Abstract
An optical true time delay (TTD) unit capable of adding independent time delays to multiple RF signals is proposed, which can be used for multi-beamforming in both transmit and receive modes. In the proposed unit, N RF signals with different center frequencies are modulated on an optical frequency comb (OFC). After transmission through a dispersive element, the RF-modulated OFC is split into N paths. In each path, a comb line is selected by a tunable optical filter. Thanks to the chromatic dispersion of the dispersive element, independently-controllable TTDs can be obtained in all paths. Then, a microwave photonic filter (MPF) is incorporated in each path, allowing a designated RF signal to undergo the TTD in that path. A proof-of-concept experiment is carried out. A two-path unit with a low-pass MPF in one path and a high-pass MPF in the other path is built. Controllable TTDs up to ~1.4 ns with a step of ~69 ps are demonstrated based on a 25-GHz-spacing OFC. In addition, a wideband multi-beam phased-array antenna system that can work in both transmit and receive modes is designed using the proposed TTD unit.
Highlights
To solve the beam-squint problem in wideband phased-array antenna systems, extensive efforts have been devoted to the beamforming technique by true time delay (TTD)
An optical TTD unit based on fiber dispersion and microwave photonic filter (MPF) has been proposed and demonstrated
In each path of the unit, TTD controlling is realized by a tunable optical filter while RF frequency selection is realized by a MPF
Summary
To solve the beam-squint problem in wideband phased-array antenna systems, extensive efforts have been devoted to the beamforming technique by true time delay (TTD). It is highly desirable to realize an optical TTD beamformer with independent and controllable TTDs for multiple RF signals To achieve this goal, some pioneer works have been reported [9,10,11,12]. We propose an optical TTD unit with independent delays for multiple RF signals, which can be used in both transmit and receive modes. An optical frequency comb (OFC) carried with N different RF signals are transmitted through a dispersive element, which are split into N paths. All the RF signals can obtain independent TTDs. If the proposed unit is applied in a phased-array antenna system operated in either transmit or receive mode, multiple independent beams steering can be realized. Based on the proposed optical TTD unit, a wideband multi-beam phasedarray antenna system that can work in both transmit and receive modes is designed
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