A Miniaturized CP Antenna Using Superstrate for Medical Applications

A compact wearable textile antenna with multiband and circular polarization characteristics is proposed in this work for Wireless Body Area Networks (WBAN). An asymmetrically connected vertical stub as a radiator with the partial ground for quad-band (3.03–3.76[Formula: see text]GHz, 5.48–6.24[Formula: see text]GHz, 7.10–7.40[Formula: see text]GHz, 7.93–8.22[Formula: see text]GHz) operation and horizontal stubs on the radiator with L-slots in the ground is proposed for the triple band (3.16–3.22[Formula: see text]GHz, 7.25–7.36[Formula: see text]GHz and 7.93–8.08[Formula: see text]GHz) circularly polarized radiation. Jeans fabric is used as substrate with dielectric constant [Formula: see text] and loss tangent ([Formula: see text]). The dimensions of the proposed antenna are [Formula: see text][Formula: see text]mm3. Various conductive fabrics are investigated and analyzed as a radiating element. The proposed jeans antenna provides the gain ([Formula: see text] dB) and radiation efficiency ([Formula: see text]%) for all operating bands. The impact of the human body right arm loading on the antenna has been presented in terms of the reflection coefficient ([Formula: see text]) and gain using the CST Microwave studio simulation environment. The proposed antenna provides stable performance under bending conditions and the SAR values that are under acceptable limits ([Formula: see text][Formula: see text]W/kg for 10[Formula: see text]g of tissue). The flexibility, compactness and radiation properties make it suitable as a wearable textile antenna for off-body communication applications.

The advent of high-speed wireless networks has accelerated the demand for wearable devices and relevant technologies in recent years. The wearable antenna is used to sense, collect, and transmit data wirelessly to nearby devices. A wearable antenna is the key component to support wireless transmission in a wireless body area network (WBAN). This wireless communication includes in/on/off body communication. For continuous health monitoring systems at remote locations, the wearable antennas can be used for people of all ages. A WBAN device ensures continuous health monitoring of an elderly person or a patient without hindering his day-to-day activities. Compact antennas are part of wearable devices. The proposed wearable antenna is a microstrip patch antenna that operates at a 2.45 GHz ISM band. The compact-size antenna is designed using the CST microwave studio suite.

This paper presents a wearable metasurface multiple-input multiple-output (MIMO) antenna for biomedical applications in a 5 GHz wireless body area network (WBAN) with broadband, circular polarization (CP), and high gain. The physical properties of the MIMO antenna element and the principles of polarization conversion are analyzed in-depth using characteristic mode analysis. For the proposed MIMO antenna, the measured −10 dB impedance bandwidth is 34.87% (4.76–6.77 GHz), and the 3 dB axial ratio bandwidth is 22.94% (4.9–6.17 GHz). By adding an isolation strip, the measured isolation of the two antenna elements is greater than 19.85 dB. The overall size of the MIMO antenna is 1.67λ0 × 0.81λ0 × 0.07λ0 at 5.6 GHz, and the maximum gain is 7.95 dBic. The envelope correlation coefficient (ECC) is less than 0.007, with the maximum diversity gain greater than 9.98 dB, and the channel capacity loss is less than 0.29 b/s/Hz. The specific absorption rate (SAR) of the wearable MIMO antenna is simulated by the human tissue model, which proves that the proposed antenna conforms to international standards and is harmless to humans. The proposed wearable metasurface MIMO antenna has CP, broadband, high gain, low ECC, and low SAR, which can be used in wearable devices for biomedical applications.

A new broadband circularly polarized (CP) metasurface (MS) antenna based on characteristic mode analysis (CMA) is proposed. The antenna consists of 4×4 truncated Γ-shaped unit cells and is fed by an improved slot coupling structure. The characteristic modes required to achieve CP are analyzed by CMA, and the CP performance is improved by changing the characteristic currents distribution. By introducing a stepped slot structure on the slot floor, the bandwidth of the antenna has been further broadened. By loading the microstrip line to feed the MS, left-handed circular polarization (LHCP) can be realized. In addition, the equivalent circuit method is used to explain how the designed MS antenna achieves CP. The overall size of the designed and fabricated MS antenna is 0.72 λ 0 ×0.72 λ 0 ×0.08 λ 0 at 6.2 GHz. The measured −10 dB impedance bandwidth of the antenna is 25.17% (5.21 GHz-6.71 GHz) and the measured 3 dB axial ratio bandwidth is 17.42% (5.87 GHz-6.99 GHz). Moreover, the highest gain in the working frequency band is 7.52 dBic. The proposed CP MS antenna has good application prospects in C-band satellite communications.

This paper presents the design process of a clock-shaped broadband circular polarized (CP) antenna based on Characteristic Mode Analysis (CMA). It is composed of a circular ring, two microstrip lines approximately perpendicular to each other, and 50-Ω improved coplanar waveguide (CPW). The two microstrip lines are introduced in the X and Y directions, respectively, to break the symmetry for CP operation. Different from the conventional method in which the operation is verified by the simulated surface current distribution, CMA provides physical insight into different modes of the antenna and reveals the mechanism of radiating CP wave. Mode currents and characteristic fields of the selected modes are studied for AR bandwidth enhancement. An improved double-sided printed CPW is introduced to excite the desired modes and achieve wideband impedance matching. To validate the proposed concept, a prototype with a compact size of 0.29λ L × 0.29λ L × 0.013λ L (λ L corresponding to the maximum operation frequency) is fabricated and measured. The measured -10 dB impedance bandwidth and 3 dB AR bandwidth are 84.6% from 2.38 GHz to 5.8 GHz and 43.4% from 2.4 GHz to 3.73 GHz, respectively. The overlapping operating bandwidth can cover the ISM band, the TD-LTE band, and the WiMAX band. Besides, the proposed antenna has a stable radiation pattern over the operating band.

In this paper, a miniaturized circularly polarized (CP) continuous wave Doppler radar system operating at 2.4 GHz is presented. The radar front end consists of one left-handed CP (LHCP) antenna and one right-handed CP (RHCP) antenna, which share a single patch antenna aperture. Orthogonal polarization is achieved through a modified ring-shaped quadrature hybrid coupler (QHC), and the resulting isolation between the two CP antennas is better than 30 dB. With 0 dBm input power to the transmitting antenna, the proposed radar system can accurately detect heartbeat and respiration movements of human test subjects under 1 m and over a wide angular range. The single dual CP antenna achieves 280% size reduction compared to a traditional two linear polarization patch antenna array with the same isolation level.

In this article, a novel design method is proposed based on characteristic mode theory (CMT). Based on the proposed method, a linearly polarised dual‐band wearable antenna with double‐layered substrates sandwiched by three layers of copper circle patches is designed and optimised step by step. The structure and excitation position of the antenna are obtained by progressively tailoring a classical circle patch antenna. Firstly, the characteristic mode analysis is performed on the middle‐layer planar circle patch to find the modes that can be excited in the designed frequency band. Secondly, the configuration of the middle layer is adjusted step by step based on the modal current distributions to realise the mode shift. Then, the top circle patch is changed to a metasurface to increase the number of modes and expand the mode bandwidth. Finally, the location of the excitation port is selected based on the modal electric fields to successfully obtain the desired performance of the antenna. The prototype of the proposed antenna with a radius of 2.6 cm fed by a single probe is fabricated and experimentally verified. The antenna operates in the 2.45 and 5 GHz bands, and the measured 10 dB impedance bandwidths on the two bands are 1.2% and 39.7%, respectively, which agrees well with the expectation predicted by the CMT. It should be noted that the desired antenna performance is achieved by step‐by‐step derivation using the CMT, rather than applying the theory to illustrate the working principle of antennas. The proposed design method can be broadly employed to various antenna designs.

The radiation characteristics of two embroidered wideband wearable slot antennas covering 3.1-10.6 GHz: Ultra Wide Band (UWB) with different yarn-spacing densities have been presented and compared with a same-size reference copper antenna. When a wearable antenna is fabricated by a conductive yarn, it is important to assess the level of loss in respect to the yarn-spacing density [yarns/mm]. Therefore, the radiation characteristics of the proposed antennas with different yarn-spacing densities have been evaluated experimentally to assess the radiation efficiencies both with and without a human equivalent phantom. Compared to the same-size copper reference antenna, the additional loss in radiation efficiency of the proposed antenna with yarn-spacing density 4 [yarns/mm] is about 10-15 % even when the embroidered antenna is placed in the vicinity of the phantom.

This article presents a miniaturized reconfigurable tri-polarization metantenna with compact size of 0.58 λ 0 × 0.58 λ 0 × 0.04 λ 0 ( λ 0 is the free space wavelength referring to the antenna center frequency). Metantenna means the metasurface is directly used as the antenna radiator aperture instead of an accessory. The metantenna is formed by miniaturized windmill like units, which is evolved from square patch units based on characteristic mode analysis, and 46% size reduction is achieved. Two PIN diodes are introduced into the feeding microstrip for switching among tri-polarization. The measured −10 dB impedance bandwidths are 24.6% (3.24–4.15 GHz) and 24.1% (3.26–4.05 GHz) for circular polarization (CP) and linear polarization (LP), respectively. The measured overlapped 3 dB axial ratio (AR) bandwidth is 15% (3.4–3.95 GHz). The measured peak gains are 5.15 dBi, 5.21 dBic, and 5.25 dBic for LP, left hand (LH) CP and right hand (RH) CP, respectively. The aperture efficiency is 77.3%, 78.5%, and 79.1% for LP, LHCP, and RHCP, respectively. The measured AR beamwidth (BW) of LHCP in XZ-plane and YZ-plane is 192° and 174°, respectively, the measured ARBW of RHCP in XZ-plane and YZ-plane is 201° and 166°, respectively. The developed metantenna has the following advantages: broadband 3 dB AR bandwidth, wide ARBW > 166°, least PIN number (tri-polarization with 2 PIN), and high-aperture efficiency.

This article presents an innovative design for a low-profile, high-gain circularly polarized (CP) antenna using a single-layer metasurface (MTS). The proposed design incorporates an MTS layer, comprising a 4 × 4 array of hexagonal-shaped patches, printed on the top layer of the substrate. The bottom layer features a coplanar waveguide-fed slotted ground. Circular polarization and broadside radiation are achieved through the application of characteristic mode analysis (CMA). CMA is employed to simultaneously excite desired modes, aiming for wideband circular polarization and gain enhancement. Experimental results validate the effectiveness of the design, with compact dimensions of 0.67λ0 × 0.67λ0 × 0.04λ0. The measurements demonstrate an impressive impedance bandwidth of 84.3% within the 3.7–9.1 GHz. Additionally, a 3-dB axial ratio bandwidth of 18.6% is observed between 4.96 and 5.98 GHz and 3.74% between 8.38 and 8.7 GHz. The antenna exhibits excellent radiation pattern characteristics, featuring a maximum gain of 10.08 dBi at 7.1 GHz. The radiation pattern is symmetrical with broadside directionality, making the antenna well-suited for sensing applications.

A new type of broadband circularly polarized (CP) antenna is proposed. The new CP antenna consists of two folded off center-fed dipoles. The operating principle of this type of CP antenna is different from those of conventional CP antennas. The 90° time-phase difference required for circular polarization is obtained by the off-center feed of a half-wave dipole. This type of CP antenna features a simple planar configuration. It is shown that the new CP antenna achieves an overlapped bandwidth of 46% (1.7-2.73 GHz) for axial ratio 15 dB. The broadband CP antenna has a gain of 8.5 dBi on average.

Rydberg atomic sensors (RASs) have garnered significant attention as a novel type of electric field sensor with high sensitivity. While the integration of electric field enhancement structure (EFES) and RASs has been proven to improve the sensitivity and the minimal detectable electric field of RAS, there are concerns regarding their omnidirectional and polarization performance. However, most existing RASs or RASs loaded with EFES operate with linear polarization, which reduces the sensitivity to circularly polarized (CP) microwave reception. It is a challenging method to change the property of the lasers to modify the RAS’s CP property, while it is simpler to use EFES to change RASs’ polarization indirectly. Meanwhile, current EFES research mainly focuses on the response of electric field enhancement at a fixed incident angle, limiting extension to 3-D CP patterns and lacking clear physical insights to guide. To address this, we propose an RAS with CP EFES to achieve CP reception capability. The EFES converts spatial CP electric field into local linearly polarized (LP) electric field, adjusting the RAS characteristics accordingly. We use characteristics mode (CM) methods, dividing the problem into modal current, governing the modal patterns, and external CP excitation sources, determining the coefficients of each modal pattern. This method reduces the complexity of the pattern analysis and improves the efficiency of optimization design. To validate the proposed method’s efficiency, we fabricate a prototype to measure reception pattern and further study the CP performance using an atomic heterodyne approach. The results indicate that the RAS with EFES achieves the right-hand CP (RHCP) omnidirectional reception capability, and the sensitivity is improved by 19.2 dB at 2.195 GHz. The cross-polarized level can be further improved to 24.5 dB using an atomic heterodyne approach.

This article studies a quad-port multi-input-multi-output (MIMO) circularly polarized antenna with good isolation properties. Using characteristic mode analysis (CMA), the first six distinct modes of the asymmetric square slot with an inverted L-strip are analyzed. In this study, modal parameter extraction is carried out for circular polarization (CP) radiation. A simple annular ring microstrip feed is excited to obtain broadband CP based on CMA. The single-unit feeding structure is replicated orthogonally four times to achieve a CP MIMO antenna. This antenna provides port isolation of more than 21 dB without the use of an additional decoupling element. The quad-port CP-MIMO antenna is simulated with a total dimension of 50 × 50 mm2. The antenna attains impedance matching (S11 < −10 dB) from 5.37 GHz to beyond 11 GHz with an axial ratio bandwidth (ARBW) of 4.65 GHz (5.61 GHz to 10.26 GHz). The peak realized gain of the MIMO antenna is measured at 5.69 dBi at 8.4 GHz. Additionally, the diversity performance parameters of the MIMO structure are computed. The advantages of the proposed structure have been evaluated by comparing it to previously reported MIMO structures. A prototype of the MIMO structure measurements was found to match the simulation results.

A reconfigurable, wideband, and low-profile circular polarization (CP) antenna is presented. Its wideband CP reconfigurability is realized by incorporating RF switches into a cross-bowtie radiator. A compact, wide bandwidth, and polarization-independent artificial magnetic conductor ground plane is developed to minimize the overall profile of the antenna while maintaining its wide bandwidth. The simplicity of this single-element design facilitates the realization of a reconfigurable, wide bandwidth CP array that achieves higher directivity without changing its overall profile. Prototypes of the single element and of a $1 \times 4$ array of these elements were fabricated and tested. The measured results for both prototypes are in good agreement with their simulated values, validating their design principles. They are low profile with a height $\sim 0.05\lambda _{\mathrm {\mathbf {0}}}$ . The array exhibits a wide fractional operational bandwidth: 1.65 GHz (21.7%), and a high realized gain: 13 dBic. Since they would enhance their channel capacity and avoid polarization mismatch issues, these reconfigurable CP antenna systems are very suitable for modern wireless systems.

Radiation performance of a circularly polarized (CP) truncated corner square patch on a conventional ground plane (GP) has been enhanced by using a simple and novel configuration of stacked dual GP. The proposed configuration employs a single fed truncated corner square patch etched onto a substrate grounded with a patch shaped small GP and having second square shaped GP of standard size separated from the first one with an air gap at an optimized distance. This configuration is ideal for many wireless and satellite communication applications. Simulated results indicate the best achievable axial ratio (AR) of about 0.4 dB for a stacked dual GP CP antenna compared to an AR of 2.7 dB for a conventional single GP CP antenna, indicating an improvement in cross polarized (XP) isolation of about 18 dB. AR bandwidth has also been improved by almost 100% with the stacked dual GP configuration when compared with conventional CP antenna. Improved radiation performance has been achieved without affecting impedance bandwidth and peak gain of the patch. Analysis based on GP size variation of the conventional CP antenna and stacked dual GP antenna reveals that stacked dual GP configuration results in compact CP antenna with good radiation performance.