WO2018229324A1

WO2018229324A1 - An antenna arrangement

Info

Publication number: WO2018229324A1
Application number: PCT/FI2017/050454
Authority: WO
Inventors: Janne HEISKANEN; Kalle Olavi TUOMINEN; Olli Talvitie
Original assignee: Radientum Oy
Current assignee: Radientum Oy
Priority date: 2017-06-16
Filing date: 2017-06-16
Publication date: 2018-12-20
Anticipated expiration: 2019-12-16

Abstract

An antenna arrangement comprising at least one signal supplying unit (100); and a plurality of antenna units (110, 120, 130,...) connected in series to each other and a first antenna unit (110) being connected to the at least one signal supplying unit (100), each antenna unit comprising at least one antenna (112, 122, 132,...); and a power dividing component (114, 124, 134,...) connected to said at least one antenna and arranged to divide a minority of received signal power to said at least one antenna and a majority of the received signal power to a subsequent antenna unit in the series.

Description

AN ANTENNA ARRANGEMENT

Field of the invention

The invention relates to antennas, and especially to an antenna arrangement suitable for challenging RF environments. Background of the invention

Transferring RF signals in environments with obstacles is often challenging. The RF signal may be provided, for example, by a transmitter, a repeater or a WLAN base station locating in the challenging environment or a mobile base station locating outside of environment. For example, in facilities like ships, houses, tunnels, parking halls, factories etc. the RF signals are reduced quickly. Typically, there is an object or a structure blocking line-of-sight and preventing free transfer of RF signals, causing the RF signal to attenuate too much. The obstacle may be a wall, roof, base floor, a turn in a corridor or tunnel or some other object. For example, a wall can attenuate the signal by tens of decibels such that when the signal strength on the better side of a wall is adequate, it is not strong enough on the other side. Currently, the problem has been mainly addressed by two alternative solutions. Repeaters can be used on the signal path before the obstacle to receive, amplify and re-transmit the signal to the other side of the obstacle. Repeaters typically operate bi-directionally. From the repeater, the signal may be conveyed to an antenna or a splitter for splitting the signal to a plurality of antennas. However, the number of active components as well as cabling easily becomes significant and yet the number of antennas supplied by one repeater is rather limited.

An alternative method is to use the so-called leaky cable or a leaky feeder for supplying the signal from a base station or a repeater. A leaky cable is a coaxial cable having slots in its outer conductor to allow the radio signal to leak into or out of the cable along its entire length so as to able the cable to emit and receive radio waves, functioning as an extended antenna. While the leaky cable is fast to install and provides uniform field strength, the field strength radiated from each slot is typically very low and the antenna coverage is typically limited to a line-of-sight area, i.e. not extending beyond obstacles in the area. Brief summary of the invention

Now, an improved arrangement has been developed to reduce the above-mentioned problems. As an aspect of the invention, we present an antenna arrangement, which is characterized in what will be presented in the independent claims.

The dependent claims disclose advantageous embodiments of the invention.

According to an aspect of the invention, there is provided an antenna arrangement comprising: at least one signal supplying unit; and a plurality of antenna units connected in series to each other and a first antenna unit being connected to the at least one signal supplying unit, each antenna unit comprising at least one antenna; and a power dividing component connected to said at least one antenna and arranged to divide a minority of received signal power to said at least one antenna and a majority of the received signal power to a subsequent antenna unit in the series.

According to an embodiment, the power dividing component comprises control means for adjusting the ratio of the signal power supplied to said at least one antenna and the signal power supplied to said subsequent antenna unit.

According to an embodiment, the antenna arrangement further comprises an attenuation arranged or connected between the at least one antenna and the power dividing component for adjusting radiated power of the at least one antenna.

According to an embodiment, for each antenna unit, the ratio of the signal power supplied to said at least one antenna and the signal power supplied to said subsequent antenna unit is arranged to be adjusted such that radiated power level of each antenna unit in the series is substantially even.

According to an embodiment, said antenna units comprise a plurality of antennas operating in different frequency ranges.

According to an embodiment, the power dividing component is a directional coupler or a signal tapper. According to an embodiment, the signal supplying unit is a repeater or a wireless base station.

According to an embodiment, said series of the plurality of antenna unit is further connected to a second signal supplying unit.

According to an embodiment, said second signal supplying unit is connected to an opposite end of the series of the plurality of antenna unit. According to an embodiment, said second signal supplying unit is connected between two antenna units in the series of the plurality of antenna unit, and a second plurality of antenna units connected in series to each other is connected to said second signal supplying unit. These and other aspects, embodiments and advantages will be presented below in the detailed description of the invention.

Brief description of the drawings

The invention will now be described in more detail in connection with preferred embodiments with reference to the appended drawings, in which:

Fig. 1 shows an antenna arrangement according to an embodiment of the invention;

Fig. 2 shows an antenna arrangement according to another embodiment of the invention; Fig. 3 shows an antenna arrangement according to yet another embodiment of the invention; and

Fig. 4 shows an antenna arrangement according to yet further embodiment of the invention.

Detailed description of the embodiments

Figure 1 illustrates an improved antenna structure is now introduced, where the antenna arrangement comprises at least one signal supplying unit (100); and a plurality of antenna units (1 10, 120, 130, ... ) connected in series to each other and a first antenna unit (1 10) being connected to the at least one signal supplying unit (100), each antenna unit comprising

- at least one antenna (1 12, 122, 132,..) ; and

- a power dividing component (1 14, 124, 134, ...) connected to said at least one antenna and arranged to divide a minority of received signal power to said at least one antenna and a majority of the received signal power to a subsequent antenna unit in the series. Thus, the antenna arrangement comprises a plurality of, such as 2, 3, 4, 5, 6, 7, 8, 9, 10 or more, antenna units connected in series. In each antenna unit, possibly excluding the last antenna unit in the series, there is a power dividing component, which is arranged to receive, either from the signal supplying unit or from the previous antenna unit in the series, a transmitted signal having a certain signal power level. From the received signal power, the power dividing component is arranged to divide only a small portion to the one or more antennas of the antenna unit and allow a majority of the signal power to pass to the next antenna unit in series. Hence, the original signal power provided by the signal supplying unit is propagated to the plurality of antenna units in series, gradually decreasing as propagated from an antenna unit to the subsequent antenna unit.

According to an embodiment, the power dividing component is a directional coupler or a signal tapper. Directional couplers are commonly used to couple a defined amount of the electromagnetic power of the received signal power to a coupled port enabling the signal to be used in another circuit, whereas the rest of the electromagnetic power of the received signal power is passed to an output port to be propagated in the original circuit. The coupled port and the output port are heavily isolated. The portion of the received signal power coupled to the coupled port of the directional coupler is defined by the coupling factor of the directional coupler. Directional couplers sample signals flowing in one direction only. The signal tapper (a.k.a. a power tapper) operates similarly to a directional coupler but without the directivity (i.e. there is no isolation between output port and coupled port). The operation of the signal tapper is not dependent on the direction of the signal. Otherwise the signal tapper taps off a portion of the signal while allowing the rest of the signal to pass through with a minimum of loss, similarly to a directional coupler.

One issue that needs to be considered in designing the antenna arrangement is passive intermodulation (PIM). PIM is a form of intermodulation distortion that may occur even when no active components are present, such as in the antenna units herein. PIM may occur in a variety of areas from coaxial connectors to cables, oxidized bolts or any joint where dissimilar metals occur. PIM occurs when two or more signals are present in a passive non-linear device or element, such as in connectors, switches, isolators of the like, and the signals will mix or multiply with each other to generate other unwanted signals. It is noted that PIM may not necessarily originate from the antenna structure itself, but the source of PIM may also reside outside the antenna structure. While directional couplers and signal tappers are generally well-designed against the effect of PIM, a signal tapper may in certain situations have a better protection against PIM.

The skilled person appreciates that instead of or in addition to a directional coupler or a signal tapper, any other component achieving a similar technical effect may be used. For example, a splitter with asymmetric splitting ratio could be used herein. According to an embodiment, the power dividing component comprises control means for adjusting the ratio of the signal power supplied to said at least one antenna and the signal power supplied to said subsequent antenna unit. Thus, a directional coupler or a signal tapper may comprise a switch, a controller or a selector for adjusting the coupling factor. There may be a predefined stepwise selection of coupling factors, such -30 dB, - 20 dB, -10 dB, - 6 dB, -3 dB, or any else fixed values. Alternatively, there may be a continuously adjustable controller for selecting any coupling factor value. The control means may be manually operatable or remotely controlled e.g. by sending a wired or a wireless control signal for adjusting the antenna unit-specific coupling factor value.

According to an embodiment, for each antenna unit, the ratio of the signal power supplied to said at least one antenna and the signal power supplied to said subsequent antenna unit is arranged to be adjusted such that radiated power level of each antenna unit in the series is substantially even. Since the antenna units are connected in series and the signal power gradually decreases as propagated from an antenna unit to the subsequent antenna unit, the coupling factors for each antenna unit are preferably adjusted such that for the first antenna units in series the coupling factor may be very low, such as -30 dB, and the gradually increasing for subsequent antenna units in series such that for the (second) last antenna unit in series it may be -6 dB or -3 dB. A skilled person appreciates that the last antenna unit in series may also be implemented without the power dividing component, i.e. the signal power received from the second last antenna unit is may be supplied as such to the antenna(s) of the last antenna unit.

The maximum number of antenna units is dependent on the original signal power provided by the signal supplying unit, distances (in other words, attenuation) between the antenna units and the restrictions provided by the space where the antennas are radiating. Figure 1 illustrates a configuration where the antenna units are placed in a common space, such as a tunnel or a corridor, and the signal supplying unit is located outside the space. In such situation, it may be desirable to have substantially uniform field strength over the whole space. Thereupon, the relationship of the distances between the antenna units and the coupling factors used in each power dividing component shall preferably be taken into account, and if either the number of antenna units or the original signal power provided by the signal supplying unit forms a bottleneck, the antenna arrangement is configured according to the limitations.

Figure 2 illustrates another configuration, where each of the antenna units are placed in a separated space, such as in cabins of ship or a train, and the signal supplying unit is located outside any of said spaces. In such situation, it may be desirable to have only sufficient field strength within each space, wherein the field strengths in each space may be mutually non-uniform. Moreover, there may exist a requirement that preferably no or at least a minimum amount of leakage of signal radiation between spaces takes place. Thus, the coupling factors are adjusted differently than in the configuration of Figure 1 , which naturally has an effect of the design in terms of the the number of antenna units and the original signal power provided by the signal supplying unit.

According to an embodiment, the antenna arrangement further comprises an attenuator (1 16, 126, ...) connected between the at least one antenna (1 12, 122, ...) and the power dividing component (1 14, 124, ...) for adjusting radiated power of the at least one antenna. Thus, the attenuator may be used to fine-tune the radiation power of the antenna(s) of the antenna unit, for example if substantially uniform field strength is desirable in the space. Thereby, it is sufficient to adjust the coupling factor only as rough-scale adjustments, e.g. stepwise predefined values, and then fine-tune the radiation power of the antenna(s) by selecting a suitable attenuation. The attenuator may be a fixed value attenuator or a stepwise or continuously adjustable attenuator.

Alternatively or additionally, no separate attenuator component is needed, but the power dividing component may comprise built-in attenuation capability for adjusting the radiation power of the antenna(s) of the antenna unit.

In certain configurations, such as the one depicted in Figure 1 where there is an openable door between the first antenna unit and the RF power supplying unit, there may exist a feedback coupling from the first antenna unit to the RF power supplying unit, causing interference to the RF power supplying unit. In such configuration, it may be advantageous to attenuate the radiated power of the antenna(s) of the first antenna unit, for example by the attenuator so as provide an improved isolation between the first antenna unit and the RF power supplying unit.

According to an embodiment, said antenna units comprise a plurality of antennas operating in different frequency ranges. The antenna arrangement is usable over a very wide frequency range, preferably at least over 380 - 2500 MHz, more preferably extending over the range of 30 MHz - 5 GHz. Thus, each of the plurality of antennas may be connected to a suitably selected filter for arranging the antenna to transmit and receive signals within a desired frequency range.

According to an embodiment, said plurality of antennas are arranged to operate in at least one of the following frequency ranges:

- a wireless cellular network operating in any subset of a frequency range within the frequency range of 450 - 2100 MHz;

- a wireless local area network (WLAN) operating in either or both of 2.4 GHz and 5 GHz band according to any of the IEEE 802.x standards;

- very high frequency (VHF) one/two-way radio systems operating in the frequency range of 30 - 300 MHz;

- a public/private TETRA safety network operating within the frequency range of 380 - 430 MHz.

Thus, the applicability of the antenna arrangement may be enhanced to any combination of wired or wireless networks including, but not limited to a wireless cellular telephone network (such as a GSM, UMTS, CDMA network etc), a wireless local area network (WLAN) such as defined by any of the IEEE 802.x standards, a Bluetooth personal area network, an Ethernet local area network, a token ring local area network, a wide area network, and the Internet. According to an embodiment, the signal supplying unit is a repeater or a wireless base station. A repeater is used to repeat and amplify a signal received from a further origin, such as from public mobile network or a WAN/LAN operated in facility where the antenna arrangement is installed. A wireless base station, such as a WLAN base station, may be used to create a WLAN network within the facility such that the antenna arrangement is utilized in spreading the coverage of the WLAN network over a significantly larger cell size than with one antenna WLAN network. According to an embodiment, said series of the plurality of antenna unit is further connected to a second signal supplying unit. The antenna arrangement is capable of feeding signals bi-directionally and/or in multiple braches. According to an embodiment, said second signal supplying unit is connected to an opposite end of the series of the plurality of antenna units. Figure 3 illustrates this embodiment, where two signal supplying units 300, 302 are included in the arrangement. Thus, in the opposite end of the series of the plurality of antenna units there may be another repeater or a wireless base station supplying signals to an opposite direction. In case of bi-directional signals, signal tappers or splitters with asymmetric splitting ratio are preferably used as the power dividing components. According to an embodiment, said second signal supplying unit is connected between two antenna units in the series of the plurality of antenna unit, and a second plurality of antenna units connected in series to each other is connected to said second signal supplying unit. Figure 4 illustrates this embodiment, where two signal supplying units 400, 402 are included in the arrangement. In this embodiment, the second signal supplying unit 402 is included in the middle of (a first) plurality of antenna units in series such that a second branch of a plurality of antenna units may be formed to the arrangement.

In a further embodiment, there may be a configuration where from the plurality of antenna units between the two signal supplying unit, one or more, possibly all, antenna units are used for dividing the antenna circuit into one or more further branches. Therein, the power dividing component supplies the small portion of the received signal power to a further antenna branch, instead of or in addition to supplying it to the one or more antennas of the antenna unit.

As becomes evident from the above, the various embodiments may provide significant advantages over prior art solutions. The advantages are especially obvious in various internal networks of facilities, such as ships, houses, tunnels, parking halls, industrial premises, etc. The antenna arrangement may be adjusted such that the radiated power level over the entire coverage of the arrangement is substantially even. The coverage area of a single base station can be spread to longer distance, whereupon a smaller amount of base stations are needed, which in turn reduces the number of handovers. The enlargement of base station cell coverage also facilitates the re-usage of frequency bands. The cabling of the antenna arrangement may be installed through metal walls or other obstacles, which enhances the applicability to configurations where separate spaces require an antenna unit of their own. Moreover, compared to the commonly used splitter based solution, significantly smaller amount of cables and components are needed.

In general, the various embodiments may be implemented in hardware or special purpose circuits or any combination thereof. While various embodiments may be illustrated and described as block diagrams or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof. A skilled person appreciates that any of the embodiments described above may be implemented as a combination with one or more of the other embodiments, unless there is explicitly or implicitly stated that certain embodiments are only alternatives to each other.

It will be obvious for a person skilled in the art that with technological developments, the basic idea of the invention can be implemented in a variety of ways. Thus, the invention and its embodiments are not limited to the above-described examples but they may vary within the scope of the claims.

Claims

Claims:

1. An antenna arrangement comprising

at least one signal supplying unit; and

a plurality of antenna units connected in series to each other and a first antenna unit being connected to the at least one signal supplying unit, each antenna unit comprising

- at least one antenna; and

- a power dividing component connected to said at least one antenna and arranged to divide a minority of received signal power to said at least one antenna and a majority of the received signal power to a subsequent antenna unit in the series.

2 The antenna arrangement according to claim 1 , wherein the power dividing component comprises control means for adjusting the ratio of the signal power supplied to said at least one antenna and the signal power supplied to said subsequent antenna unit.

3. The antenna arrangement according to claim 1 or 2, further comprising attenuation arranged between the at least one antenna and the power dividing component for adjusting radiated power of the at least one antenna.

4. The antenna arrangement according to any preceding claim, wherein for each antenna unit, the ratio of the signal power supplied to said at least one antenna and the signal power supplied to said subsequent antenna unit is arranged to be adjusted such that radiated power level of each antenna unit in the series is substantially even.

5. The antenna arrangement according to any preceding claim, wherein said antenna units comprise a plurality of antennas operating in different frequency ranges.

6. The antenna arrangement according to any preceding claim, wherein the power dividing component is a directional coupler or a signal tapper.

7. The antenna arrangement according to any preceding claim, wherein the signal supplying unit is a repeater or a wireless base station.

8. The antenna arrangement according to any preceding claim, wherein said series of the plurality of antenna unit is further connected to a second signal supplying unit.

9. The antenna arrangement according to claim 8, wherein said second signal supplying unit is connected to an opposite end of the series of the plurality of antenna unit.

10. The antenna arrangement according to claim 8, wherein said second signal supplying unit is connected between two antenna units in the series of the plurality of antenna unit, and a second plurality of antenna units connected in series to each other is connected to said second signal supplying unit.