Photonic-Assisted Dot-Shaped Beamforming for Frequency Diverse Array with Nonfixed Frequency Offset

In contrast to phased array (PA), a frequency diverse array (FDA) exhibits a superior ability to utilize the 2-D domains information on the angle and distance, attributed to its distinctive 'S'-shaped or dot-shaped beampattern. This confers increased adaptability in distance-sensitive applications. However, challenges remain due to the coupled angle and distance within the 'S'-shaped beampattern and the limited bandwidth of the traditional electronic signal generation methods. In this work, microwave photonic (MWP) technology is introduced to realize wideband dot-shaped beamforming of FDA. The angle and distance are decoupled by generating FDA signals with nonfixed frequency offset using a dual-parallel Mach-Zehnder modulator (DPMZM) and several phase modulators (PMs). This architecture fulfills the frequency shift and phase shift requirements of the input radio frequency (RF) signal. In the experiment, 16-channel FDA signals with fixed and nonfixed frequency offset are generated, including the FDA with logarithmic frequency offset (log-FDA), sinusoidal frequency offset (sin-FDA), and exponential frequency offset (exp-FDA). Beampatterns are calculated and measured based on the generated signals. The results conclusively demonstrate that the experiment accurately produces an 'S'-shaped beampattern with the fixed frequency offset, while distinct dot-shaped beampatterns are produced with all the nonfixed ones, thus underscoring the versatility and precision of the proposed method in realizing diverse FDA signal configurations.