In this paper, we developed a 2-port dual-band and dual-polarization multiple-input- multiple-output (MIMO) antenna for fifth-generation (5G) mobile applications at 28 and 38 GHz. The antenna was fabricated using a double-layer Rogers ™ RO4003 substrate with a footprint of $3.77\,\,\lambda _{0}\times 1.86\,\,\lambda _{0}$ ( $\lambda _{0}$ being the free-space wavelength at 28 GHz). The aperture-coupled patch configuration fed by a coplanar waveguide (CPW) transmission line is adopted as the elementary antenna. The top patch and the coupling aperture are designed to radiate at 38 GHz and 28 GHz respectively for dual-band operation. Further enhancement of the directivity at 28 GHz is achieved through the top patch acting as a parasitic director. A 2-by-4 array antenna for MIMO application was then constructed through physical rotation of the single element at +45 and −45 degrees to create polarization diversities. The 2-port MIMO antenna realized using this configuration demonstrated an impedance bandwidth of S11<−10 dB covering 27.6–30.3 GHz and 33.4–40.4 GHz, a gain of greater than 8 dBi, isolation of more than 20 dB and a cross-polarization level of greater than 20 dB. The important MIMO parameters such as ECC, DG, TARC, and MEG have also been characterized and presented.

This paper presents a new transceiver configuration based on the low-noise power amplifier (LNPA) approach targeting the reduction in size and the overall biasing complexity. In such configuration, the LNPA remains always at the ON state and the single-pole-double-throw (SPDT) switches control the conversion between transmitting (Tx) and receiving (Rx) modes. Different from the conventional configuration, the switching speed depends solely on the SPDT switches avoiding the settling time of the amplifiers. To ensure the stable operation of the LNPA under such condition, an over-the-air (OTA) durability test of the transceiver module is proposed for the first time. No obvious degradation was observed when the module was tested by switching between Tx and Rx modes every 30 seconds for 14 hours of continuous operation. At 38-GHz, the 1-m OTA measurement using a standard 64-QAM 5G New-Radio (NR) modulated signal exhibited an error vector magnitude (EVM) of 4.52% at an output power of 18.38 dBm in the Tx mode. The noise figure (NF) in the Rx mode was measured to be 7.07 dB. The experimental results are comparable to the state-of-the-art transceivers in single-chip solutions. It is believed that the proposed transceiver based on the LNPA configuration has great potential as the building block of the large-scale phased-array systems for 5G NR applications.

In this letter, AlGaN/GaN HEMTs with tall-gate-stem structures were realized to improve the power performance of Ka-band devices, and a film thinning process is adopted in the fabrication process to reduce the parasitic capacitance caused by the thick silicon nitride film. According to the S-parameter measurement results, devices owning a tall-gate-stem structure and undergoing the film thinning process have higher cut-off frequency (fT) and maximum oscillation frequency (fmax) values with lower extracted parasitic capacitance. For the load-pull measurement result, the AlGaN/GaN HEMT with a tall gate stem has improved output power density (Pout) and power added efficiency (PAE) at Ka-band. The device with the elevated stem shows a steady-state current density of 883 mA/mm and a maximum transconductance of 323 mS/mm at 20 V bias, and it achieves fT of 39.5 GHz, fmax of 112.9 GHz with the maximum PAE of 24.6 % and the maximum Pout of 6.6 W/mm at 38 GHz.

This paper presents the design of a dual-band power amplifier (PA) featuring similar performance at 28 GHz and 38 GHz. In the new radio (NR) of the fifth generation (5G) communication system, the inter-band carrier aggregation technique is commonly adopted for data rate enhancement. In such configuration, operation at both bands of the 5G frequency range 2 (FR2) spectrum is often necessary. The stacked-FET topology was adopted for mitigation of the gain roll-off with frequency to achieve similar performance at both frequency bands. Implemented in the commercial 0.15- $\mu \text{m}$ gallium arsenide (GaAs) pseudomorphic high electron mobility transistor (pHEMT) technology, the PA delivered a small signal gain of 18.5/18 dB, an output power at saturation (P _sat ) of 28.5/28.2 dBm, and a peak power-added efficiency (PAE) of 39%/36% at 28/38 GHz, respectively. The measurement results have demonstrated great potential of the proposed PA for 5G NR applications.