Abstract
Radar sensing has become very popular over the last two decades, and research has focused on high-bandwidth and high-resolution systems. Due to the steadily increasing center frequency of front-end circuits, on-chip antennas are the preferred choice over PCB antennas and horn antennas when frequencies get close to THz. However, conventional on-chip antennas are severely limited in bandwidth, leading to increased use of wideband and multiresonant on-chip antennas. Besides a more complex design process of multiresonant antennas, they have the disadvantage of a nonconstant dispersive group delay (GD). This reduces the resolution of sensing systems, such as the range resolution and angular resolution of a radar system. In this work, we show how GD affects the imaging properties of a radar system. The measured S-parameter data from a 240-GHz multiresonant antenna are used to generate synthetic intermediate frequency (IF) signals of a rectangular array. Subsequently, simulated 3-D radar images are generated using the backprojection algorithm. These images are compared with those of a nondispersive imaging system. Finally, two compensation methods using a phase correction method and an all-pass filter are explained, and their performance is compared.
Highlights
A KEY component of millimeter-wave and THz sensing is the antenna used to transmit the front-end signal into free-space [1]
The system model is based on an FMCW radar system with one transmit and 16 receive antennas (SIMO), which corresponds to two orthogonal uniform line arrays with four transmit and receive antennas (MIMO), respectively
It radiates a circular polarization (CP) into broadside direction over a bandwidth covering roughly 220–260 GHz, where the axial ratio of the CP declines for both directions off broadside and frequencies at the edges of the bandwidth
Summary
A KEY component of millimeter-wave (mm-wave) and THz sensing is the antenna used to transmit the front-end signal into free-space [1]. The solutions to increase efficiency are manifold and range from the off-chip ground [9], dielectric resonators [10]–[12], nonplanar antennas [13], [14], and backside radiation techniques [15]. Multiple resonant structures increase bandwidth and series capacitive elements enhance the radiation efficiency (similar to [16]). This has the advantage that no complex and additional manufacturing processes are necessary as with the previously mentioned approaches.
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