Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
  • G01R29/08—Measuring electromagnetic field characteristics
  • G01R29/10—Radiation diagrams of antennas
  • G01R29/105—Radiation diagrams of antennas using anechoic chambers; Chambers or open field sites used therefor
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
  • G01R29/08—Measuring electromagnetic field characteristics
  • G01R29/0807—Measuring electromagnetic field characteristics characterised by the application
  • G01R29/0814—Field measurements related to measuring influence on or from apparatus, components or humans, e.g. in ESD, EMI, EMC, EMP testing, measuring radiation leakage; detecting presence of micro- or radiowave emitters; dosimetry; testing shielding; measurements related to lightning
  • G01R29/0821—Field measurements related to measuring influence on or from apparatus, components or humans, e.g. in ESD, EMI, EMC, EMP testing, measuring radiation leakage; detecting presence of micro- or radiowave emitters; dosimetry; testing shielding; measurements related to lightning rooms and test sites therefor, e.g. anechoic chambers, open field sites or TEM cells
  • G01R29/0828—TEM-cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems

Definitions

• the invention relates to a method for determining at least one characteristic of an antenna according to claim 1 and an advantageous measuring device therefor according to claim 16.
• a characteristic of an antenna is understood to be any type of characteristic of the antenna, e.g. individual characteristic values, time profiles of characteristic values or direction-dependent and frequency-dependent parameters such as, for example, Abstraction Diagrams.
• the determination of such characteristic data of antennas usually takes place in the frequency domain in known methods.
• a test signal is generated by a frequency generator in such a way that a so-called frequency sweep is passed through over a certain frequency range to be examined. Each frequency is held constant for a short period of time until the antenna enters a steady state. Then, a measurement is made at the antenna to determine the characteristic data.
• a known method is, for example, the reference antenna method, which requires an absolutely defined radiating antenna, such as an open waveguide probe or a Homantenne, as a reference.
• a disadvantage of this method is that the apparatus required for measurement is relatively high in terms of time and / or costs, since a large number of reference antennas often have to be provided and measured sequentially since such reference Tennen have a limited, relatively narrow-band useful bandwidth.
• precisely fabricated and absolutely characterized reference antennas are necessary and therefore relatively expensive. The purchase therefore pays off in many cases.
• the 2-antenna method in which two identical antennas must face each other at a defined distance in an anechoic chamber. This method involves the problem of obtaining the two identical antennas, which can be difficult in individual cases.
• the 3-antenna method is known, which, although good results, but is relatively time and labor intensive.
• the invention is therefore based on the object of specifying a more rational method for determining at least one characteristic of an antenna and a measuring device therefor.
• a TEM field is a transverse electromagnetic field in which the field vector of the electric field and the field vector of the magnetic field are perpendicular to one another and both field vectors are perpendicular to the propagation direction.
• a parallel plate line consisting of an upper and a lower metal sheet, which include a specific space in which the antenna to be measured can be placed.
• the space surrounded by the waveguide does not necessarily have to be a closed space for carrying out the method according to the invention; a laterally partially open space is also conceivable, with shielding from external disturbing influences being less than with a closed waveguide, such as a waveguide with the same permanent or longitudinally widening coaxial waveguide.
• a TEM waveguide is advantageous, since it promotes propagation of the advantageous for the inventive method TEM field at the location of the antenna.
• EMC electromagnetic compatibility
• a Crawford cell may be considered a TEM cell.
• GTEM gigahertz transversal electromagnetic
• the present invention expands the field of application of TEM cells, in particular of GTEM cells, by the possibility of characterizing antennas.
• the invention now proposes a completely different approach to the known methods described in the prior art.
• an electrical excitation signal is fed into a supply terminal of the waveguide.
• An electrical response signal emitted by the antenna as a result of the excitation signal is recorded. taken, for example, with an oscilloscope or a signal analyzer such as a spectrum or network analyzer (NWA).
• the excitation signal can in principle be of any type, for example a single excitation pulse, a plurality of excitation pulses or a sequence of frequencies, as in the frequency sweep mentioned above.
• At least a portion of the response signal and a corresponding portion of the excitation signal are used to determine the at least one characteristic of the antenna.
• a specific portion of the response signal is used, namely a period of time evaluated in the following conditions: i) at the location of the antenna only one or more of the excitation signal caused by the feed terminal in the direction of antenna waves of the electromagnetic field (hereinafter also referred to as the downstream waves),
• the electromagnetic field is a TEM field at the location of the antenna.
• the TEM field may propagate on plane and / or spherically curved phase fronts.
• a period evaluated in the time domain in which the aforementioned conditions i) and ii) are satisfied which is e.g. by using a suitable waveguide, e.g. a GTEM cell, and by e.g. experimental time determination of a suitable period of the response signal can be realized.
• the evaluated portion of the response signal contains no falsifying superimpositions due to returning waves, eg due to reflections on the back wall of the GTEM cell. Instead, such a period of time is used in which at the location of the antenna only traveling waves of the electromagnetic field exist. As a result, a high measurement accuracy and reproducibility of the antenna characterization can be achieved.
• a period of time is used in which the electromagnetic field at the location of the antenna is a TEM field.
• the time interval By fixing the time interval, measurement distortions that occur as a result of temporary deviations of the field from the TEM characteristic can thus be eliminated from the measurement result and thus a falsification of the measurement result can be avoided.
• the presence of a TEM characteristic of the field has the advantage that the measurement provides equivalent field conditions which correspond to those of conventional reference antenna measurements in which the antenna to be examined is usually located in the far field of a reference antenna.
• This reference antenna far field is at the location of the antenna to be examined is a slightly spherical curved TEM-FeId and therefore largely identical to the almost flat conditions of a free-field measurement.
• the phase fronts of the TEM field within a GTEM cell are also slightly spherically curved due to the septum slope angle.
• the use of a GTEM cell has the advantage, due to its special characteristics, that the evaluation of the measurement results is simplified.
• a GTEM cell has a Dirac function as the first part of the impulse response (see IEEE publication "Pulse Propagation in Gigahertz Transverse Electro- magnetic Cells", Thye, Armbrecht, Koch) .Thus, due to its own characteristics, the GTEM cell falsifies the In particular, the influence of a convolution of the GTEM characteristics with the response signal is not to be taken into account, so that the transformation of the response signal into the signal at the location of the antenna takes place without distortion (dispersion-free) Considerations and investigations have already been made in the past To use GTEM cells for antenna measurements.
• the electrical excitation signal as well as the response signal is a time-dependent signal.
• a frequency domain signal can be used as the excitation signal.
• a frequency domain signal is understood to be a signal in which a test signal is generated by a frequency generator in such a way that a so-called frequency sweep is passed through over a certain frequency range to be examined, i. Discrete frequencies are set successively in time, each frequency being kept constant for a short period of time until a steady state occurs at the antenna.
• a short pause is advantageously provided between the setting of two frequency values of the excitation signal, which is dimensioned with respect to its length such that the electromagnetic waves within the waveguide are far enough can decay that they have no relevance to the further measurement. Then the next frequency is set.
• the frequency domain signal is used as the excitation signal
• the complete voltage response of the antenna during the application of the excitation signal is recorded as the response signal.
• the present response signal which contains the plurality of injected frequencies, is transformed from the frequency domain to the time domain, e.g. by an inverse Fourier transformation.
• a period of time for the further determination of the characteristic is used, in which only traveling waves of the electromagnetic field are present and these waves at the location of the antenna as TEM-FeId e- xist Schl.
• a portion of the response information lying at the beginning of the time beam in the time domain is used, wherein the duration is to be determined experimentally in such a way that the mentioned conditions are present.
• the expected time of reflected, returning waves can be estimated, and accordingly the evaluated period of time from the response information can be cut to lie before arrival of returning waves.
• an electrical excitation pulse in particular an excitation pulse with a high frequency bandwidth
• an excitation pulse with a high frequency bandwidth is supplied as the excitation signal
• record the response signal of the antenna is a time characteristic.
• an excitation pulse with a high frequency bandwidth has the advantage that a single pulse - or possibly several pulses - can be used to examine the antenna in a large frequency range, for example in the entire desired reception range of an antenna.
• the antenna is exposed simultaneously to a large number of frequencies at once, with the frequencies contained in the spectrum of the excitation pulse.
• the characterization of a single antenna is considerably faster than known methods of antenna characterization in which a multiplicity of reference antennas are required for this purpose.
• an increase in the achievable dynamic range can be achieved by multiple emission of pulses of the same pulse shape, for example, by the elimination of noise influences by averaging over these results of such multiple measurements.
• a Gaussian pulse is fed as the excitation pulse.
• a Gaussian pulse is understood to be a pulse form in which the amplitude variation over time corresponds or at least resembles a Gaussian distribution curve.
• Such a Gaussian pulse has the advantage of enabling excitation with a high frequency bandwidth.
• the excitation pulse is relatively steep at its first flank. At the first edge of the excitation pulse, 80% of the amplitude of the excitation pulse will be traversed in less than 1 ns (nanoseconds). Due to the steep edge of the first edge, a high frequency bandwidth of the excitation pulse can be achieved. In this way, even a ultra wideband antenna (UWB antenna) with at least 500 MHz bandwidth over its entire frequency range can be measured with a single excitation pulse. As a result, the method according to the invention is particularly time-saving applicable. As a result, the method according to the invention allows fast, reliable antenna measurements which can be carried out inexpensively using waveguides already present in particular in the industrial environment, such as, for example, GTEM cells.
• UWB antenna ultra wideband antenna
• a memory oscilloscope can be used for measuring data recording. Furthermore, only a single copy of an antenna to be examined with unknown characteristic data is necessary, ie it eliminates the need for additional precisely measured reference antennas. This avoids the cost-intensive construction of multiple copies especially for more complex prototypes of antennas.
• a further advantage of the method according to the invention is an inherent increase in the measuring accuracy, which is based on the evaluation of a portion of the response signal as a time interval evaluated in the time domain.
• the response signal is recorded in the time domain.
• the recording can, for example, with a
• the recording directly in the time domain has the Advantage of a simplified evaluation of the signal and the determination of the characteristic of the antenna.
• the response signal can directly represent the characteristic of the antenna.
• the response signal is then a two-dimensional profile, for example a voltage over time, from which the antenna expert can extract characteristics of the antenna to be examined.
• Another advantage is that the proposed measurements in the time domain make the use of electro-optical transducers for transmitting the response signal of the antenna to the measuring device possible, since only amplitude values are to be transmitted as time response and no relation to the phase position as the response signal of the antenna is required.
• the possibility of using electro-optical converters in conjunction with optical fibers has the advantage that parasitic field distortions in the surroundings of the antenna are reduced in comparison to conventional metallic cables.
• a frequency domain signal is used as the excitation signal. This has the advantage that existing vectorial network analyzers previously used for antenna measurement can continue to be used.
• a network analyzer (Network Analyzer) is used.
• the network analyzer may e.g. be set up by software expansion specifically for the execution of the method according to the invention.
• the response signal is recorded in the correct frequency range.
• the complex response variable in amplitude and phase position is thus detected directly in the antenna base point (vectorial measurement).
• the recorded in the frequency domain Response signal can then be transformed into the time domain via an inverse Fourier transformation and further evaluated in sections.
• the response signal for determining the characteristic can be further evaluated. It can e.g. be determined from the response signal frequency domain characteristics of the antenna. For this purpose, the time interval of the antenna response evaluated in the time domain is transformed into the frequency domain. In this way, for example, characteristics such as the gain, the directional characteristic and / or the efficiency of the antenna can be determined. In comparison with known antenna characterization methods in the frequency domain, according to the invention, these characteristics can already be determined extremely broadband with one measurement, i. for a very large frequency range, in particular if the antenna has already been excited simultaneously with high frequency bandwidth due to the electrical excitation pulse.
• transmission characteristics of the antenna are determined from the response signal of the antenna.
• the response signal itself characterizes the reception characteristics of the antenna since it is the reception of a wave triggered by the excitation pulse.
• the response signal of the antenna in this case in particular the received impulse response h rx (t, cpi, ⁇ j), can also be used to deduce the transmission signal, in particular the transmission impulse response h tx (t, ⁇ j, ⁇ j). This eliminates the need for expensive additional measurements to determine the transmission behavior of an antenna.
• the determination of the transmitted impulse response from the received impulse response can be carried out as follows:
• ht ⁇ (t, ⁇ i, ⁇ i) hrx (t, ⁇ i, ⁇ i)
• ⁇ j and ⁇ j are the respective coordinates of the orientation of the antenna with respect to the field in a spherical coordinate system
• ⁇ is the azimuthal coordinate
• ⁇ j is the elevation coordinate
• Co is the speed of light.
• frequency range characteristics can be derived from the reception-side impulse response. For this purpose, it is necessary to convert the time domain signal h rx Ü) into the frequency domain signal H rx ( ⁇ ) by Fourier transformation.
• ⁇ denotes the angular frequency.
• the following relationship applies to the effective gain (also known as "absolute gain") of an antenna:
• Reception side (Index “rx") means here that the antenna is used for the reception of signals
• transmitting side (index “tx”) means that the antenna is used for the transmission of signals.
• the frequency bandwidth of the excitation signal is equal to or greater than the frequency bandwidth of the antenna to be measured. This advantageously allows the measurement of the antenna to be examined in its entire frequency spectrum with a single excitation signal, in particular with a single excitation pulse.
• the antenna to be examined is an ultra-wideband antenna, in particular an antenna with at least 500 MHz frequency bandwidth. It has been found that the method according to the invention is particularly advantageous for measuring very broadband antennas.
• the antenna is arranged movably in at least one spatial dimension or at least one axis of rotation in the waveguide.
• the antenna can be rotatable by a corresponding electric drive about all three spatial coordinate axes.
• a first value of a characteristic of the antenna in a first antenna position and at least a second value of the characteristic in a second antenna position are determined quickly and with little effort.
• two- and / or three-dimensional radiation characteristics of the antenna can be determined with little expenditure of time.
• a GTEM ZeIIe in a pure 2-component TEM field is an independent, ie coupling-free, characterization of co- and cross-polarized antenna components by rotation of the antenna by 90 ° to the propagation direction possible.
• the selection of the dimensions of the waveguide and / or the positioning of the antenna in the waveguide in the longitudinal direction of the waveguide depending on the time required for a determination of the desired characteristic duration of the response signal and / or the size of the antenna takes place.
• the antenna is positioned a little farther away from its back wall for an expected relatively long duration of the response signal than expected short response signals, again precluding the influence of reflected waves. If positioning at a greater distance from the back wall of the GTEM cell does not seem possible, for example because the distance to the side walls of the GTEM cell is too low for an unadulterated measurement, a larger GTEM cell should be selected accordingly.
• the antenna is arranged at a position in the waveguide at which the ratio of mutually orthogonal components of the electric field strength and the magnetic field strength of a Cartesian 2-component TEM field, both components orthogonal to the main propagation direction of the electromagnetic field in the waveguide, which comes as close as possible to free field field impedance. This may distort gene of the measuring signal can be avoided by unwanted cross-polar couplings.
• the method according to claim 1 is supplemented by the step that characteristic data of the waveguide are determined metrologically.
• the determination of this data can be determined, for example, by positioning a field sensor with known, defined characteristic data in the waveguide and by feeding an excitation pulse, as for the GTEM cell in the IEEE publication "Pulse Propagation in Gigahertz Transverse Electromagnetic Cells", Thye, Armbrecht
• this step thus involves measuring the unknown properties of the specific GTEM cell or waveguide by means of a reference field sensor the characteristic of the antenna is determined from the response signal of the antenna, which is determined according to claim 1, in conjunction with the metrologically recorded characteristic data of the waveguide, by mathematically correcting the response signal for the characteristic data of the waveguide aumaschine the method according to the invention are further increased. Unwanted distortions through the waveguide can be eliminated by calculation.
• the invention further relates to a measuring device for determining at least one characteristic of an antenna, wherein the measuring device is adapted to carry out a method of the type described above.
• the measuring device for example, a signal generating means for generating the excitation signal and a signal receiving means for receiving the response signal and an integrated evaluation of the response signal.
• the invention also includes a separate expansion device which is adapted to determine at least one characteristic. kums an antenna according to a method of the kind explained above.
• the adaptation of the measuring device or the expansion device can e.g. by a change or extension of a software of the respective device.
• An advantageous embodiment of the invention relates to a specially adapted for carrying out a method of the aforementioned type Netzwer werkanalysator.
• Figure 1 the basic structure of a GTEM ZeIIe in perspective
• Figure 2 - an exemplary, to be examined antenna in perspective
• FIG. 5 shows schematically the main field components of a TEM field within a GTEM cell
• FIG. 6 is a plan view of a GTEM cell
• FIG. 7 shows the course of the field-wave resistance in the transverse direction of the GTEM Cell specifically as a quotient of the main field components and Figure 8 - an exemplary excitation pulse and Figure 9 - exemplary impulse responses of the antenna and
• Figure 10 another embodiment of a measuring arrangement for carrying out the method according to the invention with a GTEM ZeIIe in side view and
• FIG. 11 shows a measurement result of the effective gain measurement of a standard
• a GTEM ZeIIe 1 has a pyramid-like shape.
• the GTEM cell 1 has a metallic outer housing 2 with a rectangular cross section.
• the outer housing 2 is closed on the side facing away from the pyramid tip by a rear wall 3.
• a high-frequency absorber 7 is provided, which has a plurality of absorber elements in pyramidal shape.
• Inside the GTEM cell 1 is a decentralized flat inner conductor 5 in the form of a plate.
• the inner conductor 5 is also referred to as a septum.
• a resistance region 6 is provided in the region of the septum 5 adjoining the rear wall 3.
• the septum 5 is arranged within the GTEM-ZeIIe 1 so that a Lei wave impedance of 50 ⁇ , which is constant over the length of the GTEM ZeIIe 1.
• the GTEM cell 1 has an electrical coaxial connection 4 for a coaxial feed line.
• the inner conductor of the coaxial terminal 4 goes from the junction continuously into the septum 5 of the GTEM ZeIIe 1 over.
• the outer conductor of the coaxial terminal 4 passes continuously from the connection point into the outer conductor of the GTEM cell 1, ie into the metallic outer housing 2.
• the cone antenna 8 has a metallic antenna body 9, 10, which has an upper approximately hemispherical region 9 and a lower approximately conical region 10.
• the antenna body 9, 10 is held by a base 11 (shown by dashed lines), which is e.g. made of Plexiglas.
• the conical region 10 of the antenna 8 ends in an antenna connection 12, which is led out of the base 11.
• the antenna body 9 together with a metallic base plate 16 forms a monopole antenna structure.
• FIG. 3 shows a measuring setup for carrying out the method according to the invention.
• the GTEM ZeIIe 1 is shown in Figure 3 in side view.
• a pulse generator 13 is connected.
• an antenna 8 to be examined is arranged.
• the antenna 8 is connected via a line 15 to a signal detection device 14.
• the signal detection device 14 may be designed, for example, as a storage oscilloscope or transient recorder.
• the line 15 may advantageously be designed as an optical line, ie as an optical waveguide.
• an electro-optical converter is connected directly to the antenna connection 12, which converts signals received by the antenna 8 directly into optical signals.
• the optical signals are then converted by an opto-electrical converter in the signal detection device 14 in turn into electrical signals.
• an excitation pulse U t ⁇ (t) is fed from the pulse generator 13 into the GTEM cell 1.
• the electromagnetic wave which forms and propagates in the direction of the antenna 8 impinges on the antenna 8 at a time and generates a response signal U r ⁇ (t) which is recorded by the signal detection device 14.
• FIG. 4 shows the influencing variables of the target conflict that are to be considered for a determination of a characteristic of an antenna.
• the first influence variable is the pulse pause duration at the respective antenna position of the antenna in the GTEM cell.
• the pulse pause duration refers to the time that elapses between the complete reception of the wave propagating from the excitation pulse to the antenna and the beginning of the reception of a returning wave. In this period of the pulse pause duration, it can be assumed that no falsification of the measurement result by reflections takes place on the back wall of the GTEM cell.
• the second influencing variable is the expected length of the response pulse of the antenna.
• the expected length must be in accordance with the pulse pause duration, so that no interference by reflected waves, for example towards the end of the response signal to the traveling wave superimposed on this response signal.
• the third factor is the excitation pulse width, i. the duration of the excitation signal. This should be much shorter than the pulse pause duration, e.g. by using an ultra-wideband pulse of the type described below is possible.
• the fourth parameter to be considered is the antenna size, which should be in a reasonable ratio to the cross section of the GTEM cell, so that
• the cross-sectional area of the GTEM cell in the region of the position of the antenna to be examined should be at least 25 times as large or approximately 5% of the cross-sectional area as the cross-section of the antenna in the same cross-sectional plane.
• FIG. 5 the principal course of the main field components of a TEM field is shown schematically with reference to a Cartesian coordinate system.
• the coordinate system is defined with respect to the GTEM cell 1 such that the x-axis extends in the transverse direction of the GTEM cell, the y-axis in the vertical direction and the z-axis in the longitudinal direction.
• the field line H x of the magnetic field extends around the septum 5, which in FIG. 5, as well as the z-axis, runs perpendicular to the plane of the paper.
• the field lines E y of the electric field run in the negative y direction.
• the TEM field propagates in the direction of the z-axis.
• FIG. 6 shows the alignment of a ground-based, painted coordinate system in a plan view of the GTEM cell 1, including two cross sections (cross sections 1 and 2), along which the field-wave resistance is calculated.
• FIG. 7 shows the calculated field-wave resistance ⁇ in particular as a quotient of the main field components for two cross sections selected by way of example (cross sections 1 and 2) along the x'-coordinate.
• ⁇ 0 377 ⁇
• the characterization of the antenna 8 is particularly simple with regard to its orthogonally polarized antenna properties, since the respective co-polar field component can be measured by a rotation of the antenna by 90 ° without having contain counterfeits due to the cross-polar field component.
• FIG. 8 shows by way of example an excitation pulse Ut x (t).
• the excitation pulse is relatively steep-edged, in particular on its first, falling edge.
• the time T1 in which the instantaneous value of the amplitude of the excitation pulse passes through the range between 10% and 90% of the maximum amplitude achieved, is only about 20 ps.
• a magnitude slope of 48 V / ns accordingly results. This corresponds to a frequency bandwidth of approximately 20 GHz.
• the response signal of the antenna is recorded as a voltage curve u rx (t).
• the received impulse response h AUT rx (t) generally links the response signal of the antenna u rx (t) present as voltage magnitude to the three electrical field components (E x , Ey, E z ) incident on the antenna in the case of reception.
• the unit of such impulse response is therefore usually given in [m].
• the operator represents an inverse convolution operation.
• the Size (X PL is a typical attenuation constant for the GTEM cell used.)
• the subscript "TG” indicates that it is a temporal portion of the response signal, namely the time interval of u rx ( ⁇ ) evaluated to determine the characteristic of the antenna.
• t in which the response signal comprises only traveling waves and no interference by Reflektio- NEN and also the electromagnetic field at the location of the antenna is a TEM-FeId.
• FIG. 9 shows time courses of the impulse response h AUT rx (t) of the antenna.
• the curve h AUT rx , REF (t) (with the least waviness) was determined to check the plausibility of the measurement results using a 2-antenna reference method.
• the two other waveforms (with the greater ripple) give the impulse responses of the two conical antennas 8 of the same design used for the 2-antenna reference method, as obtained by the method according to the invention.
• the measured courses are close to the course of the reference measurement. If required, further characteristics of the antenna can be derived from the impulse response according to FIG.
• the time course of Empfangsim- impulse response h AUT rx (t) can be transformed or the other optionally, the receiving or the transmitting pulse response transformed into the frequency domain on the one hand in the transmission pulse response h AUT tx (t), for example by Fourier transformation, after which then the corresponding frequency domain characteristics of the antenna such as gain, directional characteristic or efficiency are determined.
• FIG. 10 shows a measuring arrangement similar to FIG. 3.
• a combined device 20 in the form of a network analyzer is provided.
• the network analyzer 20 is particularly suitable for the generation of a typical frequency domain signal as an excitation signal and the detection of the received quantities, ie the response signal, in the frequency domain. rich.
• the measuring setup according to FIG. 10 is fundamentally comparable to the measuring setup according to FIG. 3, but the measuring setup according to FIG. 10 allows improved measurements in the frequency range as a result of a higher dynamic range of the network analyzer 20 used as measuring device.
• Both possibilities of signal detection i. the measurement setup according to FIG. 3 and the measurement setup according to FIG. 10 are linked to one another via the Fourier transformation.
• the finiteness of the respective measuring range can lead to deviations in the transformation. It is therefore advisable to make a windowing in the respective area, i. to carry out the measurements in different frequency ranges.
• windowings that have a low so-called “processing loss” in the respective relevant area are to be preferred (also referred to as “processing gain” or “coherent gain”, depending on the technical literature.)
• the relevant area is in the frequency range due to the working area of the Antenna, in the time domain, is characterized by the time interval T1 explained with reference to Figure 8.
• Tukey window To achieve a low processing loss, a rectangular window and the so-called “Tukey window” are particularly suitable, as described in F. Harris, "On the use of Windows for harmonic analysis with a discreet Fourier transform ", Proceedings of the IEEE, Vol. 66, no. 1, pages 51 to 83, January 1978.
• the Tukey window has increased flexibility due to its parameterization.
• FIG. 11 shows an exemplary measurement using the method according to the invention on the basis of a "standard gain horn.”
• a network analyzer N5230A from Agilent was used for signal generation and detection.
• 50L used by Seavey Engineering Associates, Inc.
• the antenna was placed inside GTEM 5305 GTEM from ENCO.
• the transition from the horn to the waveguide of the antenna is located in the cell center of the GTEM cell at a distance of 1.51 m to the feed point 4 of the antenna GTEM ZeIIe.
• FIG. 11 shows by the solid line the result of the measurement, wherein the effective gain in relation to a lossless isotropic reference emitter is represented in the unit dBi over the frequency in GHz.
• the dotted line reproduces the reference given by the manufacturer of the antenna.
• the measurement results there are slight deviations between the measurement results and the reference given by the manufacturer, but the deviations are in the range of ⁇ 0.5 dBi. These deviations can be attributed to the finiteness of the time interval T1.
• a further approximation of the measurement results to the manufacturer's instructions may e.g. be determined by determining a compensation function by the measurement results.

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