The major deficiency of conventional ‘balanced antipodal Vivaldi antenna’ (BAVA) is its tilted beam over upper working frequencies. This study reports on a new BAVA to overcome this defect. By applying a dielectric lens in front of the antenna's aperture, beam‐tilting in E‐plane was improved within the ultra‐wideband frequency range, as well as higher frequencies. In the new BAVA, the authors have also achieved an acceptable cross‐polarisation. Measurements show that the antenna has better than 10 dB return loss within the aforesaid frequency range. The measurements successfully verify the simulation results. Group delay and fidelity factor as time domain characteristics of the proposed antenna have been studied. They have compared performance of the conventional BAVA, with achievements of the new BAVA as hereunder.

Conventional multistatic radar systems using microwave and millimeter-wave (mm-wave) frequencies seek to reconstruct the target in the imaging domain, employing many transmitting and receiving antenna elements. These systems are suboptimal, in that they do not take into consideration the large mutual information existing between the measurements. This work reports a new mm-wave radar system for high sensing capacity applications. The system is composed of a Compressive Reflector Antenna (CRA), whose surface is specially tailored by digitized Metamaterial Absorbers (MMAs). The MMA elements are designed to have a highly frequency-dispersive response in the operating band of the radar. This enables the CRA to create highly uncorrelated spatial and spectral codes in the imaging region. A semi-analytic method based on Drude-Lorentz model is used to approximate the reflection response of the MMAs. The performance of the developed radar system is evaluated in active mm-wave sensing systems by imaging PEC scatterers and an extended human-size model in the near-field of the radar. A computational method based on physical optics is established for solving the numerical examples. For reconstructing the image using compressive sensing techniques, a norm-1 regularized iterative algorithm based on the Alternating Direction Method of Multipliers (ADMM) and a Nesterov-based algorithm (NESTA) were applied.Index Terms-Compressive reflector antenna, millimeter-wave imaging, metamaterial absorber, coded aperture.

Conventional phased array imaging systems seek to reconstruct a target in the imaging domain by employing many transmitting and receiving antenna elements. These systems are suboptimal, due to the often large mutual information existing between two successive measurements. This chapter describes a new phased array system, which is based on the use of a novel compressive reflector antenna (CRA), that is capable of providing high sensing capacity in different imaging applications. The CRA generates spatial codes in the imaging domain, which are dynamically changed through the excitation of multiple-input-multiple-output (MIMO) feeding arrays. In order to increase the sensing capacity of the CRA even further, frequency dispersive metamaterials can be designed to coat the surface of the CRA, which ultimately produces spectral codes in near-and far-fields of the reflector. This chapter describes different concepts of operation, in which a CRA can be used to perform active and passive sensing and imaging.

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