and an upper fixed block, where the slot-array antenna is placed. Experimental results validate the proposed concept, having obtained steering angles of up to 25°, with gain levels around 20 dBi with an antenna efficiency close to 90%. A reflection coefficient below -10 dB is achieved for a wide range of rotation angles from 29.5 to 30.5 GHz. The proposed phase shifter is completely scalable to any array size and its true-time-delay nature enables wide steering ranges for closely-spaced slot arrays with wideband radiation performance.

A Ka-Band Circularly Polarized Fixed-Frequency Beam-Scanning Leaky-Wave Antenna Based on Groove Gap Waveguide With Consistent High Gains

A novel fixed-frequency beam-scanning circularly polarized (CP) leaky-wave antenna based on the groove gap waveguide (GGW) structure is presented, operating in the Ka-band. By adopting the serrated ridge, a slow-wave transmission is achieved and used to excite the 80 CP patches on the top of the GGW. The operation states of the patches can be switched between “ON” and “OFF” states by controlling the biasing of the p-i-n diodes. Thus, a beam-scanning antenna with CP characteristic is developed by manipulating the period length of the antenna. Both the simulated and measured results are given as validations of the antenna performance. A measured peak gain of 17 dBic and a beam-scanning range larger than 83° can be achieved, with good CP performance.

Millimeter-Wave Ultrawideband Circularly Polarized Planar Array Antenna Using Bold-C Spiral Elements With Concept of Tightly Coupled Array

An ultrawideband circularly polarized (CP) planar array antenna built by new radiation elements, the bold-C spiral elements, in millimeter-wave band is presented in this article. Using the tightly coupled array (TCA) technique, the embedded CP bold-C spiral element in the infinite array has achieved both impedance bandwidth and 3 dB axial ratio (AR) bandwidth of 50.7% covering 18.1-30.4 GHz for the fixed broadside beam. Then, a feeding network is designed by using the dielectric-based inverted microstrip gap waveguide (DIMGW) technology in order to have a compact layout. An 8×8 CP planar array based on the proposed radiating element and the feeding network is designed and prototyped. The measured results show that the impedance bandwidth of the whole array for the reflection coefficient below -10 dB is 49% from 18.2 to 30 GHz, and 3 dB AR bandwidth is 44.9% covering 19-30 GHz.

A Simple Asymmetric Orthomode Transducer Based on Groove Gap Waveguide

The groove gap waveguide (GGWG) technology is used to design a simple asymmetric orthomode transducer (OMT) at the Ka -band in this letter. The OMT consists of two metal layers which do not need electrical contact due to the property of the gap waveguide technology. The vertical polarization (VP) is directly fed to a standard rectangular waveguide port from the main arm of a square waveguide, while the horizontal polarization (HP) is fed to the side arm by an H-bend. No septum or iris is needed, which contributes to a simple structure. The OMT has been manufactured and measured using a back-to-back setup. A high isolation of over 40 dB is achieved within the working band from 26.1 to 29.3 GHz. The reflection coefficient is below −11.4 and −17.7 dB for the HP and VP, respectively. The higher return loss of the HP is caused mainly by the manufacturing errors. Nevertheless, the insertion loss for both polarizations is below 0.25 dB for a single OMT.

A Ka-Band Wideband Matched Load Based on Lossy Waveguide Structures

This letter presents the design of a new type of wideband waveguide matched loads. Unlike conventional loads based on absorbing materials, the proposed design relies on conductor loss of the waveguide to achieve the desired absorption level. To increase the waveguide loss and meanwhile maintain a small footprint of the whole device, gap waveguide structures are employed to reduce the group velocity of the wave inside the waveguide. Additionally, the waveguide is formed of walls with low conductivity metal, yielding much higher conductor loss. The waveguide load is designed to have a spiral shape for further reduction on size. The design is demonstrated at Ka -band (26.5–40 GHz) using 3-D printing technology. The measured $S_{11}$ of the prototype device is better than −20 dB across the entire Ka -band. This good result validates the proposed concept and reveals that the new lossy wall-based load can be a promising alternative to conventional designs particularly for applications involving high power or demanding superior stability over time.

An unequal power divider based on ridge gap waveguide with an inserted conductor plate

AbstractA novel unequal power divider based on ridge gap waveguide is proposed and investigated in this paper. The half‐height pin gap waveguide structure is applied to acquire the required stopband. The whole divider can be divided into three parts. The first part is the core of the divider which is a gap waveguide transmission line with a thin inserted conductor plate (ICP). The ICP is printed on a thin substrate for the mechanical feasibility and stability. The position of the ICP can be changed to adjust the power division ratio (PDR). The ICP separates the divider into two different layers. Then, the second and third parts are transitions from top layer and bottom layer to normal gap waveguide transmission lines. Two power dividers with different PDRs of 1:2 and 1:4 working at 28 GHz are designed and manufactured to verify this topology.

A Bandwidth-Enhanced Cavity-Backed Slot Array Antenna for mmWave Fixed-Beam Applications

A bandwidth-enhanced $8\times 8$ cavity-backed slot array antenna for fixed beam applications is presented. The antenna consists of four $2\times 2$ subarrays fed by ridge gap waveguide and a modified bow-tie coupling slot in the cavity layer. The proposed bow-tie coupling slot provides additional $\text{10}\%$ impedance bandwidth as compared to the traditional rectangular coupling slot. The fabricated prototype demonstrates an $|S_{11}|\leq -10\,$ dB fractional impedance bandwidth and a $3\,$ dB gain-drop bandwidth of approximately $\text{28}\%$ and $\text{25}\%$ , respectively, with peak gain of $26.4\,$ dBi, aperture efficiency $>\text{60}\%$ and cross-polar discrimination $>40\,$ dB. Measurements show good agreement with simulations. Moreover, we show the impact of the dimensions and shape of the cavity coupling slot on the bandwidth enhancement. The bandwidth enhancement is explained by the double-ridge slot behavior of the bow-tie coupling slot, which shows a more wideband behavior than the traditional rectangular coupling slot behaving like a cross section of a waveguide.

Bull’s-Eye Antenna With Circular Polarization at Millimeter Waves Based on Ridge Gap Waveguide Technology

In this communication, a Bull's-Eye (BE) antenna with circular polarization (CP) based on ridge gap waveguide (RGW) technology is numerically and experimentally demonstrated. The structure is excited from the bottom with a standard WR-15 waveguide ( V-band) coupled through a step transition to a ridgeline that ends in two orthogonal arms of different lengths to generate CP. Radiation is coupled to the top plate by a central diamond slot surrounded by the BE structure, which consists of four concentric periodic corrugations around the slot. Simulations and experimental results are in good agreement, with axial ratio below 1 dB at the operation frequency and peak gain of 18.4 dB. The antenna has right-handed CP (RHCP) with polarization discrimination of more than 30 dB.

Ka-Band Coplanar Magic-T Based on Gap Waveguide Technology

A coplanar Magic-T is proposed based on a combination of ridge and E -plane groove gap waveguides for Ka-band applications. All four ports of the proposed Magic-T are coplanar. The impedance bandwidth of the proposed Magic-T is about 43% covering the whole Ka-band from 26 to 40 GHz. The Magic-T isolation is better than 40 dB in the whole bandwidth while its insertion loss is about 0.25 dB.

Design and Realization of a Band Pass Filter at D-band Using Gap Waveguide Technology

Gap waveguide technology is particularly attractive for the design of passive elements in mm-wave systems. Recently, the so-called zero-gap implementation has proved to be very robust to manufacturing tolerances, while at the same time keeping the low loss associated to the contactless standard gap waveguide. In this paper, a Chebyshev filter working at 145 GHz based on this idea and intended to be used in a wireless communication system is designed and optimized. A conventional milling technique has been used in its fabrication, and good measured results have been obtained in a single-pass process.

Development of a center fed slot array antenna with very low side lobes using ridge gap waveguide (RGW) technology

A center-fed slot array antenna based on ridge gap waveguide (RGW) technology is presented. In the proposed structure, no aperture blockage is introduced which provides easy control on side lobe level (SLL) especially for low values of below −20 dB. Furthermore, thanks to the compact nature of TEM-based RGW line in E-plane, the proposed structure, unlike its TE-based groove gap waveguide (GGW) counterpart does not suffer from the grating lobe problem when applied in a two-dimensional array. For proof of concept a 4x10 slot array based on the proposed RGW-based topology is designed and fabricated for operation at 15 GHz. Both simulation and measurement results show proper radiation performance including the gain of 20 dB and the SLL of −23 dB as well as the fixed beam over the antenna operating bandwidth.

Compact Groove Diamond Antenna in Gap Waveguide Technology With Broadband Circular Polarization at Millimeter Waves

In this article, three compact antennas using the ridge gap waveguide (RGW) technology working in the millimeter-wave band (60 GHz), with a high-purity and broadband circular polarization (CP), are numerically and experimentally analyzed. The structure is fed from the bottom by means of a standard WR-15 waveguide (V-band) to make it compatible with standard measurement systems. It is coupled with a miniaturized step transition to a ridgeline that ends in two arms of different lengths. CP is generated in a simple and effective way, by means of two orthogonal feeder arms that excite a CP in a diamond-shaped slot on top. Simulations and measurements have an excellent agreement reaching a matching bandwidth (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> <; -10 dB) from 60.3 to 69.6 GHz (>9 GHz). Applying the axial ratio criterion (AR <; 3 dB) the bandwidth in CP is 14.48%, with respect to the central frequency (60.3-69.6 GHz). The maximum gain is obtained with the most evolved design incorporating a diamond aperture with a horn taper and a circular groove, reaching a value of 11.12 dB at 67.3 GHz.

Considerations of impedance sensitivity and losses in designing inverted microstrip gap waveguides

One of the versions of gap waveguide technology, the inverted microstrip, is studied in terms of the effects that the parameters of the substrate and the bed of nails used for its implementation have in the behaviour as a transmission line. Mainly, the line impedance sensitivity and the losses are evaluated for different design parameters. To this aim, a methodology based on simulations is described and some experimental verifications are as well included. The results are of great interest for designers of antennas and components in this technology.

A Gap Waveguide-Based Compact Rectangular Waveguide to a Packaged Microstrip Inline Transition

In this paper two different simple to design and easy to manufacturing transitions from a microstrip to rectangular waveguide based on ridge and groove gap waveguides are studied. The first one is based on a combination of a groove and ridge gap waveguide. In this case, the microstrip substrate occupies the whole bottom metallic housing block, namely, the transition and the gap between the bed of nails and the lid; therefore, it does not require any substrate shaping. Nevertheless, the transition needs to replace groove waveguide by ridge gap waveguide sections to avoid higher-order mode excitation. In the second approach, based on only a groove gap waveguide, the substrate is shaped to be only in the microstrip section, that is, outside the bed of nails area. This leads to a simplification of the design procedure. Prototypes of both transitions have been characterized, showing good agreement with the simulations taking into account the manufacturing tolerances. Performance comparable to the state-of-the-art in this frequency band has been achieved.