JP5195214B2 - Antenna characteristic evaluation system - Google Patents

Description

  The present invention relates to an antenna characteristic evaluation system for evaluating antenna characteristics.

  An antenna is one of the key components that influence radio transmission characteristics, and a high-performance antenna is required to realize high-quality wireless communication. For this reason, it is necessary to design an antenna that optimizes the radiation and absorption characteristics of radio waves according to the radio wave propagation environment. For optimization design, antenna characteristic evaluation technology that measures and evaluates antenna characteristics is important. It becomes.

  On the other hand, in the field of wireless communication in recent years, high-speed wireless communication using the MIMO (Multi Input Multi Output: wireless communication technology for transmitting and receiving data using a plurality of antennas) method has been developed. Even in small devices such as those, it is predicted that the mounting of a multi-antenna will be essential.

  FIG. 27 is a diagram for explaining a radiation pattern of a multi-antenna. The communication terminal MS is provided with multiple antennas A1 and A2. In the multi-antenna technique, the reception state is made different between the antennas A1 and A2, and even when it is difficult to receive with the antenna on one side, the diversity reception is made possible to receive with the antenna on the other side, thereby improving the communication quality.

  As the reception states of the antennas A1 and A2 are different, the effect of diversity reception increases. For example, as shown in FIG. 27, the directivity of the antenna A1, which is one of the antennas, strongly radiates radio waves in the left direction (in the left direction). If the radiation pattern is p1, such as radiating power is strong (radiated power is strong) or radiating radio waves weakly in the right direction (right direction is weak radiating power), the other antenna emits radio waves weakly in the left direction, An antenna A2 having directivity that forms a radiation pattern p2 that radiates radio waves strongly in the right direction is disposed at a position where the radiation patterns do not overlap.

  Here, consider a case where radio waves are transmitted from the left to the right and arrive at the communication terminal MS. Since the strength of the radio wave radiation pattern is the same as the strength of the radio wave absorption pattern, it is difficult for the antenna A2 to receive the incoming radio wave (the incoming radio wave b1) because the absorbed power is weak in the antenna A2. Then, since the absorbed power is strong, reception is possible.

  Further, if the communication terminal MS moves and the radio wave is transmitted from the right to the left direction and arrives at the communication terminal MS at the moving point, the antenna is applied to the incoming radio wave (referred to as the incoming radio wave b2). In A1, it is difficult to receive the signal because the absorbed power is weak. However, the antenna A2 can receive the signal because the absorbed power is strong.

  Thus, when designing a multi-antenna, in a radio wave propagation environment, the directivities of the antennas A1 and A2 are complemented with each other so that the reception state correlation between the antennas (inter-antenna correlation) becomes small. It is necessary to optimize the radiation pattern.

  FIG. 28 is a diagram showing the radio wave reception intensity when the correlation between the antennas is small. The vertical axis represents radio wave reception intensity, and the horizontal axis represents time. The reception intensity when the incoming radio waves b1 and b2 are received by the antennas A1 and A2 shown in FIG.

  When there is an incoming radio wave b1 at time t0 to t1, the reception intensity of the antenna A2 decreases, but the reception intensity of the antenna A1 increases. Further, when there is an incoming radio wave b2 after time t1, the reception intensity of the antenna A1 decreases, but the reception intensity of the antenna A2 increases. In this way, the correlation between the antennas can be reduced, and the deterioration of the reception intensity can be compensated between the antennas.

  FIG. 29 is a diagram showing the radio wave reception intensity when the correlation between antennas is large. The vertical axis represents radio wave reception intensity, and the horizontal axis represents time. It is assumed that the antenna A2-1 having the same radiation pattern as the antenna A1 shown in FIG. 27 is installed in the communication terminal MSa.

  When there is an incoming radio wave b1 at time t0 to t1, the reception intensity of both antennas A1 and A2-1 increases. However, when there is an incoming radio wave b2 after time t1, the reception intensity of both antennas A1 and A2-1. Will fall. As described above, when the correlation between the antennas is large, the reception strength of both the antennas A1 and A2-1 deteriorates in the portion where the radiation pattern falls.

  When designing an optimized antenna, it is essential to evaluate the antenna characteristics.In particular, when evaluating the characteristics of a multi-antenna, not only the characteristics of a single antenna but also the correlation between antennas as described above. This is an important evaluation index when determining antenna characteristics.

  On the other hand, in an actual radio wave propagation environment, the carrier wave (carrier) transmitted from the base station is a communication terminal via multipath (a phenomenon in which signal waves propagate through multiple paths due to reflections from mountains, buildings, etc.). Therefore, when the communication terminal is moving, the carrier frequency is subject to different Doppler shifts depending on the arrival angle of the carrier in each path (a new Doppler frequency is added to the carrier frequency and received). Frequency will be displaced).

  For this reason, the communication terminal receives a plurality of signals spread in the frequency domain, thereby fading that the level fluctuates drastically (a phenomenon in which the strength of the radio wave level changes due to interference of the wavelengths of radio waves that arrive with a time difference or The fluctuation wave). The reception level fluctuation due to fading causes an increase in the error rate of information transmission in wireless communication.

  Therefore, in order to accurately evaluate the correlation between antennas, it is necessary to reproduce the fading environment simulating the actual radio wave propagation environment by computer simulation etc., and optimize the value measured at that time by statistical processing By realizing the design, it is possible to improve the quality of the antenna.

  FIG. 30 is a diagram showing a state in which conventional antenna characteristic evaluation is performed. Signal generation sources 5-1 to 5-5 are arranged around the communication terminal MS. Each of the signal generation sources 5-1 to 5-5 generates a sine wave having a frequency shifted from the carrier frequency by different Doppler frequencies Δf1 to Δf5. In addition, each sine wave radio wave is radiated from the signal generation sources 5-1 to 5-5 in a state of an elementary wave (a single signal wave in which a plurality of signal waves are not combined).

  By radiating different Doppler frequency-shifted radio waves from a plurality of signal generation sources 5-1 to 5-5 arranged around the communication terminal MS to synthesize the radio waves, the communication terminal MS receives the synthesized wave. Generates a simulated fading environment.

  Here, the definition of the Doppler frequency will be described. FIG. 31 is a diagram for explaining the Doppler frequency. Consider a case where the carrier frequency fc that arrives from one path in the multipath arrives at an angle θ with respect to the traveling direction of the communication terminal MS.

  If the moving speed of the communication terminal MS is v, the wavelength of the carrier is λ, and the arrival angle is θ, the Doppler frequency Δf can be expressed by the following equation depending on the apparent wavelength of the radio wave when the traveling direction is the reference.

Δf = v / (λ / cos θ) = v cos θ / λ (1)
FIG. 32 is a diagram illustrating a change in Doppler frequency according to the traveling direction of the communication terminal MS and the arrival angle of the radio wave. (A) shows a case where radio waves are received from a path in the same direction as the traveling direction of the communication terminal MS, and (B) shows a case where radio waves are received from a direction perpendicular to the traveling direction of the communication terminal MS.

When a radio wave is received from a path in the same direction as the traveling direction of the communication terminal MS as shown in (A), θ = 0 and π are obtained, and the absolute value | Δf | of the Doppler frequency is maximized from the equation (1).
Further, as shown in (B), when receiving radio waves from the direction perpendicular to the traveling direction of the communication terminal MS, the apparent wavelength of the radio waves with respect to the traveling direction is not generated, and therefore the communication terminal MS is not moving. This is the same and is not affected by the Doppler shift (θ = π / 2, 3π / 2, and Δf = 0).

  Here, in the evaluation environment shown in FIG. 30, assuming that the communication terminal MS moves in a certain direction, the signal generation sources 5-1 to 5-5 have a radio wave arrival angle with respect to the movement direction of the communication terminal MS. A corresponding Doppler frequency is set, and radio waves having the Doppler frequency are radiated.

  For example, as shown in FIG. 30, assuming that the communication terminal MS moves in the direction of the signal generation source 5-4 indicated by the arrow X, the frequency settings of the signal generation sources 5-1 to 5-5 can be obtained from Equation (1). As can be seen, the Doppler frequency Δf4 of the signal generation source 5-4 is set to be the highest, and the Doppler frequencies from the other signal generation sources are set to be lower than the Doppler frequency Δf4.

  The communication terminal MS is fixed and is not actually moved. Instead, a change in the Doppler frequency that changes along the moving direction of the communication terminal MS is caused on the signal generators 5-1 to 5-5 side. It is set to be variable, and the set radio wave is emitted. In this way, a Doppler shift when the communication terminal MS is considered to have moved is generated on the signal generation source side, and a drop in received intensity or the like occurring at the evaluation antenna at this time is measured and evaluated.

As a conventional technique for antenna characteristic evaluation, Patent Document 1 proposes a technique for performing antenna evaluation by arranging a plurality of scatterer antennas and controlling the amplitude and phase of a radio wave. Further, Patent Document 2 proposes a technique that simulates a fading environment by moving a reflector and a scatterer around a terminal and controlling the amplitude, phase, and the like of radio waves. Further, Patent Document 3 proposes a technique in which a plurality of antennas are arranged around a terminal and a radio wave radiated from the antenna is controlled so as to have real environment characteristics in each antenna direction viewed from the terminal.
Japanese Patent Laying-Open No. 2005-227213 (paragraph number [0031], FIG. 1) JP 07-162376 (paragraph numbers [0045], [0046], FIG. 1) Japanese Patent Laid-Open No. 11-340930 (paragraph numbers [0024] to [0031], FIG. 1)

  When the evaluation environment as shown in FIG. 30 is realized by a specific system, usually, a measurement environment in which a plurality of antennas are arranged in an anechoic chamber is constructed, and antenna characteristics are evaluated in the anechoic chamber. An anechoic chamber is a room in which a radio wave absorber is attached to the entire surface of the indoor ceiling, wall, and floor to suppress reflection of radio waves in the room.

  FIG. 33 is a diagram showing a configuration of a conventional antenna characteristic evaluation system. The antenna characteristic evaluation system 5a includes an anechoic chamber 50, a baseband signal generation unit 51, upconverters 52-1 to 52-4, transmission antennas 53a to 53d, evaluation antennas 54a and 54b, an antenna characteristic evaluation board 55, and an evaluation terminal 56. (Hereinafter, an antenna that radiates radio waves for evaluation is referred to as a transmitting antenna, and an antenna to be evaluated is referred to as an evaluation antenna).

  In the anechoic chamber 50, transmission antennas 53a to 53d for transmitting radio waves and evaluation antennas 54a and 54b to be evaluated are arranged. Transmission antennas 53a to 53d are connected to each of up-converters 52-1 to 52-4, and up-converters 52-1 to 52-4 are connected to baseband signal generation unit 51. The evaluation antennas 54 a and 54 b are connected to the antenna characteristic evaluation board 55, and the antenna characteristic evaluation board 55 is connected to the evaluation terminal 56.

  The baseband signal generation unit 51 generates a baseband signal. The up-converters 52-1 to 52-4 up-convert the baseband signal into a frequency band of an RF (Radio Frequency) signal.

  The up-converter 52-1 up-converts the baseband signal into an RF signal having a frequency shifted by a Doppler frequency Δf1 with respect to the carrier frequency. The up-converter 52-2 up-converts the baseband signal into an RF signal having a Doppler frequency of Δf2.

  The up-converter 52-3 up-converts the baseband signal into an RF signal having a Doppler frequency of Δf3. The up-converter 52-4 up-converts the baseband signal into an RF signal having a Doppler frequency of Δf4.

  The transmission antenna 53a radiates radio waves having a frequency shifted by the Doppler frequency Δf1 with respect to the carrier frequency upconverted by the upconverter 52-1, and the transmission antenna 53b has the Doppler frequency upconverted by the upconverter 52-2. A radio wave of Δf2 is radiated.

  The transmission antenna 53c radiates a radio wave having a Doppler frequency of Δf3 upconverted by the upconverter 52-3, and the transmission antenna 53d radiates a radio wave of a Doppler frequency upconverted by the upconverter 52-4. To do.

  The evaluation antennas 54a and 54b receive the transmitted radio waves. The antenna characteristic evaluation board 55 down-converts the radio waves received by the evaluation antennas 54a and 54b and converts them into baseband signals. Evaluation terminal 56 analyzes antenna characteristics based on the baseband signal after down-conversion.

The system configuration using the conventional antenna characteristic evaluation system 5a mainly has the following problems.
(1) Degradation of fading accuracy.

  When an omnidirectional antenna is used as the transmitting antenna, the radio waves radiated from the omnidirectional antenna are reflected by other transmitting antennas to generate a reflected wave. When the reflected wave reaches the evaluation antenna, fading accuracy is improved. There was a problem of deterioration.

(2) The fading period may not be sufficiently long.
A plurality of transmission antennas are arranged in the anechoic chamber, but in practice, a desired number of transmission antennas cannot always be installed. In the configuration of the conventional antenna characteristic evaluation system 5a, when the number of transmission antennas is small, a sufficiently long fading period necessary for measurement cannot be obtained, and the antenna characteristic evaluation cannot be performed efficiently and accurately. was there.

  (3) If a multipath environment (including a path generated by MIMO) is to be reproduced, the number of signal generation sources and transmission antennas increases. Furthermore, the correlation between multipaths cannot be a desired value.

  In the configuration of the conventional antenna characteristic evaluation system 5a, in order to generate a multipath environment and perform antenna characteristic evaluation under frequency selective fading, a signal generator (up converter) and a transmission antenna corresponding to the number of paths are required. There is a problem that the scale of the apparatus increases. Further, it has been impossible to control the signal generated between the signal generators (upconverters) so that the correlation generated between the multipaths is an appropriate value.

  The present invention has been made in view of these points, and an object of the present invention is to provide an antenna characteristic evaluation system that efficiently and accurately evaluates antenna characteristics with a small number of devices.

  In order to solve the above problems, an antenna characteristic evaluation system for evaluating antenna characteristics is provided. This antenna characteristic evaluation system includes an evaluation antenna that is an antenna to be evaluated, a plurality of transmission antennas that radiate radio waves to the evaluation antenna, a baseband signal generation unit that generates a baseband signal, and a synthesis that generates a composite signal A signal generator, an up-converter connected to the transmitting antenna and up-converting the frequency of the combined signal to the frequency of the radio wave; and the antenna of the evaluation antenna when connected to the evaluation antenna and receiving the radio wave And an evaluation unit for evaluating characteristics.

  Here, the synthesized signal generation unit generates a plurality of sine waves having different frequencies, gives a desired correlation to the plurality of sine waves, and multiplies the given sine wave by the baseband signal. Are combined to generate a plurality of combined signals, thereby generating fading.

  A simulated multipath fading environment is generated with a small number of devices, and antenna characteristics are evaluated efficiently and with high accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a principle diagram of an antenna characteristic evaluation system. The antenna characteristic evaluation system 1 includes transmission antennas 23a to 23d, evaluation antennas 24a and 24b, a baseband signal generation unit 21, a combined signal generation unit 10, upconverters 22-1 to 22-4, and an evaluation unit 30. This is a system for evaluating antenna characteristics in the anechoic chamber 20 (in the example shown in the figure, four transmission antennas and two evaluation antennas are arranged in the anechoic chamber 20, but the number of these is arbitrary). .

  The evaluation antennas 24a and 24b are arranged in the anechoic chamber 20 and are antennas for antenna characteristic evaluation. The transmission antennas 23 a to 23 d are antennas that radiate radio waves to the evaluation antennas 24 a and 24 b, and are distributed at appropriate positions in the anechoic chamber 20.

  The baseband signal generator 21 generates a baseband signal. The synthesized signal generating unit 10 generates a plurality of sine waves having different frequencies, gives a desired correlation to the plurality of sine waves, and multiplies the correlated sine wave by the baseband signal. By combining and generating a plurality of combined signals, fading is generated (a simulated multipath fading environment is generated in the anechoic chamber 20).

  Upconverters 22-1 to 22-4 (upconverter 22 in the case of generic name) are connected to transmitting antennas 23a to 23d, respectively, and upconvert the frequency of the synthesized signal to the frequency of the radio wave. The evaluation unit 30 includes an antenna characteristic evaluation board 31 and an evaluation terminal 32. The antenna characteristic evaluation board 31 is connected to the evaluation antennas 24a and 24b.

  The antenna characteristic evaluation board 31 down-converts the radio waves received by the evaluation antennas 24a and 24b and converts them into baseband signals. The evaluation terminal 32 analyzes antenna characteristics based on the baseband signal after down-conversion.

  Next, before describing the configuration and operation of the antenna characteristic evaluation system 1, problems to be solved will be described in detail. Details of the antenna characteristic evaluation system 1 will be described with reference to FIG.

(1) Degradation of fading accuracy.
When an omnidirectional antenna is used as a transmission antenna, there is a problem that fading accuracy deteriorates. FIG. 2 is a diagram showing deterioration of fading accuracy due to the omnidirectional antenna. Antennas A3 and A4 are arranged around the communication terminal MS. The antenna A3 radiates a radio wave R1 having a Doppler frequency of Δfa, and the antenna A4 radiates a radio wave R2 having a Doppler frequency of Δfb.

  When the antenna A3 is an omnidirectional antenna, the radio wave R1 is radiated over 360 °. For this reason, there are those that go in the direction of the antenna A4, and the radio wave R1 that goes in the direction of the antenna A4 is reflected by the antenna A4, and a path is formed in which the reflected wave R1-1 reaches the communication terminal MS.

  Assuming that the communication terminal MS moves in the direction of the antenna A3 indicated by the arrow X, as described above, the Doppler frequency Δfa of the radio wave radiated from the antenna A3 is increased, and the Doppler frequency Δfb of the radio wave radiated from the antenna A4 is The antenna characteristics are evaluated by setting so as to be low.

  However, in such a situation, although the Doppler frequency of the incoming wave from a direction different from the moving direction is supposed to be smaller than the Doppler frequency of the incoming wave from the moving direction, an unnecessary reflected wave R1-1 is generated. Since it reaches the communication terminal MS, an incoming wave of the same value and a large Doppler frequency Δfa radiated from the antenna A3 is also received from the direction opposite to the moving direction. For this reason, fading fluctuations different from those assumed in advance are received, and fading accuracy deteriorates.

  Here, fading accuracy will be described. A distribution that expresses amplitude fluctuations in a fading environment is a Rayleigh distribution, and the Rayleigh distribution is widely used as a basic distribution of multiwave propagation.

  In addition, it is known that the amplitude fluctuation in a fading environment consisting of a non-line-of-sight channel with no direct wave in a multipath environment is very close to the Rayleigh distribution, and the environment where the amplitude fluctuation becomes a Rayleigh distribution is known as Rayleigh fading. It is called the environment. Furthermore, including the Doppler frequency distribution (Doppler spectrum) in consideration of the movement of the terminal and the arrival direction of the radio wave, it is referred to herein as a Rayleigh fading environment.

  Specifically, the fading environment that is simulated when performing antenna characteristic evaluation is to generate a Rayleigh fading environment. In the modeled Rayleigh fading environment, the antenna characteristics are measured and the measured values are statistically processed. Data analysis. The degree to which the fading environment generated for evaluating the antenna characteristics is close to the modeled Rayleigh fading environment is the fading accuracy.

  Therefore, if the deviation between the generated fading environment and the Rayleigh fading environment is small, the fading accuracy is good, and if the deviation is large, the fading accuracy is degraded. Or, fading accuracy is good if the amplitude fluctuation due to the generated fading is close to the Rayleigh distribution and the set Doppler spectrum, and if the amplitude fluctuation due to the generated fading does not become the Rayleigh distribution and the set Doppler spectrum, the fading accuracy is degraded. It can be said that.

  Therefore, when an unexpected reflected wave R1-1 as shown in FIG. 2 is generated, the deviation from the set Doppler spectrum becomes large (fading accuracy is deteriorated), which is different from the predicated fading environment. It becomes impossible to evaluate the antenna characteristics.

(2) The fading period may not be sufficiently long.
In the configuration of the conventional antenna characteristic evaluation system 5a shown in FIG. 33, there is a possibility that a desired fading cycle cannot be secured. FIG. 3 is a diagram showing a fading cycle. The vertical axis is power, and the horizontal axis is time.

  Fading period indicates T fading. Here, as evaluation items for antenna characteristic evaluation, for example, there are a transmission rate, a throughput, and an error rate. When these items are measured, it is assumed that fading of at least the length of the period T is necessary.

The fading amplitude distribution needs to be a Rayleigh distribution. For this purpose, fading with a sufficiently long period T must be generated.
In this way, when measuring one evaluation item, if it is necessary for the evaluation antenna to receive fading of period T, in the configuration of the conventional antenna characteristic evaluation system, one period becomes T. It is necessary to set up as many transmitting antennas as necessary to generate fading in the anechoic chamber.

  However, if the required number of transmitting antennas cannot be set in the anechoic chamber, fading with a period shorter than the period T is generated without generating a fading with a period T (having different frequencies). The more sine wave radio waves, the more random the radio wave intensity of the composite waveform and the longer the fading period, but the smaller the number of sine wave composites, the shorter the monotonic amplitude composite wave), There was a problem that it was not possible to accurately measure the items to be evaluated.

(3) When trying to reproduce a multipath environment, the number of signal generation sources and transmission antennas increases.
In the antenna characteristic evaluation system 5a shown in FIG. 33, since the radiated radio waves from the transmission antennas 53a to 53d reach the evaluation antennas 54a and 54b at the same time, a one-path environment is generated as a fading environment. Thus, the antenna characteristics are evaluated under the influence of flat fading.

  On the other hand, when it is desired to perform antenna characteristic evaluation under the influence of frequency selective fading, it is necessary to generate a multipath environment as the fading environment. For example, a two-path environment is generated by radio waves of two paths having a difference in arrival delay time to the evaluation antennas 54a and 54b.

  Here, before describing the problem (3), the 1-pass environment and the multi-path environment, flat fading and frequency selective fading will be described. FIG. 4 is a diagram showing the concept of a one-path environment and a multipath environment. The one-path environment is an environment in which there is one incoming wave path to the communication terminal MS, and FIG. 4 shows a state in which the incoming wave reaches the communication terminal MS along the path P1.

  The multipath environment is an environment when there are a plurality of paths of incoming waves to the communication terminal MS, and FIG. 4 shows a two-path environment. The state where the incoming wave generated by the path P2 thus generated reaches the communication terminal MS is shown. An arrival time difference τ is generated between the path P1 and the path P2.

  FIG. 5 is a diagram showing flat fading and frequency selective fading. The vertical axis represents power (dB), and the horizontal axis represents frequency (Hz). Flat fading is fading fluctuation in which the amplitude and phase fluctuations are substantially uniform in the frequency component of fading and attenuates at the same level at the frequencies of all channels.

Flat fading occurs in a one-pass environment.
On the other hand, frequency selective fading is fading fluctuation in which the amplitude and phase vary with time for each frequency component of the fading wave, and the attenuation level differs for each channel frequency.

Further, frequency selective fading occurs because fading waves with different delays are synthesized with different phases for each frequency in a multipath environment.
Next, the principle of frequency selective fading will be described using mathematical expressions. The function of the sine wave of the frequency f _{0 at} the time t (amplitude of the sine wave) can be expressed by Expression (2).

cos (2πf ₀ t) + jsin (2πf ₀ t) = exp (j2πf ₀ t) (2)
Further, fading of the frequency f _n at time t in the path i can be expressed by the following equation (3) (a _{i, n} is a coefficient).

マルチパス環境として、パス間の遅延時間差がτである２パス環境について考えると、周波数ｆ_cの１つ目のパスｇ₁（ｔ）と、周波数ｆ_cの２つ目のパスｇ₂（ｔ−τ）とが合成したときのフェージングをν（ｔ）とした場合、ν（ｔ）は、式（３）から以下の式（４）となる。

As a multi-path environment, considering the two-path environment delay time difference between the paths is tau, 1 single and eye path g ₁ (t) of frequency f _c, 2 nd paths g ₂ (t of frequency f _c When the fading when combined with -τ) is ν (t), ν (t) becomes the following equation (4) from equation (3).

ν (t) = g ₁ (t) exp (j2πf _c t) + g ₂ (t−τ) exp (j2πf _c (t−τ))
= [G ₁ (t) + g ₂ (t−τ) exp (−j2πf _c τ)] exp (j2πf _c t) (4)
FIG. 6 is a vector representation of fading. A vector g ₁ (t) and a vector g ₂ (t−τ) are shown on the coordinate axes. Here, the combined vector ν (t) of the vector g ₁ (t) and the vector g ₂ (t−τ) when f _c = 1 / τ is the vector g ₁ (t) + g ₂ (t−τ). It becomes. A composite vector ν (t) of the vector g ₁ (t) and the vector g ₂ (t−τ) when f _c = 1 / (2τ) is a vector g ₁ (t) −g ₂ (t− τ).

As can be seen from FIG. 6, the value of the frequency f _c, the path g ₁ (t), differs how it was synthesized in the path g ₂ (t-τ), it is different from the magnitude of the amplitude after the synthesis Become. In this way, fading with different amplitude fluctuations depending on frequency is called frequency selective fading.

  The problem (3) will be described. FIG. 7 is a diagram showing the configuration of the antenna characteristic evaluation system. The structure of the conventional antenna characteristic evaluation system which has produced | generated 2 path | pass environment within the anechoic chamber 50 is shown.

  The antenna characteristic evaluation system 5b includes an anechoic chamber 50, a baseband signal generation unit 51, upconverters 52-1 to 52-8, transmission antennas 53a to 53h, evaluation antennas 54a and 54b, an antenna characteristic evaluation board 55, and an evaluation terminal 56. The delay unit 57 is configured.

  The up converters 52-1 to 52-4 and the transmission antennas 53a to 53d are a signal generation source and a transmission antenna that generate a first-path radio wave, and the up converters 52-5 to 52-8 and the transmission antennas 53e to 53e. Reference numeral 53h denotes a signal generation source and a transmission antenna that generate radio waves of the second path.

  In the anechoic chamber 50, transmission antennas 53a to 53d and 53e to 53h for transmitting radio waves and evaluation antennas 54a and 54b to be evaluated are arranged. Transmission antennas 53a to 53d are connected to each of up-converters 52-1 to 52-4, and transmission antennas 53e to 53h are connected to each of up-converters 52-5 to 52-8.

  The up converters 52-1 to 52-8 are connected to the baseband signal generation unit 51. The evaluation antennas 54 a and 54 b are connected to the antenna characteristic evaluation board 55, and the antenna characteristic evaluation board 55 is connected to the evaluation terminal 56.

  The baseband signal generation unit 51 generates a baseband signal, and the upconverters 52-1 to 52-4 upconvert the baseband signal into an RF signal. Delay unit 57 delays the baseband signal by time D, and upconverters 52-5 to 52-8 upconvert the baseband signal delayed by time D into an RF signal.

  The transmission antenna 53a radiates a radio wave whose Doppler frequency is up-converted by the up-converter 52-1, and a transmission antenna 53b radiates a radio wave whose Doppler frequency is up-converted by the up-converter 52-2. The transmission antenna 53c radiates a radio wave having a Doppler frequency of Δf3 upconverted by the upconverter 52-3, and the transmission antenna 53d radiates a radio wave of a Doppler frequency upconverted by the upconverter 52-4. To do.

  On the other hand, the transmitting antenna 53e radiates a radio wave whose Doppler frequency is Δf5 up-converted by the up-converter 52-5, and the transmitting antenna 53f radiates a radio wave whose Doppler frequency is up-converted by the up-converter 52-6. To do. The transmitting antenna 53g radiates radio waves having a Doppler frequency of Δf7 up-converted by the up-converter 52-7, and the transmitting antenna 53h radiates radio waves having a Doppler frequency of Δf8 up-converted by the up-converter 52-8. To do. The difference in arrival time between the radio waves having the Doppler frequencies Δf5 to Δf8 and the radio waves having the Doppler frequencies Δf1 to Δf4 to the evaluation antennas 54a and 54b is time D.

  The evaluation antennas 54a and 54b receive the transmitted radio waves. The antenna characteristic evaluation board 55 down-converts the radio waves received by the evaluation antennas 54a and 54b and converts them into baseband signals. Evaluation terminal 56 analyzes antenna characteristics based on the baseband signal after down-conversion.

  Thus, in order to generate a multipath environment and perform antenna characteristic evaluation under frequency selective fading, a signal generation source (upconverter) and a transmission antenna corresponding to the number of paths are required, and the scale of the apparatus increases. There was a problem such as.

  In addition, since devices such as up-converters are composed of analog circuits, it is not always possible to generate RF signals with high frequency accuracy, and as the number of up-converters increases, errors that depend on the frequency accuracy also increase. There is a problem that the accuracy of the antenna characteristic evaluation is deteriorated.

  Next, the antenna characteristic evaluation system 1 that solves the above problem will be described in detail. First, the directivity of the transmission antenna will be described. FIG. 8 is a diagram showing how reflected waves are suppressed when a directional transmitting antenna is used. By using the directional transmission antenna A3-1 to radiate radio waves in a predetermined direction to the communication terminal MS (evaluation antenna), it is possible to suppress generation of unnecessary reflected waves in the anechoic chamber. And fading accuracy can be improved. Therefore, directional antennas are used for the transmission antennas 23a to 23d shown in FIG.

  FIG. 9 is a diagram illustrating an antenna arrangement example when a directional transmission antenna is used. Around the communication terminal MS (evaluation antenna), five transmission antennas A to E are arranged in a regular pentagon. The transmission antennas A to E are all directional antennas.

  When the highly directional radio wave R1 is radiated from the transmission antenna A to the communication terminal MS, the locations where reflection is likely to occur are the transmission antennas C and D. Therefore, the radiation pattern of the radio wave to be radiated from the transmitting antenna A is set to a radiation angle of 36 °, and the attenuation amount is small (for example, attenuation = 0 dB) at the center of the radiation pattern that is the arrival point of the communication terminal MS. The edge portion where the pattern spreads has directivity that increases the attenuation (for example, attenuation = −10 dB).

  By radiating the radio wave R1 having such directivity from the transmitting antenna A, it becomes possible to suppress the occurrence of reflection at the transmitting antennas C and D (of course, from the range where the radiation pattern spreads). Reflection does not occur at the outer transmitting antennas B and E).

  Therefore, when the five transmission antennas A to E are arranged in a regular pentagon shape in the anechoic chamber, the transmission antennas A to E emit radiation when a level decrease of −10 dB occurs to the left and right from the point where the radiated power becomes maximum. Try to have an angle directivity. Thereby, unnecessary reflection can be reduced.

  Next, a synthesized signal generator (corresponding to a synthesized signal generator) will be described. FIG. 10 is a diagram showing the configuration of the combined signal generator. The combined signal generation unit 10 includes a signal generation unit 11, a calculation unit 12, A / D units 13-1 to 13 -m, a sine wave multiplication / delay unit 14, a combination unit 15, and an output processing unit 16. The signal generation unit 11, the calculation unit 12, the sine wave multiplication / delay unit 14, and the synthesis unit 15 are components that operate by digital signal processing.

  The signal generation unit 11 includes a plurality of sine wave generation units 11-1 to 11- (m × k) (m is the number of baseband signal inputs, k is the number of paths), and the sine wave generation units 11-1 to 11-. (M × k) generates a plurality of initial sine waves having different frequencies (sine waves generated from the sine wave generator).

  The computing unit 12 multiplies the initial sine wave by a correlation parameter for giving a desired correlation, and generates a plurality of correlated sine waves that are sine waves given the desired correlation. The A / D units 13-1 to 13-m A / D convert the analog baseband signals output from the baseband signal generation unit 21 to convert them into digital baseband signals. If the number of input baseband signals is m, m A / D sections are also arranged.

  In FIG. 10, since an analog baseband signal is input from the baseband signal generation unit 21, the A / D unit is included. However, when digital input is performed from the baseband signal generation unit 21, D is not included.

  The sine wave multiplication / delay unit 14 gives a multipath delay to the received baseband signal, and multiplies the baseband signal to which the necessary delay is added by the correlated sine wave to generate a multiplication value. The synthesizer 15 weights the multiplication values and synthesizes them to generate a synthesized signal.

  The output processing unit 16 includes D / A units 16a-1 to 16a-N and filter units 16b-1 to 16b-N. The D / A units 16a-1 to 16a-N convert the digital combined signal output from the combining unit 15 into an analog combined signal. The filter units 16b-1 to 16b-N filter the analog composite signal to remove the aliasing distortion generated during the D / A conversion, generate the composite signals Dout1 to DoutN, and transmit them to the upconverter 22 side ( If N composite signals are generated, N upconverters 22 and N transmission antennas are required). Some of the transmission antennas may be antennas that transmit vertically polarized waves, and the remaining antennas may be antennas that support horizontally polarized waves.

  Next, a configuration for setting a long fading cycle will be described. The sine wave generation units 11-1 to 11- (m × k) in the signal generation unit 11 generate an initial sine wave whose period is a prime relationship.

FIG. 11 is a diagram illustrating an example of a sine wave having a prime frequency relationship. The vertical axis is amplitude, and the horizontal axis is time. The frequencies f _{1 to} f ₄ that are in a prime relationship are shown. A prime relationship is one in which there is no common divisor other than one. For example, when f ₁ = 3, f ₂ = 5, f ₃ = 7, and f ₄ = 8, there is no common divisor other than _{1 in} the frequencies f _{1 to} f ₄ , so that there is a prime relationship.

Or it can be paraphrased as a relationship in which a value obtained by multiplying all frequency values is the least common multiple. In this example, since the least common multiple of the frequencies f _{1 to} f ₄ is 840 (= 3 × 5 × 7 × 8), the frequencies f _{1 to} f ₄ have a prime relationship.

  A cycle of a synthesized wave (cycle T1) composed of a plurality of sine waves having a prime frequency and a cycle of a synthesized wave (cycle T2) synthesized of a plurality of sine waves having a non-primary frequency. And T2 <T1.

  Accordingly, the combined wave of a plurality of sine waves having a frequency that is a prime relationship can have a longer fading cycle than the combined wave of a plurality of sine waves having a frequency that is not a prime relationship.

Next, an example of a method for setting a frequency that is a prime relationship will be described. Consider a case in which frequency values that are relatively prime to each other are set for frequencies f _{1 to} f ₄ (f ₁ <f ₂ <f ₃ <f ₄ ).

First, for f ₁ and f ₄ , a frequency value that is a prime relationship is set and fixed. For f ₂ and f ₃ , f ₂ is temporarily set to a value in the vicinity of f ₁ , and f ₃ is temporarily set to a value in the vicinity of f ₄ (whether or not f ₂ and f ₃ have a prime relationship) Regardless, at this stage, it is simply set to a value in the vicinity of f ₁ and f ₄ ). The temporarily set f ₂ is f ₂ ′, and the temporarily set f ₄ is f ₄ ′.

As shown in Expression (2), a sine wave having a frequency f ₁ can be expressed as exp (j2πf ₁ t). Similarly, the frequencies f ₂ , f ₃ , and f ₄ can be expressed as exp (j2πf ₂ t), exp (j2πf ₃ t), and exp (j2πf ₄ t), respectively.

Here, in order for the frequencies f _{1 to} f _{4 to} have a prime relationship, the period (amplitude) of the sine wave of each frequency is equal.
exp (j2πf ₁ t) = exp (j2πf ₂ t) = exp (j2πf ₃ t) = exp (j2πf ₄ t) (5)
It becomes. Dividing equation (5) by exp (j2πf ₁ t)
_{1 = exp (j2π (f 2} -f 1) t) = exp (j2π (f 3 -f 1) t) = exp (j2π (f 4 -f 1) t) ··· (6)
It becomes. In order for each exponential in equation (6) to be 1, (f ₂ −f ₁ ) t, (f ₃ −f ₁ ) t, and (f ₄ −f ₁ ) t may be integers. Because, from equation (2), cos (2πft) + jsin (2πft) = exp (j2πft), so that when ft is an integer, cos (2πft) + jsin (2πft) on the left side is the term of sin and the term of sin This is because 0 becomes 0.

Therefore, if (f ₂ −f ₁ ) t = N ₂ , (f ₃ −f ₁ ) t = N ₃ , (f ₄ −f ₁ ) t = N ₄ (N ₂ , N ₃ , N ₄ are (Integer) and equation (7).
N ₂ / (f ₂ −f ₁ ) = N ₃ / (f ₃ −f ₁ ) = N ₄ / (f ₄ −f ₁ ) = t (7)
Expand Equation (7)
_{N 2 '= (f 2'} -f 1) · N 4 / (f 4 -f 1) ··· (8)
N ₂ having a prime relationship with N ₄ ′ closest to N ₂ ′ in Expression (8) is obtained (N ₄ is an integer equal to or greater than 1980).

And the calculation formula of f ₂ is
f ₂ = ((f ₄ −f ₁ ) · N ₂ / N ₄ ) + f ₁ (9)
Therefore, the obtained N ₂ is substituted into the equation (9) to obtain f ₂ .

Also, expand equation (7) and
_{N 3 '= (f 3'} -f 1) · N 4 / (f 4 -f 1) ··· (10)
Thus, N ₃ having a prime relationship with N ₄ ′ closest to N ₃ ′ in Expression (10) is obtained.

And the calculation formula of f ₃ is
f ₃ = ((f ₄ −f ₁ ) · N ₃ / N ₄ ) + f ₁ (11)
Therefore, the obtained N ₃ is substituted into the equation (11) to obtain f ₃ . With such an algorithm, values that are relatively prime to each other can be obtained for the frequencies f ₁ , f ₂ , f ₃ , and f ₄ .

  Next, each component of the synthetic signal generator 10 will be described in detail. Hereinafter, a plurality of baseband signals are represented as baseband signals B1 to Bm (m = 1, 2,...), And a plurality of paths when configuring a multipath are paths P1 to Pk (k = 1, 2) (the number of input baseband signals is m, and the number of paths assumed is k).

  Further, when a configuration example is shown with specific values, the number of input baseband signals is 4 (= m), and the number of paths is 9 (= k) as a multipath fading environment. It will be described as creating an environment.

  FIG. 12 is a diagram illustrating a configuration of the signal generation unit 11. The signal generation unit 11 includes a plurality of (m × k) sine wave generation units, and one sine wave generation unit is a digital generator that generates a plurality of initial sine waves having different frequencies.

Here, for easy understanding, it is assumed that m sine wave generation units are arranged in the row direction and k sine wave generation units are arranged in the column direction, and the sine wave generation unit located in m rows and k columns is generated. It is written as part X _mk . FIG. 12 shows the arrangement of the sine wave generation unit in the case of m rows and k columns and the arrangement of the sine wave generation unit in the case of 4 rows and 9 columns.

13 to 16 are diagrams illustrating an initial sine wave generated by the sine wave generation unit. The sine wave generation unit X _mk generates n initial sine waves corresponding to the baseband signal Bm.
That is, one sine wave generation unit generates n initial sine waves. Therefore, the entire signal generator 11 generates (n × m × k) initial sine waves having different frequencies.

  FIGS. 13 to 16 show a state in which n = 8, that is, one initial sine wave is generated from one sine wave generation unit. Therefore, the entire signal generator 11 generates 288 (= 8 × 4 × 9) types of initial sine waves having different frequencies.

In addition, in the sine wave generation unit X _mk , when there are the same number of antennas corresponding to vertical polarization and horizontal polarization, n / 2 initial sine waves corresponding to vertical polarization are changed to initial sine waves X _mVk-n . The n / 2 initial sine waves corresponding to the horizontal polarization are expressed as an initial sine wave X _mHk-n .

As an example, the sine wave generating unit X _1-1 of FIG. 13, corresponding to the base band signal B1, 4 pieces initial sinusoidal of vertical polarization, the initial sinusoidal X _1V1-1, X _1V1-2 , X _1V1-3 , and X _1V1-4 . Further, the four initial sine waves of horizontal polarization corresponding to the baseband signal B1 are expressed as initial sine waves X _1H1-1 , X _1H1-2 , X _1H1-3 , and X _1H1-4 .

The functions representing these initial sine waves are represented by X _1V1-1 = exp (j · 2π · δf _1V1-1 · t + j · θ _1V1-1 ), X _1V1-2 = exp (j · 2π · δf _1V1-2) T + j · θ _1V1-2 ), X _1V1-3 = exp (j · 2π · δf _1V1-3 · t + j · θ _1V1-3 ), X _1V1-4 = exp (j · 2π · δf _1V1-4 · t + j・ Θ _1V1-4 ), X _1H1-1 = exp (j · 2π · δf _1H1-1 · t + j · θ _1H1-1 ), X _1H1-2 = exp (j · 2π · δf _1H1-2 · t + j · θ _1H1-2 ), X _1H1-3 = exp (j · 2π · δf _1H1-3 · t + j · θ _1H1-3 ), X _1H1-4 = exp (j · 2π · δf _1H1-4 · t + j · θ _{1H1- 4} ) Note that δf (Δf) is a Doppler frequency, t is time, and θ is a phase. The same applies to other sine wave generators.

  Next, the calculation unit 12 will be described. The calculation unit 12 multiplies the plurality of initial sine waves generated by the signal generation unit 11 by a correlation parameter to generate a correlated sine wave that gives the desired correlation to the initial sine wave.

The degree of correlation can be increased or decreased depending on the value of the correlation parameter.
FIG. 17 is a diagram illustrating an example of calculation processing of the calculation unit 12. The arithmetic unit 12 _extracts the initial sine wave X _mVk-a and the initial sine wave X _mHk-a from each of the m sine wave generation units X _mk located in the k-th column shown in FIG. 1 ≦ a ≦ n / 2: a is a natural number), and a column vector of an initial sine wave composed of n elements is generated.

  Then, this column vector is multiplied by a correlation parameter having n × n matrix elements to generate a correlated sine wave column vector composed of n elements, and the total (n × m × k) Generate correlated sine waves.

For example, as shown in the calculation example shown in FIG. 17, the 4 (= m) sine wave generators X _1-1 , X _2-1 , X ₂ located in the 1 (= k) column shown in FIG. _3-1, when extracting the initial sinusoidal from each X _4-1 generates a column vector, and extracts a sine wave X _1V-1, X _1H1-1 sine wave generator X _1-1, sine from the wave generating unit X _2-1 extracts a sine wave X _2V-1, X _2H1-1, extracts the sine-wave X _3V-1, X _3H1-1 sine wave generator X _3-1, sine wave generating The sine waves X _4V-1 and X _4H1-1 are extracted from the part X _4-1 .

Extracted sinusoidal column vector _{X = (X 1V-1,} X 1H1-1, X 2V-1, X 2H1-1, X 3V-1, X 3H1-1, X 4V-1, X 4H1-1) On the other hand, since n = 8, it is an 8 × 8 matrix element and is multiplied by a correlation parameter H ₁ for determining the correlation of each element of the column vector X.

The multiplication result, a column vector _{Y = (Y 1V-1,} Y 1H1-1, Y 2V-1, Y 2H1-1, Y 3V-1, Y 3H1-1, Y 4V-1, Y 4H1-1) becomes For example, if the correlation parameter H ₁ sets the correlation to 0, the elements of the column vector Y have a correlation of 0 to each other. The matrix calculation formula is shown below.

なお、１（＝ｋ）列目に位置する４（＝ｍ）個の正弦波生成部Ｘ_1-1、Ｘ_2-1、Ｘ_3-1、Ｘ_4-1からは、上記の行列演算の他にさらに、以下の３種類の行列演算が行われる（計算式のみ示す）。

From the 4 (= m) sine wave generators _X1-1 , _X2-1 , _X3-1 , and _X4-1 located in the 1 (= k) column, the above matrix calculation is performed. In addition, the following three types of matrix operations are performed (only the calculation formula is shown).

図１２に示す正弦波生成部の配置にもとづいて、演算部１２では、１列から４種類の行列演算を行い、全部で９列あるので、３６種類の行列演算を行うことになる（２８８種類の正弦波の中から８つの正弦波を抽出して行列演算を行うので、３６種類の行列演算を行うことになる）。

Based on the arrangement of the sine wave generation unit shown in FIG. 12, the calculation unit 12 performs four types of matrix calculations from one column and has nine columns in total, so that 36 types of matrix calculations are performed (288 types). Since eight sine waves are extracted from the sine waves and matrix calculation is performed, 36 types of matrix calculations are performed).

In addition, the correlation parameters H _{1 to} H _{36 that} are 8 × 8 matrix elements may all have the same value (H ₁ = H ₂ =... = H ₃₆ ) for 36 types of matrix operations. Different values may be set. The correlation parameter is held in a storage area in the calculation unit 12, and the value of the correlation parameter can be set to an arbitrary value by the user.

  Here, as a simple example, a case where the correlation between two frequencies is determined using a 2 × 2 correlation parameter will be described. If the matrix elements of the correlation parameter are, for example, a, b, c, d, the matrix operation is expressed by the following equation (16).

式（１６）から、ｙ１＝ａ・ｘ１＋ｂ・ｘ２、ｙ２＝ｃ・ｘ１＋ｄ・ｘ２である。相関パラメータの要素が、ａ＝１、ｂ＝０、ｃ＝１、ｄ＝０のとき、ｙ１＝ｙ２＝ｘ１となる。ｙ１、ｙ２の値が同じであるので、相関性が１となり、ｙ１、ｙ２の相関性は強くなる。

From the equation (16), y1 = a · x1 + b · x2, and y2 = c · x1 + d · x2. When the correlation parameter elements are a = 1, b = 0, c = 1, and d = 0, y1 = y2 = x1. Since the values of y1 and y2 are the same, the correlation is 1, and the correlation between y1 and y2 is strong.

  When the correlation parameter elements are a = 1, b = 0, c = 0, and d = 1, y1 = x1 and y2 = x2, and y1 and y2 are completely different values. The correlation between y1 and y2 is 0, and the correlation between y1 and y2 is eliminated (the correlation can be set finely by using fractions for a, b, c, and d).

  Next, the sine wave multiplication / delay unit 14 will be described. FIG. 18 is a diagram showing the overall configuration of the sine wave multiplication / delay unit 14. The configuration when the number of input baseband signals is 4 and the number of paths is 9 is shown.

The sine wave multiplication / delay unit 14 includes multiplication processing units 14ν _{1-1 to} 14ν _1-9 and delay units 14a-1 to 14a-8 for the baseband signal B1. For baseband signal B2, multiplication processing units 14v _{2-1 to} 14v _2-9 and delay units 14b-1 to 14b-8 are arranged.

For baseband signal B3, multiplication processing units 14ν _{3-1 to} 14ν _3-9 and delay units 14c-1 to 14c-8 are arranged. For baseband signal B4, multiplication processing units 14ν _{4-1 to} 14ν _4-9 and delay units 14d-1 to 14d-8 are arranged.

Here, the baseband signal Bm is converted into a digital signal by the A / D units 13-1 to 13-4. The baseband signal Bm after A / D conversion is input without delay to the multiplication processing units 14ν _{1-1 to} 14ν _4-1 that perform multiplication processing on the path P1.

Further, when performing a multiplication process on the path Ps (2 ≦ s ≦ k: s is a natural number), when the delay unit time is D, a delay of (s−1) × D is given to the baseband signal Bm. , Input to the multiplication processing unit 14 ν _ms .

For example, when looking at the baseband signal B1, when performing the multiplication process for the path P2 (s = 2), the baseband signal B1 is given a delay of time 1D by the delay unit 14a-1, and the multiplication processing unit Input to 14ν _1-2 . Further, when performing multiplication processing for the path P9 (s = 9), the baseband signal B1 is given a delay of time 8D generated by the delay units 14a-1 to 14a-8, and the multiplication processing unit 14ν _{1. Let -9} input.

19 and 20 are diagrams showing the internal configuration of the sine wave multiplication / delay unit 14. Only the internal configuration of the portion that performs the multiplication processing of the baseband signal B1 is shown (the portion that performs the multiplication processing of the baseband signals B2 to B4 has the same configuration). Multiplication processing units 14ν _{1-1 to} 14ν _1-9 include multipliers # 1 to # 8, respectively. Each of the delay units 14a-1 to 14a-8 gives a delay of time 1D to the input signal and outputs it. By providing a delay for each path by the delay units 14a-1 to 14a-8, an environment for frequency selective fading is generated.

The baseband signal B1 after A / D conversion is input to the multipliers # 1 to # 8 in the multiplication processing unit 14ν _1-1 . The baseband signal B1 and the correlated sine wave ( _Y1V1-1 , _Y1V1-2 , _Y1V1-3 , _Y1V1-4 , _{Y1H -1} , _Y1H1-2 , Y) _1H1-3 , Y _1H1-4 ) are multiplied, and multiplied values (ν _1V1-1 , ν _1V1-2 , ν _1V1-3 , ν _1V1-4 , ν _1H-1 , ν _1H1-2 , ν _1H1-3 , ν _1H1-4 ) is output.

That is, multiplier # 1 multiplies correlated sine wave Y _1V1-1 and baseband signal B1 to generate multiplication value ν _1V1-1 . Multiplier # 2 multiplies correlated sine wave Y _1V1-2 and baseband signal B1 to generate multiplication value ν _1V1-2 . Multiplier # 3 multiplies correlated sine wave Y _1V1-3 and baseband signal B1 to generate multiplication value ν _1V1-3 . Multiplier # 4 multiplies correlated sine wave Y _1V1-4 and baseband signal B1 to generate multiplication value ν _1V1-4 . Multiplier # 5 multiplies correlated sine wave Y _1H-1 and baseband signal B1 to generate multiplication value ν _1H-1 . Multiplier # 6 multiplies correlated sine wave Y _1H1-2 and baseband signal B1 to generate multiplication value ν _1H1-2 . Multiplier # 7 multiplies correlated sine wave Y _1H1-3 and baseband signal B1 to generate multiplication value ν _1H1-3 . Multiplier # 8 multiplies correlated sine wave Y _1H1-4 and baseband signal B1 to generate multiplication value ν _1H1-4 .

On the other hand, the delay unit 14a-1 delays the baseband signal B1 immediately after the A / D conversion by a time D1. The baseband signal B1 delayed by time 1D is input to the multipliers # 1 to # 8 in the multiplication processing unit 14ν _1-2 .

The baseband signal B1 delayed by the time D1 and correlated sine waves (Y _1V2-1 , Y _1V2-2 , Y _1V2-3 , Y _1V2-4 , Y _1H2-1 , Y _1H2-2 , Y _1H2-3 , Y _1H2-4 ) are multiplied, and multiplication values (ν _1V2-1 , ν _1V2-2 , ν _1V2-3 , ν _1V2-4 , ν _1H2-1 , ν _1H2-2) , Ν _1H2-3 , ν _1H2-4 ).

The same arithmetic processing is performed in the multiplication processing units 14ν _{1-3 to} 14ν _1-9 . It is to be noted that only the final stage multiplication processing unit 14ν _1-9 is simply shown. The output signal of the delay unit 14a-8 is compared with the baseband signal B1 input to the multiplication processing unit 14ν _1-1 in time (D1 + ... + D8) is delayed. Hereinafter, the time (D1 +... + Dn) is expressed as time ΣDb (b = 1 to n).

A baseband signal B1 delayed by time ΣDb (b = 1 to 8) is input to the multipliers # 1 to # 4 in the multiplication processing unit 14ν _1-9 . The baseband signal B1 delayed by time ΣDb (b = 1 to 8) and correlated sine waves (Y _1V9-1 , Y _1V9-2 , Y _1V9-3 , Y _1V9-4 , Y _1H9-1). , Y _1H9-2 , Y _1H9-3 , Y _1H9-4 ) and multiplied by (ν _1V9-1 , ν _1V9-2 , ν _1V9-3 , ν _1V9-4 , ν _{1H9) -1} , ν _1H9-2 , ν _1H9-3 , ν _1H9-4 ).

Here, the operation contents of the sine wave multiplication / delay unit 14 are generalized and described. For the multiplication processing for the path P1, the baseband signal Bm is not delayed, and the baseband signal Bm is correlated with the correlated sine wave. by multiplying the Y _mV1-n generates the multiplication value ν _mV1-n, the baseband signal Bm, to generate a multiplication value [nu _MH1-n multiplies the correlation sine wave Y _mH1-n.

Further, when performing a multiplication process on the path Ps (2 ≦ s ≦ k: s is a natural number), the baseband signal Bm is given a delay of time ΣDb (b = 1 to m−1). a, by multiplying the correlation sine wave Y _mVs-n generates the multiplication value [nu _mVs-n, the baseband signal Bm, to generate a multiplication value [nu _MHS-n multiplies the correlation sine wave Y _MHS-n.

FIGS. 21 to 24 are matrix representations of the multiplication values of the sine wave multiplication / delay unit 14. FIG. 21 is a matrix representation of the multiplication values that are the outputs of the multiplication processing units 14ν _{1-1 to} 14ν _1-9 for the baseband signal B1. In addition, each row vector (multiplication value vector) of the 8 × 9 matrix is expressed as V _{11 to} V ₁₄ and H _{11 to} H ₁₄ .

For example, V ₁₁ = (ν _1V1-1 , ν _1V2-1 , ν _1V3-1 , ν _1V4-1 , ν _1V5-1 , ν _1V6-1 , ν _1V7-1 , ν _1V8-1 , ν _1V9-1 ). Also, H ₁₁ = (ν _1H1-1 , ν _1H2-1 , ν _1H3-1 , ν _1H4-1 , ν _1H5-1 , ν _1H6-1 , ν _1H7-1 , ν _1H8-1 , ν _1H9-1 ).

FIG. 22 is a matrix representation of the multiplication values that are the outputs of the multiplication processing units 14ν _{2-1 to} 14ν _2-9 for the baseband signal B2, and the eight row vectors are represented by V _{21 to} V ₂₄ and H _{21 to} H, respectively. ₂₄ . FIG. 23 is a matrix representation of the multiplication values that are the outputs of the multiplication processing units 14ν _{3-1 to} 14ν _3-9 for the baseband signal B3, and the eight row vectors are represented by V _{31 to} V ₃₄ and H _{31 to} H, respectively. ₃₄ . FIG. 24 is a matrix representation of the multiplication values that are the outputs of the multiplication units 14ν _{4-1 to} 14ν _4-9 for the baseband signal B4, and the eight row vectors are represented by V _{41 to} V ₄₄ and H _{41 to} H, respectively. ₄₄ .

Here, generally, the multiplication value vector of the sine wave multiplication / delay unit 14 can be expressed as V _mn = (ν _mVk−n ) and H _mn = (ν _mHk−n ). For example, if m = 1 and n = 1, V ₁₁ = (ν _1Vk-1 ) = (ν _1V1-1 , ν _1V2-1 , ν _1V3-1 , ν _1V4-1 , ν _1V5-1 , ν _{1V6 −1} , ν _1V7-1 , ν _1V8-1 , ν _1V9-1 ). H ₁₁ = (ν _1Hk-1 ) = (ν _1H1-1 , ν _1H2-1 , ν _1H3-1 , ν _1H4-1 , ν _1H5-1 , ν _1H6-1 , ν _1H7-1 , ν _{1H8 −1} , ν _1H9-1 ).

  Next, the synthesis unit 15 will be described. 25 and 26 are diagrams showing the configuration of the synthesis unit 15. The combining unit 15 includes n weighting combining units V-1 to Vn and n weighting combining units H-1 to Hn. In this example, since n = 4, the weighting synthesis units V-1 to V-4 and the weighting synthesis units H-1 to H-4 are configured.

Further, the multiplication value vector V _mn is input to the weighting synthesis unit V-n. That is, the multiplication value vector V _m1 = (V ₁₁ , V ₂₁ , V ₃₁ , V ₄₁ ) is input to the weighting synthesis unit V-1, and the multiplication value vector V _m2 = (( _{V 12, V 22, V 32} , V 42) is inputted.

Further, the multiplication value vector V _m3 = (V ₁₃ , V ₂₃ , V ₃₃ , V ₄₃ ) is input to the weighting synthesis unit V-3, and the multiplication value vector V _m4 = (( _{V 14, V 24, V 34} , V 44) is inputted.

Similarly, the multiplication value vector H _mn is input to the weighting synthesis unit H-n. That is, the multiplication value vector H _m1 = (H ₁₁ , H ₂₁ , H ₃₁ , H ₄₁ ) is input to the weighting synthesis unit H-1, and the multiplication value vector H _m2 = (( H ₁₂ , H ₂₂ , H ₃₂ , H ₄₂ ) are input.

Further, the multiplication value vector H _m3 = (H ₁₃ , H ₂₃ , H ₃₃ , H ₄₃ ) is input to the weighting synthesis unit H-3, and the multiplication value vector H _m4 = (( H ₁₄ , H ₂₄ , H ₃₄ , H ₄₄ ) are input.

Here, the weighting synthesis unit V-n _adds k weighting factors W _r (1 ≦ r ≦ k: r is a natural number) to k multiplication values ν _mVk-n that are elements of the multiplication value vector V _mn. Multiplication is performed, m addition values Vadd _mn obtained by adding the multiplication results are obtained, and the sum of the addition values Vadd _mn is generated as a combined signal corresponding to vertical polarization.

Similarly, the weighting combining unit H-n multiplies k multiplication values ν _mHk-n that are elements of the multiplication value vector H _mn by k weighting factors W _r and adds the multiplication results. obtains the sum value Hadd _mn, the sum of the sum Hadd _mn, it generates a synthesized signal corresponding to the horizontal polarized wave.

Specifically, with regard to the weighting synthesis unit V-1, the weighting factor Wk (k = 1, 2, 3, 4, 5, 6) is applied to each element of the row vector (V ₁₁ , V ₂₁ , V ₃₁ , V ₄₁ ). , 7, 8, 9), and the addition values Vadd _1-1 , Vadd _2-1 , Vadd _3-1 , and Vadd _4-1 obtained by adding the multiplication results are obtained, and the sum of these values is obtained.

That is, V ₁₁ = (ν _1V1-1 , ν _1V2-1 , ν _1V3-1 , ν _1V4-1 , ν _1V5-1 , ν _1V6-1 , ν _1V7-1 , ν _1V8-1 , ν _1V9-1 ) Is multiplied by weighting factors W _{1 to} W ₉ to obtain a sum Vadd _{1-1 of the} multiplication values (formula (17)).

Vadd _1-1 = W ₁ · ν _1V1-1 + W ₂ · ν _1V2-1 + W ₃ · ν _1V3-1 + W ₄ · ν _1V4-1 + W ₅ · ν _1V5-1 + W ₆ · ν _1V6-1 + W ₇ · ν _1V7-1 + W ₈・ ν _1V8-1 + W ₉・ ν _1V9-1
... (17)
V ₂₁ = (ν _2V1-1 , ν _2V2-1 , ν _2V3-1 , ν _2V4-1 , ν _2V5-1 , ν _2V6-1 , ν _2V7-1 , ν _2V8-1 , ν _2V9-1 ) Are multiplied by weighting factors W _{1 to} W ₉ to obtain a sum Vadd _{2-1 of the} multiplication values (formula (18)).

Vadd _2-1 ＝ W ₁・ ν _2V1-1 + W ₂・ ν _2V2-1 + W ₃・ ν _2V3-1 + W ₄・ ν _2V4-1 + W ₅・ ν _2V5-1 + W ₆・ ν _2V6-1 + W ₇・ν _2V7-1 + W ₈・ ν _2V8-1 + W ₉・ ν _2V9-1
... (18)
_{Further, V 31 = (ν 3V1-1,} ν 3V2-1, ν 3V3-1, ν 3V4-1, ν 3V5-1, ν 3V6-1, ν 3V7-1, ν 3V8-1, ν 3V9-1 ) Is multiplied by weighting factors W _{1 to} W ₉ to obtain a sum Vadd _{3-1 of the} multiplication values (formula (19)).

Vadd _3-1 ＝ W ₁・ ν _3V1-1 + W ₂・ ν _3V2-1 + W ₃・ ν _3V3-1 + W ₄・ ν _3V4-1 + W ₅・ ν _3V5-1 + W ₆・ ν _3V6-1 + W ₇・ν _3V7-1 + W ₈・ ν _3V8-1 + W ₉・ ν _3V9-1
... (19)
_{Furthermore, V 41 = (ν 41-1,} ν 4V2-1, ν 4V3-1, ν 4V4-1, ν 4V5-1, ν 4V6-1, ν 4V7-1, ν 4V8-1, ν 4V9- ₁ ) Multiply each of the elements by weighting factors W _{1 to} W ₉ to obtain a sum Vadd _{4-1 of the} multiplication values (formula (20)).

Vadd _4-1 ＝ W ₁・ ν _4V1-1 + W ₂・ ν _4V2-1 + W ₃・ ν _4V3-1 + W ₄・ ν _4V4-1 + W ₅・ ν _4V5-1 + W ₆・ ν _4V6-1 + W ₇・ν _4V7-1 + W ₈・ ν _4V8-1 + W ₉・ ν _4V9-1
... (20)
The weighting synthesis unit V-1 calculates Vadd _1-1 + Vadd _2-1 + Vadd _3-1 + Vadd _4-1 and generates a calculation result that is the sum as a digital synthesized signal, to the D / A unit 16a-1. Output. The same weighting / synthesizing unit performs the same combining operation, and the description is omitted. Note that the weighting coefficient is held in a storage area in the synthesis unit 15, and the value of the weighting coefficient can be set to an arbitrary value by the user.

  As described above, in the antenna characteristic evaluation system 1, the combined signal generation unit 10 generates a plurality of sine waves having different frequencies, combines the baseband signal and the sine wave, and combines the plurality of combined signals. And a desired correlation is given to a plurality of synthesized signals to generate multipath fading.

  This makes it possible to radiate a composite wave with a desired correlation for each path from the transmitting antenna, thus simulating a multipath fading environment with a smaller number of devices compared to the conventional system configuration. Can do. For this reason, fading accuracy can be remarkably improved, and highly accurate antenna characteristic evaluation can be performed efficiently.

(Supplementary note 1) In an antenna characteristic evaluation system for evaluating antenna characteristics,
An evaluation antenna that is an antenna to be evaluated; and
A plurality of transmitting antennas that radiate radio waves to the evaluation antenna;
A baseband signal generator for generating a baseband signal;
A combined signal generator for generating a combined signal;
An up-converter connected to the transmitting antenna and up-converting the frequency of the combined signal to the frequency of the radio wave;
An evaluation unit that is connected to the evaluation antenna and performs evaluation of the antenna characteristics of the evaluation antenna when the radio wave is received;
With
The synthesized signal generator is
Generating a plurality of sine waves having different frequencies to give a desired correlation to the plurality of sine waves;
The sine wave given correlation and the baseband signal are multiplied and combined to generate a plurality of the combined signals, thereby generating fading.
An antenna characteristic evaluation system characterized by that.

  (Additional remark 2) When the said electromagnetic wave which the said transmission antenna radiated | emitted is reflected on the said other transmission antenna, the said transmission antenna which restrict | squeezed directivity is used so that the reflected wave produced | generated may become small enough. The antenna characteristic evaluation system according to appendix 1.

(Supplementary Note 3) The synthesized signal generator is
A signal generation unit including a plurality of sine wave generation units for generating a plurality of initial sine waves having different frequencies;
An arithmetic unit that multiplies the initial sine wave by a correlation parameter for giving a desired correlation to generate a plurality of correlated sine waves that are a sine wave giving the desired correlation;
A sine wave multiplying / delaying unit that multiplies the baseband signal to which a multipath delay is given and the correlated sine wave to generate a multiplication value;
A combining unit that weights and combines the multiplication values to generate the combined signal;
The antenna characteristic evaluation system according to appendix 1, wherein each function operates by digital signal processing.

(Supplementary note 4) The antenna characteristic evaluation system according to supplementary note 3, wherein the sine wave generation unit generates the initial sine wave having a prime frequency relationship.
(Additional remark 5) The said calculating part uses the said correlation parameter so that the correlation of the said some synthesized signal becomes mutually 0, or the correlation of the said some synthesized signal becomes mutually small enough The antenna characteristic evaluation system according to Appendix 3.

(Supplementary Note 6) The plurality of baseband signals input to the combined signal generation unit are set as baseband signals B1 to Bm (m = 1, 2,...), And a plurality of paths when forming a multipath are passed. P1 to Pk (k = 1, 2,...)
The signal generator includes (m × k) sine wave generators, and is arranged in m rows and k columns, assuming that m sine wave generators are arranged in the row direction and k in the column direction. When the sine wave generator is a sine wave generator X _mk ,
The sine wave generator X _mk corresponds to the n initial sine waves X _mVk-n corresponding to the I signal component of the baseband signal Bm and the Q signal component of the baseband signal Bm. n initial sine waves X _mHk-n that are the initial sine waves are generated, and (2n × m × k) initial sine waves are generated from the signal generation unit,
The computing unit is
An initial sine wave X _mVk-a and an initial sine wave X _mHk-a are extracted from each of the m sine wave generation units X _mk located in the k-th column (1 ≦ a ≦ n / 2: a is a natural number) ), Multiplying the column vector of the initial sine wave consisting of n elements by the correlation parameter having n × n matrix elements to generate the column vector of the correlated sine wave consisting of n elements , (N × m × k) number of the correlated sine waves,
Initial sinusoidal X correlation sinusoidal said correlation sine waves corresponding to _mVk-n Y _mVk-n, the correlation sine waves corresponding to the initial sinusoidal X _MHK-n when the correlation sine wave Y _mHk-n,
The sine wave multiplication / delay unit is
When performing multiplication processing for the path P1, without giving a delay to the baseband signal Bm, the baseband signal Bm, generates a multiplied value [nu _mV1-n multiplies the correlation sine wave Y _mV1-n, wherein the baseband signal Bm, generates a multiplied value [nu _MH1-n multiplies the correlation sine wave Y _mH1-n,
When performing a multiplication process on the path Ps (2 ≦ s ≦ k: s is a natural number), when the delay between the paths is Ds−1 (2 ≦ s ≦ k: s is a natural number), the baseband signal Bm is given a delay of D1 + D2 + ··· + Ds- 1, to the baseband signals Bm, by multiplying the correlation sine wave Y _mVs-n generates the multiplication value ν _mVs-n, the baseband signal Bm, correlated Multiply the sine wave Y _{mHs -n} to generate the multiplication value ν _mHs-n ,
The multiplication value vector corresponding to the I signal component obtained by the sine wave multiplication / delay unit is V _mn = (ν _mVk−n ), and the multiplication value vector corresponding to the Q signal component is H _mn = (ν _{mHk− n} )
The combining unit includes n weighting combining units V-1 to Vn and n weighting combining units H-1 to Hn.
A multiplication value vector V _mn is input to the weighting synthesis unit Vn, and a multiplication value vector H _mn is input to the weighting synthesis unit H-n.
The weighting synthesis unit Vn multiplies k multiplication values ν _mVk-n that are elements of the multiplication value vector V _mn by k weighting factors W _r (1 ≦ r ≦ k: r is a natural number). , M addition values Vadd _mn obtained by adding the multiplication results are obtained, and the sum of the addition values Vadd _mn is generated as one synthesized signal,
The weighting synthesis unit H-n multiplies k multiplication values ν _mHk-n that are elements of the multiplication value vector H _mn by k weighting factors W _r , respectively, and adds m multiplication values. Hadd _mn is obtained, and the sum of the added values Hadd _mn is generated as one composite signal.
The antenna characteristic evaluation system according to supplementary note 3, wherein

(Supplementary note 7) In a combined signal generator for generating a combined signal by combining a plurality of signals,
A signal generation unit including a plurality of sine wave generation units for generating a plurality of initial sine waves having different frequencies;
An arithmetic unit that multiplies the initial sine wave by a correlation parameter for giving a desired correlation to generate a plurality of correlated sine waves that are a sine wave giving the desired correlation;
A sine wave multiplication / delay unit that multiplies the baseband signal delayed for each path and the correlated sine wave to generate a multiplication value;
A combining unit that weights and combines the multiplication values to generate the combined signal;
A combined signal generator.

(Supplementary Note 8) The plurality of baseband signals input to the apparatus are baseband signals B1 to Bm (m = 1, 2,...), And the plurality of paths are paths P1 to Pk (k = 1, 2,. ··)age,
The signal generator includes (m × k) sine wave generators, and is arranged in m rows and k columns, assuming that m sine wave generators are arranged in the row direction and k in the column direction. When the sine wave generator is a sine wave generator X _mk ,
The sine wave generation unit X _mk corresponds to half of the number of transmission antennas, n / 2 initial sine waves X _mVk-n corresponding to the initial sine waves, and n / 2 corresponding to the other half of the number of transmission antennas. _Generating initial sine waves X _mHk-n that are the initial sine waves, and generating (n × m × k) initial sine waves from the signal generation unit,
The computing unit is
An initial sine wave X _mVk-a and an initial sine wave X _mHk-a are extracted from each of the m sine wave generation units X _mk located in the k-th column (1 ≦ a ≦ n / 2: a is a natural number) ), Multiplying the column vector of the initial sine wave consisting of n elements by the correlation parameter having n × n matrix elements to generate the column vector of the correlated sine wave consisting of n elements , (N × m × k) number of the correlated sine waves,
Initial sinusoidal X correlation sinusoidal said correlation sine waves corresponding to _mVk-n Y _mVk-n, the correlation sine waves corresponding to the initial sinusoidal X _MHK-n when the correlation sine wave Y _mHk-n,
The sine wave multiplication / delay unit is
When performing multiplication processing for the path P1, without giving a delay to the baseband signal Bm, the baseband signal Bm, generates a multiplied value [nu _mV1-n multiplies the correlation sine wave Y _mV1-n, wherein the baseband signal Bm, generates a multiplied value [nu _MH1-n multiplies the correlation sine wave Y _mH1-n,
When performing a multiplication process on the path Ps (2 ≦ s ≦ k: s is a natural number), when the delay between the paths is Ds−1 (2 ≦ s ≦ k: s is a natural number), the baseband signal Bm is given a delay of (D1 + D2 + ··· + Ds -1, to the baseband signals Bm, generates a multiplied value [nu _mVs-n multiplies the correlation sine wave Y _mVs-n, the baseband signal Bm, Multiply the correlated sine wave Y _{mHs -n} to generate the multiplication value ν _mHs-n ,
The multiplication value vector corresponding to the I signal component obtained by the sine wave multiplication / delay unit is V _mn = (ν _mVk−n ), and the multiplication value vector corresponding to the Q signal component is H _mn = (ν _{mHk− n} )
The combining unit includes n weighting combining units V-1 to Vn and n weighting combining units H-1 to Hn.
A multiplication value vector V _mn is input to the weighting synthesis unit Vn, and a multiplication value vector H _mn is input to the weighting synthesis unit H-n.
The weighting synthesis unit Vn multiplies k multiplication values ν _mVk-n that are elements of the multiplication value vector V _mn by k weighting factors W _r (1 ≦ r ≦ k: r is a natural number). , M addition values Vadd _mn obtained by adding the multiplication results are obtained, and the sum of the addition values Vadd _mn is generated as one synthesized signal,
The weighting synthesis unit H-n multiplies k multiplication values ν _mHk-n that are elements of the multiplication value vector H _mn by k weighting factors W _r , respectively, and adds m multiplication values. Hadd _mn is obtained, and the sum of the added values Hadd _mn is generated as one composite signal.
The combined signal generator according to appendix 7, wherein

It is a principle diagram of an antenna characteristic evaluation system. It is a figure which shows deterioration of the fading accuracy by an omnidirectional antenna. It is a figure which shows a fading period. It is a figure which shows the concept of 1 path environment and multipath environment. It is a figure which shows flat fading and frequency selective fading. It is the figure which represented fading as a vector. It is a figure which shows the structure of an antenna characteristic evaluation system. It is a figure which shows a mode that a reflected wave is suppressed when a transmitting antenna with directivity is used. It is a figure which shows the example of antenna arrangement | positioning when a directional transmission antenna is used. It is a figure which shows the structure of a synthetic | combination signal generation part. It is a figure which shows an example of the sine wave from which a frequency becomes a prime relationship. It is a figure which shows the structure of a signal generation part. It is a figure which shows the initial stage sine wave produced | generated by a sine wave production | generation part. It is a figure which shows the initial stage sine wave produced | generated by a sine wave production | generation part. It is a figure which shows the initial stage sine wave produced | generated by a sine wave production | generation part. It is a figure which shows the initial stage sine wave produced | generated by a sine wave production | generation part. It is a figure which shows the example of a calculation process of a calculating part. It is a figure which shows the whole structure of a sine wave multiplication and delay part. It is a figure which shows the internal structure of a sine wave multiplication and delay part. It is a figure which shows the internal structure of a sine wave multiplication and delay part. It is the figure which expressed the multiplication value of the sine wave multiplication and the delay part by matrix. It is the figure which expressed the multiplication value of the sine wave multiplication and the delay part by matrix. It is the figure which expressed the multiplication value of the sine wave multiplication and the delay part by matrix. It is the figure which expressed the multiplication value of the sine wave multiplication and the delay part by matrix. It is a figure which shows the structure of a synthetic | combination part. It is a figure which shows the structure of a synthetic | combination part. It is a figure for demonstrating the radiation pattern of a multi-antenna. It is a figure which shows the radio wave receiving intensity when the correlation between antennas is small. It is a figure which shows the radio wave reception intensity | strength when the correlation between antennas is large. It is a figure which shows a mode when performing conventional antenna characteristic evaluation. It is a figure for demonstrating a Doppler frequency. It is a figure which shows the change of the Doppler frequency according to the advancing direction of a communication terminal, and the arrival angle of an electromagnetic wave. (A) shows a case where radio waves are received from a path in the same direction with respect to the traveling direction of the communication terminal, and (B) shows a case where radio waves are received from a direction perpendicular to the traveling direction of the communication terminal. It is a figure which shows the structure of the conventional antenna characteristic evaluation system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna characteristic evaluation system 10 Synthetic signal generation part 20 Anechoic chamber 21 Baseband signal generation part 22-1 to 22-4 Up converter 23a-23d Transmitting antenna 24a, 24b Evaluation antenna 30 Evaluation part 31 Antenna characteristic evaluation board 32 Evaluation terminal

Claims (6)

In the antenna characteristics evaluation system that evaluates antenna characteristics,
An evaluation antenna that is an antenna to be evaluated; and
A plurality of transmitting antennas that radiate radio waves to the evaluation antenna;
A baseband signal generator for generating a baseband signal;
A combined signal generator for generating a combined signal;
An up-converter connected to the transmitting antenna and up-converting the frequency of the combined signal to the frequency of the radio wave;
An evaluation unit that is connected to the evaluation antenna and performs evaluation of the antenna characteristics of the evaluation antenna when the radio wave is received;
With
The synthesized signal generator is
Generating a plurality of sine waves having different frequencies to give a desired correlation to the plurality of sine waves;
The sine wave given correlation and the baseband signal are multiplied and combined to generate a plurality of the combined signals, thereby generating fading.
An antenna characteristic evaluation system characterized by that.   The transmission antenna having a reduced directivity is used so that a reflected wave generated when the radio wave radiated from the transmission antenna is reflected by another transmission antenna is sufficiently small. The antenna characteristic evaluation system according to 1. The synthesized signal generator is
A signal generation unit including a plurality of sine wave generation units for generating a plurality of initial sine waves having different frequencies;
An arithmetic unit that multiplies the initial sine wave by a correlation parameter for giving a desired correlation to generate a plurality of correlated sine waves that are a sine wave giving the desired correlation;
A sine wave multiplying / delaying unit that multiplies the baseband signal to which a multipath delay is given and the correlated sine wave to generate a multiplication value;
A combining unit that weights and combines the multiplication values to generate the combined signal;
The antenna characteristic evaluation system according to claim 1, wherein each function operates by digital signal processing.   The antenna characteristic evaluation system according to claim 3, wherein the sine wave generation unit generates the initial sine wave having a prime frequency relationship.   The arithmetic unit uses the correlation parameter such that a plurality of the combined signals have a correlation of 0 with each other, or a plurality of the combined signals have a sufficiently small correlation with each other. 3. The antenna characteristic evaluation system according to 3. In a combined signal generator for generating a combined signal by combining a plurality of signals,
A signal generation unit including a plurality of sine wave generation units for generating a plurality of initial sine waves having different frequencies;
An arithmetic unit that multiplies the initial sine wave by a correlation parameter for giving a desired correlation to generate a plurality of correlated sine waves that are a sine wave giving the desired correlation;
A sine wave multiplication / delay unit that multiplies the baseband signal delayed for each path and the correlated sine wave to generate a multiplication value;
A combining unit that weights and combines the multiplication values to generate the combined signal;
A combined signal generator.

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