FI94300C - Device for transmitting high frequency signals - Google Patents

Abstract

An apparatus for transmitting high-frequency signals with a coaxial cable provided with apertures in the outer conductor, where the apertures recur, seen in the longitudinal direction of the cable, in groups with a period length which is selected so that the groups of apertures radiate high-frequency signals from a desired lower limit frequency f0 and that the pole positions which are allocated to the multiples of the lower limit frequency f0 are eliminated or at least substantially attenuated in the frequency response of the coupling attenuation, is designed so that the number of apertures per period is greater than 30, the apertures are slits (1) which are as narrow as possible and the slits (1) are disposed essentially perpendicular in relation to the cable axis.

Description

94300 Arrangement for transmitting high frequency signals

The invention relates to an arrangement for transmitting high frequency signals according to the type definition 5 of claim 1 and to a method for manufacturing the arrangement.

In order to maintain a radio connection to a vehicle running along the road (road, tracks), it is sufficient that the radio signal is transmitted from a limited distance to this road or that it is transmitted over a limited distance. 10 Open Coaxial cables suitable for radio communication in the 50 to 1000 MHz band, ie wires consisting of an inner conductor and an surrounding conductive conductor. With these cables, it is possible to achieve a reliable radio connection even in unfavorable environmental conditions, such as in a tunnel. The energy radiated back should vary as little in space and time as possible over the largest possible frequency range. Coaxial cables with openings and different structures have been widely used for many years. Niis-20 distinguishes between: a) non-irradiated open waveguides; these include e.g. cables with outer conductors made of coarse wire braid and cables with a through longitudinal gap, and cables with: 25 small openings at short distances, and b) radially radiating cables or leakage cables; these are discussed in more detail below. A coaxial cable with a slot for an inner and a conductor is known (DE-OS 2 103 559), in which the ul-30 conductor has a number of slots which are spaced at a fixed distance from each other periodically and whose sizes change according to a sinusoidal source distribution. On the one hand, the inclination angles of the slits change from slit to slit, and on the other hand, the length of the slits, their curvature or their geometry also change in a certain way.

94300 2 The disadvantages of this solution are the limited effective frequency range and the small number of slots per cycle, their different shape and complex manufacturing method.

A high-frequency coaxial cable comprising an inner conductor and an open conductor with a slot, isolated therefrom, is known (EP patent 0 028 500). These slits and their mutual distances are dimensioned so that the distance between adjacent slots always decreases in the longitudinal direction, whereby at one end of the row there is a maximum value of 10-distance and at the other end a minimum value of the distance. The slits are completely round. Overall, the slits cover much of the outer conductor. The disadvantage of this arrangement is that, due to the large size of the slits, only some 15 slots can be placed on the outer conductor within one cycle interval.

DE-OS 2 230 280 discloses calculation methods for preventing undesired pole points in the switching attenuation frequency curve, these points comprising various suitable functions. The products of sine-20 functions and cosine functions, their mixing products and non-periodic functions have mainly been studied.

The disadvantages of the solutions known so far are, on the one hand, a limited bandwidth which is only about 5 times the fundamental frequency and, on the other hand, a field strength which is not stable enough for all frequencies within the transmitted frequency range. In a cable comprising periodic openings, the frequency attenuation of the switching attenuation has maxima not only at the fundamental frequency but also in an unlimited number of integer-30 multiples (polar points) of the fundamental frequency. Insufficiently suppressed poles lead to interference phenomena. The transmission along the transmission path, eg in a tunnel, is then easily disturbed. Until now, it has not been possible to suppress higher-order poles over a wide frequency band and even achieve a more or less stable frequency curve.

94300 3

The object of the invention is to form a leakage cable in such a way that the largest possible frequency range is transmitted in this frequency range by means of the largest and most stable field strength. This object is solved according to the invention by means of the features given in the characterizing part of claim 1; alternative embodiments of the invention as well as a method for manufacturing a leakage cable are explained in the subclaims.

The invention is preferably suitable for communication between mobile and / or fixed radio devices, for example in rail or road traffic and in tunnels, blind spots or underground.

However, due to the strong radiation with low wave attenuation, the leakage-15 games according to the invention are particularly suitable for broadband communication along traffic routes. In this case, traffic management systems (eg motorways) are particularly relevant. The cables are suitable for both sending and receiving signals.

The invention is based on the finding that the decisive factor for the radiation intensity is not so much the size of the slots or their shape, but their number and extent perpendicular to the axis of the cable.

Unlike the known arrangements of slits: the distances of 25 during the period length do not follow a simple law. The invention is characterized in that the slits are as narrow as possible and that, through their special arrangement, in the frequency range radiated, the interfering pole points are switched off or at least strongly attenuated. Narrow slits are not only easy to manufacture, but can be placed in a predetermined section length more than any other opening shape.

The calculation of the gap gaps to attenuate the pole points 35 is done with suitable functions by means of a Fourier transform.

94300 4

It calculates from the frequency function the function of the position, which according to the invention is realized through narrow slots vertical to the axis of the cable.

The first step of this procedure is considered below. The placement of the openings, the distance between which is the same in pairs, causes polar points in the frequency frequency curve of the radiation at a certain fundamental frequency fo as well as on all integer times fQ. The 2nd, 3rd, 4th, nth order polar points should be 10 attenuated if possible. This is achieved by successively multiplying the output spectrum by the cosine functions Fj, F2, F3, F4, Fg, ... (i.e. F «F ^ · F2 · Fg, ...). The functions reach their maximum value (i.e. amplitude 1) at the frequency f * 0. At 2fQ, the function F ^ must pass through 0 in order for the 2nd-order polar point to be attenuated. 15 For 4fQ, the amplitude of this function is -1. The oscillation period thus lasts 8fQ. The Fourier transform product consisting of an all-pole output spectrum and an 8fQ cosine function of the oscillation duration is a corrugation of a periodic single-hole with a pair of apertures spaced 2/8 of the length of 20 cycles; that is, one opening per cycle forms two.

Doubling the number of apertures per spacing calculated from the first Fourier transform per cycle turns off the pole point in the frequency range 2, 6,: 25 10, 14, 18, ... The remaining poles are assumed to have the following amplitudes: no 1 2 3 4 5 6 7 8 ...

A 0.707 0.00 -0.707 -1.00 -0.707 0.00-0.707 1.0 ..

In the next step, the remaining spectrum in the frequency range F2 is multiplied by the cosine of the oscillation period 12fQ. By analogy with the first stage, the 3rd, 9th, 15th, ... pole points go out.

In the local area, each group of two openings per 35 cycles is replaced by a double opening; both new 94300 5 det openings have moved 1/12 of the cycle length to the right or left. The amplitudes are respectively: no 1 2 3 4 5 6 7 8 ...

A 0.612 0.00 0.00 0.50 0.612 0.00 -0.612 -0.5 ...

5

In the next step, the remaining spectrum is multiplied by F ^ c1, the cosine of the 16fQ of the oscillation period; in this case the 4th, 12th, 20th, ... pole points are additionally eliminated. So far, four openings per cycle are formed.

10 To attenuate the pole points Pn in the switching attenuation frequency curve, for each pole frequency fR = nxf ^, the corresponding cosine function F = cosra n (l / n + lxn / 2) must be included and the product of all cosine functions transformed by four. This method quickly results in a very large number of slits in the leakage cables for a low fundamental frequency f and a wide transmission frequency range over a period of length, and thus in part for very small slit intervals.

The pattern of the openings is, for example, a period length of 2.2 m and a number of openings of 64 per period - 20 - which corresponds to the function F = F. »F- ^ F ^ F. * F_ * F £ realization 1 2 3 4 5 6 ta - according to Figure 1.

A preferred embodiment of the invention is therefore one in which the zero points of the cosine functions are determined in such a way that one more cosine function weakens: 25 other pole points strongly. For this purpose, the position of the zero points is not chosen precisely at the pole frequencies, but in such a way that the product of all cosine functions - as an argument for the pole _2 frequencies - gives the values of £ 5x10. In this way, the number of cosine functions required to smooth the frequency curve is reduced, so that the number of slots and the minimum intervals of slots to be placed in one period length become technically feasible.

Embodiments of the invention will now be examined in more detail with reference to the drawing; Fig. 1 shows the result of the "ideal" wake-up function F in the conversion to the tilt plane, Fig. 2 shows the same for the optimized wake-up function, and Fig. 3 is a schematic representation of a cable manufacturing method.

A special feature 5 of the slot arrangement illustrated in Figure 1 is the groups of adjacent slits which are more or less separated from the following slots by large intervals. Of particular note is the space on the right side of Figure 1 with no cracks. The slot arrangement is based on the "ideal" excitation function F = Fi * F2 * F3 * F4 * F5 * F6 '10 where F ^ = cos (ηπ / 2χ2); F2 = cos (ηπ / 2 · 3); Fg = cos (nn / 2 * 4); F ^ «cos (nn / 2x5); Fg = cos (ηπ / 2 · 7); Fg = cos (ηη / 2 · 8). n is then the order of the polar points.

As a result of the already mentioned shift of the zero points of the cosine functions, the bladder configuration according to Fig. 2 is created. 15 The related optimized cosine functions are: F ^ = cos (ηπ / 2 · 2.02); F g = cos (ηκ / 2 · 3.06); Fg = cos (ηιι / 2 · 4.41); F ^ = cos (ηπ / 2 · 5.94); Fg cos (ηπ / 2 · 8.84); Fg = cos (ητι / 2 · 12, 63).

Although the zeros of the F 1 functions in the optimized wake-up function differ substantially from the "ideal" wake-up function, the slot arrangement is similar in both cases.

At a basic frequency of 63 MHz, such a leakage cable can effectively attenuate the polar points up to 15.

: Up to 25 orders. The smallest gap is then 8 mm.

When multiplying several cosine functions with the additional condition that they must also achieve a predetermined number of predetermined pole point attenuations up to a certain order n, an arrangement comprising 30 different gap lengths can also be a solution. However, for technical reasons, the same slit lengths are given in advance. The parameters used for the optimization task are the smallest possible slot spacing or the number of slots. The desired attenuation of the pole points 35 is, for example, a value of 25 db, because then there are no more 94300 7 interfering interferences. In order not to mechanically weaken the float conductor more than necessary, it may be advantageous to divide the slits through the cross-ribs.

The method for manufacturing a coaxial cable 5 according to the invention will be examined in more detail on the basis of Figure 5. It shows a schematic view of cable manufacturing. The conductor strip 3 is provided by mechanical or electrical methods with a certain slot sequence, which is always repeated in period lengths p. The period length is preferably 2.2 m. The strip with slots 10, preferably copper strip, passes through both rollers 5 simultaneously with tensile plastic strip 6. by means of heat, it is laminated to the strip 3. The strip 6 covers the slits so that they are mechanically secured against widening 15 when the tension is applied to the strip. In this way, the bending or widening of the slits is also avoided in the bending of the laminate after this step. The inner conductor 8 is surrounded by an insulator 4. This arrangement is covered with a laminate or copper strip, which is welded from the seam point by means of a welding device 7 into a pipe. 20 The coaxial cable is finished by pressing the sheath over it. In an alternative embodiment of this method, the adhesive closes the gaps. The adhesive has such a short curing or curing time that the cracks are mechanically secured before further processing into a cable causes damage.

The slits can be made by spark erosion or they can be laser cut into the conductor strip 3. One alternative is also to make the slits by means of rotating saw blades, which by means of spacers are already completed at the correct gap distance 30. Since these slits are repeated in section lengths p, it is possible in this way to produce slots of one section length in one operation with one set of saw blades. For continuous production, the copper strip 3 only has to be moved exactly to the cycle length p ver-35 before the next slit group is made.

t 94300 8

In the preferred manufacturing method, the slot pattern is placed as a convex rib on the outer circumference of the roll, which corresponds to the period length of the slot arrangement. The roller is continuously brushed with an antifoulant so that the bars can be applied to the strip of this material. The tape is made of, for example, polyester and is coated with, for example, graphite powder after application of the antifoulant. This will leave the gaps free. Finally, the strip is coppered. The coated tape is finally formed as the outer 10 conductor of the coaxial cable.

Claims (20)

An apparatus for transmitting high frequency signals along a coaxial cable, the outer conductor of which is provided with apertures, wherein the apertures in the longitudinal direction of the cable are repeated in groups with period lengths selected so that the aperture groups from and with a desired minimum limit frequency fc radiate high frequency signals pole sites corresponding to the multiples of the lowest basic frequency f0 are extinguished or at least attenuated sharply in a frequency attenuation curve, characterized in that the number of openings per period is over 30, and that the openings consist of as small slots (1) as possible and that the slots ( 1) is substantially perpendicular to the shaft of the cable. 2. Device according to claim 1, characterized in that the slot spaces are chosen so that for damping of more than 15 pole positions they do not fall below a given minimum distance, which is at least twice in relation to the slot width. 3. Apparatus according to claim 1 or 2, characterized in that a magnetization function F, in which the number of slots is predetermined at as many pole positions in the frequency curve as possible or zero locations, is chosen, and function. F is so defined that a slit device is produced upon transformation from frequency plane to local plane. Device according to any one of claims 1 to 3, characterized in that the slots (1) are divided by ribs arranged in the longitudinal direction of the slots. Device according to any of claims 1-4,. characterized in that the slots (1) are different in length. Device according to any one of claims 1-5, characterized in that the slot spaces (1) form a non-equidistant and non-periodic series for a period. 13 94300 Device according to any one of claims 1 to 6, characterized in that the width of the slots is about one thousandth of the period length. Device according to any of claims 1-7, 5, characterized in that a function F is provided for attenuation of the pole sites, which function is a product of several functions Fj in the frequency range. Device according to any one of claims 1-8, characterized in that the damping of the poist bars takes place via functions Flf whose amplitudes and / or frequencies are about 15-fold optimized with respect to the limit frequency. 10. Device according to any one of claims 1-9, characterized in that the optimization is selected so that with a minimum number of functions Fj, a predetermined attenuation of the pole positions by at least 20 dB can be achieved. 11. Device according to any of claims 1-10, characterized in that function F is a product of cosine functions with different arguments. 20 Method according to any of claims 1-11 for producing a coaxial cable, characterized in that the groups of slots (1) are performed in a tactile manner in a conductor band (3), and the conductor belt (3) is passed over a period length after each beat. and formed into a cylindrical,. 25 external external conductors. 13. A method according to claim 12, characterized in that the slots (1) are cut in the conductor band (3) by means of a laser. 14. A method according to claim 12, characterized in that the slots (1) for a peridol length. . is produced by means of a series of synchronously rotating saw blades arranged at fixed intervals. 15. A method according to claim 12, characterized in that the slits (1) are performed by punching. * • I 94300 14 The method according to claim 12, characterized in that the slots (1) are carried out through photolithography and etching. 17. A method according to claim 12, characterized in that the slots (1) are performed by spark erosion. 18. A method according to claim 12, characterized in that the slots are performed by coating a plastic strip such that a model for the slots for a period length is first placed on the outer periphery of a press roll, and the different surface properties of the model on the surface of the roll are utilized. for the purpose of placing a conductive layer on the plastic tape outside the periodic slots after the press roll has been rolled on the plastic tape. 15 19. A method according to claim 18, characterized in that, the first conductive layer is reinforced after the coating by electrolytic separation of a well-conducting metal layer. Method according to any one of claims 12 to 17, characterized in that the conductor strip (3) provided with slots (1) is laminated with a tensile-resistant plastic strip covering the slots, and that the edges of the conductor strip (3) are left free for a connection event afterwards. • «• ·«