US3286261A

US3286261A - Direction-determination system employing unequal directional patterns

Info

Publication number: US3286261A
Application number: US291355A
Authority: US
Inventors: Hofgen Gunter
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1962-07-09
Filing date: 1963-06-28
Publication date: 1966-11-15
Anticipated expiration: 1983-11-15
Also published as: BE634674A; DE1259969B; CH414774A; NL295108A

Description

N 5, 9 G. HOFGEN 3,286,261

DIRECTION-DETERMINATION SYSTEM EMPLOYING UNEQUAL DIRECTIONAL PATTERNS Filed June 28. 1963 4 Sheets-Sheet l 7 A BY M: Mm

Nov. 15, 1966 G. HOFGEN 3,286,261

DIRECTION-DETERMINATION SYSTEM EMPLOYING UNEQUAL DIRECTIONAL PATTERNS Filed June 28, 1963 4 Sheets-Sheet 2 o -2 -1 -0,6 -o,a -q100,10,3 0,6 1 o FIG. 4

no -z -Q6 230,1001 0,3 96 1 2 w Nov. 15, 1966 a. HDFGEN 3,286,261

DIRECTION-DETERMINATION SYSTEM EMPLOYING UNEQUAL DIRECTIONAL PATTERNS Filed June 28. 1963 4 Sheets-Sheet 5 w -4 .-o,a 1001 as 0,6 4 2 M w z 1 as e 2 -2 -21 -1 w United States Patent Office 3,286,261 Patented Nov. 15, 1966 3,286,261 DIRECTION-DETERMINATION SYSTEM EMPLOY- ING UNEQUA'L DIRECTIONAL PATTERNS Giinter Hiifgen, Berlin-Lichtenrade, Germany, assignor to International Standard Electric Corporation, New York,

N.Y., a corporation of Delaware Filed June 28, 1963, Ser. No, 291,355 Claims priority, application Germany, July 9, 1962, St 19,460 8 Claims. (Cl. 343107) Aircraft landing direction-determination systems (approachbeacons) are known in which the directional patterns serving the navigation purpose, are lying uniformly and symmetrically in relation to a center line (landing runway). These patterns may be e.g. directional patterns of either the modulation or frequency deviation type. These systems, however, require the additional transmission of a reference signal. The invention is based on the problem of providing a system which can be simplified by doing away with this requirement.

The present invention relates to a direction-determination system operating on the basis of unequally produced directional patterns, i.e. of such ones which are produced by two spatially separated antenna systems (with the spacing being large with respect to the wavelength) operated at different frequencies. The frequencies are thus that they can represent both the carrier and a sideband of an amplitude-modulated oscillation. In particular, the direction-determination system consists in that one of the two directional patterns is of the amplitude modulation type, while the other one is of the frequency-deviation type. As regards the mid-vertical line, the two directional patterns are preferably symmetrical with respect to the connecting line between the two antenna systems, but may also be unsymmetrical.

The invention will now be explained in detail with reference to the copending drawings, in which:

FIG. 1 shows two antenna systems with symmetrical patterns in respect to the mid-vertical to the line connecting the two arrays;

FIGS. 2 and 3 each show two antenna systems with unequally produced antenna patterns;

FIGS. 4 and 5 are plots of radiation fields of lines having a constant phase difference;

FIG. 6 is a block diagram of a navigation system according to FIG. 2; and

FIG. 7 is a block diagram of a navigation system in accordance with FIG. 3.

FIG. 1 shows two antenna systems A and B whose directional patterns extend symmetrically in relation to the mid-vertical to the common connecting line. The antenna system A is eg supposed to radiate a carrier oscillation (frequency F which is amplitude-modulated with the signal frequency f, in such a way that the degree of amplitude modulation is dependent upon the direction. The directional pattern is supposed to have a figure-ofeight characteristic. To the antenna system B there is then fed the sideband oscillation (frequency F +AF). The antenna system B consists of one row comprising a number of single antennas which are successively fed in a rhythmical succession, so that in this way, and in the conventional manner, there is simulated an antenna motion of the individual radiators on the linear antenna array. The function of the velocity is supposed to be the same as at the modulation of the carrier oscillation, hence a sine wave function with the frequency f. The frequency deviation caused on account of the Doppler effect, is direction-dependent. It reaches its maximum in the direction of the linear antenna array, while being zero vertically in relation thereto. This directional pattern likewise has a figure-of-eight characteristic.

From the basis of the two unequally produced directional patterns which, however, are of the same characteristic, there may be derived a direction-determination system which is suitable for being received with the aid of VOR-receivers. This can be realized in that symmetrically in relation to the center line there is produced a field of lines having a constant phase difference between the signal obtained from the amplitude-modulated carrier oscillation and the signal obtained from the frequencym-odulated sideband oscillation, with the phase difference on the center line itself being zero. To achieve this end a second modulation of the same kind of modulation, hence an amplitude modulation in the case of the carrier, and a frequency modulation in the case of the sideband, but with a different directional characteristic, is added to the two direction-dependent modulations in a phaseshifted manner. First of all, consideration will be given to the case (FIG. 2') where the additional modulations are undirected, and where the phase shift between the modulated oscillations of the signal frequency amounts to The local function of the received field intensity produced at the point P by the antenna system A may then be represented as follows:

The function of time, as well as the pure carrier oscillation which is radiated in an undirected manner, are not represented, because they do no longer appear after having been rectified in the receiver. The frequency deviation as produced by the antenna system B at the point P i c r spon in y H =the maximum frequency deviation of the directiondependent frequency modulation H =the frequency deviation of the additional frequency modulation.

The frequency modulation of the sideband oscillation is contained subsequently to the rectification in the receiver, in the difference oscillation (frequency AF) as constituted by the carrier and the sideband, and is con- As a corresponding example there is shOWIl in FIG. 4 the field of lines -having a constant phase difference relating to 1=2. i

There is now still to be considered the case where the additional modulation is likewise direction dependent, The directional patterns are e.g. supposed to have a figure-of-eight characteristic, as shown in FIG. 3. When e=E(m -sin w-sin wi+m 'COS w'cos wt) h=H -sin fi-sin wt+H -cos B'cos wt In this case the fields of lines having a constant phase difference is given by:

As a corresponding example there is shown in FIG. 5 a field of lines having a constant phase difference relating to k=2.

The realization of the directional patterns may be effected in the case of the antenna system A with the aid of crossed dipoles, and in the case of the antenna system B by providing an elliptical path of the simulated sideband radiation (arrangement of the single antennas in elliptical array).

For carrying out the methods described in conjunction with FIGS. 2 and 3, FIG. 6 shows the block diagram relating to a navigation system according to FIG. 2, and FIG. 7 likewise shows a block diagram of an arrangement for carrying out the method according to FIG. 3. In FIG. 6 generator 1 is an RF-generator for producing the carrier oscillation, whose angular frequency is S2 =21r-F This oscillation controls two parallel-arranged

output amplifier stages

2 and 3 in the ovenbiased condition, so that they are capable of being anode-modulated with a low distortion. The two outputs of the output amplifiers are coupled via a bridge network 4 consisting of three M4 cables 5 and one 3M4 cable 6, so that at the output A the sum voltage of both

output amplifiers

2 and 3, and at the output A the difference voltage is obtainable.

The control generator 7 produces the low-frequency signal oscillation whose function of time is cos wt(w=2'rrf :signal angular frequency). In order to produce the desired directional patterns at the system A of FIG. 2 the signal oscillation is subjected to a phase shift by +90 and by 90" with the aid of the phase-shifting devices 8 and 9. Accordingly, the functions of time at the two outputs of the phase shifters are thus +sin wt and sin wt. To the two voltages appearing at the outputs of the phase shifters 8 and 9 there is added with the aid of the adding devices 10 and 11 a portion of the signal voltage with the function of time cos wt in the necessary ratio which is dependent upon the pattern to be obtained. The sum voltages are amplified in the modulation amplifiers 12 and 13. The output voltages of these modulation amplifiers are signified as U cos wt+U sin wt and U cos wt -U sin wt; with the aid of these voltages there is carried out the amplitude modulation of the two RF-

output amplifiers

2 and 3. Accordingly, the output voltages of the output amplifiers may be expressed as follows:

is fed to an unidirectedly radiating antenna (e.g. Alford loop), and the difference voltage is fed to an antenna 4 having a figure-of-eight pattern (e.g. dipole). way the system A of FIG. 2 is realized.

A second RFagenera'tor 15 produces the sideband oscillation (angular frequency Sz +AS2=21r[F +AF]), with this oscillation serving to control the output amplifier 16. The output of this stage is fed via a distributor 17 to the individual or single antennae B B B of the linear antenna array. The distributor 17 is controlled by the low-frequency oscillation as produced in the control generator 7; it serves to forward the energy as derived from the sideband-output generator 15, in such a way to the individual or single antennae B B B that a movement of the radiation center on the linear antenna array is simulated with a sinusoidal velocity thereby. An example of such a distributor which can be used herein is disclosed in the copending patent application of E. Kramar and F. Steiner for Frequency Modulated Approach System filed April 18, 1961, Serial No. 103,805 now issued as US. Patent No. 3,094,697. The function of time of the simulated velocity of the radiation center is sin wt. In this way there is produced the frequency deviation of the sideband oscillation which, in its magnitude, is dependent upon the direction between the receiving point and the linear antenna array. The necessary additional frequency deviation is obtained by a frequency modulation of the sideband oscillation produced by generator 15, in such a way that a capacitive diode of the servo-system 20, having frequency-determining properties with respect to the oscillation produced by generator 15, is subjected to a capacitance modulation by the signal voltage of the control generator 7.

In order to maintain the frequency spacing between the carrier and the sideband with the necessary accuracy, there is provided a frequency controller. In the mixer 21 there is constituted the difference frequency between the carrier and the sideband. Whenever it deviates from the rated value a control voltage will be produced at the output of the controller 22 acting upon the capacitive diode (not shown) of the servo-system 20. In this way the generator 15 is readjusted to the rated frequency spacing between the carrier and the sideband.

FIG. 7 shows an RF-generator 30 for producing the carrier voltage (signal) which controls the three parallelarranged output amplifier stages 31, 32 and 33. Since the output voltage s of the output amplifier 31 remains unmodulated, the two others (32 and 33) are amplitudemodulated. The function of modulation is that of the control generator 34. The low-frequency signal oscillation of the control generator 34, whose function of time is cos wt, is directly fed to the modulation amplifier 35 via a -phase shifter 36 and to the second modulation amplifier 37. The output voltages of the modulation amplifiers are U sin wt and U cos wt; with the aid of these there is carried out the amplitude modulation of the two RF-

output amplifiers

32 and 33.

The output voltages of the three output amplifiers may be represented as follows:

ages between 3 and 5 or B are available at the outputs A and A respectively. Hence, the voltages are- At the output A d z9 U a sin wte o At the output A d -z9 =U a cos wte o The RF-voltage available at the output A is the un- In this modulated carrier voltage (signal) as radiated by an antenna without a directional effect (e.g. Alford loop). The RF-voltages available at the outputSgA1 and A are the pure sideband voltages (signals) differing from one another by the modulation amplitude and the modulation phase. They are fed to two antennae having a figure-ob eight pattern, whose characteristics are shifted by 90 spatially with respect to one another (e.g. crossed dipoles), with the radiation centers thereof being in agreement with that of the carrier radiation, and are radiated thereby in a directional fashion. In this way the system A of FIG. 3 is realized.

The construction of the circuit arrangement for producing the sideband oscillation (angular frequency Q -i-AQ), including the frequency controller, is the same as that shown in FIG. 6. The difference with respect to the radiation merely resides in the fact that the sideband radiation must not be moved in a simulated fashion on a linear antenna array, but on an elliptical path.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

I claim:

1. A direction-determination system operating on the basis of two directional patterns which are produced by two spatially separated antenna systems operated at different frequencies, Whose spacing is a plurality of wavelengths with respect to the transmitted wavelengths, comprising means to produce at one of said antenna systems a pattern of the amplitude modulation type, and means to produce at the other antenna system a pattern of the frequency-deviation type.

2. A direction-determination system according to claim 1 wherein a first antenna system of said two antenna systems comprises two antennas, means to produce a first signal which is the sum of two other signals, means to produce a second signal which is the difference of said two other signals, means to couple said first signal to said first antenna and means to couple said second signal to said second antenna.

3. A direction-determination system according to claim 2 wherein said first antenna is an Alford loop and said second antenna is -a dipole.

4. A direction-determination system according to claim 3 wherein said second antenna system comprises a linear antenna array, means to produce a sideband modulation of one of said signals, and means to couple sequentially said sideband signal to the antennas of said linear array.

5. A direction-determination system according to claim 1 wherein a first antenna system of said two antenna systems comprises three antennas, means to produce a carrier signal, means to produce sideband signals of said carrier and a modulation signal, means to couple said carrier signal to a first of said three antennas and means to couple each said sideband signals to respective second and third antennas of said three antennas.

6. A direction-determination system according to claim 5 wherein said first antenna is an Alford loop antenna and each of said second and third antennas is a dipole antenna.

7. A direction-determination system according to claim 6 wherein the second antenna system comprises an antenna array movable on an elliptical path.

8. A direction determination system according to claim 7 further comprising means to produce a sideband of said carrier signal and means to couple sequentially said modulation signal to the antennas of said antenna array.

References Cited by the Examiner UlSllTED STATES PATENTS 2,543,081 2/1951 Watts et al 343 107 x 2,690,558 9/;1954 Harvey 343- 104 2,717,735 9/1955 Luck.

3,130,407 4/1964 Kramar 343-407 3,181,159 4/1965 Kramar m1 343106 CHESTER L. JUSTUS, Primary Examiner. H. C. WAMSLEY, Assistant Examiner.