Frequency Range Extension of Spectrum Analyzers with Harmonic Mixers

Transcription

1 Products FSEM21/31 and FSEK21/31 or FSEM20/30 and FSEK20/30 with FSE-B21 Frequency Range Extension o Spectrum Analyzers with Harmonic Mixers This application note describes the principle o harmonic mixing and the requirements to be met by spectrum analyzers and external mixers. Subject to change Christoph Rauscher Application Note 1EF43_0E

2 Contents 1 Introduction Fundamentals... 3 Waveguides... 3 Harmonic Mixing... 5 Signal Identiication... 8 Characteristics o Mixers Spectrum Analyzer Requirements and their Realization in FSE Measurement Hints Operation o External Mixers on FSE Reerences Ordering Inormation Introduction The growing number o applications using wireless signal transmission, eg radiocommunication or collision avoidance systems, calls or an ever increasing number o requencies. Since requency requirements can no longer be met by the lower requency bands alone, requencies in the millimeter range are used to a growing extent. So this requency range is not only employed by military users but opened up also or civil applications. So ar, the requencies up to 110 GHz have been o main interest. However, with demands made on harmonic suppression getting higher and EMC directives becoming more stringent (eg FCC CFR47 Part 15), this requency limit is shited to 200 GHz. The requency range above 40 to 50 GHz is covered by spectrum analyzers usually by means o external mixers because the undamental mixing commonly employed in the lower requency range is too complex and expensive or required components such as preselectors are not available. This application note describes the principle o harmonic mixing and the criteria to be taken into account. 1EF43_0E 2 Rohde & Schwarz

3 2 Fundamentals Waveguides Wired signal transmission in the millimeter range is preerably realized by means o waveguides because they oer low attenuation and high reproducibility. Unlike coaxial cables, the requency range in which waveguides can be used is limited also towards lower requencies (highpass ilter characteristics). Wave propagation in the waveguide is not possible below a certain cuto requency where attenuation o the waveguide is very high. Beyond a certain upper requency limit, several wave propagation modes are possible so that the behaviour o the waveguide is no longer unambiguous. In the unambiguous range o a rectangular waveguide, only H 10 waves are capable o propagation. The ollowing ormula applies to the lower cuto requency c,1, rom which such waves are capable o propagation: c = (Equation 2-1) c,1 2 a r where c,1 Lower cuto requency (in Hz) c Velocity o light (in m/s) a Length o larger dimension o waveguide (in m) Dielectric constant o medium in waveguide (= 1 or air) ε r From a limit requency o c,2, the H 01 wave can propagate in addition to the H 10 wave. c,2 is thereore the upper limit requency o the unambiguous range. The ollowing applies: c c,2 = (Equation 2-2) 2 b r where c,2 Upper limit requency (in Hz) b Length o smaller dimension o waveguide (in m) Usually, a ratio o a/b = 2 o the edge lengths is selected, so that c,2 = 2 c,1. Because o the high wave attenuation near the lower cuto requency c,1, and to allow or mechanical tolerances, the ollowing transmission range is usually selected in practice [1]: 1.25 (Equation 2-3) c, c,1 The dimensions o rectangular and circular waveguides are deined by international standards such as 153-IEC or various requency ranges. These requency ranges are also reerred to as waveguide bands. They are designated using dierent capital letters depending on the standard. Table 2-1 provides an overview o the dierent waveguide bands together with the designations o the associated waveguides and langes. For rectangular waveguides, which are mostly used in measurements, harmonic mixers with matching langes are available. For connecting harmonic mixers to circular waveguides, transitions are to be used whose attenuation has to be taken into account in the evaluation o results. 1EF43_0E 3 Rohde & Schwarz

4 Table 2-1 Waveguide bands and associated waveguides Band Frequency Designations Internal dimensions o waveguide Designations o requently used langes in GHz MIL-W-85 EIA 153-IEC RCSC (British) in mm in inches MIL-F UG-XXX /U equivalent (reerence) Remarks Ka WR-28 R320 WG x x B-005 UG-599 /U - UG-381 /U Rectangular Rectangular Round Q WR-22 R400 WG x 2.84 U WR-19 R500 WG x V WR-15 R620 WG x E WR-12 R740 WG x W WR-10 R900 WG x x x x x x B-006 UG-383 /U Round 67B-007 UG-383 /U-M Round 67B-008 UG-385 /U Round 67B-009 UG-387 /U Round 67B-010 UG-383 /U-M Round F WR-08 R1200 WG x x B-M08 / UG-383 /U-M Round, pin contact D WR-06 R1400 WG x x B-M06 / UG-383 /U-M Round, pin contact G WR-05 R1800 WG x x B-M05 / UG-383 /U-M Round, pin contact Y WR-04 R2200 WG x x B-M04 / UG-383 /U-M Round, pin contact J WR-03 R2600 WG x x B-M03 / UG-383 /U-M Round, pin contact 1EF43_0E 4 Rohde & Schwarz

5 Harmonic Mixing In harmonic mixers, a harmonic o the local oscillator (LO) is used or signal conversion to a lower intermediate requency (). The advantage o this method is that the requency range o the local oscillator may be much lower than with undamental mixing, where the LO requency must be o the same order (with low ) or much higher (with high ) than the input signal (RF). Microwave spectrum analyzers use harmonic mixing also in the undamental requency range, FSEK or example rom 26.5 GHz. To ensure image- and spurious-ree spectrum display in the undamental requency range, a tracking preselection is provided at the RF input o the spectrum analyzer. In this way, signals are displayed at the desired requency only. Image-requency signals, which the mixer is not capable o distinguishing rom signals at the desired requency, are suppressed by the preselector. Preselection is not commonly used with external harmonic mixers because o the high requencies involved. Preselection would be very costly in this case and hardly possible to realize at extremely high requencies. Fig. 2-1 shows the test setup or measurements using an external harmonic mixer. The mixer is ed a high-level LO signal. The harmonics generated in the mixer because o its nonlinearity are used or conversion. Fig. 2-1: Test setup or measurements using an external two-port mixer The signal converted to the is coupled out o the line which is also used or eeding the LO signal. Because o the great requency spacing between the LO and the signal, the two signals can be separated by means o a simple diplexer. The diplexer may be realized as part o the mixer or the spectrum analyzer, or as a separate component. Mixers with an integrated diplexer are also reerred to as three-port mixers, mixers without diplexers as two-port mixers. To enable the use o both types o mixer, FSEM and FSEK oer a separate input as well as an integrated diplexer. The LO path o harmonic mixers oten contains a lowpass ilter or the suppression o harmonics o the incoming LO signal. This is to prevent LO harmonics to be superimposed on the mixer-generated harmonics. Depending on the phase o the harmonics, this may cause blanking, which leads to higher conversion loss or produces notches in the requency response characteristic. When selecting an external mixer, thereore, care should be taken that the limit requency o the integrated lowpass ilter is higher than the maximum LO requency o the spectrum analyzer. The RF signal applied to the input o the external mixer together with its harmonics is mixed with all harmonics o the LO signal. The mixer products that all within the o the spectrum analyzer are displayed. They must ulil the ollowing criterion: 1EF43_0E 5 Rohde & Schwarz

6 m = (Equation 2-4) ± n LO RF where m, n 1, 2,... if LO RF Frequency o LO signal (in Hz) Frequency o input signal (in Hz) Intermediate requency (in Hz) The local oscillator o FSEM and FSEK is tunable between 7.5 and 15.2 GHz. The intermediate requency is MHz. For an input signal with a requency o 39 GHz, the criterion according to equation 2-4 is ulilled or the LO requencies listed in Table 2-2. The variable m corresponds to the order o the harmonic o the LO signal by which the input signal is converted to the. The criterion is ulilled twice or each harmonic. The input signal is represented as the upper sideband (normal position) and also as the lower sideband (inverted position) o the local oscillator signal. Components with n 1 are harmonics o the input signal that are generated, or example, in the mixer. It can be seen that these harmonics are converted to the desired only by LO harmonics o a comparatively high order m. I the level o the input signal is well below the 1 db compression point o the mixer, such components have a markedly lower level since the harmonics o the input signal are suiciently attenuated with respect to the undamental and in addition the conversion loss o the mixer increases with increasing order m. Thereore, only responses with n 4 are listed in Table 2-2. While components with higher m and n exist, they can be neglected because o their low level. Table 2-2: LO requencies or which the criterion according to equation 2-4 is ulilled ( = MHz, n 4, m 12) m n LO / GHz m n LO / GHz m n LO / GHz Spectrum analyzers however display the received spectrum not versus the LO requency but versus the input requency. For this, the user has to enter on the spectrum analyzer the order m o the harmonic by which the input signal is to be converted. For the representation o signals in the lower sideband at the correct requency RF, the ollowing equation applies (derived rom equation 2-4): = (Equation 2-5) m RF LO where m Harmonic set by user RF Frequency at which a spectral component is displayed on the analyzer (in Hz) The LO requency LO, which is required or conversion o a signal in the lower sideband, is obtained rom equation 2-4 as ollows: 1EF43_0E 6 Rohde & Schwarz

7 LO + n RF =. (Equation 2-6) m By substituting equation 2-6 in equation 2-5, the ollowing is obtained or RF : + n = m (Equation 2-7) m RF RF The ollowing applies to components converted as the lower sideband by means o a harmonic o the order m = m : = n, (Equation 2-8) RF RF Such components are thereore represented at the correct requency. For image requency response, the ollowing corresponding equations apply: and LO n RF = (Equation 2-9) m n RF = m. (Equation 2-10) RF m The ollowing is then obtained or m = m : = (Equation 2-11) n 2 RF RF I m = 3 is selected, the spectrum displayed on the analyzer contains components at the requencies listed in Table 2-3 (see also Fig. 2-2 on next page). Components lying within the corresponding waveguide band (Ka band in this case) are highlighted grey. Table 2-3: Displayed components or m = 3 (lower sideband, = MHz); sinewave input signal with RF = 39 GHz m n LO / GHz RF / GHz m n LO / GHz RF / GHz m n LO / GHz RF / GHz The input signal converted by means o the 3 rd harmonic o the LO signal is displayed at the correct requency RF = 39 GHz. The image signal is displayed below this signal at a spacing o 2 = GHz (c. Equation 2-11). 1EF43_0E 7 Rohde & Schwarz

8 Fig. 2-2: Spectrum o 39 GHz CW signal recorded with harmonic mixer The above example illustrates that even a simple sinewave signal produces a large number o responses. I the input signal itsel contains several spectral components, intermodulation products may be generated in the mixer in addition to harmonics, such products too being converted to the. I the input signal consists o two sinewave carriers, the ollowing applies: m ± n ± k = (Equation 2-12) LO RF,1 RF,2 where k, n 0, 1, 2,... m 1, 2,... LO Frequency o LO signal (in Hz) RF,1, RF,2 Frequencies o input signals (in Hz) Intermediate requency (in Hz) The number o components increases considerably. It is advisable, thereore, to make use o the highpass ilter characteristic o waveguides to suppress unwanted input signals. Signal Identiication In the previous example, the type o input signal was known, and so it was easy to distinguish the true (or wanted) displayed signal rom unwanted mixer products obtained as a result o image requency response and mixing by other harmonics. Frequently, the spectrum to be measured is not known however so that criteria have to be ound to distinguish unwanted mixer products rom spectral components that are true components o the input signal. From equation 2-10 it can be seen that or each mixture product there exist image requencies which appear at a spacing o (m /m+1) below the mixture product. For m = m, the spacing is exactly 2 (equation 2-11). The same applies to harmonics o the input signal, ie to n 1. However, since the requency ranges o the standardized waveguide bands are considerably smaller than one octave, such mixer products will not become apparent even i the ull band is displayed. 1EF43_0E 8 Rohde & Schwarz

9 Based on this criterion, the ollowing algorithm can be realized: Apart rom the actual test sweep, in which the lower sideband is deined as wanted, a reerence sweep is perormed. For the reerence sweep, the requency o the LO signal is tuned such that the user-selected harmonic o the LO signal (order m ) is shited downwards by 2 relative to the test sweep (see Fig. 2-3). Test Sweep RF m LO Reerence Sweep m LO,Re RF Fig. 2-3: Signal identiication by means o reerence sweep For this reerence sweep, the upper sideband is the wanted sideband. Equation 2-5 is thereore modiied to take the ollowing orm: = +. (Equation 2-13) RF, Re m LO,Re where RF,Re Frequency, at which a spectral component is displayed in reerence sweep (in Hz) LO,Re LO requency in reerence sweep (in Hz) Equation 2-6 is modiied accordingly to: n RF =. (Equation 2-14) LO,Re m By substituting equation 2-14 in equation 2-13, the ollowing results: n RF = m +. (Equation 2-15) RF, Re m The ollowing applies to image requency responses: n RF + = (Equation 2-16) LO,Re m and thereore: n RF + = m +. (Equation 2-17) RF, Re ZF m By selecting m = m in equation 2-17, it will be seen that, unlike the test sweep, image requency responses are displayed at a spacing o 2 above the actual input signal (c. equation 2-8). This allows image 1EF43_0E 9 Rohde & Schwarz

10 requency responses and other unwanted mixer products to be identiied (see Fig. 2-4). Fig. 2-4: Test sweep (top) and reerence sweep (bottom) Input signal with RF = 38 GHz A true signal should be displayed at the same requency in the test sweep and the reerence sweep, ie RF = RF,Re. I m is the same or both sweeps, the ollowing is obtained or the LO requency LO,Re to be set or the reerence sweep: 2 =. (Equation 2-18) LO,Re LO m Apart rom this method o signal identiication by variation o the LO requency, it is possible to vary the level o the input signal to identiy displayed components. By varying the level o the input signal by L / db, the level o displayed true components will vary to the same extent. The levels o intermodulation products and harmonics generated in the mixer, on the other hand, will vary according to their order n, ie a variation o the input level by 1 db will cause a level variation o n db. This is subject to the condition that such intermodulation products and harmonics are generated exclusively in the mixer. Care must be taken, thereore, that the input signal is ree rom such products. Moreover, it must be ensured that the input o the spectrum analyzer is not overloaded. Since the input level can be varied only by the user, this method, unlike signal identiication by varying the LO requency, is not suitable or being implemented in a spectrum analyzer. 1EF43_0E 10 Rohde & Schwarz

11 Characteristics o Mixers Harmonic mixers are divided into single-diode and double-diode mixers. Most commercially available mixers are single-diode mixers, because these are easier to realize. Single-diode mixers basically operate with both even and odd harmonics o the LO signal. The disadvantage o this concept is that it requires biasing. To this end, the mixer is ed with a DC voltage via the LO line. The DC voltage is to be adjusted requency-dependent or minimum conversion loss o the mixer, which complicates automatic measurements at dierent requencies. Double-diode mixers are more complex but require no biasing; they are thereore also reerred to as zero-bias mixers. To attain minimum conversion loss, such mixers should normally be operated with even harmonics. Moreover, the ollowing characteristics should be taken into account in selecting the mixer: required as well as maximum permissible LO power, permissible LO requency range, conversion loss, requency response o conversion loss across small requency spans, order o harmonic or which the speciied conversion loss is valid, sensitivity o conversion loss to changes o LO level, permissible intermediate requency. In addition to the optimum LO level, at which minimum conversion loss is obtained, the maximum LO power is normally speciied at which the mixer can be used without any damage being caused. Because o the lowpass ilter contained in the LO path o the mixer (see section Harmonic mixing ), the usable LO requency range must be taken into account. I the mixer incorporates a diplexer, it must urther be ensured that the requency o the spectrum analyzer is within the bandwidth o the port o the mixer. To ensure a small level error, not only the conversion loss should be as small as possible or high sensitivity, but a continuous requency response is equally important. Narrowband notches or steps o the requency response can only with diiculty be taken into account in the level correction o the spectrum analyzer. The speciied conversion loss applies only to a speciic order o the harmonic. I a dierent harmonic is selected on the spectrum analyzer, level correction by means o the values supplied or the requencydependent conversion loss will lead to erroneous results. To obtain reproducible results, dependence o conversion loss on the LO level should be as small as possible. 1EF43_0E 11 Rohde & Schwarz

12 Spectrum Analyzer Requirements and their Realization in FSE Order o LO Harmonic To obtain low conversion loss o the external mixer, the order o the harmonic used or converting the input signal should be as low as possible. For this, the requency range o the local oscillator must be as high as possible. Spectrum Analyzers FSEM and FSEK ully meet this requirement with an LO requency range o 7.5 to 15.2 GHz. A wide LO requency range and thus a low order m is o advantage also in phase noise measurements o microwave signals. Multiplication o the signal causes an increase o the phase noise by the multiplication actor. For a harmonic o the order m, SSB phase noise is obtained as ollows [2]: L PNm ( o ) = L LO ( o ) + 20 lg (m )db (Equation 2-19) where L PNm ( o ) SSB phase noise o harmonic o the order m at a carrier oset o (in dbc(hz)) L LO ( o ) SSB phase noise o LO signal at a carrier oset o (in dbc(hz)) Fig. 2-5 shows the typical SSB phase noise o the local oscillator o FSE. typ. SSB Phase Noise in dbc(hz) /21 Model /31 Model , Carrier Oset in khz Fig. 2-5: Typical SSB phase noise o local oscillator o FSEM / FSEK The overall noise igure o the system, which consists o a spectrum analyzer and external mixer, is composed as ollows: noise igure at input o spectrum analyzer, plus conversion loss o mixer, plus eedthrough o LO SSB noise to the intermediate requency. Sensitivity is usually speciied as Displayed Average Noise Level (L DAN ) or a speciic bandwidth. The ollowing applies: B L = 174 dbm(hz) + a + NF + (10 lg )db 2,5 db DAN CVL SA Hz (Equation 2-20) where L DAN Displayed average noise level (in dbm) a CVL Conversion loss o external mixer (in db) NF SA Noise igure o analyzer at input (in db) Noise bandwidth o ilter (in Hz) B The value o 174 dbm corresponds to the noise power over 1 Hz bandwidth o a 50 Ω resistance at an ambient temperature o 290 K. The correction value o 2.5 db is necessary because o averaging o logarithmic level values. FSEM and FSEK have a noise igure o typically 7.5 db at their inputs. 1EF43_0E 12 Rohde & Schwarz

13 The eects o broadband noise o the local oscillator are not taken into account in equation Such eects may lead to urther reduction o sensitivity. I the input is open and the two-port mixer is selected, the noise displayed on FSEM and FSEK is about 3 db higher than with a three-port mixer. LO Ampliier LO LO Diplexer LO LO OUT / IN Two-Port Mixer Three-Port Mixer IN Ampliier Fig. 2-6: LO ampliier and diplexer in FSE I the signal path or a two-port mixer is selected, broadband noise at the output o the LO ampliier is applied directly to the path in the diplexer and leads to a higher displayed noise as described above (see Fig. 2-6). Intermediate Frequency The higher the requency o the spectrum analyzer, the greater the spacing at which image requency response is displayed on the requency axis (c. equation 2-11). Mixer products generated by conversion o the undamental o the input signal (n = 1 in equation 2-4) by means o harmonics o the LO signal have a level clearly above that o other mixer products and are thereore easy to identiy. For a single modulated or unmodulated input signal displayed on the requency axis, an image-ree range o 2 is obtained around this signal in which no signal identiication is necessary. Because o the high o MHz, the image-ree range or FSEM and FSEK is GHz. This is suicient or many applications, doing away with the need or signal identiication. Local Oscillator Level The level o the LO signal must be suiciently high to ensure proper unctioning o the mixer, taking into account the loss due to the cable or eeding the LO signal to the mixer. The requency response o the LO level should be as lat as possible. I a two-port mixer is used, it is o advantage i a diplexer is integrated in the spectrum analyzer. This does away with the need or an external diplexer, and thus no extra insertion loss needs to be taken into account in level measurements. FSEM and FSEK both eature an internal diplexer as well as an additional signal input ( IN connector, see Fig. 2-6). This allows the use o either two-port or three-port mixers without the need or any external components. 1EF43_0E 13 Rohde & Schwarz

14 Signal Identiication Methods Apart rom hardware requirements, signal identiication methods play an important role or the eicient use o harmonic mixers. In FSEM and FSEK, the method described in section Signal Identiication is implemented. The test and the reerence sweep can be compared manually by the user and also automatically. Unwanted mixer products are blanked in the displayed spectrum. This enables ast, continuous signal identiication. Measurement Hints To obtain accurate and reproducible results, the ollowing points should be observed: A low-loss cable with a lat requency response should be used or eeding the LO signal to the mixer. The conversion loss o the mixer is normally speciied or a deined LO level. It is thereore important to maintain this level at the LO port o the mixer in order to achieve the desired accuracy. In level correction on the spectrum analyzer, the insertion loss o the cable used or tapping the signal is to be taken into account. I an external diplexer is used or connecting a two-port mixer, the insertion loss o the path o the diplexer is to be taken into account in level correction on the spectrum analyzer. Harmonic mixers requently have a low return loss (typ. VSWR > 2.5:1). I in addition the DUT has poor output matching, the actual conversion loss may markedly deviate rom speciied values. It is thereore expedient to insert an attenuator or isolator between the mixer and the DUT in order to increase measurement accuracy. However, the insertion loss caused by such a component will reduce the sensitivity o the spectrum analyzer and mixer setup. This insertion loss has also to be taken into account in level correction on the spectrum analyzer. 1EF43_0E 14 Rohde & Schwarz

15 3 Operation o External Mixers on FSE The operation o external mixers on FSE will be explained by means o the ollowing example. A sinewave signal with = 14.5 GHz is applied to the input o a multiplier. The spectrum at the output o the multiplier is to be measured in the range 52 to 60 GHz by means o FSE and a two-port mixer or the V band. The mixer used is a double-diode mixer. Its requency-dependent conversion loss is stored in a ile on the FSE hard disk (ile name: EXTMIX_V ). First, the mixer is connected to the waveguide output o the signal source. The LO/ port is connected to the LO OUT / IN connector o FSE using a low-loss coaxial cable. External mixing is activated by: À [ INPUT : EXTERNAL MIXER ] (1) Then the BAND LOCK ON MODE is activated: À [ INPUT : EXTERNAL MIXER : BAND LOCK ON / OFF ]. (2) With À [ INPUT : EXTERNAL MIXER : SELECT BAND ] (3) the table with the parameters or the individual waveguide bands is called up. From this table the desired band, in this case band V, is selected. À [ INPUT : EXTERNAL MIXER : SELECT BAND : BAND ] (4) Selection o band by means o cursor keys and ENTER Ater selecting the band, the requency-dependent conversion loss is to be activated. To this end, the ile containing the conversion loss o the mixer used is selected. À [ INPUT : EXTERNAL MIXER : SELECT BAND : CONV LOSS TABLE ] (5) Selection o ile EXTMIX_V with cursor keys and ENTER The ile contains all the required parameters, so that no urther settings are necessary. The selected ile remains stored or the selected band. I the same mixer is selected in later measurements, only steps 1 to 4 have to be executed. Ater leaving the selection table with the key (menu up), a span is set automatically by which the complete V band is covered, ie 50 to 75 GHz. The requency range to be investigated is set with À [ FREQUENCY START : 52 GHz ] and À [ FREQUENCY STOP : 60 GHz ] To ensure reliable signal identiication by means o the AUTO ID unction, the video bandwidth is reduced as ollows: À [ SWEEP COUPLING : VIDEO BW MANUAL : 1 MHz ] The spectrum shown in Fig. 3-1 is obtained. 1EF43_0E 15 Rohde & Schwarz

16 Fig. 3-1: Output spectrum o multiplier, measured by means o external mixer To identiy the true input signal, the AUTO ID unction is activated: À [ INPUT : EXTERNAL MIXER : SIGNAL ID : AUTO ID ] AUTO ID operates on the principle described in section 2.3. In addition to the test sweep, a reerence sweep is perormed in which the LO requency is shited downwards in accordance with equation The spectra measured in the two sweeps are compared with each other automatically and the result is displayed. Unwanted mixer products are blanked in the displayed trace. The display shown in Fig. 3-2 is obtained. Fig. 3-2: Output spectrum o multiplier, measured by means o external mixer and AUTO ID unction Since the LO requency is shited downwards in the reerence sweep, the mixer conversion loss may turn out to be dierent or the test and the reerence sweep. The reasons or this are the LO output power o the spectrum analyzer varying with the requency and the non-ideal characteristics o the mixer. A certain tolerance should thereore be allowed in the comparison o the signal levels o the test sweep and the reerence sweep. The user can set this tolerance with: À [ INPUT : EXTERNAL MIXER : SIGNAL ID : AUTO ID THRESHOLD : {value} db ] 1EF43_0E 16 Rohde & Schwarz

17 The tolerance must be at least as large as the dierence between the conversion losses obtained or the test sweep and the reerence sweep. I this is not observed, the true input signal might be displayed with an incorrect level. In the above example, a tolerance o 5 db was selected. Mixer conversion loss is already taken into account in the display. Only the insertion loss a MHz o the cable used or tapping the signal is to be taken into account in determining the signal level. The actual level o the input signal is higher by a 0. 1EF43_0E 17 Rohde & Schwarz

18 4 Reerences [1] Janssen, W.: Hohlleiter und Streienleiter. Dr. Alred Hüthig Verlag Heidelberg, 1977 [2] Engelson, M.: Sideband noise measurement using the spectrum analyzer. Application note 26W-7047, Tektronix 5 Ordering Inormation Spectrum Analyzer FSEM 20 (9 khz to 26.5 GHz) FSEM 21 (9 khz to 26.5 GHz, with output or external mixer) FSEM 30 (20 Hz to 26.5 GHz) FSEM 31 (20 Hz to 26.5 GHz, with output or external mixer) FSEK 20 (9 khz to 40 GHz) FSEK 21 (9 khz to 40 GHz, with output or external mixer) FSEK 30 (20 Hz to 40 GHz) FSEK 31 (20 Hz to 40 GHz, with output or external mixer) Required Accessories or FSEM / FSEK Models 20 / 30: FSE-B21 (Output or external mixer) ROHDE & SCHWARZ GmbH & Co. KG. Mühldorstraße 15. D München P.O.B D München. Telephone Fax Internet: 1EF43_0E 18 Rohde & Schwarz