Indirectly-Non-Reciprocal Load Modulated Balanced Amplifier with Equivalent Operation at Antenna Interface

This paper presents, for the first time, a new time-divisional-duplex (TDD) front-end architecture, named Indirectly-Non-Reciprocal Load Modulation Balanced Amplifier (INR-LMBA), for emerging massive MIMO array systems. By transforming the circulator from the PA output to the low power (CA) output, it can relief the power stress on circulator by an order of magnitude, potentially enabling the non-magnetic implementation. Together with the T/R switch, it can be used to offer the same TDD functionality as the conventional front-end, as well as the quasi-isolation to antenna in transmission and low loss in reception. As proof-of-concept for this architecture, a 2-2.5 GHz INR-LMBA prototype is developed using GaN devices and a commercial circulator. The experimental results exhibit an efficiency of 62-73% for peak output power and 53-57% for 10-dB OBO, respectively. The insensitivity to load mismatch of INR LMBA is also experimentally demonstrated.