Groove Gap Waveguide Research Articles

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.

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.

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.

Groove Gap Waveguide Filter Based on Horizontally Polarized Resonators for V-Band Applications

In this article, resonators based on air-filled rectangular cavity consisting of one perfect magnetic conductor (PMC) wall and the rest of walls as the perfect electric conductor (PEC) are proposed. The proposed cavity can be engraved in the top or bottom metal plate of a gap waveguide structure, and the PMC wall is realized by the periodic metallic pins located within the gap waveguide geometry. The resonant frequency and electromagnetic (EM) field distribution of the cavity are investigated, and it is shown that the electric field is horizontally polarized with respect to the wave propagation direction. Two bandpass filters are designed by inserting the proposed cavity in the cutoff region of the gap waveguide, on the top and bottom plates. In the latter case, all pins are the same, and the cavities and coupling structure are easily implemented by engraving the top plate. Therefore, by using this concept, a common pin plate can be used to implement different passive millimeter-wave devices. For instance, three different filters working at 60, 65, and 70 GHz with a common bottom pin plate are designed and fabricated. The measured results show a minimum insertion loss of 1.4, 1.1, and 1.1 dB with 0.83%, 1.4%, and 1.8% fractional bandwidth for the three bandpass filter designs, respectively, with aluminum as metal.

Highly Integrated Beam Scanning Groove Gap Waveguide Leaky Wave Antenna Array

In this communication, a novel 2-D beam scanning antenna array is designed and fabricated in metallic 3-D printed technology with high integration and reduced fabrication complexity in millimeter waves. The array is composed of four leaky wave antennas and a Butler matrix based on groove gap waveguide (GWG) technology. One dimension of the beam scanning performance is realized by moving one row of pins along the groove based on the GWG concept. Meanwhile, the sidelobe levels of the radiation patterns are reduced to −20 dB by controlling the height and distance of pins along groove. The beam direction of the low sidelobe leaky wave antenna changes from 110° to 140°, while the frequency shifts from 25 to 35 GHz. Another dimension of the beam scanning capability is realized with the Butler matrix in groove GWGs. The design of this Butler matrix is based on the coupling between multilayered groove GWGs. By this means, the low sidelobe leaky wave antennas are connected directly to the Butler matrix with no more transition structures. The main beam direction of the antenna array shifts from −41° to 41°, when the exciting ports change in order. The simulated and measured port isolations are lower than −15 dB over the frequency band of 27–35 GHz, and they match well with each other.

Slow-Wave Substrate Integrated Groove Gap Waveguide

A slow-wave substrate integrated groove gap waveguide (SW-SIGGW) is presented for the first time in this letter. The developed SW-SIGGW consists of three stacked substrate layers with different thickness, in which asymmetric half-height mushroom-type electromagnetic bandgap (EBG) structures are utilized for the convenience of tuning the heights of each layer. The slow-wave effect is achieved by loading periodical metallic via holes inside the groove gap waveguide in the bottom layer separating the magnetic and electric fields. In both lateral and longitudinal dimensions, 41% reductions are achieved through this new topology of SW-SIGGW, since the guided wavelength decreases significantly compared to the normal SIGGW of same width and height. A prototype of the SW-SIGGW is designed, manufactured, and measured. The simulated and measured results are in good agreement, proving the validity and feasibility of the design.

Low-Dispersive Leaky-Wave Antennas for mmWave Point-to-Point High-Throughput Communications

In this article, we present two efficient leaky-wave antennas (LWAs) with stable radiation pattern, operating at 60 GHz. Both antennas exhibit attractive properties such as significantly reduced beam-squint, low loss, low sidelobes, high directivity, and simple manufacturing. The beam-squint of conventional LWAs is reduced by refracting the leaked waves in a dispersive lens and the low sidelobe levels are achieved by tapering the leakage rate along the aperture. Since the antennas are implemented in groove gap waveguide technology, the losses are low. The two antennas are different in terms of their asymmetric/symmetric leakage tapering with respect to the broadside direction. Both designs are optimized for low sidelobes, but since symmetry is enforced in one, the resulting performance in terms of sidelobes is suboptimal. However, in the symmetric design, multiple stable beams can be obtained, simultaneously or independently. Twenty percent bandwidth is obtained with less than ±0.5° beam-squint. In this frequency range, the gain is stable at 17 and 15 dBi for the asymmetric and symmetric designs, respectively. The designs are intended for point-to-point links in mmWave communication networks where low losses, directive beams, and low sidelobes are expected to be key features.

Broadband mm‐wave propagation characterization of planar groove gap waveguide

AbstractWe present, experimental broadband propagation characterization of a planar groove gap waveguide (PGGWG) from 29 to 40 GHz. The transmission line Q‐factor is found to vary from 110 to 130 over the band, which is shown by comparison of measurement data to be comparable to substrate integrated waveguide (SIW). PGGWG is found to have a phase constant of nearly double that of SIW using the same materials and manufacturing process. This is a significant result for system miniaturization.

A Wideband 3-dB Directional Coupler in GGW for Use in V-Band Communication Systems

In this article, a broadband 3-dB directional coupler is proposed using groove gap waveguide (GGW) structures. Gap waveguide technology has been introduced to overcome manufacturing and assembling challenges of different millimeter-wave components and devices. The presented coupler has wideband coupling flatness with low return loss in 60-GHz frequency band and can be easily adapted to other frequency ranges. Experimentally, a sample prototype of the proposed 3-dB coupler has been designed and fabricated. The measured return loss and isolation are better than 20 dB and the power-split unbalance within ±0.5 dB is obtained over the frequency range from 57 to 74 GHz (26% BW). The proposed structure has the capability of easily integrating with other millimeter-wave components.

3-D-Printed Modified Butler Matrix Based on Gap Waveguide at W-Band for Monopulse Radar

This article presents the design and fabrication of low-loss, -weight, and -cost, modified Butler matrix in groove gap waveguide technology at W-band, implemented by additive manufacturing. The design, simulations, and measurements of each of the elements that conform to the modified Butler matrix are presented. The proposed modified Butler matrix is asymmetric and oriented to an easy assembly with a radial antenna in order to obtain simultaneous sum and difference patterns for a narrowband radar application. The measured individual components of the modified Butler matrix fit very well with the simulations. As for the full modified Butler matrix, measurements provide a 0.7% bandwidth below −20 dB for sum and difference ports centered at 94 GHz. The amplitude and phase imbalance are below 1.5 dB and 20°, respectively. This narrow bandwidth is due to the difference in length between input and output ports due to the asymmetry of the design. The total losses of the modified Butler matrix are below 1 dB.

Glide-Symmetric Holey Leaky-Wave Antenna With Low Dispersion for 60 GHz Point-to-Point Communications

In this article, two novel efficient leaky-wave antennas (LWAs) with stable radiation patterns operating in the 60 GHz band are proposed. The LWAs are implemented in groove-gap waveguide (GGW) technology. To mitigate the beam squint due to the dispersive nature of LWAs, complementary-dispersive prisms are coupled to the LWA radiation aperture. The antennas are implemented in fully metallic purely holey periodic structures, resulting in a more cost-effective and robust manufacturing process compared to previously reported pin-based structures. Two prisms are proposed, one with mirror symmetry and one with glide symmetry. When the prism possesses a glide symmetry, much fewer holes are required while maintaining a similar performance, which even further decreases the fabrication costs. The complex propagation constant is optimized for low sidelobe levels (SLLs) with tailored hole diameters and waveguide dimensions, thus for the first time demonstrating the capability of using glide-symmetric holes to control the leakage rate. Two prototypes with mirror- and glide-symmetric prisms are theoretically synthesized and validated by the simulated and experimental results. A frequency bandwidth of 11% is achieved for both prototypes with the beam squint within ±0.9° (mirror) and ±1.7° (glide), SLLs below -15 dB (mirror) and -13 dB (glide), total efficiency almost 90%, and realized gain of 17 ± 0.5 dB at a fixed observing angle. The developed antennas are intended for mm-wave point-to-point communications.

Radial Line Slot Antenna Design With Groove Gap Waveguide Feed for Monopulse Radar Systems

Radial line slot arrays (RLSAs) are well suited to be used in monopulse radar systems. The excitation of the sum and difference patterns can be achieved by the design of simple feeds as shown in this paper. In this work, a feed system based on the use of a cavity made in groove gap waveguide technology (GGW) is presented. The design is made at 24 GHz but can be easily scaled to higher frequencies as the technology is contact-less and fully made in metal. A good isolation between the sum and difference ports together with a good matching of the two of them is obtained. The radiation patterns of the manufactured antenna are also in good agreement with the simulated ones.

Ku Band Bethe Hole Coupler Using Gap Waveguide Technology

The gap waveguide technology is a new technique used for designing and fabricating microwave components, ensuring a low-loss and easy fabrication process, especially at high frequencies, and allowing for the production of multilayer structures due to the lack of requirement of an electrical connection between the metal layers of the waveguide structure. This paper presents the design and areas of implementation of single-hole and multi-hole 20 dB Bethe couplers, using the groove gap waveguide (GGW) technology for Ku band. Simulation results show that the operating bandwidth of the proposed design is over 40% wider, and its isolation rate is more than 25 dB higher. By using the multi hole configuration, a bandwidth that is more than 59% wider and the isolation rate of over 30 dB may be obtained.

An Air Cavity-Fed Circularly Polarized Magneto-Electric Dipole Antenna Array With Gap Waveguide Technology for mm-Wave Applications

In this communication, a low profile $4 \times 8$ air cavity-fed circularly polarized (CP) planar antenna array with high performance for W -band is proposed. This antenna array is composed of two parts: low-loss gap waveguide (GWG) feeding network and high performance magneto-electric (ME) dipole antennas. The antenna elements are fed by the transverse coupling slots right above an air-filled high-mode cavity with checkerboard structure. Moreover, a four-way ridge GWG (RGWG) power divider with transition from RGWG to groove GWG (GGWG) is designed to excite the high-mode cavity. By properly arranging the position and size of coupling slots, each ME dipoles are excited with in-phase property. Periodic pins are arranged around both the GWG transmission line and the air cavity to create a stop band and resonant frequency. The high-mode air cavity is realized using shorted pins to split the electromagnetic field into shorted-end GGWG. Thus, the normal GWG feeding technology with a GWG power divider and a $2 \times 2$ air cavity in different layers are combined in a single layer. The transmission loss and substrate loss of this metallic single-layer feeding network are reduced, as well as the array profile. Each CP ME dipole antenna is etched on the printed circuit board (PCB) with stable radiation pattern and wide axial ratio (AR) bandwidth performance. The proposed $4 \times 8$ planar antenna array is simulated and fabricated to validate the design. A measured 3 dB AR bandwidth of 17% and a gain of up to 23 dBi have been achieved. The impedance matching is lower than −10 dB over the frequency band with an overall boresight gain of above 19 dBi.

Ka-Band 3-D-Printed Wideband Groove Gap Waveguide Orthomode Transducer

An orthomode transducer (OMT) that falls into the twofold symmetry category is designed at the Ka-band with 33.33% bandwidth. Groove gap waveguide (GGWG) technology is adapted to implement the design due to its suitability for millimeter-wave (mm-wave) frequencies as electrical contacts between different parts are not necessary. Moreover, two transitions are deployed to broaden the operating bandwidth. The first transition is GGWG to WR-28 standard waveguide, which also acts as a power combiner. The second transition is placed between two layers of GGWGs. This new OMT consists of two main sections, the OMT core section, and the assembly section of different parts. Each section is investigated and simulated separately; then the whole structure is simulated to validate the performance. A prototype is built using 3-D-printing technology with copper-electroplated surfaces. A back-to-back measurements technique indicated matching and isolation level better than 12.5 and 25 dB, respectively, for both polarizations over the entire band. Nevertheless, the insertion loss has an acceptable level over such bands.

A Chebyshev Transformer-Based Microstri-to-Groove-Gap-Waveguide Inline Transition for MMIC Packaging

The gap waveguide technology has become an alternative to millimeter- and submillimeter-wave electronic circuit packaging thanks to the loss reduction associated with its use. In this paper, a simplified design of an inline transition between a microstrip and a groove gap waveguide (GGW) operating at the $W$ -band is presented. The transition consists of a tapered microstrip line and a Chebyshev adapter that couple the quasi-TEM mode of the microstrip line to the so-called vertical mode of the GGW. The simplicity of this design makes this transition appropriate for monolithic microwave integrated circuit (MMIC) packaging at millimeter frequencies and above. The simulation results have been experimentally validated in the $W$ -band. A good performance has been achieved, resulting in a return loss better than 10 dB and a mean insertion loss lower than 2 dB.

Gap Waveguide With Interdigital-Pin Bed of Nails for High-Frequency Applications

A new kind of contactless electromagnetic bandgap (EBG) structure in the form of interdigital-pin bed of nails is introduced for the first time in this paper. It consists of two metal plates with interdigital-pin bed of nails face to face with each other, where each pin is surrounded by four pins on the other plate. The working mechanism of the interdigital-pin contactless EBG structure is suppressing the modes supported by the parallel plate waveguide (PPW) by loading interdigital pins inside the PPW. The advantage of the interdigital-pin lattice is there is a significant pin gap increase. This lattice makes the minimum pin gap that could be processed by the machining center, after assembling, reduced from the diameter of the milling clutter to its radius. It provides a way to process EBG structures at higher frequency band with the same milling cutter. The cases the pins allocated between the two plates in a random manner are also studied. Compared to its traditional counterpart, the stopband is stable with a small variation. A W-band groove gap waveguide (GGW) prototype with interdigital-pins and a Ka-band GGW with randomly allocated pins are designed, manufactured, and tested. The measured results agree well with the simulation.

60 GHz Single-Layer Slot-Array Antenna Fed by Groove Gap Waveguide

A V-band single-layer low-loss slot-array antenna is presented in this letter. Radiating slots are backed by coaxial cavities, which are fed through a groove gap waveguide E-plane corporate feed network. Cavity resonances are created by shortening nails with respect to the surrounding ones. This fact enables a compact single-layer architecture since coaxial cavities and feeding network can share the same bed of nails. A 16 × 16 array is designed, constructed, and measured to demonstrate the viability of this concept for high-gain single-layer slot-array antennas. In addition, this solution can be extended to circular polarization by seamlessly adding a polarizer above the slots without changing the feeding network piece. Measurements show a relative bandwidth of 10% with input reflection coefficient better than $-$ 10 dB and a mean antenna efficiency above 70% within the operating frequency band (57–66 GHz)

Compact Combline Filter Embedded in a Bed of Nails

In this paper, we propose a compact topology for high-frequency bandpass filters using coaxial cavities embedded in a bed of nails, including a complete design procedure combining equivalent circuit models and full-wave simulators. The resonance generated around a shortened cylindrical nail of the bed hosting structure is used as the basic element of the proposed filter, which is fed through groove gap waveguides. For design purposes, an equivalent circuit model of the considered resonance is first obtained, and then the coupling levels between resonators are recovered with the distance between adjacent shortened nails. In order to validate the proposed structure and its design procedure, a filter prototype with a bandpass response (centered at 30 GHz and with relative bandwidth of 1.7%) has been designed, manufactured, and measured. Good experimental results, in terms of insertion losses (with a minimum value of 1.6 dB) and return losses (greater than 16.6 dB in the whole passband), have been achieved.

Design of slot array antenna in groove Gap waveguide technology

This paper presents a step-by-step procedure for the design of a slot array antenna in groove gap waveguide technology. The design procedure is based on defining an effective width for groove gap waveguides. To accomplish this, a direct equivalent correspondence is assumed between the groove gap waveguide and a rectangular waveguide. It is demonstrated that once the effective width of the groove gap waveguide is found, conventional equations for the design of slot-array rectangular waveguide antenna can be utilised to accurately design a slot array antenna in gap waveguide technology. Thus, unlike other methods available in literature, the proposed method only requires the knowledge of propagation constant in the dominant mode of the groove gap waveguide. Since analytic equations are utilised, the design of a slot array groove gap waveguide antenna with very good impedance matching and desired side-lobe level can be accomplished in a fast optimisation process. Using the proposed method, slot array antennas with uniform and Chebyshev distribution of slots are designed. Finally, a prototype of a designed antenna is fabricated and its reflection coefficient and radiation pattern are measured to provide an experimental verification.