WO2009050417A1

WO2009050417A1 - Transmitter/receiver horn

Info

Publication number: WO2009050417A1
Application number: PCT/GB2007/050785
Authority: WO
Inventors: Erik Geterud
Original assignee: Global View Systems Ltd
Priority date: 2007-10-16
Filing date: 2007-12-21
Publication date: 2009-04-23
Also published as: GB0720198D0

Abstract

A corrugated feed horn developed specifically to match a waveguide lens antenna (WGLA). For maximized efficiency the illumination taper must match the focal distance to diameter (F/D) ratio of the antenna. Also, and more important, the phase centre of the feed must coincide with the focal point of the antenna for all specified frequencies. Most lens antennas exhibit frequency dispersion to some extent i.e. the focal point changes with frequency. The phase centre shift of the described feed is designed to specifically match the frequency dispersion of the WGLA. The horn is flare angle controlled which also makes it wideband.

Description

Transmitter/Receiver Horn

This invention relates to a transmitter/receiver horn, particularly, but not limited to, a transmitter/receiver horn for use with a waveguide lens antenna.

Corrugated feed horns have for several decades been popular choices as antenna for e.g. feeds for reflector antennas and lenses due to their circular symmetry and very controlled electro-magnetic behaviour.

It is an object of the present invention to improve the efficiency of a transmitter/receiver horn.

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

According to a first aspect of the present invention there is provided a transmitter/receiver horn adapted for use with a waveguide lens antenna, the horn comprising a horn section having a plurality of corrugated sections therein, wherein dimensions of the horn section and corrugated sections are chosen so that phase centres for a plurality of frequencies substantially coincide with focal points of a waveguide lens antenna for the same plurality of frequencies .

Preferably, the horn has a value of Δ greater than substantially 0.7, where A = —tan-²- = —sin 6> tan —

K K

where a is the aperture radius and R the distance between the apex and a spherical wave front at the aperture and θ₀ is the semi flare angle of the horn.

More preferably, the value of Δ is greater than substantially 0.75. Preferably, the horn is an aperture controlled horn.

The horn preferably has substantially infinite longitudinal impedance.

According to another aspect of the invention there is provided a transmitter/receiver horn adapted for use with a waveguide lens antenna, the horn comprising a horn section having a plurality of corrugated sections therein, wherein the horn has a value of Δ that is at least substantially 0.7, where

where a is the aperture radius and R the distance between the apex and a spherical wave front at the aperture. θ₀ is the semi flare angle of the horn.

According to an aspect of the present invention there is provided an assembly comprising a transmitter/receiver horn and a waveguide lens antenna, wherein the horn is constructed so that phase centres for a plurality of frequencies substantially coincide with focal points of the waveguide lens antenna for the same plurality of frequencies .

The horn preferably comprises corrugations, the dimensions and/or number of which, together with dimensions of a horn section and/or a waveguide section of the horn are chosen to specify the locations of the phase centres.

The dimensions may include, aperture diameter, throat diameter, horn length, waveguide length, throat length and/or semi-flare angle.

The semi-flare angle is preferably chosen so that a solid angle of the horn section substantially intersects an outer perimeter of the waveguide antenna for a chosen separation of the horn and the waveguide antenna.

All of the features described herein may be combined with any of the above aspects, in any combination.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure Ia a front view of a transmitter/receiver horn;

Figure Ib is a schematic cross-sectional view of the transmitter/receiver horn;

Figure Ic is a schematic rear view of the transmitter/receiver horn; Figure 2 is a schematic cross-sectional view of the transmitter/receiver horn showing the positions of phase centres for incoming waves of different frequencies;

Figure 3 is a schematic view of the transmitter/receiver horn in use with a waveguide lens antenna; and

Figure 4 is a schematic cross-sectional view of the horn showing relevant variables

As shown in Figures Ia to Ic a horn comprises a flange 10 for attachment of the horn to suitable equipment, a waveguide, or throat, section 12 and a horn section 14. The horn is circular in plan and has a semi-flare angle, θ₀ , as indicated in Figure Ib. The horn section 14 comprises circular corrugations 16 stepping inwards to the waveguide 12.

With correctly chosen depths of the corrugations infinite longitudinal impedance is obtained. The radiation pattern characteristics of the horn can be normalized by using the dimensionless parameter Δ

_Λ a θ₀ R . _Λ θ₀ A = — tan-²- = — sin θ₀ tan —

A₀ 2 A₀ 2

where a is the aperture radius (see Figure 1) and R the distance between the apex 15 and a spherical wave front at the aperture. θ₀ is the semi flare angle of the horn. For

Δ<0.4 the beam width is mainly determined by the aperture dimension ka (where (k=2π/λ) ) and is therefore frequency dependent. The phase centre moves towards the throat when

Δ increases. This type of horn is often named aperture controlled. When Δ>0.75 the beam width is determined mainly by the semi flare angle of the horn and the phase centre is near the throat. The far field pattern of this type is less frequency dependent and often denoted flare angle controlled horn.

A conical horn with circumferential corrugations will support a balanced HE₁₁ mode and the radiation pattern will be circular symmetric and resulting in ideal zero cross polarisation in E- and H-plane.

The phase centre of the horn is the phase reference point which minimizes the phase variations in the far field for a given solid angle. By placing the phase centre of the feed in the focal point we maximize the aperture efficiency of the lens.

The horn is used to feed a waveguide lens antenna (WGLA) . The frequency bandwidth is to a large extent determined by frequency dispersion i.e. the focal distance to diameter (F/D) ratio of the antenna increases with frequency. As a result sufficient efficiency can only be achieved for a limited frequency band. The frequency dispersion can to a large extent be reduced by wide band convex WGLA designs which provide almost equal time delay for all frequencies in e.g. a 1.3:1 band. The bandwidth is calculated as the operational frequency band divided with the centre frequency as (fmax-fmin) /fcentre*100% . There can be a need to tune the phase centre over frequency also for wide band designs to maximize efficiency.

In order to achieve a phase centre shift the horn should initially be of aperture controlled type i.e. Δ>0. can be achieved with a WGLA having the dimensions and characteristics set in Table 1 below. By optimizing the key dimensions such as the aperture diameter, flare angle and corrugation parameters towards matching the WGLA required performance is obtained. Thus, taking into account the distance of the horn from the lens, the flare angle is chosen so that a solid angle from the horn hits the outer rim of the waveguide lens, as shown in Figure 3.

The phase centre positions of the horns can have the positions as shown in Figure 2, where fi<f<f_n is our frequency band. The axial distance between fl and fn then corresponds to the focal dispersion of the WGLA.

Maximised efficiency is achieved when focal points fl to fn of a waveguide lens antenna (WGLA) 30 coincide with phase centres of a feed horn as illustrated in Fig 3. Thus, the dimensions of horns set out in Table 1 below are chosen so that the phase centre positions for frequencies fl to fn in Figure 2 substantially coincide with the focal points of the waveguide lens antenna for the frequencies fl to fn.

In table 1 the measurements for seven different horns are given. Corr 3 has three corrugations and measurements are given. Similarly, Corr5 has five corrugations and so on to Corrl2 having twelve corrugations. The abbreviations for the measurements given correspond to the measurements illustrated in Figure 4. Table 1

Corr3 Corr5 Corr7 Corr8 Corr9 Corr11 Corrl2

Nr of corr 3 5 7 8 9 11 12

Aperture diameter 44 56 68 74 80 92 100

Throat diameter 26 26 26 26 26 26 28

Horn length 29 39 41,6 48 50 59 66,5

Waveguide length 35 35 35 35 35 35 35

Throat length 14 14 12 12 12 12 15

Ridge width 0,8 0,8 0,8 0,8 0,8 0,8 0,8

Corr width 2,2 2,2 2,2 2,2 2,2 2,2 2,2

Semi flare angle 34 31 33 34 34 34 34

Corr depth inner 1 6 6,2 6,4 6,8 6,6 6,4 6,2

Corr depth outer 1 11 11,2 11,0 11,3 11,1 10,9 10,7

Corr depth inner 2 6 6,0 6,2 6,4 6,3 6,1 5,9

Corr depth outer 2 11 11,0 10,8 10,9 10,8 10,6 10,4

Corr depth inner 3 6 5,8 6,0 6,2 6,1 5,9 5,8

Corr depth outer 3 11 10,8 10,6 10,7 10,6 10,4 10,3

Corr depth inner 4 5,6 5,9 6,0 5,9 5,8 5,7

Corr depth outer 4 10,6 10,5 10,5 10,4 10,3 10,2

Corr depth inner 5 5,4 5, 8 5,9 5, 8 5,7 5,6

Corr depth outer 5 10,4 10,4 10,4 10,3 10,2 10,1

Corr depth inner 6 5,7 5,8 5,7 5,6 5,5

Corr depth outer 6 10,3 10,3 10,2 10, 1 10,0

Corr depth inner7 5,6 5,7 5,6 5,5 5,4

Corr depth outer 7 7,6 10,2 10, 1 10,0 9,9

Corr depth inner 8 5,6 5.5 5,4 5,4

Corr depth outer 8 10, 1 10,0 9,9 9,9

Corr depth inner 9 5,4 5,3 5,3

Corr depth outer 9 7,4 9,8 9,8

Corr depth inner 10 5,2 5,3

Corr depth outer 10 9,7 9,8

Corr depth inner 11 5,2 5,2

Corr depth outer 11 7,2 9,7

Corr depth inner 12 5,2

Corr depth outer 12 9,7 By careful choice of the focal points of a waveguide lens antenna and the phase centres of a matching transmitting/receiving horn the efficiency of the system can be greatly improved to allow transmission and reception over a range of frequencies from 10 to 14GHz.

With the parameters of the horn chosen as describe above a very high efficiency of horn is achieved. For satellite communication a separation of 2 degrees between satellites can be possible where two horns are used. Also a signal at an angle of 20 degrees to an axis of the horn and lens can be used whilst still receiving a sufficiently strong signal .

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A transmitter/receiver horn adapted for use with a waveguide lens antenna comprises a horn section having a plurality of corrugated sections therein, wherein dimensions of the horn section and corrugated sections are chosen so that phase centres for a plurality of frequencies substantially coincide with focal points of a waveguide lens antenna for the same plurality of frequencies.

2. The transmitter/receiver horn of claim 1, which has a value of Δ greater than substantially 0.7, where

3. The transmitter/receiver horn of claim 1 or claim 2, which has substantially infinite longitudinal impedance.

4. A transmitter/receiver horn adapted for use with a waveguide lens antenna, the horn comprising a horn section having a plurality of corrugated sections therein, wherein the horn has a value of Δ that is at least substantially 0.7, where

_{Δ =} A_tan^L ₌ A_sin ø tan ^.

/L₀ 2 /L₀ ° 2 where a is the aperture radius and R the distance between the apex and a spherical wave front at the aperture. θ₀ is the semi flare angle of the horn.

5. An assembly comprising a transmitter/receiver horn and a waveguide lens antenna, wherein the horn is constructed so that phase centres for a plurality of frequencies substantially coincide with focal points of the waveguide lens antenna for the same plurality of frequencies.

6. The assembly of claim 5, in which the horn comprises corrugations, the dimensions and/or number of which, together with dimensions of a horn section and/or a waveguide section of the horn are chosen to specify the locations of the phase centres.

7. The assembly of claim 6, in which the dimensions include, aperture diameter, throat diameter, horn length, waveguide length, throat length and/or semi-flare angle.

8. The assembly of claim 7, in which the semi-flare angle is chosen so that a solid angle of the horn section substantially intersects an outer perimeter of the waveguide antenna for a chosen separation of the horn and the waveguide antenna.