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A wideband, low-profile endfire antenna with polarization reconfiguration is proposed. The endfire antenna can be electronically switched among the left-hand circular polarization (LHCP), right-hand circular polarization (RHCP), and linear polarization (LP) using six PIN diodes in conjunction with biasing lines. The proposed antenna consists of a wideband half-mode substrate integrated waveguide (HMSIW) cavity (vertically polarized magnetic dipole) and tapered switchable electric dipole (horizontally polarized) with a feed line. The impedance bandwidth of the HMSIW cavity is increased by combining the resonance frequencies of quasi-TE1,0.5,0 mode with quasi-TE3,0.5,0 mode by placing the two slotted pairs at the null of quasi-TE3,0.5,0 mode. At LHCP/RHCP states, the proposed endfire antenna exhibited a stacked 10-dB impedance bandwidth (IBW) of 11.66% (6.54-7.35 GHz) and a 3-dB axial ratio bandwidth (ARBW) of 11.23% (6.515-7.29 GHz) with a peak gain of approximately 4.20 dBic. When switched to the LP state, it shows a 10-dB impedance bandwidth of 11.58% (6.87-7.715 GHz) with a peak gain of 5.35 dBi. Therefore, it can exhibit good effective bandwidths (stacked 10-dB IBW and 3-dB ARBW) of 5.93% (6.87-7.29 GHz) and 10.84% (6.54-7.29 GHz) across the three polarization states (LP/RHCP/LHCP) and two CP states (RHCP/LHCP), respectively.

A two-stage beamforming technique for a wide tilt angle is proposed in this letter. The proposed structure has the potential to overcome the limitations of Butler matrix-based beamforming technique and reconfigurable frequency selective surfaces (FSS)-based beamforming technique, both of which normally lag behind in the present generation of wireless communication due to lesser number of radiating beams. The composite system comprises three parts: a 4 × 4 Butler matrix, an antenna array of 1 × 4 elements, and a reconfigurable FSS layer. Four semi-rigid coaxial cables are employed to connect the Butler matrix to the four-element antenna array. The reconfigurable FSS is mounted on top of antenna layer using air spacers. The FSS superstrate layer consists of 6 × 6 reconfigurable unit cells, which have been further divided into two equal sections to increase the number of radiating beams. Combining the four-port Butler matrix with reconfigurable FSS allows the system to generate 12 unique radiating beams in 12 distinct directions in 3-D space. The proposed system is designed, fabricated, and measured for operating frequency of 5.5 GHz. The proposed system attains a maximum tilt of 72$^\circ$ and a peak gain of 11.8 dBi.

In this Letter, we report the design, analysis, and characterization of first- and second-order plasmonic metamaterial-based multi-mode filtering structures. Further, electronic adaptivity in filter transfer functions is introduced and characterized. First, the basic operating principle of the engineered multi-mode resonator-based bandpass filter is presented. Then the concept is extended by introducing electronic (dynamic) tuning of the bandwidth using semiconductor varactor diodes. Afterwards, to enhance the selectivity and out-of-band filtering response, second-order multi-mode designs are realized. For experimental verification, the hardware prototype is fabricated and characterized using the Keysight analyzer N9918A. The design filtering structures will pave an important role in tunable plasmonic circuits and systems.

ABSTRACTIn this paper, a new time-domain (TD) solution is proposed for corner diffraction by finite-edge flat plate structures. First, TD solution is considered for corner amplitude diffraction by edges of a flat plate, and then for corner slope diffraction (CSD) which takes into account the finiteness of the plate edges. To show the significance of CSD, results have been shown for diffraction of ultra-wideband signals by edges of a horn antenna which is a structure made by interconnected flat plates. The comparison between the TD solution and the numerical inverse fast Fourier transform of the corresponding frequency-domain solution validates the proposed solution. Finally, the computation times of both methods have been compared.