US3587099A - Sector radio beacon - Google Patents

Abstract

To provide a rotating radiation pattern in a given sector, an antenna which radiates a carrier frequency F is flanked, substantially along a line, on one side by a directional antenna which radiates a frequency F- 15 Hz. and on the other side by a directional antenna radiating a frequency F+15 Hz. and a directional antenna radiating a frequency F+135 Hz. The directional antennas radiate in a direction substantially perpendicular to said line. The antenna spacing is dependent upon the carrier frequency and the desired width of said sector.

Description

OR EeSBY vU Q U nlwu Dlflltib r atclu.

Ernst Kramar Ptorzhclm, Germany Mar. 4, 1969 June 22, 1971 International Standard Electric Corporation New York, N.Y.

Inventor Appl. No. Filed Patented Assignee SECTOR RADIO BEACON 4 Claims, 5 Drawing Figs:

U.S.Cl

Int. Cl Field of Search References Cited UNITED STATES PATENTS l/ 1951 Luck F-75Hz F F 75Hz 2,978,701 4/1961 Pickles 3.305.866 2/1967 Earp Primary Examiner-Richard A. Farley Assistant Examiner-Richard E. Berger Attorneys-C. Cornell Remsen, .lr., Walter J. Baum, Percy P.

Lantzy, Philip M. Bolton, Isidore Tqgut and Charles L. Johnson, Jr.

PATENTEBJUNZZIHH 3,587,099

Fig. 3 Fig.4

INVENTOR ERNST KRAMAR Maw 4% ATTORNEY ssc'ronnxmo BEACON BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beacon, and in particular to onewhich provides a rotating pattern in a predetermined sector.

2. Description of Prior Art Many interesting instrument landing systems have been proposed, however, their implementation requires .either modification or addition of equipment on board aircrafts.

However, airborne T acan receivers presently being used for .en route navigation may be used without modification for landing guidance provided that a Tacan type signal is made present in a sector which includes the runway approach.

. Directional beacons which provide rotating Tacan signals are well known. However, these beacons are not effective if one simply desires rotating radiation patterns to be present in a sectorfGenerally these. conventional beacons use physically rotating parasitics to produce the. rotating field and are relatively cumbersome and difficult to transport.

SUMMARY OF THE INVENTION radiating a secondfrequency located at a distance from said first means, which distance is determined by said first carrier frequency and the desired width of said sector, and'third means for radiating a third frequency located at asecond distance from said first means.

BRIEF DESCRIPTION OFTHE DRAWINGS The above-mentioned and other objects of the invention will become apparent by reference to the following description in conjunction with the I accompanying drawings, in which: I

FIG. 1 illustrates a radiation pattern resulting from the applicationof in-phase signals to spaced dipoles.

FIG. 2 illustrates a radiation pattern resulting from the application of antiphase signals to spaced dipoles.

FIG. 3 illustrates a radiation pattern in a sector resulting from. the application of different frequencies to spaced dipoles.

FIG. 4 illustrates an in-line arrangement of spacedantennas according to the invention.

FIG. 5 illustrates a second in-line arrangement of spaced antennas according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To explain the mode of operation of the invention, it is assumed that two dipoles spaced, for example, one wavelengthapart, radiate the same frequency. A four-lobe radiation pattern is thus obtained having an approximately 60 aperture angle. By shifting in-phase one or both feed voltages, with respect to each other, the entire pattern may be arbitrarily placed. FIG. I and FIG. 2 show respectively the patterns produced by feeding the dipoles with in-phase and out-ofphase voltages. If, for example, thetphase of the feed voltage for dipole 2 is continuously shiftedywitli respect to the feed voltage coupled to dipole I, Ethe -radiatioh lobes rotate clockwise; if the frequency of dipole 2 is, for example, Hz.

higher than the frequency fed to dipole l, the entire radiation pattern rotates clockwise l5times per second.

Within a sector of 60, assuming :for example purposes, which is formed by both zeros of the pattern perpendicular to the dipole plane in the approach direction, 360 electrical degrees are passed within 60 of azimuth so that 1 of azimuth corresponds to 6 electrical degrees.

However, in order to make the scale reading easier, the width of the sector could have been chosen such that, for example, 1 of azimuth corresponds to 1.0 electrical degrees of an airborne indicator. This would require a i 18 sector width. The dipole spacing required to achieve the above is d 5111') -A= 1.6 A.

In order to make the above-described approach beacon compatible with Tacan receivers, it should be considered that the modulation sidebands of 15 Hz. and Hz. produced by a Tacan ground beacon are each radiated with a modulation index of 18 percent. The current ratio between the dipole 1 radiating the frequency F and the dipole 2 as illustrated in FIG. 3 radiating the frequency F+f, where f=l5 Hz. must be selected in a ratio 110.18. Reference pulse trains may be transmitted by the dipole fed withthe frequency F as in the standard Tacan system so that a phase comparison can be made as is usual in the receiver.

The single sideband radiation above-described can be converted to double sideband modulation by the addition of another dipole 3 as illustrated in FIG. 4 and fed with energy of a frequency F- where f is, for example, 15 Hz. The resulting radiation field has the characteristics of pure amplitude modulation. This is particularly useful because of a resulting reduction of nonlinear distortion.

The accuracy of the above-described embodiment is sufficiently accurate for establishing a clearance pattern. To improve the accuracy, however, a nine-lobe pattern is superimposed on the single lobe pattern within the sector. This is achieved, for example, by placing another dipole 4, as shown in FIG. 4, at a distance of 9 '(5/1r) A from the dipole 1, said dipole 4 being fed with a frequency F+9f(F+l35 Hz.). With the same amplitude ratio of 1:0.18 of the If energy with respect to the dipole 1 (main antenna) nine radiation maxima and minimal in total are obtained within the sector of i 18.3 1 which rotate at a speed of I35 Hz. The reference signals required for fine phase measurement transmitted in the same manner as the reference signals for coarse phase measurement to wit, as a modulation of the carrier wave. Thus, the amplitude modulation resulting from the antenna arrangement and the particular feeding of said antenna, detected in the airborne receiver within said sector of 36, corresponds to the radiation of a conventional Tacan transmitting system.

At a dipole spacing of 15 A, the antenna arrangement constitutes a wide-base system and offers well known advantages with respect to multipath propagational effects of the rf signals, the system therefore, operates more favorably than an omnidirectional Tacan antenna.

It is suitable to concentrate radiation, for example, with the aid of horn radiators, as shown in FIG. 4, having a radiation pattern of approximately 45 at the half-power points. This prevents a lateral and backward radiation of rf energy and considerably reduces the ambiguity of the measurement at the receiving end.

In order to ensure that the antenna system radiates mainly in the desired forward direction and that the energy radiated in the backwarddirectionis as low as possible, the main antenna (1, FIG. 4) is offset forward by one-eighth wavelength. This means can however be used successfully only, if a double sideband system is used, i.e. if also the antenna 3, FIG. 4 exists and is fed by lower sideband energy (F-IS cls).

If the transmitter feeding dipole l is designed as a transponder, the receiver of which picks up distance interrogation signals from aircraft by which the transmitter is modulated, in a way known per se, the aircraft may determine its distance from the beacon. If, however, interrogation signals arenot received, the carrier wave may be modulated by random pulses.

In practice it has been found that it is often important to know at least the distance at any azimuth angle also outward said predetermined sector when approaching said radio beacon, or when flying round the radio beacon during a waiting period, particularly after an unsuccessful landing attempt.

It is, therefore, another important feature of the invention that the main antenna is an omnidirectional antenna, whilst the sideband antennae are unidirectional antennae (F IG. 5

Assuming that for the main transmitter (dipole l) a pulse peak energy of approximately 1 kw. is required, it is sufficient to have approximately 40 w. pulse peak energy for the sideband transmitters.

It will be noted that the output of the transmitter feeding the main antenna 1 must be somewhat greater in the case of an omnidirectional antenna than for a unidirectional antenna. lt will be selected in known manner such that the desired degree of modulation is achieved in conjunction with the sideband energy for azimuth determination.

Between the main transmitter and the sideband transmitters, a fixed phase relationship must exist with respect to the difference frequencies as well as in respect to the pulse trains. The generation of separate carrier and sideband frequencies having such proper phase relationship is well known.

1 claim:

1. A beacon for providing a rotating radiation field in a predetermined sector, comprising:

an omnidirectional antenna for radiating a first carrier frequency;

a first directional antenna located at a first distance from said omnidirectional antenna, which distance is determined by said first carrier frequency and the desired width of said sector, said first directional antenna radiating a second frequency higher than said carrier frequency by a predetermined difference; and

a second directional antenna for radiating a third frequency located at a second distance from said omnidirectional antenna, said second distance equal to an integral multiple of said first distance, said third frequency being higher than said carrier frequency by an integral multiple of said predetermined difference, and said first and second directional antennas arranged substantially in a line with said omnidirectional antenna.

2. A beacon, according to claim 1, further including means for radiating a fourth frequency located at a distance from said omnidirectional antennas which is a multiple, including one, of said first distance. 3

3. A beacon, according to claim 2, wherein said second and fourth frequencies are higher and lower respectively than said carrier frequency by a predetermined frequency difference.

4. A beacon, according to claim 2, wherein said means includes a third directional antenna.

Claims (4)

1. A beacon for providing a rotating radiation field in a predetermined sector, comprising: an omnidirectional antenna for radiating a first carrier frequency; a first directional antenna located at a first distance from said omnidirectional antenna, which distance is determined by said first carrier frequency and the desired width of said sector, said first directional antenna radiating a second frequency higher than said carrier frequency by a predetermined difference; and a second directional antenna for radiating a third frequency located at a second distance from said omnidirectional antenna, said second distance equal to an integral multiple of said first distance, said third frequency being higher than said carrier frequency by an integral multiple of said predetermined difference, and said first and second directional antennas arranged substantially in a line with said omnidirectional antenna.

2. A beacon, according to claim 1, further including means for radiating a fourth frequency located at a distance from said omnidirectional antennas which is a multiple, including one, of said first distance.

3. A beacon, according to claim 2, wherein said second and fourth frequencies are higher and lower respectively than said carrier frequency by a predetermined frequency difference.

4. A beacon, according to claim 2, wherein said means includes a third directional antenna.

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