Patent Application
20190372200
This invention is related to the field of wide-band wireless communications and, more specifically, to reconfigurable multiple-input multiple-output (MIMO) antenna systems for cognitive radio platforms in compact wireless devices.
As new features and services are added to wireless devices and mobile terminals in modern wireless communication systems, high data rates and efficient spectral utilization are indispensable. High data rates can be achieved by utilizing multiple-input multiple-output (MIMO) systems covering several frequency bands. MIMO is a technique by which, among other things, a data signal is split into multiple streams and each stream is transmitted from a different transmit antenna. If these signals arrive at receiver antennas with sufficiently different spatial signatures and the receiver has accurate channel state information (CSI), it can separate these streams into parallel transmission/reception channels.
Spectral efficiency may be achieved using a system such as cognitive radio (CR), by which a wireless communication transceiver can determine which communication channels are in use and which are not, and can utilize vacant channels while avoiding occupied ones. A CR senses unoccupied or under-utilized frequency bands then changes the operating frequency band to the unoccupied band, thus achieving better spectral utilization. A CR based system must be aware of its environment by sensing spectral usage and must have the capability to switch operating points among different unoccupied frequency bands. A CR based system typically implements various features including spectral sensing, switching between different frequency bands and transmitter power level adjustment.
The radio front end of a CR typically consists of two antennas, (1) an ultra-wideband (UWB) sensing antenna and (2) a reconfigurable communication antenna. A UWB sensing antenna is utilized to scan a wide frequency band while the reconfigurable antenna dynamically changes the basic radiating characteristic of the antenna system to utilize the available bandwidth.
Accordingly one aspect of the present disclosure is to provide a configurable antenna apparatus that exhibits wide tuning range operation is suitable for use in wireless handheld devices and mobile terminals in second generation cognitive radio (CR) platforms for cellular communication.
A dielectric substrate for a configurable antenna has an upper surface and an opposing lower surface. An upper conductor patch is disposed on the upper surface of the substrate and a lower conductor patch is disposed on the lower surface of the substrate. A sensing antenna is formed in the upper conductor patch. An upper set of slot antennas is formed in the upper conductor patch and a lower set of slot antennas is formed in the lower conductor patch. Each of the slot antennas is loaded with a variable reactance component.
In one aspect of the invention, the slot antennas are annular slot antennas, each having a varactor diode connected across the corresponding slot as the variable reactance component.
In another aspect of the invention, each of the slot antennas includes a central void lacking conductive material.
In another aspect of the invention, a transmission line is disposed on an opposing side of the substrate of each of the slot antennas.
In another aspect of the invention, the upper conductor patch comprises a trapezoidal section forming a monopole antenna as the sensing antenna, the lower conductor patch being the reference plane of the monopole antenna.
In another aspect of the invention, the upper set of slot antennas is removed from the trapezoidal section.
In another aspect of the invention, a biasing circuit for the reactance component of each of the slot antennas is disposed on the substrate.
The present inventive concept is best described through certain embodiments thereof, which are described in detail herein with reference to the accompanying drawings, wherein like reference numerals refer to like features throughout. It is to be understood that the term invention, when used herein, is intended to connote the inventive concept underlying the embodiments described below and not merely the embodiments themselves. It is to be understood further that the general inventive concept is not limited to the illustrative embodiments described below and the following descriptions should be read in such light.
Additionally, the word exemplary is used herein to mean, “serving as an example, instance or illustration.” Any embodiment of construction, process, design, technique, etc., designated herein as exemplary is not necessarily to be construed as preferred or advantageous over other such embodiments. Particular quality or fitness of the examples indicated herein as exemplary is neither intended nor should be inferred.
Example planar antenna system 100 comprises two conducting planes 130a and 130b, representatively referred to herein as conducting plane(s) 130, which are disposed on opposing surfaces 151a and 151b and at opposing ends 153a and 153b of a dielectric substrate 150. Conducting planes 130 may be formed of a conductive material, such as copper. Each conducting plane 130 occupies the width W of substrate 150. Conducting plane 130a extends a distance d5 from substrate end 153a and conducting plane 130b extends a distance d6 from substrate end 153b. Distances d5 and d6 may be chosen so as to leave a narrow gap 159 between the distal end of conducting plane 130a and the distal end of conducting plane 130b. This gap may be dimensioned for feed point tuning of UWB sensing antenna 110 by a reactive impedance created in the gap.
Conducting planes 130 may be electrically connected to outer conductors of coaxial connectors 170a-170e, representatively referred to herein as coaxial connectors 170. The center conductors of coaxial connectors 170 may be electrically connected to microstrip transmission lines that feed the antennas of planar antenna system 100: center conductor of coaxial connector 170a is electrically coupled to microstrip transmission line 142a; center conductor of coaxial connector 170b is electrically coupled to microstrip transmission line 142b; center conductor of coaxial connector 170c is electrically coupled to microstrip transmission line 142c; center conductor of coaxial connector 170d is electrically coupled to microstrip transmission line 142d and center conductor of coaxial connector 170e is electrically coupled to microstrip transmission line 144. Microstrip transmission lines 142a-142d are representatively referred to herein as microstrip transmission line(s) 142. It is to be understood that connectors other than coaxial connectors 170 may be used in embodiments of the present invention to connect planar antenna system 100 with external radio components. The outer conductor of coaxial connectors 170 may be electrically connected to ground in which case conducting planes 130 serve as ground planes. However, the present invention is not so limited.
Microstrip transmission lines 142 have a width w3 and length l3 and are positioned to be electromagnetically coupled to corresponding MIMO antenna elements 125 from the opposing side of substrate 150. The width w3 and length l3 may be selected in a conventional fashion to realize a characteristic impedance, e.g., 50Ω of the corresponding microstrip transmission lines 142 when loaded by MIMO antenna elements 125. Microstrip transmission line 144 is electrically coupled to UWB sensing antenna 110 and may be likewise constructed to realize a characteristic impedance. In certain embodiments, microstrip transmission line 144 is tapered from a width w2 to a width w1 for purposes of impedance matching. The reference plane for microstrip transmission lines 142a and 142b is conducting plane 130a and the reference plane for microstrip transmission lines 142c, 142d and 144 is conducting plane 130b. Conducting plane 130b also serves as the reference plane for UWB sensing antenna 110.
As illustrated in
On the outer edges of substrate 150 where trapezoidal section 132 and rectangular section 134 meet are a set of notches 136a and 136b, representatively referred to herein as notch(es) 136. Notches 136 serve to widen the bandwidth of UWB sensing antenna 110.
As illustrated in
Annular slot 128 may be suitably sized and positioned to load the resonator formed from central void 124 with a predetermined reactance. Such reactance is made tunable by a variable reactance element, such as a varactor 115, illustrated in
Having described various structural features of embodiments of the present invention, a specific example will now be provided to demonstrate certain operational characteristics of an embodiment of the present invention. In one embodiment, planar antenna system 100 is constructed in an RO-4350 substrate with a relative permittivity (εr) of 3.48. With a design wavelength of 50 mm, the various dimensions of planar antenna system 100 are W=60 mm, L=120 mm, T=1.5 mm, d1=36 mm, d2=33.45 mm, d3=16 mm, d4=32 mm, d5=55.65 mm, d6=59.8 mm, d7=15.5 mm, w1=1.5 mm, w2=3 mm, w3=3.1 mm, w4=1.15 mm, w5=0.5 mm, l3=13 mm, r1=8.5 mm, r2=9.65 mm, r3=10.1 mm and 0=45°. Conducting planes 130 are connected to electrical ground, such as when the outer conductors of coaxial connectors 170 are grounded. Accordingly, conducting planes 130 serve as ground planes. Parametric sweeps may be performed to optimize the various lengths of the UWB antenna including the length of the microstrip feed line 142. Parametric sweeps may also be performed for varactor diode placement on the specific location to reactively load the slot. The current position of varactor diode has maximal effect on the antenna resonance. The varactor diodes used are type SMV 1233. The varactor diode terminals are connected to a biasing circuit 160 using two shorting posts 117a and 117b, as shown
The biasing circuitry 160, as shown in
Using the dimensions and characteristics described above, example UWB sensing antenna 110 realizes frequency coverage from 0.75 to 7.65 GHz. The simulated and measured reflection coefficients curves of the UWB antenna are given in
For annular slot based MIMO antenna operation, the varactor diode reverse bias voltage is varied between 0-15 volts. The resonating frequency is smoothly changed over the frequency band 1750-2480 MHz. The capacitance of the diode is varied from 1 pF to 6 pF. A significant bandwidth is achieved at all resonating bands. The minimum −6 dB operating bandwidth is 50 MHz. The simulated reflection coefficients are shown in
The example MIMO antenna system may be tuned over wide and continuous frequency bands from 1.75 GHz to 2.48 GHz. The MIMO antenna covers the well-known frequency standards of GSM1800/LTE/UMTS/WLAN along with several others. The MIMO antenna system is compact and suitable for CR platforms in wireless handheld devices.
CR 1200 may include a suitable information storage device 1220 to store policies, rules, etc. 1222, such as spectral bands or frequencies to which the user has authorized access (licensed bands, etc.), geographic regions in which a set of regulations apply, situations in which transmit power must be limited, and so on. Storage device 1220 may also store radio resource utilization models 1224 that can be trained and utilized to determine a best radio resource utilization strategy based on a current radio environment 1260. Additionally, storage device 1220 may store a database 1226 containing information from which a radio resource utilization strategy can be derived based on a current state of radio environment 1260. Such a radio resource utilization strategy may include transmit/receive frequency bands, transmit power and so on.
Information storage device 1220 may be implemented by any quantity of any type of conventional or other memory or storage device, and may be volatile (e.g., RAM, cache, flash, etc.), or non-volatile (e.g., ROM, hard-disk, optical storage, etc.), and include any suitable storage capacity. The storage areas may be, for example, one or more databases implemented on a solid state drive or in a RAM cloud
Sensing component 1240 may be electrically coupled to UWB sensing antenna 110 of planar antenna system 100 to obtain spectral information indicative of radio environment 1260. In one example, sensing component 1240 detects the occupancy state (occupied/unoccupied) of specific frequencies through suitable spectral analysis.
Learning/reasoning component 1230 may utilize information provided by sensing component 1240 and other available information in database 1220 to infer possible radio resource utilization strategies for given sets of conditions. Machine learning and artificial intelligence techniques may be brought to bear to determine a MIMO configuration that will achieve best transmission/reception characteristics based on a range of information including the current state of radio environment 1260. Radio resource utilization models 1224 are continually updated to assist in making a radio resource utilization decision. In certain embodiments, a radio resource utilization decision includes selecting a MIMO antenna configuration that includes specification of a set of voltages that are to be applied to a set of respective varactors. Decision processing component 1270 determines the best radio resource allocation based on the given state of radio environment 1260 and information stored in information storage device 1220. Such decision may be provided to reconfigurable radio component 1250 whereby the radio resource allocation is put into effect. For example, reconfigurable radio component 1250 may provide a voltage to each biasing network 160 of planar antenna system 100 on signal lines 1252a-1252d whereby each MIMO antenna element 125 is configured to transmit/receive using a frequency band that is appropriate to the MIMO configuration. Communication signals consistent with the MIMO configuration, e.g., transmit/receive signals of a selected frequency band, are conveyed to reconfigurable radio 1250 through transmission lines 1255a-1255d connected to planar antenna system 100 through, for example, coaxial connectors 170.
Learning/reasoning component 1230, sensing component 1240 and decision processing component, as well as certain circuits of reconfigurable radio 1250 may be realized by one or more data processing devices such as microprocessors, microcontrollers, systems on a chip (SOCs), or other fixed or programmable logic, that executes instructions for process logic stored the memory. The processors may themselves be multi-processors, and have multiple CPUs, multiple cores, multiple dies comprising multiple processors, etc.
Aspects of the present invention are described 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 program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.
The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, method 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 code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, 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 sometime be executed in the reverse order, depending on 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 combinations of special purpose hardware and computer instructions.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more features, integers, steps, operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form 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 invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
The descriptions above are intended to illustrate possible implementations of the present inventive concept and are not restrictive. Many variations, modifications and alternatives will become apparent to the skilled artisan upon review of this disclosure. For example, components equivalent to those shown and described may be substituted therefore, elements and methods individually described may be combined, and elements described as discrete may be distributed across many components. The scope of the invention should therefore be determined not with reference to the description above, but with reference to the appended claims, along with their full range of equivalents.
