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A novel technique is shown to improve the isolation between radiators in antenna arrays. The proposed technique suppresses the surface-wave propagation and reduces substrate loss thereby enhancing the overall performance of the array. This is achieved without affecting the antenna’s footprint. The proposed approach is demonstrated on a four-element array for 5G MIMO applications. Each radiating element in the array is constituted from a 3 × 3 matrix of interconnected resonant elements. The technique involves (1) incorporating matching stubs within the resonant elements, (2) framing each of the four-radiating elements inside a dot-wall, and (3) defecting the ground plane with dielectric slots that are aligned under the dot-walls. Results show that with the proposed approach the impedance bandwidth of the array is increased by 58.82% and the improvement in the average isolation between antennas #1&2, #1&3, #1&4 are 8 dB, 14 dB, 16 dB, and 13 dB, respectively. Moreover, improvement in the antenna gain is 4.2% and the total radiation efficiency is 23.53%. These results confirm the efficacy of the technique. The agreement between the simulated and measured results is excellent. Furthermore, the manufacture of the antenna array using the proposed approach is relatively straightforward and cost effective.

In this paper, a multiple-input and multiple-output (MIMO) antenna with high gain and high isolation based on the metamaterial concept is proposed at 30 GHz for millimeter-wave applications such as 5G communication systems. The edge-to-edge distance between the radiation patches is 1.5 mm or 0.1 λ g at 30 GHz. In order to realize the metamaterial environment, a novel unit-cell (Σ-shaped structure) with negative permeability and permittivity was designed. Fifteen unit-cells were used to increase the antenna gain. The gain enhancement is more than 8 dB at 30 GHz. Also, to reduce mutual coupling, 2 unit-cells were loaded in a gap created on the ground plane. Isolation improvement is more than 32 dB at 30 GHz. The radiation efficiency of the proposed MIMO antenna at 30 GHz is equal to 68%. The final dimensions of the proposed antenna are 19.4 × 13 × 0.254 mm 3 or 0.11 λ g 3 at 30 GHz.

An innovative off-chip antenna (OCA) is presented that exhibits high gain and efficiency performance at the terahertz (THz) band and has a wide operational bandwidth. The proposed OCA is implemented on stacked silicon layers and consists of an open circuit meandering line. It is shown that by loading the antenna with an array of subwavelength circular dielectric slots and terminating it with a metamaterial unit cell, its impedance bandwidth is enhanced by a factor of two and its gain on average by about 4 dB. Unlike conventional antennas, where the energy is dissipated in a resistive load, the technique proposed here significantly reduces losses. The antenna is excited from underneath the antenna by coupling RF energy from an open-circuited feedline through a slot in the ground-plane of the middle substrate layer. The feedline is shielded with another substrate layer which has a ground-plane on its opposite surface to mitigate the influence of the structure on which the antenna is mounted. The antenna has the dimensions 12.3 × 4.5 × 0.905 mm 3 and operates across the 0.137–0.158 THz band corresponding to a fractional bandwidth of 14.23%. Over this frequency range the average measured gain and efficiency are 8.6 dBi and 77%, respectively. These characteristics makes the proposed antenna suitable for integration in sub-terahertz near-field electronic systems such as radio frequency identification (RFID) devices with high spatial resolution.

This paper presents an efficient analysis of a substrate integrated waveguide (SIW) single-layer hybrid ring coupler (rat-race) for millimeter-wave and microwave applications. The scattered field from each circular cylinder is expanded by cylindrical eigenfunctions with unknown coefficients that have been solved by electric and magnetic tangential boundary on each metallic via. The coupler S-matrix is calculated by using mode matching that uses the cylindrical vector expansion analysis to minimize the computational time and provides more physical insight. To achieve higher bandwidth, the radiuses of the coupler under analysis have been optimized in Matlab code by invasive weed optimization (IWO) method, and the results have been verified by CST package. The return loss and the isolation are less than −15 dB, and −18 dB, respectively. The insertion loss is divided equally - 3 ± 0.2 dB, with 0 ± 5 and 180 ± 10 degrees in output ports over the operating frequency bandwidth and the agreement of phase differences in output ports has been examined objectively by feature selective validation (FSV) technique.

The design and analysis of an ultra wideband aperture antenna with dual-band-notched characteristics are presented. The proposed antenna consists of a circular ring exciting stub on the front side and a circular slot on the back ground plane. By utilizing a parasitic strip and a T-shaped stub on the antenna structure, two notched bands of 850 MHz (3.5-4.35 GHz) and 900 MHz (5.05-5.95 GHz) are achieved. The proposed antenna is fabricated and measured. Measured results show that this antenna operates from 2.3 GHz to upper 11 GHz for voltage standing wave ratio less than 2, except two frequency notched bands of 3.5-4.35 and 5.05-5.95 GHz. Moreover, the experimental results show that proposed antenna has stable radiation patterns and constant gain. A conceptual circuit model, which is based on the measured impedance of the proposed antenna, is also shown to investigate the dual-band-notched characteristics.

This paper presents a novel miniaturized parallel coupled-line bandpass filter by etching some slot resonators on the strip for suppressing the first spurious response. These slots perform a serious LC resonance property in certain frequency and suppress the spurious signals. By properly tuning these slot dimensions, multiple closed notches can be generated in the vicinity of spurious harmonic and a wide stopband can be obtained. Slot on the strip that is called Defected Microstrip Structure (DMS). The DMS interconnection disturbs the current distribution only across the strip, thereby giving a modified microstrip line with certain stop band and slow-wave characteristics. The simulation and measurement of a 4.7 GHz prototype bandpass filter are presented. The measured results show a satisfactory rejection level more than 30 dB at first spurious passband without affecting the passband response. Good agreement between the experimental and full-wave simulated results has been achieved.

A novel printed crossed dipole antenna with reconfigurable circular and linear polarization is proposed. This antenna consists of a pair of L-shape elements and a narrow gap on each arm for inserting a conductive metal tab as an ideal switch in the center of the gap to control its on-off status. The theory of characteristic modes has been used to design and analyze the proposed antenna. Based on the presented idea, a prototype of such antenna has been constructed with the center operating frequency at about 2500 MHz. The experimental results have been presented and compared with those obtained from the simulation showing a good agreement. The antenna is low cost and possesses simultaneous circular and linear polarization which has not been reported in the literature for single-feed crossed dipole antennas.