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.

A compact dual-band, dual-polarized, implantable antenna was designed using the characteristic mode method for operation in the wireless medical telemetry service (WMTS) band (1.4 GHz) and the industrial, scientific, and medical (ISM) band (2.45 GHz). By utilizing slotting techniques and materials with high dielectric constants, the antenna volume was minimized to 47.4 mm³, and circular polarization was gained in the WMTS band by using the characteristic mode method. A three-layer physical model of human tissues was constructed in a simulation, and a biogel and minced pork were used in the measurements. The measured peak gains are −20.85 dBi (1.4 GHz) and −22.15 dBi (2.45 GHz). The measured effective axis ratio bandwidth in the WMTS band is 170 MHz (1.33–1.50 GHz, 12.0%), and the impedance bandwidth in the ISM band is 390 MHz (2.21–2.60 GHz, 16.2%). At 1.4 GHz and 2.45 GHz, the largest 1 g average SAR values are 376 W/Kg and 318 W/Kg, which comply with IEEE C95.1-1999. Moreover, when the communication chain affinity exceeds 20 dB for 1.4 GHz and 2.4 GHz, the transceiver range reaches 8.2 m and 9.7 m. This antenna can be used for implantable wireless telemetry systems.

A miniaturized enhanced isolation 8-unit MIMO antenna for smartphones is proposed in this paper. The units are planar inverted-F antennas with the same structure, and we use the slotting method and shorted probe to miniaturize them. The size of every unit is 14×6mm² (0.149×0.064λ²). We insert an L-shaped decoupling element into the middle of adjacent radiating elements and connect the decoupling element to the GND. Note that the decoupling elements are on the outer side of the substrate, and the radiating elements are on the inner side of the substrate. Finally, a prototype is fabricated and measured. The measured results show that the bandwidth of the MIMO antenna is from 3.0GHz to 5.3GHz (55.4), which fully supports the n77, n78, and n79 in the 5G nR frequency band and the 4G LTE 42 frequency band (S₁₁ less than 6dB). The measured isolation of the MIMO antenna is greater than 25dB by using the decoupling method in this paper. The envelope correlation coefficient of the proposed MIMO antenna is less than 0.08, its radiation efficiency is greater than 50, and its gain is between 4.2 and 5.3dBi in the whole operating frequency band.

This paper presents a miniaturized triband implantable planar antenna that covers the industrial, scientific, and medical (ISM) band and the Wireless Medical Telemetry Service (WMTS) band which can be used in a continuous blood glucose monitoring device. The antenna consists of a slotted radiating patch and a ground plane with a cross slot to miniaturize its size. The overall antenna size is only 51.35mm³ (7.6×7.6×0.889mm³) due to the reduced size by the slotting technique. Compared to other implantable antennas with similar performance, the proposed antenna is smaller in size, simple in construction, and easy to be fabricated. By cutting a cross slot in GND, impedance matching is improved, especially at the two higher frequency bands. We have fabricated the prototype and carried out measurements. The results show its gains are 32.2dBi, 18.8dBi, and 19.1dBi at 0.9GHz, 1.4GHz, and 2.45GHz, respectively. Its radiation patterns have good symmetry in the two lower operating frequency bands. In addition, the maximum SAR values comply with the IEEE standard safety guidelines (IEEE C95.1-2019).