Differentiator-Based Photonic Instantaneous Frequency Measurement for Radar Warning Receiver

Radar warning receiver (RWR) plays a significant role in detecting weapon radar. The instantaneous frequency measurement (IFM) section with fast measuring response, large measurement bandwidth, moderate accuracy, and sensitivity is important for an all-threat-covered RWR. In this IFM method, a phase modulator (PM) in combination with a differentiation structure is employed to get rid of the DC drifting and makes the power response is a strict monotonous function of the input frequency. Therefore, the unambiguous determination can be made in a very large range, which guarantees the fast measuring response. According to the theoretical analysis, a strict monotonous amplitude comparison function (ACF) with the covering range higher than 40 GHz can be achieved. Besides, no filter or dispersion elements (DE) such as optical fibers are required, which makes the structure be very concise to meet the potential of integrating in any receiving systems. Due to the limit operation range of the PM, only the range from 0.1 GHz to 25 GHz is demonstrated. The measurement error can be lower than 3%. Especially, benefited by the balance photo-diode (BPD), the sensitivity is good without any noise cancellation processing. The error of lower than 10% will be promised when the RF power level is -40 dBm.