Meter Wave Radar Cross Section Analysis: What Does “Resonance” Really Mean?

Meter wave radar is regarded as an effective detection scheme against low observable aircraft for several beliefs: 1): The radar absorption material (RAM) at this regime is less unlikely to be effectively applied due to the large thickness required. 2) The resonance effect between wavelength and the size of the aircraft leads to a larger radar cross section (RCS). 3) The cheaper RF front end price of the meter wave radar provides a larger power-aperture product, therefore a higher detection probability. Based on these thinking, very large active electronically scan array (AESA) meter wave phased array radar receives a revival enthusiasm at some part of the world. However, the disadvantage of low spatial and time resolution still exist, which some claim can be resolved by advanced digital signal processing techniques. In this article, we investigate the true meaning of “resonance” effect of meter wave radar against some simple shapes via finite-difference-time-domain (FDTD) and multi-level-fast-multipole-method (MLFMM) simulations. Resonance can only occur when the surface wave makes a round trip and return to the radar incident direction, and a constructive interference occurs at that entry point. The propagation constant of the surface wave depends on several factors: the radar wave incident angle relative to the surface, the surface material property, and the path length. All these factors can vary dramatically in a real low observable aircraft, so we found the so-called “resonance” is in fact hard to achieve, and only a few dB of RCS differences is possible.