Millimeter-wave Substrate Integrated Waveguide Research Articles

Fabrication of Substrate-Integrated Waveguide Using Micromachining of Photoetchable Glass Substrate for 5G Millimeter-Wave Applications

A millimeter-wave substrate-integrated waveguide (SIW) was firstly demonstrated using the micromachining of photoetchable glass (PEG) for 5G applications. A PEG substrate was used as a dielectric material of the SIW, and its photoetchable properties were used to fabricate through glass via (TGV) holes. Instead of the conventional metallic through glass via (TGV) array structures that are typically used for the SIW, two continuous empty TGV holes with metallized sidewalls connecting the top metal layer to the bottom ground plane were used as waveguide walls. The proposed TGV walls were fabricated by using optical exposure, heat development and anisotropic HF (hydrofluoric acid) etching of the PEG substrate, followed by a metal sputtering technique. The SIW was fed by microstrip lines connected to the waveguide through tapered microstrip-to-waveguide transitions. The top metal layer, including these feedlines and transitions, was fabricated by selective metal sputtering through a silicon shadow mask, which was prefabricated by a silicon deep-reactive ion-etching (DRIE) technique. The developed PEG-based process provides a relatively simple, wafer-level manufacturing method to fabricate the SIW in a low-cost glass dielectric substrate, without the formation of individual of TGV holes, complex time-consuming TGV filling processes and repeated photolithographic steps. The fabricated SIW had a dimension of 6 × 10 × 0.42 mm3 and showed an average insertion loss of 2.53 ± 0.55 dB in the Ka-band frequency range from 26.5 GHz to 40 GHz, with a return loss better than 13.86 dB. The proposed process could be used not only for SIW-based devices, but also for various millimeter-wave applications where a glass substrate with TGV structures is required.

Homotopy Optimization and ANN Modeling of Millimeter-Wave SIW Cruciform Coupler

The development of millimeter-wave and terahertz (THz) passive components such as couplers and filters is an intimidating task because of underlying ultrasensitivity of electrical performances to geometric dimensions and processing tolerances. It is a common practice for us to use an integrated optimizer of commercial electromagnetic (EM) software packages for the design and optimization of such geometric parameters. However, those optimizers may fail to achieve a desired performance if initial variables are not in a range close enough to the optimal solution. In this article, we introduce an homotopy approach to optimizing the geometric parameters of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula> -band cruciform coupler based on substrate integrated waveguide (SIW) technique in conjunction with an artificial neural network (ANN) model. Starting from a set of initial variables, a homotopy optimization is set to search for an optimum solution. The ANN technique is adopted as the surrogate in place of a usual time-consuming EM model to accelerate the homotopy optimization process of the cruciform coupler. We propose a feed-forward computational formulation inspired by the fundamental transmission line impedance equation. Such a transmission line knowledge-based feedforward network results in a faster convergence with better accuracy than its conventional counterpart. To demonstrate the homotopy optimization method based on the ANN model, an example of multiparameterized cruciform coupler design is detailed. This cruciform coupler with optimized geometric dimensions is simulated, fabricated, and measured. Measured and simulated results validate the combined ANN model and homotopy method. An equivalent lumped-element circuit model of the cruciform coupler is also proposed in this work. An ANN model development technique is described how to extract the equivalent circuit parameters for given coupler specifications. Extracted circuit parameters in connection with the desired coupler performance are then compared with published results which verify the ANN model development algorithm.

Study on Millimeter-Wave SIW Rectenna and Arrays With High Conversion Efficiency

A novel aperture-coupled patch rectenna backed by a substrate integrated waveguide (SIW) cavity operated at 35 GHz for millimeter-wave power transmission (MMPT) with high conversion efficiency is presented in this article. A four-element SIW patch array with a harmonic suppression function based on the barbell-type defect ground structure (DGS) is proposed as the receiving antenna; thus, the low-pass filter in the rectifying circuit can be omitted. The Schottky diode is parallel-mounted in the rectifying circuit, which has a measured rectifying efficiency of 61.2% with a 500 Ω load when the received power is 100 mW. The maximum conversion efficiency of the rectenna element is 60.9% when the received power is 79.4 mW. Additionally, 4-8-and 16-element rectenna arrays are also investigated to obtain high direct current power. When the power density is 9.2 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the conversion efficiencies of the rectenna element, 2×2 array, 2×4 array and 2×8 array are 50.5%, 44.1%, 41.9%, 38.9%, respectively. The measured conversion efficiency of the 2×8 rectenna array at 35 GHz is 49.2% when the input power is 1259 mW. The low profile and easy integration of the studied rectenna will make it easy to expand its use to large-scale arrays for high-power MMPT applications.

Generating and 2-D Steering Large Depth-of-Field Beam by Leaky-Wave Antenna Array With a Modified Parabolic Reflector

A millimeter-wave substrate-integrated waveguide (SIW) antenna with the ability of generating 2-D steerable large depth-of-field beam is presented in this article. First, a transverse antenna topology feeding with the series- and the parallel-network is employed to generate the limited-diffractive beam with large depth of field to overcome the problem that the conventional radial generator cannot steer its beam electronically. The proposed antenna is achieved by combining a modulated leaky-wave slot array antenna with a modified multibeam SIW parabolic reflector. The modulated leaky-wave slot array with stepped-width is designed to able to steer the limited-diffractive beam in the horizontal dimension with the frequency, which validates the frequency scanning feasibility of the limited-diffractive beam. Then a modified SIW parabolic reflector with matching loads is used to feed the modulated leaky-wave SIW slot array antenna to generate multiple limited-diffractive beams in the vertical dimension. A large depth of field of about 43λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is achieved of the central limited-diffractive beam. The measurements are in good agreement with the simulated results.

A Tunable Circuit Model for the Modeling of Dielectric Resonator Antenna Array

An efficient, accurate, and tunable circuit model is presented for modeling of the substrate integrated waveguide (SIW) series-fed dielectric resonator antenna (DRA) array. For much improved model flexibility, the mutual coupling between antenna elements is taken into account and represented by a fully adjustable model, allowing the design parameters to be varied. Development of the circuit model is straightforward. Only one or two antenna elements from the array need to be simulated with a full-wave solver. Furthermore, the model is applicable for antenna arrays with different numbers of elements. The circuit model enables efficient iterative design and optimization of antenna arrays. Millimeter-wave SIW series-fed DRA array examples are used to validate the model. The simulation results using the proposed circuit model agree well with the full-wave solver and measurement results.