A dual-band wideband composite patch antenna constructed from a modified circular primary patch and secondary parasitic patch element is presented in this work. A microstrip feed line is employed to inset-feed the primary patch. The secondary patch is fed indirectly through edge coupling with the main patch. The composite antenna is printed on Rogers Ro3003TM with ϵr = 3 and thickness 0.25 mm. The antenna design stages are presented in detail. A MIMO antenna system is constructed from two elements of the proposed composite patch with two different configurations. A prototype is fabricated for the single element and the two-port MIMO antenna configurations. Numerical and experimental results are presented showing good performance regarding impedance matching at the operating bands 28 and 38 GHz, bandwidth, radiation patterns, and gain. The impedance matching bandwidths are 1.23 GHz at 28 GHz and about 1.06 GHz at 38 GHz. The minimum value of the reflection coefficient for 28 GHz band is -34.5 and is -27.3 dB for 38 GHz. The gain of the radiation pattern has a peak of 6.6 dBi at 28 GHz and 5.86 dBi at 38 GHz. For both bands, the radiation patterns are balloon-like omnidirectional. The antenna total dimensions are 7.5 × 8.8 × 0.25 excluding the transmission line. The MIMO system with two-ports for both proposed configurations has appropriate values for ECC and the DG which are calculated through electromagnetic simulations.

The present work proposes a novel design of a dual-band-printed antenna for operation at the millimeter-wave frequencies 28 and 38 GHz that are utilized for the modern and future generations of mobile communications. The antenna is composed of two radiating elements. The first element is the main patch that is fed through a microstrip line with inset feed, and the second element is a parasitic element that is fed through capacitive coupling with the main patch. The design parameters of the proposed antenna are optimized through a complete parametric study to give excellent impedance matching at 28 GHz over the band 27.7–28.3 GHz and at 38 GHz over the band 37.7–38.3 GHz. The surface current distributions at the two operational frequencies are investigated. The designed antenna is used to construct a four-port efficient multi–input–multi–output (MIMO) system. The MIMO system performance is investigated regarding the envelope correlation coefficient (ECC), diversity gain (DG), and the channel capacity loss (CCL) showing very good performance. The single-element antenna and the MIMO are fabricated and experimentally evaluated showing excellent impedance matching over the lower and higher frequency bands, which come in agreement with the simulation results. It is shown that the antenna produces maximum gain of 7.4 and 8.1 dBi at 28 and 38 GHz, respectively. The average radiation efficiencies of the proposed antenna are 88% and 88.8% over the lower and higher frequency bands, respectively. In addition, the coupling coefficients between the MIMO antenna systems are measured experimentally showing very low coupling values resulting in an efficient MIMO system that is suitable for future millimeter-wave (mm-wave) applications.

A novel design for Vivaldi antenna is introduced to operate in more than one frequency band in the millimeter-wave spectrum range with high gain. The proposed Vivaldi antenna is planar and printed on both sides of Rogers 3003C flexible substrate. A parasitic annular ring is added to each arm of the Vivaldi antenna to adjust the impedance matching and maximize the gain. The dimensions of the antenna are optimized using the CST microwave simulator to obtain the best impedance matching bandwidths and highest gain in a compact-size antenna. The 28-GHz band is then selected due to its importance to enhance the gain and improve the operating bandwidth for the 5G applications. A gain of 10 dBi and bandwidth of 6.1 GHz are obtained at 28 GHz. A multiple-input multiple-output (MIMO) antenna system is then designed for pattern diversity for the fifth-generation mobile applications. The performance of the MIMO system is evaluated regarding the envelope correlation coefficient and the diversity gain showing good results. The optimized antenna is fabricated and its return loss and radiation patterns are measured showing good consent between the simulations and the practical work. The MIMO antenna system is also fabricated, and its performance is measured regarding the reflection and coupling coefficients showing good agreement between the measurements and simulations.

A circularly-polarized (CP) printed antenna is proposed for millimeter-wave mobile communications. The antenna has a defected ground structure (DGS), and it operates at 28 GHz. The geometries of the antenna on the upper surface and the DGS are symmetric about a $$45^\circ$$ -diagonal to produce perfect circular polarization. The antenna is fed through a three-stage microstrip line that acts as an impedance transformer for perfect matching of the antenna impedance to $$50\,{\Omega\:}$$ at $$28\:\text{G}\text{H}\text{z}$$ . The development of the antenna design is described in detail, starting with a square patch that is subjected to progressive geometrical modifications in the design stages to reach the final design of the patch antenna. The simulation results show that the antenna has a reflection coefficient magnitude of less than $$-35\:\text{d}\text{B}$$ at an axial ratio of less than 0.5 dB at 28 GHz. The technique used to generate the radiated circular polarized waves is demonstrated by investigating the surface current on the printed patch at the resonant frequency. The primary objective of the proposed design is not to produce a high-gain antenna, but rather to produce a low-profile planar antenna to serve as a building block for CP antenna systems such as multiple-input-multiple-output (MIMO) antennas, beam steering, and beamforming antenna arrays operating at 28 GHz. The designed antenna is fabricated and subjected to experimental evaluation. The numerical simulation results and the practical measurements came in good consent from the impedance matching and axial ratio (AR) of the radiated circular polarized wave perspectives. The input impedance is matched to the feeding line over a 1-GHz band, from 27.5 GHz to 28.5 GHz. The radiated wave is circularly polarized with AR less than 3 dB over about 0.4 GHz band starting from 27.8 GHz to 28.2 GHz. The peak gain of the designed antenna is 7 dBi and the radiation efficiency exceeds 90% all over the band of impedance matching. The performance of the antenna is compared with those of other antenna designs presented in some recent publications.

The present paper introduces a design methodology to extend the operation of a microstrip patch antenna to operate efficiently at multiple higher-order resonances. This method depends on the geometrical modification of the antenna structure by adding well-designed inductively-loaded and capacitively-coupled elements to the primary patch so that it can efficiently radiate at the desired higher frequency bands. It is explained quantitatively how to use the geometrical parameters of the inductively and capacitively coupled elements for accurate tuning of the multiple resonant frequencies of the antenna. The proposed method is applied to modify a primary hexagonal patch antenna (designed to principally radiate at 28 GHz as its first-order resonance) so as to operate at additional higher frequency bands around 43, 52, and 57 GHz. Also, an alternative design is provided for a quad-band printed antenna of composite patch structure that operates in the same millimetric-wave (mm-wave) bands, 28, 43, 52, and 57 GHz with high radiation efficiency, excellent impedance matching, and satisfactory values of the antenna gain. The corresponding frequency bands are, respectively, (27.7-28.3 GHz), (42.7-43.3 GHz), (51.2-53.0 GHz), and (55.7-57.5 GHz). The dimensions of the area occupied by the primary patch and the parasitic elements are 5.2 × 3.3 mm².– The two antennas are fabricated for experimental assessment of their performance including the impedance matching and radiation patterns. It is shown that the experimental measurements come in agreement with the simulation results over all the four operational mm-wave frequency bands. One of the advantages of the proposed method is that it can be applied to patch antennas of arbitrary shapes and is not restricted to hexagonal patch antennas. Furthermore, this method is not restricted by extending the operation of the antenna to radiate at four frequency bands. It is capable of adding any desired number of frequency bands so that the antenna can operate at five or, even, more bands.

The present work proposes three MIMO antennas with different configurations for the future applications of wireless communications in the Q-band of the frequency to realize both spatial and polarization diversities. A circularly polarized (CP) printed antenna operating over two frequency bands at 37.8 and 50 GHz is utilized as a single element to construct the proposed MIMO antennas. Two-element MIMO antenna systems arranged in two configurations, side-by-side and face-to-face, are proposed to achieve spatial diversity. Also, a four-element MIMO antenna system is designed to achieve polarization diversity in addition to spatial diversity. The proposed MIMO antenna systems are designed with the aid of the CST simulator. The three MIMO antennas are fabricated and their performance is experimentally evaluated regarding the circular polarization, impedance matching, antenna gain, envelope correlation coefficient (ECC), and diversity gain (DG). The experimental results for the single-element as well as the MIMO antennas come in good agreement with simulation results showing high performance. Both the numerical and experimental investigations reveal that the mutual coupling between any two ports of the proposed MIMO antennas is below $$-25 {\text{dB}}$$- 25 dB . Also, for any two ports it is shown that the ECC is below $$1\times {10}^{-7}$$1 × 10 - 7 and the diversity gain is higher than $$9.99$$9.99 . The impedance matching bandwidths (for $$\left|{S}_{11}\right|<-10 {\text{dB}}$$S 11 < - 10 dB ) are shown to be $$1.53$$1.53 and $$1.88$$1.88 GHz at $$37.8$$37.8 and $$50\mathrm{ GHz}$$50 GHz , respectively, and the corresponding 3-dB axial ratio bandwidths are $$700$$700 and $$130\mathrm{ MHz}$$130 MHz , respectively.