Millimeter-Wave Quasi-Optical Feeds for Linear Array Antennas in Gap Waveguide Technology

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.

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 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.

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.

This paper presents a Ka-band linearly-polarized 4-antenna array fed with a novel corporate distribution network that uses a half-mode groove gap waveguide (HM-GGW). The antenna feed has no contact with the top cover where the array antenna is located, thanks to the features inherent in gap waveguide technology (GW). This technology, with many advantages, sometimes suffers from a complex mechanization, which in this case is reversed by the novel network proposed in this paper.

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.

A single mode dielectric cavity and a dual mode cavity are proposed and studied for newly introduced ridge air gap waveguide. These cavities are realized by creating defects in periodic structure of EBG surface made of bed of conducting nails, which are used in ridge air gap and groove gap waveguides. These cavities and resonators are used to realize some filters. As an example, a dual bandstop notch filter is designed and simulated. In addition, a narrow bandpass filter is designed, fabricated, and measured using the proposed cavities in the X-band.

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 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.

A novel substrateless power amplifier module realized by ridge gap waveguide (RGW) technology is proposed in Ka-band. Up to our knowledge, this is the first time that an active device is directly integrated with an RGW structure. No substrate is used in the RF section of the implemented power amplifier and the whole structure is made by machining a piece of metal. The amplifier was made of two pieces and was easily assembled without needing a precise contact between the two sections. The cavity resonance of the amplifier is suppressed using a pining structure. The fabricated amplifier module is self-packaged and does not need any packaging. It is shown that the simulated and measured results are in good agreement. This paper shows the capability of RGW technology for implementing the whole RF frontend in microwave- and millimeter-wave systems.

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

A low insertion loss wideband mm-Wave crossover with three-section branch-line structure based on ridge gap waveguide technology

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

High-efficiency single-layer corporate-feed gap waveguide based circularly polarized antenna array with compact size