Abstracts:This study presents a systematic parameter study on orbital angular momentum (OAM)-based communication between antenna arrays. The recently proposed mixed-mode matrix representation is applied for investigating the dependencies of OAM-based communication on array configuration parameters. It is demonstrated that the performance of multi-phased systems including the OAM-based array is optimised in terms of the numerical perspective using a mixed-mode matrix.

Abstracts:Α feasibility study of using components such as conductive Velcro tape and zip fastener to change the polarisation of a textile patch antenna from linear (LP) to circular (CP) is presented. The antennas are designed to operate at 2.3–2.5 GHz frequency band, are made using felt substrate and conductive cloth and their size is 100.4 mm × 74.2 mm × 4.26 mm. It is proved, via simulations and measurements, that such components are strong candidates as means for polarisation reconfiguration of textile antennas. Both Velcro and zip textile patch antennas at the LP mode yield axial ratio (AR) larger than 10 dB at the operating frequency range. In the CP mode, the Velcro antenna gives AR equal to 3.1 dB at 2.35 GHz and the zip antenna 1 dB at 2.31 GHz. Repeatability measurements of interchanging polarisation modes (LP–CP) for both antennas have been conducted presenting acceptable repeatability. Great advantage of both antennas (Velcro and zip) is that the polarisation can be changed at will by a simple manipulation (detach the Velcro or unzip); thus, providing to the user the flexibility of adjusting the antenna characteristics depending on wearable application and environment of operation.

Abstracts:A ten-element multi-antenna terminal for massive multiple-input&#x2013;multiple-output (MIMO) in the fifth-generation (5G) sub-6&#x2009;GHz with wide impedance bandwidth (IBW) is proposed. A grounded coplanar waveguide is employed to feed an inverted-F stub coupled to a hybrid loop antenna element. Through tuning, the multiple resonant modes are combined so that a wide IBW is achieved. Antenna element sites are selected along the periphery of the typical smartphone back plane of size <inline-formula><alternatives><tex-math notation="LaTeX">$120,{rm mm}times 70,{rm mm}$</tex-math><mml:math overflow="scroll"><mml:mn>120</mml:mn><mml:mspace width="thinmathspace" /><mml:mrow><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow><mml:mo>&#xd7;</mml:mo><mml:mn>70</mml:mn><mml:mspace width="thinmathspace" /><mml:mrow><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow></mml:math><inline-graphic xlink:href="IET-MAP.2019.0980.IM1.gif" /></alternatives></inline-formula>. To improve the diversity performance, two elements are placed along the horizontal edge orthogonal to the rest of elements placed along the vertical side. The prototype of the antenna is fabricated and measured exhibiting a wide IBW of (<inline-formula><alternatives><tex-math notation="LaTeX">$|S_{ii}| leq -6$</tex-math><mml:math overflow="scroll"><mml:mrow><mml:mo>|</mml:mo></mml:mrow><mml:msub><mml:mi>S</mml:mi><mml:mrow><mml:mi>i</mml:mi><mml:mi>i</mml:mi></mml:mrow></mml:msub><mml:mrow><mml:mo>|</mml:mo></mml:mrow><mml:mo>&#x2264;</mml:mo><mml:mo>&#x2212;</mml:mo><mml:mn>6</mml:mn></mml:math><inline-graphic xlink:href="IET-MAP.2019.0980.IM2.gif" /></alternatives></inline-formula>&#x2009;dB) 63% centred around 4.68&#x2009;GHz. The minimum measured isolation achieved is 18&#x2009;dB. The maximum simulated envelope correlation coefficient is found to be <inline-formula><alternatives><tex-math notation="LaTeX">$- sim $</tex-math><mml:math overflow="scroll"><mml:mo>&#x223c;</mml:mo></mml:math><inline-graphic xlink:href="IET-MAP.2019.0980.IM3.gif" /></alternatives></inline-formula>0.21 and while the minimum antenna efficiency is 78.4%. Each element has a form factor of <inline-formula><alternatives><tex-math notation="LaTeX">$17.2times 3.8,{rm mm}{^2} (0.018 lambda _{mathrm {g}}^2)$</tex-math><mml:math overflow="scroll"><mml:mn>17.2</mml:mn><mml:mo>&#xd7;</mml:mo><mml:mn>3.8</mml:mn><mml:mspace width="thinmathspace" /><mml:mrow><mml:mi mathvariant="normal">mm</mml:mi></mml:mrow><mml:mrow><mml:msup><mml:mrow /><mml:mn>2</mml:mn></mml:msup></mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:mn>0.018</mml:mn><mml:msubsup><mml:mi>&#x3bb;</mml:mi><mml:mrow><mml:mrow><mml:mi mathvariant="normal">g</mml:mi></mml:mrow></mml:mrow><mml:mn>2</mml:mn></mml:msubsup><mml:mo stretchy="false">)</mml:mo></mml:math><inline-graphic xlink:href="IET-MAP.2019.0980.IM4.gif" /></alternatives></inline-formula> and printed on a 1.52&#x2009;mm thick Rogers 4003 substrate with <inline-formula><alternatives><tex-math notation="LaTeX">$epsilon _r = 3.38$</tex-math><mml:math overflow="scroll"><mml:msub><mml:mi>&#x3f5;</mml:mi><mml:mi>r</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mn>3.38</mml:mn></mml:math><inline-graphic xlink:href="IET-MAP.2019.0980.IM5.gif" /></alternatives></inline-formula> and <inline-formula><alternatives><tex-math notation="LaTeX">$tan ,delta =0.0027$</tex-math><mml:math overflow="scroll"><mml:mi>tan</mml:mi><mml:mspace width="thinmathspace" /><mml:mi>&#x3b4;</mml:mi><mml:mo>=</mml:mo><mml:mn>0.0027</mml:mn></mml:math><inline-graphic xlink:href="IET-MAP.2019.0980.IM6.gif" /></alternatives></inline-formula>. The proposed multi-antenna terminal is suitable for 5G sub-6&#x2009;GHz (3.2&#x2013;6.1&#x2009;GHz) communication including long-term evolution bands 42, 43 and 46.

Abstracts:Enhancing the horizontal gain of the omnidirectional patch antenna is always a problem with great difficulty. Inspired by near-zero-index metamaterial (NZIM) cover that can improve the vertical gain of a directional patch antenna, the authors designed two kinds of NZIMs that are placed above the broadband omnidirectional antenna to enhance the horizontal gain. Simulated and measured results indicate that both covers can increase the values of horizontal gain >50% (1&#x2005;dBi) at various frequencies in all directions, which provides a new approach to improve the horizontal gain of the broadband omnidirectional patch antenna.

Abstracts:The design and analysis of a compact dual-wideband multi-mode resonant printed quasi-Yagi antenna with dual-driven element is presented. In the design, an orthogonal dual-bowtie dipole is applied as the driven element to achieve the dual-band characteristic with minimal size. The dual-bowtie dipole is designed to operate in the multi-mode resonance to expand its bandwidth. The structure is 60% smaller than the wideband printed Yagi antennas in the literature. Besides, the designed antenna achieves two wide fractional bandwidths of 44% (0.84&#x2013;1.31&#x2005;GHz) and 115% (1.56&#x2013;5.78&#x2005;GHz) with a stable high gain of 3.4&#x2009;&#xb1;&#x2009;0.8 and 3.6&#x2009;&#xb1;&#x2009;1.6&#x2005;dBi, respectively. Simulation and measurement results are included.

Abstracts:One patch antenna with dual-band dual-mode (DMDB) characteristic based on mushroom structure is designed and analysed in this study. The antenna operates at two modes: the bidirectional mode with endfire radiation patterns and the directional mode with broadside radiation patterns. The equivalent circuit, dispersion diagrams, field distributions, reflection coefficients and radiation patterns are given for confirming the working principle. Compared with the former DMDB antennas, array antenna could be designed to realise gain enhancement for both the two modes. Both element and 1&#x2009;&#xd7;&#x2009;2 array antenna prototypes were fabricated for verification. The measured results show that the two modes resonant at about 9.8 and 11.95&#x2005;GHz, respectively. Comparing with the element, gain enhancement of about 2.8 and 2.1&#x2005;dB are realised by the array for the endfire and broadside modes, respectively. With pattern diversity and array realisation, this antenna type owns potential application value in wireless communication systems.

Abstracts:In this study, the authors propose a new numerically stable digital predistorter for the linearisation of RF Power amplifiers. The proposed predistorter is based on the parameterised Gegenbauer polynomials that can be optimised for maximum predistorter efficiency and stability under different input signal distributions. The robustness and the efficiency of the proposed predistorter are experimentally demonstrated and compared to the ones of previously published polynomial model-based predistorters. The obtained results revealed exceptional numerical stability regardless of the input signal statistics, making the proposed predistorter suitable for the linearisation of multimode and broadband non-linear wireless transmitters.

Abstracts:A dual-band dual-polarised antenna for on-/off-body wireless body area network (WBAN) applications is presented, operating at Industrial, Scientific, and Medical bands of 2.45&#x2005;GHz with circular polarisation and 5.8&#x2005;GHz with vertical polarisation. The TM₁₁ mode is used for the off-body mode in the first band because of its broadside radiation pattern, meanwhile, the TM₀₂ mode is chosen for on-body mode due to its monopole-like radiation pattern in the second band. Composed of a circular patch with eight slots, the structure of the proposed antenna is simple, and it is fabricated with textile material. The performance of the antenna is investigated in free space and on the body. Then, the performance influenced by the bending of the antenna is discussed with a different bending radius. The specific absorption rate distribution is simulated on body tissue. And the maximum value at both bands is below the IEEE C95.3 standard of 1.6&#x2005;W/kg. The acquired performance demonstrates that the proposed antenna can be applied to the applications of WBAN.

Abstracts:A novel low-profile substrate integrated waveguide (SIW) cavity-backed slot antenna with an enhanced gain is proposed. By etching four parallel transverse slots at the edges of the hexagonal SIW cavity as the radiating elements, higher resonance mode of quasi-TM₃₁₀ can be excited to achieve gain enhancement. A fabricated prototype with a size of 1.3 <italic>&#x3bb;</italic>₀&#x2009;&#xd7;&#x2009;1.3 <italic>&#x3bb;</italic>₀&#x2009;&#xd7;&#x2009;0.025 <italic>&#x3bb;</italic>₀ has been measured. Results show that the proposed design achieves a 10-dB impedance matching bandwidth of 195&#x2005;MHz and a maximum boresight gain of 10.74&#x2005;dBi. The proposed antenna exhibits a high front-to-back ratio and low cross-polarisation level. It still retains the advantages of low cost, ease of fabrication, and easy integration with planar circuits, making it a good candidate for low-cost mass-production.