Patent Document ID: 9921287
Application ID: 14914181
Patent Flag: 1

Claim One:
1. A method for calibrating a test apparatus, having a first and a second directional coupler, for testing a two-port test object (DUT—Device Under Test), which has a first port and a second port in a calibration plane; wherein for the purpose of calibrating the test apparatus a vectorial network analyzer (VNA) having a first, a second, a third, a fourth, a fifth and a sixth test port is connected to the first and second ports in the calibration plane such that the first test port is connected to the first port in the calibration plane, the second test port is connected to the second port in the calibration plane, the third and fourth test ports are connected to the first directional coupler and the fifth and sixth test ports are connected to the second directional coupler via a respective waveguide for electromagnetic waves; wherein at the first test port an electromagnetic wave a 1 runs out in the direction of the first port in the calibration plane and an electromagnetic wave b 1 runs in from the direction of the first port in the calibration plane; wherein at the second test port an electromagnetic wave a 2 runs out in the direction of the second port in the calibration plane and an electromagnetic wave b 2 runs in from the direction of the second port in the calibration plane; wherein at the first port in the calibration plane an electromagnetic wave a DUT,1 runs in from the direction of the first test port and an electromagnetic wave b DUT,1 runs out in the direction of the first test port; wherein at the second port in the calibration plane an electromagnetic wave a DUT,2 runs in from the direction of the second test port and an electromagnetic wave b DUT,2 runs out in the direction of the second test port; wherein between the first test port and the first port in the calibration plane a component of the wave a 1 is coupled out by the first directional coupler as a Mess,1 and fed to the third test port of the VNA; wherein between the first test port and the first port in the calibration plane a component of the wave b 1 is coupled out by the first directional coupler as b Mess,1 and fed to the fourth test port of the VNA; wherein between the second test port and the second port in the calibration plane a component of the wave a 2 is coupled out by the second directional coupler as a Mess,2 and fed to the fifth test port of the VNA; wherein between the second test port and the second port in the calibration plane a component of the wave b 2 is coupled out by the second directional coupler as b Mess,2 and fed to the sixth test port of the VNA; wherein in order to calibrate the test apparatus, instead of the DUT at least three different calibration standards are arranged in the calibration plane; wherein for each calibration standard K and for each desired frequency point of a frequency f of a 1 or a 2 scatter parameters S xy,K,f , where x=1, 2, 3, 4, 5 or 6 and y=1 or 2, are determined between the y-th and the x-th test port of the VNA for the calibration standard K and the frequency f is determined from the known values a 1,K,f and a 2,K,f as well as from the measured values b 1,K,f , b 2,K,f , a Mess,1,K,f , b Mess,1,K,f a Mess,2,K,f , b Mess,2,K,f , whereby [ b 1 , K , f b 2 , K , f ] = [ S 11 , K , f S 12 , K , f S 21 , K , f S 22 , K , f ] ⁡ [ a 1 , K , f a 2 , K , f ] ⁢ [ a Mess , 1 , K , f b Mess , 1 , K , f ] = [ S 31 , K , f S 32 , K , f S 41 , K , f S 42 , K , f ] ⁡ [ a 1 , K , f a 2 , K , f ] ⁢ [ a Mess , 2 , K , f b Mess , 2 , K , f ] = [ S 51 , K , f S 52 , K , f S 61 , K , f S 62 , K , f ] ⁡ [ a 1 , K , f a 2 , K , f ] wherein a scatter matrix S unkorr,K,f S unkorr , K , f = [ S 11 , unkorr , K , f S 12 , unkorr , K , f S 21 , unkorr , K , f S 22 , unkorr , K , f ] , describing the transmission via the directional coupler is calculated from the measured scatter parameters S xy,K,f of the calibration standards, where x=3, 4, 5, 6 and y=1, 2, with scatter parameters S 11,unkorr,K,f , S 12,unkorr,K,f , S 21,unkorr,K,f and S 22,unkorr,K,f , according to S 11 , unkorr , K , f = b MESS , 1 , K , f a MESS , 1 , K , f = S 42 , K , f S 32 , K , f = σ 11 S 21 , unkorr , K , f = b MESS , 2 , K , f a MESS , 2 , K , f = S 61 , K , f S 31 , K , f = σ 21 S 12 , unkorr , K , f = b MESS , 1 , K , f a MESS , 2 , K , f = S 42 , K , f S 32 , K , f = σ 12 S 22 , unkorr , K , f = b MESS , 2 , K , f a MESS , 2 , K , f = S 62 , K , f S 52 , K , f = σ 22 whereby a scatter matrix S I,K,f describing the transmission between the first test port of the VNA and the first port in the calibration plane on the one hand, as well as between the second test port of the VNA and the second port in the calibration plane on the other hand, is determined with the measured scatter parameters S xy,K,f of the calibration standards, where x=1, 2 and y=1, 2, as S I , K , f = [ S 11 , K , f S 12 , K , f S 21 , K , f S 22 , K , f ] whereby, with the measured scatter parameters S xy,K,f of the scatter matrix S I,K,f , where x=1, 2 and y=1, 2, terms i 00 , i 01 ·i 10 and i 11 of an error matrix I A with I A = [ i 00 i 01 i 10 i 11 ] are determined for a signal transmission between the first test port on the one hand and the first port in the calibration plane on the other hand depending on a frequency f of the waves a 1 or a 2 by means of a predetermined calibration algorithm, where I A is a scatter matrix according to [ b 1 a DUT , 1 ] = I A ⁡ [ a 1 b DUT , 1 ] whereby, with the measured scatter parameters S xy,K,f of the scatter matrix S I,K,f , where x=1, 2 and y=1, 2, terms i 22 , i 23 ·i 32 and i 33 of an error matrix I B with I B = [ i 22 i 23 i 32 i 33 ] are determined for a signal transmission between the second test port on the one hand and the second port in the calibration plane on the other hand depending on a frequency f of the waves a 1 or a 2 by means of a predetermined calibration algorithm, whereby I B is a scatter matrix according to [ a DUT , 2 b 2 ] = I B ⁡ [ b DUT , 2 a 2 ] such that for each frequency step with the frequency f of a 1 or a 2 and for each calibration standard K a correction of the scatter matrix S unkorr,K,f is carried out to produce a corrected scatter matrix S c,K,f according to the formula S c , K , f = 1 D ⁡ [ σ 11 - σ 12 ⁢ σ 21 ⁢ Γ F , K , f σ 12 - σ 11 ⁢ σ 12 ⁢ Γ R , K , f σ 21 - σ 22 ⁢ σ 21 ⁢ Γ F , K , f σ 22 - σ 12 ⁢ σ 21 ⁢ Γ R , K , f ] where D=1−σ 12 σ 21 Γ F,K,f Γ R,K,f , and Γ F , K , f = S 51. ⁢ K , f S 61. ⁢ K , f describes the ratio of propagated to reflected wave measured at the output of the second directional coupler on feeding through the first test port of the VNA and Γ R , K , f = S 32. ⁢ K , f S 42. ⁢ K , f describes the ratio of propagated to reflected wave measured at the output of the first directional coupler on feeding through the second test port of the VNA; whereby, with the scatter parameters of the scatter matrix S c,K,f , terms e 00 , e 01 ·e 10 and e 11 of an error matrix E A = [ e 00 e 01 e 10 e 11 ] are determined for a signal transmission between the third and fourth test port on the one hand and the first port in the calibration plane on the other hand depending on a frequency f of the waves a 1 or a 2 by means of a predetermined calibration algorithm, where E A is a scatter matrix according to [ b MESS , 1 a DUT , 1 ] = E A ⁡ [ a MESS , 1 b DUT , 1 ] whereby, with the scatter parameters of the scatter matrix S c,K,f , terms e 22 , e 23 ·e 32 and e 33 of an error matrix E B = [ e 22 e 23 e 32 e 33 ] are determined for a signal transmission between the fifth and sixth test port on the one hand and the second port in the calibration plane on the other hand depending on a frequency f of the waves a 1 or a 2 by a predetermined calibration algorithm, whereby E B is a scatter matrix according to [ a DUT , 2 b MESS , 2 ] = E B ⁡ [ b DUT , 2 a MESS , 2 ] whereby the isolated terms i 01 and i 10 from the product i 01 ·i 10 as well as the isolated terms i 23 and i 32 from the product i 23 ·i 32 are determined according to the formulas 
 i 01 =i 10 =±√{square root over ( i 10 i 10 )} 
 And 
 i 23 =i 32 =±√{square root over ( i 23 i 32 )} whereby the sign is in each case determined starting out from a frequency point with known phase through continuous extrapolation, whereby a phase difference from one frequency point to a next frequency point is reduced by 180° if this phase difference exceeds a predetermined threshold value; whereby the isolated term e 10 is calculated from the product e 10 ·e 01 according to the formula e 10 = i 10 · a 1 a MESS , 1 · 1 - e 11 ⁢ S 11 , DUT , K * 1 - i 11 ⁢ S 11 , DUT , K * and the isolated term e 01 is determined from this, whereby S 11 , DUT , K * = ( S 11 , K * , f - i 00 ) ( i 10 · i 01 + i 11 · ( S 11 , K * , f - i 00 ) ) and K* designates a calibration standard without transmission; whereby the isolated term e 23 from the product e 32 ·e 23 is calculated according to the formula e 23 = i 23 · a 2 a MESS , 2 · 1 - e 22 ⁢ S 22 , DUT , K * 1 - i 22 ⁢ S 22 , DUT , K * and the isolated term e 23 is determined from this, whereby S 22 , DUT , K * = ( S 22 , K * , f - i 22 , f ) ( i 32 · i 23 + i 33 · ( S 22 , K * , f - i 22 , f ) ) and K* designates a calibration standard without transmission.