This paper reviews on the latest advances in microwave photonics applied to radar systems, tracing the evolutions of functionalities in the photonic radar toward a new generation of enhanced-performance systems. Photonics is demonstrated to enable a new generation of miniaturized, heterogeneous and distributed radars, i.e. future radars on chip with different features, working in different radio spectral regions, and organized in spatially distributed sensors for the enhanced detection of a wider range of target properties. In these systems, the use of photonics assures benefits in terms of frequency flexibility, accuracy and computational load reduction. Innovative capabilities supported by the photonic approach are presented, such as the use of coherent sparse bands for the synthesis of ultra-wide bands, the use of distributed sensors for multiple-input multiple-output detections, and the use of an ultra-wide band photonics-based receiver for radio frequency (RF) spectrum scanning. The presented novel concepts will open the way to new research activities both in photonic technology and radar systems, contributing to the development of a new generation of remote sensing systems. This expanding cross-fertilization will lead to exciting and challenging research activities in the years to come.

The evolution of microwave and mm-wave systems for communication and remote sensing is heading towards a massive deployment of phased-array antennas with beamforming capabilities. 5G wireless access networks are expected to employ beamforming to optimize resources allocation, whereas radars will benefit from precise and fast-switching antennas. Moreover, in the next future, those systems are expected to widely employ photonic technologies for signal generation, acquisition, and distribution. In this scenario, photonics can allow for the development of high-performance beamforming networks, which can easily be integrated in photonics-assisted RF systems, combining broad operational bandwidth, low signal distortion, and high pointing precision with unprecedented flexibility. In this paper, a phase shift-based beamforming network for microwave applications is presented and its performance analyzed. The Si-photonics integrated phase shifters exhibit large phase shift (> 360°) and limited amplitude fluctuations (~ 2.5 dB). The packaged beamforming network elements show extremely low signal distortion, low steering error (<3°), and fast switching time (< 5 ns), demonstrated by the transmission with beam-steering of a 2-Gb/s communication signal and of a 1-GHz chirped radar waveform. A comparison with commercial RF devices shows that the photonics-assisted beamforming network is well-suited for high bit-rate 5G communications and for wideband radar applications.

Auto-regressive gap filling algorithms have been demonstrated for interpolation among spectral gaps created by incoherent dual band radar systems. The required synchronized reconstruction leads to a heavy computational load. The recent use of photonics in microwaves systems, has resulted in coherent multiband radars that allow implementing these auto-regressive algorithms without the need to recover the coherence, and consequently with a reduced computational complexity. In a previous work, a modified auto-regressive algorithm with optimization control for coherent multiband radar has been presented. The algorithm has shown the ability to interpolate among two coherent sub-bands, obtaining the same performance of equivalent radar with a total band equal to the sum of the used sparse sub-bands. Therefore, the application of the modified auto-regressive algorithm to radar with sparse sub-bands overcomes the bandwidth limitations of RF front-ends and the frequency regulation restrictions. In the previous work, the algorithm was verified in simple scenarios and using only two sub-bands. Here, the algorithm using two sub-bands is applied and verified to scenarios with increased complexity, including the case of a boat as target. Moreover, for the first time we extend the algorithm to the case of several sub-bands (more than two) and we analyze the performance. We demonstrate that the benefit of using the auto-regressive gap filling algorithm instead of data fusion, increases as the number of sub-bands gets higher.

This paper presents a wide input range, low-power operational transconductance amplifier (OTA) in weak inversion. The OTA is implemented with tanh-triplets differential pairs, degenerated by a composite configuration to augment the input linear range, thus reducing further the harmonic distortion. Using MATLAB, the mismatch factor (A) of a typical multi-tanh triplet has been optimised for minimum harmonic distortion. The OTA is designed in UMC 0.13um CMOS technology with 1.2V supply. Simulations show that the input range can be extended to 300 mV, while keeping the HD3 below -80 dB. The average power consumption is 13nW, with an open loop-gain of 76 dB and a unity gain frequency of 250 Hz. The low harmonic distortion OTA can find potential applications in low-power and long time constant filters.

In this paper, the performance of a photonic beamforming network based on phase shift for microwave applications is analysed. The proposed beamforming network elements are realised as Si-photonic integrated circuits, exhibiting large phase shift (> 360°) and limited amplitude fluctuations (~ 3 dB). Extremely low signal distortion is demonstrated, by emulating the transmission of a 1-GHz chirped signal by a 4-element phased array antenna operating beam steering, driven by the proposed beamforming network.

This paper presents a planar antenna using low temperature co-fired ceramics (LTCC) substrate for extreme environment applications. An ultra wideband (UWB) elliptical patch antenna was designed and fabricated using an LTCC Ceramtec GC substrate to demonstrate the capabilities of the technology for wideband applications. The simulated results were further validated experimentally. The fabricated antenna provides a peak gain of 5dB over a bandwidth of 4 GHz (3 GHz-7 GHz) with return loss better than -10dB. The radiation pattern is omni-directional in the horizontal plane (θ=900) over the whole frequency range.