Narrowband Radar Research Articles

High-speed multi-target detection with narrowband radar

High-speed multi-target detection is a challenging problem in radar applications. Typically, targets with high speed go through several range cells in the observation period, which makes it more difficult to obtain each target's power coherently accumulated for target detection. In this study, novel multi-target detection with a narrowband radar system is proposed. In order to remove range migration and obtain coherent integration of the target energy, the Keystone transform is applied to the moving targets. However, because of the high target velocity and the low radar pulse repetition frequency phase ambiguity will occur, so the range migration will not be corrected properly. Then the phase ambiguity function of the kth target is compensated, and the envelope of the kth target concentrates in a certain range cell. Following by frequency modulation rate search a quadratic phase term is compensated, and the signal energy is finally coherently accumulated by FT analysis. The target is detected if the ratio of peak value to noise is higher than a predetermined threshold. For target detection in low signal-to-noise ratio (SNR), the Clean technique is applied. The proposed algorithm is verified by simulation and raw radar data results.

Approximate Cramér–Rao bound on Doppler error in correlation-processing relatively narrowband noise radar

Limitations on accuracy of Doppler estimation in continuous-wave noise radar with correlation processing are studied. Second-order properties of output of the correlation receiver are evaluated and an approximate Cramér–Rao bound on errors of Doppler measurement is derived. The accuracy of Doppler measurements is found to be affected by the following factors: power spectral density of noise signal, frequency response of the low-pass filter in correlator, observation time, velocity of the target and signal to noise ratio. It is shown that the random nature of the transmitted signal induces additional fluctuations at the output of correlator which limit the accuracy even in the infinite signal to noise case. Qualitative extension of the results to a case covering multiple targets and clutter is made. It is argued that the performance will decrease and that increasing transmitted power may not provide significant improvement when clutter is present.

Phase-Coded Waveforms and Their Design

The design of radar waveforms has received considerable attention since the 1950s. In 1953, P.M. Woodward (1953; 1953) defined the narrowband radar ambiguity function or, simply, ambiguity function. It is a device formulated to describe the effects of range and Doppler on matched filter receivers. Woodward acknowledged the influence that Shannon's communication theory from 1948 had on his ideas; and he explained the relevance of ambiguity in radar signal processing, perhaps best conceived in terms of a form of the uncertainty principle (see the sections Motivation and Ambiguity Functions). However, in the 50 or so years since Woodward's book was published, radar signal processing has used the ambiguity function as an intricate and flexible tool in the design of waveforms to solve diverse problems in radar. In the process, substantial connections were established in mathematics, physics, and other areas of signal processing. As such, we are introducing two new methods, discussed in sections CAZAC Sequences and Aperiodic Simulations.

0mから測定可能な高精度狭帯域レーダ

0mから測定可能な高精度狭帯域レーダ

Senrad: an advanced wideband air-surveillance radar

The generic characteristics and performance of an experimental long-range air-surveillance radar, known at the Naval Research Laboratory as Senrad, is described. Its distinguishing feature is that it can operate with simultaneous transmissions over a very wide bandwidth-from 850 to 1400 MHz. The technology and type of experimental radar equipment employed are discussed and examples are given of its performance capabilities obtained by means of very wideband operation. The unusually wide bandwidth of this radar allows 1) improved detection and tracking performance because of the absence of the nulls that are common in the antenna elevation radiation-pattern of a single-frequency radar; 2) moving target indication (MTI) without loss of targets due to blind speeds and without the need for multiple PRFs (pulse repetition frequencies); 3) accurate height finding with a fan-beam radar by taking advantage of the multipath time difference as a function of target height; 4) a form of limited target recognition based on high range-resolution; and 5) a reduction of the effectiveness of electronic countermeasures that can seriously degrade more narrowband radars.

Doppler and acceleration tolerances of high-gain, wideband linear FM correlation sonars

An analysis is presented of the decorrelation effects of target velocity and acceleration on high-gain, wideband linear FM correlation sonars that the received signal against a family of velocity reference functions, each of which is a different time-compressed or -expanded replica of the transmitted signal. Such sonars are shown to have velocity (i.e., Doppler) and acceleration tolerances far different from that predicted by narrowband radar theory. Unlike the narrowband case, the wideband velocity tolerance may be quite small and is approximately independent of the carrier frequency and inversely proportional to the time-bandwidth product (TW). Narrowband radar-type calculations of velocity tolerance can give erroneous results far in excess of the true value. This is because the narrowband velocity tolerance is derived entirely on the basis of temporal overlap loss, whereas the actual tolerance depends primarily on the slope difference between the frequency-time sweeps of the received and reference signals. High acceleration tolerance, without separate acceleration processing channels, can be achieved by cross-correlating the acceleration return with a best match velocity reference function. The resultant wideband acceleration tolerance is approximately inversely proportional to WT2and better than the narrowband tolerance by a factor of 12 Q (Q = carrier frequency/bandwidth). This improvement arises because the wideband reference functions are able to partially compensate for the nonlinearity imparted to the transmitted frequency-time sweep by an accelerating target, whereas such compensation is not possible in narrowband systems employing carrier-shifted reference functions.