Abstract:
An electromagnetic coupler comprising: a transmitter configured to operate at a first central frequency, a first termination configured to connect to the transmitter and having a second resonant frequency, a receiver configured to operate at the first frequency, a second termination configured to connect to the receiver and having a third resonant frequency, wherein when the first and second terminations are bought into close proximity when engaged, the equivalent resonant frequency is substantially the first frequency, and wherein the second and/or third frequencies being substantially spectrally spaced from the first frequency.

Description:
FIELD 
     The present disclosure relates to a coupler. 
     BACKGROUND 
     A connector or coupler is used for electrically connecting two devices so as to pass a signal. A connector may include a female metal contact on one side, which engages with a male metal contact on the other side. However, such connectors may suffer from the following problems: 
     1. The connection performance may degrade due to oxidation and wear after time. 
     2. When the data rate is ultra high (&gt;10 Gb/s) the area of each contact becomes very small. 
     3. The small mechanical parts are very easily damaged. 
     4. The fabrication is expensive. 
     An alternative to metal connectors 1s a wireless signal connection. However, a wireless connection is less ideal due to electromagnetic interference (EMI) and limited frequency resource. A further promising alternative is a dielectric connector, for example U.S. Pat. No. 7,481,672. However, such prior art dielectric connectors are mainly useful for DC isolation and still suffer from EMI problems, especially in the unconnected state. EMI problems can relate to the device being overly susceptible to interference from other devices, and/or that the device causes excessive interference in other devices. 
     SUMMARY 
     In general terms the present embodiments propose a resonant electromagnetic (EM) coupler which does not radiate significantly in an unconnected state. This may have the advantages(s) that: 
     1. no metal contacts are required, 
     2. EMI may be substantially eliminated for both connected and disconnected state, 
     3. consistent performance over the device lifetime, 
     4. longer life-time, 
     5. water resistant, 
     6. wideband &gt;10 GHz bandwidth @centre frequency 60 GHz (or relative bandwidth&gt;16%) and hence much higher data rate (&gt;10 Gb/s) can be achieved, 
     7. no radio frequency license needed, 
     8. safer data transmission because there is no radiation leakage to the environment, any information transmission is point-to-point. Thus, the connection security is higher than common wireless communications where the transmission can be detected by many others besides the desired receiver, and/or 
     9. better looking compared with a metal cable connector and may not be visible. 
     In a first specific aspect there is provided an electromagnetic coupler comprising a transmitter configured to operate at a first central frequency, a first termination configured to connect to the transmitter and having a second resonant frequency, a receiver configured to operate at the first frequency, a second termination configured to connect to the receiver and having a third resonant frequency, wherein when the first and second terminations are bought into close proximity when engaged, the equivalent resonant frequency is substantially the first central frequency, and wherein the second and/or third resonant frequencies are substantially spectrally spaced from the first central frequency. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       One or more example embodiments will now be described, with reference to the following figures, in which: 
         FIG. 1  is a schematic of a dielectric connector according to a first embodiment, 
         FIG. 2(   a ) is an equivalent resonance circuit diagram and graph of frequency response of the dielectric connector in a disconnected state, 
         FIG. 2(   b ) is an equivalent resonance circuit diagram and graph of frequency response of the dielectric connector in a connected state, 
         FIG. 3(   a ) is a perspective view of a dielectric coupler pair according to a second embodiment, 
         FIG. 3(   b ) is a perspective view of a Tx termination according to the second embodiment, 
         FIG. 4(   a ) is a frequency response graph of the second embodiment in a connection state, 
         FIG. 4(   b ) is a frequency response graph of the second embodiment in a disconnection state, 
         FIG. 5(   a ) is a cross section of an inserting type Rx termination in a disconnected state according to a third embodiment, 
         FIG. 5(   b ) is a cross section of an inserting type Tx termination in a disconnected state according to the third embodiment, 
         FIG. 5(   c ) is a cross section of an inserting type connector in a connected state according to the third embodiment, 
         FIG. 6(   a ) is a cross section of a touching type Rx termination in a disconnected state according to a fourth embodiment, 
         FIG. 6(   b ) is a cross section of a touching type Tx termination in a disconnected state according to the fourth embodiment, 
         FIG. 6(   c ) is a cross section of a touching type connector in a connected state according to the fourth embodiment, and 
         FIG. 7  is a cross section of a two-way connector according to a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A dielectric coupler  100  is illustrated in  FIG. 1  according to the first embodiment. A data stream to be transmitted first may be up/down converted to a millimeter wave (MMW) frequency by modulator  102 . The signal from the modulator  102  passes to a transmitter (Tx) side termination  104 , which is engaged with a receiver (Rx) side termination  106 , whereby the signal will be transmitted via RF from one to the other. The signal passes from the Rx termination to a demodulator  108  for down/up conversion. 
     When the two terminations  104 ,  106  are disconnected, the signal will be reflected back instead of radiated into the atmosphere. When two terminations  104 ,  106  are connected, the couplers have just dielectric touching and the signal is transferred without any significant leakage. So whether the coupler is connected or not, there is no external RF signal radiation and the leakage may be insignificant. 
     The coupler is based on a resonant frequency shifting principle, which is illustrated in  FIG. 2(   a ) and  FIG. 2(   b ). When the connector is “disconnected”, the Tx termination  104  has an original resonant frequency  200  which is higher than the working frequency  202  of the MMW modulator  102 , as a result, the Tx termination  104  impedance is significantly mismatched with respect to the Rx termination  106  and hence the RF power is transferred externally as shown in  FIG. 2(   a ). Therefore, equivalent capacitance of the resonance circuit  206  does not increase and hence the radiation efficiency is very low when there is no high dielectric material connected to the Tx termination  104  as shown in  FIG. 2(   a ). However, when the connector is “connected”, a high dielectric constant material sheet is sandwiched between Tx and Rx terminations  104 ,  106  as shown in  FIG. 2(   b ). This high dielectric constant sheet material will increase the equivalent capacitance of the resonance circuit  208  of the terminations  104 ,  106  as shown in  FIG. 2(   b ). Hence the resonance frequency  204  is reduced. By carefully designing the structure size in terms of the material dielectric constant, the connected state will may have a resonant frequency equal to the working central frequency of the Tx and Rx as shown in  FIG. 2(   b ). Thus, the coupler will pass the signal when the terminations are engaged. If the gap between Tx and Rx is very small, almost all signal power is transmitted from Tx to Rx, except for the material loss. The radiation leakage is small. 
       FIG. 3(   a ) shows a dielectric coupler according to the second embodiment. It includes a Tx termination  300  and a Rx termination  302 . The Tx termination  300  is shown in  FIG. 3(   b ). The arrangement of the dielectric coupler of  FIG. 3(   a ) and the Tx termination of  FIG. 3(   b ) is shown with respect to the rectangular coordinates x, y, z. The Tx termination  300  includes a substrate  304  and antenna  306  without a high dielectric constant material plane as shown in  FIG. 3(   b ). The Rx termination  302  has almost the same structure as the Tx termination  300  except a high dielectric constant plane  308  is attached as shown in  FIG. 3(   a ). 
     The Tx termination  300  is made on PCB material (e.g., FR408). In  FIG. 3(   b ), the Tx termination  300  includes metal parts exposed (top layer). However, the Tx termination  300  can be covered by another non-metal film (e.g., polytetrafluroethylene, commonly known as TEFLON®). The dielectric constant of this nonmetal film should be very different as compared with the high dielectric constant material on the Rx termination  302  as shown in  FIG. 3(   a ). The backing substrate is FR408. Other low dielectric constant PCB substrate materials can also be used. For 60 GHz working frequency, the design dimensions of the antenna  306  may be: loop diameter 1 mm, slot width 0.075 mm, patch inside dipole 0.38 mm×0.15 mm, and dipole width 0.6 mm. The coupler is fed by a micro-strip line to the centre of the metal patch from the back of the PCB. 
     The coupler performance according to the second embodiment is shown in  FIG. 4(   a ) and  FIG. 4(   b ). The central frequency is 58 GHz. In the connected state ( FIG. 4  ( a )), the propagation (S 21 ) is high at the central frequency and −3 dB bandwidth is &gt;15 GHz. The impedance matching frequency bandwidth (S 11 &lt;−10 dB) is 10 GHz. The wide impedance bandwidth is contributed by the slot loop plus slot dipole structure of the antenna  306  shown in  FIG. 3(   b ). By carefully designing the centre frequencies for the slot loop and slot dipole structure of the antenna  306  shown in  FIG. 3(   b ), the bandwidth may be maximised. 
     The slot loop and slot dipole structure of the antenna  306  shown in  FIG. 3(   b ) may be used to enlarge the bandwidth by locating two resonant frequencies close to each other so that the corresponding pass-bands are partially overlaid as shown in  FIG. 4(   a ). This will result in a wider bandwidth. Two resonant frequencies are controlled by the slot loop and slot dipole structure of the antenna  306  shown in  FIG. 3(   b ), respectively. For example, by increasing the slot loop diameter of the antenna  306 , one of the resonant frequencies is reduced, while by shortening the length of the slot dipole of the antenna  306 , the other resonant frequency is increased. 
     The propagation loss is 1.38 dB at the central frequency in the connected state as shown in  FIG. 4(   a ). That means more than 70% of the energy may be transferred from Tx to Rx. The remainder is mainly material losses, and a small part is radiation leakage. In the disconnected state ( FIG. 4(   b )), the return loss is small (0.7 dB). Thus, most of the energy (85%) is reflected back to the Tx instead of radiated to air. 
     A coupler may be modified by designing the bandwidth (e.g., 10 GHz), dielectric constant material (e.g., −11) and radiation leakage rate according to the requirements of a given application. 
     To further reduce any RF leakage, an absorber may surround the terminations. The absorber should have small effect to coupler parameters. Thus, less dielectric constant absorber foam or rubber is preferred. The absorbing rate should be as high as possible. 
     The dielectric connector can be modified according to the requirements of a given application. Three examples are introduced below. 
       FIGS. 5(   a ),  5 ( b ) and  5 ( c ) show an inserting type coupler  500 . In  FIG. 5(   b ), the Tx termination  502  includes a surround structure  504  with a slot opening  506  and the surround structure  504  is an absorber. In the disconnected state, the small radiation leakage from the Tx element  510  is absorbed by the absorber  504 . In  FIG. 5(   a ), the Rx termination  512  includes a high dielectric constant material  514 . In the connected state, shown in  FIG. 5(   c ), the Rx termination  512  shown in  FIG. 5(   a ) is inserted in the slot opening  506  shown in  FIG. 5(   b ), then the signal is transmitted from Tx to Rx through high dielectric material  514 . The small radiation leakage in connected state is also further absorbed by the absorber  504 . 
       FIG. 6(   c ) shows a touching type coupler  600 . The Tx termination  602  and Rx termination  604  face each other. To maximise the terminations alignment, some self-alignment structure is needed. For example, with a central working frequency of 60 GHz and the dielectric constant of 10.2, then the mechanical tolerance is about ±0.1 mm to ensure good coupling. There are many kinds of self-alignment systems that can be used, such as magnetic or embossing. An absorber  606  placed under the Tx termination to further reduce the radiation leakage in the connected and disconnected states. 
     In the previous embodiments, the Rx resonant frequency may be fixed at the working frequency because the high dielectric constant material is permanently provided on the Rx side. To achieve two-way communications, an individual reverse connector  702  made of high dielectric constant material is provided as shown in  FIG. 7 . By using the same principle of resonance frequency shifting, frequency shifting for both sides of the individual reverse connector  702  can be achieved. Namely, the Tx can be at right side and/or left side of the following individual reverse connector  702  for two-way communications in single dielectric connector. Here the high dielectric constant material of the individual reverse connector  702  neither touches a right side coupler  704  nor a left side coupler  706  until connected, and thus leakage from either side is prevented in the unconnected state. 
     While example embodiments have been described in detail, many variations are possible within the scope of the disclosure as will be clear to a skilled reader.