Frequency-diverse microwave imaging using planar Mills-Cross cavity apertures

Abstract

We demonstrate a frequency diverse, multistatic microwave imaging system based on a set of transmit and receive, radiating, planar cavity apertures. The cavities consist of double-sided, copper-clad circuit boards, with a series of circular radiating irises patterned into the upper conducting plate. The iris arrangement is such that for any given transmitting and receiving aperture pair, a Mills-Cross pattern is formed from the overlapped patterns. The Mills-Cross distribution provides optimum coverage of the imaging scene in the spatial Fourier domain (k-space). The Mills-Cross configuration of the apertures produces measurement modes that are diverse and consistent with the computational imaging approach used for frequency-diverse apertures, yet significantly minimizes the redundancy of information received from the scene. We present a detailed analysis of the Mills-Cross aperture design, with numerical simulations that predict the performance of the apertures as part of an imaging system. Images reconstructed using fabricated apertures are presented, confirming the anticipated performance.

On the Coherence Relationship between Measurement Matrices and Equivalent Radiation Sources in Microwave Computational Imaging Applications

“…The matrix H is generated by the inner productions of the electric fields according to Equation (14). Firstly, we start with the validation of the low-pass filter in the k-space by the first numerical simulation.…”

“…However, these heuristic works do not give an explicit formulation of the coherences' formation, which burdens further theoretical analysis and optimization. For the antenna apertures assembled by elements with random resonant frequencies, it has been widely examined that the increase of the elements' quality factors leads to the decreases in both the coherences and radiation efficiency [14,15]. However, this superficial phenomenon is still far from an explicit explanation of the mechanism underlying the generation of the coherences.…”

Microwave Imaging Using a Disordered Cavity with a Dynamically Tunable Impedance Surface

“…The Q of the loaded cavity (i.e. with the radiative layer) is computed using the decay rate of its impulse response [31,43]. To do this, the Fourier transform of the return loss is taken over the entire K band with sufficient sampling so that there is no aliasing in the time domain response-depicted in Fig.…”

“…The resulting waveforms show significant spatial variation as a function of frequency, enabling retrieval of a scene's reflectivity via a frequency sweep. While volumetric and planar cavities have both shown promise in experiments [37,[40][41][42][43], they require a large operational bandwidth. Large frequency bandwidth, though required in part for range resolution [44,45], may not be readily available in practice and can complicate the design of a coherent RF transceiver.…”

Indirect microwave holography and Through-Wall imaging

“…In this framework, what is required is a reliable, low-cost and rapid method for the imaging of metallic and non-metallic (dielectric) concealed objects. Solving the inverse problem is a computationally demanding task and is conventionally done by linearizing the forwardmodel and solving it to retrieve a qualitative estimate of the object function, such as the susceptibility distribution [28][29][30][31][32][33][34]. The linear inverse scattering algorithms, which are conventionally based upon a Born approximation, have the advantage of requiring a small amount of computational time due to their linear approach.…”