This paper presents an imaging technique using the MUSIC algorithm to localize cylindrical reflectors in cross-borehole radar arrangements. Tomographic measurement, in which a transmitting and a receiving antenna are individually moved in separate boreholes, can be considered as a combination of a transmitting and a receiving array. A decorrelation technique with the transmitting array, which has been proposed for imaging point reflectors, is applied for imaging cylindrical reflectors using the MUSIC algorithm. Simulated and experimental results are shown to verify the validity of this algorithm for cylindrical targets. We analyze the evaluation error caused by the increase in the radius of the cylinder.

This paper shows the applicability of the integral equation formulation of the measured equation of invariance (IE-MEI) to two-dimensional dielectric scatterers. That is, a relationship between the scattered electric and magnetic fields, which is derived from the new formulation of the IE-MEI, is applicable to lossless dielectric materials as well as perfect electric conductors (PEC). In addition, we show that the IE-MEI does not suffer from internal resonance problems. These two facts are validated by numerical examples for a circular cylinder and a square cylinder illuminated by Transverse Magnetic (TM) plane wave or a TM line source very close to the scatterers. The numerical results calculated by the IE-MEI agree well with the ones by moment methods that employ combined field formulations with exact boundary conditions.

This paper describes the advanced underground radar techniques developed by authors using signal processing to noise and clutter rejection, to pulse compression, to antenna beam compression and to target's identification. Underground radars which were developed and are developing in Japan are also introduced.

The application of subsurface radar using electromagnetic waves in the VHF band is wide and includes surveying voids under the ground and archaeological prospecting. To achieve a wider application range, the survey depth must be deeper. In this paper, a method of pulse compression using a chirp signal as one of the methods to fulfill this requirement is described, and its advantages and problems are discussed. First, a delay correlation method is proposed as a processing method of pulse compression. It converts RF band chirp signal directly into a pulse. Moreover, the method improves the S/N ratio by over 40 dB compared with conventional pulse radar. Therefore, it has the same detection ability as conventional pulse radar even though it uses less transmitting power. Next, the influences of RF amplifier saturation and underground propagation characteristics on the chirp signal are discussed; both are shown to have little influence on the detection ability of the method.

A method to measure the displacement from the phase rotation of the Doppler signal including the displacement information of the moving body is proposed, where the displacement resolution can be improved 4 times by making the phase rotation faster. Furthermore, this test system is applied in clinical use. The test system is built up by using a two-phase microwave Doppler sensor covering a 10GHz band, where the Doppler frequency is multiplied 4 times by signal processing. Thus, the resolution is improved from a conventional 12.6mm (in case of 11.9GHz) to 3.15mm, and practical utilization has been attained. The microwave Doppler radar system described in this paper is adequate for the displacement measurement for a relatively fast moving body. As a medical sensor for clinical use, measurement examples of head movement in a vestibule examination (vestibule oculomotor reflexive inspection) and finger movement in a cerebellum function test are given. Furthermore by using two sets of this Doppler radar system, a 2-dimensional measurement of head movement is possible.

The use of a chirp signal is one of the methods to expand the detection range in subsurface radar. However, the presence of time-sidelobes after a conventional pulse-compression makes the detection range degraded because weak signals from underground objects are covered with a large time-sidelobe due to a ground surface reflection. In this paper, we propose a new pulse compression subsurface radar using a short chirp signal in which the echoes from the ground surface and the object are not overlapped. We show that the short chirp signal can improve the detection ability compared with a conventional chirp signal and examine the influence that the decreases of the signal duration and the compression ratio exert on the detection range. By the new pulse compression subsurface radar, the steel pipes buried down to 5 m in depth can be detected.

The size and weight of marine pulse radar systems must be limited in order to mount them on board boats. However, the azimuthal resolution of a marine radar with a small antenna is degraded by the antenna beam width. It is desirable to use signal processing techniques to increase both the azimuthal resolution and the range resolution of such systems without changing their external configuration. This paper introduces a resolution enhancement method based on deconvolution, which is a kind of inversion. The frequency domain deconvolution method is described first. The effectiveness of the proposed method is shown by simulation. Then, an example of resolution enhancement processing is applied to a pulse radar. The results of practical experiments show that this method is a promising way of upgrading radars by simply processing the received signals.