GB2303489A - Antenna circuit - Google Patents
Antenna circuit Download PDFInfo
- Publication number
- GB2303489A GB2303489A GB9514672A GB9514672A GB2303489A GB 2303489 A GB2303489 A GB 2303489A GB 9514672 A GB9514672 A GB 9514672A GB 9514672 A GB9514672 A GB 9514672A GB 2303489 A GB2303489 A GB 2303489A
- Authority
- GB
- United Kingdom
- Prior art keywords
- antenna circuit
- circuit according
- loop
- antenna
- emitter
- 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.)
- Withdrawn
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q7/00—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
- H01Q7/005—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop with variable reactance for tuning the antenna
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- Details Of Aerials (AREA)
- Support Of Aerials (AREA)
Description
ANTENNA CIRCUIT
Field of the Invention
The present invention relates to antennae circuits.
Background to the Invention
Relatively low power (typically less than 200 mW) antennae for ultra high frequency ("UHF") or very high frequency ("VHF") transmissions are known. In practice, however, it has been found that there are severe practical limitations to their use. A limitation that has been encountered by the inventor of the present invention is that the effective transmission distance of such antennae is very small when they are substantially enclosed within a conductive body, such as a metal box.
Embodiments of the present invention aim to obviate or overcome disadvantages encountered with the prior art, whether referred to herein or otherwise.
Summary of the Invention
According to the present invention, in a first aspect, there is provided an antenna circuit comprising an input feeder from which a feeder signal can be supplied to the circuit, a primary antenna loop and means to electrically couple the primary antenna loop to an emitter.
Suitably, the primary antenna loop comprises a loop antenna substantially resonant at the frequency of the input signal. Preferably, the resonance remains independent of the emitter.
Suitably, the primary antenna loop is a physically open loop. Suitably, the ends of the open loop comprise a capacitive element, which capacitive element may comprise a tuning termination whereby the loop is tuned to the wavelength of the input signal. Preferably, the capacitive element has a capacitance of about 3.3 picoFarads. Suitably, the capacitive tuning element comprises two generally opposed feet.
Suitably, the input feeder of the primary antenna loop comprises two arms which join the loop at points along a side of the loop or at an end thereof. Suitably, a length of the arm of an input feeder is approximately in accordance with the equation:
Lf = 0.2L
where Lf = a length of the input feeder arm, and
L = the length of a long side of the loop.
Suitably, the loop comprises at least one and preferably two long sides, and at least one and preferably two shorter side strips.
Suitably, a long side of the loop has a length L.
Suitably, a long side of the loop is connected to the coupling means.
Suitably, a side strip has a length of approximately 0.2L.
Suitably, the length of the feed line is approximately 0.2L.
Suitably, the feed line joins a long side of the loop approximately 0.2L from one end of a long side of the loop.
Suitably, a feeder input joins a long side of the loop approximately 0.2L from one end of a long side of the loop.
Suitably, the length (L) of a long side of the loop approximately satisfies the equation:
1.4L=R
4
where n is an integer, and X is the wavelength of the input signal.
Suitably, the entire loop approximately satisfies the above equation.
Preferably, n = 1.
Preferably, the lengths and equations are substantially as set out above or substantially satisfied.
Suitably, the two long sides are of substantially equal length. Suitably, the two short strips are of substantially equal lengths. Suitably, the outline of the loop is generally rectangular.
Suitably, the primary antenna loop is coupled to the emitter by a capacitive coupling. Suitably, the emitter is connected to the primary antenna by a feed line, which feed line is preferably of a reactance substantially equal to that of the feed line. Suitably, the feed line has a length of substantially m(X/2), where X is the wavelength of the input signal and m is an integer.
Suitably, the emitter comprises a metallic body.
Suitably, the emitter comprises a metallic casing.
Suitably, the circuit is adapted for an input signal of less than 200mW.
Suitably, the circuit is mounted on a printed circuit board ("pcb"). As an alternative for the tuning element, at least one track may be laid on the opposite side of the pcb. The at least one track may comprise an antenna circuit, which may be as described herein.
Suitably, the corners of the primary loop antenna are non-perpendicular. They may be rounded or at about 450.
Suitably, the corners have a length of about 0.04L.
Suitably, the circuit is partly enclosed by a conductive body. Suitably, the circuit is substantially enclosed by a conductive body. Suitably the conductive body comprises the emitter. Suitably, the conductive body is metallic.
According to the present invention in a second aspect, there is provided a printed circuit board carrying an antenna circuit according to the first aspect of the present invention.
According to the present invention in a third aspect, there is provided an antenna system comprising a signal generator, an antenna circuit and an emitter, in which the antenna circuit accords to the first aspect of the present invention.
Brief Description of the Drawings
The present invention will now be described, by way of example only, with reference to the drawings that follow; in which:
Figure 1 is a functional block diagram showing elements of an apparatus incorporating a circuit of the present invention
Figure 2 is a schematic line diagram of a circuit according to the present invention.
Description of the Preferred kmhodiments Referring to Figure 1 of the drawings that follow, there is shown, functionally, an antenna system comprising a signal generator 2 the output of which is connected to the input of an antenna circuit 4, the output of which is connected to the input of an emitter 6 comprising a metallic body.
Referring to Figure 2 of the drawings that follow, the antenna circuit 4 is shown in more detail.
In Figure 2, the antenna circuit 4 can been seen to comprise a feeder having two arms 8, 10 extending to a loop 12. The loop 12 is not physically closed and terminates in a capacitive tuning element 14. From the side of the loop 12 opposite the feeder arms 8, 10 extends a feed line 16 which terminates in a capacitive coupling element 18. The antenna circuit 4 is mounted on a pcb shown generally by dashed lines 20.
The dimensions, and in particular the proportions, of the antenna circuit 4 are important to maintaining high performance of the circuit. These dimensions are shown in
Figure 2, based on a basic length unit L. To maintain best performance of the system it has been found that the conditions set out below in equation (1) should be satisfied: 1.4L=nA
4 Where: L is the length unit referred to above
n is an integer less than or equal to 4
X is the wavelength of the input signal
In Figure 2, n = 1.
The antenna circuit 4 in Figure 2 has a long side 22 of length L from which the feed line 16 extends for a length of 0.2L to the capacitive coupling element 18. The feed line 16 is spaced a length 0.2L from one end of the long side 22.
The 0.8L length of the long side 22 from feed line 16 turns through 900, via a 450 angled section 24, to a first side strip 26 of 0.2L length . First side strip 26 turns through 900, via a 450 section 28, to a second long side 30 of length L, interrupted 0.2L along from first side strip 26 by a first input feeder line 32, via 450 sections 34, 36. The remainder of second long side 30 is 0.8L long, terminating at second side strip 38 which, is 0.2L long. A distance of 0.04L from the feeder input side of second side strip 38 is a termination of the loop in two parallel feet 40 forming a 3.3pF capacitive tuning element 14.
The length X of the feeder line 32 substantially parallel to long side 30 is adjusted to provide a 50 Ohm impedance and is thus variable. It is dependent upon the feeder length and the overall wavelength of the antenna system.
Maintaining the length of long side 22 which is connected to feeder line 32 has been found to be significant. The length L should be such that the equation L = m (X/2) is satisfied where X is the wavelength of the input signal and m is an integer.
A second feeder input line 42 is connected to the circuit at the junction of the second long side 30 and second side strip 38. The second feeder input line 42 includes a strip 44 substantially parallel to the long side 30 which strip is 0.2L long.
Other dimensions, not given, have been found to be of less importance and can be varied to maximise performance.
Typical lengths for a 418MHz signal are 2.5mm for the lengths indicated with reference letter "At'.
The two long sides 22, 30 and side strips 26, 38 form the antenna loop. The loop 22, 26, 30, 38 is generally rectangular in outline.
A discussion of the operation of the circuit follows.
The primary antenna circuit 4 is essentially a closed loop system with a near centre feed and capacitive ground reference point at a specific node junction along its dipole conductor.
Each branch from the antenna loop 22, 26, 30, 38 acts as a resonator, resonant at specific frequencies or at specific decimals of the fundamental input signal frequency. The antenna circuit as a whole is resonant because of its proportions relative to the input signal wavelength, and appears to remain so independent of the presence or properties of the emitter.
The system can be regarded as a loop system acting as a magnetic dipole for transmission purposes. By connecting the circuit to a metal body emitter, it effectively adds windings to the loop thus improving the impedance of the system. In most other antenna designs the effect on impedance is to the contrary.
The system is most suitable for UHF or VHF transmissions at low power, typically less than 200mW. The antenna system described above has been tested within a sealed steel box to which the capacitive coupling element 18 has been connected for capacitive coupling thereto.
In experiments it has been found that the antenna loop has a directivity of 3/2 and a beam width of 900.
By capacitively coupling the circuit 4 to the secondary emitter 6 (the sealed metal box), the gain is substantially reduced, but effective transmission of the input signal is achieved without overloading the circuit.
It is in such location, partly or substantially enclosed by a conductive body, that the circuit described herein finds particular advantage. In that case it can use the body as the emitter and because of the configuration of the circuit, does not lose resonance as would normally be expected. Some applications, therefore, include the use of the antenna circuit coupled to a vehicle wheel or a cash till.
By way of example, with the signal generator 2 and circuit 4 in a 1" wall thickness enclosed steel box comprising the emitter 6, using a RadioMetrix 418MHz signal and a 1S wavelength whip receiving antenna a satisfactory signal is received up to 50 metres away.
This performance substantially exceeds that of other antenna circuits tested in this configuration which were effective only up to a few centimetres.
The performance of the system has been found to be substantially independent of the size and shape of the emitter 6.
In practice it has been found that at high frequencies the length of the feed line 16 to the emitter becomes crucial to ensuring transmission of the signal from the antenna. The important dimension is that the feed line 16 has a length of m(X/2), where X is the wavelength of the input signal and m is an integer. This ensures that at the junction of the feed line 16 and the emitter 6 is a node of the signal.
As an alternative to the tuning capacitor 14, the antenna circuit can be replicated on the other side of the pcb as a second antenna circuit (not shown) and connected to the first antenna circuit at the same points as feet 40. The capacitance of element 14 is still desired to be 3.3pF, and this can be achieved by offsetting the second antenna circuit relative to the first antenna circuit to increase the pcb thickness therebetween.
As another alternative to the tuning capacitor 14, an antenna tuning unit (not shown) can be attached to the feeder arms 8, 10 in which case the element 14 is instead wired through (short circuit) to form a closed loop.
The capacitive tuning element 14 described above in relation to Figure 2 is, however, preferred at this stage.
The reader's 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 (42)
1. An antenna circuit comprising an input feeder from which a feeder signal can be supplied to the circuit, a primary antenna loop and means to electrically couple the primary antenna loop to an emitter.
2. An antenna circuit according to Claim 1, in which the primary antenna loop comprises a loop antenna substantially resonant at the frequency of the input signal.
3. An antenna circuit according to Claim 2, in which the resonance is independent of the emitter.
4. An antenna circuit according to any preceding claim, in which the primary antenna loop is a physically open loop.
5. An antenna circuit according to Claim 4, in which the ends of the open loop comprise a capacitive element.
6. An antenna circuit according to Claim 5 in which the capacitive element comprises a tuning termination whereby the loop is tuned to the wavelength of the input signal.
7. An antenna circuit according to Claim 5 or Claim 6, in which the capacitive element has a capacitance of about 3.3 picoFarads.
8. An antenna circuit according to any one of Claims 5 to 7, in which the capacitive tuning element comprises two generally opposed feet.
9. An antenna circuit according to any preceding claim, in which the input feeder of the primary antenna loop comprises two arms which join the loop at points along a side of the loop or at an end thereof.
10. An antenna circuit according to Claim 9, in which a length of the arm of an input feeder is approximately in accordance with the equation:
Lf = 0.2L where Lf = a length of the input feeder arm, and
L = the length of a long side of the loop.
11. An antenna circuit according to Claim 9 or Claim 10, in which the loop comprises at least one and preferably two long sides, and at least one and preferably two shorter side strips.
12. An antenna circuit according to Claim 10 or Claim 11, in which a long side of the loop is connected to the coupling means.
13. An antenna circuit according to any one of Claims 10 to 12, in which a side strip has a length of approximately 0.2L.
14. An antenna circuit according to any one of Claims 10 to 13, in which the length of the feed line is approximately 0.2L.
15. An antenna circuit according to any one of Claims 10 to 14, in which the feed line joins a long side of the loop approximately 0.2L from one end of a long side of the loop.
16. An antenna circuit according to any one of Claims 10 to 15, in which a feeder input joins a long side of the loop approximately 0.2L from one end of a long side of the loop.
17. An antenna circuit according to any one of Claims 9 to 16, in which the length (L) of a long side of the loop approximately satisfies the equation: 1.
4 where n is an integer, and
X is the wavelength of the input signal.
18. An antenna circuit according to Claim 17, in which the entire loop approximately satisfies the equation of
Claim 17.
19. An antenna circuit according to Claim 17 or Claim 18, in which n = 1.
20. An antenna circuit according to any one of Claims 10 to 19, in which the two long sides are of substantially equal length.
21. An antenna circuit according to any one of Claims 10 to 20, in which the two short strips are of substantially equal lengths.
22. An antenna circuit according to any preceding claim, in which the outline of the loop is generally rectangular.
23. An antenna circuit according to any preceding claim, in which the primary antenna loop is coupled to the emitter by a capacitive coupling.
24. An antenna circuit according to any preceding claim, in which the emitter is connected to the primary antenna by a feed line.
25. An antenna circuit according to Claim 24, in which the feed line is of a reactance substantially equal to that of the feed line.
26. An antenna circuit according to Claim 24 or Claim 24, in which the feed line has a length of substantially m(X/2), where X is the wavelength of the input signal and m is an integer.
27. An antenna circuit according to any preceding claim, in which the emitter comprises a metallic body.
28. An antenna circuit according to Claim 27, in which the emitter comprises a metallic casing.
29. An antenna circuit according to any preceding claim, in which the circuit is adapted for an input signal of less than 200mW.
30. An antenna circuit according to any preceding claim, in which the circuit is mounted on a printed circuit board ("pcb").
31. An antenna circuit according to any preceding claim, in which the corners of the primary loop antenna are nonperpendicular.
32. An antenna circuit according to Claim 31, in which the corners are rounded or at about 450.
33. An antenna circuit according to Claim 31 or Claim 32, in which the corners have a length of about 0.04L.
34. An antenna circuit according to any preceding claim, in which the circuit is partly enclosed by a conductive body.
35. An antenna circuit according to Claim 34, in which the circuit is substantially enclosed by a conductive body.
36. An antenna circuit according to Claim 34 or Claim 35, in which the conductive body comprises the emitter.
37. An antenna circuit according to Claim 36, in which the conductive body is metallic.
38. A printed circuit board comprising an antenna circuit according to any preceding claim.
39. An antenna system comprising a signal generator, an antenna circuit and an emitter, in which the antenna circuit is according to any one of Claims 1 to 37.
40. An antenna circuit substantially as described herein, with reference to and as shown in Figures 1 and 2 of the accompany drawings.
41. A printed circuit board comprising an antenna circuit according to Claim 40.
42. An antenna system comprising a signal generator, an antenna circuit and an emitter, which antenna circuit is according to Claim 40.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9514672A GB2303489A (en) | 1995-07-18 | 1995-07-18 | Antenna circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9514672A GB2303489A (en) | 1995-07-18 | 1995-07-18 | Antenna circuit |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9514672D0 GB9514672D0 (en) | 1995-09-13 |
| GB2303489A true GB2303489A (en) | 1997-02-19 |
Family
ID=10777843
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9514672A Withdrawn GB2303489A (en) | 1995-07-18 | 1995-07-18 | Antenna circuit |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2303489A (en) |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0360594A2 (en) * | 1988-09-21 | 1990-03-28 | Harada Industry Co., Ltd. | Automobile loop antenna |
| US5257033A (en) * | 1991-04-16 | 1993-10-26 | Design Tech International, Inc. | Transmitter with a reduction of power of signals transmitted at harmonics |
-
1995
- 1995-07-18 GB GB9514672A patent/GB2303489A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0360594A2 (en) * | 1988-09-21 | 1990-03-28 | Harada Industry Co., Ltd. | Automobile loop antenna |
| US5257033A (en) * | 1991-04-16 | 1993-10-26 | Design Tech International, Inc. | Transmitter with a reduction of power of signals transmitted at harmonics |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9514672D0 (en) | 1995-09-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |