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In this paper, an end-fire antenna for 28 GHz broadband communications is proposed with its multiple-input-multiple-output (MIMO) configuration for pattern diversity applications in 5G communication systems and the Internet of Things (IoT). The antenna comprises a simple geometrical structure inspired by a conventional planar helical antenna without utilizing any vias. The presented antenna is printed on both sides of a very thin high-frequency substrate (Rogers RO4003, εr = 3.38) with a thickness of 0.203 mm. Moreover, its MIMO configuration is characterized by reasonable gain, high isolation, good envelope correlation coefficient, broad bandwidth, and high diversity gain. To verify the performance of the proposed antenna, it was fabricated and verified by experimental measurements. Notably, the antenna offers a wide −10 dB measured impedance ranging from 26.25 GHz to 30.14 GHz, covering the frequency band allocated for 5G communication systems with a measured peak gain of 5.83 dB. Furthermore, a performance comparison with the state-of-the-art mm-wave end-fire antennas in terms of operational bandwidth, electrical size, and various MIMO performance parameters shows the worth of the proposed work.

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This paper presents a compact and simple reconfigurable antenna with wide-band, dual-band, and single-band operating modes. Initially, a co-planar waveguide-fed triangular monopole antenna is obtained with a wide operational frequency band ranging from 4.0 GHz to 7.8 GHz. Then, two additional stubs are connected to the triangular monopole through two p-i-n diodes. By electrically switching these p-i-n diodes ON and OFF, different operating frequency bands can be attained. When turning ON only one diode, the antenna offers dual-band operations of 3.3–4.2 GHz and 5.8–7.2 GHz. Meanwhile, the antenna with single-band operation from 3.3 GHz to 4.2 GHz can be realized when both of the p-i-n diodes are switched to ON states. The proposed compact size antenna with dimensions of 0.27λ0 × 0.16λ0 × 0.017λ0 at the lower operating frequency (3.3 GHz) can be used for several wireless applications such as worldwide interoperability for microwave access (WiMAX), wireless access in the vehicular environment (WAVE), and wireless local area network (WLAN). A comparative analysis with state-of-the-art works exhibits that the presented design possesses advantages of compact size and multiple operating modes.

A new simple design of a triple-band microstrip antenna using metamaterial concept is presented in this paper. Multi-unit cell was the key of the multi resonance response that was obtained by etching two circular and one rectangular split ring resonator (SRR) unit cells in the ground plane of a conventional patch operating at 3.56 GHz. The circular unit cells are resonating at 5.6 GHz for the upper band of Wi-MAX, while the rectangular cell is designed to produce a resonance at 2.45 GHz for the lower band of WLAN. WiMAX's/WLAN's operating bands are covered by the triple resonances which are achieved by the proposed antenna with quite enhanced performance. A detailed parametric study of the placement for the metamaterial unit cells is introduced and the most suitable positions are chosen to be the place of the unit cells for enhanced performance. A good consistency between simulation and measurement confirms the ability of the proposed antenna to achieve an improved gain at the three different frequencies.

In this paper, a compact 4-port band-notched multi-input-multi-output (MIMO) antenna with asymmetric coplanar strip (ACS) feed is presented for ultra-wide band (UWB) applications. The MIMO antenna is comprised of four semi-elliptical radiators with ACS feed for UWB applications and it is printed on inexpensive FR4 substrate of size 48 × 52 mm2 with ɛr = 4.4 and 1.6 mm height. The impedance characteristics of the suggested MIMO antenna ranges from 2.7 to 11 GHz with a band-notched behavior from 3 to 4 GHz to reduce the interception with WiMAX applications, and the isolation level over the achieved band is more than 20 dB between any two adjacent elements. Moreover, the radiation pattern of the proposed UWB antenna is almost omnidirectional with an average realized gain of 3.5 dBi over the entire achieved frequency band. The proposed ACS-fed antenna is confirmed by fabricating and measuring it's impedance and radiation characteristics. Finally, good consistency between simulation and measured outcomes is obtained confirming the validity of the MIMO antenna for real-life UWB wireless systems.