Field of the invention

The present invention relates to communication systems such as telecommunication links and antennas for such telecommunication systems. More specifically, the invention relates to dual-polarized duplex point-to-point communication systems and units for such systems. Moreover, the invention relates to terrestrial telecommunication links.

Background of the invention

In typical two-way communication systems, signals are both transmitted and received by a common radio unit utilising a single polarisation, typically via a single antenna over a single antenna port. In such an arrangement, the transmit branch (e.g., post-PA (power amplifier) and the receive branch (e.g. pre-LNA low noise amplifier) must be combined such that the single antenna port can be accessed, e.g., with a duplex filter or a circulator. A corresponding combiner unit must provide sufficient isolation (between transmit and receive branches) and VSWR (Voltage Standing Wave Ratio) in order to avoid interference while the power amplifier is active.

An alternative point-to-point solution, which has been indicated in figs. 1 - 3, is to use separate antenna ports for the transmit and receive branches. In such a system, the ports correspond to two separate antenna beams, which can be implemented by using for example two orthogonal polarizations associated with respective separate antenna hardware units.

In fig 1, the complete antenna system of mating antenna units has been indicated. Fig. 2 shows a first communication unit 1 and fig. 3 shows a second communication unit 2 adapted for communication with one another. As appears, waves in a first polarisation direction is transmitted via TX1 of communication unit 1 and received by RX2 by communication unit 2. Likewise, signals are transmitted in a second polarisation direction between TX2 and RXl

One example of a full duplex point-to-point communication system utilising orthogonal polarisations for redundancy and with identical communication units at both ends of the communication link has been shown in US-2002-70065053.

One problem associated with the above known communication unit is that either a manual coupling activation or an automatic electrical switching means is required for a correct coupling of receive and transmit antenna elements to peripheral signalling process- ing equipment for establishing a correct alignment of the polarised signals to a mating communication unit, cf. fig. 1.

US-6519478 shows a base station antenna having 45 degree slanted antenna elements with regard to vertical that can be individually selected to communicate with a terminal transmitting / receiving in an unknown polarisation orientation.

J P-2002- 166508 shows two antenna sections arranged side by side forming an orthogonally polarized wave slot array antenna, the first antenna section having first slots (5) arranged for transmission and the second antenna section having second slots (6) arranged for reception. The first and second slots are arranged orthogonally thereby enabling duplex communication without a duplexer. In J P-2002- 166508 the respective slots are arranged at pair-wise angles of 30 and 60; 35 and 55; 40 and 50; or 45 and 45 degrees with regard to the antenna structure. The orientation of the apparatus is not dealt with.

Summary of the invention

It is a first object of the invention to provide a compact, uniform duplex communication unit.

This object has been accomplished according to claim 1.

It is a second object of the invention to provide a terrestrial uniform duplex communica- tion unit requiring no modification at installation.

This object has been accomplished by the subject matter according to claim 7.

It is a third object of the invention to provide a uniform duplex communication unit for communicating over a common channel, the communication unit being adapted to be

coupled to receive / transmit terminals of surrounding equipment in a predetermined way requiring no modification at installation.

This object has been achieved by claim 9.

Further advantages will appear from the following detailed description of the invention.

Brief description of the drawings

Fig. 1 shows a prior art communication system comprising two antennas, each antenna having elements for transmitting in a first polarization direction and elements for receiving in a second polarisation direction,

fig. 2 is a face view of the first unit of fig. 1 (beam direction BD out of the plane of the paper),

fig. 3 is a face view of the second unit of fig. 1 (beam direction BD out of the plane of the paper),

fig. 4 is a side view of a communication unit according to a first preferred embodiment of the invention mounted via a fixture to a solid object, a peripheral signal- processing unit moreover being indicated,

fig. 5 and 6 are front views of two respective identically configured communication units of fig. 4 being adapted to communicate with one another (beam direction BD out of the plane of the paper),

fig. 7 and 8 are two face views of a various elements of a first embodiment of an antenna for generating two orthogonal polarisations according to the invention,

fig. 9 and 10 are side views of the antenna shown in fig. 7 and 8,

fig. 11 is a face view of a second embodiment of an antenna for generating two orthogonal polarisations according to the invention,

fig. 12 is a detailed view of a crossed dipole used in fig 11 to generate two orthogonal polarisations, and

fig. 13 is a third embodiment of an antenna with a common aperture for generating two orthogonal polarisations.

Detailed description of a preferred embodiment of the invention

Fig. 4, 5 and 6 show a preferred communication system according to the invention com- prising two antennas, AN, each antenna having antenna elements for transmitting in a first polarization direction and antenna elements for receiving in a second polarisation direction.

Each Communication unit 3, 4, comprises first antenna elements TX1 , such as an an- tenna, for transmitting polarized waves of a first orientation, second antenna elements RX1 , such as an antenna, for receiving polarized waves of a second orientation, whereby the first and second orientations preferably are substantially orthogonal to one another and the first and second elements preferably forms a common antenna aperture.

The Communication unit 3, 4 comprises at least a dual polarised antenna with a first antenna element TX1 for transmitting polarized waves in a first orientation, a second antenna element RX1 for receiving polarized waves in a second orientation, the first and second orientations preferably being substantially orthogonal to one another.

The first and second respective antennas elements TX1 , RX1 are arranged such that the first and second orientations are arranged at substantially equal angles a with regard to vertical b'.

In this manner the communication unit is being adapted for communicating with at least a mating communication unit, wherein the first and second respective antennas TX1 , RX1 of the mating unit are being arranged having the same configuration of polarisations as the communication unit in question, such that at least the receiving polarisations for both the communication unit and the mating communication unit are arranged at an identical angle with regard to vertical as seen from the beam direction BD.

The communication unit moreover comprises a transmit termination point TXC and a receive termination point RXC serving for coupling signals between a processing unit DM and at least one of the first and second antenna elements RX1 , TX1.

The communication unit may comprise a fixture FX, as shown in fig. 4, over which the communication unit can be mounted to a fixed structure SO, the communication unit having an indication means b adapted for being arranged substantially parallel to a ref- erence axis b' relating to the fixed structure.

Therefore, neither is a special reconfiguration on-site nor are two separate dedicated products required to ensure that polarizations are correctly aligned between two mating units when the mating units are mounted in the same manner with regard to the refer- ence axis b'. The two communications units are automatically mated with correct polarisation alignment thereby producing an inherently proper installation.

The communication unit can be fixed in a vertical mast, as is the usual practice, whereby the unit may rotate around the reference axis b' being parallel to the mast for ease of installation. During installation, the fixture prevents the antenna from being rotated around an axis perpendicular to the vertical axis b' but allows the unit to be inclined and directed towards a mating unit, in a manner corresponding to fig. 1.

In a terrestrial communication system, the reference axis can either be vertical or hori- zontal.

According to the invention, an optimum channel isolation is accomplished when the first and second means are orthogonal to one another, the angle, a, amounts to ±45 degrees.

Each unit may be fabricated and mounted in a uniform fashion requiring no modification for being put into operation with other units of the same type, a system may be provided comprising a pair of communication units as shown in fig. 5 and 6, for communicating with one another.

Moreover, the transmit and receive termination points TXC, RXC may advantageously be adapted to be physically arranged in the same fashion in relation to a respective signal processing unit for both communication units.

Point-to-multipoint systems are also envisaged, provided that antennas have a sufficiently wide beam width. It should be noted that, according to the invention, a given agreed polarisation configuration, as shown e.g. on fig. 5 and 6 could form basis of a regulatory standard for link systems. In this way, new generations of equipment would be adapted for communicating with older equipment without the problems as mentioned above with regard to adapting and fitting the actual polarisations to the given mating link. In fig. 7 - 10, a patch antenna array adapted for being used in the above communication unit of fig. 4 - 6 is shown.

The dual polarised antenna comprises a first dielectric layer 12 comprising, a ground plane 11 , a first dielectric layer comprising a first distribution net RXE, a second ground plane 13, a second dielectric layer 14 comprising a second distribution second net TXE, a first antenna element TX1 associated with a first direction of polarisation being connected with the first distribution net, a second antenna element RX1 associated with a second direction of polarisation being connected with the second distribution net.

According to the embodiment shown in figs. 7 - 10, the first and second antenna elements are constituted by a common patch element P, the first and second distribution nets RXE, TXE feeding respective orthogonal sides of the patch P.

Layers 11, 12, 13, 14 and 15 in figure 9 could form two separated strip-line layers, where 11, 13 and 15 are metallic planes, forming ground planes, and 12 and 14 are supporting layers formed by a dielectric material or air.

A second possibility is that layers 11 and 13 are metallic planes (ground planes) and layers 12 and 14 are supporting layers (dielectric or air). Layers H , 12 and 13 then form

a strip-line circuit while layers 13 and 14 form a micro-strip circuit (no ground plane on top). Layer 15 then contains only the metallic patches, as illustrated in figure 10.

The output impedance from a power amplifier TX and the input impedance of a low- noise amplifier RX of the processing unit DM may not have the same impedance level. Therefore, the feeding networks may have different impedance levels to match to the impedance level of the corresponding amplifier.

In fig. 11 - 13, a crossed dipole antenna adapted for being used in the above communi- cation unit of fig. 4 - 6 is shown.

This antenna may be constructed using the same layer structure shown in fig. 9.

According to one embodiment, the first distribution net feeds a first dipole element, DP, and the second distribution net feeds a second dipole element, the first and second dipole elements being orthogonally arranged.

The dipole elements form a cross, the distribution nets feeding the dipole elements from the centre of the cross.

Alternatively a single pair of dipole elements DP may be arranged in a reflector RFL structure as shown in fig. 13.