Self-calibration method of switched array antenna radar

Abstract

Disclosed is a self-calibration method and apparatus for an array antenna system. According to an embodiment of the present disclosure, a correction method of an array antenna system includes: deriving, at a first time, a correction factor R.sub.i,j for a path connecting an i-th (i is an integer equal to or greater than one and equal to or less than m) transmission antenna and a j-th (j is an integer equal to or greater than one and equal to or less than n) reception antenna; deriving, at a second time, a calibration factor {circumflex over (Q)}.sub.i,j for the path connecting the i-th transmission antenna and the j-th reception antenna; and performing, based on the {circumflex over (Q)}.sub.i,j, calibration on the path connecting the i-th transmission antenna and the j-th reception antenna.

Claims

1. A correction method of an array antenna system including m transmission antennas and n reception antennas, wherein m and n are integers greater than one, the correction method comprising: deriving, at a first time, a correction factor R.sub.i,j for a path connecting an i-th transmission antenna and a j-th reception antenna, wherein i is an integer equal to or greater than one and equal to or less than m, and j is an integer equal to or greater than one and equal to or less than n; deriving, at a second time, a calibration factor {circumflex over (Q)}.sub.i,j for the path connecting the i-th transmission antenna and the j-th reception antenna; and performing, based on the calibration factor {circumflex over (Q)}.sub.i,j, calibration on the path connecting the i-th transmission antenna and the j-th reception antenna, wherein the deriving of the correction factor R.sub.i,j comprises: deriving a first reference inverse system response Q.sub.ref for a reference path; deriving an inverse system response Q.sub.i,j for the path connecting the i-th transmission antenna and the j-th reception antenna; and deriving the correction factor R.sub.i,j based on the first reference inverse system response Q.sub.ref and the inverse system response Q.sub.i,j.

2. The correction method of claim 1, wherein the correction factor R.sub.i,j has a time-invariant constant value.

3. The correction method of claim 1, wherein the deriving of the correction factor R.sub.i,j is performed only once during operation of the array antenna system.

4. The correction method of claim 1, wherein the deriving of the calibration factor {circumflex over (Q)}.sub.i,j comprises: deriving a second reference inverse system response {circumflex over (Q)}.sub.ref for the reference path; and deriving the calibration factor {circumflex over (Q)}.sub.i,j based on the correction factor R.sub.i,j and the second reference inverse system response {circumflex over (Q)}.sub.ref.

5. The correction method of claim 1, wherein the second time is a time subsequent to the first time.

6. The correction method of claim 1, wherein the deriving of the calibration factor {circumflex over (Q)}.sub.i,j is periodically performed at predetermined time intervals.

7. The correction method of claim 1, wherein the correction factor R.sub.i,j or the calibration factor {circumflex over (Q)}.sub.i,j is derived for all paths connecting one of the m transmission antennas and one of the n reception antennas.

8. The correction method of claim 1, wherein the reference path is a path connecting a transmission reference port of a transmitter antenna switch for selecting one of the m transmission antennas and a reception reference port of a receiver antenna switch for selecting one of the n reception antennas.

9. The correction method of claim 8, wherein the reference path or the path connecting the i-th transmission antenna and the j-th reception antenna is selected based on a time-division-multiplexing (TDM) control signal input to the transmitter antenna switch and the receiver antenna switch.

10. A calibration apparatus for an array antenna system, the calibration apparatus comprising: m transmission antennas, wherein m is an integer equal to or greater than one; n reception antennas, wherein n is an integer equal to or greater than one; and a signal processing unit is configured to: derive, at a first time, a correction factor R.sub.i,j for a path connecting an i-th transmission antenna and a j-th reception antenna, wherein i is an integer equal to or greater than one and equal to or less than m, and j is an integer equal to or greater than one and equal to or less than n; derive, at a second time, a calibration factor {circumflex over (Q)}.sub.i,j for the path connecting the i-th transmission antenna and the j-th reception antenna; and perform, based on the calibration factor {circumflex over (Q)}.sub.i,j, calibration on the path connecting the i-th transmission antenna and the j-th reception antenna, wherein the signal processing unit is further configured to derive the correction factor R.sub.i,j by deriving a first reference inverse system response Q.sub.ref for a reference path, deriving an inverse system response Q.sub.i,j for the path connecting the i-th transmission antenna and the j-th reception antenna, and deriving the correction factor R.sub.i,j based on the first reference inverse system response Q.sub.ref and the inverse system response Q.sub.i,j.

11. The calibration apparatus of claim 10, wherein the correction factor R.sub.i,j has a time-invariant constant value.

12. The calibration apparatus of claim 10, wherein the deriving of the correction factor R.sub.i,j is performed only once during operation of the array antenna system.

13. The calibration apparatus of claim 10, wherein the signal processing unit is further configured to: derive a second reference inverse system response {circumflex over (Q)}.sub.ref for the reference path, and derive the calibration factor {circumflex over (Q)}.sub.i,j based on the correction factor R.sub.i,j and the second reference inverse system response {circumflex over (Q)}.sub.ref.

14. The calibration apparatus of claim 10, wherein the second time is a time subsequent to the first time.

15. The calibration apparatus of claim 10, wherein the deriving of the calibration factor {circumflex over (Q)}.sub.i,j is periodically performed at predetermined time intervals.

16. The calibration apparatus of claim 10, wherein the correction factor R.sub.i,j or the calibration factor {circumflex over (Q)}.sub.i,j is derived for all paths connecting one of the m transmission antennas and one of the n reception antennas.

17. The calibration apparatus of claim 10, wherein the reference path is a path connecting a transmission reference port of a transmitter antenna switch for selecting one of the m transmission antennas and a reception reference port of a receiver antenna switch for selecting one of the n reception antennas.

18. The calibration apparatus of claim 17, wherein the reference path or the path connecting the i-th transmission antenna and the j-th reception antenna is selected based on a time-division-multiplexing (TDM) control signal input to the transmitter antenna switch and the receiver antenna switch.

19. A correction method of an array antenna system including m transmission antennas and n reception antennas, wherein m and n are integers greater than one, the correction method comprising: deriving, at a first time, a correction factor R.sub.i,j for a path connecting an i-th transmission antenna and a j-th reception antenna, wherein i is an integer equal to or greater than one and equal to or less than m, and j is an integer equal to or greater than one and equal to or less than n; deriving, at a second time, a calibration factor {circumflex over (Q)}.sub.i,j for the path connecting the i-th transmission antenna and the j-th reception antenna; and performing, based on the calibration factor {circumflex over (Q)}.sub.i,j, calibration on the path connecting the i-th transmission antenna and the j-th reception antenna, wherein the deriving of the calibration factor {circumflex over (Q)}.sub.i,j comprises: deriving a reference inverse system response {circumflex over (Q)}.sub.ref for a reference path; and deriving the calibration factor {circumflex over (Q)}.sub.i,j based on the correction factor R.sub.i,j and the reference inverse system response {circumflex over (Q)}.sub.ref.

20. A calibration apparatus for an array antenna system, the calibration apparatus comprising: m transmission antennas, wherein m is an integer equal to or greater than one; n reception antennas, wherein n is an integer equal to or greater than one; and a signal processing unit is configured to: derive, at a first time, a correction factor R.sub.i,j for a path connecting an i-th transmission antenna and a j-th reception antenna, wherein i is an integer equal to or greater than one and equal to or less than m, and j is an integer equal to or greater than one and equal to or less than n; derive, at a second time, a calibration factor {circumflex over (Q)}.sub.i,j for the path connecting the i-th transmission antenna and the j-th reception antenna; and perform, based on the calibration factor {circumflex over (Q)}.sub.i,j, calibration on the path connecting the i-th transmission antenna and the j-th reception antenna, wherein the signal processing unit is further configured to derive the calibration factor {circumflex over (Q)}.sub.i,j by deriving a reference inverse system response {circumflex over (Q)}.sub.ref for a reference path, and deriving the calibration factor {circumflex over (Q)}.sub.i,j based on the correction factor R.sub.i,j and the reference inverse system response {circumflex over (Q)}.sub.ref.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and other advantages of the present disclosure will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a view illustrating a receiver self-calibration method of a conventional array antenna system;

(3) FIG. 2 is a view illustrating an embodiment of an SAA radar structure;

(4) FIG. 3 is a view illustrating an embodiment of a radar system to which a self-calibration method according to the present disclosure may be applied;

(5) FIG. 4 is a control timing diagram illustrating an embodiment of a control signal for controlling a transmitter antenna switch or a receiver antenna switch or both of the SAA radar system of FIG. 3;

(6) FIG. 5 is a view schematically illustrating self-calibration target portions in the SAA radar system of FIG. 3;

(7) FIG. 6 is a view illustrating a process of deriving a correction factor R.sub.m,n according to an embodiment of the present disclosure;

(8) FIG. 7 is a view illustrating an embodiment of a self-calibration method of an SAA radar system according to the present disclosure;

(9) FIG. 8 is a view illustrating TDM-MIMO operation including a self-calibration algorithm according to an embodiment of the present disclosure;

(10) FIGS. 9A, 9B, and 9C are views illustrating system response characteristics before applying a self-calibration algorithm, in a 4-by-4 SAA radar system;

(11) FIGS. 10A, 10B, and 10C are views illustrating system response characteristics after applying a self-calibration algorithm, in a 4-by-4 SAA radar system; and

(12) FIG. 11A-11D illustrating time response characteristics for four paths of TX1-RX1, TX2-RX2, TX3-RX3, and TX4-RX4 after applying a self-calibration algorithm, in a 4-by-4 SAA radar system.

DETAILED DESCRIPTION OF THE INVENTION

(13) Hereinbelow, exemplary embodiments of the present disclosure will be described in detail such that the ordinarily skilled in the art would easily understand and implement an apparatus and a method provided by the present disclosure in conjunction with the accompanying drawings. However, the present disclosure may be embodied in various forms and the scope of the present disclosure should not be construed as being limited to the exemplary embodiments.

(14) In describing embodiments of the present disclosure, well-known functions or constructions will not be described in detail when they may obscure the spirit of the present disclosure.

(15) Further, parts not related to description of the present disclosure are not shown in the drawings and like reference numerals are given to like components.

(16) In the present disclosure, it will be understood that when an element is referred to as being connected to, coupled to, or combined with another element, it can be directly connected or coupled to or combined with the another element or intervening elements may be present therebetween. It will be further understood that the terms comprises, includes, have, etc. when used in the present disclosure specify the presence of stated features, integers, steps, operations, elements, components, and/or combinations thereof but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or combinations thereof.

(17) It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element and not used to show order or priority among elements. For instance, a first element discussed below could be termed a second element without departing from the teachings of the present disclosure. Similarly, the second element could also be termed as the first element.

(18) In the present disclosure, distinguished elements are termed to clearly describe features of various elements and do not mean that the elements are physically separated from each other. That is, a plurality of distinguished elements may be combined into a single hardware unit or a single software unit, and conversely one element may be implemented by a plurality of hardware units or software units. Accordingly, although not specifically stated, an integrated form of various elements or separated forms of one element may fall within the scope of the present disclosure.

(19) In the present disclosure, all of the constituent elements described in various embodiments should not be construed as being essential elements but some of the constituent elements may be optional elements. Accordingly, embodiments configured by respective subsets of constituent elements in a certain embodiment also may fall within the scope of the present disclosure. In addition, embodiments configured by adding one or more elements to various elements also may fall within the scope of the present disclosure.

(20) Hereinbelow, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Throughout the drawings, the same reference numerals will refer to the same or like parts.

(21) FIG. 1 is a view illustrating a receiver self-calibration method of a conventional array antenna system.

(22) The conventional array antenna system shown in FIG. 1 may include a signal processing unit 110, a transmitter 120, n analog-to-digital converters (A/Ds) 130-1 to 130-n, a transmitter antenna switch 140, receiver antenna switches 150-1 to 150-n, amplifiers 160 and 170-1 to 170-n, phase delay elements 180-1 to 180-n, a transmission antenna TX, and/or reception antennas RX1 to RXn.

(23) In order to calibrate the array antenna system shown in FIG. 1, it is required to connect a calibration path for each antenna path. For calibration of a receiver array antenna, the transmitter antenna switch 140 connects output signals of the transmission antenna TX of FIG. 1 to respective reception antenna paths via the receiver antenna switches SW1 150-1 to SWn 150-n. When the receiver antenna switches SW1 150-1 to SWn 150-n are connected to the output signals of the transmission antenna TX, a calibration unit (not shown) of the signal processing unit 110 may receive signals output from the A/Ds 130-1 to 130-n and may calibrate respective reception paths.

(24) The self-calibration method of the array antenna system of FIG. 1 requires a calibration connection line for each reception path, and thus the circuit is complex. Also, since connection lines on the circuit are increased, signal interference on the circuit occurs. Also, in order to calibrate the array antenna system of FIG. 1, it is required to periodically perform calibration by path on the respective reception antenna paths as well as a transmission antenna path in the same manner.

(25) Recently, the structure of the array antenna has been extended from a conventional one-dimensional array to a two-dimensional array. Particularly, in the field of an automotive radar where high resolution is required or a buried bio-signal radar where weak signal detection is required, the structure of the array antenna is more complex.

(26) As the structure of the array antenna is complex, studies have been conducted for enhancing the structure of the array antenna where the amplifier or the phase delay element or both are provided for each antenna path. Recently, a switched array antenna (SAA) or time-division multiplexing (TDM) multiple-input multiple-output (MIMO)-based radar has been widely studied.

(27) FIG. 2 is a view illustrating an embodiment of an SAA radar structure.

(28) As shown in FIG. 2, the SAA radar may include a signal processing unit 210, a transmitter 220, an A/D 230, a receiver antenna switch 250, amplifiers 240 and 260, a phase delay element 270, a transmission antenna TX, and/or reception antennas RX1 to RXn.

(29) The array antenna system of FIG. 1 includes amplifiers and phase delay elements for respective paths. However, in the SAA radar shown in FIG. 2, multiple reception antennas RX1 to RXn are connected to a single receiver antenna switch 250. Also, the multiple reception antennas RX1 to RXn may be connected to a single amplifier 260 or a single phase delay element 270 or both.

(30) The SAA radar of FIG. 2 is simple in structure and the number of used elements is smaller than that of the array antenna system of FIG. 1, and thus the SAA radar of FIG. 2 is suitable for optimizing the price, reliability, and size.

(31) The SAA radar may be applied as an automotive FMCW radar, a miniature radar for mobile devices, and a Through-Wall imaging radar, etc. Recently, studies have been conducted on a method of optimizing a switching sequence of the SAA, but studies have yet to be conducted on a calibration method of the SAA radar. The present disclosure relates to a calibration method of an array antenna system, particularly, a self-calibration method of an SAA radar system.

(32) FIG. 3 is a view illustrating an embodiment of a radar system to which a self-calibration method according to the present disclosure may be applied.

(33) The radar system of FIG. 3 may have a structure of the SAA radar system having time-division-multiplexing-MIMO (TDM-MIMO) function.

(34) The SAA radar system of FIG. 3 may include a signal processing unit 310, a transmitter 320 generating radar signals, an analog-to-digital converter (A/D) 330, a (m+1)-port transmitter antenna switch 340 for transmitter antenna switching, a (n+1)-port receiver antenna switch 350 for receiver antenna switching, amplifiers 360 and 370, mixers 380 and 390, a frequency control oscillator 395, transmission antennas TX1 to TXm, and/or reception antennas RX1 to RXn.

(35) The signal processing unit 310 may perform control functions of respective components or a self-calibration function of the system or both through a control line. In FIG. 3, lines connecting components as well as the signal processing unit 310 may be used as the control line, a signal line, or a communication line, or all.

(36) FIG. 4 is a control timing diagram illustrating an embodiment of a control signal for controlling a transmitter antenna switch or a receiver antenna switch or both of the SAA radar system of FIG. 3.

(37) Controlling of the transmitter antenna switch 340 and the receiver antenna switch 350 may be performed by selecting the transmission antennas TX1 to TXm and the reception antennas RX1 to RXn in the time-division-multiplexing (TDM) manner as shown in the timing diagram of FIG. 4.

(38) In FIG. 3, a TXr port and an RXr port of the transmitter antenna switch 340 and the receiver antenna switch 350 may be reference ports used in self-calibration. Specific functions of the TXr port and RXr port will be described with the description of the self-calibration method below.

(39) In FIG. 3, x and y correspond to an input signal and an output signal respectively in a self-calibration algorithm below.

(40) In the SAA radar system of FIG. 3, self-calibration target portions may include the (m+1)-port transmitter antenna switch 340, the (n+1)-port receiver antenna switch 350, the amplifiers 360 and 370, or the mixers 380 and 390, or all.

(41) FIG. 5 is a view schematically illustrating self-calibration target portions in the SAA radar system of FIG. 3.

(42) In FIG. 5, a transmission path 510 may include transmission path elements, such as the mixer 380 or the amplifier 360 or both of FIG. 3. Also, a reception path 520 may include reception path elements, such as the mixer 390 or the amplifier 370 or both of FIG. 3.

(43) In FIG. 5, inverse system response Q.sub.ref for a reference path 530 may be derived as Equation 1 below.

(44) $\begin{array}{cc}{Q}_{\mathrm{ref}}\left(f\right)=\frac{X\left(f\right)}{Y\left(f\right)}& \left[\mathrm{Equation}1\right]\end{array}$

(45) The inverse system response for a path other than the reference path 530, e.g. the path between the i-th transmission antenna port and the j-th reception antenna port may be designated by Q.sub.i,j(f). i may be an integer equal to or greater than one, and equal to or less than m. j may be an integer equal to or greater than one, and equal to or less than n. Here, a correction factor R.sub.i,j for a path between the i-th transmission antenna port and the j-th reception antenna port may be defined as Equation 2 below.

(46) $\begin{array}{cc}{R}_{i,j}\left(f\right)=\frac{Q_{i,j}\left(f\right)}{Q_{\mathrm{ref}}\left(f\right)}& \left[\mathrm{Equation}2\right]\end{array}$

(47) Equation 2 may be represented by Equation 3 below.

(48) $\begin{array}{cc}{R}_{i,j}=\frac{Q_{i,j}}{Q_{\mathrm{ref}}}=\frac{H_{\mathrm{ref}}}{H_{i,j}}=\frac{H_S{H}_{\mathrm{CC}}}{H_S{H}_{i,\mathrm{jC}}}=\frac{H_{\mathrm{CC}}}{H_{i,\mathrm{jC}}}& \left[\mathrm{Equation}3\right]\end{array}$

(49) In Equation 3, H.sub.CC is the time-invariant response part of the reference path 530, and H.sub.i,jC is the time-invariant response part of the i-th transmission and j-th reception path. Also, H.sub.S is the time-variant response part of the system.

(50) As shown in Equation 3, the correction factor R.sub.i,j for the path between the i-th transmission antenna port and the j-th reception antenna port is derived from the time-invariant response parts H.sub.CC and H.sub.i,jC. Therefore, the correction factor R.sub.i,j has the time-invariant value, i.e., a constant value.

(51) The correction factor R.sub.i,j used in the self-calibration algorithm according to the present disclosure may be obtained in advance. In order to obtain the correction factor R.sub.i,j, the i-th transmission antenna port is connected to the j-th reception antenna port to form a path, and then the inverse system response Q.sub.i,j is obtained. The obtained inverse system response Q.sub.i,j and the inverse system response Q.sub.ref for the reference path 530 are substituted into Equation 2, such that the correction factor R.sub.i,j can be obtained.

(52) FIG. 6 is a view illustrating a process of deriving the correction factor R.sub.i,j according to an embodiment of the present disclosure.

(53) At step S610, the inverse system response Q.sub.ref for the reference path 530 may be derived using Equation 1. The reference path 530 may be always connected, or may be connected by control of the signal processing unit 310. When the reference path 530 is connected, the signal processing unit 310 may select the transmission antenna and the reception antenna as TXr and RXr, and may obtain Q.sub.ref using Equation 1. The control signal 420 of FIG. 4 may be used to select the transmission antenna and the reception antenna as TXr and RXr.

(54) At step S620, the inverse system response for the path between the i-th transmission antenna port and the j-th reception antenna port may be derived using Equation 1. When there are multiple transmission antennas and reception antennas, inverse system responses Q.sub.1,1, Q.sub.1,2, . . . , and Q.sub.m,n for all transmission antenna-reception antenna combinations may be derived.

(55) At step S630, the time-invariant correction factor R.sub.i,j may be calculated using Equation 2. In calculation of Equation 2, one of Q.sub.ref, Q.sub.1,1, Q.sub.1,2, . . . , and Q.sub.m,n derived at steps S610 and S620 may be used. When there are multiple transmission antennas and reception antennas, correction factors R.sub.1,1, R.sub.1,2, . . . and R.sub.m,n for all transmission antenna-reception antenna combinations may be derived.

(56) Since the correction factor R.sub.i,j is a time-invariant constant value, it is sufficient to obtain the correction factor R.sub.i,j only once. For example, when the SAA radar system is initially assembled, the correction factor R.sub.i,j is obtained once, and after that, it is unnecessary to obtain the correction factor R.sub.i,j.

(57) Self-calibration of the SAA radar system according to the present disclosure may be performed after or immediately after the SAA radar system is turned on. Self-calibration of the SAA radar system according to the present disclosure may be periodically performed according to a calibration period 410 of FIG. 4.

(58) FIG. 7 is a view illustrating an embodiment of a self-calibration method of an SAA radar system according to the present disclosure.

(59) At step S710, the inverse system response {circumflex over (Q)}.sub.ref of the reference path 530 may be obtained. The reference path 530 may be always connected, or may be connected by control of the signal processing unit 310. When the reference path 530 is connected, the signal processing unit 310 may select the transmission antenna and the reception antenna as TXr and RXr, and may obtain {circumflex over (Q)}.sub.ref using Equation 1. The control signal 420 of FIG. 4 may be used to select the transmission antenna and the reception antenna as TXr and RXr. After obtaining {circumflex over (Q)}.sub.ref, a self-calibration factor {circumflex over (Q)}.sub.i,j of the i-th transmission antenna port and the j-th reception antenna port may be calculated. When there are multiple transmission antennas and reception antennas, self-calibration factors {circumflex over (Q)}.sub.1,1, {circumflex over (Q)}.sub.1,2, . . . {circumflex over (Q)}.sub.m,n for all transmission antenna-reception antenna combinations may be derived. For calculation of {circumflex over (Q)}.sub.i,j, Equation 4 below may be used.
{circumflex over (Q)}.sub.i,j(f)={circumflex over (Q)}.sub.ref(f).Math.R.sub.i,j[Equation 4]

(60) Equation 4 may be described as Equation 5 below.

(61) $\begin{array}{cc}{\hat{Q}}_{\mathrm{ref}}\left(f\right).Math.R_{i,j}=\frac{1}{{\hat{H}}_S{H}_{\mathrm{CC}}}\frac{H_{\mathrm{CC}}}{H_{i,\mathrm{jC}}}=\frac{1}{{\hat{H}}_S{H}_{i,\mathrm{jC}}}={\hat{Q}}_{i,j}& \left[\mathrm{Equation}5\right]\end{array}$

(62) As shown in Equation 5, Equation 4 may be viewed as a Equation for deriving a new calibration factor of the i-th transmission antenna port and the j-th reception antenna port at the time of measuring {circumflex over (Q)}.sub.ref.

(63) The self-calibration method described with reference to FIG. 7 may be periodically performed after the SAA radar system is turned on or during system operation. Consequently, the SAA radar system can always be maintained in a calibrated state.

(64) FIG. 8 is a view illustrating TDM-MIMO operation including a self-calibration algorithm according to an embodiment of the present disclosure.

(65) At step S810, whether or not the correction factor R.sub.i,j exists may be checked. When there are multiple transmission antennas and reception antennas, whether or not correction factors R.sub.1,1, R.sub.1,2, . . . , and R.sub.m,n for all transmission antenna-reception antenna combinations exist may be checked.

(66) When the correction factor R.sub.i,j is absent (in the case of no at step S810), step S820 may be performed. At step S820, the correction factor R.sub.i,j may be derived. When there are multiple transmission antennas and reception antennas, correction factors R.sub.1,1, R.sub.1,2, . . . , R.sub.m,n for all transmission antenna-reception antenna combinations may be derived. In order to derive the correction factor R.sub.i,j, for example, the process of deriving the correction factor R.sub.i,j described with reference to FIG. 6 may be performed.

(67) When the correction factor R.sub.i,j exists (in the case of yes at step S810), step S830 may be performed. As described above, since the correction factor R.sub.i,j has the time-invariant value, once the correction factor R.sub.i,j is obtained, it is unnecessary to calculate the correction factor R.sub.i,j. Therefore, when the correction factor R.sub.i,j exists, it is unnecessary to perform step S820 again.

(68) Through steps S830 and S840, the self-calibration factor {circumflex over (Q)}.sub.i,j of the i-th transmission antenna port and the j-th reception antenna port may be calculated. When there are multiple transmission antennas and reception antennas, self-calibration factors {circumflex over (Q)}.sub.1,1, {circumflex over (Q)}.sub.1,2, . . . , {circumflex over (Q)}.sub.m,n for all transmission antenna-reception antenna combinations may be calculated. In order to calculate the self-calibration factor {circumflex over (Q)}.sub.i,j, for example, the process of calculating the calibration factor described with reference to FIG. 7 may be performed.

(69) When the self-calibration factors {circumflex over (Q)}.sub.1,1, {circumflex over (Q)}.sub.1,2, . . . , {circumflex over (Q)}.sub.m,n are calculated at steps S830 and S840, these can be used to calibrate respective paths.

(70) At step S850, a TDM-MIMO switching operation may be performed through the calibrated paths.

(71) At step S860, whether it is a self-calibration period may be determined. As described above, self-calibration may be periodically performed. When determining it is a self-calibration period at step S860, step S830 may be performed, new self-calibration factors may be calculated, and calibration may be performed using the new calculated self-calibration factors. When determining it is not a self-calibration period at step S860, a normal TDM-MIMO switching operation may be further performed at step S850.

(72) Although not shown in FIG. 8, at step S860, whether self-calibration is necessary may be performed regardless of determining the self-calibration period. Alternatively, when self-calibration is not periodically performed, whether self-calibration is necessary may be determined by another criterion at step S860. Whether self-calibration is necessary may be determined by various criteria. Alternatively, self-calibration may be performed based on an external input from the system manager, etc.

(73) FIGS. 9A, 9B, and 9C are views illustrating system response characteristics before applying a self-calibration algorithm, in a 4-by-4 SAA radar system.

(74) FIGS. 9A, 9B, and 9C are views respectively illustrating frequency response, phase response, and time response for TX1 and RX1 paths before applying a self-calibration algorithm.

(75) FIGS. 10A, 10B, and 10C are views illustrating system response characteristics after applying a self-calibration algorithm, in a 4-by-4 SAA radar system.

(76) FIGS. 10A, 10B, and 10C are views respectively illustrating frequency response, phase response, and time response for TX1 and RX1 paths after applying a self-calibration algorithm.

(77) From comparison between FIGS. 9A, 9B, and 9C and FIGS. 10A, 10B, and 10C, calibration results in frequency response, phase response, and time response may be verified.

(78) FIG. 11 is a view illustrating time response characteristics for four paths of TX1-RX1, TX2-RX2, TX3-RX3, and TX4-RX4 after applying a self-calibration algorithm, in a 4-by-4 SAA radar system.

(79) As shown in FIG. 11, time response characteristics in which four paths are equally calibrated may be verified.

(80) As described above, the present disclosure proposes a self-calibration method for an SAA radar system that is effective in simplifying the complex structure of an array antenna in the field of an array antenna radar technology of which an application range thereof has expanded.

(81) According to the self-calibration method of the present disclosure, calibration of the SAA radar system in real time can be performed in a very short time. Also, calibration is can be periodically performed, and thus the SAA radar system can always have the optimum performance.

(82) Although exemplary methods of the present disclosure are described as a series of operation steps for clarity of a description, the present disclosure is not limited to the sequence or order of the operation steps described above. The operation steps may be simultaneously performed, or may be performed sequentially but in different order. In order to implement the method of the present disclosure, additional operation steps may be added and/or existing operation steps may be eliminated or substituted.

(83) Various embodiments of the present disclosure are not presented to describe all of available combinations but are presented to describe only representative combinations. Steps or elements in various embodiments may be separately used or may be used in combination.

(84) In addition, various embodiments of the present disclosure may be embodied in the form of hardware, firmware, software, or a combination thereof. When the present disclosure is embodied in a hardware component, it may be, for example, an application specific integrated circuit (ASIC), a digital signal processor (DSP), a digital signal processing device (DSPD), a programmable logic device (PLD), a field programmable gate array (FPGA), a general processor, a controller, a microcontroller, a microprocessor, etc.

(85) The scope of the present disclosure includes software or machine-executable instructions (for example, operating systems (OS), applications, firmware, programs) that enable methods of various embodiments to be executed in an apparatus or on a computer, and a non-transitory computer-readable medium storing such software or machine-executable instructions so that the software or instructions can be executed in an apparatus or on a computer.