Patent Application
20170093039
The present invention relates to an antenna for use in a communication system, although not exclusively, to a parallel-plate antenna adapted to operates at two frequencies in a communication system.
In a radio signal communication system, information is transformed to radio signal for transmitting in form of an electromagnetic wave or radiation. These electromagnetic signals are further transmitted and/or received by suitable antennas.
In general, antennas are designed to work in particular frequency or frequency range. In some communication systems, the signal generators may generate electrical signals of multiple frequencies. Accordingly, multiple antennas operating in different operation frequencies or frequency ranges may be used to transmit and/or receive electromagnetic signals in different frequencies.
In accordance with a first aspect of the present invention, there is provided an antenna for use in a communication system comprising: a plurality of plates connected to a ground plane, wherein when the plurality of plates are excited by at least two electrical signals, the plurality of plates are arranged to radiate at least two electromagnetic signals each having an independent resonant frequency.
In an embodiment of the first aspect, each of the plurality of plates is parallel to each other.
In an embodiment of the first aspect, the plurality of plates includes a plurality of folded plates.
In an embodiment of the first aspect, each of the plurality of folded plates includes a plurality of plate portions, wherein each of the plurality of plate portions is parallel to each other.
In an embodiment of the first aspect, the plurality of folded plates are positioned on the ground plane in a back-to-back configuration.
In an embodiment of the first aspect, the plurality of plates includes a plurality of straight plates.
In an embodiment of the first aspect, the plurality of plates are positioned on the ground plane with a predetermined separation between each pair of the plurality of plates.
In an embodiment of the first aspect, a first resonant frequency of one of the at least two electromagnetic signals is determined by the predetermined separation.
In an embodiment of the first aspect, further comprising a probe feeder arranged to feed the plurality of plates.
In an embodiment of the first aspect, the probe feeder is in an L-shape and includes a vertical portion connected to a horizontal portion.
In an embodiment of the first aspect, the probe feeder is positioned between a pair of the plurality of plates.
In an embodiment of the first aspect, further comprising a half-ring sleeve coupled to the probe feeder.
In an embodiment of the first aspect, the half-ring sleeve is arranged to suppress a crosspolarized field within the plurality of plates.
In an embodiment of the first aspect, further comprising a plurality of ridges positioned at the sides of the plurality of plates.
In an embodiment of the first aspect, the plurality of ridges are arranged to suppress a side lobe of one of the at least two electromagnetic signals radiating from the Fabry-Perot resonator antenna.
In an embodiment of the first aspect, the combination of the plurality of plates, the ground plane and the probe feeder is arranged to operate as a Fabry-Perot resonator antenna.
In an embodiment of the first aspect, the Fabry-Perot resonator antenna is arranged to operate in a millimeter-wave frequency range.
In an embodiment of the first aspect, further comprising a strip feedline arranged to feed the plurality of plates.
In an embodiment of the first aspect, the strip feedline is in a hook-shape and includes a horizontal arm portion and an open stub portion.
In an embodiment of the first aspect, the strip feedline traverses across the thickness of at least two of the plurality of plates and a distance between the at least two of the plurality of plates.
In an embodiment of the first aspect, the strip feedline protrudes apertures on the plurality of plates.
In an embodiment of the first aspect, the combination of the plurality of plates, the ground plane and the strip feedline is arranged to operate as a waveguide resonator antenna.
In an embodiment of the first aspect, the waveguide resonator antenna is arranged to operate in a microwave frequency range.
In an embodiment of the first aspect, a second resonant frequency of one of the at least two electromagnetic signals is determined by a height of the plurality of the plates.
In an embodiment of the first aspect, the ground plane and the plurality of plates are monolithically integrated.
In an embodiment of the first aspect, the ground plane and the plurality of plates are fabricated from a unify block of metal.
In an embodiment of the first aspect, the unify block of metal includes aluminum.
Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:
The inventors have, through their own research, trials and experiments, devised that in designing a dual-frequency antenna, the lower and higher frequency parts may be individually designed and then combined together either horizontally or vertically. This approach is straightforward at the expense of increasing the overall antenna size. Alternatively, antenna may be designed to consist of a set of antenna plates which may operate with different resonant frequencies so as to minimize the size of the antenna.
With reference to
In this embodiment, the antenna 100 may operate as a Fabry-Perot resonator antenna (FRPA) and a waveguide resonator antenna (WRA), by receiving electrical signals via antenna ports 106, preferably via two separate ports 106 connected to the antenna 100. Preferably, the FPRA is arranged to operate in a millimeter-wave frequency range and the WRA is arranged to operate in a microwave frequency range, such that the antenna 100 may operate simultaneous at a millimeter-wave frequency and a microwave frequency.
With reference to
In one example embodiment, the plates 102 are made with metal, and the ground plane 104 and the plurality of plates 102 are monolithically integrated. For example, the ground plane 104 and the plurality of plates 102 are fabricated from unify block of metal such as aluminum. This may simplify the assembling of the antenna 100 and may minimize process variations which may lead to degradation or a shift in performance of the antenna 100. An aluminum block with a volume of LG×LG×HP may be used for the fabrication of the antenna 100. Alternatively, methods such as three-dimensional printing may be used to fabricate the integrated ground plane and the plates. Alternatively, the plates and the ground plane are separately fabricated and then assembled or coupled together (physically and/or electrically) by any suitable method such as welding, soldering, or combining the components using other attachment means.
Preferably, the plurality of plates 102 includes a plurality of folded plates 102. Referring to
In one example, all the plate portions include a width of WP. The first (grounded) plate portion 102A has a height of HP and the second plate portion 102B has a height of (HP−g) and is offset (horizontally) from the grounded plate portion 102A at a distance of L1. The folded plates 102 are positioned on the ground plane 104 in a back-to-back configuration opposite to each other, i.e. the first (grounded) plate portion 102A of a first folded plate 102 are facing the grounded plate portion 102A of a second folded plate 102 on the same ground plane 104, and the folded plates 102 are separated by a predetermined separation dF on the ground plane 104.
The predetermined separation dF between the parallel plates 102 determines the resonant frequency of the at least one of electromagnetic signals radiated by the antenna 100, preferably the of resonant frequency of the FPRA part of the antenna 100.
As mentioned above, the antenna 100 may operate as a FPRA. In this example, the antenna 100 comprises a probe feeder 110 such as an L-shape probe or an L-probe. The probe feeder 110 is arranged to feed the parallel plates 102. Preferably, the L-probe 110 includes a vertical portion (arm) 110V connected to a horizontal portion (arm) 110H with lengths of LV and LH respectively. The L-probe 110 is positioned between the grounded plates 102 and substantially at the centre of the two edges at two opposite sides 102S of the plates 102, and with the vertical portion 110V coupled to an antenna port 106 provided on the opposite surface 104B of the ground plane 104. In addition, the horizontal arm 110H is aligned with an axis substantially parallel to the parallel plates 102 on the ground plane 104.
A crosspolarized field is mainly caused by a current on the vertical arm of the L-probe 110, and it could be suppressed by introducing a current which is opposite to that on the L-probe 110. Preferably, the antenna 100 further comprises a half-ring sleeve 112 coupled to the probe feeder 110, wherein the inner diameter of the sleeve 112 is the same as that of the aperture 104C where the L-probe 110 protrudes.
Optionally, the antenna 100 further comprises a plurality of ridges 114 positioned at the sides 102S of the plurality of plates 102, and the ridges 114 are arranged to suppress a side lobe of the electromagnetic signals. For example, as shown in
The antenna 100 may also operate as a waveguide resonator antenna arranged to operate in a frequency range or resonant frequency which is independent to the operation frequency of the FPRA, such as a frequency in a microwave frequency range. With reference to
In the WRA structure, the plate 102 height HP was arbitrarily chosen as 0.163λ0, where λ0 is the resonance wavelength of the WRA. As such, the resonant frequency of one of the electromagnetic signals is determined by the height HP of the plates 102. In this example, the excitation hook-strip 108 protrudes from the ground plane 104 and wraps around the two folded plates 102. To let the hook-strip 108 pass through the horizontal parts of the folded plates 102, a rectangular hole 102C of size L1×W1 is fabricated at the top of each folded plate 102 as shown in
With reference to
In this embodiment, the ground plane 104, the feeders 108, 110 and the ports 106 are substantially the same as the previous embodiment as shown in
These embodiments are advantageous in that a new compact dual-frequency antenna 100 with a large frequency ratio is provided, which consists of a pair of folded parallel plates. It integrates the microwave parallel-plate waveguide resonator antenna 100 (WRA) with the millimeter-wave Fabry-Perot resonator antenna 100 (FPRA), with their resonant frequencies being independent of each other. Due to the folded structure, the profile of the proposed antenna 100 is lower than that of the conventional parallel plate waveguide resonator antenna 100. The WRA part is excited by a hook-shaped strip on its top, whereas the FPRA is excited by an L-probe with a half-ring sleeve. The WRA and the FPRA share the same ground plane.
The dual-frequency antenna 100 may be fabricated by using a pair of folded parallel plates, compactly integrating the microwave WRA with the millimeter-wave FPRA. Advantageously, the use of folded parallel plates decreases the profile of the proposed dual-frequency antenna 100.
The resonant frequency of the WRA and FPRA are determined by the plate height and the distance between of the folded parallel plates, respectively, which makes it very easy to obtain a large frequency ratio.
In an example embodiment as discussed earlier, the antenna 100 may be made from a single aluminum block. Therefore, no soldering is needed to connect the folded parallel plates and ground plane.
The WRA of the antenna 100 is simply fed by a hook-strip, which protrudes from the ground plane and wraps around the two folded plates. It is very easy to match the WRA by adjusting the lengths of the horizontal arm and open stub of the hook-strip.
The FPRA is excited by an L-probe with a half-ring sleeve. The half-ring sleeve can provide a vertical current which is opposite to that on the vertical arm of the L-probe. Due to the cancellation of the two vertical currents, the crosspolarized field of the FPRA can be desirably suppressed.
In one example embodiment, a dual-frequency antenna 100 that covers the 2.4-GHz and 24-GHz ISM bands was designed using ANSYS HFSS and fabricated. The detailed dimensions are given by LG=100 mm, HG=4 mm, WP=30 mm, LP=22.7 mm, HP=20 mm, DP=2 mm, LR=5 mm, WR=1 mm, L1=4 mm, W1=6.5 mm, LS=7.5 mm, WS=2.33 mm, DS=0.5 mm, LH=3 mm, LV=2.8 mm, D1=2 mm, Ø1=6 mm, dF=6.7 mm, t=0.5 mm, and g=1.6 mm.
The measurement was divided into the microwave and millimeter-wave parts. In the former, the S-parameters were measured with an Agilent E5071C network analyzer, whereas the radiation pattern, realized gain, and the antenna 100 efficiency were measured by a Satimo StarLab system. For the millimeter-wave part, the S-parameters were measured using an E8361A network analyzer, and the radiation pattern and realized gain were measured with an NSI measurement system. Since the antenna 100 efficiency cannot be directly measured by the NSI system, the antenna 100 efficiency of the FPRA is calculated from the ratio between its measured realized gain and directivity.
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It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
Any reference to prior art contained herein is not to be taken as an admission that the information is common general knowledge, unless otherwise indicated.
