1×4 Antenna Array corporately fed by a Novel Half-Mode Groove Gap Waveguide network

This article presents the design of a flat Luneburg metalens antenna at V-band using gap waveguide (GW) technology. The metalens consists of a parallel plate waveguide (PPW) loaded with metallic pins whose height is modulated to get an effective refractive index that follows the Luneburg equation. A Groove GW (GGW) H-plane horn is used to illuminate the metalens, such that the rays are collimated and a planar wavefront is generated in the direction of propagation. Since the structure at hand is planar, it can be efficiently integrated on flat surfaces. Moreover, the fully metallic structure is mechanically robust and presents lower losses than lenses including dielectric substrates. A prototype has been fabricated and tested, simulations and experimental results are in very good agreement. The metalens yields an input reflection coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula> ) below −10 dB from 45 to 70 GHz, whereas the −3 dB gain fractional bandwidth is 26.2% with respect to a center frequency of 60 GHz, with a peak of 22.5 dB at 61 GHz. These features make this design an interesting solution for millimeter-wave (MMW) applications.

A realization of the quasi-optical (QO) feed concept for linear millimeter-wave (sub-)array antennas is demonstrated in gap waveguide technology. The proposed feed architecture employs an input transition from a ridge gap waveguide (RGW) to a groove gap waveguide (GGW), a radial (H-plane sectoral) GGW section, and a transition to an output RGW array. A design decomposition approach is presented to reduce simulation complexity. Several 20-element QO feed implementations are investigated at W-band demonstrating a 20% relative bandwidth (85–105 GHz), 0.5 dB insertion loss, and a capability of an amplitude taper control within the 10–20 dB range.

A single-layer spatial power splitter-combiner structure is packaged in gap waveguide technology. The measured metal-only back-to-back structure features an average insertion loss less than 2.3 dB and a return loss larger than 10 to 20 dB over the entire 75–110 GHz W-band. The design procedure is outlined and the measured and simulated results are shown to be in good agreement. The structure can be used as a stand-alone power splitter and/or combiner (single-mode, all-excited in-phase channels), a quasi-optical beamformer to excite an array of slot antennas in the top ground plane by ridge gap waveguides, or as a back-to-back RF component in grid amplifier designs.

This article presents a wideband design of a rotary joint based on groove gap waveguide technology. The proposed design includes two coax-to-groove gap waveguide (GGW) transitions, connected together in a back-to-back arrangement. As the gap waveguide structure does not require electrical connections between different parts, the rotor part is placed on top of the stator with an air gap distance while the wave leakage is suppressed. Therefore, the rotating choke, which is a critical and bulky part in the previous designs, is eliminated. By introducing some matching posts in the structure, a wideband design is achieved with 55% bandwidth covering from 11 to 19.5 GHz, where the insertion loss is lower than 0.28 dB. Some parameter sweeps are presented to investigate the effect of the rotor displacement during rotation. A prototype of the proposed rotary joint was fabricated using CNC milling for verification of the design. The measured results agree well with the simulated ones and prove the excellent performance of the proposed rotary joint.

The Gap Waveguide technology utilizes an Artificial Magnetic Conductor (AMC) to prevent the propagation of electromagnetic (EM) waves under certain conditions, resulting in various gap waveguide configurations. In this study, a novel combination of Gap Waveguide technology and the traditional coplanar waveguide (CPW) transmission line is introduced, analyzed, and demonstrated experimentally for the first time. This new line is referred to as GapCPW. Closed-form expressions for its characteristic impedance and effective permittivity are derived using traditional conformal mapping techniques. Eigenmode simulations using finite-element analysis are then performed to assess its low dispersion and loss characteristics. The proposed line demonstrates an effective suppression of the substrate modes in fractional bandwidths up to 90%. In addition, simulations show that a reduction of up to 20% of the dielectric loss can be achieved with respect to the traditional CPW. These features depend on the dimensions of the line. The paper concludes with the fabrication of a prototype and validation of the simulation results in the W band (75-110 GHz).

Dual circular polarization 2 × 2 slot array antenna based on printed ridge gap waveguide technology in Ka band

In this article, a slot array with double-layered full-corporate-fed distribution network by ridge gap waveguide (RGW) in the G-band is presented. The array antenna proposed in this article contains 16 × 16-element radiation slots fed by air-filled ridge gap waveguide distribution network that achieves high-efficiency. Gap waveguide technology avoids the demand for perfect electrical contact in millimeter waves, therefore the expensive diffusion bonding and the laser welding processes are not demanded. Moreover, the high-accurate Computerized Numerical Control (CNC) machining is applied for the fabrication. Due to the limited layout space for the distribution network, two types of universal stepped cavity power dividers are presented in this article. The proposed array antenna is fed by a standard WR-5 waveguide at the bottom. Furthermore, the tested outcomes show that the proposed 16×16-element array has a gain larger than 30 dBi with over 50% antenna efficiency in the frequency range of 155-171 GHz.

A broadband 3-way power divider based on gap waveguide for Ka-band applications

Empty substrate integrated waveguide (ESIW) is a hollow SIW with its inner dielectric removed to achieve a reduced insertion loss. One of the drawbacks is the top and bottom covers need to be soldered to the middle substrate. Gap waveguide (GW) technology solves the contact issue utilising contactless electromagnetic band‐gap (EBG) structures. Therefore, empty substrate integrated GW (ESIGW) is a transmission line having both advantages of ESIW and GW. In this Letter, a wideband transition from rectangular waveguide (RW) to ESIGW is presented. RW is firstly matched to reduced‐height RW using E ‐plane stepped waveguides. Then, a short substrate integrated GW (SIGW) section is introduced between the reduced‐height RW and the ESIGW. This section not only serves as an impedance matching component, it also connects the two sides of the ESIGW and maintains the integrity of the substrate. To broaden the bandwidth of the transition, a triangular dielectric is added at the end of the ESIGW. A Ka‐band back‐to‐back prototype of the transition is designed and fabricated. In addition, TRL calibration is used to measure the transmission performance of the ESIGW. The measured results show that the transition works well over the entire Ka‐band.

A dual circularly polarized (CP) slot array antenna is proposed for V-band applications. A sliding mechanism based on the groove gap waveguide is employed to achieve the left hand circular polarization (LHCP) and the right hand circular polarization (RHCP). Due to the use of gap waveguide technology, there is no electrical contact between the different parts of the switch and the leakage of the electromagnetic wave is suppressed. The simulation results show that the proposed antenna has axial ratio (AR) below 3 dB, and pick gain of 14 dB in the desired impedance matching bandwidth from 58–62 GHz.

3-D printed triple-band metasurface filter based on groove gap waveguide technology

This paper presents a novel design of a low-loss, reconfigurable broadband phase shifter based on groove gap waveguide (GGW) technology. The proposed phase shifter consists of a folded GGW and three bends with a few pins forming the GGW and one bend attached to a movable plate. This movable plate allows for adjustments to the folded waveguide length, consequently altering the phase of electromagnetic waves. The advantage of GGW technology is that it does not require electrical contact between different parts of a structure. Therefore, it enables the moving parts to slide freely without electromagnetic energy leakage, resulting in improved insertion loss in high-power applications. In addition, in the proposed design, the position of the input and output waveguide ports of the phase shifter remains fixed, which is advantageous from a practical point of view. As shown by measurement and simulation results, there is nearly 37% impedance bandwidth with the highest insertion loss of 0.6 dB, and the developed device has a maximum phase shift of 770° at the center frequency of 13 GHz. The phase shifter can be used for various radar and satellite applications that require phase control, such as beamforming networks and phased array antennas.

This paper describes a simple, low loss, compact tuneable band pass filter based on ridge gap waveguide (RGW) technology for the Ku-band applications. This is achieved by keeping the height of the air gap in the gap guide structure equal to the thickness of the substrate or base of the structure. The resonant frequency and electromagnetic (EM) field distribution of the structure is investigated. This filter is designed by inserting the proposed ridge in the cut-off region of the gap waveguide. The frequency of tuning has been carried out using the slot created on ridge, which generates capacitive effect. Experimental results of the manufactured structure show an insertion loss of approximately 0.15 dB and a return loss of 16.38 dB over 4.5% relative bandwidth in Ku-band. The structure, put forwarded here, has been designed and optimized in the CST microwave studio environment and simulated results are validated by experimental results. The size of the structure is 64.65 mm × 64.65 mm × 7 mm.

A D-band corporate-feed gap-cavity slot array is proposed with wide bandwidth and high aperture efficiency. The cavity with higher order modes is implemented by using the gap waveguide (WG) technology, namely, a gap cavity. To ensure that the gap cavity is operating with the desired higher order mode over a wide bandwidth, the corporate-feed architecture is applied for uniform excitation and with alternating-phase between adjacent slots. The gap cavity is split into multiple elements by using zero-thickness virtual perfect electric conductor (PEC) walls. With this unique approach, the design, fabrication, and assembly complexities are reduced. For experimental verification, a gap cavity with 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 slot array is designed in the 120 GHz band, and an E-plane WG feeding network is proposed to excite the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">880</sub> -mode. Two metal fences are introduced on either side of the radiating slot, and an inductive metal pin is introduced below the radiating slot to improve the radiation performance and broaden the bandwidth. The measured impedance matching bandwidth is around 110–144.8 GHz (27.3%). The measured peak gain is 26.22 dBi at 137.64 GHz, and the measured peak aperture efficiency is 86.2% at 115.325 GHz. The 3 dB gain bandwidth is the same as the impedance matching bandwidth.

In this work, a symmetric pillbox antenna with low side lobes is designed, simulated and fabricated by using gap waveguide technology. The proposed antenna operates on the basis of the reflector antenna principle and provides a fan‐beam radiation pattern. In the proposed structure, the antenna aperture is loaded by a stepped discontinuity and a corrective pin to improve the side‐lobe level (SLL) and gain. The designed antenna impedance bandwidth (S11 &lt; −10 dB) is 42% at the Ku band. Also, −15 dB &lt; SLL &lt; −10 dB and a gain of 16.6–18.7 dBi are achieved over the operating bandwidth. There is a good agreement between the simulated and measured results.