HF Distributed Network Radar System: Theory And Implementation

High Frequency Ground Wave Radars (HFGWR) are advanced devices developed in recent 40 years, which can be used to measure the ocean surface dynamic parameters such as wind, wave and current and detect the moving targets on the sea surface with relatively low speeds. HFGWR has the advantages of wide coverage, high accuracy, low costs, immunity to influence of weather, real-time measurement and so on, and can be widely used in the fields of ocean development and military early warning. However, there are many problems eager to be solved in application:(1) RCS of the detected target is in the resonance region, where the RCS varies a lot with the radar frequency and target attitude. The difference between the maximum RCS and the minimum one is about several tens dB, which makes the target detection performance of HFGWR very unstable; (2) when the Doppler frequency due to the radial velocity of target movement is comparable to the Bragg peak frequency, the target will be submerged by the strong sea echo; (3) current HFGWRs which take the warning responsibility work continuously in exclusive bands, which makes the development and application of HFGWRs which work in a nearly saturated spectrum very difficult; (4) The electromagnetic waves radiated by HFGWRs propagate along the ground surface in the ideal state, but in application there is always some energy radiated toward the sky. This part of energy propagates in sky mode, and returns to radar after scattered by ionosphere, which generates the severe ionospheric clutter. very flexible, which makes the distributed networking systems have stronger ability of anti-scouting, anti-inference and anti-destruction in the electronic wars.This paper researches several key problems of distributed networking radars. The main content is as follows:1. The architecture of distributed networking radar system is designed on the basis of monostatic HFGWR. Much attention is paid to the technology of synchronizing different radar stations. This paper takes advantage of GPS signals in keeping long-time, highly accurate phase synchronization between all the transmitters and receivers in the system.2. The principles of waveform parameters design of distributed networking radar are concluded based on the theory of OFDM. The design method prevents the mutual inference between all the transmitters and receivers working at the same spectra, and enables the receiver to unbiasly separate echoes transmitted by different trans-mitters.3. The signal processing method of distributed networking radar systems is addressed. The receivers in the distributed networking system need to extract useful infor-mation from echoes produced by multiple transmitting systems and performs data fusion. This paper concentrates on the method of extracting ocean surface current in the bistatic mode.4. There are many users in the HF spectrum. In order to guarantee the performance Considering these problems, this paper proposes the concept of distributed net-working radar. A distributed networking radar system consists of multiple transmitting systems with the same architecture and multiple receiving systems with the same ar-chitecture. The transmitting and receiving systems can be located in the same station, which form a monostatic radar, or located in a large distance, which forms a bistatic radar. The echoes coming from any transmitting system in the network can be received by multiple receiving systems, and any receiving system can utilize echoes from multiple transmitting systems. The whole network forms a distributed phase-parametric radar system. A networking radar containing M transmitting systems and N receiving sys-tems can form M x N monostatic or bistatic radars. The number of equivalent radar systems increases in geometric progression without extra hardware costs.Compared to the traditional HFGWR systems, the distributed networking radar systems have many advantages, which are listed as follows:(1) a distributed networking radar can observe a target from multiple view angles, which makes the target detection performance immune to the changes of target attitude and velocity; (2) the target echoes corresponding to different transmitting systems are in different range bins in the receiving systems, which prevents the occurrence of the situation that the radar cannot detect the target because the ionospheric clutter and the target echo are in the same range bin; (3) the distributed networking radar can obtain more target information without extra hardware costs, and so owns the potential of improving the coverage and measurement accuracy; (4) the configuration of transmitting and receiving systems are of radar, we should put the radar in a relatively quiet spectra. Based on the theory of cognitive radio, this paper proposes the spectrum watching scheme of distributed networking radar, and realize this function in a monostatic radar.