Patent Grant
10547107
This invention relates generally to the field of wide-band wireless communication systems and consumer electronic devices. More particularly, it relates to reconfigurable multiple-input-multiple-output (MIMO) antenna systems for cognitive radio (CR) platforms for compact wireless devices and LTE mobile handsets. The complete antenna setup can be used in radio frequency based applications, including 4G cellular systems.
New trends in modern communication systems have emerged as a result of the growing data rate requirements for modern wireless systems and the need for multi-standard operation in smart wireless devices. The increasing demand of wireless services has made the radio spectrum a very scarce and precious resource. Most current wireless networks characterized by fixed spectrum assignment policies are inefficient, with only 15% to 85% of the licensed spectrum utilized on average.
To meet the high data rate requirements, reconfigurable MIMO antenna systems have gained in popularity over the past few years. This is because of their ability to operate according to the system requirements while keeping the MIMO functionality. A frequency reconfigurable antenna system can operate in MIMO configuration to enhance the system throughput and can support multiple wireless standards by switching its operation across different frequency bands. Thus, it helps to mitigate the spectrum congestion by efficiently utilizing the spectrum resources, which is the prime purpose of a CR platform.
CR is an adaptive, intelligent radio and network technology that can automatically detect available channels in a wireless spectrum and change transmission parameters enabling more communications to run concurrently and also improve radio operating behavior. The major advantage of a CR technique is its ability to utilize the idle or under-utilized spectrum resources. CR uses a number of technologies including Adaptive Radio (where the communications system monitors and modifies its own performance) and Software Defined Radio (SDR) where traditional hardware components including mixers, modulators and amplifies have been replaced with intelligent software.
Frequency reconfigurable MIMO antennas are the key front-end in a CR antenna system. Frequency agile MIMO slot antennas are suitable to be used as CR front-end antennas because of several advantages they offer. In addition to their capability to enhance system throughput, they are also easy to fabricate and are compatible with other microwave integrated circuits.
To enhance the capacity of a multiband or wideband communication system, it is necessary to implement reconfigurable characteristics in the system. These topologies are used to efficiently utilize the available frequency spectrum. The concept of CR is all about efficient frequency spectrum use. A CR based system has the ability to sense unoccupied frequency bands and has switching capability to change the operating point with increased data reliability and channel capacity. Moreover, MIMO technology is increasing in popularity because it provides high data rates with increased range and reliability. MIMO antennas are being utilized in 4G wireless standards.
Frequency agile antennas are an essential component of CR platforms. For efficient spectrum utilization, it is highly desirable to have antennas with wide-band operation or which can switch across several frequency bands. Reconfigurability is the fundamental requirement for CR applications in wireless devices. In addition, reconfigurable MIMO antenna systems are widely adopted in current communication systems to achieve the high data rate requirements within the available limited power and bandwidth channels. The key feature of a MIMO antenna system is its ability to multiply data throughput with enhanced data reliability, using the available bandwidth and hence resulting in improved spectral efficiency.
Exemplary prior includes the systems disclosed in issued U.S. Pat. No. 9,537,223 to Hall et al. and U.S. Pat. No. 8,957,817 to Jiang et al., and in published US patent application 2017/0062943 to Patron et al.
Hall et al. (U.S. Pat. No. 9,537,223) disclose a reconfigurable multi-output antenna (16) that comprises one or more radiating elements (12, 14), at least two matching circuits (42, 44, 50, 52) coupled to the or each radiating element (12, 14) via e.g. a splitter (30, 32) or a duplexer; and wherein each matching circuit (42, 44, 50, 52) is associated with a separate port (38, 40, 46, 48) arranged to drive a separate resonant frequency so that the or each radiating element (12, 14) is operable to provide multiple outputs simultaneously. Each matching circuit may be reconfigurable to enable their respective ports to tune their outputs to different frequencies. The matching circuits may comprise one or more than one inductor or capacitor (e.g. in the form of an L-C circuit) and may comprise a variable capacitor (i.e. varactor). (See figures and col. 10, lns. 47-col. 11, lns. 49).
Jiang et al. (U.S. Pat. No. 8,957,817) disclose a wireless communication system which is both miniaturized and reconfigurable. The antenna is a CPW (coplanar wave guide) square-ring slot antenna which is miniaturized and reconfigurable by the integration of ferroelectric (FE) BST varactors at the back edge of the inner conductor, or patch, of the antenna. The frequency of the antenna is reconfigurable due to the tunable capacitance of the FE varactors. (See figures and summary).
Patron et al. (2017/0062943) disclose a reconfigurable leaky-wave antenna that includes a plurality of cascaded metamaterial unit cells where each cell has a complementary resonator in its ground plane and adjustable varactor diodes that are biased to change a propagation constant through the plurality of cascaded metamaterial unit cells so that a directive beam from the antenna can be steered around an azimuth plane. (See figures and [0012]-[0014]).
To applicant's knowledge, no one has developed a compact, MIMO antenna for CR platforms for cellular communication front ends, wherein the antenna is frequency agile and has a wide tuning range covering several well-known wireless standards, including, among others, GSM1800, LTE, UMTS and WLAN.
Accordingly, there is need for a compact, MIMO antenna for CR platforms for cellular communication front ends, wherein the antenna is frequency agile and has a wide tuning range covering several well-known wireless standards, including, among others, GSM1800, LTE, UMTS and WLAN.
The present invention is a compact, frequency-agile, MIMO antenna for CR platforms for cellular communication front ends, wherein the antenna has a wide tuning range covering several well-known wireless standards and enables switching between operating bands in CR platforms.
Slot-reconfigurable antennas are integrated in the CR platform and continuous frequency tuning is achieved using varactor diodes. Frequency-reconfigurable MIMO antenna systems combine the advantages of high throughput capability and the ability to switch between several bands/standard coverage.
The invention uses a low profile, 4-element, slot-based, frequency reconfigurable MIMO antenna. The MIMO antenna is on a board having typical smart phone dimensions. The proposed antenna covers a wide frequency band from 1800 MHz to 2450 MHz and supports several well-known wireless standards bands, including GSM1800, LTE, UMTS and WLAN, as well as many others.
The proposed antenna design can be tuned to other frequency bands by choosing different sizes of the annular slot. The antenna design is miniaturized by loading the slot using reactive impedance. With the invention, four antenna elements are accommodated in a small area. At least a 50% size reduction is obtained at the lowest resonating band, and the 4-element MIMO antenna system is realized on board dimensions of 60×120×0.76 mm3. Furthermore, the proposed antenna elements exhibited a tiled radiation pattern that helped in lowering the field coupling between antenna elements and hence enhanced the MIMO performance.
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
The foregoing, as well as other objects and advantages of the invention, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like reference characters designate like parts throughout the several views, and wherein:
The geometry of the proposed 4-element, slot-based MIMO antenna system is shown in
As seen best in
The bottom layer 40 contains four annular slot, reconfigurable MIMO antenna elements 1, 2, 3 and 4, respectively, fed via system input SMA connectors 5, 6, 7 and 8, respectively. A single antenna element consists of a circular slot CS having a radius 17 of 8.5 mm, and an annular slot AS having a radius 18 of 10.1 mm. The slot AS has a width of 0.5 mm (radius 16 minus radius 18—see
The varactor diodes 19, 20, 21 and 22 are placed so that they span the width of the outer annular slot AS and are used to load the antenna by reactive capacitance. The diodes connect the inner and outer edges of the annular slot and thus bridge the slot with capacitive reactance. The varactor diode terminals, on the GND plane 40, are connected with the associated biasing circuit 28 using two shorting posts 23 as shown on the bottom layer. The GND plane layer 40 acts as a co-planar reflector for the MIMO antenna elements, enabling beam tiling and thus lowering the field coupling for better MIMO performance.
As shown in
The SMA connectors 5, 6 and 7, 8 at the ends of the board are spaced apart a distance 11 of 36 mm. The longitudinal spacing 13 between the centers of the circular slots CS at one end of the board and the centers of the circular slots at the opposite end is 80 mm. The lateral spacing 14 between the centers of the circular slots at each end of the board is 36 mm, and the lateral spacing 15 between the annular slots AS at each end of the board is 15.5 mm. As noted previously, each annular slot has a width of 0.5 mm. The board has a thickness of 0.76 mm and the dielectric constant of the substrate is εr=3.48. The varactor diodes used are SMV 1233.
For antenna operation, the varactor diode reverse bias voltage is varied between 0˜15 volts. The capacitance of a varactor diode has a significant effect on its resonating frequency. When the resonating frequency is smoothly changed over the frequency band 1800˜2450 MHz, the capacitance of the diode varies from 0.7 pF to 6 pF. A significant bandwidth is thus achieved at all resonating bands. The minimum −6 dB operating bandwidth is 40 MHz.
The gain patterns for the four antenna elements at 2000 MHz is shown in
As can be seen, the antenna system of the invention is slot-reconfigurable and continuous frequency tuning is achieved using varactor diodes. Frequency-reconfigurable MIMO antenna systems combine the advantages of high throughput capability and the ability to switch between several bands/standard coverage. The covered bands can be changed according to the design requirements by changing the slot width, inter-slot spacing, etc. The very wide bandwidths obtained are essential for future wireless standards to support higher data rates as well as backward compatibility with current standards.
While the invention has been described in connection with its preferred embodiments, it should be recognized that changes and modifications may be made therein without departing from the scope of the appended claims.
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| Number | Date | Country | |
|---|---|---|---|
| 20190305423 A1 | Oct 2019 | US |
