A compact and low-profile wearable antenna is presented for on-body wireless body area network (WBAN) applications. The proposed triangular patch antenna is designed using low-cost widely available vinyl polymer-based flexible substrate. The final antenna topology is obtained by the combination of Koch fractal geometry, meandering slits and defected ground structure, to achieve a novel hybrid structure with compact footprint, good structural conformability and enhanced impedance bandwidth to operate in the Industrial, Scientific, and Medical (ISM) band with center frequency at 2.45GHz. The fabricated prototype of the antenna has shown good agreement between numerical and experimental results. In comparison to state of the art prototypes, our design has more compact-form-factor of $\rm 0.318\lambda_o \times 0.318\lambda_o \times 0.004\lambda_o$ , along with 7.75% impedance bandwidth, a peak gain of 2.06dBi and overall radiated efficiency of 75%. For the assessment of Specific Absorption Rate (SAR) performance of our design, it is tested on realistic heterogeneous HUGO voxel model. Both numerical and experimental investigations revealed extremely good robustness to both human body loading and structural deformation, making it an ideal candidate for flexible and body-worn devices.

The microstrip patch antenna (MPA) has been in use and has been studied extensively during the past three decades. This antenna, which consists of a metallic patch printed on a dielectric substrate over a ground plane, offers several advantages including ease of design and fabrication; low profile and planar structure; and ease of integration with circuit elements. The minimum dimension of a conventional MPA is in the order of half a wavelength. In recent years, with the advent of new standards and compact wireless devices, there has been a need to reduce the size of this type of antenna. This study discusses some of the principal techniques that have been reported in the literature to reduce the size of an MPA. These miniaturisation techniques include material loading, reshaping the antenna, shorting and folding, introducing slots and defects in the ground plane and the use of metamaterials. The major features and drawbacks of each of these approaches are highlighted in this study along with their effects on the antenna performance metrics.

A 2 × 2 (four-element) multiple-input multiple-output (MIMO) patch antenna system is designed and fabricated for a 2.45-GHz ISM band operation. It uses complementary split-ring resonator (CSRR) loading on its ground plane for antenna miniaturization. This reduces the single-element antenna size by 76%. The total board size of the proposed MIMO antenna system, including the GND plane is 100 × 50 × 0.8 mm³, while the single-patch antenna element has a size of 14 × 18 mm². The antenna is fabricated and tested. Measured results are in good agreement with simulations. A minimum measured isolation of 10 dB is obtained given the close interelement spacing of 0.17λ. The maximum measured gain for a single operating element is -0.8 dBi.

A novel dual-band 4-shaped printed multiple-input-multiple-output (MIMO) antenna system of two elements is designed and fabricated for Long Term Evolution (LTE) wireless handheld and portable terminals. The low frequency band covered is 803-823 MHz, and the high frequency band covered is 2440-2900 MHz. The isolation between the two elements was more than 17 dB in the low band after using a defected ground plane structure (DGS) between the two antenna elements. The overall size of the printed MIMO antenna system was 50× 100×1.56 mm³.

The correlation coefficient (ρ) is an important metric for the evaluation of multiple-input–multiple-output (MIMO) antenna systems because it describes the relationship between the channels in a particular propagation environment. Highly correlated channels will degrade the MIMO system performance. Various methods to calculateρare analyzed in this work using three different types of antennas with different efficiencies and radiating properties. While the field-based method for findingρgives the most accurate results and should be used all the time. It is independent of antenna efficiency. The the S-parameter-based method might give reasonable results only when the antenna efficiency is very high and the patterns are separated in space, but in most cases, it underestimatesρvalues and thus is not a reliable method and should be avoided. Incorporating the antenna efficiency can improve theρestimates using the S-parameters method under some specific conditions. The equivalent circuit method provides reasonable results for symmetric antenna structures only, and is the most complex in formulation. As part of the evaluation, two existing methods incorporating the radiation efficiency of the antennas are generalized to N-ports for the first time. Although less accurate than the field-based method, these extensions allow the evaluation ofρfor N-port antennas using only the radiation efficiency and the S-parameters of the antenna. The effect of the beam tilts onρestimation is investigated for the first time.

An eight‐element, dual‐frequency, multiple‐input–multiple‐output (MIMO) antenna system is proposed. Cylindrical dielectric resonator antennas (cDRAs) were used as the radiating elements in the MIMO antenna system. One group of four cDRAs covers the 2.45 GHz band, whereas another four cover the second band at 5.8 GHz. A reflector element was also proposed to tilt the radiated beam patterns and reduce field correlations for the MIMO antenna system. The high‐band antenna elements were rotated 45° with respect to their low‐band counterparts, on the antenna ground plan, for compactness and printed circuit board integration such that the complete antenna system occupies a volume of 160 mm×160 mm×14.8 mm. The measured bandwidths (BWs) were at least 90 and 200 MHz for the two bands of operation while the envelope correlation coefficient (ECC) was <0.17. A study of different metallic reflectors was also provided in terms of the impedance matching, isolation, BW, andECC. Specific applications for the proposed design include wireless local area networks and other fourth generation access points.