Time domain ultra-wideband TEM horn antenna for ground penetrating radar
Technical Field
The invention relates to the technical field of radars, in particular to a time domain ultra wide band TEM horn antenna for a ground penetrating radar.
Background
Ground Penetrating Radar (GPR) is a physical method of rapid, efficient, non-destructive detection. The ground penetrating radar transmits high-frequency electromagnetic waves by utilizing one transmitting antenna, receives reflected waves from an underground target medium interface by utilizing the other antenna, and then analyzes and processes the acquired data to further obtain the distribution state of the underground target. The radar antenna is the most critical component in the ground penetrating radar system, and the performance of the antenna greatly influences the performance of the ground penetrating radar and the depth and detection precision of target detection. The conventional ground penetrating radar antenna mainly comprises a butterfly antenna, is narrow in bandwidth, low in center frequency, limited in emission energy and low in efficiency, is difficult to meet the fine detection requirement in a larger distance range, has limited bandwidth and poorer signal resolution capability, has a relatively lower signal-to-noise ratio, is larger in size, and is not beneficial to the engineering application of a radar system.
In order to harmonize the depth of detection and resolution, a new ground penetrating radar antenna needs to be developed. The TEM horn antenna has the advantages of high gain, ultra wide band, no dispersion, simple feed structure, small pulse distortion and the like, and is widely researched in the field of ground penetrating radar.
Disclosure of Invention
Technical problem to be solved
In view of the technical problems, the invention provides a time domain ultra-wideband TEM horn antenna for a ground penetrating radar, which has the advantages of small overall size, high gain, good waveform fidelity, bandwidth reaching 0.9-12.6 GHz, good broadband characteristic, ultra-wideband characteristic and capability of meeting the requirements of a system on detection distance and precision.
(II) technical scheme
According to one aspect of the invention, a time domain ultra wide band TEM horn antenna for a ground penetrating radar is provided, comprising:
the radiation arm comprises an upper radiation arm and a lower radiation arm symmetrically arranged with the upper radiation arm; the outlines of the upper and lower radiation arms are in a parabolic shape or an exponential function curve shape;
the plurality of extension surfaces are respectively arranged at one ends of the upper radiation arm and the lower radiation arm;
and the feeding balun is arranged at the other ends of the upper radiating arm and the lower radiating arm and is used for coaxial feeding.
In some embodiments, the exponential function is an exponential asymptotic function satisfying the following equation:
in the formula, a, b and c are constants; x and y represent the abscissa and the ordinate, respectively.
In some embodiments, the feed balun includes:
a coaxial line structure;
the first radiation piece is connected with the coaxial line structure; the first radiation piece comprises a first upper radiation piece and a first lower radiation piece; and
the second radiation piece comprises a second upper radiation piece and a second lower radiation piece;
the tail end of the first upper radiation piece is connected with the second upper radiation piece, and the tail end of the first lower radiation piece is connected with the second lower radiation piece; the tail end of the second upper radiation piece is connected with the upper radiation arm, and the tail end of the second lower radiation piece is connected with the lower radiation arm.
In some embodiments, the first upper radiating patch is parallel to the first lower radiating patch, the first upper radiating patch is connected to the feed point at the inner end of the coaxial line and used for radiating electromagnetic waves, and the first lower radiating patch is connected to the outer end of the coaxial line and used for grounding, so as to realize the unbalanced-to-balanced conversion from the coaxial line to the antenna.
In some embodiments, the extension surface is triangular for extending a current distribution path of the radiating arm.
In some embodiments, further comprising: the shielding cavity is of a hollow trapezoidal platform structure with three open sides; the shielding cavity comprises a bottom surface and two side surfaces which are respectively connected with two ends of the bottom surface; the feed balun is accommodated in the shielding cavity, and the radiation arm is at least partially accommodated in the shielding cavity.
In some embodiments, the radiating arm and the extension face together form a radiator of the antenna, and the space between the radiator and the shielding cavity is filled with porous foam.
In some embodiments, further comprising: and the loading resistors are respectively arranged at the tail ends of the extension surfaces and are connected with the extension surfaces of the antennas and the side surfaces of the shielding cavities.
In some embodiments, the plurality of extending surfaces includes a first extending surface, a second extending surface, a third extending surface, and a fourth extending surface; the first extension surface and the second extension surface are arranged at the tail end of the upper radiating arm of the antenna in parallel, the third extension surface and the fourth extension surface are arranged at the tail end of the lower radiating arm of the antenna in parallel, the upper radiating arm and the lower radiating arm are identical in structure, and the four extension surfaces are identical in structure.
In some embodiments, the plurality of loading resistors comprises a first loading resistor, a second loading resistor, a third loading resistor, and a fourth loading resistor; the first loading resistor and the second loading resistor are arranged at the tail ends of a first extension surface and a second extension surface of the antenna in parallel, the first loading resistor is connected with the first extension surface and the side surface of the shielding cavity, and the second loading resistor is connected with the second extension surface and the side surface of the shielding cavity; the third loading resistor and the fourth loading resistor are arranged at a third extending surface and a fourth extending surface of the antenna in parallel, the third loading resistor is connected with the third extending surface and the side surface of the shielding cavity, and the fourth loading resistor is connected with the fourth extending surface and the side surface of the shielding cavity; the four loading resistors have the same structure.
(III) advantageous effects
According to the technical scheme, the time domain ultra-wideband TEM horn antenna for the ground penetrating radar has at least one of the following beneficial effects:
(1) the parabolic or exponential function curve type antenna radiation arm is adopted, the whole size of the antenna is small, the gain is high, the waveform fidelity is good, the broadband characteristic is good, the ultra-wideband characteristic is achieved, and the requirements of a system on the detection distance and the precision are met.
(2) The triangular extension surface is loaded at the tail end of the antenna, so that the current distribution path of the radiation sheet can be prolonged, and the tail end of the extension surface is sharpened, so that the residual current at the tail end of the antenna arm is better concentrated.
(3) The feed balun structure is adopted, the first upper radiation piece and the first lower radiation piece are parallel, the first lower radiation piece is connected with the outer end of the coaxial line and used for being grounded so as to realize the conversion from the unbalance to the balance of the coaxial line and the antenna, and the first upper radiation piece is connected with the feed position at the inner end of the coaxial line and used for radiating electromagnetic waves.
(4) The antenna arm and the extension surface form a radiator which is connected with the shielding cavity through the loading resistor, and the antenna and the shielding cavity are filled with porous foam, so that the fixing is convenient.
Drawings
Fig. 1 is a schematic diagram of an antenna structure according to an embodiment of the invention.
Fig. 2 is a schematic diagram of an antenna radiation arm structure according to an embodiment of the invention.
Fig. 3(a) is a top view of an antenna radiation arm according to an embodiment of the present invention.
Fig. 3(b) is a side view of an antenna radiating arm according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of an antenna feed balun structure according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of antenna simulation and actual measurement results according to an embodiment of the invention.
Fig. 6 is a waveform diagram of an antenna measurement according to an embodiment of the invention.
Detailed Description
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.
It should be noted that in the drawings or description, the same drawing reference numerals are used for similar or identical parts. Implementations not depicted or described in the drawings are of a form known to those of ordinary skill in the art. Additionally, while exemplifications of parameters including particular values may be provided herein, it is to be understood that the parameters need not be exactly equal to the respective values, but may be approximated to the respective values within acceptable error margins or design constraints. In addition, directional terms such as "upper", "lower", "front", "rear", "left", "right", and the like, referred to in the following embodiments, are directions only referring to the drawings. Accordingly, the directional terminology is used for purposes of illustration and is in no way limiting.
In one exemplary embodiment of the invention, a time domain ultra-wideband TEM horn antenna for a ground penetrating radar is provided. Fig. 1 is a schematic diagram of an antenna structure according to an embodiment of the invention. As shown in fig. 1, the time domain ultra wide band TEM horn antenna for ground penetrating radar of the present embodiment includes:
a radiating arm comprising an upper radiating arm 2; the lower radiation arm 3 is symmetrically arranged with the upper radiation arm; the outlines of the upper and lower radiation arms are in a parabolic shape or an exponential function curve shape;
a plurality of extension surfaces 4A, 4B, 5A, 5B respectively provided at one end of the radiation arm;
and the feeding balun 1 is arranged at the other ends of the upper radiation arm and the lower radiation arm and is used for coaxial feeding. The radiating arm and the extension surface jointly form a radiator of the antenna; and the radiator and the shielding cavity are filled with porous foam, so that the radiator and the shielding cavity are convenient to fix.
The extension surface is preferably triangular for extending the current distribution path of the radiating arm, while the residual current at the end of the antenna arm is better concentrated by sharpening the end of the extension surface. With continued reference to fig. 1, the antenna may further include:
the shielding cavity 8 is of a hollow trapezoidal platform structure with three open sides; and
the loading resistors 6A, 6B, 7A and 7B are respectively arranged at the tail ends of the extension surfaces and are connected with the extension surfaces of the antennas and the shielding cavities;
the shielding cavity 8 comprises a bottom surface and two side surfaces respectively connected with two ends of the bottom surface; the feed balun and the antenna body are accommodated in the shielding cavity.
The shielding cavity structure is adopted, so that the interference of an external electromagnetic field on the antenna can be shielded, and the performance of the antenna is improved.
Preferably, the number of the extension surfaces is four, and the extension surfaces are a first extension surface 4A, a second extension surface 4B, a third extension surface 5A and a fourth extension surface 5B; the first extension surface and the second extension surface are arranged at the tail end of the upper radiating arm 2 of the antenna in parallel, and the third extension surface and the fourth extension surface are arranged at the tail end of the lower radiating arm 3 of the antenna in parallel. The upper and lower radiating arms have the same structure; the four extension surfaces have the same structure.
The number of the loading resistors can be four, and the four loading resistors are respectively a first loading resistor 6A, a second loading resistor 6B, a third loading resistor 7A and a fourth loading resistor 7B; the first loading resistor and the second loading resistor are arranged on the extending surfaces 4A and 4B of the end part of the radiation arm 2 on the antenna in parallel, the first loading resistor is connected with the first extending surface and the end part of the side surface of the shielding cavity, and the second loading resistor is connected with the second extending surface and the end part of the side surface of the shielding cavity; the third loading resistor and the fourth loading resistor are arranged at the extending surfaces 5A and 5B of the end part of the lower radiating arm 3 of the antenna in parallel, the third loading resistor is connected with the third extending surface and the end part of the side surface of the shielding cavity, and the fourth loading resistor is connected with the fourth extending surface and the end part of the side surface of the shielding cavity; the four loading resistors have the same structure.
The antenna arm of an embodiment of the present invention is described in detail below with reference to fig. 2-3. Fig. 2 is a schematic diagram of an antenna arm structure according to an embodiment of the invention. Fig. 3(a) is a top view of an antenna arm according to an embodiment of the invention. Fig. 3(b) is a side view of an antenna arm according to an embodiment of the present invention. As shown in fig. 2-3, the width dimension of the antenna is preferably 150mm, W1; the length of the antenna is L2-102 mm; the height dimension of the antenna is d 1-150 mm; the height dimension between the upper antenna arm and the lower antenna arm at the feeding position is d 2-2.6 mm; the initial maximum width w2 of the feed balun lower radiation piece is 30 mm; the initial minimum width w3 of the radiation patch on the feed balun is 5 mm; the maximum width w4 of the feed balun terminal is 24 mm; the middle end width w5 of the feed balun is 12 mm; the height d5 of the middle end of the feed balun is 2.6 mm; the height d4 of the feed balun terminal is 3.4 mm; the whole radiating arm gradually expands in the form of an exponential function curve, the front part of the radiating arm changes smoothly, and the rear part of the radiating arm changes greatly so as to reduce reflection caused by impedance gradual change.
Preferably, the exponential function is an exponential asymptotic function, and satisfies the following formula (1):
in the formula, a, b and c are constants; t is an independent variable, x and y are dependent variables, and x and y represent an abscissa and an ordinate; specifically, a may be 46, b may be 200, and c may be-0.32.
Fig. 4 is a schematic diagram of a feeding balun structure according to an embodiment of the present invention. As shown in fig. 4, the antenna feed balun includes:
a coaxial line structure;
the first radiation piece is connected with the coaxial line structure; the first radiation piece comprises a first upper radiation piece and a first lower radiation piece which are arranged in parallel;
the second radiation piece comprises a second upper radiation piece and a second lower radiation piece which are arranged in an open mode;
the tail end of the first upper radiation piece is connected with the second upper radiation piece, and the tail end of the first lower radiation piece is connected with the second lower radiation piece; the second upper radiation piece is connected with the upper radiation arm, and the second lower radiation piece is connected with the lower radiation arm.
The first upper radiating piece and the first lower radiating piece are parallel to each other as much as possible, similar to microstrip gradual change, the first lower radiating piece is connected with the outer end of the coaxial line and used for being grounded so as to realize the conversion from the unbalance to the balance of the coaxial line and the antenna, and the first upper radiating piece is connected with the feed part at the inner end of the coaxial line and used for radiating electromagnetic waves.
Fig. 5 is a graph of measured and simulated voltage standing wave ratios of an ultra-wideband TEM horn antenna according to an embodiment of the invention. As shown in FIG. 5, the voltage standing wave ratio is <2 in the frequency band of 0.9 to 12.6 GHz. Wherein, the voltage standing wave ratio is converted into return loss, namely when the standing wave coefficient is 2, the return loss is about-9.6 dB. According to the application of the ordinary highway detection ground penetrating radar antenna S11< -10 >, the antenna can well meet the requirements within the frequency band range of 0.9-12.6 GHz.
Fig. 6 is a waveform diagram actually measured by the antenna according to the embodiment of the present invention, specifically, a waveform result diagram obtained by performing time domain waveform measurement on the TEM horn antenna by using a signal generator, a GEOZONDAS 2GHz pulse source, and a Tektronix oscilloscope. As shown in fig. 6, the received echo signal has small ringing and good waveform fidelity, and can meet the system requirements for the highway ground penetrating radar.
In conclusion, the time domain ultra-wideband TEM horn antenna for the ground penetrating radar has the advantages of small overall size, high gain, good waveform fidelity, and good broadband characteristic, the bandwidth reaches 0.9-12.6 GHz, and the ultra-wideband antenna has the characteristics of ultra-wideband and meets the requirements of a system on detection distance and precision.
Up to this point, the present embodiment has been described in detail with reference to the accompanying drawings. From the above description, those skilled in the art should clearly recognize that the time-domain ultra-wideband TEM horn antenna for ground penetrating radar of the present invention.
Furthermore, the above definitions of the various elements and methods are not limited to the various specific structures, shapes or approaches mentioned in the examples, which may be easily modified or substituted by one of ordinary skill in the art:
besides the triangle, the extension surface can be in other shapes such as rectangle, semicircle and the like, and the invention can be realized.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.