FIELD OF INVENTION
[0001] The present invention relates to an antenna for transmitting and/or receiving signals
via electromagnetic radiation, e.g. radio waves. Specifically, the present invention
relates to an antenna incorporating an electrically conductive liquid suspended within
a cavity of a housing.
BACKGROUND
[0002] Antennas are an essential component of all radio equipment, for both transmission
and reception of radio signals. They provide the interface between received/transmitted
radio waves and electric signals sent to and received from radio tuning equipment.
A traditional antenna may comprise an array of solid electrical conductors, known
as elements, electrically connected to a receiver and/or a transmitter. The size and
shape of an antenna element affects the wavelength(s) at which it performs most efficiently,
as both a transmitter and a receiver. The frequency range (or "impedance bandwidth")
over which an antenna functions is therefore dependent upon, amongst other factors,
the design and form factor of the antenna and its element(s). In order to provide
the greatest range of bandwidth, adjustable antenna elements can be used, or multiple
fixed antenna elements may be used in parallel. However variable-length antenna elements
introduce additional moving parts which reduces the reliability of the antenna, and
multiple fixed antennas together (known as "antenna farms") take up a lot of space.
Previous attempts have been made to address this problem, for example in
WO2014042486 and
GB2435720, which both describe the use of an adjustable liquid antenna.
[0003] The present invention seeks to provide a more versatile antenna adapted to operate
over a broader range of frequencies.
SUMMARY OF INVENTION
[0004] According to a first aspect of the invention there is provided an antenna comprising
a housing having an internal cavity, and the cavity comprises an adjustable amount
of electrically conductive liquid. The antenna also comprises a twin-conductor feedline
connecting the antenna to a receiving and/or transmitting device. The conductive liquid
in the cavity of the housing acts as a first element and is adapted to receive/transmit
a signal from/to the first feedline conductor, and the second feedline conductor is
attached to electrical ground. This provides an antenna that can be easily adjusted
to cover a different range of radio frequencies.
[0005] Preferably, the antenna also comprises a second element which is separated from the
first element by an insulator. The second element may be a conductive ground plane
and connected to the second feedline conductor.
[0006] Preferably still, the insulator is a foam, providing a lightweight dielectric to
maintain electrical separation between the first and second elements.
[0007] In one example, the twin-conductor feedline is a coaxial cable which connects the
antenna to a receiving and/or transmitting device. Coaxial cables provide lower error
rates in data transmitted over the feedline, offering low transmission losses and
a well-defined characteristic impedance value. Preferably, the conductive liquid is
a liquid metal or liquid metal alloy. Preferably still, the conductive liquid suspended
in the internal cavity is Galinstan®, which is comparatively low toxicity, a liquid
at room temperature with reasonable viscosity, and has good 'wetting' and electrical
characteristics.
[0008] In another example, the antenna also comprises a pump, a battery to power the pump,
and a reservoir for storing conductive liquid. Preferably, the pump is adapted to
pump the conductive liquid into and out of the internal cavity within the first element.
This adjusts the size (and shape) of the conducting liquid element, and therefore
the frequency range over which the antenna can efficiently operate.
[0009] Preferably still, the housing comprises a vent to allow air (or whatever the surrounding
atmosphere is) to escape or enter the internal cavity as the conductive liquid is
pumped into or out of it.
[0010] In one example, the first element is planar, e.g. a patch antenna, and the cavity
has a circular cross-section tapered or concave downwards forming a shallow bowl or
cone. The low profile of the antenna means it can be easily incorporated into clothing
or portable wireless devices. Preferably, the first element is flexible, allowing
it to be incorporated into flexible materials, such as clothing.
[0011] In another example, the first element housing is conical. Preferably, the antenna
comprises a second element. The second element is a disc, narrower than the broadest
diameter of the first element cone.
[0012] In another example, the first element housing is the housing comprises two elongate
arms extending at an angle from each other in a "V" formation.
[0013] Preferably still, the housing comprises a metallic unit at the base of the below
the cavity in the housing element. The small metallic cone is connected to the first
feedline conductor. The antenna is adapted to receive and/or transmit the signal from
the first feedline conductor from/to the conductive liquid within the cavity of the
first element via capacitive coupling. This means that there is no need for the first
feedline conductor to come into direct electrical contact with the conductive liquid
within the cone (i.e. the first element). Without the need to pierce the first element
housing, there is less chance of a leak forming, and the antenna is more robust.
[0014] In one example, the first feedline conductor engages the conductive liquid directly
by passing through the first element into the cavity.
FIGURES
[0015] The present invention will now be described, by way of example only, with reference
to the accompanying drawings, in which:
Figures 1a and 1b show a schematic drawing, in perspective and a cross-sectional view
respectively, of an antenna according to a first example;
Figure 2 is a schematic drawing of an antenna according to a second example;
Figure 3 is a graph of the simulated reflection loss magnitude of an antenna according
to the second example;
Figure 4 is the estimated radiation pattern of an antenna according to the second
example;
Figure 5 is a schematic drawing of a pump and reservoir arrangement according to a
first example;
Figure 6 is a schematic drawing of an antenna according to a third example;
Figure 7 is a graph of the simulated reflection loss magnitude of an antenna according
to the third example;
Figure 8 is a perspective schematic view of an antenna according to a fourth example;
Figure 9 is a side-on schematic drawing of an antenna according to the fourth example;
Figure 10 is a graph of the simulated reflection loss magnitude of an antenna according
to the fourth example;
Figures 11a and 11b are simulated radiation patterns of an antenna according to the
fourth example;
Figure 12 is a schematic drawing of an antenna according to a fifth example;
Figure 13 is a graph of the simulated reflection loss magnitude of an antenna according
to the fifth example;
Figure 14 is a schematic drawing of an antenna according to a sixth example;
Figure 15 is a graph of the simulated reflection loss magnitude of an antenna according
to the sixth example; and
Figure 16 is a schematic drawing of an antenna according to a seventh example.
DESCRIPTION
PATCH ANTENNA
[0016] Figures 1a and 1b show an example antenna 100 according to the first embodiment of
the present invention. In this example, the antenna 100 is a monopole antenna comprising
a radiating element housing 110 having an internal cavity 115. The internal cavity
is substantially fully enclosed within the housing 110. In the example shown in Figures
1a and 1b, the housing 110 has a low profile, e.g. much wider and longer than it is
tall, known as a "patch antenna". Patch antennas are practical at microwave frequencies
and are widely used in portable wireless devices.
[0017] The antenna 100 also comprises a feedline 150 connecting the antenna 100 to a receiving
and/or transmitting device (not shown). The feedline 150 is a specialized transmission
cable (or other structure) designed to conduct an alternating current at radio frequencies.
The feedline comprises twin-conductor channels, example configurations of which include:
parallel line (ladder line); coaxial cable; stripline; and microstrip. In one example,
the feedline 150 is a coaxial RF cable with SMA connectors for ease of connection.
[0018] As can be seen in the cross-sectional view across line "A" in Figure 1b, in one example
the cavity 115 within the housing 110 has a circular cross-section across the horizontal
plane and is tapered (or concave) downwards towards the centre-bottom of the disc,
thus forming a shallow bowl or cone shaped cavity 115. The cavity 115 is adapted to
hold and retain an electrically conductive liquid (not shown) in electrical communication
with one channel of the twin-conductor feedline 150, so that the electrically conductive
liquid within the cavity 115 acts as a first element to transmit and/or receive radio
waves, converted from/to electrical signals transmitted along the feedline 150. The
other channel of the twin conductor feedline (the ground wire) is attached to a ground
plane. A ground plane is an electrically conductive surface, usually connected to
electrical ground, which is larger than the operating wavelength of the antenna, and
serves as a reflecting surface for radio waves transmitted from the first element.
[0019] The amount of conductive liquid in the cavity 115 may be adjusted so as to tune the
antenna 100 for use at different frequencies, and frequency ranges. The shallow bowl
or inverted cone shape of the cavity 115 means that the conductive liquid collects
in the centre of the cavity 115, therefore always forming a circular conductive element
no matter how much conductive liquid is present in the cavity 115. The shape of the
cavity is fashioned to suit the antenna's requirements. In some examples the cavity
may comprise channels, providing pathways for the conductive liquid. The channels
can be designed to shape the conductive liquid antenna as needed, e.g. providing radial
"arms".
[0020] Figure 2 shows a second example of the first embodiment of the invention, incorporating
a second electrically conductive element 120. The second element 120 is located below
the housing 110, and separated from the housing 110 by a distance "
d". The housing 110 and second element 120 are separated by a layer of insulating material
130, e.g. a dielectric material such as foam. The second element 120 may be formed
on top of, for example, a thin sheet of FR4 or similar material with a hole for the
feedline 150 to pass through to reach the housing 110 (and the first element formed
of a conductive liquid within the internal cavity 115). The second element 120 acts
as a ground plane to reflect the radio waves from the first element within the housing
110, and the conducting surface formed by the second element 120 is at least a quarter
of the wavelength (λ/4) of the targeted radio waves in diameter. In some examples,
the ground plane 120 has a discontinuous surface, e.g. several wires λ/4 long radiating
from the base of a quarter-wave whip antenna.
[0021] In this example, one channel of the twin-conductor feedline 150 is electrically connected
to the first element formed by the conductive liquid in the cavity 115 of the housing
110, and the second channel of the feedline 150 is in electrical contact with the
ground plane 120.
[0022] In a preferred example of the first embodiment, the antenna is formed with the following
dimensions:
- Second element 120 square length (e.g. FR4 length) - 22 cm;
- Separation distance "d" (e.g. foam thickness) - 15 mm;
- Second element 120 (e.g. FR4) thickness <1 mm;
- First element housing 110 (e.g. 3D printed upper section) thickness <5 mm; and
- Cavity (e.g. circular patch) diameter - 13 cm.
[0023] Figure 3 is a graph of the simulated reflection loss magnitude achieved over 0.4
- 1.6 GHz, and Figure 4 shows the resultant radiation pattern expressed as realised
gain at 1.2 GHz for an antenna as described by the above example and dimensions.
[0024] Figure 5 shows a schematic view of a pump and reservoir arrangement 200 which comprises
a pump 210, a battery 220 (or other self-contained power source) to power the pump
210, and a reservoir 230 to hold a supply of electrically conductive liquid 235. The
reservoir 230 of the pump and reservoir arrangement 200 is in fluidic communication
with the cavity 115 of the housing 110 via a channel 240. The pump and reservoir arrangement
200 is adapted to pump the conductive liquid 235 into and out of the cavity 115 of
the housing 110, and may be operated by control means (not shown). The control means
may be operated either wirelessly or by wired means, or may be fully autonomous (e.g.
pre-programmed).
[0025] The pump and reservoir arrangement 200 may be incorporated into the antenna 100 as
shown in the example in Figure 6, located on top of the housing 110 of the antenna
100. By adjusting the amount of conductive liquid in the cavity 115, the bandwidth
and operating frequency of the antenna 110 can be adjusted (or "tuned") as desired.
[0026] In order to allow the change in volume of the conductive liquid inside the cavity
115, the element housing 110 of the first element also comprises a vent 160 to allow
air (or other liquid/gas depending on the surrounding operating environment or atmosphere
of the antenna 100) to escape or enter the cavity 115 as required.
[0027] The pump and reservoir arrangement 200 may be spaced away from the housing 110 by
the incorporation of more foam. Any wires carrying power to the pump and reservoir
arrangement 200 from outside of the antenna 100 would likely impact the antenna's
performance. Therefore a self-contained battery-powered unit is preferable. To examine
the operational impact of a battery 220, conductive liquid reservoir 230 and pump
210 when placed above the antenna 100, a metallic box was simulated with dimensions
4cm x 4cm x 2cm (height), positioned 0.5cm above the antenna 100. The effect of the
pump and reservoir arrangement 200 located on top of the antenna 100 can be seen in
Figure 7, and the simulations suggest that positioning these items above the housing
110 have little impact on the antenna's 100 performance.
[0028] In one example (not shown) the housing 110 also comprises a small metallic body,
for example a disc, beneath the cavity 115 at the base of the housing 110, connected
to the first conductive channel of the twin-conductor feedline 150. The signal from
the first feedline 150 conductor is received and/or transmitted from/to the conductive
liquid within the housing 110 via capacitive coupling with the metallic disc. This
removes the need to have the conductive feedline 150 in direct electrical contact
with the conductive liquid within the cavity 115.
DISCONE ANTENNA
[0029] Figure 8 and Figure 9 show a second embodiment of the present invention, in perspective
and side-on respectively. In this embodiment, an antenna 300 is a discone antenna,
comprising a hollow conical housing 310 for a first antenna element. The conical walls
of the housing 310 have a width of "
h", and comprise an internal cavity 315 within the walls of the housing 310. The cavity
315 retains an electrically conductive liquid, and requires a relatively small amount
of conductive liquid compared to other types of antenna. The conductive liquid held
within the cavity 315 of the housing 310 acts a first element for the antenna 300.
The antenna 300 is able to maintain a good match over a broad band and provide a uniform
pattern with maximum gain near or on the horizon at all azimuth angles.
[0030] The amount of conductive liquid in the cavity 315 may be adjusted so as to tune the
antenna 300 for use at different frequencies or frequency ranges. The hollow conical
shape of the cavity 315 results in the conductive liquid collecting in the bottom
of the cavity 315, therefore forming a (sometimes truncated) conical conductive element
no matter how much conductive liquid is present in the cavity 315. The design has
advantages over the first embodiment (i.e. a patch antenna) in that it is inherently
wide-band (1 GHz to 6 GHz), and can be adapted to work over a range of frequencies
by partially filling the internal cavity 315 inside the cone 310.
[0031] The antenna 300 also incorporates a second element 320 acting as a ground plane.
In one example, the ground plane 320 is narrower than the broadest diameter of the
housing cone 310 (and therefore the broadest possible diameter of the first element
formed by the conductive liquid held in the cavity 315). The ground plane 320 and
the housing 310 are separated from each other by an insulating layer 330, e.g. a dielectric
material such as foam.
[0032] In the example shown, the housing 310 also comprises a small metallic cone 340 at
the base of the housing 310, connected to a first conductive channel of a twin-conductor
feedline 350. The signal from the first feedline 350 conductor is received and/or
transmitted from/to the conductive liquid within the housing 310 via capacitive coupling
with the metallic cone 340, which excites the surface currents in the conductive liquid
element. This removes the need to have the conductive feedline 350 in direct electrical
contact with the conductive liquid within the cavity 315, reducing the risk of a leak
of the conductive liquid. The second conductive channel of the feedline 350 is in
electrical contact with the ground plane 320, and the rest of the feedline 350 may
be fed through a small hole in the ground plane 320 and insulating layer 330 to reach
the metallic cone 340.
[0033] In a preferred example of the second embodiment, the antenna 300 has dimensions as
follows:
- Ground plane 320 diameter - 70 mm;
- Conical housing 110 height - 10 cm;
- Metallic cone 340 capacitive coupling element - 1 cm;
- Coupling gap - 1 mm; and
- Conical housing 110 upper diameter - 12 cm.
[0034] Figure 10 shows the simulated reflection loss magnitude achieved over 1-6 GHz for
an antenna 300 according to the above example and dimensions, wherein the discone
cavity 315 is fully filled with a conductive liquid.
[0035] Figures 11a and 11b show the radiation patterns (or "realised gain") at 2.4 GHz and
6 GHz, respectively, for the antenna 300 according to the present example described
above. In this simulation, the discone cavity 315 is filled with a conductive liquid,
and can be seen to produce a good uniform gain on or near the horizon.
[0036] In the example shown in Figure 12, a pump and reservoir arrangement 200, as previously
described, is located within the hollow space inside of the discone antenna 300. The
pump 210, reservoir 230, battery 220 and any control means are positioned in a region
of minimum radiated electric field so as to have minimal effect on the electrical
characteristics of the antenna 300. An electrically conductive liquid 235 maybe be
pumped in or out of the hollow cavity 315 of the housing 310 from/to the reservoir
235 as desired. Where the volume of conductive liquid is adjustable, the cavity 315
also comprises a vent 360 so as to allow air (or any other liquid/gas depending on
the surrounding operating environment or atmosphere of the antenna 300) in and out
of the cavity 315 as the volume of the conductive liquid inside the cavity 315 is
adjusted. In the example shown in Figure 12 the discone cavity 315 is full of the
conductive liquid.
[0037] A metallic cone, representative of the pump and reservoir arrangement 200 shown in
Figure 12, was simulated in the centre of the conical housing 310 and the resultant
reflection loss magnitude is shown in Figure 13. As can be seen, since there are no
radiating fields inside the conical housing 310 of the discone antenna 300, the impact
of metallic objects placed inside the cone 310 on the signal match and patterns is
negligible.
[0038] Figure 14 shows another example of the second embodiment of the antenna 300 wherein
the discone cavity 315 is only semi-filled with a conductive liquid. The resultant
match pattern is shown in Figure 15. Comparison with the match pattern shown in Figure
13 demonstrates that that match has changed, potentially degrading at lower frequencies
and shifting the operating impedance bandwidth to shorter wavelengths. In this way,
by careful design of the conductive liquid pathways (e.g. the internal shape of the
cavity), it may be possible to optimise the antenna 300 performance for certain bands
by partially filling the cavity 315, or to shift the overall operating band to different
frequencies by adjusting the overall extent of filling of the cavity 315.
V-SHAPED ANTENNA
[0039] In a further embodiment of the present invention, and as shown in Figure 16, an antenna
400 comprises a housing formed of two elongate arms 410 extending at an angle from
each other in a "
V" formation. The "
V" shaped arms 410 comprise an internal cavity 415 for retaining an electrically conductive
liquid. The conductive liquid is held within the cavity 415 of the arms 410, and acts
a first element for the antenna 400. The amount of conductive liquid in the cavity
415 may be adjusted using a pump and reservoir arrangement 200 as described before,
so as to tune the antenna 400 for use at different frequencies and frequency ranges.
The hollow "
V' shape of the cavity 415 results in the conductive liquid collecting in the bottom
of the arms 410, therefore forming a "
V" shaped conductive element no matter how much conductive liquid is present in the
cavity 415. The antenna 400 also incorporates a second element 420 acting as a ground
plane. In one example, the ground plane 420 is narrower than the broadest diameter
(i.e. the top) of the "
V" shaped arms 410. The ground plane 420 and the arms 410 are separated from each other
by an insulating layer 430, e.g. a dielectric foam. In the example shown, the arms
410 also comprise a small metallic cone 440 at the base of the arms 410, connected
to a first conductive channel of a twin-conductor feedline 450. The signal from the
first feedline 450 conductor is received/transmitted from/to the conductive liquid
within the cavity 415 via capacitive coupling with the metallic cone 440. This removes
the need to have the conductive feedline 450 in direct electrical contact with the
conductive liquid within the cavity 415. The second conductive channel of the feedline
450 is in electrical contact with the ground plane 420. The rest of the feedline 450
may be fed through a small hole in the ground plane 420 and insulating layer 430 to
reach the metallic cone 440.
[0040] In a preferred example of any of the above-described embodiments of the invention,
the electrically conductive liquid is a liquid metal, either alone or mixed with another
inert (i.e. dielectric) liquid. In another example, the liquid metal may be either
a pure metal or a metal alloy, and in a preferred example the liquid metal is a eutectic
alloy of Gallium, Indium and Tin, such as Galinstan®. Compared to other liquid metals,
such as Mercury, Galinstan® is comparatively non-toxic, and is a liquid at room temperature
with reasonable viscosity and good electrical characteristics. Galinstan® has a room
temperature conductivity of approximately 3.46×10
6 S/m, which is around 6% that of pure copper but is comparable to mild steel and somewhat
better than stainless steel. To all intents and purposes, at microwave frequencies,
it may be regarded as a "perfect electrical conductor" (PEC).
[0041] In one example, the hollow housing/arms 110;310;410 are 3D printed or PLA manufactured.
[0042] In another example, the antenna device 100;300;400 is tuned to microwave wavelengths,
i.e. between 300 MHz (100 cm) and 300 GHz (0.1 cm). In a further example, the conductive
liquid patch antenna 100 can be incorporated into a cavity within a flexible housing
110. This could provide a means to incorporate a microwave (or other frequency range)
antenna into fabrics, or other flexible materials. By adjusting the amount of conductive
liquid in the patch antenna cavity 115, the bandwidth and range of the antenna 100
can be adjusted as desired.
[0043] It is also anticipated that the novel and inventive features of the present invention
may be incorporated into a phase shift module, connecting and disconnecting different
lengths of transmission line, potentially at high microwave powers where conventional
semiconductor devices are unsuitable.
[0044] In alternative examples to those described above, the discone 300 and "
V" shaped 400 antennas are truncated, i.e. having a substantially flat base at the apex
where the conical walls 310 or arms 410 would meet. In another example, the cavity
315;415 may be formed by placing two cones, or
"V' shaped housing articles, one inside the other. In some examples of the present invention,
the cavity 315;415 formed within the housing may be shaped to guide the conductive
liquid into channels and pathways within the housing, forming differently shaped antennas.
The walls of the housing surrounding the internal cavity 315;415 may be separated
from each other by struts or other supports which can act to maintain the void, and/or
channel the conductive liquid within the void into pathways so as to tune the operating
frequency of the antenna.
[0045] In another example, the second element may also be formed by an electrically conductive
liquid within a cavity of a housing. In some examples, the amount of conductive liquid
within the second element cavity may also be adjusted as desired. As will be appreciated
by anyone skilled in the art, the discone housing may be moulded in other shapes,
for example, although not limited to: pyramidal, parabolic, cupola, etc. Furthermore,
the patch antenna housing may have non-circular horizontal cross-section, e.g. hexagonal.
1. An antenna, comprising:
a housing having an internal cavity, the cavity comprising an adjustable amount of
electrically conductive liquid; and
a twin-conductor feedline connecting the antenna to a receiving and/or transmitting
device,
wherein the conductive liquid in the cavity of the housing acts as a first element
and is adapted to receive/transmit a signal from/to the first feedline conductor,
and the second feedline conductor is attached to electrical ground.
2. The antenna according to claim 1, comprising:
a second element, separated from the housing by an insulator, wherein the second element
is a conductive ground plane and connected to the second feedline conductor.
3. The antenna according to any proceeding claim, wherein the insulator is a foam.
4. The antenna according to any proceeding claim, wherein the twin-conductor feedline
is a coaxial cable.
5. The antenna according to any proceeding claim, wherein the conductive liquid is a
metal or metal alloy.
6. The antenna according to claim 5, wherein the liquid metal is Galinstan®.
7. The antenna according to any proceeding claim, comprising:
a pump;
a battery to power the pump; and
a reservoir for the conductive liquid,
wherein the pump is adapted to pump the conductive liquid into and out of the cavity
within the housing.
8. The antenna according to claim 7, wherein the housing comprises a vent to allow the
surrounding atmosphere to escape or enter as the conductive liquid is pumped into
or out of the internal cavity.
9. The antenna according to any proceeding claim, wherein:
the housing is planer; and
the cavity has a circular cross-section tapered or concave downwards forming a shallow
bowl or cone.
10. The antenna according to claim 9, wherein the housing is flexible.
11. The antenna according to any of claims 1 to 8, wherein the housing is conical.
12. The antenna according to claim 11, wherein the second element is narrower than the
broadest diameter of the conical housing.
13. The antenna according to any of claims 1-8 wherein the housing comprises two elongate
arms extending at an angle from each other in a "V" formation.
14. The antenna according to any preceding claim, wherein the housing comprises a metallic
unit beneath the cavity and connected to the first feedline conductor, and wherein
the signal from the first feedline conductor is received/transmitted from/to the conductive
liquid within the housing via capacitive coupling.
15. The antenna according to any of claims 1 to 13 wherein the first feedline conductor
engages the conductive liquid within the cavity directly.