A recently proposed method for realizing frequencyreconfigurable antennas across a wideband is based on adjusting the feed amplitudes and phases of a multiport antenna. In this article, we demonstrate the feasibility of the method, for the first time, with a conjunction of an integrated RF transmitter and a four-element antenna cluster. The implementation performs on-chip amplitude and phase tuning with supply scaling and delay tuning circuits to tune the antenna cluster without requirement of matching network. The antenna cluster is built with four closely spaced antenna elements implemented on a printed circuit board. The transmitter integrated circuit (IC) is implemented in a 28-nm CMOS process with the chip size of 0.85 mm × 0.95 mm, including pads. The proof-of-concept implementation demonstrates tunability across a wideband from 1.5 to 5 GHz.

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This paper presents the prototype demonstration where an integrated transmitter circuit drives a mobile handset terminal antenna in order to provide frequency tunability and multiple input multiple output (MIMO) operation across the 0.5–4.5 GHz frequency range. The transmitter implementation incorporates on-chip weighted signal generation, i.e. amplitude and phase scaling to provide sufficient MIMO performance in the low band (700–960 MHz) and in the high band (1.5–4.5 GHz). In the transmitter, two antenna elements are used for MIMO operation in the low band and another two in the high band. The transmitter integrated circuit (IC) is fabricated in a 28 nm bulk CMOS technology with an active on-chip area of 0.2 mm$^2$. A custom antenna measurement procedure is proposed here in order to support and verify active antenna measurements with transmitter IC. A measurement procedure for the transmitter system comprising the transmitter IC and four antenna clusters is developed and discussed in comparison with traditional passive antenna measurements. The measurement results demonstrate that the transmitter IC driving the antenna clusters provides total antenna efficiency of $-6.5$ dB to $-1.5$ dB, and envelope correlation coefficient below 0.4 across the designated frequency bands. The results indicate that the implemented transmitter IC successfully tunes frequency response of the antenna clusters, and enhances the MIMO operation of such mobile antennas.

Active reconfiguring of the frequency response of an antenna cluster was recently demonstrated involving an integrated transmitter and antenna cluster. The tuning method solely relies on scaling the antenna cluster feed amplitudes and phases, and entirely eliminates the typically required on-chip or off-chip matching networks. This work now advances the prior art by demonstrating and presenting improved solutions for on-chip amplitude and phase scaling blocks. In this paper, we present an optimization for phase resolution, resulting in 5 bit phase tuning architecture. Furthermore, we present an analysis of amplitude tuning on the efficiency and impedance variation for antenna cluster feeds. Two different amplitude scaling alternatives are considered: formerly studied switched capacitor power amplifier (SCPA) topology and a new low-dropout-regulator (LDO) based supply scaling of the class-D power amplifier. The designs are simulated in a 28-nm bulk CMOS technology at 1.5 GHz and 5 GHz respectively. The simulation results indicate that the LDO-based supply tuning method is superior to SCPA in terms of variation on efficiency and output impedance over the amplitude tuning code. The proposed circuit provides 15 dB amplitude tuning range with a 54 Ω impedance interface and 48% drain efficiency at 1.5 GHz whereas it provides an impedance interface of 84 Ω with 23% drain efficiency at 5 GHz.

This paper presents a transmitter IC with two identical signal paths, including base-band amplifier, up-converting mixer, and power amplifier (PA) stages. The design is focused on wide modulation bandwidth, and the use of a resonatorless small die-area class-D power amplifier at cm-wave frequencies. This work also incorporates a local oscillator (LO) signal distribution network with phase tuning elements. The circuit is implemented in a 22-nm CMOS process, and the active die area is 0.8 mm 2 . Operation over the 6-20 GHz range of carrier frequencies through the transmission of both continuous wave (CW) and wideband quadrature phase shift keying (QPSK) modulated signals were verified with measurements. Results with 20/40/100, and 400 MHz modulation bandwidths are presented, and for instance for a 20-MHz QPSK modulated input signal the measured adjacent channel leakage ratio (ACLR) of the transmitter is 28 dBc and error vector magnitude (EVM) is 5%.