This paper presents a full wave simulation and characteristic mode-based design of a multiple-input-multiple-output (MIMO) antenna at 5.8 GHz for wireless local area network applications. The driven analysis comprises two antennas that are placed orthogonal to each other. A metamaterial unit structure in the form of a rectangular loop resonator is placed around the antenna element to reduce the electromagnetic interference and to increase the isolation between the two monopoles. A characteristic mode technique is employed to find out the dominant mode of the proposed antenna without a feeding port. It was revealed that mode 1 was the dominant mode among the three modes used. The MIMO antenna is constructed and measured using a vector network analyzer. A good isolation of less than 25 dB was attained with a wide impedance bandwidth of 65.5%.

This research proposes a miniature circular polarization antenna used in a wireless capsule endoscopy system at 2.45 GHz for industrial, scientific, and medical bands. We propose a method of cutting a chamfer rectangular slot on a circular radiation patch and introducing a curved radiation structure into the centerline position of the chamfer rectangular slot, while a short-circuit probe is added to achieve miniaturization. Therefore, we significantly reduced the size of the antenna and made it exhibit circularly polarized radiation characteristics. A cross-slot is cut in the GND to enable the antenna to better cover the operating band while being able to meet the complex human environment. The effective axis ratio bandwidth is 120 MHz (2.38–2.50 GHz). Its size is π × 0.032λ₀² × 0.007λ₀ (where λ₀ is the free-space wavelength of at 2.4 GHz). In addition, the effect of different organs such as muscle, stomach, small intestine, and big intestine on the antenna when it was embedded into the wireless capsule endoscopy (WCE) system was further discussed, and the results proved that the WCE system has better robustness in different organs. The antenna’s specific absorption rate can follow the IEEE Standard Safety Guidelines (IEEE C95.1-1999). A prototype is fabricated and measured. The experimental results are consistent with the simulation results.

This paper postulates a novel omnidirectional low-profile ultra-wideband (UWB) antenna, which is structured by discrete embedded dielectric resonator antenna with features of both low-profile dielectric resonator (DR) and thin planar monopole antenna, where the laminated equilateral triangular DR and the rectangular metal patch monopole are stacked up. This new design can lower the profile of the antenna. Furthermore, the symmetric DR and the monopole structure are able to make the surface currents in some operating modes opposite in phase, together with the characteristics of the coplanar waveguide (CPW) feed structure and the DR, the cross-polarization is reduced effectively. The mode analysis has been done to show how the antenna achieves the UWB. The CPW which can integrate with integrated circuits easily is used to provide the excitation source. The antenna provides consistent omnidirectivity, consistent gain, low cross-polarization, and high-radiation efficiency within the entire operation band. A prototype (dimensions are 17.6 mm $\times33.6$ mm and 1.524 mm thickness) is fabricated and measured. The measurements are well correlated with the simulations.

The characteristic mode method is used to design a miniaturized dual-band dual circularly polarized (CP) implantable antenna operating in ISM bands. The miniaturization and dual-band characteristics are gained by using the slotting method and by inserting a short-circuit probe between the radiation patch and the ground plane. We use the characteristic mode method to study the current distribution of circular radiation patches with T-shaped slots in different modes. After opening a cross-shaped slot at the center of the radiation patch and the ground plane, we obtained two orthogonal modes with equal amplitude and phase difference of 90° in two operating frequency bands, ultimately achieving CP characteristics of the antenna. Its overall size is only $$\pi$$π ×(0.014 $$\uplambda$$λ ₀)² × 0.0027 $$\uplambda$$λ ₀, smaller than other CP implantable antennas with similar performances, and it has satisfactory radiation efficiency and gain characteristics. Measurements show that it can operate in the ISM bands of 0.9 and 2.4 GHz with an effective 3 dB axial ratio bandwidth greater than 220 MHz (0.87 to 1.09 GHz, 22.45%) and 230 MHz (2.31 to 2.54 GHz, 9.48%), and its peak gain is − 29.5 dBi and − 19.2 dBi, respectively. And, this design complies with IEEE safety guidelines.

To address the current demands for antenna miniaturization, ultra-bandwidth, and circular polarization in advanced medical devices, a novel ISM band implantable antenna for blood glucose monitoring has been developed. This antenna achieves miniaturization by incorporating slots in the radiation patch and adding symmetric short-circuit probes, resulting in a compact size of only 0.054λ₀ × 0.054λ₀ × 0.005λ₀ (λ₀ is the wavelength in free space in respect of the lowest working frequency). By combining two resonance points and utilizing a differential feed structure, the antenna achieves ultra-broadband and circular polarization. Simulations indicate a |S₁₁| bandwidth of 1.1 GHz (1.65–2.75 GHz) and an effective axial ratio (based on 3 dB axis ratio) bandwidth of 590 MHz (1.89–2.48 GHz), able to cover both the ISM frequency band (2.45 GHz) and the mid-field frequency band (1.9 GHz). The antenna exhibits CP gains of −20.04 dBi at a frequency of 2.45 GHz, while it shows gains of −24.64 dBi at 1.9 GHz. Furthermore, a superstrate layer on the antenna’s radiating surface enhances its biocompatibility and minimizes its impact on the human body. Simulation and experimental results indicate that the antenna can establish a stable wireless communication link for implantable continuous blood glucose monitoring systems.

This paper presents a miniaturized circularly polarized (CP) implantable antenna Ultra-wide bandwidth for continuous blood pressure monitoring. The miniature and CP of the antenna are gained by using a new slot method. The symmetry slots in the radiation patch, two T-shape slots in the GND, coupled with the use of a short pin make the designed antenna with good physical and radiation properties. In simulation, the fractional effective axial ratio bandwidth is 23.6% (2.36–2.94 GHz), and the peak gain is − 28.9 dBi. Its total size is only 17.78 mm³ (0.056 × 0.04 × 0.004 λ₀³), which size is smaller compared to other antennas with similar performance. A prototype is fabricated and measured. The experimental results are in good agreement with the simulation results. And, the radiation patterns have good symmetry both in the simulation and measurement. In addition, the maximum SAR value is in accordance with the IEEE standard safety guidelines (IEEE C95.1-2019).