TECHNICAL FIELD

The present disclosure relates to a coaxial balun device and a balun arrangement.

BACKGROUND

A balun (balanced to/from unbalanced) device is utilized in a majority of all microwave hardware. A balun may, in the most general form thereof, transform a single-ended signal to a differential signal or vice versa. Moreover, baluns are used in for example impedance transformation and/or as out-phasing power splitters/combiners for enhanced suppression of in-band unwanted harmonics.

There exist a variety of balun device types, one being the coaxial balun which is a balun device that performs at high standards in the GHz frequency region. However, the coaxial balun is seldom or never used in actual products since it has a design which doesn't fulfil requirements relating to at least robustness and manufacturing convenience.

Specifically, the coaxial balun is sensitive to mechanical shock and vibration as the coaxial cable thereon is easily disoriented. Moreover, the general design of the coaxial balun device (having a coiled coaxial and a conducting cable) is challenging and thus expensive to manufacture.

Based on the above there is in the present art room for improvements in order to have a coaxial balun device that can be manufactured in a convenient manner so to allow for mass-production and/or be more robust. Specifically, the coaxial balun device should be more robust and/or manufacturing convenient while maintaining performance in accordance with requirements

Even though some currently known solutions work well in some situations it would be desirable to provide a coaxial balun device that specifically fulfils requirements relating to manufacturing convenience and/or robustness while maintaining operating performance.

SUMMARY

It is therefore an object of the present disclosure to provide a coaxial balun device in order to mitigate, alleviate or eliminate one or more of the above-identified deficiencies and disadvantages.

This object is achieved by means of a coaxial balun device as defined in the appended claims. The present disclosure is at least partly based on the insight that by providing a coaxial balun device in accordance with the appended claims, the manufacturing convenience and/or robustness will be improved while maintaining, or improving, an operating performance of said coaxial balun device.

The present disclosure discloses a coaxial balun device comprising a sheet of dielectric comprising a first port and a pair of second ports. Moreover, the coaxial balun device comprises an oblong dielectric rod attached to a first surface of said sheet of dielectric. Further comprising a coaxial winding and a wire winding for electrically connecting said first port to said second ports. The coaxial winding comprises an inner conductor and an outer conductor. The coaxial winding is wound around a first half of said rod and said wire winding is wound around a second half of said rod. Each winding comprises first end portions, each first end portion extending beyond a diameter of said rod. The second ports are associated to a first side of said sheet of dielectric, wherein said rod axially extends in a direction parallel to said first side. The dielectric sheet may be a printed circuit board.

An advantage of the coaxial balun herein compared to other coaxial baluns is that it is more convenient to manufacture while maintaining performance in accordance with requirements. The dielectric rod provides increased robustness to the balun so that the coaxial balun is less sensitive to mechanical shock and vibration. Further, the dielectric rod allows for a more rapid and efficient coiling of the coaxial balun as the wires can simply be wound about the rod.

Moreover, the first end portions of the wires extending beyond a diameter of said rod when assembled, also allows for increased manufacturing convenience as the points are accessible for e.g. a solder pen during assembly. In other words, the present disclosure allows for attachment to the sheet of dielectric at points that are situated away from the rod (not directly beneath) thereby increasing manufacturing convenience.

Further, the arrangement of the rod being parallel to said first side allows for less disturbance of the balun, specifically when used in series with other balun devices In other words, unwanted feedback between ports is avoided/reduced. Also, it advantageously provides for a more compact arrangement of the coaxial balun device. In some aspects herein, the outer conductor at said first end portion (of the coaxial winding) may be connected to a first output transmission portion on said sheet of dielectric, the first output transmission portion being connected to one of said second ports (which may be an output port). Further, the inner conductor at said first end portion may be connected to a second output transmission portion on said sheet of dielectric, the second output transmission portion being connected to the other one of said second ports (e.g. a second output port). It should be noted that the inner conductor may be enclosed/surrounded by the outer conductor on said coaxial winding. The inner conductor may have a greater length than the outer conductor such that the part of the inner conductor connected/attached to the second output transmission portion extends out from an end of the outer conductor. Further, the first end portion of said wire winding may be connected to said second output transmission portion.

An advantage of the configuration of the first end portions as disclosed herein is that it optimizes the manufacturing convenience of the coaxial balun device. Thus, fulfilling requirements of providing an electromagnetic field coupling input ports to ouput ports while being manufacturing convenient and space efficient in arrangement on said sheet of dielectric.

Each winding may comprise second end portions, wherein the outer conductor at said second end portion is grounded, wherein the inner conductor at said second end portion is electrically connected to the first port. The second end portions may be on the opposite side of the first end portions.

The second end portions may extend beyond a diameter of said rod from opposing edge portions thereof respectively.

An advantage of this is that it allows for the first end portions to extend from a center of the rod, thereby space efficiency is increased.

The rod may comprise a dielectric constant equal to or less than 3. An advantage of this is that it allows for sufficient electrical performance with low loss in the 0.5-6 GHz range. The rod may be formed in rexolite or any other suitable dielectric material.

The coaxial wire and the wire may have diameters of 0. -0.5 mm, preferably 0.3-0.4 mm. Such diameter range allow for sufficient electrical performance without increasing the manufacturing complexity allowing for convenient coiling of the wires.

The first port (which may be an input port) may be positioned at a side opposite the first side of the sheet of dielectric.

The balun device may further comprise resistance pads associated to at least one of the second ports. An advantage of such resistance pads is that it may provide impedance matching at second (output) ports of the coaxial balun device. The resistor pads may be film resistors and may be specifically included in case when e.g. a specific output impedance is sought. For example if a 50 ohm impedance is sought the coaxial balun device may comprise surface mount resistor pads associated to said outlet ports.

The coaxial balun device may further comprise an electromagnetic shielding unit enclosing the windings. The shielding allows for enclosing the magnetic field provided by the windings, thereby reducing leakage.

There is further disclosed a coaxial balun arrangement comprising at least a pair of coaxial balun devices wherein axial extensions of the rods of each coaxial balun device are directed away from other balun devices.

The balun arrangement may be a balanced amplifier unit, wherein said amplifier unit is connected between second ports of the pair of balun devices such that one balun device is connected to an input of said amplifier unit and the other balun device to an output thereof.

An advantage of this is that any feedback between input ports and output ports thereof will be minimized. Thus, the risk of unwanted feedback possibly causing instabilities in an balanced amplifier unit utilizing the said balun is significantly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the disclosure will be described in a non-limiting way and in more detail with reference to exemplary embodiments illustrated in the enclosed drawings, in which:

Figure 1 illustrates a top view of a coaxial balun device;

Figure 2 illustrated an objective view of a coaxial balun device;

Figure 3 schematically illustrates a coaxial balun arrangement in a balanced amplifier configuration;

Figure 4 illustrates a simulation of the performance of a coaxial balun device in accordance with some aspects of the present disclosure. DETAILED DESCRIPTION

In the following detailed description, some embodiments of the present disclosure will be described. However, it is to be understood that features of the different embodiments are exchangeable between the embodiments and may be combined in different ways, unless anything else is specifically indicated. Even though in the following description, numerous specific details are set forth to provide a more thorough understanding of the provided device and arrangement, it will be apparent to one skilled in the art that the device and arrangement may be realized without these details. In other instances, well known constructions or functions are not described in detail, so as not to obscure the present disclosure. Directions and orientations such as above, below, upwards, downwards etc., are generally described herein with reference to the drawings in the usual gravitational frame of reference.

Figure 1 illustrates a coaxial balun device 1 from a top view comprising a sheet of dielectric 6 comprising a first port 2 and a pair of second ports 3a, 3b. The first port 2 may be an input port, and the second ports 3a, 3b may be output ports or vice versa. Further, the coaxial balun device 1 comprises an oblong dielectric rod 4 attached to a first surface 5 of said sheet of dielectric 6.

Moreover, the coaxial balun device comprises a coaxial winding 7 and a wire winding 8 for electrically connecting said first port 2 to said second ports 3a, 3b. Further, the coaxial winding 7 comprises an inner conductor 7a and an outer conductor 7b. Further, the coaxial winding 7 is wound around a first half pl of said rod 4 (lengthwise of the rod 4) and said wire winding 8 is wound around a second half p2 of said rod 4. Further, Figure 1 illustrates that each winding 7, 8 comprises first end portions 9a, 9b, each first end portion 9a, 9b extending/protruding beyond a diameter dl/thickness of said rod 4. Specifically, each first end portion 9a, 9b extends/protrudes beyond a diameter dl of said rod 4 towards the first side si, such that the end portions 9a, 9b are neither above or below the rod. Figure 1 further illustrates that the second ports 3a, 3b are associated to a first side si of said sheet of dielectric 6, wherein said rod 4 axially extends in a direction parallel to said first side si. In other words, the end portions 9a, 9b may protrude away from said rod 4.

The first side 1 may also be referred to as an edge portion of the sheet of dielectric extending along a length thereof. The sheet of dielectric may be a PCB. Figure 1 illustrates that the outer conductor 7b may enclose the inner conductor 7a such that a tip of the inner conductor 7a extends out from the outer conductor at opposing ends of the coaxial winding 7. Thus, the outer conductor 7b may form a tube and the inner conductor may be enclosed within the tube.

Figure 1 further illustrates that in some aspects, the outer conductor 7b at said first end portion 9a is connected to a first output transmission portion 10 on said sheet of dielectric 6. The first end portion 9a may be referred to as an end section of said windings 7, 8 (e.g. extending from an end thereof inwards covering e.g. 1-25% of a total length of the windings 7, 8. The first output transmission portion 10 being connected to the first port 3a. The output transmission portion 10 may be e.g. a transmission line at said sheet of dielectric serving as a path for transmitting electric signals . Further, the inner conductor 7a at said first end portion 9a is connected to a second output transmission portion 11 on said sheet of dielectric 6, the second output transmission portion 11 being connected to the other one of said second ports 3a, 3b so to facilitate the transfer of electric signals from the first port 2.

Figure 1 further illustrates that each winding 7, 8 comprises second end portions 12a, 12b. The outer conductor 7b at said second end portion 12a may be grounded (e.g. by ground pads), wherein the inner conductor 7a at said second end portion 12a is electrically connected to the first port 2. As illustrated in Figure 1, the inner conductor 7b extends out from an end of the outer conductor 7b. As illustrated in Figure 1, the second end portions 12a, 12b are on opposing sides of the first end portions 9a, 9b along the length of each winding 7, 8. Moreover, the wire winding 8 is also grounded at its second end portion 12b. The wire winding may comprise a conductive material. The wire winding may be copper winding or any other suitable conductive material.

Figure 1 further illustrates that the first end portions 9a, 9b extend from a centre portion cl (along its length) of said rod intermediate opposing edge portions el, e2 of said rod 4, in other words, the first end portions 9a, 9b extend away (i.e. are not in contact with the rod) from the rod 4 from a center portion cl thereof. Further, as shown in Figure 1, the second end portions 12a, 12b of both the coaxial winding and the wire winding extend beyond a diameter dl of said rod 4, from opposing edge portions el, e2 of said rod 4. In other words, "beyond a diameter" may refer to that the windings 7, 8 extend away from the rod 4 such that the end portions 9a, 9b. 12a, 12b are not in contact with the rod 4 and that the end portions 9a, 9b, 12a, 12b are neither above or below the rod. The windings 7, 8 may extend away from a portion of the rod being associated to said first surface 5. Accordingly, e.g. soldering points that attach the windings 7, 8 to the sheet 6 may be more easily attained as the rod 4 is not an obstacle during a soldering operation. The rod 4 may be a hollow rod 4. This is in some cases advantageous as it allows for reduced effective permittivity of the rod 4. Figure 1 illustrates that the first end portions 9a, 9b protrudes beyond a diameter of the rod 4 towards the first side si, wherein the first side si is associated with a first side portion 31 of the sheet of dielectric 6, wherein the second side s2 is associated with a second side portion 32 of the sheet of dielectric 6. Accordingly, the end portions 9a, 9b are each positioned at said first side portion 31 (such that they are neither above or beneath the rod). Moreover, the rod 4 is positioned at an intermediate portion 30, between said first side portion 31 and said second side portion 32. The term "end portion" may in some instances be referred to as "the end point". Figure 1 illustrates that the second end portions 12a, 12b may protrude beyond a diameter of the rod 4 towards the second side s2, wherein the second side s2 is associated with a second side portion 32 of the sheet of dielectric 6. Accordingly, the end portions 12a, 12b are each positioned at said second side portion 32 (such that they are neither above or beneath the rod).

As illustrated in Figure 1, the first port 3a may be positioned at a side opposite the first side si of the sheet of dielectric 6. Moreover, the coaxial balun device 1 may further comprise resistance pads 13 associated to at least one of the second ports 3a, 3b allowing for impedance matching.

Figure 2 illustrates an objective view of said coaxial balun device according to some aspects of the present disclosure. As illustrated in Figure 2 the coaxial balun device 1 may comprise an electromagnetic shielding unit 14 enclosing said wires 7, 8. Moreover, Figure 2 illustrates how the wires 7, 8 are wound around said rod.

Figure 2 further illustrates that the coaxial balun device 1 may comprise holding means 15 for attaching the rod 4 to the sheet of dielectric 6. The holding means 15 may be a thread attached at one end at the sheet 6 and having an opposing end enclosing the rod 4 circumferentially. The holding means 15 may also be any other type of holding means 15. The holding means 15 provides the advantage of allowing the rod to be easily mounted to the sheet 6, thereby the wires 7, 8 may be wound around the rod 4 in a convenient manner. The holding means 15 may be arranged to provide a space between the rod and the first surface of the sheet 5, when said rod 4 is attached thereto. Thereby, the attachment of the windings 7, 8 to the rod 4 will be more convenient.

Figure 2 further illustrates that the windings 7, 8 are arranged mirrored relative each other. In other words, the windings 7, 8 are reflection symmetric. Figure 2 illustrates that the windings 7, 8 are reflection symmetric relative each other along a plane of symmetry si. The plane of symmetry si may be associated to a centre portion cl (see Figure 1) of said rod 4, the plane of symmetry si radially slicing a centre portion cl of the rod 4.

It should be noted that at least the length of the coaxial winding and the wire winding influence a frequency range of the coaxial balun device 1. Accordingly, the coaxial balun device 1 in accordance with the present disclosure (e.g. as shown in Figures 1 and 2) allow for more flexibly choosing the frequency operational range of the coaxial balun device 1.

Figure 3 illustrates a balun arrangement 100 in accordance with some aspects herein, wherein the balun arrangement is a balanced amplifier arrangement. Accordingly, Figure 3 illustrates that the balun arrangement 100 is a balanced amplifier unit comprising a pair of amplifier devices 101 connected between second ports 3a, 3b of the pair of balun devices 1 (in some aspects only one amplifier device is connected therebetween) such that one balun device 1 is connected to inputs 100a of said amplifier units and the other balun 1 to outputs 100b thereof. As illustrated in Figure 1 an axial extension of each rod 4 is extending in a direction such that the output ports 3a, 3b are on a common side opposite to the side of the input 2.

Figure 4 illustrates a plot disclosing a simulation of an operation of the coaxial balun device in accordance with some aspects of the present disclosure. The purpose of the simulation is to further describe the disclosure as presented herein accompanied with advantages thereof. It should be noted that the simulations are based on embodiments for a disclosing purpose, however it is not limited to said embodiments and may be varied within the present disclosure. Figure 4 illustrates a first and second plot 31, 32. The first plot 31 illustrates a amplitude mismatch of a coaxial balun device 1 in accordance with the present disclosure. Figure 4 illustrates that the maximum amplitude error is only 0.1 dB. Moreover, the second plot 32 illustrates an phase mismatch of the coaxial balun device 1 herein. As illustrated by the second plot, the error error is at a maximum 1.2 degrees relative to the ideal 180 degrees. As illustrated in Figure 4 there coaxial balun device 1 performs with low error at a frequency range of 0.5-6 GHz.