SE419906B - COUPLES IN AN AUTOMATIC ANGLE FOLLOW SYSTEM - Google Patents

Description

* ràeiess-s 5 f "10 AF * - 15 izo * få, 2s- fa a 30 basic mode and a difference signal from the higher mode TMÛ1. The error signals, for example in height and side angle joints are determined in the tracking system 'receiver by means of difference and the sum signals, the amplitude and phase position of the difference signal relative to the sum signal determining the magnitude of the angular deviation of the target from the antenna axis and the deviation direction, respectively. To achieve good accuracy in this system, very good phase similarity between As also shown in the said article, the system is sensitive to changes in the polarization of the beacon. In another known system operating according to the same principle and described in U.S. Pat. No. 3,821,741, a first and a second higher mode TM01 and TE21, respectively, and the basic mode are used. TE11 .to form the error signals This known system contains a mode switch, which consists of three waveguide sections, which together form d a circular waveguide connected to the feed horn of the system.

Two of said guide sections are each provided with a pair of rectangular guides, which with a certain aperture are connected to the main guide to divert the desired higher modern ones and to form difference signals. Together with the sum signal which is extracted elsewhere in the system, the said error signals are then formed. The utilization of two higher modes TMU1 and TE21 makes it possible for the system to work with not fully circularly polarized signals and to deliver mutually isolated difference signals for two angular plane, which leads to lower phase similarity requirements between the signal paths compared with the previous system. However, the different cut-off points from the circular waveguide of the two higher modern and basic modern ones cause difficulties in maintaining phase similarity between difference and sum signals at varying temperature or frequency. Phase differences between these signals Lead to varying sensitivity in reception and especially in non-zero point tracking to a direct point error.

DISCLOSURE OF THE INVENTION In systems of the above kind, error signals shall be formed in two planes, for example the height and side angle planes, which depend only on 10 15 20 25 30 - -, -. ~ -....- f ~ - t .. ~ --- «---« - 7901055-9 the deviation angles of the target in these planes but not by variations in the strength of the bearing signal (fading) and polarization (depolarization) within certain limits. Such variations arise, for example, through the effect of the atmosphere on road propagation. Furthermore, the system should, as far as possible, be insensitive to the changes in the properties of the components that inevitably occur, for example over time or at varying temperatures. Of importance here is its use of suitable waveguide modes, its connection of these in a suitable manner to form sum and difference signals and partly of letting the signals be conducted the same or as far as possible equal paths from the antenna to the receiver. Otherwise, varying sensitivity is received on reception and any pointing errors. Especially with non-zero point tracking, pointing errors are also obtained as a result of the sensitivity variation.

According to the present invention, two over-modes TM01 and TE21 and the basic modes TE11V and TE11H in mowing guide or E02 and HE21 and HE11v and HE11H in corrugated guide are used and all utilized modes are disconnected in the same section by the circular main guide, after which two sums are formed. and two difference signals conducted through a common receiver channel, thereby avoiding the difficulties of keeping the signals phase-like. In the receiver, the error signals in the two planes are produced by using the sum and difference signals associated with each plan. The object of the present invention is thus to provide a mode switch which diverts two higher modes and two basic modes in order to form two difference signals (e.g. called Ax and Ay) and two sum signals (e.g. Ex and Ey), the recovered modern and sum-difference signals travel the same length of wave through the tracking system and also in pairs (ZX, Ax and Zy, Ay) show the same effect from depolarization of the bearing signal. The invention is then characterized as can be seen from the characterizing part of claim 1.

DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 7 shows a frequency diagram indicating the position of the transmission channel, receiver channel and bearing frequency in the tracking system in which the mode switch according to the invention is included.

Figure 2 shows a simplified field view of the two utilized higher modes together with the basic mode in the main waveguide included in the tracking system.

Figures 3a-3f schematically illustrate how the error signals in the tracking system are formed from the two higher modes shown in Figure 2.

Figure 4 shows a perspective view of the mode switch according to the invention.

Figure 5 shows a side view of the part of the mode switch according to Figure 4, which filters out the two higher modes.

Figure 6 shows in more detail a rectangular waveguide arm which is included in the mode switch according to figure 4.

Figure 7 shows a circuit diagram which illustrates the formation of reference signal and error signals.

PREFERRED EMBODIMENT Before describing the mode switch according to the present invention, the known principle for generating the error signals during tracking by means of two higher waveguide modes will be further elucidated as described above.

"The tracking system, which includes the proposed mode switch, forms part of the communication equipment of a satellite, which receives, processes and forwards the signals received from the ground station to a number of other ground stations. The transmission is by RF signals and for this purpose two frequency bands, which are schematically shown in Figure 1. The band f1-fa (for example 400 MHz) with the center frequency fT forms the transmitter channel for a certain ground station and the band f3-f4 with the center frequency fR forms the receiver channel for the station.the transmission of the transmitter and receiver channels within the GHz band and by means of a reflector antenna, with a horn antenna as a feeder. For transmitting directional information there is a sense frequency fb, for example 12,498 GHz. The two bands f1-fa and f3-f4 can either be shown in Figure 1 are below or above this frequency, in some cases only one band (antenna for transmission only from or receiving satellite).

Figure 2 shows in more detail the two higher modes, which appear in the main waveguide of the tracking system, which are connected to the antenna and which are used to indicate any deviation between the directions of the antenna reference signal and the target direction.

Furthermore, both the basic modes TE11V and TE11H are shown (smooth guide; HE11V and HE11H for corrugated guide). These are used for transmitting the communication signals and for normalizing the difference signals. The principle of the follow-up is that the two modern TE21 and TM01 in smooth waveguide (or corresponding mother HE21 and E02 in corrugated waveguide) according to figure 2, which have the same amplitude and phase in the y-direction and opposite phase but the same amplitude in the x-direction, added to form the error signals Ax and Ay. The principle is shown schematically in Figures 3a-3f. Figures Sa-3c show addition of the two modes, whereby a signal representing the error in the y-direction (height error) is obtained, while Figures 3d-3f show subtraction of the two modes, whereby a signal representing the error in the x-direction (side error) is obtained.

The structure of the counter-coupler in the tracking system is shown in Figure 4. The pen consists of a circular waveguide 1, which is connected to the feed horn (not shown) in the tracking system and to a polarization unit not shown here. The main waveguide 1 can either form an integral part of the feed horn or also form a separate part connected to it. The guide walls can either be made with smooth or corrugated surfaces. Arranged to the circular main guide 1 are four rectangular guide arms 2a-2d, each of which is connected to the guide 1 by means of the apertures 3a-3d. The apertures 3a-3d are arranged mutually offset 900 around the outer circumference of the waveguide 1.

In Figure 4, the front part 11 of the waveguide 1 is shown in the cut-up condition for the positions of the apertures to be clearly visible.

Characteristic of the proposed mode switch is that the rectangular guide arms 2a-2d are connected to the main guide 1 in the same cross section. The front part 11 constitutes the feed horn or is connected to it in a known manner, wherein in this part the circularly polarized waveguide field in the TE11 mode transmits the two communication channels f1-fz, fs-f4 and the bearing frequency signal fb according to Figure 1. In accordance with known principles, both higher modern TE21 and TM01 occurring in the main waveguide at a certain angular deviation of the incoming signals to the tracking system to form the error signals Ax and Ay. Disconnection of these higher modes is performed by exciting the TE10 mode in the waveguide arms 2a-2d from the field in the main waveguide 1 by means of coupling openings in the form of apertures 3a-3d. The apertures 3a-Sd are suitably of rectangular shape and its dimension is chosen so that sufficient disconnection of the TE10 mode is obtained from the waveguide 1 to the rectangular waveguide arms 2a-2d. However, the internal cross-sectional dimension of these must be dimensioned in a known manner so that the TE1D mode is propagated in the waveguides 2a-2d at the frequency fb. The amplitude and phase of the TE10 mode appearing in the rectangular waveguides 2a-2d is then determined by the amplitude and phase position of the higher modern TE21, TM01 and the basic mode TE11 appearing in the main waveguide 1, all of these modes making a certain contribution to the field in the rectangular guides 2a-2d.

Figure 5 shows in more detail the circular guide guide 1 of the counter-coupler, where for the sake of clarity the rectangular guide arms 2a-2d have been omitted. the rear part 12 of the guide 1 has a tapered part 13, containing two sections I and II. The section I is located at a distance d1 from the section defined by the guides 2a-2d, wherein d1 for a certain value of the radius R of the circular guide is selected so that a standing path for the TE21 mode is formed in the guide section bounded by the distance d1 and so that the maximum value of the mode falls at the apertures Sa-3d or close to them. The section II is located at the distance da from said section, wherein dz is selected so that a standing wave for the TMU1 mode is formed in the waveguide part limited by the distance da and which assumes maximum value at the apertures 3a-3d or near them. The distances d1 and dz then constitute an even (but not necessarily the same) number of quartz wavelengths of modern TE21 resp.

TM01. The tapered part 13 of the circular waveguide constitutes a mode filter for filtering out the undesired modern TE21 and TM01, which in the short-circuit plan formed in sections I and II are reflected back towards the apertures 3a-3d and as above assume maximum value there. However, the mode filter 13 does not affect the TE11 mode which transmits the communication signals within the frequency bands i1-fa, f3-f4, which thus appears at the output of the mode switch. The tapered portion 13 has a non-linear contour, which can be determined by experimental measurements.

As previously mentioned, disconnection from the waveguide field in the circular main waveguide 1 takes place by means of the four apertures 3a-3d and the TE1Û mode is excited in the four waveguide arms 2a-2d. In Figure 6, such a waveguide arm is shown in more detail. It consists of a wider part connected to the main guide and has the cross-sectional dimensions indicated by a and b in figure 6. The dimension b1 is chosen so that all frequencies of the field in the guide 2a from f1 up to fb can be propagated in the guide as TE10- Courage.

W * The waveguide 2a has a tapered portion which is substantially limited by the sections III and IV. At the section III at the distance d3 from the aperture 3a, the dimension bz of the waveguide is such that the center frequency fT of the band, h f1 ~ 2 is reflected, i.e. ba is such that the section III forms a short-circuit plane for the TE10 mode at the frequency iT. According to the same principle, the distance d4 of the section IV must be chosen so that the dimension b3 is such that the center frequency fR of the band fs-f¿ is reflected. The waveguide sections III and IV thus define a frequency filter for filtering out the communication signals, the distances d3 and d4 constituting a number (not necessarily the same) half wavelengths for the TE10 mode at the center frequencies f1 and fR, i.e. the sections III and IV constitute the to the apertures 3a-3d transformed the short-circuit plan for the frequencies fR and fT, respectively. Thus, from the path guide Za and the other path guides 2b-2d, only the signals corresponding to rsa1oss-9 10 15 20 25 the TE11 mode having the frequency fb are obtained, and furthermore the signals corresponding to the two modern TE21 and TMÜ1 at the frequency fb in the main waveguide 1. i Figure 7 schematically shows how a waveguide network consisting of so-called magic T is connected to the four rectangular waveguide arms 2a-2d for extracting the error signals Ax, Ay and the reference signals Ex and Ey. Each node m1-m4 represents a magic T with two inputs 1 and 2 and a sum and a difference output s and A, respectively. Figure 7 shows the signals which appear on the outputs of the four waveguide arms 2a-2d and which are derived from the four modern TE21, TMO1 and TE11H and TE11V appearing in the main waveguide 1, cf. Figure 2. Of these, the error signals Ax and Ay are extracted from modern TE21 and TM01, while the reference signals Xx and Zy are extracted from the TE11H and TE11v modes, respectively. Figure 7 shows that the signals Ax and Ay are separated in three different steps. In the first step, the signals derived from the TE21 and TM01 modes are separated in the nodes m1 and m2. In the second step a separation of the two modern TE21 and TM01 takes place in the node m3 and in the third step the desired error signals are formed. Ax and Ay by vectorial addition in the node m4 in the manner shown in figure 3. Between m3 and m4, phase and amplitude adjustments can be introduced (tuning and temperature compensation). In some cases this is not required, whereby m3 and m4 can be omitted. Here, instead, correct phase and amplitude ratios can be obtained by careful selection of the distances d1 and da in Figure S, of the phase gap difference between TE21 and TM01 modes, as they extend from the mouth of the horn and of f dimensions on apertures 3a-3d in Figure 5. .... .v -... vr-.w- fi.- -. ..-, - f-

Claims (1)

1. 0 15 20 25 30 7901055-9 CLAIMS 1 Mod switch in an automatic angle tracking system included in a telecommunication system for transmitting one or more communication frequency bands together with a certain measuring frequency, containing a microwave antenna, in which a basic mode and higher order mode are generated when it the radiation received by the antenna is incident in a plane which does not coincide with the plane perpendicular to the reference axis of the antenna, said higher order mode being used to form a pair of error signals, which are measured on the deviation between said plane together with associated reference signals, a smooth or corrugated circular main waveguide, which forms part of or is connected to the feed horn of the antenna and in which the basic mode and the mother of the higher order are propagated and which has four apertures arranged in a plane perpendicular to the waveguide axis arranged circles symmetrically about the main waveguide in the plane perpendicular to the waveguide axis, characterized in that said apertures (3a-Sd) are so dimensioned that a certain waveguide mode (TE10) is formed in them, the amplitude and phase of which is determined by the amplitude and phase of the main waveguide (1) behaving basic mode (TE11 or HE11) and at least two higher order modes (TE21 or HE21 and TMO1 or E02), and that a guide network (m1, m2, m3, m4) is connected to the exit ports of the guide arms, which has four exit ports over which output signals are obtained, of which the first and the second (Xx and ty), constituting said reference signals, are formed from the difference between the signals from a first and a second pair of oppositely located waveguide frames (Za, 2c and 2b, 2d), respectively, from the basic mode lTE11) appearing in the main guide, the third and the fourth (Ax and Ay, respectively), constituting said error signals, are formed from the sum of the signals from said first and second pairs opposite gna waveguide arms (Za, 2c and Zb, Zd) derived from said higher mother (TE21, TM01). Module coupler according to claim 1, characterized in that the part (12, 13, 14, 15) of the circular main waveguide which is located between the waveguide arms (2a-2d) and its output port is designed as a mode filter for reflection of the two higher modes (TE21, THO1). Mod coupler according to claim 2, characterized in that said part of the main waveguide consists of a main portion (12), of a tapered portion (13) and of an end portion (15) of smaller inner radius, which portions are delimited by two sections ( I, II), the distances of which (d1 and dz, respectively) to said planes perpendicular to the waveguide axis are chosen so that the sections form short-circuit planes for the two higher modern ones (TE21, TM01 or HE21, E02). Counter coupler according to claim 1, characterized in that each of the four waveguide arms (2a-2d) is designed as a frequency filter for filtering out the communication frequency bands. Mod coupler according to claim 4, characterized in that each of the four waveguide arms (2a-2d) has an evenly thick base portion of a certain cross-sectional dimension (a, b1) connected to the main waveguide (1), a continuous or in step tapered portion and a - evenly thick end portion of smaller cross-sectional dimension (a, b4), wherein tv8 sections (III, IV) located at a distance (d3, d4) from said apertures (3a-3d), correspond to the cards transformed into the respective aperture - basic mode closing plan (TE10) for the center frequencies in the communication frequency bands. Head coupler according to claim 4, characterized in that each of the four waveguide arms (2a-2d) contains filters such that the communication frequency bands (f1-fz, f3-f¿) are reflected with the reflection plane substantially coinciding with the inner wall. of the cylindrical waveguide (1), while the bearing frequency (fb) is passed with negligible attenuation. Mod coupler according to claims 1-6, characterized in that the waveguide network comprises a first and a second directional coupler (m1 and ma, respectively) with two inputs (1, 2) together with difference and sum output (A and s, respectively). ), each of which is connected to the output ports of two oppositely located waveguide arms (Za, Ze and Zb, Zd), respectively, to form said reference signals, a third directional switch (m3) having two inputs connected to the sum outputs of the first and the the second directional coupler, a fourth directional coupler (mh) with two inputs connected to the difference and sum output of the third direction coupler (m3) in order to obtain the said error signals (Ax, Ay) via the difference and sum output of the fourth direction coupler, which indicate the deviation between said plan. Counter-coupler according to Claim Z, characterized in that each directional coupler (m1-m4) consists of a magic T. e: