GB2132022A - Radio frequency antenna and radio direction finding apparatus incorporating such antenna - Google Patents
Radio frequency antenna and radio direction finding apparatus incorporating such antenna Download PDFInfo
- Publication number
- GB2132022A GB2132022A GB08215098A GB8215098A GB2132022A GB 2132022 A GB2132022 A GB 2132022A GB 08215098 A GB08215098 A GB 08215098A GB 8215098 A GB8215098 A GB 8215098A GB 2132022 A GB2132022 A GB 2132022A
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- GB
- United Kingdom
- Prior art keywords
- antenna
- spiral
- radio
- frequency
- signals
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000005855 radiation Effects 0.000 claims abstract description 15
- 230000001419 dependent effect Effects 0.000 claims description 8
- 230000005684 electric field Effects 0.000 claims description 4
- 238000010586 diagram Methods 0.000 description 3
- 238000010276 construction Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 208000004350 Strabismus Diseases 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
- H01Q13/02—Waveguide horns
- H01Q13/04—Biconical horns
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
- H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
- H01Q19/102—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces wherein the surfaces are of convex toroïdal shape
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
- H01Q9/04—Resonant antennas
- H01Q9/16—Resonant antennas with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole
- H01Q9/26—Resonant antennas with feed intermediate between the extremities of the antenna, e.g. centre-fed dipole with folded element or elements, the folded parts being spaced apart a small fraction of operating wavelength
- H01Q9/27—Spiral antennas
Landscapes
- Variable-Direction Aerials And Aerial Arrays (AREA)
Abstract
A conical reflector 13 is located centrally of an Archimedian two-wire spiral antenna 10 to reflect axial radiation from the spiral 11 evenly in all directions in the plane of the spiral. The phase of a signal transmitted or received by the antenna is then dependant on the angle in the plane of the spiral. When used with an omnidirectional (non-phase sensitive) antenna, phase comparison of a signal received by the two antennae can measure the direction of the remote transmitter. <IMAGE>
Description
SPECIFICATION
Radio frequency antenna and radio direction finding
apparatus incorporating such antenna
The present invention relates to a radio frequency
antenna and to a radio direction finding apparatus
incorporating such an antenna.
The use of Archimedian two-wire spiral antennas
has been known for some time and a summary of
the theory of operation of such antennas is given in
the paper by Kaiser entitled "Archimedian Two-Wire
Spiral Antennas" in IRE Transactions - Antennas and
Propagation Vol.AP8 No.3 May 1960, Pages 312
323". Such a spiral antenna operating in "first
mode" provides a radiation pattern in the form of a
broad symmetrical beam centred on the axis of the
spiral. Radiation from the spiral along the axis is
circularly polarised. It is a known feature of such a
spiral antenna in first mode that the phase of the
radiation pattern off axis is dependent in the angular
position relative to the spiral. In fact, the phase of the
radiation field off the axis varies by one electrical
degree for each degree of angular rotation of the
spiral antenna about its axis.
According to the present invention, a radio fre
quency antenna comprises an Archimedian two-wire
spiral and a conical reflector located centrally of the
spiral to reflect axial radiation from the spiral evenly in all directions in the plane of the spiral. This
construction produces an antenna which, when
arranged with the spiral axis vertical, has an -omni- directional radiation pattern. However, the phase
characteristics ofthe spiral radiation field are pre
served so that there is a direct relationship between
the bearing from the antenna and the phase of the
signal radiated by the antenna. Conversely, when
the antenna is used for reception, the phase of a
received signal is directly dependent on the bearing
ofthesignal.
An antenna ofthe form described above can
provide a signal having a phase indicative of the
bearing, for signals received substantially parallel to
the plane ofthe spiral. In this horizontal plane the
antenna is responsive primarily to horizontally pola
rised signals and any vertical or cross polarised
component is received at approximately -8dB.
However, at increasing angles of elevation relative to
the plane of the spiral, the antenna becomes increas
ingly responsive to vertically polarised components.
It has been found desirable, therefore, to reduce
response of the antenna to vertically polarised
signals. Thus, preferably the antenna includes resis
tive elements in planes parallel to the axis of the
spiral to absorb electric field components in said
axial planes. Such resistive elements can conve
niently be located between the plane of the spiral
and the reflecting surface of the cone as radial
extending vanes. This form of antenna is then
responsive primarily to horizontally polarised sig
nals.
A further embodiment of the antenna may include
a further conical reflector located centrally on the
opposite side of the spiral from the first mentioned
reflector, to reflect radiation from said opposite side of the spiral. With this arrangement the sensitivity of the antenna can be increased. The horizontally polarised components from the upper and lower conical reflectors enforce each other.
A particular use of the above-described antenna envisaged by the present invention is in radio direction finding apparatus with the spiral antenna having its axis substantially vertical, and the apparatus further including an omnidirectional antenna responsive to radio frequencies in the band exciting the first mode of the spiral and located on the axis of the spiral antenna, and a receiver incorporating a phase discriminator, responsive to radio frequency signals in said band received at a common frequency by both said spiral antenna and said omnidirectional antenna to detect the phase difference in said signals received by respective said antennas, thereby to provide an indication of the bearing of the source of said signals.The reference to "omnidirectional antenna" in the above is to be taken throughout herein as meaning an antenna with a constant response in azimuth with no phase variation. Thus, the omnidirectional antenna serves to provide a reference signal with which the same signal received by the spiral antenna can be compared in phase to provide an indication of the bearing of the source.
One problem with such a radio direction finding apparatus is that the datum phase for the spiral antenna is at a bearing dependent on the received frequency. Thus, the bearing of a signal received by the spiral antenna in phase with the reference antenna varies at different frequencies. However, for the arrangement described, this frequency dependence is predictable for a particular construction of spiral and can be determined theoretically or empirically so that a correction can be applied. In a preferred form, the receiver of the radio direction finding apparatus includes instantaneous frequency measuring means providing a signal indicative of said common frequency of the radio frequency signals and means responsive to said frequency indicative signal to provide a frequency dependent correction to the bearing indication.The means responsive to said frequency indicative signal is arranged in accordance with the predetermined frequency dependent characteristic of the spiral antenna to provide a proper correction to the bearing indication.
Another problem with the radio direction finding apparatus described above is that the vertical spacing between the apertures ofthe spiral antenna and the omnidirectional antenna results in a phase difference for signals entering these apertures at elevation angles greater than zero. Thus, the apparatus described so far can be accurate only for signals received at near zero elevation.
The effect of this elevation error can be minimised by ensuring said omnidirectional antenna is located as close as possible to the spiral antenna.
However, in a preferred embodiment, the apparatus includes a second said omnidirectional antenna located on the axis of the spiral antenna, the axial distance between the centres of the vertical apertures of the spiral antenna and said first mentioned omnidirectional antenna being predetermined and the corresponding said distance for said two omnidirectional antennas being also predetermined, and the receiver further incorporating a second phase discriminator, responsive to signals at said common frequency received by said two omnidirectional antennas to provide a signal indicative of any phase difference between the signals, and means responsive to said phase difference indicative signal to provide an elevation correction to the bearing indication.With this arrangement the phase difference between the signals received at the two omnidirectional antennas can be used in effect to calculate the angle of elevation of the received signal and thereby used to apply a correction to the phase difference determined between the spiral antenna and said first mentioned omnidirectional antenna.
Examples of the present invention will now be described with reference to the accompanying drawings in which:
Figure 1 is a perspective view of one form of antenna embodying the present invention;
Figure 2 is a perspective view of a further embodiment of antenna;
Figure 3 is a simple block schematic diagram illustrating an example of radio direction finding apparatus incorporating the antenna of Figure 1 or
Figure 2; and
Figure 4 is a further embodiment of radio direction finding apparatus incorporating elevation correction.
In Figure 1, a spiral antenna 10 is formed with a two-wire Archimedian spiral 11 printed on an insulating substrate. The two wires of the spiral are fed at the centre of the spiral from a co-axial feed line 12 only the end stub of which is shown in the Figure.
The interconnection between the co-axial feed 12 and the wires ofthe spiral is via a balun arranged to ensure proper matching between the co-axial feed and the spiral and to convert the co-axial line feed to balanced antiphase signals for application to the wires of the spiral. The precise design of the balun used for this conversion is not important and it is well within the ability of one experienced in this art to design an appropriate form of balun. For example, a convenient design employs microwave printed circuit techniques.
In the above the spiral antenna and feed arrangement is described for the antenna in transmit mode, but it will be appreciated that the same arrangement is equally applicable for using the antenna for receiving.
An inverted metallic cone reflector 13 is located above and co-axial with the spiral 11. The angle of the cone is approximately 45" and is arranged to reflect radiation from the spiral which is parallel to the spiral axis outwards relative to the spiral axis equally in all directions as indicated by the broken line 14. It has been found that using a conical angle of exactly 45" in fact causes the antenna to have a slight upward squint, i.e. the centre of the radiation distribution in elevation is at a slight positive angle to the horizontal plane. This can readily be corrected by selecting for the cone an angle slightly greater than 45" and the correct angle can readily be found empirically.
The antenna shown in Figure 1 further includes a plurality of resistive elements of vanes 15. Each vane is a plate-like element arranged in an axial plane relative to the spiral 11 between the spiral and the reflecting surface of the cone 13. Sufficient elements are distributed evenly about the antenna as shown in
Figure 1 to ensure substantial absorption of the electric field components in the axial direction.
As has already been explained herein, the field emitted by the spiral 11 alone has a maximum on the axis of the spiral and is circularly polarised. The resistive elements 15 are arranged to ensure substantially only horizontally polarised radiation is emitted in all directions by the antenna with the reflecting cone. Conversely, the elements 15 render the antenna responsive as a receiver to horizontally polarised signals.
The arrangement described provides an omnidirectional antenna in which the bearing angle is directly related to the phase of the signal received by the antenna.
An alternative form of antenna is shown in Figure 2 which includes a further conical reflector 16 located on the opposite side of the spiral 11 from the first cone 13. The cone 16 is orientated the opposite way to the cone 13 so as to reflect outwardly the radiation from the opposite side of the spiral. Again resistive elements 17 are disposed in the same manner as resistive elements 15 to absorb axial components of electric field so that the field reflected by the cone 16 is also horizontally polarised and enforces the field 14 from the cone 13.
As explained previously, an application of the embodiments of spiral antenna described with reference to Figures 1 and 2 is in radio direction finding apparatus. Referring to Figure 3, a simple form of apparatus incorporating the spiral antenna shown in
Figure 1 or Figure 2 is illustrated in a block diagram.
The spiral antenna is indicated by the box 20 and is orientated with its axis 21 substantially vertical. A second omnidirectional antenna 22 is mounted adjacent the spiral antenna 20 on the axis 21 and as close as possible to the antenna 20. The omnidirectional antenna 22 is arranged to be equally responsive to signals from any direction and without any phase dependency.Signals received from the spiral antenna 20 and the omnidirectional antenna 22 are fed on lines 23 and 24 respectively to a phase discriminator 25 which detects the phase difference between signals received by the two antennas at a common frequency and produces an output signal on a line 26 representing the bearing of the received signal
The datum phase ofthe spiral antenna 20 is frequency dependent, that is to say the bearing for a received signal from the spiral antenna 20 which would be in phase with the corresponding signal from the reference antenna 22 is different at different frequencies for the signal. However, this frequency dependency is predictable for a particular design of spiral antenna. The received signal from the reference antenna 22 is also fed to an instantaneous frequency measuring device 27 which provides on a line 28 an immediate indication of the frequency of the received signal which is fed as a correction signal to the phase discriminator 25. The phase discriminator 25 is arranged to respond to this frequency correction on line 28 by appropriately correcting the bearing signal on line 26 to account for the frequency of the received signal.
Referring now to Figure 4, a further example of direction finding apparatus is illustrated in block diagram and corresponding components are given the same reference numbers as Figure 3.
As explained previously, the phase difference between the signal received at the spiral antenna 20 and the reference antenna 22 is dependent on the elevation relative to the horizontal plane of the source of the signal. It can be appreciated that for a finite vertical spacing a between the apertures of the spiral antenna 20 and the reference antenna 22, a received signal arrives at the apertures of the antennas at different phases for elevation angles greater than zero.
In the example of Figure 4, there is provided a further reference antenna 30 at a known vertical spacing b from the first reference antenna 22. The signals from the antennas 22 and 30 are both fed to a second phase discriminator 31 which provides on an output line 32 a signal representing any phase difference between the signals received at a common frequency by the two antennas 22 and 30. This phase difference is representative of the angle of elevation of the received signal and is supplied on line 32 to phase discriminator 25 as an elevation correction.In order to obtain an unambiguous elevation correction signal, it is important that the distance b be less than a predetermined distance corresponding to a phase difference of one wavelength between the signals received at the
reference antennas 22 and 30 at the highestfrequen- cies under consideration and the greatest angle of elevation.
In the example of Figure 4, the bearing signal on
line 26 is thus corrected both for frequency dependency and for elevation dependency.
A significant advantage of direction finding appar
atus embodying the present invention is that the
antenna arrangements of the apparatus may be
extremely compact so that the complete direction finding apparatus can be readily made as a hand
holdable device which can provide instantaneous
bearings of received signals in the microwave
region.
Although the above described example of the
invention has been concerned primarily with use of
the antenna for receiving in a radio direction finding
apparatus, the antenna may also form a component
in a transmitting system having a steerable beam in
the horizontal plane. By feeding a radio frequency
signal at the same frequency and a predetermined
phase difference to each of a spiral antenna and
reference antenna arranged co-axially, a transmitted
beam may be produced having a maximum power at
a corresponding predetermined bearing and a gen erallycardioid power distribution.
Claims (9)
1. A radio frequency antenna comprising an
Archimedian two-wire spiral, and a conical reflector located centrally of the spiral to reflect axial radiation from the spiral evenly in all directions in the plane of the spiral.
2. An antenna as claimed in Claim 1 and including resistive elements in planes parallel to the axis of the spiral to absorb electric field components in said axial planes.
3. An antenna as claimed in Claim 1 or Claim 2 and including a further conical reflector located centrally on the opposite side of the spiral from the first mentioned reflector, to reflect radiation from said opposite side of the spiral.
4. Radio direction finding apparatus including a radio frequency spiral antenna as claimed in any preceding claim and with its axis substantially vertical, an omnidirectional antenna responsive to radio frequencies in the band exciting the first mode of the spiral and located on the axis of the spiral antenna, and a receiver incorporating a phase discriminator, responsive to radio frequency signals in said band received at a common frequency by both said spiral antenna and said omnidirectional antenna to detect the phase difference in said signals received by respective said antennas, thereby to provide an indication of the bearing of the source of said signals.
5. Radio direction finding apparatus as claimed in Claim 4, wherein the receiver includes instantaneous frequency measuring means providing a signal indicative of said common frequency of the radio frequency signals and means responsive to said frequency indicative signal to provide a frequency dependent correction to the bearing indication.
6. Radio direction finding apparatus as claimed in either of Claims 4 and 5, wherein said omnidirectional antenna is located as close as possible to the spiral antenna.
7. Radio direction finding apparatus as claimed in any of Claims 4 to 6 and including a second said omnidirectional antenna located on the axis of the spiral antenna, the axial distance between the centres of the vertical apertures of the spiral antenna and said first mentioned omnidirectional antenna being predetermined and the corresponding said distance for said two omnidirectional antenna being also predetermined, and the receiver further incorporating a second phase discriminator, responsive to signals at said common frequency received by said two omnidirectional antennas to provide a signal indicative of any phase difference between the signals, and means responsive to said phase difference indicative signal to provide an elevation correction to the bearing indication.
8. A radio frequency antenna substantially as
hereinbefore described with reference to and as
illustrated in Figures 1 or 2 of the accompanying drawings.
9. Radio direction finding apparatus substantial
ly as hereinbefore described with reference to and as
illustrated in Figures 3 or 4 of the accompanying
drawings. ~~~~~~~~~~~~~~~~~~
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08215098A GB2132022B (en) | 1982-05-21 | 1982-05-21 | Radio frequency antenna and radio direction finding apparatus incorporating such antenna |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08215098A GB2132022B (en) | 1982-05-21 | 1982-05-21 | Radio frequency antenna and radio direction finding apparatus incorporating such antenna |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2132022A true GB2132022A (en) | 1984-06-27 |
| GB2132022B GB2132022B (en) | 1985-07-24 |
Family
ID=10530582
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB08215098A Expired GB2132022B (en) | 1982-05-21 | 1982-05-21 | Radio frequency antenna and radio direction finding apparatus incorporating such antenna |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2132022B (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2000059071A1 (en) * | 1999-03-31 | 2000-10-05 | The University Court Of The University Of St. Andrews | Antenna system |
| US20130249762A1 (en) * | 2010-10-01 | 2013-09-26 | Thales | Broadband antenna reflector for a circular-polarized planar wire antenna and method for producing said antenna reflector |
| US20140266956A1 (en) * | 2013-03-15 | 2014-09-18 | Wal-Mart Stores, Inc. | Wide angle planar antenna assembly |
| CN105932405A (en) * | 2016-06-21 | 2016-09-07 | 南京濠暻通讯科技有限公司 | Broadband miniature antenna for 5G mobile communication |
| GB2550693A (en) * | 2016-05-24 | 2017-11-29 | Wal Mart Stores Inc | Wide angle planar antenna assembly |
| US10181651B2 (en) | 2013-03-15 | 2019-01-15 | Walmart Apollo, Llc | Wide angle planar antenna assembly |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB677860A (en) * | 1949-11-19 | 1952-08-20 | Standard Telephones Cables Ltd | Antenna of small dimensions |
| GB869783A (en) * | 1959-04-15 | 1961-06-07 | Marconi Wireless Telegraph Co | Improvements in or relating to polarisation screens and filters for radio waves |
| GB1126670A (en) * | 1966-04-29 | 1968-09-11 | Rohde & Schwarz | Feed arrangement for ring-shaped antennae |
| GB1258282A (en) * | 1968-12-03 | 1971-12-30 |
-
1982
- 1982-05-21 GB GB08215098A patent/GB2132022B/en not_active Expired
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB677860A (en) * | 1949-11-19 | 1952-08-20 | Standard Telephones Cables Ltd | Antenna of small dimensions |
| GB869783A (en) * | 1959-04-15 | 1961-06-07 | Marconi Wireless Telegraph Co | Improvements in or relating to polarisation screens and filters for radio waves |
| GB1126670A (en) * | 1966-04-29 | 1968-09-11 | Rohde & Schwarz | Feed arrangement for ring-shaped antennae |
| GB1258282A (en) * | 1968-12-03 | 1971-12-30 |
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2000059071A1 (en) * | 1999-03-31 | 2000-10-05 | The University Court Of The University Of St. Andrews | Antenna system |
| US20130249762A1 (en) * | 2010-10-01 | 2013-09-26 | Thales | Broadband antenna reflector for a circular-polarized planar wire antenna and method for producing said antenna reflector |
| US9755317B2 (en) * | 2010-10-01 | 2017-09-05 | Thales | Broadband antenna reflector for a circular-polarized planar wire antenna and method for producing said antenna reflector |
| US20140266956A1 (en) * | 2013-03-15 | 2014-09-18 | Wal-Mart Stores, Inc. | Wide angle planar antenna assembly |
| US9515389B2 (en) * | 2013-03-15 | 2016-12-06 | Wal-Mart Stores, Inc. | Wide angle planar antenna assembly |
| GB2526484B (en) * | 2013-03-15 | 2018-10-10 | Walmart Apollo Llc | Wide angle planar antenna assembly |
| US10181651B2 (en) | 2013-03-15 | 2019-01-15 | Walmart Apollo, Llc | Wide angle planar antenna assembly |
| US10756439B2 (en) | 2013-03-15 | 2020-08-25 | Walmart Apollo, Llc | Wide angle planar antenna assembly |
| GB2550693A (en) * | 2016-05-24 | 2017-11-29 | Wal Mart Stores Inc | Wide angle planar antenna assembly |
| GB2550693B (en) * | 2016-05-24 | 2020-10-07 | Walmart Apollo Llc | Wide angle planar antenna assembly |
| CN105932405A (en) * | 2016-06-21 | 2016-09-07 | 南京濠暻通讯科技有限公司 | Broadband miniature antenna for 5G mobile communication |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2132022B (en) | 1985-07-24 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |