Experimental Investigation of Decoupling Effect on the Nonlinearity of Power Amplifiers in Transmitter Array

Abstract

In a practical compact massive multiple-input multiple-output (MIMO) transmitter array, each antenna or subarray is connected to an independent power amplifier (PA) with a modest power capacity in order to avoid the challenging demand of high-power capacity of a single PA for the whole array and to facilitate the power dissipation of the transmitter array. In this case, there is simply not enough space for an isolator between the antenna and the PA. As a result, the array mutual coupling changes the load impedances of the PAs and thus further increases the MIMO transmitter’s nonlinearity. In this work, the decoupling effect on the transmitter array’s linearity is investigated experimentally by using an array prototype with PAs. The mutual coupling of the array can be effectively suppressed using a hybrid decoupling structure. Two continuous-wave (CW) signals at different frequencies are injected into the PAs, and the output signal of each PA is measured via a coupler. The measured results show that with effective mutual coupling reduction, the PA interference is greatly suppressed by up to 16 db and the amplitude of the desired signal is enhanced by up to 10 db.

A Circularly Polarized Patch Antenna Array with Reduced Mutual Coupling Using the Aperture-Loading Decoupling Technique

“…For instance, an active VSWR of the MIMO antennas would be higher than 6 at 15 dB isolation, and if the isolation is improved to more than 25 dB, the VSWR can be less than 2 [10][11][12]. Moreover, strong coupling in communication systems impacts radiation patterns of antenna elements and will cause nonlinear effects that decrease the amplifier efficiency [13,14]. Therefore, the isolation level among massive MIMO elements is recommended to be better than 25 dB [15][16][17].…”

Isolation Improvement Using the Field-Circuit Combined Method for In-Band Full-Duplex MIMO Antenna Arrays

“…When fullduplex antennas are used in MIMO antenna arrays, the antenna elements are closely arranged due to the limited space. Signal interference is generated between the receiving and transmitting antennas, and mutual coupling is generated between the receiving/transmitting antennas, which significantly deteriorate the performances of the wireless communication systems (including receiver performance, error rate, dynamic range, and channel capacity) [5][6][7]. Notably, 100 dB isolation between the transmitter and receiver is generally required for fullduplex systems, which is usually achieved by combining the antenna, analog and digital domains [8,9].…”