| The true time delay phased array based on microwave photonics has the characteristics of low transmission loss,instantaneous bandwidth and anti-electromagnetic interference,which accord with the requirement of phased array radar system.Optically controlled phased array antenna system has a strong capacity to the positioning measurement(the measurement accuracy,the measured velocity and the ability to intercept)and anti-jamming capability,high sensitivity,ability to adapt to the wideband signal,which has a broad development prospect value.Optically controlled phased array antenna system based on microwave photonics depends on the core technology of microwave photon signal generation,transmission and processing.In this paper,the key problems of microwave photonic signal generation,filtering,phase shifting,transmission and phase stabilization are discussed in order to realize the engineering of optically controlled phased array antenna.The prototype and experimental test of the optically controlled phased array antenna with continuous delay are realized.Firstly,the technology of the microwave signal generation and filtering in optical domain is discussed.In this paper,two necessary conditions for the output of the RF signal are analyzed.It is proposed to replace the traditional optical fiber storage unit with dispersion fiber grating to shorten the oscillation time.Base on the discussion of the nonlinear polarization rotation effect mechanism in the SOA,the dual-ring oscillator based on two-mode of the SOA is achevied to avoid the use of narrowband filters.The above scheme achieves X-band high-speed sweep signals with phase noise below-100 dBc / Hz @ 10 kHz.Also,the second-order IIR filter based on the SOA is proposed to realize the band-pass filter with an Q value up to 13000 and tunable center frequency.Secondly,the phase shifter technology in the optically controlled phased array antenna is studied.The experimental scheme of microwave phase shift using fiber gratings,polarization maintaining fiber gratings and SOA is proposed.The chirped fiber gratings with apodization are designed and fabricated.The mechanism of nonlinear polarization effect in polarization maintaining fiber grating is analyzed and realized in the phase shifter which is immune to the optical wavelength jitter interference.Different phase shift of the output RF signal is got by changing the SOA injection current and optical power.On this basis,the three schemes are experimentally demonstrated respectively to achieve a 100 ps optical delay or 0 to 360 ° continuously adjustable phase shifter function.Then,for the situation that the phase jitter is generated by the influence of the optical fiber on the external environment at the long-distance transmission of optical control phased array antenna system,a compensated steady-state method based on the Michelson interference method is proposed,which can realize the phase compensation of the IF 10 MHz signal feedback control.The mechanism of the realization is theoretical derivation and experimental verification.The results show that 500 meters of fiber signal transmission phase jitter is better than 100 meters without any compensation in a large vibration environment,Finally,the experimental prototype of the optical control phased array antenna system is built,including the generation of the signal source,the optical modulation / transmission link of the microwave signal,the multi-wavelength laser output 4 different wavelengths of light to realize 4-channel RF output phase shift,the end RF signal processing,antenna transmission and feedback control to maintain phase stability and so on.At last,the experimental verificatioin is got in the microwave darkroom,which can achieve accurate beam direction angle. |
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