Performance analysis for single-fed ESPAR in the presence of impedance errors and imperfect CSI

Existing MIMO precoding techniques assume conventional antenna arrays with multiple radio-frequency (RF) chains each connected to a different antenna. Towards small portable devices and base stations, single-fed compact arrays, also known as electronically steerable parasitic antenna radiators (ESPAR) have recently emerged as a new antenna structure that requires only a single RF chain. In this paper, we study the ESPAR based antenna arrays and explore linear precoding schemes for ESPAR antennas. The closed-form expression for the computation of the tunable loads and the feeding voltage is firstly shown and the impact of impedance errors and imperfect CSI on the performance is also investigated analytically. It will be shown that the impedance errors will act as an additional noise source that is independent of the SNR and thus result in an error floor at high SNR. We further study the energy efficiency of both conventional MIMO and ESPAR-based MIMO systems. Simulation results validate our analysis and show that ESPAR without impedance errors can achieve a similar performance to conventional antenna arrays and a higher energy efficiency, while the performance degradation due to impedance errors motivates the design of robust precoding schemes.