BACKGROUND

The present invention, in some embodiments thereof, relates to antennas for dual-band multiple-input-multiple-output (MIMO) wireless communications, and, more specifically, to compact antennas for dual-band MIMO wireless communications.

As demand for increased throughput in wireless networks is continually growing, several advanced transmission technologies were introduced and evolved to address that demand.

One of the technologies may be, for example, multi-band transmission where the transmission may be conducted over a spectrum of frequencies rather than in a single frequency band as was done in the past. Typically, for home and/or offices environments, dual-band is applied, for example, utilizing a 2.4 GHz and a 5 GHz frequency bands for co-existing transmission.

Another technology may be employing MIMO antenna cells in which the antenna cell includes a plurality of ports all transmitting/receiving in the same frequency band using spatial multiplexing.

SUMMARY

According to an aspect of some embodiments of the present invention there is provided a dual-band MIMO antenna cell, comprising:

A slot layer comprising a ground plane with an electrically conductive slot antenna cut in the ground plane.

An electrically conductive microstrip dipole antenna located directly and

symmetrically above the slot antenna, the dipole antenna comprises two radiating elements that are symmetrically fed.

Wherein the slot antenna is adapted to operate in a first frequency band of a dual band and the dipole antenna is adapted to operate in a second frequency band of the dual band.

According to some embodiments of the present invention the slot antenna in the slot layer is a simple shaped slot antenna constructed for single-polarized transmission. One or more electrically conductive microstrip transmission lines that are electrically coupled to a radiating element of the simple slot antenna feed a signal to the radiating element.

The simple shaped slot antenna is disposed on a first wide dimension side of a dielectric substrate and a feeding layer comprising the one or more electrically conductive microstrip is disposed on a second wide dimension side of the dielectric substrate opposite to the first wide dimension side.

According to some embodiments of the present invention the slot antenna in the slot layer is a cross shaped slot antenna constructed for dual-polarized transmission. At least a first and a second electrically conductive microstrip transmission lines are connected respectively to a first and a second polarized radiating elements of the cross shaped slot antenna. Wherein the first electrically conductive microstrip transmission line that is electrically coupled to the first polarized radiating element feeds a first signal to the first polarized radiating element and the second electrically conductive microstrip transmission line that is electrically coupled to the second polarized radiating element feeds a second signal to the second polarized radiating element.

The cross shaped slot layer is disposed on a first wide dimension side of a first dielectric substrate, a first feeding layer comprising the first electrically conductive microstrip transmission line is disposed on a second wide dimension side of the first dielectric substrate opposite to the first wide dimension side with respect to a direction of polarization and a second feeding layer comprising the second electrically conductive microstrip transmission line is disposed on a wide dimension side of a second dielectric substrate above the slot layer with respect to the direction of polarization.

The dipole antenna is constructed in a dipole layer disposed on a wide dimension side of a third dielectric substrate, the dipole antenna is rotated in a plane of the slot antenna with respect to the slot antenna.

The center frequency of the first frequency band is lower than the center frequency of the second frequency band.

The length of the dipole antenna is adapted to be approximately a half of a wavelength of the second frequency band.

The dipole antenna is rotated in a horizontal axis (in layer) compared to a layout of the slot antenna.

The slot layer performs as reflector for reflecting radio frequency, RF, signals transmitted by the dipole antenna.

Optionally, the dual-band MIMO antenna cell includes a reflector layer comprising an electrically conductive ground plane for reflecting signals transmitted from the slot antenna and/or the dipole antenna. The dual-band MIMO antenna cell is constructed such that the slot layer is located between the reflector layer and the dipole antenna. Optionally, a dual-band MIMO antenna array comprises a plurality of dual-band MIMO antenna cells.

According to an aspect of some embodiments of the present invention there is provided a method for constructing a dual-band multiple input multiple output, MIMO, antenna cell, comprising:

Disposing a slot layer on a first wide dimension side of a dielectric substrate, the slot layer comprising a ground plane with a slot antenna cut in the ground plane.

Disposing a feeding layer comprising at least one electrically conductive microstrip transmission line on a second wide dimension side of the dielectric substrate opposite to the first wide dimension side to feed the slot antenna.

Disposing a dipole layer on another dielectric substrate, the dipole layer comprising an electrically conductive microstrip dipole antenna located directly and

symmetrically above the slot antenna, the dipole antenna comprises two radiating elements that are symmetrically fed.

Wherein the slot antenna is adapted to operate in a first frequency band of a dual band and the dipole antenna is adapted to operate operation in a second frequency band of the dual band.

The slot antenna in the slot layer is a simple shaped slot antenna comprising one radiating element constructed for single-polarized transmission or a cross shaped slot antenna comprising two radiating elements constructed for dual-polarized transmission.

Optionally, another feeding layer is disposed. The other feeding layer comprises one or more other electrically conductive microstrip transmission lines for feeding a second of the two radiating elements of the cross shaped slot antenna on an additional dielectric substrate. Wherein the additional dielectric substrate is located between the slot layer and the dipole layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

In the drawings: FIG. 1 A is a top perspective view of an exemplary compact dual-band MIMO antenna cell, according to some embodiments of the present invention;

FIG. IB is a bottom perspective view of an exemplary compact dual-band MIMO antenna cell, according to some embodiments of the present invention;

FIG. 1C is a transparent top perspective view of an exemplary compact dual-band

MIMO antenna cell, according to some embodiments of the present invention;

FIG. ID is a transparent top view of an exemplary compact dual-band MIMO antenna cell, according to some embodiments of the present invention;

FIG. 2 is a schematic illustration of a printed circuit board (PCB) stack-up of an exemplary compact dual-band MIMO antenna cell, according to some embodiments of the present invention;

FIG. 3A is a schematic illustration of an exemplary simple shaped slot antenna cell with symmetrical (dual) excitation included in an exemplary compact dual-band MIMO antenna cell, according to some embodiments of the present invention;

FIG. 3B is a schematic illustration of an exemplary cross shaped slot antenna cell having 2 with symmetrical (dual) excitations (for each polarization) included in an exemplary compact dual-band MIMO antenna cell, according to some embodiments of the present invention;

FIG. 4A is a schematic illustration of an electric field (E) distribution over an exemplary simple shaped slot antenna with symmetrical excitation, according to some embodiments of the present invention;

FIG. 4B and FIG. 4C are schematic illustrations of electric field (E) distributions over an exemplary cross shaped slot antenna, according to some embodiments of the present invention;

FIG. 4D is a schematic illustration of an electric field (E) distribution over an exemplary dipole antenna, according to some embodiments of the present invention;

FIG. 5A is a schematic illustration of an exemplary compact dual-band MIMO antenna cell with a reflector, according to some embodiments of the present invention;

FIG. 5B, is a schematic illustration of an exemplary compact dual-band MIMO antenna cell with additional passive orthogonal elements, according to some embodiments of the present invention;

FIG. 6 is a schematic illustration of an exemplary compact dual-band MIMO antenna array, according to some embodiments of the present invention; and FIG. 7 is a flow chart of an exemplary process for constructing a compact dual-band MIMO antenna cell, according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The present invention, in some embodiments thereof, relates to antennas for dual-band

MIMO wireless communications, and, more specifically, to compact antennas for dual-band MIMO wireless communications.

The present invention presents systems and methods for constructing compact dual- band MIMO antenna cells. The compact dual-band MIMO antenna cell employs an innovative design in which two antennas each operating in a different frequency band are constructed in close proximity utilizing a small form factor without inducing interference of each other's transmission. In particular, the compact dual-band MIMO antenna cell may be a directional high gain (narrow beam) low side-lobes antenna cell where each of the two antennas may include one or more ports (may be regarded as polarizations) to support the MIMO operation.

The compact dual-band MIMO antenna cell is constructed with a slot antenna operating at a first frequency band, for example, 2.4 GHz and a dipole antenna operating at a second frequency band, for example, 5.0 GHz. The slot antenna may be a slot cut in a ground plane of a slot layer and may be a simple shaped slot antenna constructed for single polarization transmission or a cross shaped slot antenna constructed for dual-polarization transmission. The dipole antenna is constructed in a dipole layer for dual-polarization transmission and is located directly and symmetrically above the slot antenna in a direction of polarization (transmission).

The slot antenna and the dipole antenna are symmetrically fed with a signal for transmission such that each section (half) of the antenna is fed from a separate feeding source. Due to the symmetrical feeding, odd wave modes generated (excited) in each section of the slot antenna cancel each other since the excited wave modes have the same amplitude (strength) and opposite phases. Therefore, higher wave modes may be hardly excited in the slot, in particular the second mode that may typically be in the 5.0 GHz frequency band. Consequently, the 5.0 GHz dipole antenna that is located symmetrically above the slot antenna and excited in its middle point, may be hardly affected by the slot antenna and vice- versa.

Each of the slot antenna and the dipole antenna is further constructed to have their length equal approximately half the wavelength of the operational frequency band. The length of the slot antenna may be adapted to be approximately half the wavelength corresponding to the first frequency band, for example, 2.4 GHz, while the length of the dipole antenna may be adapted to be approximately half the wavelength corresponding to the second frequency band, for example, 5.0 GHz.

As result, each of the slot antenna and the dipole antenna may transmit only their dominant (first) wave mode with significant power while all other wave modes are significantly decayed. Decaying the higher wave modes may be specifically important for decaying the second harmonics of the first frequency band, for example, 2.4 GHz that is approximately 5 GHz to avoid the interference with the dominant wave mode of the second frequency band, for example, 5 GHz.

Transmission of only the dominant wave mode with significant power coupled with the fact that the dipole antenna is located directly and symmetrically above the slot antenna may result in significantly reduced mutual interference between the wave modes transmitted (excited) by the dipole antenna and the slot antenna. The reduced interference (may typically be negligible) may allow each of the dipole antenna and the slot antenna to achieve transmission rates (throughput) performance that may be similar to the transmission rates performance achieved when each of the dipole antenna and the slot antenna operate separately as stand-alone antennas (without the presence of the other antenna).

Optionally, the compact dual-band MIMO antenna cell comprises a reflection layer located below the slot antenna (opposite the direction of transmission) in order to reflect the wave modes transmitted by the slot antenna and/or the dipole antenna towards the direction of transmission.

Optionally, a plurality of compact dual-band MIMO antenna cells is integrated to create a compact dual-band MIMO antenna array.

The symmetrically fed compact dual-band MIMO antenna design may present significant advantages compared to currently existing technologies for constructing and/or designing dual-band MIMO antennas.

In order to avoid and/or reduce the mutual interference between the antennas of the two frequency bands and/or ports, the currently existing technologies may typically construct the dual-band MIMO antennas such that each of the antennas and/or ports isolated from each other by physically separating them. This approach may lead to increased form factor and/or size of the dual-band MIMO antenna cell.

The symmetrically fed compact dual-band MIMO antenna cell on the other hand applies a tight design in which the two antennas (for the dual-band transmission) are constructed in close proximity while avoiding and/or significantly reducing the mutual interference between transmission in the first and the second frequency bands. Moreover, the construction of the compact dual-band MIMO antenna cell is such that the dipole antenna is constructed in a vertical dimension above the slot antenna thus avoiding increasing the horizontal dimensions of the compact dual-band MIMO antenna cell. The vertical dimension size increase is negligible as it is smaller in several magnitudes from the horizontal dimensions. The tight design and construction may therefore allow significant reduction of the size and/or form factor of the compact dual-band MIMO antenna cell.

In addition, the tight design and construction of the compact dual-band MIMO antenna cell may allow easy scaling by duplicating the compact dual-band MIMO antenna cell to create a compact dual-band MIMO antenna array.

Moreover, the slot layer that is substantially a ground plane may function as a reflector for the wave modes transmitted from the dipole antenna to improve the transmission rate and/or performance of the dipole antenna.

Furthermore, integrating the reflector layer in the compact dual-band MIMO antenna cell may significantly increase the transmission rate and/or performance of the dipole antenna and/or the slot antenna.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

The present invention may be a system, a method, and/or a computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention.

The computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing.

Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The computer readable program instructions may execute entirely on the user's computer, partly on the user's computer such as the user equipment (UE), as a stand-alone software package, partly on the user's computer and partly on a remote computer such as the network apparatus or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical function(s). In some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.

Preferred embodiments of compact dual-band MIMO antenna cells are described hereinafter, however the preferred embodiments should not be construed as limiting since multiple other implementations, dimensions and/or geometries that employ the concepts described throughout the present invention are possible.

Reference is now made to FIG. 1A, FIG. IB, FIG. 1C and FIG. ID which are views of an exemplary compact dual-band MIMO antenna cell, according to some embodiments of the present invention.

FIG. 1A and FIG. IB present perspective top and bottom views of an exemplary compact dual-band MIMO antenna cell 100. In particular, the compact dual-band MIMO antenna cell 100 is a directional high gain (narrow beam) low side-lobes antenna cell.

The compact dual-band MIMO antenna cell 100 comprises a cross shaped slot antenna 116 constructed for dual polarization transmission at a first frequency band, for example, 2.4GHz and a dipole antenna 112 constructed for single polarization transmission at a second frequency band, for example, 5GHz. In particular, the compact dual-band MIMO antenna cell 100 is a directional high gain (narrow beam) low side-lobes antenna in both bands.

The cross shaped slot antenna 116 comprises two radiating/receiving elements 116A and 116B that are symmetrically fed with signals from two electrically conductive microstrip transmission lines 114 and 118 respectively. The electrically conductive microstrip transmission line 114 is electrically coupled to the radiating/receiving element 116A for feeding the signal to the radiating/receiving element 116A, i.e. a first polarization. The electrically conductive microstrip transmission line 118 is electrically coupled to the radiating/receiving element 116B for feeding the signal to the radiating/receiving element 116B, i.e. a second polarization.

The cross shaped slot antenna 116 is cut in a ground plane of a slot layer 106 disposed on a first wide dimension side of a first dielectric substrate. The electrically conductive microstrip transmission line 114 is constructed in a first (lower) feeding layer 104 disposed on a second wide dimension side of the first dielectric substrate opposite the first wide dimension, i.e. opposite the cross shaped slot antenna 116. The electrically conductive microstrip transmission line 118 is constructed in a second (upper) feeding layer 108 disposed on a wide dimension side of a second dielectric substrate located above the slot layer 106. Each of the two electrically conductive microstrip transmission lines 114 and 118 are fed with the signals through two feeding points 124 and 128 respectively.

The dipole antenna 112 comprises two radiating/receiving elements 112A and 112B that are symmetrically fed with signal and ground through a port defined by the two points 122A and 122B respectively. The dipole antenna 112 is constructed in a dipole layer 102 disposed on a first wide dimension side of a third dielectric substrate such that the dipole antenna 112 is located directly and symmetrically above the cross shaped slot antenna 116.

Optionally, the dual-band MIMO antenna cell comprises a simple shaped slot antenna constructed for single polarization transmission at the first frequency band. The simple shaped slot antenna may comprise a single radiating/receiving element such as, for example, the radiating/receiving element 116A that is fed with the signal from the electrically coupled electrically conductive microstrip transmission lines 114. For the simple shaped slot antenna 116A, the second feeding layer 108 (upper layer) may not be implemented.

FIG. 1C presents a transparent perspective top view of the compact dual-band MIMO antenna cell 100 to visualize all elements of the exemplary dual-band MIMO antenna cell 100.

FIG. ID presents a transparent top view of the exemplary compact dual-band MIMO antenna cell 100 to visualize all the elements of the compact dual-band MIMO antenna cell 100.

Reference is now made to FIG. 2, which is a schematic illustration of a printed circuit board (PCB) stack-up of an exemplary compact dual-band MIMO antenna cell, according to some embodiments of the present invention. An exemplary PCB stack-up 200 may be constructed to implement a compact dual-band MIMO antenna cell such as the compact dual- band MIMO antenna cell 100.

The PCB stack-up 200 may be constructed as a single multi-layer PCB comprising a slot layer such as the slot layer 106 and a dipole layer such as the such as the dipole layer 102. The slot layer 106 hosting a slot antenna such as the simple shaped slot antenna 116A or the cross shaped slot antenna 116 may be disposed on a first (top) wide dimension of a first dielectric substrate of a PCB layer 1 (bottom layer with respect to a polarization/transmission direction). A first (lower) feeding layer such as the feeding layer 104 is disposed on a second (bottom) wide dimension of the first dielectric substrate of the PCB layer 1. In case the slot layer 106 is constructed with a cross shaped slot antenna such as the cross shaped slot antenna 116, the PCB stack-up 200 may further include a second (top) feeding layer such as the feeding layer 108 disposed on a top wide dimension of a second dielectric substrate of a PCB layer 2. The dipole layer 102 hosting a dipole antenna such as the dipole antenna 112 may be disposed on a top wide dimension of a third dielectric substrate of a PCB layer 3. The dipole antenna 112 is fed through microstrip transmission lines that may be disposed in the dipole layer 102 and/or in a dipole feeding layer 102A disposed on the PCB layer 3 dielectric substrate opposite the dipole layer 102. A dielectric gap 110A may be applied between the PCB layer 2 and the PCB layer 3. The dielectric gap 11 OA may be a dielectric substrate applied to adjust the distance between the slot layer 106 and the dipole layer 102 in order to achieve optimal immunity to mutual interferences between the slot antenna (the simple shaped slot antenna 1 16A or the cross shaped slot antenna 1 16) and the dipole antenna 1 12.

Optionally, the PCB stack-up 200 is constructed of two separate single and/or multi- layer PCBs. The first multi-layer PCB comprises the PCB layer 1 and the PCB layer 2 while the second PCB comprises the PCB layer 3. The dielectric gap 1 10A may be an air gap applied between the first and the second PCBs. Additionally and/or alternatively, the dielectric gap 1 1 OA may include one or more material layers, for example, a dielectric substrate, a plastic resin and/or the like to adjust the distance between the slot layer 106 and the dipole layer 102.

The PCB stack-up 200 may further include a dielectric gap HOB above the PCB layer

3 (dipole layer 102) to verify proper clearance from the dipole layer 102.

Reference is now made to FIG. 3A and FIG. 3B, which are schematic illustrations of an exemplary simple shaped slot antenna cell and an exemplary cross shaped slot antenna cell respectively, according to some embodiments of the present invention.

Reference is also made to FIG. 4A, FIG. 4B, FIG. 4C and FIG. 4D, which are schematic illustrations of electric fields (E) distribution over an exemplary simple shaped slot antenna, an exemplary cross shaped slot antenna, and an exemplary dipole antenna, according to some embodiments of the present invention.

An exemplary simple shaped slot antenna cell 300A for single polarized transmission comprises a simple shaped slot antenna that includes a single radiating/receiving element such as simple shaped slot antenna 1 16A that is cut in a ground plane of a slot layer such as the slot layer 106. The simple shaped slot antenna cell 300 A also includes an electrically conductive microstrip transmission line such as the electrically conductive microstrip transmission line 1 14 that is constructed in a first feeding layer such as the feeding layer 104. The electrically conductive microstrip transmission line 1 14 is fed from a feeding point such as the feeding point 124.

A schematic illustration 400A presents an electric field (E) distribution for the simple shaped slot antenna cell 300 A. As shown, the electrically conductive microstrip transmission line 1 14 feeds a signal to simple shaped slot antenna 1 16A in a symmetrical manner such that an electrically conductive microstrip section 1 14A feeds a section 116A1 of the simple shaped slot antenna 1 16A and an electrically conductive microstrip section 1 14B feeds a section 1 16A2 of the simple shaped slot antenna 1 16A. The length of each of the sections 1 16A1 and 116A2 is equal to half of a length a of the simple shaped slot antenna 116A, i.e. the length of the sections 116A1 and 116A2 is -.

2

For the simple shaped slot antenna 116A, the electric field (E) distribution E _y (m, n) where (m, n) are the indexes of the electrical wave mode developed in the slot antenna may be expressed by equation 1 below.

Equation 1 :

E _y (rn, ri) = A^ ^ ¹ — - sinQ3 _x m) ^■ x) cos(p _y (n) ^■ y)

Where β _χ = m ^ and β _γ ^{= n} ~, A _mn is the amplitude of the wave mode (m, ri) and β _χ (τη) and /? _y (n) are the propagation values of the wave mode (m, n) in direction X and in direction Y respectively.

The wave number K for each wave mode and, in particular, for the first wave mode may be expressed by equation 2 below.

Equati

Assuming a width b of the simple shaped slot antenna 116A is narrow such that b « λ (where λ is the wavelength of the transmitted wave), the total electric field E _{y tot} may be expressed by equation 3 below.

Equation 3 :

M-lW-l M-1 ? ( )

^E y tot = ^ ^ E _y (m, n) * ^ A _m ^x ™ sin(/? _x (m) ^■ x)

771 = 0 77 = 0 777=0

The simple shaped slot antenna 116A may support all wave modes. However, the simple shaped slot antenna 116A may be designed mainly for the first frequency band, for example, 2,4GHZ such that the length a of the simple shaped slot antenna 116A is set to a «

X

-. Setting the length a of the simple shaped slot antenna 116A may lead to the transmitting the dominant wave mode with high strength while higher wave modes may be excited in a degraded strength, for example, evanescent modes and/or decayed modes.

While the higher wave modes may be decayed, they may still affect a transmission pattern of the dominant (first) wave mode. This may be overcome by the symmetrical feeding (exciting) of the simple shaped slot antenna 116A. By symmetrically feeding (exciting) the simple shaped slot antenna 116A, the odd wave modes may be substantially decayed as they are cancelled due to the symmetrically feed as shown in the schematic illustration 400A. An electric field (E) 402 is generated by the signal fed to the first (right) side of the simple shaped slot antenna 116A by the electrically conductive microstrip section 114A while an electric field (E) 404 is generated by the signal fed to the second (left) side of the simple shaped slot antenna 116A by the electrically conductive microstrip section 114B. The odd wave modes excited by the two sides of the simple shaped slot antenna 116A may cancel each other as the odd wave modes have the same strength but an opposite phase. As result, it may be assumed that only the even wave modes are excited by the simple shaped slot antenna 116A. Since the simple shaped slot antenna 116A is designed

X

such that the slot length a of the simple shaped slot antenna 116A is set to a « -, it may be further assumed (approximated) that only the dominant (first), wave mode is excited by the simple shaped slot antenna 116A. Due to the construction of the simple shaped slot antenna 116A, it may be further assumed that the developed electrical field (E) may be dominated by the wave mode component in the Y direction. The electric field (E) distribution of the simple shaped slot antenna 116A may therefore be approximated as a sinusoidal distribution as expressed in equation 4 below.

Equation 4:

Ey tot ^¾ A sin ^—^-x j The symmetrical feeding (excitation) may be extended for the cross shaped slot antenna

116.

An exemplary cross shaped slot antenna cell 300B for dual polarized transmission comprises a cross shaped slot antenna such as the cross shaped slot antenna 116. The cross shaped slot antenna cell 300B also includes two electrically conductive microstrip transmission lines such as the electrically conductive microstrip transmission line 114 and 118 that are constructed in a first feeding layer such as the feeding layer 104 and a second feeding layer such as the feeding layer 108. The electrically conductive microstrip transmission lines 114 and 118 are fed from two feeding point such as the feeding points 124 and 128 respectively.

Schematic illustrations 400B and 400C present distribution for the cross shaped slot antenna cell 300B.

As shown in the illustrations 400B and 400C when symmetrically excited, the dominant wave mode as well as all even wave modes of the excited slot, excite odd wave modes in the cross slot. This means that when symmetrically exciting the radiating element (slot) 1 16A of the cross shaped slot antenna 1 16 as described for the simple shaped slot antenna 1 16A, the even wave modes generated by each of the sections 1 16A1 and 1 16A2 of the radiating element 1 16A excite the odd wave modes in the other (cross) radiating element 116B. The electric field (E) of the odd wave modes excited in the (cross) radiating element 1 16B by each of the sections 1 16A1 and 1 16A2 have the same amplitude (strength) and opposite phases such that they may significantly cancel each other.

Similarly, when symmetrically exciting the radiating element (slot) 1 16B of the cross shaped slot antenna 1 16, the even wave modes generated by each of two sections 1 16B1 and 1 16B2 of the radiating element 1 16B excite the odd wave modes in the other (cross) radiating element 1 16A. The radiating element sections 1 16B1 and 1 16B2 are symmetrically fed with a signal by electrically conductive microstrip sections 1 18B and 1 18A respectively, where the sections 1 18B and 1 18A are sections of the electrically conductive microstrip 1 18. The electric fields (E) of the odd wave modes excited in the (cross) radiating element 1 16A by each of the sections 1 16B1 and 1 16B2 have the same amplitude (strength) and opposite phases such that they may significantly cancel each other.

The result of the symmetrical feeding (excitation) is that the isolation between the electric fields (E) of the radiating elements 1 16A and 1 16B of the cross shaped slot antenna 1 16 (the polarizations) may be significantly high and typically negligible coupling may be observed between the polarizations.

Schematic illustrations 400D presents an electric field (E) distribution 406 for a dipole antenna such as the dipole antenna 1 12 designed for the second frequency band, for example, 5 GHz.

When feeding a symmetrical dipole such as the dipole antenna 1 12, mainly the dominant (first) wave mode may be excited while the other wave modes may decay.

The dipole antenna 112 may be designed such that the length of the dipole antenna 1 12 is set to half the wavelength of the second frequency band, for example, 5 GHz. It may therefore be further assumed (approximated) that only the dominant (first), wave mode is excited by the dipole antenna 1 12. The dominant wave mode excited by the dipole antenna 1 12 generates the electric field (E) 406 that may be dominated by the wave mode component in the X direction and the distribution of the electric field (E) 406 may therefore be approximated as expressed in equation 5 below. Equation 5 :

E _x * l ₀ si (j x)

As shown in FIG. 1A, FIG. IB , FIG. 1C and FIG. ID the dipole antenna 1 12 is placed directly and symmetrically above the slot antenna, either the simple shaped slot antenna 1 16A or the cross shaped slot antenna 1 16 to create the compact dual-band MIMO antenna cell 100.

Moreover, rotating the dipole antenna 1 12 with respect to the slot antenna may further reduce interference between the slot antenna and the dipole antenna 1 12. In case the slot antenna is the cross shaped slot antenna 1 16, the dipole antenna 1 12 may be rotated by 45 degrees in the horizontal plane with respect to the cross shaped slot antenna 1 16. In case the slot antenna is the simple shaped slot antenna 1 16A, the dipole antenna 1 12 may be placed perpendicular to the simple shaped slot antenna 116A.

As discussed before, since each of the dipole antenna and the slot antenna transmits only their dominant wave mode with significant power, by placing the dipole antenna 1 12 directly and symmetrical above the slot antenna, the dipole antenna and the slot antenna may not excite the higher wave modes and hence may not interfere with each other. For example, in case the dipole antenna 1 12 radiates in the dominant 5 GHz wave mode and the slot antenna radiates in the dominant 2.4 GHz wave mode, the dominant wave mode from each of the antennas may not induce interference on the dominant wave mode radiated by the other antenna. This means that mutual interference between the wave modes radiated by the dipole antenna 1 12 and the slot antenna (either the simple shaped slot antenna 116 or the cross shaped slot antenna 1 16) may be significantly reduced and typically negligible. The reduced mutual interference may be especially significant for maintaining low side lobes in the patterns of the electric field (E) distribution.

The reduced mutual interference may in turn allow high transmission throughput (performance) for each of the dipole antenna 1 12 and the slot antenna that may be similar to the transmission throughput achieved by each of the dipole antenna 1 12 and the slot antenna operating separately, i.e. as a stand-alone antenna.

The low mutual coupling of the dipole antenna 1 12 and the slot antenna is independent of the distance (proximity) between the dipole antenna 1 12 and the slot antenna. Since the mutual coupling may be avoided regardless of the proximity of the dipole antenna 1 12 and the slot antenna, a size of the compact dual-band MIMO antenna cell 100 may be significantly reduced. The construction of the compact dual-band MIMO antenna cell 100 may further improve directional radiation of the dipole antenna 112 since the ground plane of the slot layer 106 may perform as a reflector reflecting the waves transmitted by the dipole antenna 112 towards the desired direction.

Optionally, an additional ground layer may be placed bellow the feeding layer 104 to improve the transmission pattern of the dipole antenna 112 and/or the slot antenna, either the simple shaped slot antenna 116 or the cross shaped slot antenna 116.

Reference is now made to FIG. 5A, which is a schematic illustration of an exemplary compact dual-band MIMO antenna cell with a reflector, according to some embodiments of the present invention. A compact dual-band MIMO antenna cell 100 A comprises a compact dual-band MIMO antenna cell such as the compact dual-band MIMO antenna cell 100 with an additional reflector layer 502. The reflector layer 502 that may comprise a ground plane is placed under the feeding layer 104 with respect to the direction of transmission. The waves transmitted by the dipole antenna 112 and/or the slot antenna (either the simple shaped slot antenna 116 or the cross shaped slot antenna 116) may be reflected back from the reflector layer 502 towards the direction of transmission. Reflecting the reflected waves towards the direction of radiation may significantly improve the transmission rate (throughput) for the dipole antenna 112 and/or the slot antenna.

Optionally, passive orthogonal elements may be incorporated in the compact dual-band MIMO antenna cell 100 in order to improve the ability to match the radiating slot antenna 116 and/or 116A by providing means to control the total field distribution thus improving the ability to control the side- lobe- level.

Reference is now made to FIG. 5B, which is a schematic illustration of an exemplary compact dual-band MIMO antenna cell with additional passive orthogonal elements, according to some embodiments of the present invention. A compact dual-band MIMO antenna cell 100B comprises a compact dual-band MIMO antenna cell such as the compact dual-band MIMO antenna cell 100 with additional one or more passive orthogonal elements 510 in one or more passive layers 504. The passive layer(s) 504 may be disposed on one or more dielectric substrates of one or more additional PCB layers to improve the matching of the radiating slot antenna, for example, the simple shaped slot antenna 116A and/or the cross shaped antenna 116. The passive layer(s) 504 may be adapted to control the total field distribution of the radiating slot antenna that may allow for better control over the side-lobe-level.

The compact dual-band MIMO antenna cell 100 may be constructed to include combinations of the reflector layer 502 and the passive layer(s) 504. Optionally, the compact dual-band MIMO antenna cell 100 is duplicated to construct dual-band MIMO antenna arrays of various dimensions and/or geometries.

Reference is now made to FIG. 6, which is a schematic illustration of an exemplary compact dual-band MIMO antenna array, according to some embodiments of the present invention. A compact dual-band MIMO antenna array 600 includes a plurality of compact dual- band MIMO antenna cells such as the compact dual-band MIMO antenna cell 100 comprising a cross shaped slot antenna such as the cross shaped slot antenna 116 and a dipole antenna such as the dip[ole antenna 112. Each element of the dual-band MIMO antenna cell 100 is duplicated for the plurality of cells in the compact dual-band MIMO antenna array 600, however each element is designated only once in FIG. 6 in order to avoid overloading the drawing, rendering it unreadable. Moreover, some element of the dual-band MIMO antenna cell 100 may not be visible in FIG. 6, for example, a transmission line such as the electrically conductive microstrip transmission line 114 feeding a radiating/receiving element such as the radiating/receiving element 116A of the cross shaped slot antenna 116.

The compact dual-band MIMO antenna array 600 may include one or more sub-arrays such as, for example, a sub-array 602A and/or a sub-array 602B. The exemplary sub-arrays 602A and/or 602B may each include, for example, four compact dual-band MIMO antenna cells 100. The compact dual-band MIMO antenna array 600 may further include a passive layer such as the passive layers 504 disposed with a plurality of passive orthogonal elements such as the passive orthogonal elements 510. The compact dual-band MIMO antenna array 600 may also include a reflector layer such as the reflector layer 502.

Reference is now made to FIG. 7, which is a flowchart of an exemplary process for constructing a compact dual-band MIMO antenna cell, according to an exemplary embodiment of the present invention. A process 700 is executed (followed) to construct a compact dual- band MIMO antenna cell such as the compact dual-band MIMO antenna cell 100. The compact dual-band MIMO antenna cell 100 comprises a plurality of antennas that may be implemented as a simple shaped slot antenna such as the simple shaped slot antenna 116A or a cross shaped slot antenna such as the cross shaped slot antenna 116.

Naturally, the process 700 may be extended to create a compact dual-band MIMO antenna array such as the compact dual-band MIMO antenna array 600.

As shown at 702, the process 700 starts with disposing a slot layer such as the slot layer 106 on a first (top) wide dimension of a dielectric substrate such as, for example, the PCB layer 1 (bottom layer with respect to the polarization/transmission direction). The slot layer may be constructed of a ground plane with an antenna slot cut in the ground plane. The antenna slot may be a simple shaped slot antenna such as the simple shaped slot antenna 116A or a cross shaped slot antenna such as the cross shaped slot antenna 116.

As shown at 704, a feeding layer such as the feeding layer 104 is disposed on a second (bottom) wide dimension of the dielectric substrate of PCB layer 1. In case of the simple shaped slot antenna 116 A, the feeding layer 104 is the only feeding layer included in the compact dual- band MIMO antenna cell 100. However, in case of the cross shaped slot antenna 116, the feeding layer 104 is a first feeding layer. The feeding layer 104 comprises an electrically conductive microstrip transmission line such as the electrically conductive microstrip transmission line 114 that is electrically coupled to a radiating/receiving element such as the radiating/receiving element 116 A. The electrically conductive microstrip transmission line 114 feeds a signal to the radiating/receiving element 116A. A feeding point such as the feeding point 124 feeds the signal to the electrically conductive microstrip transmission line 114.

As shown at 706, which is an optional step applied only for the cross shaped slot antenna 116, a second feeding layer as the feeding layer 108 is disposed on a first (top) wide dimension of a dielectric substrate such as, for example, the PCB layer 2. The feeding layer 108 comprises an electrically conductive microstrip transmission line such as the electrically conductive microstrip transmission line 118 that is electrically coupled to a second radiating/receiving element such as the radiating/receiving element 116B of the cross shaped slot antenna 116. The electrically conductive microstrip transmission line 118 feeds the signal to the radiating/receiving element 116B. A feeding point such as the feeding point 128 feeds the signal to the electrically conductive microstrip transmission line 118.

As shown at 708, a dipole layer such as the dipole layer 102 is disposed on a first (top) wide dimension of a dielectric substrate. For the simple shaped slot antenna 1 16A, the dipole layer 102 may be disposed on the first wide dimension of the dielectric substrate of the PCB layer 2. For the cross shaped slot antenna 116, the dipole layer 102 may be disposed on the first wide dimension of a dielectric substrate, such as the PCB layer 3. Optionally, a dielectric gap such as the dielectric gap 110A (for example, air, a dielectric substrate and/or another one or more other materials) may be applied between the dipole layer and the slot antenna layer. The dipole layer 102 comprises a dipole antenna such as the dipole antenna 112 that is constructed to include two radiating/receiving elements such as the radiating/receiving elements 112A and 112B. The radiating/receiving elements 112A and 112B are constructed with one port having two feeding points such as the feeding points 122A and 122B respectively for symmetrically feeding the signals to the radiating/receiving elements 112A and 112B. As shown at 710, which is an optional step, one or more passive orthogonal elements such as the passive orthogonal element 510 are applied in one or more passive layers such as the passive layer 504. The passive layer(s) 504 may be disposed on one or more dielectric substrates of one or more additional PCB layers.

As shown at 712, which is an optional step, a reflector layer such as the reflector layer

502 is disposed on the dielectric substrate of an additional PCB layer that is located below the first feeding layer 104. The reflector layer 502 may comprise of a ground plane such that waves that originate from the dipole antenna 112 and/or the slot antenna (either the simple shaped slot antenna 116 or the cross shaped slot antenna 116) and hit the reflector layer 502 are reflected back towards the direction of radiation.

The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

It is expected that during the life of a patent maturing from this application many relevant MIMO technologies will be developed and the scope of the term MIMO technologies is intended to include all such new technologies a priori.

As used herein the term "about" refers to ± 10 %.

The terms "comprises", "comprising", "includes", "including", "having" and their conjugates mean "including but not limited to". This term encompasses the terms "consisting of and "consisting essentially of.

The phrase "consisting essentially of means that the composition or method may include additional ingredients and/or steps, but only if the additional ingredients and/or steps do not materially alter the basic and novel characteristics of the claimed composition or method.

As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments.

The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". Any particular embodiment of the invention may include a plurality of "optional" features unless such features conflict.

Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases "ranging/ranges between" a first indicate number and a second indicate number and "ranging/ranges from" a first indicate number "to" a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals there between.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting.