A 24 GHz industrial, scientific and medical (ISM)-band Doppler radar antenna with high isolation is proposed for moving target sensing applications. Both transmit (Tx) and receive (Rx) antennas consist of 2×2 microstrip patch antenna arrays. High isolation of the proposed antenna is achieved by inserting periodic Jerusalem cross slot array between Tx port and Rx port and thus the surface wave from Tx port to Rx port is significantly suppressed. The −10 dB reflection coefficient bandwidth of the proposed antenna is 510 MHz and the isolation between Tx port and Rx port is higher than 36.7 dB over the 24 GHz ISM band. The simulated half power beamwidth are 58.53° for E-plane and 47.54° for H-plane. Experimental results show that high isolation can lead to improve Doppler radar performance. The proposed antenna can be a good candidate for contact-free monitoring of the heart rate and respiration rate in health care applications.

In this paper, a 28 GHz fifth-generation (5G) phased array antenna with air-hole slots for beam width enhancement is proposed. The proposed antenna consists of eight dipole radiators on a mobile handset-sized ground with air-hole slots between the two adjacent elements for enhancing the half power beam width (HPBW) in the elevation plane. The dimensions of the proposed antenna are 130 mm × 42 mm × 0.127 mm. The proposed array antenna satisfies a −10 dB reflection coefficient in the frequency range from 27.2 to 29.2 GHz with a peak gain of 10.33 dBi and a side lobe level (SLL) of 13 dB. In addition to its good performance, the proposed antenna has a very wide HPBW (measured) in the elevation plane, up to 219 degree with a scan coverage of ±45 degree in the azimuth plane. The proposed antenna demonstrates excellent hemispheric beam coverage for 5G mobile handset devices and can enable cost-effective mass production.

A quasi-Yagi slotted array antenna with fan-beam characteristics is proposed for 28 GHz 5G mobile terminals. The antenna is composed of a 1 × 8 slot antenna array with directors to enhance the half-power beamwidth (HPBW). The proposed antenna has a fan-beam radiation pattern with a simulated HPBW of 256.72° and a peak gain of 11.16 dBi. In addition, the proposed antenna covers ±48° using a beam steering mechanism. Mutual coupling reduction is achieved by inserting slits between the adjacent slot radiators on the ground plane. The simulated −10 dB reflection coefficient bandwidth of the proposed antenna is 1.79 GHz (27.03–28.82 GHz), and the mutual coupling between each of the slot radiators is lower than −25.02 dB over the 28 GHz target band (27.5–28.35 GHz). To investigate the effect of a human body in a practical environment, the power density was considered to estimate the electromagnetic exposure with a simplified skin model. The measured results were in good agreement with the simulated ones and demonstrated that the proposed antenna could be used for 5G mobile terminals.

The feasibility study of a 24 GHz industrial, scientific, and medical (ISM) band Doppler radar antenna in electromagnetic aspects is numerically performed for near-field sensing of human respiration. The Doppler radar antenna consists of a transmitting (Tx) antenna and a receiving (Rx) antenna close to the human body for a wearable device. The designed slot-type Doppler radar antenna is embedded between an RO4350B superstrate and an FR-4 substrate. To obtain the higher radiation pattern of the antenna towards the human body, a ground plane reflector is placed underneath the substrate. The measured −10 dB reflection coefficient (S₁₁) bandwidth is 23.74 to 25.56 GHz and the mutual coupling (S₂₁) between Tx and Rx antennas is lower than −30 dB at target frequencies. The Doppler radar performance of the proposed Doppler radar antenna is performed numerically by investigating the signal returned from the human body. The Doppler effect due to human respiration is investigated through the I/Q and arctangent demodulation of the returned signal. According to the results, the phase variation of the returned signal is proportional to the displacement of the body surface, which is about 0.8 rad in accordance with 1 mm displacement. The numerical experiments indicate that the proposed Doppler radar antenna can be used for near-field sensing of human respiration in electromagnetic aspects.

한국전자파학회논문지 (The Journal of Korean Institute of Electromagnetic Engineering and Science)