Time sharing type multi-beam radar apparatus having alternately arranged transmitting antennas and receiving antennas

[0002] 1. Field of the Invention

[0003] The present invention relates to a time sharing type multi-beam radar apparatus.

[0004] 2. Description of the Related Art

[0005] Time sharing type multi-beam radar apparatuses using microwaves and millimeter waves have been mounted on vehicles to obtain an azimuth angle and distance of a near object.

[0006] A prior art time sharing type multi-beam radar apparatus is constructed by a plurality of transmitting/receiving antennas each connected to one transmitter, one receiver and one diplexer such as one circulator (see JP-A-6-242230, JP-A-7-5252 & JP-A-8-262133). In this case, each of the transmitting/receiving antennas has a transmitting antenna pattern and a receiving antenna pattern the same as the transmitting antenna pattern, so that a transmitting/receiving operation is carried out by a mixed antenna pattern of the transmitting antenna pattern and the receiving antenna pattern. Therefore, if the number of the transmitting/receiving antennas if four, the number of mixed antenna patterns is four.

[0007] In the above-described prior art time sharing type multi-beam radar apparatus, however, in order to enhance the detection accuracy, the number of transmitting/receiving antennas needs to be increased, which would increase the manufacturing cost. In addition, if the number of transmitting/receiving antennas is increased, the side lobe characteristics are deteriorated, which deteriorates the antenna gain. As a result, the detection accuracy cannot be enhanced.

[0008] It is an object of the present invention to provide a time sharing type multi-beam radar apparatus capable of enhancing the detection accuracy without increasing the manufacturing cost.

[0009] According to the present invention, in a time sharing type multi-beam radar apparatus, a plurality of transmitting antennas are arranged in a first row, and each of the transmitting antennas has a first antenna pattern. Also, a plurality of receiving antennas are arranged in a second row in parallel with the first row, and each of the receiving antennas has a second antenna pattern. The first and second antenna patterns adjacent to each other spatially and partly overlap each other.

[0010] Thus, if the number of transmitting antennas if four and the number of receiving antennas is four, which correspond to the case where the number of transmitting/receiving antennas is four, the number of mixed antenna patterns is seven, thus substantially decreasing the number of antennas. Also, since the side lobe characteristics are improved, the antenna gain can be enhanced, which would enhance the detection accuracy.

[0011] The present invention will be more clearly understood from the description set forth below, with reference to the accompanying drawings, wherein:

[0012] FIG. 1 is a block diagram illustrating an embodiment of the time sharing type multi-beam radar apparatus according to the present invention;

[0013] FIG. 2 is a timing diagram for explaining the operation of the apparatus of FIG. 1;

[0014] FIG. 3 is a timing diagram showing examples of a transmitting radio frequency (RF) signal, a received RF signal and a beat signal of FIG. 1;

[0015] FIG. 4 is a diagram for explaining a mixed antenna pattern obtained by an antenna pattern of one of the transmitting antennas and its adjacent receiving antenna of FIG. 1;

[0016] FIG. 5 is a diagram for explaining a mixed antenna pattern in the prior art time sharing type multi-beam radar apparatus;

[0017] FIG. 6 is a diagram showing examples of the transmitting antenna pattern, the receive antenna pattern and the mixed antenna pattern of FIG. 4;

[0018] FIG. 7 is a diagram showing the relationship between the antenna spacing and the side lobe characteristics of FIG. 6;

[0019] FIG. 8 is a diagram for showing the antenna patterns of the apparatus of FIG. 1; and

[0020] FIGS. 9, 10, 11 and 12 are diagrams showing the arrangement of the antennas of FIG. 1.

[0021] In FIG. 1, which illustrates an embodiment of the time sharing type multi-beam radar apparatus according to the present invention, an antenna section 10 is constructed by four transmitting antennas 11a, 11b, 11cand 11dand receiving antennas 12a, 12b, 12cand 12dalternately with the transmitting antennas 11a, 11b, 11cand 11d. The antennas 11athrough 11dand 12athrough 12dare arranged horizontally and substantially in a row.

[0022] An antenna pattern of one of the receiving antennas 12a, 12b, 12cand 12dspatially and partly overlaps an antenna pattern of its adjacent transmitting antenna. For example, one null point of the antenna pattern of one of the receiving antennas such as 12ais located within a first side lobe of the antenna pattern of one of the transmitting antenna such as 11a. This will be explained later in detail.

[0023] Reference numeral 20 designates a timing control circuit for controlling the entirety of the apparatus.

[0024] A signal generating circuit 30 is constructed by a voltage controlled oscillator (VSO) 31, a local multiplying amplifier 32, and a distributor 33. The VCO receives a frequency modulation (FM) control signal from the timing control circuit 20 to generate a Ku-band FM signal in response to the voltage level of the FM control signal. Also, the local multiplying amplifier 32 amplifies the Ku-band FM signal while multiplying the frequency of the Ku-band FM signal by three, thus generating a Ka-band FM signal. Further, the distributor 33 distributes the Ka-band FM signal to a transmitting circuit 40 and a receiving circuit 50.

[0025] The transmitting circuit 40 is constructed by radio frequency (RF) multiplying amplifiers 41a, 41b, 41cand 41dfor amplifying the Ka-band FM signal from the distributor 33 while multiplying the frequency of the Ka-band FM signal by two, generating W-band RF signals whose frequency f is changed as shown in FIG. 2. One of the W-band RF signals of the RF multiplying amplifiers 41a, 41b41cand 41dis selected by a selector 42 which is controlled by the timing control circuit 20 to generate selection signals TX_a, TX_b, TX_cand TX_d, as shown in FIG. 2. Thus, the W-band RF signals are supplied to the transmitting antennas 11a, 11b, 11cand 11d, so that the W-band RF signals are time-sharingly radiated from the transmitting antennas 11a, 11b, 11cand 11d.

[0026] The receiving circuit 50 is constructed by multiplying mixers 51a, 51b, 51cand 51dwhich mix received RF signals from the receiving antennas 12a, 12b, 12cand 12d, respectively, with twice the frequency of the W-band RF signals to generate beat signals BS_a, BS_b, BS_cand BD_d, respectively. The beat signals BS_a, BS_b, BS_cand BS_dare amplified by amplifiers 52a, 52b, 52c, 52d. One of the amplifiers 52a, 52b, 52cand 52dis selected by a selector 53 which generates a selection signals RX_a, RX_b, RX_cand RX_das shown in FIG. 2. Then, the selected beat signal is supplied to a mixer 54 which is connected to a detection circuit 60.

[0027] The detection circuit 60 is constructed by an analog/digital (A/D) converter 61 for performing an A/D conversion upon the output signal of the receiving circuit 50, a fast Fourier transform (FFT) circuit 62 for performing a Fourier transformation upon the output signal of the A/D converter 61 to generate a frequency spectrum signal, and a determination circuit 63 for detecting the azimuth angle and distance of an object in accordance with the frequency spectrum signal. The determination circuit 63 is controlled by a synchronization signal from the timing control circuit 20.

[0028] In FIG. 3, which is a timing diagram showing the frequency of examples of a transmitting RF signal, a received RF signal and a beat signal BS, it is assumed that the transmitting RF signal is radiated from the transmitting antenna 11a, and the received RF signal is received by the received antenna 12afor a first time period T1, as shown in FIG. 2 where only the antennas 11aand 12aare activated. In this case, the transmitting RF signal and the received RF signal are both centered at a frequency f₀which is the center frequency of the W-band. The received RF signal is delayed as compared with the transmitting RF signal by a time T which corresponds to the distance d of an object. That is,

[0029] T=2d/c

[0030] where c is light speed. Therefore, since the frequency f_bof the beat signal BS_ais represented by the difference in frequency between the transmitting RF signal and the received RF signal, the distance d is calculated by

[0031] d=(c/(4·ΔF·f_a))·f_b

[0032] where ΔF is the width of the frequency modulation; and

[0033] f_ais a frequency of a triangular waves of the RF signals. Therefore, in the detection circuit 60, the determination circuit 63 detects the maximum frequency component from the frequency spectrum signal to determine the distance d of the object and simultaneously, the azimuth angle of the object.

[0034] In FIG. 4, which is a diagram for explaining a mixed antenna pattern MP₁obtained by an antenna pattern TP₁of the transmitting antenna 11aand an antenna pattern RP₁of the receiving antenna 12a, the antenna pattern TP₁and the antenna pattern RP₁spatially and partly overlap each other, in other words, a main lobe B of the antenna pattern TP₁spatially and partly overlaps a main lobe B′ of the antenna pattern RP₁. As a result, a left-side null point N_1Lof the antenna pattern TP₁is located within a left-side first-order side lobe SL_1L′ of the antenna pattern RP₁, and a right-side null point N_1R′ of the antenna pattern RP₁, is located within a right-side first-order side lobe SL_1Rof the antenna pattern TR₁. Thus, in the mixed antenna pattern MP₁, a main lobe is narrowed, and also, the side lobe characteristics are suppressed.

[0035] Note that, in the prior art as shown in FIG. 5, since a transmitting antenna pattern TP₁′ of one transmitting/receiving antenna is the same as a received antenna pattern RP₁′ of the same transmitting/receiving antenna, a mixed antenna pattern MP₁′ has a wide main lobe while the side lobe characteristics are not suppressed.

[0036] An example of the antenna pattern TP₁, the antenna pattern PR₁and the mixed antenna pattern MP₁of FIG. 4 is explained with reference to FIG. 6. In FIG. 6, the −3 dB width of the main lobe B of the antenna pattern TP₁and the −3 dB width of the main lobe B′ of the antenna pattern RP₁are both 3 degrees. Also, the null points N_1Land N_1Rare about 3.2 degrees apart from the center of their main lobe B, and the null points N_1L′ and N_1R′ are about 3.2 degrees apart from the center of their main lobe B′. Further, the first-order side lobes SL_1Land SL_1Rhave a height of about −13 dB and are about 4.6 degrees apart from the center of the main lobe B, and the first-order side lobes SL_1L′ and SL_1R′ have a height of about −13 dB and are about 4.6 degrees apart from the center of the main lobe B′.

[0037] In FIG. 6, if the spacing (azimuth angle) between the transmitting antenna 11aand the receiving antenna 12ais about 1.4 degrees, the mixed pattern MP₁has a peak of −2 dB where those of the main lobes B and B′ are 0 dB, and the −3 dB width of the mixed pattern MP₁is about 2 degrees, which means that the mixed pattern MP₁is remarkably narrowed. Also, the height of the first-order side lobes of the mixed pattern MP₁is −24 dB, which means that the side lobe characteristics are remarkably suppressed.

[0038] As shown in FIG. 7, as the spacing (azimuth angle) between the transmitting antenna 11aand the receiving antenna 12ais changed, the height of the first-order side lobes of the mixed pattern MP₁is first decreased and then increased. That is, when the spacing is about 1.4 degrees, the height of the side lobes of the mixed pattern MP₁is minimum. In other words, when the left-side null point N_1Lof the transmitting pattern TP₁coincides with the center of the left-side first-order side lobe SL_1L′ of the received pattern RP₁and the right-side null point N_1R′ of the received pattern RP₁coincides with the center of the right-side first-order side lobe SL_1Rof the transmitting pattern TP₁, the height of the side lobes of the mixed pattern MP₁is minimum.

[0039] Note that, in FIG. 7, in the prior art, the spacing between the transmitting antenna and the receiving antenna is zero. Therefore, the side lobe characteristics are not sufficiently suppressed.

[0040] The antenna patterns of the apparatus of FIG. 1 time-sharingly operated by the timing signals TX_a, TX_b, TX_c, TX_d, RX_a, RX_b, RX_cand RX_das shown in FIG. 2 will be explained next with reference to FIG. 8.

[0041] During a time period T1 of FIG. 2, the transmitting antenna 11aand the receiving antenna 12aare activated. As a result, a mixed pattern MP₁as shown in FIG. 8 is obtained by a transmitting antenna pattern TP₁and a receiving antenna pattern RP_1.An object pattern obtained by the mixed pattern MP₁is stored in a memory of the determination circuit 63.

[0042] During a time period T2 of FIG. 2, the transmitting antenna 11band the receiving antenna 12aare activated. As a result, a mixed pattern MP₂as shown in FIG. 8 is obtained by a transmitting antenna pattern TP₂and a receiving antenna pattern RP_1.An object pattern obtained by the mixed pattern MP₂is stored in a memory of the determination circuit 63.

[0043] During a time period T3 of FIG. 2, the transmitting antenna 11band the receiving antenna 12bare activated. As a result, a mixed pattern MP₃as shown in FIG. 8 is obtained by a transmitting antenna pattern TP₂and a receiving antenna pattern RP_2.An object pattern obtained by the mixed pattern MP₃is stored in the memory of determination circuit 63.

[0044] During a time period T4 of FIG. 2, the transmitting antenna 11cand the receiving antenna 12bare activated. As a result, a mixed pattern MP₄as shown in FIG. 8 is obtained by a transmitting antenna pattern TP₃and a receiving antenna pattern RP_2.An object pattern obtained by the mixed pattern MP₄is stored in the memory of determination circuit 63.

[0045] During a time period T5 of FIG. 2, the transmitting antenna 11cand the receiving antenna 12care activated. As a result, a mixed pattern MP₅as shown in FIG. 8 is obtained by a transmitting antenna pattern TP₃and a receiving antenna pattern RP_3.An object pattern obtained by the mixed pattern MP₅is stored in the memory of determination circuit 63.

[0046] During a time period T6 of FIG. 2, the transmitting antenna 11dand the receiving antenna 12care activated. As a result, a mixed pattern MP₆as shown in FIG. 8 is obtained by a transmitting antenna pattern TP₄and a receiving antenna pattern RP_3.An object pattern obtained by the mixed pattern MP₆is stored in the memory of determination circuit 63.

[0047] During a time period T7 of FIG. 2, the transmitting antenna 11dand the receiving antenna 12dare activated. As a result, a mixed pattern MP₇as shown in FIG. 8 is obtained by a transmitting antenna pattern TP₄and a receiving antenna pattern RP_4.An object pattern obtained by the mixed pattern MP₇is stored in the memory of determination circuit 63.

[0048] Thus, in the above-described embodiment where the number of transmitting antennas is four and the number of receiving antennas is four, seven mixed antenna patterns are obtained. Note that, in the prior art where the number of transmitting/receiving antennas is four, only four mixed antenna patterns are obtained.

[0049] In FIG. 9, which illustrates a first example of the arrangement of the antennas of FIG. 1, the transmitting antennas 11a, 11b, 11cand 11das a primary radiator are arranged horizontally in a row and are associated with a common transmitting reflector 13, thus forming a defocus parabola antenna. In this case, the transmitting antennas 11a, 11b, 11cand 11dare located at a focus face of the common transmitting reflector 13, so that transmitting RF signals are radiated from the transmitting antennas 11a, 11b, 11cand 11dto the common transmitting reflector 13. On the other hand, the receiving antennas 12a, 12b, 12cand 12das a primary radiator are arranged horizontally in a row in parallel with the row of the transmitting antennas 12a, 12b, 12cand 12dand are associated with a common receiving reflector 14, thus forming a defocus parabola antenna. In this case, the receiving antennas 12a, 12b, 12cand 12dare located at a focus face of the common receiving reflector 14, so that received RF signals are radiated from the common receiving reflector 14 to the receiving antennas 12a, 12b, 12cand 12dto.

[0050] In FIG. 9, the transmitting antennas 11a, 11b, 11cand 11dand the receiving antennas 12a, 12b, 12cand 12dare arranged so that a null point of one transmitting antenna pattern coincides with the center of a first-order side lobe of a received antenna pattern.

[0051] In FIG. 10, which illustrates a second example of the arrangement of the antennas of FIG. 1, the transmitting antennas 11a, 11b, 11cand 11das a primary radiator and the receiving antennas 12a, 12b, 12cand 12dfor a primary radiator are arranged alternately and horizontally in a row and are associated with a common transmitting/receiving reflector 15, thus forming a defocus parabola antenna. In this case, the antennas 11a, 12a, 11b, 12b, 11c12c, 11dand 12dare located at a focus face of the common transmitting/receiving reflector 15, so that transmitting RF signals are radiated from the transmitting antennas 11a, 11b, 11cand 11dto the common transmitting/receiving reflector 15. On the other hand, received RF signals are radiated from the common transmitting/receiving reflector 15 to the receiving antennas 12a, 12b, 12cand 12d.

[0052] Even in FIG. 10, the transmitting antennas 11a, 11b, 11cand 11dand the receiving antennas 12a, 12b, 12cand 12dare arranged so that a null point of one transmitting antenna pattern coincides with the center of a first-order side lobe of a received antenna pattern. Also, since the common transmitting/receiving reflector 15 is provided instead of the common transmitting reflector 13 and the common receiving reflector 14 of FIG. 9, the apparatus of FIG. 10 can be reduced in size.

[0053] In FIG. 11, which illustrates a third example of the arrangement of the antennas of FIG. 1, the transmitting antennas 11a, 11b, 11cand 11das a primary radiator and the receiving antennas 12a, 12b, 12cand 12dfor a primary radiator are arranged alternately and horizontally in a row and are associated with a common main transmitting/receiving reflector 16 and a common sub transmitting/receiving reflector 17, thus forming a defocus parabola antenna. In this case, the antennas 11a, 12a, 11b, 12b, 11c12c, 11dand 12dare located at a focus face of the common transmitting/receiving reflectors 16 and 17, so that transmitting RF signals are radiated from the transmitting antennas 11a, 11b, 11cand 11dvia the common main transmitting/receiving reflector 16 to the common sub transmitting/receiving reflector 17. On the other hand, received RF signals are radiated from the sub common transmitting/receiving reflector 17 via the common main transmitting/receiving reflector 16 to the receiving antennas 12a, 12b, 12cand 12dto.

[0054] Even in FIG. 11, the transmitting antennas 11a, 11b, 11cand 11dand the receiving antennas 12a, 12b, 12cand 12dare arranged so that a null point of one transmitting antenna pattern coincides with the center of a first-order side lobe of a received antenna pattern. Also, since the power supply lines to the antennas 11a, 11b, 11c, 12a, 12b, 12cand 12dcan be shortened, the apparatus of FIG. 11 can be reduced in size and power.

[0055] In FIG. 12, which illustrates a fourth example of the arrangement of the antennas of FIG. 1, the transmitting antennas 11a, 11b, 11cand 11das a primary radiator and the receiving antennas 12a, 12b, 12cand 12dfor a primary radiator are arranged alternately and horizontally in a row and are associated with a common main transmitting/receiving lens 18, thus forming an offset defocus parabola antenna. In this case, the antennas 11a, 12a, 11b, 12b, 11c12c, 11dand 12dare located at a focus face of the common transmitting/receiving lens 18, so that transmitting RF signals are radiated from the transmitting antennas 11a, 11b, 11cand 11dto the common transmitting/receiving lens 18. On the other hand, received RF signals are radiated from the common transmitting/receiving lens 18 to the receiving antennas 12a, 12b, 12cand 12d.

[0056] Even in FIG. 12, the transmitting antennas 11a, 11b, 11cand 11dand the receiving antennas 12a, 12b, 12cand 12dare arranged so that a null point of one transmitting antenna pattern coincides with the center of a first-order side lobe of a received antenna pattern. Also, since the power supply lines to the antennas 11a, 11b, 11c, 11d, 12a, 12b, 12cand 12dcan be shortened, the apparatus of FIG. 12 can be reduced in size and power.

[0057] As explained hereinabove, according to the present invention, since the number of mixed antenna patterns is increased, the number of antennas can be substantially decreased, which would decrease the manufacturing cost. Also, since the side lobe characteristics are improved, the antenna gain can be enhanced, which would enhance the detection accuracy.