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Abstract
Phased array radars have remarkable advantages over radars with single-element antenna in terms of agility, flexibility, robustness, and reconfigurability. Current pure-electronic phased array radars face challenges when operating with a large frequency tunable range and/or with broad instantaneous bandwidth. Microwave photonics, which allows wide bandwidth, flat frequency response, low transmission loss, and immunity to electromagnetic interference, is a promising solution to cope with issues faced by pure electronics. In this paper, we introduce a general architecture of microwave photonic array radar systems and review the recent advancement of optical beamforming networks. The key elements for modelling the response of the true time delay (TTD) and/or phase-shifting unit are presented and discussed. Two typical array antenna structures are introduced, i.e., microwave photonic phase shifter based array and optical true time delay based array, of which the principle and typical implementations are described. High-resolution inverse synthetic aperture radar (ISAR) imaging is also realized based on a microwave photonic array radar. The possibility of on-chip integration of the microwave photonic array radar is discussed.
Highlights
Phased array radars can be dated back to the 1930s [1]
We introduce some of the recent progress of microwave photonic arrays intended for radar applications, which consists of a theoretical model capable of revealing the characteristics of the array in the broadband scenario and several approaches to implementing the microwave photonic arrays
The definition of the theoretical model in (7) is based on the assumptions of ideally identical antenna elements with isotropic radiation pattern, frequency-independent response, and accurate geometric arrangement, the model is still acceptable in the study of microwave photonic arrays since it can fully reflect the influence of each photonic processing unit on the array performance
Summary
Phased array radars can be dated back to the 1930s [1]. A typical phased array is an array of antenna elements, of which the phase of the transmitted or received signal to/from each antenna element is controlled independently by a phase shifter [2]. For multi-band radar or frequency-agile radar, even if it is operated in the mode of narrow instantaneous bandwidth, the carrier frequency covers a wide frequency range The required devices such as broadband electrically controlled phase shifters would be expensive and usually have poor performance due to the non-uniform response over a large spectral range. Benefiting from the high-frequency and broadband operation capability of the optoelectronic devices and subsystems, microwave photonic array radar can have a large bandwidth of ∼50 GHz. In addition, a very flat amplitude and phase response in such a frequency range can be achieved. The second category of microwave photonic arrays uses an optically controlled true time delay beamforming network to deal with the beam-squint problem for broadband radars. The advancement of photonic integrated techniques for array radars is overviewed
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