HANDHELD VECTOR NETWORK ANALYZER (VNA) OPERATING AT A HIGH FREQUENCY BY MIXING LO AND RF SIGNALS HAVING OFFSET ODD HARMONICS

Abstract: A vector network analyzer (VNA) has a first harmonic generator multiplying an RF signal by an odd number M1 to produce incident and reflected test signals received at inputs of mixers providing IF signals. A second harmonic generator multiplies an LO signal by an odd number M2 offset by 2 from M1 to provide signals to additional inputs of the mixers providing IF signals. With the harmonic generators providing odd harmonics separated by 2, a single filter removes remaining harmonics from IF signals provided from each mixer. Each harmonic generator includes two step recovery diodes (SRDs) with opposing ends connecting the signal path to ground, the SRDs functioning to cancel even harmonics. A first coupler provides the output of the first harmonic generator to the mixers, the first coupler having a minimal size enabling its output power to increase with frequency. With the first harmonic generator having power decreasing with frequency and the first coupler having power increasing with frequency, the VNA test signal will have a substantially flat power vs. frequency response. Additional couplers having a minimal size provide the incident and reflected test signals to the mixers. With the second harmonic generator providing an LO signal with power decreasing with frequency to the mixers, and the additional couplers providing power increasing with frequency, the IF signals from the mixers will also have a flat power vs. frequency response.

Description: HANDHELD VECTOR NETWORK ANALYZER (VNA) OPERATING AT A HIGH FREQUENCY BY MIXING LO AND RF SIGNALS HAVING OFFSET ODD HARMONICS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a VNA with circuitry to provide a high frequency test signal by providing an RF signal through a harmonic generator. More particularly, the present invention relates to such circuitry configured for use in a handheld VNA. 2. Description of the Related Art VNAs transmit a microwave signal to a test device and receive a return signal to enable characterization of the test device. With a VNA, a user can easily identify a fault in a test device, such as a transmission line, and measure the distance from the VNA to the fault or discontinuity. Test measurements are first typically made using a VNA operating in the frequency domain to determine whether a fault exists as indicated by an undesirable standing wave ratio (SWR). If a fault is discovered, an analysis of the results derived from the frequency domain measurement is made in the time domain to locate the position of the fault. A VNA also enables calibration to extend a VNA test port connection to the end of a cable connected to the test port. By using a VNA to extend the test port to the end of a cable, errors in the cable will not be taken into account when measuring a device through the cable. Scalar devices which measure only amplitude and not phase do not enable extension of the test port υ to the end of a cable as does a VNA. A remote transmitter may transmit signals which are received by a device being tested by a VNA. With a tuned receiver, a VNA provides the ability to distinguish such extraneous signals. Scalar devices which receive a broadband of frequencies without discrimination, such as with a tuned receiver, cannot distinguish the extraneous signals Most VNAs are large and not easily transportable. Typical VNAs have a housing greater than two feet on a side, and with a power supply may weigh 50 pounds or more. The SiteMaster manufactured by Wiltron Company of Morgan Hill, California, in contrast, has dimensions equal to or less than 8 inches by 6 inches by 2 i inches and a weight of less than three pounds, including batteries, when operating over a 25 MHz to 3.3 GHz frequency range. With such weight and size, the SiteMaster can be easily transported by one person. Components used in the SiteMaster are described in U.S. Patent No. 5,642,039, entitled "Handheld Vector Network Analyzer", and incorporated herein by reference. SUMMARY OF THE INVENTION The present invention enables increasing the test signal frequency of the handheld VNA described in U.S. Patent No. 5,642,039 without providing a significant increase in size, weight, or power consumption so that the VNA can still be easily transported by one person. The present invention is a circuit for a VNA including a first harmonic generator which multiplies an RF signal by an odd number Ml to produce incident and reflected test signals which are received at inputs of mixers providing IF signals. A second harmonic generator is also included in the VNA for multiplying a LO signal by an odd number M2 offset by 2 from Ml to provide signals to additional inputs of the mixers providing IF signals. With the harmonic generators providing odd harmonics separated by 2, a single filter removes remaining harmonics from IF signals provided from each mixer. Each harmonic generator includes two step recovery diodes (SRDs) with opposing ends connecting the signal path to ground. The SRDs connected in an opposing manner cancel even harmonics and enhance odd harmonics provided from the harmonic generators. The VNA further includes a first coupler for coupling the output of the first harmomc generator to the mixers. The first coupler has a minimal size enabling its output power to increase with its input signal frequency. With the first harmomc generator providing power decreasing with frequency and the first coupler providing power increasing with frequency, the overall test signal provided from the VNA will have substantially a flat power vs. frequency response. Additional couplers are further used to provide the incident and reflected test signals to the mixers. The additional couplers also have a minimal size to provide output power increasing with input signal frequency. With the second harmonic generator providing a LO signal with power decreasing with frequency to the mixers, the IF signals from the mixers in the VNA will have a flat power vs. frequency response to prevent mixer saturation. With a limited size for the couplers in the VNA, the size for the overall VNA using harmonic generators to increase test signal frequency can be minimized enabling the VNA to be handheld. BRTEF DESCRIPTION OF THE DRAWINGS Further details of the present invention are explained with the help of the attached drawings in which: Fig. 1 shows components for the VNA of the present invention; Fig. 2 shows circuitry utilized in the harmonic generators of Fig. 1; Fig. 3 shows the response of individual step recovery diodes (SRDs) in the harmonic generators of Fig. 2 to an input signal; Fig. 4 shows the output of the harmomc generators with each harmonic generator including two SRDs as shown in Fig. 2; Fig. 5 shows a representative frequency vs. power response for odd harmonics of a harmonic generator as well as the frequency vs. power response for a coupler; Fig. 6 shows the combined frequency vs. power response for the harmonic generator 124 and coupler 130 as combined from the responses in Fig. 5. Fig. 7 shows first, third, fifth and seventh harmonics of a selected signal provided from the harmomc generators of Fig. 1; and Fig. 8 plots desired test signal frequency vs. IF signals provided from the mixers of Fig. 1 at each test signal frequency. DETAILED DESCRIPTION The present invention includes components for a VNA described in U.S. Patent 5,642,039, referred to previously, and modifies those components as described subsequently to enable the VNA to operate at a higher frequency. Fig. 1 shows components for the VNA of the present invention. In Fig. 1, representative values for frequencies and frequency division numbers for frequency dividers are shown for purposes of illustration, although other values may be used depending on desired operating conditions. The test circuitry of Fig. 1 initially includes two phase locked loops (PLLs), or synthesizers, including a test signal synthesizer 100 and a first LO signal synthesizer 102. Each of the synthesizers 100 and 102 include a phase detector receiving an input signal to the synthesizer, and an amplifier, oscillator and frequency divider connecting the output of the phase detector back to a second input of the phase detector. The oscillator then provides an output of the synthesizers 100 and 102. The input of the test signal synthesizer 100 is coupled to receive a reference signal from a reference signal oscillator 104 through a frequency divider 106. The frequency divider 106 divides the frequency from the oscillator 104 by a number Rl to provide an input to the test signal synthesizer 100. The input to the first LO signal synthesizer 102 is coupled to receive the output of the test signal synthesizer 100 through a frequency divider 108. The frequency divider 108 divides the frequency from the test signal synthesizer 100 by a number N2 to provide an input to the first LO signal synthesizer 102. Frequency dividers 110 and 112 in the respective test signal synthesizer 100 and tracking signal synthesizer 102 divide by respective numbers Nl and (R2 X 128). The frequency divider 112 is preferably formed with series connected frequency dividers, one dividing by 128 and the next R2, rather than a single frequency divider due to potential limitations in operation speed when using a single frequency divider dividing by R2 X 128. Although a number 128 is chosen, other numbers may be utilized depending on the range of values desired for R2. The value for the RF output from the test signal synthesizer 100, F RFA , is F RPA = F R N1/R1. Resolution, or the steps between frequencies which can be provided for the RF signal F OA can be defined as follows: RES = F R (N1-1)/(R1-1)-F R N1/R1 = F R (N1-R1)/(R1(R1-1)) Wherein F R is the frequency from the reference signal oscillator 104. Settling time for the signal F^ is further defined as t,^ = 4.5/(2πF R /10Rl). The values for Rl and Nl are chosen to optimize resolution and settling time for a particular frequency as described in detail in copending U.S. Patent Application No. 08/719,763 entitled "Frequency Synthesizer Using A Ratio Sum Topology, filed September 25, 1996, and incorporated herein by reference. By interactively selecting Nl , N2, Rl and R2, as further indicated the U.S. Patent Application No. 08/719,763 referred to above, output signal resolution and settling time for the LO signal F LOA provided from the first LO signal synthesizer 102 can be minimized. With the test signal provided from the VNA of the present invention having a high frequency, a second LO signal synthesizer 114 is included to provide a second downconversion to increase operation speed from a VNA using only one downconversion. Using two downconversions enables increased operation speed by enabling use of more coarse resolution synthesizers 102 and 114, the coarse resolution reducing settling time relative to a single fine resolution synthesizer used to provide only one downconversion. As with the synthesizers 100 and 102, the second LO signal synthesizer 114 includes a phase detector receiving an input signal to the synthesizer, and an amplifier, oscillator and frequency divider connecting the output of the phase detector back to a second input of the phase detector. The oscillator then provides the output of synthesizer 114. The input of the second LO signal synthesizer 114 is coupled to receive the output of the test signal synthesizer 100 through a frequency divider 118. The frequency divider 118 divides the frequency from the oscillator 104 by a number N3 to provide an input to the second LO signal synthesizer 114. The frequency divider 116 in the synthesizer 114 divides signals received at its input by a number R3. By interactively selecting Nl , Rl, N3 and R3, output signal resolution and settling time for the LO signal F LOB provided from the second LO signal synthesizer 114 can be minimized. A series connected frequency divider 120 and amplifier 122 provide the test signal synthesizer 100 output to the input of a harmomc generator 124. The output of the LO signal synthesizer 102 is provided through an amplifier 126 to an additional harmonic generator 128. The frequency divider 120 divides the output of the test signal synthesizer 100 by a number D, which is either l or 1, to provide a signal F RFB to the harmomc generator 124. The frequency divider 120 is utilized to increase the range of frequencies provided to the harmonic generator 124. For instance, with the test signal synthesizer operating over the range 800- 1600 MHZ, the range of signals provided to harmonic generator 124 with a direct connection will be 800-1600 MHZ. However, by dividing the frequency of the signal from test signal synthesizer by Vz, signals in the range of 400-1600 MHZ can be appl ed to the harmonic generator 124. The harmonic generator 124 multiplies the frequency of its input signal F FB by Ml, as well as by other numbers to create multiple harmonics. Similarly, the harmomc generator 128 multiplies the frequency of its input signal F LOA by M2, as well as by other numbers to create multiple harmomcs. The signal frequencies F RPJ , and F L0A , however, are selected so that only the particular harmomcs Ml and M2 will create an IF signal which is not filtered out, as described in more detail subsequently. Fig. 2 shows circuitry utilized in the harmomc generators 124 and 128 of Fig. 1. As shown, the harmonic generators 124 and 128 include two step recovery diodes (SRDs) 200 and 202. With the SRDs being p-n type diodes, the p side terminal of SRD 200 is connected to node 204 while its n side terminal is connected to ground. The SRD 202 then has a p side terminal connected to ground and an n side terminal connected to node 204. An inductor 206 connects the input of each harmomc generator to node 204. A capacitor 208 connects the output of each harmonic generator to node 204. Fig. 3 shows a response 300 of individual ones of the SRDs 200 and 202 to an input signal 302. As shown, in contrast to a conventional diode, an SRD stores charge when forward biased and releases the stored charge when becoming reverse biased to create an impulse voltage, such as 304. Fig. 4 shows the output 400 of the harmomc generators 124 and 128 in response to an input signal 402, with each harmomc generator including two SRDs as shown in Fig. 2. As indicated, the pulse of each SRD is limited by charge storage capability in an opposing SRD, but edges of the output signal are very fast. With SRDs having opposing ends connected to the signal path as shown in Fig. 2, the signals having even harmomcs will be canceled out, and only the odd harmonic signals will provide an output for the harmonic generators. With the SRDs connected in an opposing manner, the odd harmonics provided from the harmonic generators 124 and 128 will be enhanced relative to odd harmonics provided from a single SRD. The inductor 206 of Fig. 2 serves to prevent the current provided from the pulses of the SRDs 200 and 202 from traveling back to components providing an input signal to the harmonic generator. Similarly, the capacitor 208 prevents the input signal, separate from the pulses provided by the SRDs 200 and 202, from being provided to circuit connected downstream from the harmonic generator. The output of harmomc generator 124 is connected to a coupler 130. A through path of the coupler 130 connects the harmonic generator 124 to a termination. The coupling path of coupler 130 then connects a termination through the thru path of couplers 132 and 134 to a test port 136. The coupler 130 is utilized to provide the signal from the output of harmomc mixer 124 to the test port 136, rather than using a direct connection to the test port 136, to provide a flat power vs. frequency response. Fig. 5 shows a representative frequency vs. power response for odd harmomcs 1-19 of harmonic generator 124 as well as a frequency vs. power response of coupler 130. As shown, with higher harmonics and, thus, higher frequency, the output power of the harmonic generator 124 decreases exponentially. The response of the coupler 130, as shown, provides increasing power with increasing frequency. Fig. 6 shows the combined frequency vs. power response for the harmonic generator 124 and coupler 130 as combined from the responses in Fig. 5. As shown in Fig. 6, the response of the higher harmonics is substantially flat. Further, the difference from the fundamental XI to higher harmonics is approximately 12 dB in Fig. 6, while without coupler 130 the difference from the fundamental to higher harmomcs is as high as approximately 24 dB as shown in Fig. 5. To provide a coupler 130 having a response as shown in Fig. 5, component sizes for the coupler can be substantially reduced from a more typical coupler with components structured to provide a more flat frequency vs. power response. For representative frequencies shown in Fig. 1, the size of a coupler 130 can be less than .05 in. by .05 in. and provide a desirable response. The coupling path of coupler 132 provides an incident RF signal to a first input of mixer 138. The coupling path of coupler 134 provides a reflected RF signal to a first input of mixer 140. Although a direct connection could be provided from coupler 130 to mixer 138, coupler 132 is used for a similar reason to coupler 130, as described below. Couplers 132 and 134 preferably have a limited size to provide output power increasing with frequency, similar to coupler 130 as illustrated in Fig. 5. The output of harmonic generator 128 decreases in power with increasing frequency, similar to harmonic generator 124 as illustrated in Fig. 5, and is provided to second inputs of mixers 138 and 140. With the power output of couplers 132 and 134 increasing with frequency and the power output of harmonic generator 128 decreasing with frequency, the power output of mixers 138 and 140 will be substantially flat with frequency. With the power output of mixers 138 and 140 being substantially flat, saturation of the mixer outputs when higher power is provided can be minimized. To assure a substantially equal loss is provided by the VNA to the incident and reflected RF signals so that incident and reflected signals can be later compared relative to one another, attenuation pads can further be provided between the couplers 132 and 134 and respective mixers 138 and 140. For representative frequencies shown in Fig. 1, the size of a couplers 132 and 134 can be less than .05 in. by .05 in. and provide a desirable response. For frequencies shown in Fig. 1 , the total space required for couplers 130, 132 and 134 as well as the attenuation pads provided between coupler 132 and mixer 138 and coupler 134 and mixer 140 can be on the order of a .5 in. by .75 in. area. For a conventional system operating at 3.3 GHz, and couplers 130, 132 and 134 sized to provide a flat power vs. frequency response, each coupler would occupy a 3 in. by .5 in. area. The limited size for couplers 130, 132 and 134 in the present invention enables a VNA made using such components to have a minimal size to assure the VNA can be easily handheld by one person. With mixer 138 mixing the incident RF signal with an LO signal, an incident intermediate frequency (IF) signal is provided from mixer 138 to bandpass filter 142. With mixer 140 mixing the reflected RF signal with a LO signal, a reflected IF signal is further provided from mixer 140 to bandpass filter 144. The frequency of signals provided to harmomc mixers 124 and 128 are set so that the harmonic of a desired test signal Fo provided from harmomc generator 124 and the harmonic of a LO signal provided from harmomc generator 128 are both odd and offset by 2 and when mixed provide an IF signal within the pass band of filters 142 and 144. The passband of filters 142 and 144 are set so that the IF signal created by the desired test signal and selected LO signal will be passed, while remaining harmonics are filtered out. The ability to filter out undesired harmonics for a 3.3 GHz test signal Fo using filters 142 and 144 is illustrated in Fig. 7. Fig. 7 shows first, third, fifth and seventh harmonics (XI RJ ,, X3 RF , Xδ^ and Xl^) °f a signal provided from harmomc generator 124, along with first, third, fifth and seventh harmonics (Xl LO , X3 LO , X5 LO and X7 LO ) of a signal provided from harmomc generator 128. The first harmomc Xl^ from harmonic generator 124 is shown set at 660 MHZ in Fig. 7, while the first harmomc Xl LO provided from harmonic generator 128 is shown set to 1093 MHZ. The difference between the first harmomcs Xl^ and Xl LO , as would be provided from either of mixers 138 and 140, will be 443 MHZ which is outside the frequency bandwidth of filters 142 and 144. Similarly the difference in other combinations of harmonics as shown in Fig. 7 will be outside the bandwidth of filters 142 and 144, except the difference between Xδ^ and X3 LO . The difference between X5 RP and X3 L0 is approximately 18 MHZ, a frequency within the bandwidth of filters 142 and 144. Note that the signal X5 RF is at 3300 MHZ, which is the desired test signal Fo frequency. Fig. 8 illustrates how desired output test signal Fo frequencies ranging from 3.3 - 27.2 GHz can be provided and undesired harmomcs removed using filters 142 and 144. Fig. 8 plots desired test signal frequency Fo from 3.3 - 27.2 GHz vs. IF signal frequencies provided from mixers 138 and 140 for each test signal frequency. Harmomcs numbers of the respective RF and LO signals forming the IF signals are further indicated in Fig. 8 with the plotted IF signals. As shown, for each desired Fo signal frequency in the range of 3.3-27.2 GHz, one IF signal be in the 13.53-19.00 MHZ bandwidth of the filters 142 and 144, the IF signal having been formed by RF and LO signals having odd harmonics separated by 2. Remaining IF signals formed by other harmomcs of the RF and LO signals at each desired Fo signal frequency will be outside the 13.53-19.00 MHZ frequency band of filters 142 and 144. To control the frequency of the first harmonic for the harmonic generators 124 and 128, the values for D, Nl, Rl, N2, and R2 are appropriately set. Appendix A includes a sample basic program used to calculate values for D, Nl, Rl, N2 and R2 to provide a set of test signals Fo ranging from 3.3 to 27.2 GHz. For each test signal frequency Fo, the program determines the signal F^ provided to harmomc generator 124, the signal F LOA provided to harmonic generator 128, and the harmonics Ml and M2 provided from harmonic generators 124 and 128 which will create an IF signal with a frequency ¥ σ within the passband region of filters 142 and 144. A result of a run of the program of Appendix A is shown in Appendix B. Referring to the program of Appendix A, the program operates by reading 24 values for Fo beginning at lines 50 and 60. The data for the desired values of Fo are stored at lines 210, 220 and 230. After each value for Fo is read, results are calculated in a subroutine called at line 70 and results are then printed in lines 110-180. In the subroutine which begins at line 2000, the value for the reference frequency F R = 6 MHZ is first set in line 2110. In line 2020, M2 is then set to change every 1600 MHZ because the maximum value for F LOA is approximately 1600 MHZ. Step 2030 assures that M2 is odd, and step 2040 sets Ml to M2+2. Steps 2050-2060 set D to Vz when the desired frequency for will be less than 800 MHZ and otherwise sets D to 1. The remaining steps 2070-2260 of the subroutine calculate the values for Nl, Rl, N2, R2, N3, R3, F^, F LOA , and Fπ, for each particular value of Fo. The output of filter 142 is provided through an amplifier 146 to a first input of mixer 150, while the output of filter 144 is provided through an amplifier 148 to a first input of mixer 152. Second inputs to mixers 150 and 152 are provided from the second LO signal synthesizer 114. The numbers R3 and N3 for frequency dividers 116 and 118 are set so that the IF signal provided from filters 142 and 144 will be downconverted to approximately 190 KHz. The outputs of mixers 150 and 152 are provided through respective filters 154 and 156 to synchronous detectors 160. Two downconversions are utilized in the circuit of Fig. 1, one through mixers 138 and 140 and the other through mixers 150 and 152. Although components could be configured in the circuit of Fig. 1 to make the output of mixers 138 and 140 approximately 190 KHz using one conversion, two downconversions are preferably used to increase operation speed, as discussed previously. The filters 154 and 156 are band pass filters having a center frequency of approximately 190 KHz to filter out undesired harmonics from the output of mixers 150 and 152. The output of the mixers 150 and 152 is controlled to be approximately 190 KHz which is typically required at the input of the synchronous detectors 160. The synchronous detectors 160 function to convert the incident and reflected signals received into digital signals indicative of real and imaginary components of the incident signal and real and imaginary components of the reflected signal received. Components for a synchronous detector are described in U.S. Patent No. 5,642,039, referred to previously. A digital signal processor can be utilized in place of the synchronous detectors, also as indicated in U.S. Patent No. 5,642,039. The synchronous detectors 160 may also include a dither line connected to reference oscillator 104 to enable operation of the VNA with minimal interference from external signals. The reference oscillator 104 operates at a frequency F R which is a chosen reference frequency with an offset, for example 6 MHZ ±. 600 Hz. The dither line provides a signal causing the reference oscillator 104 to sweep the entire +_ 600 Hz range during each cycle of the IF signals from mixers 150 and 152 provided to the synchronous detectors 160. A signal provided from an external source at a particular frequency will interfere with only a portion of the signals in the ±_ 600 Hz range, enabling the outputs of the synchronous detectors to be substantially unaffected by the external signal source. Specific circuitry for providing the dither line is disclosed in U.S. Patent No. 5,642,039, referred to previously. Although the invention has been described above with particularity, this was merely to teach one of ordinary skill in the art how to make and use the invention. Many modifications will fall within the scope of the invention, as that scope is defined by the following claims. APPENDIX A 20 REM ! 3.3 to 2.7 GHz For Fo DISPLAYED ! 30 PS = 128 0CNT = 0 50 FOR I = 1 to 24 60 READ F 70 GOSUB 2000 80 IF CNT>0 THEN 110 90 PRINT "F 0 F RFB M, F L0A M 2 F IF " 100 PRINT " " 110 PRINT USING "##### ";F; 120 PRINT USING "#####.### ";FRFA*D; 130 PRINT USING "## ";M1; 140 PRINT USING "#####.### ";FLOB; 150 PRINT USING "## ";M2; 160 PRINT USING "##.### ";FIF1 170CNT = CNT+1 180 IFCNT = 3 ORCNT = 6 ORCNT = 9 ORCNT = 12 ORCNT = 15 ORCNT = 18 OR CNT = 21 THEN PRINT " " 190 NEXT I 200 END 210 DATA 3300, 4050, 4799, 4800, 6400, 7999, 8000, 9600, 11199, 11200, 12800 220 DATA 14399, 14400, 16000, 17599, 17600, 19200, 20799, 20800, 22400, 23999 230 DATA 24000, 25600, 27199 2000 REM ! CALCULATE D, Nl, R1, N2, R2, N3, R3, GIVEN Fo ! 2010 FR = 6 : PS = 128 2020 M2 = 1 + INT(F/1600) 2030 IF M2 MOD 2=0 THEN M2=M2 + 1 2040 M1 =M2 + 2 2050 D = 1 2060 IF F/MK 800 THEN D = 1/2 2070 R1N = INT(9600*FR*D* 1/F) 2080 FOR R1 =R1N TO R1N +37 2090 N1 =INT (F*R1/(FR » D*M1) + .5) 2100FRFA = FR»N1/R1 2110F0 = FRFA*D*M1 2120FE = F0-F 2130 IF ABS(FE)< 1/38 THEN 2170 2140 NEXT R1 2150 PRINT "NO SOLUTION AT";F;"MHZ" 2160 END 2170 K = (FRFA*D*M1-19)/(FOA*M2) 2180FOBT=K*FRFA 2190 R2A =INT(FOBT/(PS*.285» 2200R2 = R2A*PS 2210N2 = INT(R2/K) 2220 FLOA = FRFA*R2/N2 2230 FIF1 =FRFA*D*M1-FLOA*M2 2240 R3=INT (N2*(FIF1 +.19)/FRFA) 2250 N3 = INT <(FRFA*R3)/(FIF1 +.19)) 2260 RETURN APPENDIX B 3300 660.000 5 1093.714 3 18.857 4050 810.000 5 1344.069 3 17.793 4799 959.800 5 1593.586 3 18.241 4800 685.714 7 956.236 5 18.820 6400 914.286 7 1276.539 5 17.306 7999 1142.706 7 1596.308 5 17.401 8000 888.909 9 1140.379 7 17.531 9600 1066.667 9 1369.033 7 16.767 11199 1244.348 9 1597.223 7 18.572 11200 1018.179 11 1242.600 9 16.562 12800 1163.633 11 1420.304 9 17.229 14399 1309.021 11 1597.883 9 18.289 14400 1107.692 13 1307.632 11 16.053 16000 1230.783 13 1452.841 11 18.918 17599 1353.768 13 1598.270 11 18.004 17600 1173.346 15 1352.719 13 14.854 19200 1280.000 15 1475.704 13 15.854 20799 1386.585 15 1598.610 13 16.846 20800 1223.510 17 1385.592 15 15.799 22400 1317.628 17 1492.204 15 16.613 23999 1411.714 17 1598.781 15 17.430 24000 1263.184 19 1410.821 17 16.533 25600 1347.349 19 1504.764 17 18.639 27199 1431.512 19 1598.832 17 18.592

Claims: What Is Claimed Is: 1. A vector network analyzer (VNA) comprising: an RF signal source; a LO signal source; a first harmonic generator having an input coupled to the RF signal source and an output, the first harmomc mixer for multiplying frequency of a signal from the RF signal source by an odd number Ml to form a signal a second harmonic generator having an input coupled to the LO signal source and an output, the second harmonic mixer for multiplying frequency of a signal from the LO signal source by an odd number M2 offset from the number Ml to form a signal LO M2 ; a first coupler having a first path coupling the output of the first harmomc generator to a test port and a second path coupling the test port to a first coupler output terminal; a first mixer having a first input coupled to the output of the first harmonic generator, a second input coupled to the output of the second harmonic generator, and having an output; a second mixer having a first input coupled to the first coupler output terminal, a second input coupled to the output of the second harmonic generator, and having an output; a first filter having an input coupled to the output of the first mixer and an output passing an incident signal formed from the signals RF M1 and LO M2 , and filtering out signals formed from other harmomcs provided from the first and second harmonic generators; and a second filter having an input coupled to the output of the second mixer and an output passing a reflected signal formed from the signals RF M1 and LO MJ , and filtering out signals formed from other harmomcs provided from the first and second harmomc generators. 2. The VNA of Claim 1 wherein the number Ml is offset from the number M2 by two. 3. The VNA of Claim 1 wherein each of the first and second harmomc generators each comprise: a first p-n diode having a p side terminal coupled to the input of the harmonic generator and an n side terminal coupled to a voltage potential; and a second p-n diode having an n side terminal coupled to the input of the harmonic generator and a p side terminal coupled to a voltage potential. 4. The VNA of Claim 3, wherein the first and second p-n diodes comprise step recovery diodes. 5. The VNA of Claim 1 further comprising: a second coupler coupling the output of the first harmonic generator to the first path of the first coupler and to the first input of the first mixer, the second coupler having a through path connecting a termination to a second coupler input terminal which is coupled to the output of the first harmomc generator, the second coupler further having a coupling path connecting a termination to a second coupler output terminal which is coupled to the first path of the first coupler and to the first input of the first mixer. 6. The VNA of Claim 5, wherein the second coupler is sized to provide power to the second coupler output terminal increasing with frequency of a constant power signal provided to the second coupler input terminal. 7. The VNA of Claim 1 further comprising: a third coupler having a through path coupling the output of the first harmomc generator to a test port and a coupling path connecting a termination to a third coupler output which is coupled to the first mixer. 8. The VNA of Claim 7, wherein the first coupler is sized to provide power to the first coupler output terminal increasing with frequency of a constant power signal provided through the first path of the first coupler, and wherein the third coupler is sized to provide power to the third coupler output terminal increasing with frequency of a constant power signal provided through the through path of the third coupler. 9. A vector network analyzer (VNA) comprising: an RF signal source; a LO signal source; a first harmonic generator having an input coupled to the RF signal source, and having an output; a second harmomc generator having an input coupled to the LO signal source, and having an output, wherein the first harmonic generator and the second harmonic generator each comprise: a first p-n diode having a p side terminal coupled to the input of the harmonic generator and an n side terminal coupled to a voltage potential; and a second p-n diode having an n side terminal coupled to the input of the harmonic generator and a p side terminal coupled to a voltage potential; a first coupler having a first path coupling the output of the first harmomc generators to a test port and a second path coupling the test port to a first coupler output terminal; a first mixer having a first input coupled to the output of the first harmonic generator, a second input coupled to the output of the second harmonic generator, and having an output; and a second mixer having a first input coupled to the first coupler output terminal, a second input coupled to the output of the second harmomc generator, and having an output. 10. The VNA of Claim 9, wherein the first and second p-n diodes comprise step recovery diodes. 11. The VNA of Claim 10 further comprising: a second coupler coupling the output of the first harmomc generator to the first path of the first coupler and to the first input of the first mixer, the second coupler having a through path connecting a termination to a second coupler input terminal which is coupled to the output of the first harmonic generator, the second coupler further having a coupling path connecting a termination to a second coupler output terminal which is coupled to the first path of the first coupler and to the first input of the first mixer, wherein the second coupler is sized to provide power to the second coupler output terminal increasing with frequency of a constant power signal provided to the second coupler input terminal. 12. The VNA of Claim 10 further comprising: a third coupler having a through path coupling the output of the first harmomc generator to a test port and a coupling path connecting a termination to a third coupler output which is coupled to the first mixer, wherein the first coupler is sized to provide power to the first coupler output terminal increasing with frequency of a constant power signal provided through the first path of the first coupler, and wherein the third coupler is sized to provide power to the third coupler output terminal increasing with frequency of a constant power signal provided through the through path of the third coupler. 13. A vector network analyzer (VNA) comprising: an RF signal source; a LO signal source; a first harmomc generator having an input coupled to the RF signal source and an output coupled to a first node; a first coupler having a through path connecting the first node to a termination and a coupling path coupling a second node to a termination; a second coupler having a first path coupling the second node to a test port and a second path coupling the test port to a third node; a first mixer having a first input coupled to the second node, a second input coupled to the LO signal source, and having an output providing an incident signal; and a second mixer having a first input coupled to the third node, a second input coupled to the LO signal source and an output providing a reflected signal. 14. The VNA of Claim 13, wherein the second coupler is sized to provide power to the second node increasing with frequency of a constant power signal provided to the first node. 15. A vector network analyzer (VNA) comprising: an RF signal source connected to a first node; a LO signal source; a first harmomc generator having an input coupled to the RF signal source and an output; a first coupler having a through path coupling the first node to a test port and a second path coupling the test port to a second node; a second coupler having a through path coupling the first node to the test port and a second path coupling the test port to a third node; a first mixer having a first input coupled to the second node, a second input coupled to the output of the first harmonic generator, and having an output providing an incident signal; and a second mixer having a first input coupled to the third node, a second input coupled to the output of the first harmomc generator, and having an output providing a reflected signal. 16. The VNA of Claim 15, wherein the first coupler is sized to provide power to the second node increasing with frequency of a constant power signal provided through the through path of the first coupler, and wherein the third coupler is sized to provide power to the third node increasing with frequency of a constant power signal provided through the through path of the third coupler.

Inventors: BRADLEY DONALD A, BRADLEY, DONALD, A.
Applicants: ANRITSU CO, ANRITSU COMPANY
Application year: 1998
Main classification: G01R27
IPC codes: G01R27