DE3322947A1 - TRANSVERSAL FILTER FOR ELECTROMAGNETIC SHAFTS - Google Patents

Description

_ "Z"

G.-G.Gassmann-116

Transversal filter for electromagnetic waves

The invention is based on a transversal filter as in FIG The preamble of claim 1 specified. Transversal filter are known a LIgemeiη, e.g. from the article "Transversal Filters "by H.E. Kalmann, Proceedings of I.R.E. July 1940, pages 302-310. There are numerous publications which describe how transversal filters must be dimensioned in order to obtain the desired transmission or blocking range. The well-known -Transverse I-filter are used to select carrier vibrations i e ren.

In receivers it is common to use different frequencies for signal processing To separate carrier waves that are modulated with one or more modulation signals, demodulate these separate carrier waves and then to divide the demodulated signal into its individual modulation signals. For carrier oscillations with frequencies In the optical area, the optical signal must first be converted into an electrical signal, what is done in an optical / electrical converter.

Such converters are mostly non-linear and often generate cross modulation, which results in interference frequencies in the make further signal processing noticeable. this is particularly the case when several coherent carrier shafts (e.g. in the HF range) are modulated and another carrier wave (e.g. in the optical frequency range) with These modulated carrier waves are intimately modulated.

An improvement in signal processing could then be obtained if one considers the frequencies causing the disturbance

ZT / Pi-Sm / Chr

Stuttgart, June 13, 1983

G.-G.Gassmann-116

(or the individual frequency bands containing the information) if possible at the beginning of the signal processing blocks or only allows the desired frequency (s) to pass. In the case of carrier oscillations with frequencies in the optical range this would have to be done before the conversion of the optical into the electrical signal. However, this is known with the TransversaIfi 11ern - and also with other well-known ones Filtering - not possible.

After it was recognized that it was used for signal processing It is advantageous to have interference frequencies before demodulation to block or select useful frequencies) is It is the object of the invention to provide a filter with which this is possible.

This object is achieved with the means specified in claim 1. This is done by a transversal filter went out. Advantageous further training are the Refer to subclaims.

With the new filter, it is irrelevant whether the carrier oscillation is intensity-modulated with useful and / or interference signals is a frequency in the HF range, for example or in the optical range. The filter can be implemented as a pass-through or as a blocking filter.

The new transversal filter is very suitable for several coherent and modulated carrier waves, which in turn have intensity-modulated a "further" incoherent carrier wave.

The new transversal filter can be particularly advantageous Way in a frequency discriminator, in which the demodula-

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tion the frequency modulated into an amp volume modulated Signal that is converted to be used - The frequency deviation of the frequency-modulated signal can be very large (e.g. equal to half the frequency of the carrier oscillation). A frequency discriminator with such a filter leaves can be realized very easily.

The invention is based on the drawings, for example explained in more detail. It show the

1 to 4 are schematic representations of exemplary embodiments the new transversal filter,

Fig. 5 and 6 the transfer function of the transversal filter for a sinusoidal (Fig. 5) or rectangular (Fig. 6) intensity modulated electromagnetic Wave, and FIGS. 8 to 11 transfer functions for different filter arrangements.

The following description assumes that the intensity-modulated and to be filtered electromagnetic Wave is a wave of light. However, it is specialist knowledge to modify the exemplary embodiments in such a way that that they are for electromagnetic waves with frequencies in other frequency ranges are suitable.

In the exemplary embodiment according to FIG. 1, an optical waveguide leads 1 to an optical branch 2. Two further branches lead from the optical branch 2 and are different long optical fibers 3 and 4 to another optical Branching 5, which is connected via a light path 6 is connected to an optical / electrical converter 7. Conditional due to the different lengths (and given

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if other sizes) the light wave has different transit times through the two light waveguides. The optically / electrical converter emits an electrical signal via a line 8. The components used are general known. Optical branches are for example in the essay "Principles and Properties of Branches for Mu Itimode fibers "by F.Auracher in frequency, issue 34, 1980, pages 52 to 57.

To explain the principle of the new filter, a simple case assumed. The optical carrier oscillation is associated with an interference signal (frequency ωό) and a useful signal (Frequency ωη) intensity modulus I iert. Then it is blocked of the interference signal is the difference in transit times through the two

x
the light wave conductor - with τ equal to the period duration of the disturbance

signals (frequency ω). It should be noted that τ is the period of the signal with which the light wave is intensity-modulated and not the period of the light wave, ie the carrier oscillation. If this is the case and the light wave is split into two light waves of equal intensity in the first splitter 2, then the two partial waves are superimposed in the second splitter so that the intensity modulation with the interference signal (period τ) of the light wave is eliminated, i.e. it is present Blocking filter for the intensity modulation with the period duration τ.

It is advantageous here if the light wave is incoherent, because then it is not necessary to ensure that at the frequency of the existing light wave (not the modulation frequency) no erasure occurs.

If the light wave is sinusoidal with a modulation frequency ωο intensity modulated, then results in the Fig. 5 illustrated cos-shaped transfer function as a function of

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Modulation frequency ω.

In the case of an intensity modulation with rectangular pulses, which have a pulse train frequency of ωο, results the triangular transfer function shown in FIG. The pulse repetition frequency is equivalent to the frequency of a sinusoidal modulation signal.

A further exemplary embodiment is described with reference to FIG. An optical waveguide 10 leads to a first one Splitter 11. However, in contrast to the exemplary embodiment according to FIG. 1, this divides the light wave into three partial waves with different intensities on and these are made via three fiber optic cables of different lengths 12, 13, 14 routed to a second branch 15. The filtered signal is transmitted via a fiber optic cable forwarded. The dimensions are selected as follows: is the transit time through the longest optical waveguide 12 around τ and the transit time through the light wave guide 14, the has an average length τ / 2 longer than the transit time through the shortest light wave conductor 13. If the Intensity of the partial wave in the light wave guide 14, which the has mean length, denoted by I, then the intensity of the partial waves in the other two light wave guides 12 and 13 each 1/2. The desired energy distribution is done by the branch. However, it could also be caused by different attenuation in the light paths be generated.

Fig. 7 is a vector diagram with the sinusoidal modulation signals 12 ', 13' and 14 ', with which the partial waves that propagate in the light wave guides 12, 13 and 14, are modulated. Since the partial wave in the optical waveguide 14

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twice the intensity of the other two partial waves has, the amount of the modulation signal 14 ' twice as large as the amounts of the modulation signals 12 'and 13' chosen. If the frequency ω of the signal with which the light wave is intensity-modulated increases, then the vectors of the two modulation signals rotate 12 'and 13' with respect to different directions of rotation on the vector of the modulation signal 14 '. At the frequency ωο the two vectors 12 'and 13' are opposite to the vector 14 'aligned so that a total of one Cancellation of the modulation signals and thus an elimination the intensity modulation of the light wave with frequency ωο results.

In the embodiments according to FIGS. 1 and 2 can the fiber optic cable is implemented as an optical fiber be.

However, the new transversal filters can also be used on numerous other types can be realized. However, at least two partial waves must always be generated and these have to each other after different periods of time are superimposed.

In the embodiment according to FIG. 3, the light wave arrives via an optical waveguide 20 to a first beam splitter 21 and is divided there into two partial waves 28 and 29. One partial wave is via two mirrors 22 and 25 passed to a second beam splitter 26. The two beam splitters 21 and 26 correspond to the two branches 2 and 5 in the embodiment of FIG. The other partial wave arrives at a pair of mirrors 23, 24. Depending on the chosen arrangement of the mirrors, it is repeated several times reflected back and forth between the mirrors. After

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Last reflection, the partial wave arrives at the second beam splitter 26 and is there superimposed on the other partial wave. The light wave generated by the superposition is passed on via an optical waveguide 27. Regarding the time difference to be selected between the Because of the partial waves, the explanations are given in relation to the exemplary embodiment in accordance with Fig. 1 to be used accordingly.

In the exemplary embodiment according to FIG. 4, a light wave arrives Via an optical fiber guide 40 to a beam splitter 41 and is there divided into two partial waves 60 and 61. The one partial wave 61 becomes one at a mirror 42 Component 45 is reflected. This component is a substrate in which several optical waveguides of different lengths 46, 47, 48, 49 are formed ("integrated optics").

The other partial wave 60 reaches a Bragg cell 44. It it is known that a Bragg cell depends on a light beam the frequency of a control signal applied to them distracts greatly. This is used here to convert the partial wave, depending on the control signal, to one of the To guide optical fibers 46 to 48. These in turn are each tuned to a different modulation frequency. this is particularly advantageous when it is not an intensity modulation of the light wave that is to be suppressed, but rather if only a certain intensity modulation for 5 further processing is to be forwarded. When using the waveguide 46 is for a first modulation frequency the voting condition is met; Using of waveguide 47 for a second modulation frequency etc. So you can easily control which modulation frequency with which the light waves intensity is smodu I iert via the optical waveguide 51 to the further Processing should be forwarded. It is possible

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Lent, all of the components shown in FIG to implement integrated optical equipment.

For the dimensioning of the new transversal filter, the measurement rules known for the known transversal filter can be used. It is also possible to implement filters with the desired blocked areas or desired passage areas, each with the desired slope. Since known rules are applicable for the choice and combination of the individual sections of the route, the dimensioning itself will not be discussed in more detail. It is important, however, that when dimensioning the new transversal filter, not the frequency of the carrier oscillation, but the frequency of the modulation signal with which the carrier oscillation is intimately modulated, should be used. Furthermore, care must be taken that if the carrier oscillation is coherent, there is no disturbance due to the interference between the parts. In the case of non-coherent carrier oscillations, the frequency of the carrier oscillation only plays a role with regard to the selection of the components to be used.

In FIGS. 8 to 11, some transfer functions are qualitative as a function of the modulation frequency DISPLAYED. The curve shown in FIG. 8 is obtained with a filter according to FIG. 1. With a filter 2 one obtains the curves according to FIGS. 9 to 11, where Fig. 9 a filter, in Fig. 10 two and in Fig. 11 four Identical and series-connected filters are provided are.

From Fig.6 it can be seen that with the new Transversa L f i L tern transfer functions ^ the e of the modulation frequency depend on, received. This is done in an advantageous manner

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exploited for frequency demodulation. A particularly good one Result is obtained when the light wave with a rectangular shape Signal that is frequency modulated in itself, is intensity-modulated, because in this case the transfer function is linear over a large area. the Center frequency of the frequency with which the frequency modulation takes place, is chosen, for example, so that it is in the The transfer function specified in Fig. 6 is the same

ω + 2 ω ω

- = or is equal to ■ = -. After passing the fiI

ters is the frequency modulation into an amplitude modulation converted. If this signal is passed through an optical Waveguide (Figure 1; 6) to an optical / electrical converter 7, then corresponds to the electrical output signal of the optical / electrical converter the signal with which the light wave was frequency modulated.

With such a frequency discriminator it is possible Light waves that emit a very high frequency signal (e.g. 200MHz) and a large frequency deviation of e.g. B. - 100 MHz are frequency modulated to be demodulated. The steepness of the discriminator characteristic (Fig. 6) depends, among other things, on the selected Differences in transit time for the various propagation paths for the light wave in the filter and from which one Place the transfer function according to Fig. 6 is the center frequency the signal with which the frequency modulation takes place, lies.

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Claims (7)

STANDARD ELECTRICS LORENZ
Aktiengesellschaft
STUTTGART G.-G.Gassmann-116 Claims Transversal filter for electromagnetic waves, at
the electromagnetic waves through at least two
Propagation paths (3,3 ') between a first branch
(2), which divides the electromagnetic wave into several partial waves, and a second branch (4), which combines the partial waves again, different transit times
have, characterized in that
the transit times and the attenuations for the propagation paths are chosen so that one or more frequencies
at least one signal with which the electromagnetic Because intensity is modulated, a given transmission behavior receives. 2. transversal filter according to claim 1, characterized in that that the propagation paths are realized as light wave guides are. 3. transversal filter according to claim 2, characterized in that that the optical fibers are optical fibers. 4. transversal filter according to claim 2, characterized in that that the optical waveguide from an integrated optical device are formed. 5. TransversaIfiLter according to claim 1, characterized in that that the path of propagation is at least partially through ZT / P1-Sm / Chr Stuttgart, June 13, 1983 _ 2 - G.-G.Gassmann-116 Mirrors and steel dividers are formed. 6. Frequency discriminator with a transversal filter according to one of claims 1 to 5. 7. transversal filter according to claim 4, characterized in that that the transversal filter (Fig.4) by switching can be tuned to other frequencies.