Performance Analysis of Frequency-Invariant Multi-System for Broadband Direction Finding

This study estimates the direction of radio signals radiated by high-speed mobile platforms and analyzes detection performance using a frequency-invariant multisystem for broadband direction finding (DF). The discrete Fourier transform (DFT)-based frequency-invariant beamforming (FIB) algorithm was used to generate a constant beam pattern regardless of the frequency utilized. DFT-based FIB enables the rapid derivation of FIB weights. When applying FIB to a monopulse, a wide unambiguous range can be achieved. This can be used for monopulse DF that utilizes auxiliary systems. When the unambiguous region of the monopulse is narrower than the error of the auxiliary system, the DF errors increase. However, by employing FIB, a broader unambiguous region can be achieved, enhancing DF accuracy. The monopulse receiver example in this study was composed of 16 elements and detected arbitrary signals in the range of 6~20 GHz. Assuming a single-system setup with an incoming signal within ±30°, the system showed a DF error of 1.04° at an SNR of 20°dB. With a multi-system setup and a ±45° incoming signal range, the error was reduced to 3.82° at an SNR of 5 dB.