reference Figure 13 According to another exemplary embodiment, the alternative downstream control system 244 ( Picture 10 ) Includes a power measurement circuit 244a (for example, VSA) and a control circuit 244b (for example, a digital signal processor (DSP)). The power level of the composite signal 235 is measured by the power measurement circuit 244a to provide the power measurement data 245a to the control circuit 244b. Subsequently, the control circuit 244b provides appropriate phase control signals 245ba, 245bb, ..., 245bn to the phase shifters 236a, 236b, ..., 236n.
 reference Figure 14 ,Such as Figure 13 The operation mode 420 of the test environment in the test environment can proceed as shown. First, in step 421, the phase shifters 236a, 236b, ..., 236n are initialized by pre-setting one or more corresponding phase shift values. Next, in step 422, the power level of the composite signal 235 is measured, and then in step 423, the current measured power is compared with the previously measured power level. In step 424, if the current measured power level is higher than the previously measured power level, the current phase shift value and the measured power are stored, and used in step 425 to determine whether the desired criterion (for example, a Maximize the measured power level). In step 426, if the desired criterion is met, stop adjusting the phase. If the expected criterion is not met, continue to adjust the phase.
 Similarly, if the current measured power is not higher than the previously measured power, continue to adjust the phase. Therefore, the phase shifters 236a, 236b, ..., 236n are adjusted according to an optimization algorithm (for example, a GA or PSA) to give the received test signals 105a, 105b, ..., 105n another set of phase shift values.
 reference Figure 15 , According to another exemplary embodiment, the in-line system 242 ( Picture 10 ) Includes phase detection circuits 242ca, 242cb, ..., 242cn and a control circuit 242d (for example, a DSP). The phase detectors 242ca, 242cb, ..., 242cn can detect the corresponding signal phases of the phase controlled signals 237a, 237b, ..., 237n, and provide corresponding phase data 243ca, 243cb, ..., 243cn to the control circuit 242d. Based on the data, the control circuit 242d provides appropriate phase control signals 243da, 243db, ..., 243dn to the phase shifters 236a, 236b, ..., 236n.
 reference Figure 16 ,Such as Figure 15 The operation mode 430 of the test environment in the can be performed as shown. First, in step 431, the phase shifters 236a, 236b..., 236n are initialized by giving one or more corresponding phase shift values. Next, in step 432, the corresponding phases of the phase-controlled signals 237a, 237b,... 237n (for example, relative to the same or reference signal phase) are measured.
 Then, according to the measured phase of the test signal, in step 433, the phase shifters 236a, 236b..., 236n are configured for phase adjustment according to the optimized phase shift value. After this step, in step 434, the power level of the composite signal 235 is measured to confirm that the desired composite signal power level is reached, and then the phase adjustment is stopped in step 435.
 reference Figure 17 , The exemplary received signal 203 radiated from the broadband antenna 202a of the constant-power device under test (DUT) 200a is placed in the shielded housing 300 (for example, Image 6 ) Has a good response in the frequency range of 700 to 6000 MHz, which is essentially as shown in the figure. It can be clearly understood that based on the rich multi-path signal environment in the shielded housing 300, the power distribution graph is not flat. Taking the packet data signal for communication according to the IEEE standard 802.11ac as an example, the special emphasis is on the 160MHz broadband frequency band between 5000 and 5160MHz. As shown in the figure, within this frequency band 511 (as shown in the enlarged part 510 of the signal 203 distribution diagram), the received signal shows a power variation of approximately 25 decibels (dB). According to an exemplary embodiment, using the test environment as described above, and using a plurality of phase shifters to control the phases of the test signals used to drive the plurality of antenna elements, this distribution diagram can be compensated to make the key frequency band 511 appear substantial flat.
 reference Figure 18 According to an exemplary embodiment, this goal can be achieved by using multiple (for example, 16) antenna elements 102 and corresponding phase shifters 236. For example, by using an optimization algorithm (described in further detail below) and only using quadrature phase adjustments of 0, 90, 180, and 270 degrees, it is possible to achieve the optimal flat response condition 523. As shown, before compensation, the response profile 522 has a variation of more than 5 decibels between the 160 MHz bandwidth 511 of the exemplary test signal. Furthermore, even if the antenna array has achieved the optimization of the power level at the frequency midpoint of 5080 MHz, as shown in the upper distribution diagram 521, the variation of the received signal is still about 5 decibels. However, when the plurality of phase adjusters 236a, 236b,..., 236p are properly adjusted, even if only quadrature phase adjustment is restricted, it is still possible to achieve a response profile 523 with a variation of not more than 0.5 decibels. ,
 reference Figure 19 ,in Figure 18 The compensation shown in can be achieved by using the flow 440 shown. First, in step 441, define multiple frequency values within the desired signal bandwidth, and then in step 442, define a set of initial phase shift values for the phase shifter. In step 443, use the defined phase value to set the phase shifter, and in step 444, measure the power of each frequency. Next, in step 445, the difference between the measured powers of the multiple pairs of defined frequencies is calculated, and in step 446, the sum is used to evaluate the function F, which is equal to the difference between the defined maximum power difference and the sum of the calculated power Difference.
 If the current operation function F current Greater than the previous operation function F before , The phase shifter value is retained in step 448, and is combined in step 449 to determine whether the desired condition is satisfied (for example, a maximization function F is reached). If it is satisfied, the phase adjustment is stopped in step 450. If the expected criterion is not met, continue to adjust the phase. Similarly, if the current operation function F current Not greater than the previous operation function F before , Continue to adjust the phase. In step 451, the phases are continuously adjusted by defining another set of phase shifter values, and the phase adjustment step 443, the power measurement step 444, the power difference calculation step 445, and the calculation function F step 446 are repeated. This process is repeated until the condition is met in step 449.
 reference Picture 20 According to an exemplary embodiment, when a cableless test of a plurality of wireless devices under test (DUT) is performed, similar compensation can be achieved when a cross-coupling signal is used in the shielding housing 300. (For the purpose of this example, two antenna arrays 235a, 235b are used to test two devices under test (DUT) 200a, 200b. However, it is clear that other numbers of devices under test and antenna arrays can be used here. Further, it should be clearly understood that the respective "devices under test (DUT)" 200a, 200b described herein can be corresponding receivers in a single MIMO device under test (DUT) 200.) As described above, the signal source ( For example, the VSG) 110 can provide a test signal 111, which is replicated by a signal distributor 234 to provide a copy of the test signal 235, which is used for phase shifting through a plurality of phase shifters 231 to drive the antenna of the antenna array 235 Component 102. The antenna arrays 235a, 235b provide radiation signal components 103aa, 103ab, 103ba, 103bb, which correspond to the direct-coupling and cross-coupling coefficients of the channel matrix H (eg, as described above). These signal components 103aa, 103ab, 103ba, 103bb are received by the antennas 202a, 202b of the device under test (DUT) 200a, 200b. The received signal data 201a, 201b are provided by the device under test (DUT) 200a, 200b to the control system 206 (for example, DSP), which then provides appropriate phase control signals 207ap, 207bp to the phase shifters 236aa,...236am, 236ba,... , 236bm, to control the phase of the signal radiated by the antenna elements 102aa,..., 102am, 102ba,... 102bm of the antenna arrays 235a, 235b.
 By repeatedly adjusting the phase of the radiation signal, as described above, the direct-coupled channel matrix H coefficients 103aa, 103ba can be maximized and the cross-coupling coefficients 103ab, 103bb can be minimized (for example, by making the final cross-coupling The coefficient ideally becomes at least 10 dB below the direct-coupling coefficient).
 reference Figure 21 According to another exemplary embodiment, the control system 206 may be further configured to provide gain control signals 207ag, 207bg to control the size of the replicated test signals 111a, 111b for transmission to the device under test (DUT) 200a, 200b. Control signal gain stages (for example, variable gain amplifiers or signal attenuators) 232a and 232b can control the magnitude of these signals. It can further optimize the relative magnitudes of the direct-coupling coefficients 103aa, 103ba and the cross-coupling coefficients 103ab, 103bb of the channel matrix H. For example, the magnitudes of the direct-coupling coefficients 103aa, 103ba can be standardized, while still maintaining sufficient cross-coupling coefficients 103ab, 103bb attenuation (for example, 10 decibels or higher).