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This article presents a novel method for the forward modeling and inverse design of a class of Schiffman phase shifters using deep neural networks (DNNs). Since DNNs are capable of mapping the highly nonlinear correlations between inputs and outputs, we constructed a fully connected DNN to predict the electromagnetic (EM) responses of Schiffman phase shifters given their physical dimensions. Based on this fast and accurate modeling tool, a cascaded inverse design DNN was then built and trained to achieve instant on-demand phase shifter designs. This approach is versatile and can be easily modified to accomplish different design goals. To demonstrate its efficacy, we trained two DNNs to realize Schiffman phase shifter designs with different bandwidths (40% and 60%) and arbitrary phase shift targets (0°–180°). Simulation results and experimental verifications substantiate that their performances are comparable with the state-of-the-art designs. Moreover, we discussed the proposed methods’ potential in dealing with design tasks that are nonintuitive and beyond the scope of the existing approaches. We envision that this DNN approach can be extended to the design of various EM components including but not limited to antennas, filters, power dividers, and frequency selective surfaces (FSS). [ABSTRACT FROM AUTHOR]

In this paper, a symmetric four-port microwave varactor based 90^\circ directional coupler with tunable coupling ratios and reconfigurable responses is presented. The proposed coupler is designed based on the modified structure of a crossover, where varactors are loaded. By applying suitable biasing voltages to the varactors, the power-dividing ratios between the two output ports (i.e., port 2 and port 3) of the coupler can be easily controlled. Moreover, it is found that the realizable power ratio using the proposed structure is very flexible (it could be extremely large or small). Therefore, under the special case when the coupling ratio is tuned to be 1, the proposed coupler is reconfigured to be a crossover. Good isolation and return-loss performance have been maintained for different power-dividing ratios. To theoretically analyze the proposed device, closed-form design equations are derived using the even–odd mode method. Based on these analytical equations, an experimental prototype working at 1 GHz is designed, fabricated, and characterized. The measurement results match well with the simulation and theoretical results, validating the proposed design theory. [ABSTRACT FROM AUTHOR]

In this paper, a new fully symmetrical four-port microstrip crossover and its dual-frequency application are presented. The proposed single-band crossover has a simple structure and an easily controlled bandwidth; and its dual-frequency application can provide flexible frequency ratio between the two working frequencies. Moreover, analytical design equations are derived using the even–odd-mode method. The final explicit design equations are concise. To verify the design concepts, both a single-band crossover working at 1 GHz and a dual-frequency crossover working at 1/2.3 GHz are fabricated and tested. The measurement results agree well with the design theory. [ABSTRACT FROM AUTHOR]