Patent Application
20190372241
This invention relates to antenna systems especially configured for wide-band wireless communication, consumer electronic devices, and reconfigurable multiple-input-multiple-output (MIMO) systems.
In modern wireless communications, the exponential growth of wireless services results in an increasing data rate requirements and data reliability. Communication services may include high-quality audio/video calls, online video streaming, video conferencing, and online gaming. These demanding services may require wide bandwidth operation or operation across several frequency bands. This requires efficient utilization of the available spectrum via sensing of available unused bands. The concept of cognitive radio (CR) overcomes the inefficient and highly underutilized spectrum resources. A CR system is based on a software defined radio (SDR) structural design and is intended to enhance spectrum utilization efficiency by interacting with the operating environment. CR based systems are aware of the communications environment by sensing spectrum usage and have the capability to switch operating points among different unoccupied frequency bands. CR based systems may include various features such as sensing spectrum of nearby devices, switching between different frequency bands, and power level adjustment of transmitting antennas.
The front end of a CR includes two antennas: (1) an ultra-wide-band (UWB) sensing antenna and (2) a reconfigurable communication antenna. UWB antenna is used to sense the entire spectrum of interest while reconfigurable antennas are used to dynamically change the basic radiating characteristic of the antenna system to utilize the available bandwidth. Frequency reconfigurable multiple-input-multiple-output (MIMO) antenna systems provide potential advantages such as having several frequency bands/multi-band operations, high system throughput and enhancing the data rate capability of MIMO systems. Reconfigurable MIMO antennas are also utilized at the front-ends of cognitive radio (CR) applications. CR is being utilized in communication systems to avoid spectrum congestion by switching the operating bands. Slot-based reconfigurable antennas are highly suitable to be used in CR system because of their low profile structure and ease of integration with other components.
It is therefore an object of the present disclosure to describe an antenna system having PIFA elements that operates at the wireless local area network (WLAN) band and annular slots that act as an isolation enhancement structure for the PIFA elements. The slots are made reconfigurable using varactor diodes by applying reverse bias voltage across their terminals.
The foregoing “Background” description is for the purpose of generally presenting the context of the disclosure. Work of the inventor, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
The present disclosure relates to an antenna system. The antenna system includes a dielectric substrate. The dielectric substrate has a top surface and a bottom surface. The antenna system also includes a first planar inverted-F antenna (PIFA) radiating element and a second PIFA radiating element disposed on the top surface of the dielectric substrate. The PIFA radiating element has a F-head portion. The antenna system also includes at least two defected ground structures (DGSs) disposed on the bottom surface of the dielectric substrate. The at least two DGSs are configured to provide isolation between the first and the second PIFA radiating element. Each DGS antenna includes a varactor diode. The antenna system also includes a bias circuit corresponding to each of the at least two DGSs.
In another aspect, the present disclosure relates to an apparatus. The apparatus includes an antenna system and wireless circuitry that uses the antenna system to handle signals in one or more communication bands. The antenna system includes a dielectric substrate. The dielectric substrate has a top surface and a bottom surface. The antenna system also includes a first planar inverted-F antenna (PIFA) radiating element and a second PIFA radiating element disposed on the top surface of the dielectric substrate. The PIFA radiating element has a F-head portion. The antenna system also includes at least two DGSs disposed on the bottom surface of the dielectric substrate. The at least two DGSs are configured to provide isolation between the first and the second PIFA radiating element. Each DGS antenna includes a varactor diode. The antenna system also includes a bias circuit corresponding to each of the at least two DGSs.
In another aspect, the present disclosure relates to a method for configuring an antenna system. The method includes forming two planer inverted F antennas for operation at a desired frequency at a top surface of a dielectric substrate; forming at least two defected ground structures (DGSs) at a bottom surface of the dielectric substrate to provide isolation between the two PIFA antennas, each of the DGS including a varactor diode to reactively load the DGS; forming a bias circuit for each of the DGS; and controlling, using processing circuitry, a voltage to the varactor diode based on a desired resonant frequency.
The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.
A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
The terms “a” or “an”, as used herein, are defined as one or more than one. The term “plurality”, as used herein, is defined as two or more than two. The term “another”, as used herein, is defined as at least a second or more. The terms “including” and/or “having”, as used herein, are defined as comprising (i.e., open language). The term “coupled”, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.
Reference throughout this document to “one embodiment”, “certain embodiments”, “an embodiment”, “an implementation”, “an example” or similar terms means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, the appearances of such phrases or in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments without limitation.
The term “or” as used herein is to be interpreted as an inclusive or meaning any one or any combination. Therefore, “A, B or C” means “any of the following: A; B; C; A and B; A and C; B and C; A, B and C”. An exception to this definition will occur only when a combination of elements, functions, steps or acts are in some way inherently mutually exclusive.
Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout several views, the following description relates to an integrated multiple-input-multiple-output (MIMO) antenna system.
The MIMO antenna system may be used in the field of wide-band wireless communication systems and consumer electronic devices, reconfigurable multiple-input-multiple-output (MIMO) antenna systems for cognitive radio platform for compact wireless devices, and long-term evolution (LTE) mobile handsets. The complete antenna setup can be used in radio frequency based applications including 4G cellular systems.
An integrated MIMO antenna system is described herein. The antenna includes two planar inverted F-antenna (PIFA) elements integrated with two annular slot based frequency agile antennas to form a dual MIMO antenna system. The isolation is improved between the two PIFA elements as the annular slots acts as a defected ground structure (DGS). The annular slots are utilized as a frequency reconfigurable MIMO antenna system. The dual function frequency reconfigurable MIMO configuration increases the system throughput by increasing the number of antenna elements in wireless handheld devices by reusing DGS structures as separate set of antennas without modifying the board size.
The geometry of the integrated dual MIMO antenna system 100 is shown in
The top layer also includes microstrip feed-lines 116, 118 for annular slot-based antennas 146, 148, and biasing circuitry 120,122, for varactor diodes 144, 155.
The PIFA antenna elements 104, 106 are fed with 50Ω probe-feed connectors 128, 130. In one implementation, the antenna dimensions are set for resonance at 2.45 GHz. The antenna dimensions may be set for resonance at a frequency in the range of 2.295 to 2.68 GHz. A considerable mutual coupling value is observed between the two PIFA antenna elements. In order to enhance the isolation, the set of two annular slots 146, 148 are created between them. The dimensions and location of the slots are optimized to improve the isolation between the PIFA antenna elements at 2.45 GHz. The antenna dimensions may be optimized to resonate at other frequencies as would be understood by one of ordinary skill in the art.
Open-end microstrip transmission-lines 116,118 with 500 characteristic impedance are used to feed the annular slots 146, 148. The DGS structure (i.e., annual slot antennas 146, 148) is utilized as a frequency reconfigurable antenna. In one implementation, an electrical length of λ/2 corresponds to resonance at 3.1 GHz where λ is the wavelength. The antenna dimensions of the slot are optimized such as the antenna resonates at 3.1 GHz without any reactive loading. The antenna dimensions of the slot may be set such as the antenna resonates at a frequency in the range of 2.9 GHz to 3.3 GHz. In one implementation, the frequency may be in the range of 2.5 GHz to 4 GHz.
The slot antennas 146, 148 may include reactive elements. The slot antennas 146, 148 including reactive element are frequency reconfigurable. Parametric sweeps may be performed to properly place the reactive elements (e.g., varactor diodes) and to effectively load the slot antenna. The current positions of the varactor diodes as shown in
In one implementation, the antenna system 100 may include additional varactor diodes to provide more flexibility to tune the antenna over a wide band as would be understood by one of ordinary skill in the art.
A biasing circuit similar to biasing circuit 300 may be used to bias each of the varactor diodes of the antenna system 100. The biasing circuit 120 associated with the first varactor diode 144 includes resistors 132a, 132b and RF chokes 134a, 134b. The varactor diode 144 is reverse biased by applying a variable voltage source (not shown) between a positive terminal 108 and GND pad 110. The biasing circuit 122 associated with the second varactor diode 150 includes resistors 138a, 138b and RF chokes 140a, 140b. The varactor diode 144 is reverse biased by applying a variable voltage source between a positive terminal 112 and GND pad 114.
The varactor diode is utilized to tune the resonance frequency of the annular slot antenna over a wide operation band. In one implementation, the varactor diode may be a SMV 1235 varactor diode. The varactor diode package may be 0805 with standard dimensions of 2.0 mm×1.2 mm. Other varactor diode packages may be used as would be understood by one of ordinary skill in the art. In one implementation, the varactor diode package may have dimensions in the range of about 1.5 mm to 2.5 mm by about 0.8 mm to about 1.5 mm.
In one implementation, the bias circuit may be tuned using control signals from control circuitry or a controller. The controller may be associated with an electronic device including the antenna system 100. Control signals may be provided to adjust the variable voltage source 312 and therefore the capacitance. By selecting a desired capacitance value using the control signals, the radiating element can be tuned to cover operating frequencies of interest.
In one implementation, the PIFA elements 104, 106 may have the following dimensions: D=7.4 mm, E=4.4 mm, and H=3.48 mm. A length of the micorstrip feed-line 118 may be 36 mm (indicated by F in
To illustrate the capabilities of the antenna system described herein, exemplary results are presented.
A professional software high frequency structural simulator (HFSS™) is used to observe the reflection response and the radiation properties of the antenna system. A prototype of the antenna system described herein is fabricated using a LPKF S103 machine.
The annular slots on the GND plane are acting as DGS as well as utilized to get frequency reconfigurability in the MIMO antenna system 100. Varactor diodes 144, 150 are used to get the frequency agility in the design. Each varactor diode is modeled as a variable capacitor with values ranging between 2.38 pF to 9.91 pF. In the simulations, the capacitance values used are C1=2.38 pF, C2=12.61 pF, C3=4.11 pF, C4=7.36 pF and C5=9.918 pF. This resulted in antennas tuning between 1.76 to 2.3 GHz. The particular position of the varactor diode is selected such as the capacitance has the maximum effect on the frequency sweep of the design.
The simulated and measured reflection coefficient curves for antenna 146, 148 are shown in
Mutual coupling between annular slots antenna 146 and 148 was analyzed. The simulated and measured isolation curves are shown in
The 3D gain patterns of the proposed PIFA based MIMO antenna system 104, 106 is shown in
A system which includes the features in the foregoing description provides numerous advantages to users. In particular, an integrated multiple-input-multiple-output (MIMO) antenna system is provided. The PIFA elements operates at the wireless local area network (WLAN) band while the annular slots act as an isolation enhancement structure for the PIFA elements. Further, the annular slots are tuned over a wide frequency bands from 1.73 GHz to 2.28 GHz with a minimum bandwidth of 60 MHz. The slots are made reconfigurable using varactor diodes by applying reverse bias voltage across their terminals. All the antenna elements are of small size, low profile and planar in structure and hence can easily be accommodated in wireless devices for second generation cognitive radio applications. The antenna system described herein is realized on a substrate area of 50×110 mm2. The antenna system described herein supports several well-known wireless standards bands as would be understood by one of ordinary skill in the art.
Obviously, numerous modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
Thus, the foregoing discussion discloses and describes merely exemplary embodiments of the present invention. As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting of the scope of the invention, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, defines, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.
