Spatial IDFT for Squint-Free Massive Arrays

TL;DR

A novel technique to build squint-free massive phased arrays is presented by explicitly implementing a spatial IDFT to cancel out the DFT imposed by the array nature which causes beam squint.

Abstract

This paper presents a novel technique to build squint-free massive phased arrays. This is accomplished by explicitly implementing a spatial IDFT to cancel out the DFT imposed by the array nature which causes beam squint. In addition, the paper analyzes the beam-squint issue, which arises from two mechanisms: the coherent bandwidth limitations and the systematic delay spread in the array. These mechanisms reduce the signal-to-noise ratio and cause inter-symbol interference. This work also highlights the importance of utilizing OFDM modulation to enhance signal quality by mitigating the self-interference issue. A numerical solver is used to simulate and verify the IDFT squint-free implementation and to estimate the signal quality limitations in massive arrays.

Figures (13)

• Figure 1: Block diagram of a phased-array transmitter with true-time delay.
• Figure 2: Block diagram and space factor at the center frequency and band edges of a phased-array transmitter with phase shifters.
• Figure 3: Baseband model of a transceiver with single TX and N-elements phased array RX using phase shifters and processing single-carrier signal.
• Figure 4: SSIR over array size $N_{elements}$ and steering angle $\theta_o$ assuming a wideband single-carrier signal for (a) $5\%$, (b) $10\%$, (c) $15\%$, and (d) $20\%$ fractional bandwidth
• Figure 5: Constellation and EVM simulation results for a single-carrier signal with $20\ \text{dB}$ SNR received by an 8-elements RX at $30^o$ steering angle and (a) $1\%$ bandwidth (b) $20\%$ bandwidth, and a 16-elements RX with $20\%$ bandwidth and (c) $30^o$ steering angle (d) $45^o$ steering angle