28-GHz SiGe Bidirectional 4-Element Beamformer Chip for 5G Applications Based on a 4-Way Ultracompact Switchable Power Divider

This article describes the design of a 28-GHz bidirectional 4-element beamformer chip based on a 4-way ultracompact switchable power divider (SPD). The addition of the divider solves the ineffective power splitting and the inefficient use of valuable chip area. Therefore, this work is devoted to remove the drawbacks associated with the Wilkinson power dividers (PDs) and single-pole double-throw switches (SPDTs) leveraging a single-inductor N-way PD topology. In this article, the PD design is presented and its analysis is carried out, extending the previous literature. In addition, the embedding of the SPDTs within the PD is described in detail. Employing the proposed technique, the chip size is limited only to the dimensions of the main RF building blocks, analog circuitry, and digital logic; hence, eliminating the cumbersome divider chain which connects the transmitting/receiving (TRx) elements before going on-board. Finally, the measured performance of the beamformer designed in the IHP SG13S SiGe BiCMOS technology is reported. The beamformer achieves an $ {{\mathrm {OP}} {_{\text {1 dB}}}}$ of 11 dBm in Tx-mode with a power consumption of 231 mW for each element, whereas an ${{\mathrm {IP}} {_{\text {1 dB}}}}$ of -28 dBm in Rx-mode is achieved consuming only 92 mW per element. The chip occupies a silicon area of $2.9\times 2.2$ mm2. Moreover, a shift step of 11.25° is achieved with 2.4° and 0.4 dB of phase and amplitude root-mean-square error (RMSE), respectively. To the best of the authors’ knowledge, this is the first beamformer which substitutes the divider chain with a novel SPD. In this way, the chip length could be reduced by 1 mm with respect to their previous design, which proves that the proposed technique is promising for chips with high number of TRx elements.

I. Introduction

New mobile communication generations always brings new features. The fifth-generation (5G) mobile network introduces the use of phase-antenna array systems (PhAAs) for communications purposes [1], [2]. However, effective PhAAs which maximize the spectral efficiency must rely on precise and agile beamformer chips. So far, excellent works on PhAAs have been published in literature [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. Nevertheless, keeping the chip dimensions compact is essential and will become even more crucial in the near future, as further scaling with a greater number of elements is required to increase the effective isotropic radiated power (EIRP), improve the signal-to-noise ratio (SNR), and achieve better spatial filtering capabilities as well as a longer link range [15]. Therefore, miniaturizing the size of the beamformers is of paramount relevance from the system perspective.