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We have designed and proposed the edge modes supported by graphene ribbons and the planar band-pass filter consisting of graphene ribbons coupled to a graphene ring resonator by using the finite-difference time-domain numerical method. Simulation results show that the edge modes improve the electromagnetic coupling between devices. This structure works as a novel, tunable mid-infrared band-pass filter. Our studies will benefit the fabrication of planar, ultra-compact nano-scale devices in the mid-infrared region. A power splitter consisting of two output ribbons that is useful in photonic integrated devices and circuits is also designed and simulated. These devices are useful for designing ultra-compact planar devices in photonic integrated circuits.

In this article, a slot array antenna with circular polarization is presented. The structure is designed based on GasperPeano fractal as a feed line. By use of the Minimum mean square error method, the array has been optimized for the best radiation power. First, the theory of a single feed line with a radiation element is presented, then extend this theory to the double and N radiation elements. At each step, the coupling factor and radiation power are calculated. And three error function is defined as goal functions for reaching uniform distribution, maximum efficiency and the combination of them. Due to the goal functions, a genetic algorithm is represented to reach the best results by altering and tuning the parameters. The circular polarization bandwidth of the final structure is 5%, and the radiation efficiency is 85%. This theory and structure can be useful for making circular polarization in applications. K E Y W O R D Santenna theory, circular polarization, fractal antennas, transmitting antennas, slot antenna

In this study, the design and analysis of a seven‐port radar duplexer for tracking a target in X‐band operation are presented. The S‐parameters of the structure are calculated and compared with experimental results. The simulations and experimental results are in good agreement. This device enables radars to calculate the horizontal difference, vertical difference, and sum of four beams of a monopulse antenna based on amplitude discriminator. Three magic‐Ts and one T‐junction are used, four input ports are connected to a monopulse antenna and three other ports are output ports. The output data give three equations between input signals that allow the radar to track a target. Results show that the S‐parameters of this device are affected by magic‐Ts and the T‐junction structure, and an optimum structure for the magic‐Ts and T‐junction is proposed. A comprehensive study has been carried out for determination and comparison of properties of the structure in theory, simulation, and experimental results. This device is useful in radar tracking systems.