CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC § 119 and the Paris Convention to United Kingdom Patent Application No. 1717995.3 filed on Oct. 31, 2017.

TECHNICAL FIELD

The disclosure relates to the field of radar systems, particularly for compact, close range applications. One application would be ground penetration radar in the context of a machine work tool such as an excavator bucket.

BACKGROUND

Radar systems that detect the presence of objects in an environment are well known, including ground penetrating radar systems. The majority of such systems employ a pulsed radar technique, such that they transmit a train of short pulses (impulses) of electromagnetic energy with a high peak power (e.g. of the order of tens of kilowatts). The pulse energy is reflected by dielectric discontinuities such that the radar receives echoes in one to one correspondence with the transmitted pulses. This energy is reflected by dielectric discontinuities and received by the radar to produce a profile of the subsurface objects. This allows a profile of the reflecting objects to be produced. Since the time intervals involved are very short (typically sub-nanosecond), the sampling of the echoes must be stroboscopic. To obtain high resolutions, such systems require large instantaneous bandwidth and high peak power. This results in a wastage of energy since the interval of echo delay must be visited sequentially, whereas each transmission penetrates and excites echoes from the entire delay space.

Stepped frequency radar systems overcome many of the issues just described in relation to impulse radar systems. In particular, the energy efficiency of a stepped radar frequency system is much higher than that of a pulsed radar system. However, stepped frequency radar systems tend not to be employed in small scale, low cost radar systems because of difficulties in implementation, generally resulting in higher cost.

There are two approaches to stepped frequency radar systems, homodyne and heterodyne. Homodyne systems are simple to implement but require detection of signals at DC with competition against flicker noise and DC drift. Heterodyne systems require use of a sinusoidal carrier mixed to an intermediate frequency. This necessitates phase coherence between the transmitted and received signals which, in turn, requires a second receiver to sample the outgoing signal. This arrangement, however, introduces substantial complexity because of the need to match the two receivers accurately.

Digital frequency generation (Direct Digital Synthesis (DDS)) is not capable of operating directly at the frequencies required for a ground penetrating radar and requires at least frequency doubling, which is costly.

SUMMARY OF THE DISCLOSURE

Against this background there is provided a radar system in accordance with claim1.

The use of a direct digital synthesiser to generate an intermediate frequency (I.F.) off-set frequency; an up-converter comprising a quadrature mixer, single-side mixer or complex mixer to add the off-set frequency to the transmitted frequency; and a down-converter in the receive path driven by the off-set frequency as a local oscillator, enables the received information to be transferred to the I.F. frequency. This in turn can be sampled synchronously in such a way as to provide a complex data stream carrying amplitude and phase information. In this way, there is no need for a second receiver to recover the transmitted phase since phase coherence is intrinsic to the scheme. Accordingly, the system is implementable with only a single transmit channel and a single receive channel.

Furthermore, the radar system is implementable using a single analogue printed circuit board (PCB) and a single digital PCB. Moreover, the low bandwidth achieved using low frequency I.F. reduces the sampling frequency required in digitising so that the data transfer between the analogue and digital PCBs is achievable via the serial programmable interface (SPI) of the digital PCB. This has a beneficial impact on cost since the need for custom interface circuitry is removed.

Accordingly, the radar system of the present disclosure is low power, low data bandwidth and low cost, while achieving a high measurement bandwidth at radio frequency (R.F.).

