In this letter a four-port multi-input-multi-output (MIMO) antenna for 5G applications is proposed. This antenna is compact with a size of 11 mm × 31 mm excluding feed lines. The radiation patterns of the antenna show pattern diversity in the azimuthal plane, and each antenna element has an end-fire gain about 10 dBi by employing an array of metamaterial unit cells. The isolation between the antenna elements with edge to edge separation < λ 0 /5.5 at 28 GHz is enhanced by trimming the corners of the rectangular high refractive index metamaterial region along with a ground stub between antennas. The proposed antenna is fabricated, and each antenna element has return loss, S nn < −10 dB with isolation, S nm > 21 dB in the frequency range 26 GHz to 31 GHz, which makes this antenna potential candidate for MIMO application at 28 GHz band enabling 5G cellular communications.

In this paper, design of a triple band ultrathin compact polarization insensitive metamaterial absorber for S-, C-and X-band applications is proposed. The proposed absorber consists of periodic arrangement of a modified triple circular slot ring resonator as unit cell printed on the top of a continuous metal backed FR-4 dielectric substrate. The proposed absorber is ultrathin having thickness of λ 0 /135.66 at the lowest absorption center frequency. The measured wide stable absorption bands of 0.40 GHz, 0.45 GHz and 0.47 GHz with absorption peaks of 97%, 96.45% and 98.20% at absorption center frequencies of 2.90 GHz, 4.18 GHz and 9.25 GHz respectively are observed. The temperature profile of absorber is measured by using lock in infrared thermography, and a temperature increase of 1 • C at absorbing frequency as compared to non-absorbing frequency is observed. The absorber is demonstrated to be polarization insensitive to TE and TM polarized angles of incidence of electromagnetic wave with wide angular stability up to 45 •. The absorber is fabricated and tested in an anechoic chamber. Experimental results agree well with measured ones.

A highly miniaturized significant gain triple band patch antenna loaded with a new modified double circular slot ring resonator (MDCsRR) metamaterial unit cell is presented in this paper. New MDCsRR is a compact low frequency slot ring resonator. The principle of the proposed patch antenna element is based on adding series capacitance to decrease the half wavelength resonance frequency, thus reducing the electrical size of the proposed patch antenna. The transmission line model is used to analyze passband and stopband characteristics of the radiating bands. Circulating current distribution around MDCsRR slot with increased interdigital capacitor finger length causes multiple modes to propagate. The MDCsRR metamaterial unit cell consists of a new modified circular slot ring resonator (MCsRR) with metallic strip finger. The proposed structure is compact in size with radiating element dimensions of 0.20λ × 0.20λ × 0.008λ at first resonating frequency. The proposed antenna offers triple band operation with significant calculated antenna gain of 3.28 dBi at first center frequency of 3.2 GHz, 2.76 dBi at second center frequency of 5.4 GHz and 3.1 dBi at third center frequency of 5.8 GHz. The electrical size of the proposed antenna is miniaturized by about 68.83% as compared to the conventional patch antenna operating at first resonating frequency.

In this paper, a co-planar waveguide fed circular slot antenna with an operational impedance bandwidth of 20-28 GHz is proposed. In order to reduce the effective occupied volume when the antenna is integrated onto a typical mmWave 5G smartphone, a conformal topology is investigated. Since the radiating aperture is not backed by an electrically large ground plane, it leads to a bidirectional beam resulting in an inherently low forward gain of 4 dBi with a front to back ratio of 1 dB. Hence, a compact exponentially tapered copper film reflector is integrated electrically close (0.046λ at 28 GHz) to the radiating aperture to achieve a forward gain of 8-9 dBi with an effective radiating volume of 0.24λ 3. The impedance bandwidth is from 25 to 30 GHz (18.2%) with a 1-dB gain bandwidth of 34.7% indicating high pattern integrity across the band. Since the proposed antenna element offers wideband with high gain, it is a potential candidate for mmWave 5G smartphones.

A coplanar waveguide (CPW) fed uniplanar all-metallic antenna is proposed for mmWave 5G access points. The antenna has an impedance bandwidth from 26 to 30 GHz with a corresponding end-fire gain of 8 dBi at 28 GHz. The effective radiating volume is 0.0031λ 3 0 indicating a high gain yield for minimal physical footprint. The radiation efficiency is 99.5%, and the losses are primarily due to finite conductivity of copper. The pattern integrity is high across the band with cross-polarization level below 30 dB, due to lack of electrically thick dielectric substrate. Industry standard low-cost chemical etching technique is used for fabrication of the prototype. A compact, co-polarized stacked beam switching module is also proposed for wide angular coverage with three-ports. This module houses the proposed all-metallic antennas for beam switchability. A customized 3D-printed scaffolding using polylactic acid (PLA) is designed to house the proposed antennas. The antenna module has a wide angular coverage of ±50 • . Since the proposed antenna has high radiation efficiency with high gain for minimal physical footprint, it could be a potential solution for mmWave 5G access points. Detailed simulated and measured results are presented with technical justification.