In this communication, the novel compact tightly arranged pairs are employed to form a $4 \times 4$ multiple-input-multiple-output (MIMO) system and an $8 \times 8$ MIMO system operating at 3.4–3.6 GHz for fifth-generation (5G) mobile phones. Each tightly arranged pair is composed of a bent monopole and an edge-fed dipole with a compact size of $7 \times 12$ mm ² . The orthogonal-mode method is presented to mitigate the mutual coupling of the tightly arranged pairs without any external decoupling structure. With the help of the orthogonal mode, isolation performances across the desired band of the $4 \times 4$ MIMO system and the $8 \times 8$ MIMO system are better than 20 and 17 dB, respectively, with the elements closely spaced. The measured efficiencies are 51.7%–84.5%/49%–72.9%, and the measured envelope correlation coefficients are less than 0.06/0.07 for the $4 \times 4/ 8 \times 8$ MIMO system. The proposed MIMO systems provide a promising solution to compact 5G MIMO mobile phone antennas with good isolation and diversity performance.

In this paper, we propose a beam-oriented digital predistortion (BO-DPD) technique for power amplifiers (PAs) in hybrid beamforming massive multiple-input multiple-output (MIMO) transmitters, which can achieve linearization of the transmitted signal in the main beam direction and address the DPD implementation issue in the hybrid beamforming array. In massive MIMO hybrid beamforming transmitters, the conventional DPD to linearize each PA is impractical to implement for that the number of digital chains is less than the number of PAs; however, the BO-DPD can resolve this issue by constructing and linearizing the “virtual” main beam signal rather than single PAs. According to the beamforming weights for array elements, the feedback path combines all PA's outputs to estimate the main beam signal for DPD processing. In addition, an average estimation method is also presented to broaden the linearized angle range around the main beam direction. A $4 \times 16$ (four subarrays and 16 antennas in each subarray) uniform linear array (ULA) simulation along with a $1 \times 2$ ULA at 2.5 GHz and a $2 \times 2$ ULA at 3.5-GHz experimental tests was performed. The experimental results show that the proposed technique and linearization angle range broadening method achieve up to 15-dB adjacent channel power ratio improvement and 10° linearization angle range in the main beam direction.

The flipped-voltage-follower-based low-dropout regulator (LDO) has drawn attention for its fast response and reduced complexity, while super source follower can be combined to push the pole at the gate of the pass device to high frequency. But the maximum load current and minimum load capacitance of this topology are limited, especially when the poles and zero from the SSF are omitted in previous designs. This paper proposes a solution to extend the ranges of the load current and load capacitance, by implementing a small feed-forward capacitor (C _F ) and a damping factor control circuitry. In addition, a slew rate enhancement circuit is applied to reduce the voltage undershoot. The proposed LDO is verified in a 65-nm CMOS process with 0.008 mm ² active area. The measured voltage undershoot is 80 mV with a load steps from 100 μA to 50 mA with 2-ns edge times, with no external capacitor. And the maximum load capacitance can be extended to 2 nF. A figure-of-merit of 0.8 mV is achieved.

A low profile end-fire leaky-wave antenna is proposed in this paper. The proposed low profile antenna utilizes microstrip line to excite planar inverted-L antenna (PILA) elements. Air media is utilized in the proposed array to realize the end-fire property. By using air media, the proposed leaky-wave array maintains phase constant slightly larger than the wavenumber in free space and achieves end-fire radiation. PILA elements are periodically spaced to radiate and the spacing period is designed as λ0/4 (λ0 is the wavelength in free space) to achieve a relatively wide impedance bandwidth. A prototype of the proposed end-fire antenna is fabricated and tested. The measured results are consistent with full-wave simulation results. The length of the whole leaky-wave array is about 6λ0, and the measured gain in the end-fire direction is 11.5 dBi at 5.1 GHz.

This paper presents magPEEC, a new 3D electro-magnetic modeling technique that extends existing PEEC approach to analyze arbitrary conductor-magnet structures by accounting for fictitious magnetized currents on magnetic material surface. Applications of magPEEC for magnetic-cored RF IC inductors are discussed with examples of stacked spiral inductors in 0.18 /spl mu/m CMOS. The observed upper-limit effect of enhancing inductance by increasing magnetic permeability is also discussed.

An 800M/1.8G/2.4GHz multi-band multi-standard single chain transceiver is presented to support terminals under NB-IoT, BLE and Zigbee protocols. The multi-branch co-wound transformer structure co-designed with RF front-end blocks (i.e. LNA & Power Mixer) is proposed and adopted for compact and efficient in-out matching with moderate Q value. Such co-designed topology enables the single transceiver chain to cover wide-spreading frequency ranging over three times of its minimum band frequency, without compromising performance. The measurement shows that, in receiver chain, the sensitivity is better than -102 dBm, consuming less than 20mW, in transmitter chain, the EVM is 4.63% and 5.2% for NB-IoT multi-tone 12-tone transmission with 0dBm output power in LB and MB. The transceiver has been implemented in 65nm CMOS process, with 1.5mm2 and 0.6mm2 for receiver and transmitter, respectively. The design is consistent with the requirement of low-cost multi-standard Internet-of-Things (IoT) applications.