A conformal circularly polarized (CP) capsule antenna, designed for ingestible wireless capsule endoscope (WCE) systems at industrial, scientific, and medical (ISM) band (2.4-2.48 GHz), is presented. The antenna consists of a rectangular loop, an asymmetric U-shaped strip and a protruding L-shaped stub printed on the top of the dielectric substrate. The CP wave is generated by the corner-fed U-shaped strip protruding into the rectangular slot. Further, by adjusting the size of the U-shaped strip and the L-shaped stub, the 3-dB axial-ratio (AR) band can be fully covered by 10-dB impedance band. The simulated 10-dB impedance bandwidth (BW) and 3-dB AR bandwidth (ARBW) are 31.58% and 13.11%, respectively. Simulated results show that the overlapped impedance BW and ARBW is from 2.28 GHz to 2.6 GHz, which completely covers the 2.4 GHz ISM band. The measured 10-dB impedance BW is 39.21%. Finally, the radiation performance, safety consideration and link budget of the antenna are examined and characterized. Owing to the broad overlapped impedance BW and ARBW, the minimized in-capsule foot print and ease of fabrication, the designed antenna is a capable candidate for a wireless capsule endoscope system.

A conformal ultrawideband (UWB) dual-polarized capsule antenna is designed for ingestible wireless capsule endoscope (WCE) systems. To the best of our knowledge, this is the first time to study the UWB dual-polarized antenna for a capsule endoscope system. Dual polarization is realized by a step-shaped monopole and an irregular rectangular loop antenna, which are printed on the top and bottom side of the dielectric substrate, separately. The simulated antenna has very wide -10 dB impedance bandwidth of 2.15-14.75 GHz, which can cover 2.4-2.48 GHz, 5.725-5.875 GHz Industrial, Scientific, and Medical (ISM) band, 3.5-4.5 GHz impulse radio UWB (IR-UWB) and 3.1-10.6 GHz UWB. Moreover, because of the orthogonally polarized waves generated by two types of antennas, the simulated isolation between them is better than 40 dB in the whole band. Considering the application of the antenna in the wireless body area network system, this design focuses on 1-7 GHz frequency band, especially 4 GHz IR-UWB. An antenna prototype is fabricated and measured, and the measured S-parameters and radiation pattern demonstrate a reasonable agreement with the simulation results. Furthermore, specific absorption rate and link budget of the antenna are analyzed.

An eight-element multiple-input multiple-output (MIMO) frame antenna array in the 3.5 GHz band (3400–3600 MHz) for 5G mobile terminal systems was presented. By using the adjacent grounding and electromagnetic coupling feeding technology, the loop antenna element could generate two resonant frequencies, thus effectively expanding its bandwidth. By adopting double-sided parallel strip line (DSPSL) technology, the electromagnetic coupling inside the loop antenna could be adjusted, and the size of the loop antenna could be effectively reduced so that the MIMO antenna array could obtain a low-profile structure. The total size of the MIMO array was 150 mm × 75 mm × 5.3 mm. Without additional isolation measures, the measured −6 dB impedance bandwidth (BW) was 3400–3660 MHz, and the minimum isolation between antenna elements was better than −20 dB. The proposed antenna was expected to be applied to 5G mobile terminals based on its low-profile, high-isolated characteristics, and good MIMO performance.

We present a 3D printed metallic K-band (18-26.5 GHz) passive frontend for satellite communication. It is intended to be used as a unit cell in a large antenna array. The proposed frontend is composed of a two-stage one-by-four power divider, rectangular-to-circular waveguide tapers, and a linear four-element conical antenna array, which are too complex to be fabricated by traditional machining process in a whole piece. Taking the advantage of the 3D printing technology in realizing complex structures, we achieve a highly-integrated passive module. Good agreement is achieved between simulation and measurement. The proposed frontend has impedance bandwidth 19 $\times$ 21 GHz, the maximum gain of 15.5 dBi at 21 GHz, and desirable radiation patterns on both E- and H-planes. The influence of fabrication tolerance like the surface roughness and dimensional tolerance are observed and analyzed. Compared with traditionally fabricated metallic microwave passive devices, the proposed work has a shorter turn-around time and a lower cost. Compared with dielectric 3D printed microwave devices, it features more simplicity in terms of process and better physical robustness. It opens up new possibilities for microwave device fabrication.

The 3D printing technology is catching attention nowadays. It has certain advantages over the traditional fabrication processes. We give a chronical review of the 3D printing technology from the time it was invented. This technology has also been used to fabricate millimeter-wave (mmWave) and terahertz (THz) passive devices. Though promising results have been demonstrated, the challenge lies in the fabrication tolerance improvement such as dimensional tolerance and surface roughness. We propose the design methodology of high order device to circumvent the dimensional tolerance and suggest specific modelling of the surface roughness of 3D printed devices. It is believed that, with the improvement of the 3D printing technology and related subjects in material science and mechanical engineering, the 3D printing technology will become mainstream for mmWave and THz passive device fabrication.

A compact broadband implantable patch antenna is designed for the field of biotelemetry and experimentally demonstrated using the Medical Device Radiocommunications Service (MedRadio) band (401–406 MHz). The proposed antenna can obtain a broad impedance bandwidth by exciting dual-resonant frequencies, and has a compact structure using bent metal radiating strips and a short strategy. The total volume of the proposed antenna, including substrate and superstrate, is about 479 mm³ (23 × 16.4 × 1.27 mm³). The measured bandwidth is 52 MHz (382–434 MHz) at a return loss of −10 dB. The resonance, radiation and specific absorption rate (SAR) performance of the antenna are examined and characterized.