Measurements by incoherent scatter radars (ISRs) play very important roles in modern ionospheric and geospace studies. The ionospheric parameters are normally extracted from echo signals of ISR using nonlinear iteration algorithms. The processing speed and accuracy significantly rely on the iteration algorithm. The Levenberg–Marquardt (LM) method is a widely used algorithm for nonlinear iteration in modern ISR data processing. In the present letter, a new iteration algorithm, which is the so-called dog leg (DL) method, was introduced. Comparing with the LM method, the step size for the iteration with the DL method is not fixed. The iteration step size for the DL method keeps being adjusted in accordance with the trust region during the iteration process. The performance of the DL method was compared with that of the LM method using the simulation tests of ionospheric parameter extraction from ISR power spectra. The results showed that the DL method has better accuracy and iteration speed than that of the LM method. In addition, the error of the DL method is more stable than that of the LM method. Moreover, the DL method is more convergent than the LM method, which helps avoid the lack of ionospheric parameter due to the divergence of iteration with the LM method. Therefore, the DL method could be a more appropriate iteration algorithm for data processing of ISR measurements.

The performance of an antenna is impacted by the electromagnetic characteristics of the media surrounding the antenna. Most antennas work in neutral air. However, the surrounding media for the spaceborne antenna is space plasma, which is dispersive dielectric media. It could significantly change the performance of a spaceborne broadband antenna. In the present study, a broadband dipole antenna was taken for example to investigate the impacts led by space plasma. The working parameters in neutral air and space plasma were compared. The space plasma taken into account in the present study was supposed to be time-varying dispersive media. The study revealed that the space plasma could significantly influence the antenna voltage standing wave ratio (VSWR) and the antenna impedance. For those spaceborne radars working in active mode, there was a minimum detection range which makes it hard to detect the plasma area within the range. Since antenna working parameters vary with the variation of the surrounding plasma, a method to sensing the local plasma electron density based on VSWR of spaceborne broadband antennas was proposed. The method makes the antenna system work as a plasma sensor and could complement the radar minimum detection range. The results show the good performance of the method.

The incoherent scattering radar (ISR) is the only ground device on Earth that can detect the parameters of the ionospheric plasma because of its large detection range, high detection accuracy, and high spatial resolution. The prototype ISR system of Nanchang University has been completed now. Compared to the existing ISR systems in the world, which have a high radio frequency (RF) power and antenna array, high power consumption, expensive equipment operation, and maintenance costs, the radar has the advantages of low power consumption, low cost, and modularity. This radar system uses novel techniques of software-defined radio (SDR) and active phased array antennas to detect changes in the ionosphere. This article introduces the system design and antenna array of the software-defined radar prototype. The built-in radar transmitting and receiving equipment and specific radar parameters are described in detail and the radar detection results under different detection conditions are presented.

An incoherent scatter radar (ISR) simulation system based on matrix laboratory (MATLAB) platform was introduced in this letter. The simulation system adopts a modular design concept and establishes a complete working link for ISRs according to the real ISRs principle of operation. Every ISR working stage that could have an effect on the ionosphere detection performance is simulated, such as signal transmission, ionosphere model, ISR spectrum, signal reception, and ionosphere parameters' extraction. The simulation platform can be used to perform incoherent scatter spectrum modeling and ionosphere parameters' extraction in various modes. In particular, the target ionosphere is modeled with the International Reference Ionosphere (IRI) model. An example is demonstrated in this letter, which shows that the simulation system could be helpful for the early design of an ISR and for designing the operation modes for ISRs. Furthermore, the simulation system has the potential to be optimized and upgraded to improve its efficiency and accuracy.

Incoherent scatter radar can measure a variety of ionospheric plasma parameters, but the associated radar echo signals are very weak. To extract the effective ionospheric parameters, complex coding schemes are used with modern incoherent scatter measurements. Long pulse code, Barker code, alternating code, and alternating code modulated by Barker code (i.e., composite code) are some of the more frequently used coding systems. In practice, ionospheric signals are easily disturbed by external factors, and thus, the echo signals contain substantial amounts of noise. Therefore, it is important to investigate the antinoise performances of these codes. According to the basic theory of the ambiguity function, simulations of the 2-D ambiguity functions of these four codes were conducted. In addition, waveform processing simulations were performed for the four codes. According to this letter, the composite code exhibits a greater range of detection, a higher range resolution, and better antinoise performance than the other three types of codes and is more conducive to the detection of weak signals.

Ionospheric sounding is a technique that provides real-time data on high-frequency ionospheric-dependent radio propagation. This letter presents a Universal Software Radio Peripheral-based ionospheric sounding radar, which relies on a basic system consisting of a synchronized transmitter and receiver. The radar has the advantages of miniaturization, modularization, low power, and low cost. The three most significant features of the radar system are that it is software-defined and universal platform-based and that it has low transmitting power. This novel software-defined vertical-incidence radar system can probe the ionosphere and obtain real-time plasma parameters according to the simulation. Ionograms that directly express probe results are generated by MATLAB after data processing and simulation. Successful development of such an ionospheric sounding software radar will allow universalization and miniaturization of an ionosonde radar system. This letter introduces the implementation of the novel ionospheric sounding radar.

In this letter, a new high-frequency (HF) skywave multistatic radar that is used for ionospheric sensing and aircraft detection is presented. With multiple receiving sites, this radar can detect the aircraft in much larger surveillance with high probability and can obtain the characteristics of many ionospheric paths simultaneously. In addition, this radar adopts a binary-phase-coded continuous waveform to achieve a high Doppler resolution, a large signal processing gain, and a low probability of interception. Details of the system configuration, the ambiguity function of the sounding waveform, and the signal processing algorithm are described. The experimental results show that backscatter ionograms and oblique ionograms can be simultaneously obtained and that the aircraft with different flying conditions can be clearly detected with an HF skywave multistatic experimental radar.

Incoherent scatter radar (ISR) is the only ground-based instrument that can detect space plasma parameters from tens to thousands of kilometers above the earth. The Prototype Incoherent Scatter Radar System of Nanchang University, a versatile space detection radar, will be built at Nanchang University to detect the ionosphere over China in the end of 2013. Software-defined radio (SDR)-based and active phased antenna array are the two most significant features of this radar system. It can probe real time plasma parameters in the altitude range of the ionosphere (80-400 km) according to simulation. The novel ISR introduced in this letter has the advantages of low power, low cost, and modularization. When properly configurated, this system can also carry out coherent scatter detection and wind profile detection. Successful development of such an ISR will resolve the problem of continuous detection of ionospheric electric field and other parameters. This letter introduces the design of this software defined ISR prototype system.

Vertical ionograms suffer from artifacts and distortion due to other users of the high-frequency channel and the ionosphere. The traces of each layer have variable shapes, so the automatic scaling of the vertical ionograms is rather complicated. New algorithms for signal identification and trace extraction are developed to support automatic scaling. Different features of the signals, such as signal-to-noise ratio, Doppler shift, and virtual height, are converted to certainty factors and combined to identify signals. Kalman filtering, which is widely used in trace extracting, is introduced to form traces and separate the ordinary trace and the extraordinary trace. These algorithms are effective without using information on the wave polarization and can be applied to the ionograms recorded by single-antenna systems.

Monostatic radar, whether using interpulse or intrapulse coded pulse trains, will suffer from the blind zones caused by eclipsing. This letter proposes a novel biphase interpulse coded radar waveform using diverse Pulse Repetition Intervals (PRIs) instead of a consistent PRI within each coherent processing interval (CPI). This waveform can achieve long unambiguous range, high-range resolution and high Doppler resolution without blind zones, and is specially suitable for a monostatic ionosonde.

Vertical-incidence (VI) ionosonde is a kind of high-frequency radar. The sounding waveform is an important characteristic for measurement by ionosondes. This letter compares, both theoretically and practically, four different biphase-coded pulse compression radar waveforms which can be employed in the Wuhan Ionosphere Comprehensive Sounding System at VI sounding, including interpulse-coded m sequence, interpulse-coded Wolfman-Goutelard sequence, intrapulse-coded Barker sequence, and intrapulse-coded complementary sequence pairs. The experimental results demonstrate that among the four waveforms, the intraphase-coded complementary-sequence pairs have the best performance.