Apparatuses, methods and computer programs for phase estimation

Abstract

A MIMO transceiver includes a first antenna port 210, a second antenna port 220, a first amplitude detector path 213, a second amplitude detector path 223 including a receive phase shifter 251, a comb

Description

In radio access networks, multiple-input and multiple-output (MIMO) is a method for multiplying the capacity of a radio link using multiple antennae for transmission and reception to exploit multipath propagation. The relative phase difference between signals conveyed to the antennae (transmit) or conveyed from the antennae (receive) can be different, even when the transmit and receive signals are at the same frequency. This is partially due to the different pathways the signals take and the physical components in these pathways. The best signal performance can be achieved when the relative phase difference between reception (Rx) pathways, is equal or very close to the relative phase difference between transmission (Tx) pathways. BRIEF SUMMARY According to various, but not necessarily all, examples there is provided an apparatus comprising: a first antenna port; a second antenna port; a first transmission pathway for a first antenna port; a second transmission pathway for a second antenna port; a first reception pathway for the first antenna port; a second reception pathway for the second antenna port; a first additional pathway for the first antenna port; a second additional pathway for the second antenna port; means for switching between a first state in which a first signal is conveyed from the first reception pathway along the first additional pathway and a second signal is conveyed from the second reception pathway along the second additional pathway and a second state in which a third signal is conveyed from the first transmission pathway along the first additional pathway and a fourth signal is conveyed from the second transmission pathway along the second additional pathway; an amplitude detector configured to detect a combined amplitude of a signal in the first additional pathway and a signal in the second additional pathway; means for adjusting a relative phase between a signal in the first additional pathway and a signal in the second additional pathway based at least in part on the detected combined amplitude; and means for adjusting a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway based at least in part on the detected combined amplitude. The means for adjusting the relative phase between a signal in the first additional pathway and a signal in the second additional pathway may be configured to adjust the relative phase when the means for switching is in the first state. The means for adjusting a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway may be configured to adjust the relative phase when the means for switching is in the second state. The means for adjusting the relative phase between a signal in the first additional pathway and a signal in the second additional pathway may comprise means for optimizing the relative phase between a signal in the first additional pathway and a signal in the second additional pathway to produce a largest combined amplitude. The means for adjusting a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway may comprise means for optimizing a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway to produce a largest combined amplitude. The means for optimizing the relative phase between a signal in the first additional pathway and a signal in the second additional pathway, and the means for optimizing the relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway may be configured such that: whilst the relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway is optimized, the relative phase between a signal in the first additional pathway and a signal in the second additional pathway is kept at an optimized value previously determined by the means for optimizing the relative phase between a signal in the first additional pathway and a signal in the second additional pathway. The means for optimizing the relative phase between a signal in the first additional pathway and a signal in the second additional pathway, and the means for optimizing a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway, may both be configured to maintain the relative phase once it has been optimized. The second additional pathway may comprise a first phase shifter, and the first transmission pathway may comprise a second phase shifter. The first phase shifter may be configured to control the relative phase between a signal in the first additional pathway and a signal in the second additional pathway. The second phase shifter may be configured to control the relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway. The first transmission pathway may comprise an amplifier. The amplifier may be positioned closer to the first antenna port than the second phase shifter is positioned relative to the first antenna port. The first additional pathway may comprise an attenuator. The attenuator may be configured to match the attenuation caused by the first phase shifter. The amplitude detector may be an envelope detector. The amplitude detector may be for detecting a peak amplitude of the combined signals. The first transmission pathway, second transmission pathway, first reception pathway, second reception pathway, first additional pathway and second additional pathway may each be a pathway for conveying electrical signals. The first transmission pathway may be for conveying a signal to the first antenna port. The second transmission pathway may be for conveying a signal to the second antenna port, the first reception pathway may be for conveying a signal from the first antenna port, and the second reception pathway may be for conveying a signal from the second antenna port. The apparatus may further comprise a first antenna element configured to couple to the first antenna port and a second antenna element configured to couple to the second antenna port. The apparatus may further comprise a first coupler configured to couple at least a portion of a signal from the first transmission pathway to the first additional pathway, and a second coupler configured to couple at least a portion of a signal from the second transmission pathway to the second additional pathway. The apparatus may further comprise a combiner, configured to combine the signal in the first additional pathway and the signal in the second additional pathway. The apparatus may further comprise a variable amplifier which is positioned between the combiner and the amplitude detector. The variable amplifier may be configured to adjust the combined amplitude. The apparatus may be a user equipment. The apparatus may further comprise: a third antenna port; and a third reception pathway for the third antenna port. The apparatus may further comprise: further means for switching between a signal being conveyed from the second reception pathway along the second additional pathway; and a signal being conveyed from the third reception pathway along the second additional pathway. The first state of the means for switching may comprise a second signal being conveyed from the second reception pathway along the second additional pathway or a second signal being conveyed from the third reception pathway along the second additional pathway. The apparatus may, further comprise a third transmission pathway for the third antenna port; and a third additional pathway for the third antenna port. The means for switching may comprise means for switching between a first state in which a first signal is conveyed from the first reception pathway along the first additional pathway and a second signal is conveyed from the second reception pathway along the second additional pathway, a second state in which a third signal is conveyed from the first transmission pathway along the first additional pathway and a fourth signal is conveyed from the second transmission pathway along the second additional pathway; a third state in which the first signal is conveyed from the first reception pathway along the first additional pathway and a fifth signal is conveyed from the third reception pathway along the third additional pathway; and a fourth state in which the third signal is conveyed from the first transmission pathway along the first additional pathway and a sixth signal is conveyed from the third transmission pathway along the third additional pathway. The amplitude detector may be configured to detect a combined amplitude of a signal in the first additional pathway and a signal in the second additional pathway, or a combined amplitude of a signal in the first additional pathway and a signal in the third additional pathway. The apparatus may further comprise means for adjusting a relative phase between a signal in the first additional pathway and a signal in the third additional pathway based at least in part on the detected combined amplitude. According to various, but not necessarily all, examples there is provided a method comprising: causing switching between a first state in which a first signal is conveyed from the first reception pathway along a first additional pathway and a second signal is conveyed from a second reception pathway along a second additional pathway and a second state in which a third signal is conveyed from a first transmission pathway along the first additional pathway and a fourth signal is conveyed from a second transmission pathway along the second additional pathway; causing detection of a combined amplitude of a signal in the first additional pathway and a signal in the second additional pathway; causing adjustment of a relative phase between a signal in the first additional pathway and a signal in the second additional pathway based at least in part on the detected combined amplitude; and causing adjustment of a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway based at least in part on the detected combined amplitude. Causing adjustment of the relative phase between a signal in the first additional pathway and a signal in the second additional pathway may comprise optimizing the relative phase between a signal in the first additional pathway and a signal in the second additional pathway to produce the largest combined amplitude. Causing adjustment of the relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway may comprise optimizing a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway to produce the largest combined amplitude. According to various, but not necessarily all, examples there is provided a computer program comprising program instructions for causing an apparatus to perform at least the following: causing switching between a first state in which a first signal is conveyed from the first reception pathway along a first additional pathway and a second signal is conveyed from a second reception pathway along a second additional pathway and a second state in which a third signal is conveyed from a first transmission pathway along the first additional pathway and a fourth signal is conveyed from a second transmission pathway along the second additional pathway; causing detection of a combined amplitude of a signal in the first additional pathway and a signal in the second additional pathway; causing adjustment of a relative phase between a signal in the first additional pathway and a signal in the second additional pathway based at least in part on the detected combined amplitude; and causing adjustment of a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway based at least in part on the detected combined amplitude. According to various, but not necessarily all, examples there is provided examples as claimed in the appended claims. While the above examples of the disclosure and optional features are described separately, it is to be understood that their provision in all possible combinations and permutations is contained within the disclosure. It is to be understood that various examples of the disclosure can comprise any or all of the features described in respect of other examples of the disclosure, and vice versa. Also, it is to be appreciated that any one or more or all of the features, in any combination, may be implemented by / comprised in / performable by an apparatus, a method, and / or computer program instructions as desired, and as appropriate. BRIEF DESCRIPTION Some examples will now be described with reference to the accompanying drawings in which: FIG. 1 shows an example of the subject matter described herein; FIG. 2 shows another example of the subject matter described herein; FIG. 3 shows another example of the subject matter described herein; FIG. 4 shows another example of the subject matter described herein; FIG. 5 shows another example of the subject matter described herein; FIG. 6 shows another example of the subject matter described herein; FIG. 7 shows another example of the subject matter described herein; FIG. 8 shows another example of the subject matter described herein; FIG. 9 shows another example of the subject matter described herein; FIG. 10 shows another example of the subject matter described herein; and FIG. 11 shows another example of the subject matter described herein. The figures are not necessarily to scale. Certain features and views of the figures can be shown schematically or exaggerated in scale in the interest of clarity and conciseness. For example, the dimensions of some elements in the figures can be exaggerated relative to other elements to aid explication. Similar reference numerals are used in the figures to designate similar features. For clarity, all reference numerals are not necessarily displayed in all figures. DEFINITIONS 3GPP Third Generation Partnership Project 5G 5th Generation Al Artificial Intelligence AoA Angle of Arrival BB BaseBand BS Base Station CSI Channel State Information 7 DL Downlink DPEC Differential Phase Estimation Circuit E-UTRAN Evolved Universal Terrestrial Radio Access Network FPGA Field-Programmable Gate Array gNB LNA 5G / NR base station Low Noise Amplifier LTE Long-Term Evolution MIMO Multiple Input Multiple Output NG-RAN Next Generation Radio Access Network NR New Radio PA Power Amplifier PUSCH Physical Uplink Shared Channel RAN Radio Access Network RF Radio Frequency RRC Radio Resource Control RSSI Received Signal Strength Indicator Rx Receive SPDT Single Pole Double Throw TDD Time Domain Duplex Tx Transmit UE User Equipment UL Uplink DETAILED DESCRIPTION Until recently, user equipment 110 such as smartphones have not supported more than one transmitted data layer in uplink (UL) MIMO. The cost (for example, in bill of materials, printed circuit board area and / or power consumption) of adding relevant power amplifiers to support more than one antenna transmitting at the time has not previously been seen as worth the performance benefit. However the use of more than one transmitted data layer in uplink MIMO has the potential to overcome bottlenecks in uplink performance. Embodiments of this disclosure relate to downlink analogue signal estimation of the phase seen at different antennas used for receiving a signal, such as the downlink reference signal. The applied phase compensations for the UL MIMO signals are based on a comparison of downlink and uplink relative phase. This may be using an analogue signal phase estimator. The best UL MIMO performance (in terms of capacity, coverage and / or latency) can be obtained when UL signals are transmitted with a phase alignment fitting the current channel conditions. This may involve the relative phase difference between UL / Tx pathways, being the same as or very close to the relative phase difference between DL I Rx pathways or applying compensation of possible differences. FIG. 1 illustrates an example of a network 100 comprising a plurality of network nodes including terminal nodes 110, access nodes 120 and one or more core nodes 129. The terminal nodes 110 and access nodes 120 communicate with each other. The one or more core nodes 129 communicate with the access nodes 120. The network 100 is in this example a radio telecommunications network, in which at least some of the terminal nodes 110 and access nodes 120 communicate with each other using transmission / reception of radio waves. The one or more core nodes 129 may, in some examples, communicate with each other. The one or more access nodes 120 may, in some examples, communicate with each other. The network 100 may be a cellular network comprising a plurality of cells 122 each served by an access node 120. In this example, the interface between the terminal nodes 110 and an access node 120 defining a cell 122 is a wireless interface 124, and the nodes 110, 120, 129 are wireless network nodes. The access node 120 is a cellular radio transceiver. The terminal nodes 110 are cellular radio transceivers. In the example illustrated the cellular network 100 is a third generation Partnership Project (3GPP) network in which the terminal nodes 110 are user equipment (UE) and the access nodes 120 are base stations. In the particular example illustrated the network 100 is an Evolved Universal Terrestrial Radio Access network (E-UTRAN). The E-UTRAN consists of E-UTRAN NodeBs (eNBs) 120, providing the E-UTRA user plane and control plane (RRC) protocol terminations towards the UE 110. The eNBs 120 are interconnected with each other by means of an X2 interface 126. The eNBs are also connected by means of the S1 interface 128 to the Mobility Management Entity (MME) 129. In other example the network 100 is a Next Generation (or New Radio, NR) Radio Access network (NG-RAN). The NG-RAN consists of gNodeBs (gNBs) 120, providing the user plane and control plane (RRC) protocol terminations towards the UE 110. The gNBs 120 are interconnected with each other by means of an X2 / Xn interface 126. The gNBs are also connected by means of the N2 interface 128 to the Access and Mobility management Function (AMF). A user equipment 110 comprises a mobile equipment. Where reference is made to user equipment 110 that reference includes and encompasses, wherever possible, a reference to mobile equipment. FIG. 2 shows a first example of an apparatus 200. The apparatus 200 may be network node 110 of a radio telecommunications network 100. In some examples, the apparatus 200 is a user equipment 110. The illustrated apparatus 200 comprises: a first antenna port 210; a second antenna port 220; a first transmission pathway 211 for the first antenna port 210; a second transmission pathway 221 for the second antenna port 220; a first further pathway 212 for the first antenna port 210; a second further pathway 222 for the second antenna port 220; a first additional pathway 213 for the first antenna port 210; a second additional pathway 223 for the second antenna port 220; means for switching 230; an amplitude detector 240; a first phase adjustment means 251; and a second phase adjustment means 252. The first transmission pathway 211 is for conveying a signal to the first antenna port 210, and the second transmission pathway 221 is for conveying a signal to the second antenna port 220. The first further pathway 212 is for conveying signals from or to the first antenna port 210 depending on the state of the switching means 230. The second reception pathway 222 is for conveying a signal from or to the second antenna port 220 depending on the state of the switching means 230. In the example of FIG. 2, the first further pathway 212 and the second further pathway 222 can function as reception pathways 212,222 or as part of the transmission pathways 211, 221 depending on the state of the switching means 230. In other examples, such as in the example of FIG. 3, all or part of the first further pathway 212 and the second further pathway 222 may function as reception pathways but not as transmission pathways. The first further pathway 212 may be considered to be the first reception pathway 212 and the second further pathway 222 may be considered to be the second reception pathway 222. The means for switching 230 is means for switching between a first state in which a first signal is conveyed from the first further / reception pathway 212 along the first additional pathway 213 and a second signal is conveyed from the second further / reception pathway 222 along the second additional pathway 223, and a second state in which a third signal is conveyed from the first transmission pathway 211 along the first additional pathway 213 and a fourth signal is conveyed from the second transmission pathway 221 along the second additional pathway 223. The amplitude detector 240 is configured to detect a combined amplitude of a signal in the first additional pathway 213 and a signal in the second additional pathway 223. In some, but not necessarily all examples, the amplitude detector 240 is an envelope detector 240, such as a diode detector 240. In some examples, the amplitude detector 240 is for detecting a peak amplitude of the combined signals. The first phase adjustment means 251 is means 251 for adjusting a relative phase between a signal in the first additional pathway 213 and a signal in the second additional pathway 223, based at least in part on the combined amplitude detected by the amplitude detector 240. The second phase adjustment means 252 is means 252 for adjusting a relative phase between a signal in the first transmission pathway 211 and a signal in the second transmission pathway 221, based at least in part on the combined amplitude detected by the amplitude detector 240. The illustrated first phase adjustment means 251 may be positioned in the first additional pathway 213 and / or the second additional pathway 223. The illustrated second phase adjustment means 252 may be positioned in the first transmission pathway 211 and / or the second transmission pathway 221. The first phase adjustment means 251 and second phase adjustment means 252 are shown in FIG. 2 with dashed lines to illustrate this. In some, but not necessarily all examples, the first phase adjustment means 251 is configured to adjust the relative phase when the means for switching 230 is in the first state; and the second phase adjustment means 252 is configured to adjust the relative phase when the means for switching 230 is in the second state. In some, but not necessarily all examples, the first phase adjustment means 251 comprises means for optimizing the relative phase between a signal in the first additional pathway 213 and a signal in the second additional pathway 223 to produce a largest combined amplitude; and the second phase adjustment means 252 comprises means for optimizing a relative phase between a signal in the first transmission pathway 211 and a signal in the second transmission pathway 221 to produce a largest combined amplitude. The combined amplitudes are as measured by the amplitude detector 240. In some examples, the largest combined amplitude is at or close to the largest combined amplitude. In some examples, the first phase adjustment means 251 determines an optimized value of the relative phase between a signal in the first additional pathway 213 and a signal in the second additional pathway 223, and subsequently, whilst the relative phase between a signal in the first transmission pathway 211 and a signal in the second transmission pathway 221 is being optimized by the second phase adjustment means 252, the relative phase between a signal in the first additional pathway 213 and a signal in the second additional pathway 223 is kept at the optimized value which was previously determined by the first phase adjustment means 251. In some examples, the first phase adjustment means 251 and / or the second phase adjustment means 252 are configured to maintain their relative phases once the relative phases have been optimized. The first phase adjustment means 251 and / or the second phase adjustment means 252 may be configured to maintain the relative phase for subsequent transmission of a signal by the first transmission pathway 211 and / or the second transmission pathway 221. In some examples, the first phase adjustment means 251 is not used for subsequent transmission or reception and so it does not need maintain the relative phase value. The first transmission pathway 211, second transmission pathway 221, first further / reception pathway 212, second further / reception pathway 222, first additional pathway 213 and second additional pathway 223 are each a pathway for conveying electrical signals. The pathways are configured for conveying radio frequency signals. In some examples the pathways are transmission lines and may comprise, and are not limited to: microstrip, stripline, coplanar waveguides (CPW), coplanar strips, slotline, coaxial cables, microwave tubes, and / or waveguides. An example of a method of use of the apparatus 200 is described below: The switching means 230 is set to the first state and a signal, such as a reference signal, is received by the antenna ports 210, 220. A first signal received by the first antenna port 210 is conveyed from the first reception pathway 212 along the first additional pathway 213 and a second signal received by the second antenna port 220 is conveyed from the second reception pathway 222 along the second additional pathway 223. The first and second signal are conveyed along their respective additional pathways 213, 223 until the signals reach the amplitude detector 240. Here the amplitude detector 240 detects the combined amplitude of the first and second signals. Whilst the switching means 230 is in the first state, the first phase adjustment means 251 adjusts the relative phase between the first and second signals. This may involve sweeping through a range of phases. The first and second signals likely originated from the same or a similar signal, when it was transmitted by another node, and so are largely similar. However, the first and second signals may have different amplitudes and phases due to a number of different factors. For example, the different characteristics of antennas connected to antenna port 210 and 220 and used for receiving the signals. The characteristics of the antennas connected to antenna port 210 and 220 including the relative phase difference is dependent on the angular direction of the incoming signal. Other factors, include the different paths the signals have taken and any components in the paths. For example, the tolerances of one or more electrical / electronic components in a path can vary in terms of mechanical (i.e. dimensional) variance due to manufacturing tolerances and / or temperature effects of one or more electrical / electronic component during operation / use. If the first and second signals are added in phase the detected combined amplitude will be at, or close to, its largest, whereas if the first and second signals are not added in phase, the detected combined amplitude will be smaller. The first phase adjustment means 251 will adjust the relative phase until the largest combined amplitude is found. The relative phase value providing the largest combined amplitude is considered the optimum phase value and represents a phase difference which is at least partially caused by antennas connected to antenna port 210 and 220 for that given angular direction of the received signals. Subsequently, the first phase adjustment means 251 maintains its optimum phase value, the switching means 230 switches from the first state to the second state, and a signal, such as a reference signal, is transmitted along the transmission pathways 211,221. A third signal is conveyed from the first transmission pathway 211 along the first additional pathway 213 and a fourth signal is conveyed from a second transmission pathway 221 along the second additional pathway 223. The third and fourth signal are conveyed along the respective additional pathways 213, 223 until the signals reach the amplitude detector 240. Here the amplitude detector 240 detects the combined amplitude of the third and fourth signals. The apparatus 200 generates the third and fourth signals to be the same or similar, and so they are largely similar. However, they may have different amplitudes and phases. This can be due to a number of factors, including the different paths the signals have taken and any components or obstacles in these paths. Whilst the switching means 230 is in the second state, the second phase adjustment means 252 adjusts the relative phase between the third and fourth signals until the largest combined amplitude is found. The relative phase value providing the largest combined amplitude is considered the optimum phase value and represents the relative phase difference of the transmitted signals to ensure optimum power combining at the antennas connected to antenna port 210 and 220 for the given angular direction. This optimum relative phase difference is then maintained for transmission of signals along the transmission pathways 211, 221 and by the antenna ports 210, 220. For future reception of signals, the first phase adjustment means 251 may be set to zero phase shift, or separate reception pathways 416, 426 may be used as shown in FIG. 4. The above calibration is dynamic. It may be repeated periodically, for example with a period of 100-200 ms, or in response to a trigger such as a receiving a valid reference signal. This above method sets the second phase adjustment means 252 at a value that ensures optimum power combining at antennas connected to antenna port 210, 220 of a transmission signal. Therefore, the relative phase difference between antennas for transmission is set to be substantially the same to the relative phase difference between antennas for reception. This leads to the best signal performance, as this can be achieved when the relative phase difference between reception (Rx) paths, is equal or very close to the relative compensated phase difference between transmission (Tx) paths. The apparatus 200, provides the technical effect of optimizing relative phase differences in a simple energy efficient manner, whilst minimizing the need for new components. FIG. 3 shows a second example of an apparatus 300. The second example of an apparatus 300 can comprise some or all of the features of the first example of an apparatus 200 of FIG. 2. The apparatus 300 further comprises a first antenna element 310 configured to couple to the first antenna port 210 and a second antenna element 320 configured to couple to the second antenna port 220. An antenna element 310, 320, may couple to an antenna port 210, 220 by conductive I galvanic coupling means and / or by electromagnetic I capacitive / inductive coupling means. An antenna element 310, 320 may optionally also be grounded to a radio frequency ground plane provided by the apparatus 300, where the grounding of one or both antennas 310, 320 may be provided by conductive I galvanic coupling means and / or by electromagnetic / capacitive I inductive coupling means. The first antenna element 310 is for transmission or reception of signals from and to the first antenna port 210 and the second antenna element 320 is for transmission or reception of signals from and to the second antenna port 220. In some examples, an antenna port 210, 220 can be coupled to more than one antenna element 310, 320. The apparatus 300 further comprises transceiver / baseband circuitry 360. In the illustrated apparatus 300, the first transmission pathway 211 is for conveying a signal from the transceiver 360 to the first antenna port 210; the second transmission pathway 221 is for conveying a signal from the transceiver 360 to the second antenna port 220; the first reception pathway 212 and first additional pathway 213 together are for conveying a signal from the first antenna port 210 to the transceiver 360; and the second reception pathway 222 and second additional pathway 223 together are for conveying a signal from the second antenna port 220 to the transceiver 360. The illustrated apparatus 300 further comprises a combiner 342, configured to combine the signal in the first additional pathway 213 and the signal in the second additional pathway 223. This combined signal is then passed to the amplitude detector 240 to detect the combined amplitude. The illustrated means for switching 230 comprises a first switching means 231 and a second switching means 232. In some examples, the first switching means 231 and second switching means 232 may comprise single pole double throw (SPDT) switches. The first switching means 231 is configured to switch between a first signal being conveyed from the first reception pathway 212 along the first additional pathway 213, and a third signal being conveyed from the first transmission pathway 211 along the first additional pathway 213. The second switching means 232 is configured to switch between a second signal being conveyed from the second reception pathway 222 along the second additional pathway 223 and a fourth signal being conveyed from the second transmission pathway 221 along the second additional pathway 223. Therefore, the first switching means 231 and second switching means 232 together are configured to switch between the first state and the second state. In the example of FIG. 3, the apparatus 300 also comprises a third switching means 333 and a fourth switching means 334. These may be considered part of the switching means 230. The third switching means 333 is configured to switch between the first antenna port 210 being connected to the first transmission pathway 211 or being connected to the first reception pathway 212. The fourth switching means 334 is configured to switch between the second antenna port 220 being connected to the second transmission pathway 221 or being connected to the first reception pathway 222. The illustrated apparatus 300 also comprises a first coupler 335 and a second coupler 336. The first coupler 335 is configured to couple at least a portion of a signal from the first transmission pathway 211 to the first additional pathway 213. The second coupler 336 is configured to couple at least a portion of a signal from the second transmission pathway 221 to the second additional pathway 223. The first coupler 335 and second coupler 336 may be directional couplers. In the illustrated example, the first phase adjustment means 251 comprises a first phase shifter 351, and the second phase adjustment means 252 comprises a second phase shifter 352. The illustrated first phase shifter 351 is positioned in the second additional pathway 223 and the illustrated second phase shifter 352 is positioned in the first transmission pathway 211. As such, the second additional pathway 223 comprises a first phase shifter 351, and the first transmission pathway 211 comprises a second phase shifter 352. In other examples the first and second phase shifters 351, 352 may be positioned differently, for example, the first phase shifter 351 is positioned in the first additional pathway 213 and / or the second phase shifter 352 is positioned in the second transmission pathway 221. The first phase shifter 351 is configured to control the relative phase between a signal in the first additional pathway 213 and a signal in the second additional pathway 223; and the second phase shifter 352 is configured to control the relative phase between a signal in the first transmission pathway 211 and a signal in the second transmission pathway 221. As such, when the signals are combined different relative phases will lead to different combined amplitudes. The illustrated first and second transmission pathways 211, 221 each comprises a first part 211a, 221a from the transceiver 360 to the coupler 335, 336 and a second part 221b from the coupler 355, 366 to the third / fourth switching means 333, 334. A further part 315, 325 from the third / fourth switching means 333, 334 can be considered to form part of the respective transmission pathway 211, 221 or the respective reception pathway 212, 222. In some examples the transmission pathway 211, 221 only comprises the first part 211a, 221a. The illustrated apparatus 300 further comprises a controller 370 configured to control aspects of the apparatus 300, for example, the controller 370 is configured to control the switching means 230, the phase shifters 351, 352 and / or to control transmission and / or reception of signals. FIG. 4 shows a third example of an apparatus 400. The third example of an apparatus 400 can comprise some or all of the features of the first and second examples of an apparatus 200, 300. The third example of an apparatus 400 is similar to the second example of an apparatus 300 with a number of differences. The apparatus 400 comprises a first further reception pathway 416 and a second further reception pathway 426. The first further reception pathway 416 is for conveying a signal from the first antenna port 210 to the transceiver 360, and the second further reception pathway 426 is for conveying a signal from the second antenna port 220 to the transceiver 360. In some examples, the first and second reception pathways 212, 222 are used for calibration I optimization of the relative phase difference for the transmission pathways 211,221; and the first and second further reception pathways 416, 426 are used for subsequent reception of signals. In the example of FIG. 4, the third switching means 433 and fourth switching means 434 are each configured to switch between their respective antenna port 210, 220 being connected to their respective transmission pathway 211, 221, reception pathway 212, 222, and further reception pathway 416, 426. The illustrated third and fourth switching means 433, 434 are set to the reception pathway 212, 222 for calibration of the phase difference between signals in the additional pathways 213, 223. The third and fourth switching means 433, 434 may be set to any of the three positions for calibration of the phase difference between signals in the transmission pathways 211, 221, however being set to the transmission pathway 211, 221 may lead to more accurate phase calibration as the load on any components will be close to or the same as for transmission. The illustrated third and fourth switching means 433, 434 may be set to the further reception pathways 416, 426 for reception of subsequent signals. In some examples, a pre-tuning of calibration of the second phase shifter 352 may be performed whilst the third and fourth switching means 433, 434 are not set to the transmission pathway 211, 221 and subsequently a final calibration of the second phase shifter 352 is performed whilst the third and fourth switching means 433, 434 are set to the transmission pathway 211, 221. This reduces the amount of time that the apparatus 400 is transmitting a signal, which can reduce resources used by other network nodes which can receive and process the signal. The illustrated transmission pathways 211, 221 each comprise an amplifier 417, 427 for amplifying signals in the transmission pathway 211,221. In some examples these amplifiers 417, 427 are power amplifiers. The illustrated further reception pathways 416, 426 each comprise an amplifier 418, 428 for amplifying signals in the further reception pathway 416, 426. In some examples these amplifiers 418, 428 are low noise amplifiers. In the illustrated example, the amplifier 417 in the first transmission pathway 211 is positioned closer to the first antenna port 210 than the second phase shifter 352 is positioned relative to the first antenna port 210. In other words, in a direction along the first transmission pathway 211 from the transceiver 360 to the first antenna port 210, the second phase shifter 352 is positioned before the amplifier 417. In other examples, the second phase shifter 352 is positioned after the amplifier 417. The illustrated first additional pathway 213 comprises an attenuator 443 which is configured to match the attenuation caused by the first phase shifter 351 in the second additional pathway 223. The attenuator 443 is configured to achieve same power relation between signals at the inputs to the combiner 342 as at the antenna ports 210, 220. In the example of FIG. 4, the apparatus 400 further comprising a variable amplifier 441 which is positioned between the combiner 342 and the amplitude detector 240. The variable amplifier 441 is configured to adjust the combined amplitude. This can be advantageous as there may be a significant difference in amplitude between transmitted and received signals, which may be larger than the dynamic range of the amplitude detector 240. The variable amplifier 441 can thus adjust the amplitude of signals so as to be within the dynamic range. It will be appreciated that it is advantageous to not to vary the variable amplifier 441 whilst changing the relative phase of the first or second phase adjustment means 251,252 so as to avoid errors in determining the optimum relative phase. In some examples, the apparatus 400 may comprise more than two reception pathways 212, 222, 212n, more than two transmission pathways 211, 221,211n and more than two antenna ports 210, 220, 210n. The number of reception pathways 212, 222, 212n, the number of transmission pathways 211, 221,211n and the number of antenna ports 210, 220, 21 On could be the same or different. Three different examples of apparatuses with more than two antenna ports 210, 220, 210n can be seen in FIGs 5, 6 and 7. FIG. 5 shows a fourth example of an apparatus 500. The fourth example of an apparatus 500 can comprise some or all of the features of the first, second and third examples of an apparatus 200, 300, 400. The fourth example of an apparatus 500 is similar to the third example of an apparatus 400 with a number of differences. The apparatus 500 of FIG. 5 comprises more than two antenna elements 310, 320, 310n, and more than two antenna ports 210, 310, 31 On. In the illustrated example three antenna elements 310, 320, 31 On are present, however in other examples, more antenna elements 310, 320, 31 On may be present as indicated by the three dots. In some examples, in a similar manner to for the first and second antenna elements 310, 320, the n additional antenna elements 31 On (only one additional antenna element 31 On being illustrated) have switching means 433n amplifiers 418n, reception pathways 212n and further reception pathways 416n associated with the additional antenna element 31 On. In FIGs 5, 6 and 7, the further reception pathways 416, 426, 416m, 416n are not shown in full to improve clarity of the figures. For example in FIG. 5 for the first further reception pathway 416 the two parts labeled RX1 are linked together. The illustrated apparatus 500 also comprises a multiplexer 230 which may form at least part of the switching means 230. In some examples, a multiplexer 230 is used even if only two antenna ports 210, 220 are present. The multiplexer 230 is configured to switch between the first and second states as discussed above. Additionally, the illustrated multiplexer 230 is configured to switch between further states. For example, a state in which a first signal is conveyed from the first reception pathway 212 along the first additional pathway 213 and a further signal is conveyed from the nth reception pathway 212n along the second additional pathway 223. In some examples, the optimum relative phase between the antenna ports 210, 220, 210n may be calibrated in pairs. For example, for the first and second antenna ports 210, 220, and subsequently for the first and third antenna ports 210, 220n and then subsequently for the first and nth antenna ports 210, 220n. In some examples, calibration of pairs may include additional and / or different pairs, such as the second and nth antenna ports 220, 210n, third and nth antenna ports 21 On, etc. The illustrated apparatus 500 comprises a front-end 560 and a transceiver 360. In the example of FIG. 5 the amplitude detector 240 is located within the transceiver 360, whereas in the examples of FIGs 3 and 4 the amplitude detector 240 is located outside the transceiver 360, in the front-end 560. As such, in the example of FIG. 5 the amplitude detector 240 is configured to receive signals after down-conversion and system band filtration, instead of receiving signals in the radio frequency (RF) domain, before conversion. In some examples, the amplitude detector 240 may be positioned after an analogue to digital converter 504. In such examples, the amplitude detector 240 is configured to receive signals in the digital domain. In other examples, other components may be positioned within the transceiver 360, instead of or in addition to the amplitude detector 240, such as the combiner 342 and the first phase shifter 351. In some examples, any or all of the components in the front-end 560, other than the antenna elements 310, 320, 31 On, can be positioned within the transceiver 360 as analogue and / or digital versions of the components. In some examples, the transceiver 360 is a chipset such as a radio-frequency integrated circuit (RFIC). In some examples, the front-end 560 is a separate chipset I RFIC. The transceiver 360 may be of any suitable form and comprise any suitable components. The illustrated transceiver 360 comprises a controller 370, a demodulator 502, an analogue to digital converter 504, a correlator 506, timing circuitry 508, a data store 510 and a receiver 512. FIG. 6 shows a fifth example of an apparatus 600. The fifth example of an apparatus 600 can comprise some or all of the features of the first, second, third and fourth examples of an apparatus 200, 300, 400, 500. In the example of FIG. 6 an existing receiver pathway already present in smartphones is used for the combined power detection. The fifth example of an apparatus 600 is similar to the third and fourth examples of an apparatus 400, 500 with a number of differences. The apparatus 600 of FIG. 6 comprises four antenna elements 310, 320, 310m, 310n, four antenna ports 210, 220, 210m, 21 On, four further switching means 433,434, 433m, 433n, four reception pathways 212, 222, 212m, 212n, four further reception pathways 416, 426, 416m, 416n, two transmission pathways 211,221, and two additional pathways 213, 223. This is one of a number of examples in which there are equal numbers of reception pathways 212, 222, 212m, 212n and antenna ports 210, 220, 210m, 210n, and a smaller number of transmission pathways 211,221. The illustrated apparatus 600 also comprises a diversity front-end module 650, first additional switching means 637, second additional switching means 638 and third additional switching means 639. In the example of FIG 6, the switching means 230 comprises the first, second, third and fourth switching means 231, 232, 433, 434, 433m, 433n and the first, second and third additional switching means 637, 638, 639. In this example, the switching means 230 comprises further means for switching between a signal being conveyed from the second reception pathway 222 along the second additional pathway 223; and a signal being conveyed from the third reception pathway 212m along the second additional pathway 223. This may involve the first and / or the second additional switching means 637, 638 switching between a signal being conveyed from the second reception pathway 222 along the second additional pathway 223; and a signal being conveyed from the third reception pathway 212m along the second additional pathway 223. Additionally, in this example, the first state of the means for switching 230 can comprise a second signal being conveyed from the second reception pathway 222 along the second additional pathway 223 or a second signal being conveyed from the third reception pathway 212m along the second additional pathway 223. Many other switching variations are possible, as can be seen in FIG. 6. FIG. 7 shows a sixth example of an apparatus 700. The sixth example of an apparatus 700 can comprise some or all of the features of the first, second, third, fourth and fifth examples of an apparatus 200, 300, 400, 500, 600. The sixth example of an apparatus 700 is similar to the third, fourth and fifth examples of an apparatus 400, 500, 600 with a number of differences. The apparatus 700 of FIG. 7 comprises four antenna elements 310, 320, 310m, 310n, four antenna ports 210, 220, 210m, 21 On, four further switching means 433,434, 433m, 433n, four reception pathways 212, 222, 212m, 212n, four further reception pathways 416, 426, 416m, 416n, four transmission pathways 211, 221, 211m, 211n and four additional pathways 213, 223, 213m, 213n. The illustrated apparatus 700 also comprises four couplers 335, 336, 335m, 335n, which are positioned between the antenna ports, 210, 220, 210m, 210n and the switching means 230. In the example of FIG. 7, the amplitude detector 240 is not shown and it is positioned inside the transceiver 360. Each of the illustrated four additional pathways 213, 223,213m, 213n comprises an attenuator 443, and three of the additional pathways 223, 213m, 213n comprise a first phase shifter 351, 351m, 351 n. Each of the illustrated four transmission pathways 211, 212, 211m, 211n comprises an amplifier 417, 427, 417m, 417n, and three of the transmission pathways 212, 211m, 211n comprises a second phase shifter 352, 352m, 352n. This is one of a number of examples in which there are an equal number of reception pathways 212, 222, 212m, 212n, transmission pathways211,212, 211m, 211n and antenna ports210, 220, 210m, 210n. In the example of FIG 7, the switching means 230 comprises the first, second, third and fourth switching means 231,232, 231m, 231 n, 433, 434, 433m, 433n and the third additional switching means 639. In this example, the means for switching 230 comprises means for switching 230 between a first, second, third and fourth state. In the first state a first signal is conveyed from the first reception pathway 212 along the first additional pathway 213 and a second signal is conveyed from the second reception pathway 222 along the second additional pathway 223 In the second state a third signal is conveyed from the first transmission pathway 211 along the first additional pathway 213 and a fourth signal is conveyed from the second transmission pathway 221 along the second additional pathway 223. In the third state the first signal is conveyed from the first reception pathway 212 along the first additional pathway 213 and a fifth signal is conveyed from the third reception pathway 212m along the third additional pathway 213m. In the fourth state the third signal is conveyed from the first transmission pathway 211 along the first additional pathway 213 and a sixth signal is conveyed from the third transmission pathway 211m along the third additional pathway 213m. Many other switching variations are possible, as can be seen in FIG. 7. In this example, the amplitude detector 240 is configured to detect a combined amplitude of a signal in the first additional pathway 213 and a signal in the second additional pathway 223, or a combined amplitude of a signal in the first additional pathway 213 and a signal in the third additional pathway 213m. The apparatus 700 comprises means 351m for adjusting a relative phase between a signal in the first additional pathway 213 and a signal in the third additional pathway 213m based at least in part on the detected combined amplitude. The apparatus 700 may be configured to detect a combined amplitude and / or adjust a relative phase for other pairs of signals. Such as: signals in the first and fourth additional pathways 213, 213n; signals in the second and third additional pathways 223, 213m; signals in the second and fourth additional pathways 223, 213n; and / or signals in the third and fourth additional pathways 213m, 213n. A prerequisite for well performing uplink (UL) MIMO when using baseband channel estimation in downlink (DL) as a reference (based on radio channel reciprocity in time division duplex (TDD) mode) to control the uplink signal precoding is: • the phase signal difference between selected Rx paths 212, 222 from antenna ports 210, 220 to the baseband 360, is equal or very close to the phase signal difference between selected Tx paths 211, 221 from baseband 360 to the antenna ports 210, 220. FIG. 8 illustrates an example Rx-Tx MIMO system 800 at a user equipment 110, with two antennas 310 (T) and 320 (‘2’). The example system 800 comprises two antenna ports 210, 220, two antenna tuners / switches 805, 806, and two switches 831, 832 which switch between reception paths and transmission paths. The two illustrated reception paths comprise, a DL baseband unit 860a, a RF transceiver 360a, low noise amplifiers 418, 428, filters 821, 822 and optionally other component such as multiplexers. The two illustrated transmission paths comprise, a UL baseband unit 860b, a RF transceiver 360b, power amplifiers 417, 427, filters 823, 824 and optionally other component such as multiplexers. Phase values can be measured at different measurement points as given by the following variables, where the feed points are at or near the antenna ports 210, 220 and the baseband points is at or near the basebands 360a 360b: > Antenna 1 for reception: feed point Rx ‘0_ant1_rx1’, Baseband 1 Rx 0_bb_rx1’. > Antenna 2 for reception: feed point Rx ‘0_ant1_rx2’, Baseband n Rx ‘0_bb_rx2’. > Antenna 1 for transmission: feed point Tx ‘0_ant1_txT, Baseband 1 Tx ‘0_bb_tx1’. > Antenna 2 for transmission: feed point Tx ‘0_ant1_tx2’, Baseband n Tx ‘0_bb_tx2’. In the example of FIG. 8 the feed points are the same for both reception and transmission whilst the baseband points are different for reception and transmission. The phase differences between the above variables can be defined as: > at antenna feed points Rx : ‘△0_ant_rx’ = 0_ant1_rx1 - 0_ant1_rx2 > at antenna feed points Tx : ‘A0_ant_tx’ = 0_ant1_tx1 - 0_ant1_tx2 > at baseband points Rx : A0_bb_rx’ = = 0_bb_rx1 - 0_bb_rx2 > at baseband points Tx : A0_bb_tx - 0_bb_tx1 - 0_bb_tx2. A prerequisite for best precoding (both codebook and non-codebook based) of an UL signal based on and Rx signal is that the downlink relative phase variation between ‘A0_ant_rx’ and ‘△0_bb_rx’ would be close or equal to the uplink relative phase variation between ‘A0_bb_tx’ and ‘A0_ant_tx’. Consider the example system 800 of FIG. 8, in which Rx is DL and Tx is UL. The signals received in the DL direction may go through an antenna switch / tuner 805 or 806, RF filters 821 or 822, multiplexers, and a low noise amplifier (LNA) 418 or 428 to the transceiver unit 360a where it is digitized into IQ samples before reaching the baseband unit (BB DL) 860a. In the baseband unit 860a, the signal phase per path is estimated by a channel estimation process and can be used as reference for the UL phase control of the signal, which is controlled at the uplink baseband unit (BB UL) 860b. From the BB UL unit 860b these signals may go through a UL RF transceiver 360b, a Power Amplifier (PA) 417 or 427 and other RF filters 823 or 824 and multiplexers, before going to an antenna switch I tuner unit 805 or 806 and an antenna element 310 or 320. A key for accurate uplink phase control is phase variation symmetry between the downlink paths and the uplink paths. However, there are numerous sources of DL-UL phase asymmetry difference between paths: > LNAs have different properties than PAs > The phase behavior of filters in DL and UL > The antenna tuner > Difference caused by the external conditions. For example a user hand / finger grabbing the device. A possible approach for this is to calibrate out the sources of phase asymmetry in a laboratory setting, and then use calibration tables to compensate for the phase differences in the UL baseband unit. Such a calibration may be done in a conductive manner (50 Q) in the lab and provide a table of values. The problems with such a calibration approach are not only the expensive and time-consuming procedure it involves but also that the compensation / calibration is static for a given set of settings. However, antennas 310, 320 change their impedance as a function of frequency and will actually rarely be 50 Q. This affects the input impedance of the LNA 418, 428 and the output impedance of the PA 417, 427. The input of an LNA 418, 428 is less sensitive to impedance changes than the output of a PA 417, 427, whereby the PA 417, 427 will contribute to larger variation of the phase than the LNA 418, 428, making a conducted calibration inaccurate. In addition, user behavior will affect the antenna impedance even more. As such a dynamic real-life calibration of the phase differences between DL and UL is advantageous to ensure best possible UL performance. In order to quantify the combined antenna gain loss due to either unknown or wrong phase calibration at the UE 110 a series of simulations were conducted. Some examples of the gain loss due to phase error are presented in Table 1 below, where it can be seen that incorrect phase setting can result in a combined antenna gain loss more than 30 dB. Incorrect phase settings 0° 30° 60° 90° 120° 150° 180° Gain improvement 3.3 dB 3.1 dB 2.0 dB 0.0 dB -4.0 dB -10.0 dB -27.3 dB Delta Gain loss OdB 0.2 dB 1.3 dB 3.3 dB 7.3 dB 13.3 dB 30.6 dB Table 1: Extract of simulations with the impact of phase error for a two antenna 310, 320 system. A problem to solve is: how to enable a more accurate uplink dynamic real-life phase control between antennas 310, 320 in a UE 110 or another network node 110? This problem can be broken down into two sub-problems: Sub-problem one: how to measure / estimate the received phase difference between antenna feeding points? With digital estimation of phase inaccuracies between signal paths per used antenna 310, 320, the UE 110 modem estimates the phase difference at the BB DL unit and is thus unaware of how much the signal phase has changed from the antenna feeding points all the way down to the baseband unit. Therefore, the BB DL unit does not know the potential phase asymmetry between the DL received paths from antenna feeding point all the way to the BB DL. Sub-problem part two: how to measure / estimate the transmitted phase difference between antenna feeding points? The UL phase control may be controlled digitally in the BB UL module by using the estimated phase values in the BB DL unit. However, the UE 110 is unaware of how much the signal phase is affected from the BB UL unit to the antenna feeding points. Embodiments of the disclosure enable the UE 110 to estimate received and transmitted phase differences at individual antenna feed points 210, 220 or as close to the antennas 310, 320 as the RF front-end 560 design allows. This is achieved by using an analogue Differential Phase Estimation Circuit (DPEC) as shown in FIGs 3 and 4. In the example of FIG. 3, the DPEC comprises the first phase shifter 351, the combiner 342, the amplitude detector 240, the first, second, third and fourth switching means 231, 232, 333, 334, as well as relevant pathways. In the example of FIG. 4 the DPEC comprises the first phase shifter 351, the combiner 342, the amplitude detector 240, the first, second, third and fourth switching means 231,232, 433, 434, the variable amplifier 441 and the attenuator 443, as well as relevant pathways. In other examples the DPEC may comprise different elements. In this example, one or two UL layers are mapped onto two antenna elements 310, 320. The DPEC may be integrated into a RF front-end 560 by the addition of its components. In this example, received DL signals can be switched (using third and fourth switching means 333, 334 433, 434) to the DPEC, which can then optimize these combined received signals for the peak / maximum power, by quickly (within a symbol time) sweeping the first phase shifter 351, and using the amplitude detector 240 to find the power level. The phase setting of the first phase shifter 351 for maximum power at the amplitude detector 240 represents the current phase difference of the received signals. The UE 110 can perform this DL phase estimation using any appropriate DL reference signals. In the illustrated example, it may be preferable to use signals for which it is not required to feedback demodulated results to the gNB 120, for example reference signals like synchronization signal block beam (SSB) or channel state information reference signal (CSI-RS). The amplitude detector 240 is placed in the RF domain in this example. However, in other examples the amplitude detector 240 is placed in the transceiver 360. This may be a practical implementation with better accuracy. The UL phase calibration is performed by switching the forward feedback receiver signals, from couplers 335, 336 to the DPEC. The optimum DL phase setting of the phase shifter 351 is kept constant, while the second phase shifter 352 (analog or digital) is quickly swept for the maximum power level at amplitude detector 240. The couplers 335, 336 help to ensure that the UL phase alignment / calibration is performed with the correct load at the output of the power amplifiers (PA) 417, 427. In some examples, these couplers 335, 336 are already part of the RF front-end 560 design, as they are used for PA 417, 427 power control, like digital predistortion and envelope tracking. The UL phase optimization / calibration can be performed on any UL signals, as long as the feedback receiver paths from the couplers 335, 336 are switched to the DPEC. That is, the switching means 230 is set to the second state in which a third signal is conveyed from the first transmission pathway 211 along the first additional pathway 213 and a fourth signal is conveyed from the second transmission pathway 221 along the second additional pathway 223. The feedback receiver path from the couplers 335, 336, may be used for PA 417, 427 power control. In this example they are directly connected to the DPEC. However, in other examples further switches are present such as a SPDT switch to toggle between the DPEC and the RF transceiver 360. Keeping the optimum DL value of the first phase shifter 351 constant, while optimizing the second phase shifter 352, will ensure an optimized relative UL phase setting at the antennas 310, 320, for the current channel conditions, user interaction and angle of arrival (AoA) at the UE 110. The following provides an example of calibration to find the optimum phase setting for the UL signal: 1. Rx dynamic calibration, switch 433 set to the bottom and switch 434 set to the top in FIG. 4: A reference signal is provided by a gNB 120 in the downlink direction to the UE 110. During reception of the reference signal the first phase shifter 351 is tuned to different settings. The RF power output from the combiner 342 is maximized when the RF signals from the two antenna ports, 210, 220 are phase aligned and added together. The optimum phase setting is the phase setting used at the first phase shifter 351 when the largest detected signal or voltage is observed at the output of the amplitude detector 240. 2. Tx dynamic calibration, switches 433 and 434 set to the middle in FIG. 4: The second phase shifter 352 is set to a default state, for example 0 degrees. The optimum Tx phase difference can be determined by any transmitted signal as those signals are coupled to the DPEC circuit via couplers 335, 336. As such, no special reference signal is needed. The second phase shifter 352 is tuned, while the first phase shifter 351 is kept constant at the optimized value, until a maximum signal is measured at the output of the amplitude detector 240. The phase setting of the second phase shifter 352, where a maximum signal is observed at the output from the amplitude detector 240 is the optimum phase setting for the UL transmission. 3. Switch 433 set to the top, switch 434 set to the bottom in FIG. 4: Normal Rx / DL mode using the further reception pathways 416, 426. Examples of the disclosure ensure optimum power combining between the selected antennas 310, 320 at any AoA for the UL MIMO signals. In addition, the concept is agnostic against, and so accounts for: > Fading and multipath. > The AoA of the RF signal. > Details about reflected and direct signals and combinations thereof. > Antenna radiation pattern. > Head and hand effects due to user interaction. Amplitude and phase balance for the DPEC concept help to ensure optimum UL phase calibration. As such, for the phase balance, it can be advantageous for the following electrical distances to be short (compared to the wavelength), symmetrical and / or known: 1. The electrical distance from the couplers 335, 336, which in this example is the reference point for the UL phase calibration, to the third and fourth switching means 433, 434, which in this example is the reference point for the DL phase calibration. 2. The electrical distance from the couplers 335, 336 to the DPEC phase reference point at the combiner 342. 3. The electrical distance from the third and fourth switching means 433, 434, to the DPEC phase reference point at the combiner 342. In some examples, these electrical distances can be calculated from the physical distances and the currently used system frequency. In some examples, electrical distances might not be short for practical implementation reasons, in particular if very high frequencies are used (greater than 24.25 GHz which may be the case for Frequency Range 2 in 5G). In these examples, if the electrical distances are not short relative to the wavelength, phase symmetry can be obtained by ensuring that the same phase or delay is obtained from the first antenna port 210 to the combiner 324 as from the second antenna port 220 to the combiner 342. Likewise from the couplers 335 and 336 to the combiner 342. The amplitude balance at the combiner 342 is controlled by the tunable attenuator 443, which is to match the insertion loss of first phase shifter 351 for different phase delay settings, to ensure that power imbalance at the antennas 310, 320 is equal to the power imbalance at the combiner 342. Alternative placement of the DPEC amplitude detector 240: In FIG. 4 the amplitude detector 240 is placed in the RF domain and the measurements are performed as Received Signal Strength Indicator (RSSI) values. Such an implementation is valid in conditions with low interference, as received signals are the intended signals. However, that is not necessarily the situation for mobile communication, which can lead to incorrect phase estimations. This issue can be counteracted by moving the amplitude detector 240 inside the transceiver 360, after the down-conversion and system band filtration, as shown in FIG. 5. This implementation helps to ensure that the phase measurements are performed on signals received at the correct frequency range. The received signal can also be decoded in parallel to the calibration to ensure that the phase measurements are done on the correct and intended signals. Dual-layer MIMO support on an RF front-end 560 with four antennas 310, 320, 310m, 310n: A RF front-end 560 implemented with four antennas 310, 320, 310m, 310n and with support for dual layer MIMO including the DPEC concept is shown in FIG. 6. Switches 231, 232, 433, 434, 433m, 433n are of the substantially the same design as for the implementation described in FIG. 4 and the functionally is also substantially the same. Added complexity can be seen in the first and second additional switching means 637, 638, which switch received signals from the antennas 310, 320, 310m, 310n to either the transceiver 360 or the DPEC and also switch transmitted signals to either the antenna 310, 320, 310m, 310n or the DPEC. Such complex switching arrangements can be already present in smartphones with more antennas 310, 320, 310m, 310n than supported UL layers, which reduces the number of additional components needed. Four-layer MIMO support on an RF front-end 560 with four antennas 310, 320, 310m, 310n: a RF front-end 560 implemented with four antennas 310, 320, 310m, 310n and support for four-layer MIMO including the DPEC concept is shown in FIG. 7. This implementation is similar to the implementation described in FIG. 4. However, this implementation has more phase shifters 351, 352 and tunable attenuates 443 since signals for four antennas 310, 320, 310m, 310naretobe combined with optimum phase settings. This implementation will increase the number of the total phase setting stages of the first phase shifters 351, 351m, 351 n to sweep through the used / possible combinations. In some examples where only one MIMO layer is supported, phase alignment / calibration between multiple received signals may be performed in the baseband / transceiver 360 by use of digital signaling means. However, since the apparatuses 300, 400, 500, 600 &700 all enable phase alignment / calibration for received signals to be performed in the RF front-end hardware 560, and if the output from the power combiner 342 is fed into a receiver after the calibration of the DPEC circuitry, the receiver is already optimized for the optimum receive beamforming as the received signals are already added in phase in the combiner 342. Therefore, embodiments of the disclosure have the advantage of optimizing the relative phase of received signals for beamforming. This advantage exists even in situations where phase alignment can be performed in the baseband 360. In some examples, during reception, by use of all of the (4) antenna elements 310,320,310m, 31 On it is only required to turn on one receive chain (RF transceiver 360 and baseband). This allows for significant power to be saved. In this example, phase alignment, tuning and addition of the received signals are performed as described herein. Settings are maintained during normal reception and the phase shifters 351, 351m, 351 n are calibrated / tuned during reception of reference signals. In some examples, the amplitude detector 240 is connected in parallel with an alternative receive chain for reception of signals. This allows for signals to be received whilst the phase calibration / tuning occurs without the signals being affected by the phase calibration. FIG. 9 illustrates an example method 900 according to examples of the disclosure. In some examples the method performed by one of the examples of an apparatus 200, 300, 400, 500, 600, 700. At block 902, the apparatus 200, 300, 400, 500, 600, 700 causes switching between a first state in which a first signal is conveyed from the first reception pathway 212 along a first additional pathway 213 and a second signal is conveyed from a second reception pathway 222 along a second additional pathway 223 and a second state in which a third signal is conveyed from a first transmission pathway 211 along the first additional pathway 213 and a fourth signal is conveyed from a second transmission pathway 221 along the second additional pathway 223. At block 904, the apparatus 200, 300, 400, 500, 600, 700 causes detection of a combined amplitude of a signal in the first additional pathway 213 and a signal in the second additional pathway 223. At block 906, the apparatus 200, 300, 400, 500, 600, 700 causes adjustment of a relative phase between a signal in the first additional pathway 213 and a signal in the second additional pathway 223 based at least in part on the detected combined amplitude. At block 908, the apparatus 200, 300, 400, 500, 600, 700 causes adjustment of a relative phase between a signal in the first transmission pathway 211 and a signal in the second transmission pathway 221 based at least in part on the detected combined amplitude. FIG. 10 illustrates an example of a controller 370 suitable for use in an apparatus 200, 300, 400, 500, 600, 700. Implementation of a controller 370 may be as controller circuitry. The controller 370 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware). As illustrated in FIG. 10 the controller 370 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 1006 in a general-purpose or special-purpose processor 1002 that may be stored on a computer readable storage medium (disk, memory etc.) to be executed by such a processor 1002. The processor 1002 is configured to read from and write to the memory 1004. The processor 1002 may also comprise an output interface via which data and / or commands are output by the processor 1002 and an input interface via which data and / or commands are input to the processor 1002. The memory 1004 stores a computer program 1006 comprising computer program instructions (computer program code) that controls the operation of the apparatus 200, 300, 400, 500, 600, 700 when loaded into the processor 1002. The computer program instructions, of the computer program 1006, provide the logic and routines that enables the apparatus to perform the methods illustrated in the accompanying Figs. The processor 1002 by reading the memory 1004 is able to load and execute the computer program 1006. The apparatus 200, 300, 400, 500, 600, 700 comprises: at least one processor 1002; and at least one memory 1004 including computer program code the at least one memory 1004 and the computer program code configured to, with the at least one processor 1002, cause the apparatus 200, 300, 400, 500, 600, 700 at least to perform: causing switching between a first state in which a first signal is conveyed from the first reception pathway 212 along a first additional pathway 213 and a second signal is conveyed from a second reception pathway 222 along a second additional pathway 223 and a second state in which a third signal is conveyed from a first transmission pathway 211 along the first additional pathway 213 and a fourth signal is conveyed from a second transmission pathway 221 along the second additional pathway 223; causing detection of a combined amplitude of a signal in the first additional pathway 213 and a signal in the second additional pathway 223; causing adjustment of a relative phase between a signal in the first additional pathway 213 and a signal in the second additional pathway 223 based at least in part on the detected combined amplitude; and causing adjustment of a relative phase between a signal in the first transmission pathway 211 and a signal in the second transmission pathway 221 based at least in part on the detected combined amplitude. FIG. 10 illustrates an example of a controller 370 suitable for use in an apparatus 200, 300, 400, 500, 600, 700. Implementation of a controller 370 may be as controller circuitry. The controller 370 may be implemented in hardware alone, have certain aspects in software including firmware alone or can be a combination of hardware and software (including firmware). As illustrated in FIG. 10 the controller 370 may be implemented using instructions that enable hardware functionality, for example, by using executable instructions of a computer program 1006 in a general-purpose or special-purpose processor 1002 that may be stored on a computer readable storage medium (disk, memory etc.) to be executed by such a processor 1002. The apparatus 200, 300, 400, 500, 600, 700 comprises: at least one processor 1002; and at least one memory 1004 storing instructions that, when executed by the at least one processor 1002, cause the apparatus at least to: causing switching between a first state in which a first signal is conveyed from the first reception pathway 212 along a first additional pathway 213 and a second signal is conveyed from a second reception pathway 222 along a second additional pathway 223 and a second state in which a third signal is conveyed from a first transmission pathway 211 along the first additional pathway 213 and a fourth signal is conveyed from a second transmission pathway 221 along the second additional pathway 223; causing detection of a combined amplitude of a signal in the first additional pathway 213 and a signal in the second additional pathway 223; causing adjustment of a relative phase between a signal in the first additional pathway 213 and a signal in the second additional pathway 223 based at least in part on the detected combined amplitude; and causing adjustment of a relative phase between a signal in the first transmission pathway 211 and a signal in the second transmission pathway 221 based at least in part on the detected combined amplitude. As illustrated in FIG. 11, the computer program 1006 may arrive at the apparatus 200, 300, 400, 500, 600, 700 via any suitable delivery mechanism 1008. The delivery mechanism 1008 may be, for example, a machine readable medium, a computer-readable medium, a non-transitory computer-readable storage medium, a computer program product, a memory device, a record medium such as a Compact Disc Read-Only Memory (CD-ROM) or a Digital Versatile Disc (DVD) or a solid-state memory, an article of manufacture that comprises or tangibly embodies the computer program 1006. The delivery mechanism may be a signal configured to reliably transfer the computer program 1006. The apparatus 200, 300, 400, 500, 600, 700 may propagate or transmit the computer program 1006 as a computer data signal. Computer program instructions for causing an apparatus 200, 300, 400, 500, 600, 700 to perform at least the following or for performing at least the following: causing switching between a first state in which a first signal is conveyed from the first reception pathway 212 along a first additional pathway 213 and a second signal is conveyed from a second reception pathway 222 along a second additional pathway 223 and a second state in which a third signal is conveyed from a first transmission pathway 211 along the first additional pathway 213 and a fourth signal is conveyed from a second transmission pathway 221 along the second additional pathway 223; causing detection of a combined amplitude of a signal in the first additional pathway 213 and a signal in the second additional pathway 223; causing adjustment of a relative phase between a signal in the first additional pathway 213 and a signal in the second additional pathway 223 based at least in part on the detected combined amplitude; and causing adjustment of a relative phase between a signal in the first transmission pathway 211 and a signal in the second transmission pathway 221 based at least in part on the detected combined amplitude. The computer program instructions may be comprised in a computer program, a non-transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program. Although the memory 1004 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable and / or may provide permanent / semi-permanent / dynamic / cached storage. Although the processor 1002 is illustrated as a single component / circuitry it may be implemented as one or more separate components / circuitry some or all of which may be integrated / removable. The processor 1002 may be a single core or multi-core processor. References to 'computer-readable storage medium’, ‘computer program product’, ‘tangibly embodied computer program’ etc. or a ‘controller’, ‘computer’, ‘processor’ etc. should be understood to encompass not only computers having different architectures such as single / multi- processor architectures and sequential (Von Neumann) / parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc. The blocks illustrated in the accompanying Figs may represent steps in a method and / or sections of code in the computer program 1006. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted. Elements may be operationally coupled and any number or combination of intervening elements can exist (including no intervening elements). Where a structural feature has been described, it may be replaced by means for performing one or more of the functions of the structural feature whether that function or those functions are explicitly or implicitly described. The above-described examples find application as enabling components of: automotive systems; telecommunication systems; electronic systems including consumer electronic products; distributed computing systems; media systems for generating or rendering media content including audio, visual and audio visual content and mixed, mediated, virtual and / or augmented reality; personal systems including personal health systems or personal fitness systems; navigation systems; user interfaces also known as human machine interfaces; networks 100 including cellular, non-cellular, and optical networks; ad-hoc networks; the internet; the internet of things; virtualized networks; and related software and services. The apparatus 200, 300, 400, 500, 600, 700 may be a network node 110 of a radio telecommunications network 100. In some examples, the apparatus 200, 300, 400, 500, 600, 700 is a user equipment 110. In other examples, the apparatus 200, 300, 400, 500, 600, 700 can be a different network component such as a base station 120, a repeater, an access point, or an integrated access and backhaul (IAB) node. In some examples the apparatus 200, 300, 400, 500, 600, 700 may communicate with other nodes using ISM bands, such as: Bluetooth, Wi-Fi, and ultra-wideband (UWB). The apparatus 200, 300, 400, 500, 600, 700 can be provided in an electronic device, for example, a mobile terminal, according to an example of the present disclosure. It should be understood, however, that a mobile terminal is merely illustrative of an electronic device that would benefit from examples of implementations of the present disclosure and, therefore, should not be taken to limit the scope of the present disclosure to the same. While in certain implementation examples, the apparatus 200, 300, 400, 500, 600, 700 can be provided in a mobile terminal, other types of electronic devices, such as, but not limited to: mobile communication devices, hand portable electronic devices, wearable computing devices, portable digital assistants (PDAs), pagers, mobile computers, desktop computers, televisions, gaming devices, laptop computers, cameras, video recorders, GPS devices and other types of electronic systems, can readily employ examples of the present disclosure. The apparatus can be used in any vehicle (land based, water based or airborne or combinations thereof). Furthermore, devices can readily employ examples of the present disclosure regardless of their intent to provide mobility. The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise 3 / more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one...” or by using “consisting”. In this description, the wording ‘connect’, ‘couple’ and ‘communication’ and their derivatives mean operationally connected / coupled / in communication. It should be appreciated that any number or combination of intervening components can exist (including no intervening components), i.e., so as to provide direct or indirect connection / coupling / communication. Any such intervening components can include hardware and / or software components. As used herein, the term "determine / determining" (and grammatical variants thereof) can include, not least: calculating, computing, processing, deriving, measuring, investigating, identifying, looking up (for example, looking up in a table, a database or another data structure), ascertaining and the like. Also, "determining" can include receiving (for example, receiving information), accessing (for example, accessing data in a memory), obtaining and the like. Also, "determine / determining" can include resolving, selecting, choosing, establishing, and the like. In this description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘can’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’, ‘can’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example as part of a working combination but does not necessarily have to be used in that other example. Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims. Features described in the preceding description may be used in combinations other than the combinations explicitly described above. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain examples, those features may also be present in other examples whether described or not. The term ‘a’, ‘an’ or ‘the’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising a / an / the Y indicates that X may comprise only one Y or may comprise more than one Y unless the context clearly indicates the contrary. If it is intended to use ‘a’, ‘an’ or ‘the’ with an exclusive meaning then it will be made clear in the context. In some circumstances the use of ‘at least one’ or ‘one or more’ may be used to emphasis an inclusive meaning but the absence of these terms should not be taken to infer any exclusive meaning. The presence of a feature (or combination of features) in a claim is a reference to that feature or (combination of features) itself and also to features that achieve substantially the same technical effect (equivalent features). The equivalent features include, for example, features that are variants and achieve substantially the same result in substantially the same way. The equivalent features include, for example, features that perform substantially the same function, in substantially the same way to achieve substantially the same result. In this description, reference has been made to various examples using adjectives or adjectival phrases to describe characteristics of the examples. Such a description of a characteristic in relation to an example indicates that the characteristic is present in some examples exactly as described and is present in other examples substantially as described. The above description describes some examples of the present disclosure however those of ordinary skill in the art will be aware of possible alternative structures and method features which offer equivalent functionality to the specific examples of such structures and features described herein above and which for the sake of brevity and clarity have been omitted from the above description. Nonetheless, the above description should be read as implicitly including reference to such alternative structures and method features which provide equivalent functionality unless such alternative structures or method features are explicitly excluded in the above description of the examples of the present disclosure. Whilst endeavoring in the foregoing specification to draw attention to those features believed to be of importance it should be understood that the Applicant may seek protection via the claims in respect of any patentable feature or combination of features hereinbefore referred to and / or shown in the drawings whether or not emphasis has been placed thereon. 5 l / we claim:

Claims

1. An apparatus comprising:a first antenna port;a second antenna port;a first transmission pathway for the first antenna port;a second transmission pathway for the second antenna port;a first reception pathway for the first antenna port;a second reception pathway for the second antenna port;a first additional pathway for the first antenna port;a second additional pathway for the second antenna port;means for switching between a first state in which a first signal is conveyed from the first reception pathway along the first additional pathway and a second signal is conveyed from the second reception pathway along the second additional pathway and a second state in which a third signal is conveyed from the first transmission pathway along the first additional pathway and a fourth signal is conveyed from the second transmission pathway along the second additional pathway;an amplitude detector configured to detect a combined amplitude of a signal in the first additional pathway and a signal in the second additional pathway;means for adjusting a relative phase between a signal in the first additional pathway and a signal in the second additional pathway based at least in part on the detected combined amplitude; andmeans for adjusting a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway based at least in part on the detected combined amplitude.

2. The apparatus of claim 1, wherein the means for adjusting the relative phase between a signal in the first additional pathway and a signal in the second additional pathway is configured to adjust the relative phase when the means for switching is in the first state, and the means for adjusting a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway is configured to adjust the relative phase when the means for switching is in the second state.

3. The apparatus of claim 1 or 2, wherein the means for adjusting the relative phase between a signal in the first additional pathway and a signal in the second additional pathway comprises means for optimizing the relative phase between a signal in the first additional pathway and asignal in the second additional pathway to produce a largest combined amplitude; and the means for adjusting a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway comprises means for optimizing a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway to produce a largest combined amplitude.

4. The apparatus of claim 3, wherein the means for optimizing the relative phase between a signal in the first additional pathway and a signal in the second additional pathway, and the means for optimizing the relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway are configured such that: whilst the relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway is optimized, the relative phase between a signal in the first additional pathway and a signal in the second additional pathway is kept at an optimized value previously determined by the means for optimizing the relative phase between a signal in the first additional pathway and a signal in the second additional pathway.

5. The apparatus of claim 4, wherein the means for optimizing the relative phase between a signal in the first additional pathway and a signal in the second additional pathway, and the means for optimizing a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway, are both configured to maintain the relative phase once it has been optimized.

6. The apparatus of any of the preceding claims, wherein the second additional pathway comprises a first phase shifter, and the first transmission pathway comprises a second phase shifter.

7. The apparatus of claim 6, wherein the first phase shifter is configured to control the relative phase between a signal in the first additional pathway and a signal in the second additional pathway; and the second phase shifter is configured to control the relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway.

8. The apparatus of claim 6 or 7, wherein the first transmission pathway comprises an amplifier, wherein the amplifier is positioned closer to the first antenna port than the second phase shifter is positioned relative to the first antenna port.

9. The apparatus of claim 6, 7 or 8, wherein the first additional pathway comprises an attenuator, wherein the attenuator is configured to match the attenuation caused by the first phase shifter.

10. The apparatus of any of the preceding claims, wherein the amplitude detector is an envelope detector.

11. The apparatus of any of the preceding claims, wherein the amplitude detector is for detecting a peak amplitude of the combined signals.

12. The apparatus of any of the preceding claims, wherein the first transmission pathway, second transmission pathway, first reception pathway, second reception pathway, first additional pathway and second additional pathway are each a pathway for conveying electrical signals.

13. The apparatus of any of the preceding claims, wherein the first transmission pathway is for conveying a signal to the first antenna port; the second transmission pathway is for conveying a signal to the second antenna port, the first reception pathway is for conveying a signal from the first antenna port, and the second reception pathway is for conveying a signal from the second antenna port.

14. The apparatus of any of the preceding claims, further comprising a first antenna element configured to couple to the first antenna port and a second antenna element configured to couple to the second antenna port.

15. The apparatus of any of the preceding claims, further comprising a first coupler configured to couple at least a portion of a signal from the first transmission pathway to the first additional pathway, and a second coupler configured to couple at least a portion of a signal from the second transmission pathway to the second additional pathway.

16. The apparatus of any of the preceding claims, further comprising a combiner, configured to combine the signal in the first additional pathway and the signal in the second additional pathway.

17. The apparatus of claim 16, further comprising a variable amplifier, positioned between the combiner and the amplitude detector, the variable amplifier configured to adjust the combined amplitude.

18. The apparatus of any of the preceding claims, wherein the apparatus is a user equipment.

19. The apparatus of any of the preceding claims, further comprising: a third antenna port; and a third reception pathway for the third antenna port.

20. The apparatus of claim 19, further comprising: further means for switching between a signal being conveyed from the second reception pathway along the second additional pathway; and a signal being conveyed from the third reception pathway along the second additional pathway, wherein the first state of the means for switching comprises a second signal being conveyed from the second reception pathway along the second additional pathway or a second signal being conveyed from the third reception pathway along the second additional pathway.

21. The apparatus of claim 19, further comprising:a third transmission pathway for the third antenna port; and a third additional pathway for the third antenna port;wherein the means for switching comprises means for switching between a first state in which a first signal is conveyed from the first reception pathway along the first additional pathway and a second signal is conveyed from the second reception pathway along the second additional pathway, a second state in which a third signal is conveyed from the first transmission pathway along the first additional pathway and a fourth signal is conveyed from the second transmission pathway along the second additional pathway; a third state in which the first signal is conveyed from the first reception pathway along the first additional pathway and a fifth signal is conveyed from the third reception pathway along the third additional pathway; and a fourth state in which the third signal is conveyed from the first transmission pathway along the first additional pathway and a sixth signal is conveyed from the third transmission pathway along the third additional pathway;wherein the amplitude detector is configured to detect a combined amplitude of a signal in the first additional pathway and a signal in the second additional pathway, or a combined amplitude of a signal in the first additional pathway and a signal in the third additional pathway; andfurther comprising means for adjusting a relative phase between a signal in the first additional pathway and a signal in the third additional pathway based at least in part on the detected combined amplitude.

22. A method comprising:causing switching between a first state in which a first signal is conveyed from the first reception pathway along a first additional pathway and a second signal is conveyed from a second reception pathway along a second additional pathway and a second state in which a third signal is conveyed from a first transmission pathway along the first additional pathway and a fourth signal is conveyed from a second transmission pathway along the second additional pathway;causing detection of a combined amplitude of a signal in the first additional pathway and a signal in the second additional pathway;causing adjustment of a relative phase between a signal in the first additional pathway and a signal in the second additional pathway based at least in part on the detected combined amplitude; andcausing adjustment of a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway based at least in part on the detected combined amplitude.

23. The method of claim 22, wherein causing adjustment of the relative phase between a signal in the first additional pathway and a signal in the second additional pathway comprises optimizing the relative phase between a signal in the first additional pathway and a signal in the second additional pathway to produce the largest combined amplitude; and causing adjustment of the relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway comprises optimizing a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway to produce the largest combined amplitude.

24. A computer program comprising program instructions for causing an apparatus to perform at least the following:causing switching between a first state in which a first signal is conveyed from the first reception pathway along a first additional pathway and a second signal is conveyed from a second reception pathway along a second additional pathway and a second state in which a third signal is conveyed from a first transmission pathway along the first additional pathwayand a fourth signal is conveyed from a second transmission pathway along the second additional pathway;causing detection of a combined amplitude of a signal in the first additional pathway and a signal in the second additional pathway;causing adjustment of a relative phase between a signal in the first additional pathway and a signal in the second additional pathway based at least in part on the detected combined amplitude; andcausing adjustment of a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway based at least in part on the detected combined amplitude.

25. The computer program of claim 24, wherein causing adjustment of the relative phase between a signal in the first additional pathway and a signal in the second additional pathway comprises optimizing the relative phase between a signal in the first additional pathway and a signal in the second additional pathway to produce the largest combined amplitude; and causing adjustment of the relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway comprises optimizing a relative phase between a signal in the first transmission pathway and a signal in the second transmission pathway to produce the largest combined amplitude.

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