This letter presents a 28 GHz 2-dimensional (2-D) multi-beam array antenna fed by a planar 4 × 4 cascaded Butler matrix (CBM). Utilizing the proposed concept of 3—D to planar CBM topology transition, the 4 × 4 U-slot antenna array integrated with planar CBM can be implemented with a multi-layers lamination without additional connectors or routing lines. Due to the simplified topology of the circular sub-BM, whose width is only 0.5 $\lambda_0$ (free space wavelength at 28 GHz), none of the crossovers is needed to assemble the radiation elements at the outputs of the CBM. The dimension of the proposed 2-D beam steering system has been dramatically reduced to $3.3 \ \lambda_0 \times 5.9 \ \lambda_0$ , which is, to best of our knowledge, the smallest in this application area. A prototype has been fabricated and measured. The measured results show a well-controlled input matching in the operation band from 26 GHz to 29 GHz. Besides, 16 spatial orthogonal beams with maximal 15.22 dBi gain at 28 GHz scanning a conical space with the maximal cone angle of 77.4° in the elevation plane and 136.8° in the azimuth plane by feeding at different inputs, which agree well with the simulated results.

This paper presents an ultra-miniaturized implant antenna with a volume of 22.22 mm ³ in the Medical Implant Communication Service (MICS) frequency band 402-405 MHz to be integrated with a leadless cardiac pacemaker. The proposed antenna has a planar spiral geometry with a defective ground plane exhibiting a radiation efficiency of 3.3% in the lossy medium with more than 20 dB of improved forward transmission, while the coupling can be further enhanced by adjusting the thickness of the antenna insulation and the antenna size according to the application area. The implanted antenna demonstrates a measured bandwidth of 28 MHz, covering beyond the MICS band needs. The proposed circuit model of the antenna describes the different behaviors of the implanted antenna over a wide bandwidth. The antenna interaction within human tissues and the improved behavior of the electrically small antenna are explained in terms of radiation resistance, inductance, and capacitance that are obtained from the circuit model. The results are demonstrated using electromagnetic computations and are validated by the measurement using liquid phantom and animal experiments.

In this letter, we propose fundamental path loss (PL) models which play vital roles in promoting the intraheart communication system design of future deeply implanted leadless pacemakers inside the cardiac chambers. Initially, employing a plane wave approach yields the attenuation of the electric field in homogeneous heart tissue, while a modified Friis equation in the lossy medium is utilized to evaluate the power transmission between transmitting and receiving antennas in homogeneous heart tissue in the far-field zone. An Hertzian dipole excitation is used to separate the mismatch and ohmic losses of the antenna from the path loss in an anatomical human body simulation environment. Based on this theoretical and full-wave simulation setup, PL models are derived and comprehensively compared at different potential frequency bands [Medical Implant Communication Service (MICS) 402-405 MHz, Wireless Medical Telemetry Service (WMTS) 608-614 MHz, Industrial, Scientific, and Medical (ISM) 867-869 MHz, and 2400-2500 MHz], and the validity of applying the Friis equation in this scenario is verified.

This letter presents the design, analysis and measurement of a miniaturized (7 × 7.5 mm) electrically small helical dipole antenna with the introduction of a flexible magnetic sheet of high permittivity and permeability for biomedical implants. The proposed helical dipole, operating at 402-405 MHz Medical Implant Communication Services (MICS) band, supports wider bandwidths (10 dB bandwidth: simulated 33 MHz; measured 49.5 MHz) compare to the state-of-the-art designs. In addition, as a hybrid between a magnetic loop antenna and an electric dipole antenna and operating in the normal mode with small radian (ka < 0.36), enhanced radiation efficiency has been achieved as a result of the magnetic sheet. Measured in-body to on-body transmission verifies the antenna performance.