Ka-band microwave photonic ultra-wideband imaging radar for capturing quantitative target information

Abstract

Extracting precise target characteristics from microwave image is needed and calls for high-resolution microwave imaging radar systems. In this paper, a Ka-band ultra-wideband microwave photonic (MWP) imaging radar is developed and experimentally demonstrated. In the transmitter, continuous ultra-wideband linear frequency modulation (LFM) wave is generated based on optical frequency sextupling technique. In the receiver, a combination of optical frequency mixer with fiber delay lines and electric analog-to-digital converter (ADC) is capable of receiving target echoes and imaging targets with different distances. The maximum instantaneous bandwidth of the transmitted waveform is measured to be 10.02 GHz and corresponding range resolution is calibrated to be 1.68 cm. Out-field tests with demonstrator working at synthetic aperture radar (SAR) or inverse synthetic aperture radar (ISAR) mode are carried out. Different targets such as an unmanned aerial vehicle (UAV), airliner and Leifeng pagoda are imaged. Based on corresponding high-resolution microwave images, quantitative information of the targets can be identified, which shows the great potential of the radar demonstrator for various remote sensing applications.

Microwave Photonic Radars

“…With this scheme, a dual-band LFM radar signal (18∼22 GHz, 28∼32 GHz) was produced based on a low-frequency electrical dual-band signal (4.5∼5.5 GHz, 7∼8 GHz) [160]. Thanks to the high quality and high stability of the generated signal, several ultrahighresolution imaging radars were built based on this method [147], [217], [218], [224]- [228].…”

“…Most of the currently reported optoelectronic hybrid radars for high-resolution imaging are realized through de-chirping processing, where an LFM signal is used as the radar waveform [32], [217], [218], [222], [224]- [228], [323], [375]- [379]. The principle of de-chirp processing of the LFM signal is illustrated in Fig.…”

“…The de-chirped signal is sampled by an ADC and then sent to a DSP unit to calculate the image of the target. Based on this architecture, many experiments and field trials have been conducted to achieve high-resolution and real-time imaging [32], [218], [227], [228], [375]. In [32], an LFM signal with a bandwidth of 8 GHz was generated and radar imaging with a range resolution of ∼2 cm was achieved.…”

“…The image resolution was further improved by increasing the center frequency and bandwidth of the LFM signal to the Ka band and 12 GHz, respectively, and a range resolution of ∼1.3 cm was achieved [218]. In addition, real-time ISAR or SAR imaging of non-cooperative targets was demonstrated, which successfully achieved the ultrahigh-resolution microwave images or videos of a Boeing 737 airplane [227], an unmanned aerial vehicle (UAV) [375], and Leifeng pagoda [228].…”

“…In order to remove the image-frequency interferences and false targets in the single-channel photonic de-chirping receiver with real-valued outputs used in [32], [218], [226]- [228], [375], a photonics-based radar architecture using in-phase and quadrature (I/Q) de-chirping receiver with balanced detection was proposed [225], as shown in Fig. 33.…”