A microwave photonics deceptive RF regeneration method with multi-characteristic regulatory is proposed for radar jamming. In this scheme, Doppler frequency shift (DFS) is implemented by a Serrodyne structure based on the modulation of a sawtooth wave signal. This structure can effectively fulfill a small frequency shift of the original carrier through carrier-suppressed single sideband modulation without any filter, which makes a small frequency shift possible for a wideband radio frequency signal. The phase shifting of the RF signal is achieved by adjusting the bias voltage of the modulator. The RF modulation pulse signal is stored in an optical loop. Two semiconductor optical amplifiers and an Erbium-doped optical fiber amplifier are combined to control the delay time and ensure the fidelity. The experimental results show that the DFS from 100 Hz to 5 MHz can be realized and its minimum frequency step is 50 Hz. The phase shift covers from −180° to 180°. Furthermore, the RF signal can be delayed more than 100 μs with a small signal-to-noise degradation (<7.32 dB). This method supplies flexibility of multi-parameter adjustment, and has broad potential applications in modern radar interference.

Focusing on distributed antenna systems, we propose a photonics-assisted self-interference cancellation and down-conversion method based on a Sagnac loop structure. Two inversely cascaded modulators form a Sagnac loop through polarization multiplexing. To support in-band full duplex (IBFD) communication, a double parallel Mach–Zehnder modulator (DPMZM) operated in a clockwise direction is used as a self-interference canceller (SIC) to achieve the phase conversion in the optical domain. Another MZM modulator working in the counterclockwise direction is used to modulate the local oscillation (LO) signal for frequency down-conversion. The adjustment of bias voltage is analyzed to optimize the conversion efficiency of the system. The power fading effect generated by fiber dispersion is compensated by a polarization-sensitive phase modulator (PS-PM). The experimental results show that the average cancellation depth is 56.4 dB at a single frequency in the operating frequency range of 6–22 GHz, and 29.1 dB and 23.7 dB for 20 MHz and 100 MHz bandwidth signals, respectively. In addition, the error vector map is improved from 16.50% to 6.26% after dispersion compensation. The self-interference cancellation, down-conversion and dispersion compensation are integrated in a microwave photonics link. Two cascaded modulators are equivalent to a parallel structure by the Sagnac loop, simultaneously ensuring high LO isolation and conversion efficiency. The proposed method provides an alternative for IBFD-based distributed antenna communication applications.

In order to increase the scalability and reduce the complexity of photonic multipath SIC systems, a photonic multipath self-interference cancellation (SIC) method based on optical frequency comb (OFC) is proposed. The OFC is generated by continuously frequency-shifting the seed laser in the re-circulating frequency shifter (RFS) loop. The reference signal is modulated to the multiple combs of the OFC via a Mach-Zehnder modulator (MZM), and the received signal is loaded into another MZM. These two MZMs work at opposite quadrature bias points to reverse the phase of the received signal and the reference signal. After splitting and filtering with a dense wavelength division multiplexer, the reference modulation signals are injected into a multipath amplitude-delay matched link, where the amplitude and delay time are accurately controlled by several sets of optical variable attenuators and tunable delay lines. Both the inversion and amplitude-delay matching of the reference signals are realised in the optical domain, contributing to a broad bandwidth and high operational frequency. Experimental results show that the cancellation depth is greater than 45.9 dB for single-frequency signals, and 23.9 dB for signals with a bandwidth of 100 MHz in a setup with three self-interference paths. The proposed method is characterized by easy scalability, good flexibility, and low cost, making it suitable for complex multipath SIC in in-band full-duplex wireless systems.

A Doppler velocity simulation method based on serrodyne modulation is proposed to achieve the frequency shift from hundred hertz to megahertz. One sub-phase modulation (PM) in a dual-parallel dual-drive Mach–Zehnder modulator loads a sawtooth signal to achieve a small frequency shift of the optical carrier. The other three sub-PMs implement carrier-suppressed double-band modulation of the RF signal. The RF signal is directly coupled from the receiving antenna to the modulator’s RF port without any electrical devices like a 90° hybrid, which ensures a broad operational bandwidth of the system. After filtering out one of the RF modulation sidebands by an optical filter, Doppler frequency shifting (DFS) is realized through frequency beating. The half-wave voltage of modulators rapidly decreases at low frequency shifts, leading to an increase in spurious signals. In order to improve the spurious suppression ratio (SSR) of DFS, a digital pre-distortion compensation based on the measured half-wave voltage is implemented in the frequency domain. Experimental results show that SSRs are larger than 35 dB when frequency shifts range from 0.1 kHz to 1 MHz. The RF operation bandwidth covers 2–40 GHz. The effectiveness of a Doppler velocity simulator is evaluated, and the simulation velocity error is less than 0.06 km/h. The proposed method has potential applications in both broadband electronic warfare and traffic metering applications.

In distributed interferometric antenna arrays, accurate measurement and long-term stabilization of transmission delay are essential for coherent combining and accurate target localization. This paper presents a fiber-based delay measurement and stabilization system. The employed dual-tone probe enables accurate measurement of delay variations and the absolute delay simultaneously, while a phase-locked loop provides long-term delay stabilization. Experimental results demonstrate a delay measurement accuracy better than 20 fs and a stabilized delay fluctuation of 15.7 fs (standard deviation) over a 45 km fiber link for 3600 s. The proposed system realizes highly stable microwave transmission with accurately measured absolute delay, making it well-suited for coherent combining and localization in distributed antenna arrays.