Patent Application
20230268664
Aspects of the present disclosure were described in “Independent and Concurrent Tunable 5G MIMO Antenna Design,” Rifaqat Hussain, IET Microwaves, Antennas & Propagation Journal (Feb. 24, 2021).
The present disclosure is directed to a fifth generation (5G) antenna design and, more specifically, is directed to a slot frequency reconfigurable (FR) 5G dual-band, multi-input, multiple-output (MIMO) antenna using concentric, annular elements.
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, 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.
Fifth generation (5G) wireless technology has been developed to provide high data rates, low latencies, improved reliability, and enhanced energy and spectral efficiencies when compared to previous standards. However, use of the existing standards simultaneously with early stages of 5G commercialization for both sub-6 GHz along with mm-wave bands are envisioned to enable a smooth transition. As a result, the sub-6 GHz bands will be used to support and enhance mobile broadband in conjunction with existing 4G resources that can be reused for 5G communication.
The 5G radio access networks (RANs) are specified to support multiple-input-multiple-output (MIMO) antenna systems. Based on that aspect, 5G RANs will use multi-band antenna designs with independent or concurrent tuning capabilities for frequency agility. Several common challenges arise for sub-6 GHz antenna designs, including large bandwidth requirements, multi-band antenna designs, and MIMO implementation with maximum antenna elements within the given space. Accordingly, concurrent and independent tuning for frequency reconfigurable (FR) antennas, in addition to multi-band operation with multiple connection and very wide sweep, are features being implemented for 5G sub-6 GHz communication systems.
Various types of antennas have been proposed for enabling these technologies, such as dipole, monopole, patch (e.g., U.S. Patent Application 2017/0033461A1), cube (e.g., U.S. Patent Application 2008/0303733A1), and slot-based approaches. However, slot-based antenna designs have provided the greatest number of advancements. Slot-based antennas are typically compact planar designs, can be flexibly integrated with other system components, are potentially suitable for FR operation, and possess wide-band tuning capabilities.
Numerous slot-based solutions previously developed enabled two or more bands, tuning, and/or planar concepts. For example, U.S. Patent Application 2018/0219292A1 discloses a multi-band slotted solution. Slot-based designs with 4-antenna elements or with three covered frequency bands have been proposed. Some developments, such as JP 2004320115A, have relied on composite annular layouts. However, many have either limited tuning capabilities or relatively large board dimensions.
Each of the aforementioned antennas suffers from one or more drawbacks hindering their adoption. Accordingly, it is one object of the present disclosure to provide a small antenna suitable for FR operation, that can be flexibly integrated with other system components, while still possessing wide-band tuning capabilities.
In an exemplary embodiment, a reconfigurable dual-band MIMO antenna apparatus includes a dielectric planar substrate, a first element, a second element, two varactor diodes per element, and a microstrip feed-line. The first element and the second element each have slotted concentric annular rings. The second element is separated on the dielectric planar substrate from the first element, but is coplanar on the dielectric planar substrate with the first element. The two varactor diodes are placed in series with biasing circuitry, the biasing circuitry including RF chokes and current-limiting resistors. The microstrip feed-line feeds both antenna elements. The dual-band antenna elements can each be independently and concurrently tunable to two signal frequencies bands.
In some embodiments, both concentric slots are approximately 0.5 mm in width and are excited by the same microstrip feed-line placed on the dielectric planar substrate at the opposite side of the slot. In certain embodiments, a voltage is applied to a terminal of one or more of the varactor diodes to change a capacitance of the varactor diodes, thereby tuning an independent external signal frequency of either of the first element or the second element of the antenna apparatus. In certain embodiments, the varactor diodes change in capacitance due to a reverse bias voltage. In embodiments, each antenna element can be configured to transmit or receive a signal frequency between two different ranges as the capacitance of the varactor diodes change.
In certain embodiments, the varactor diode locations on the antenna elements are selected to provide an impedance match of the antenna apparatus to an electrical load of the microstrip feed-line. In some embodiments, the antenna apparatus has a compact planar structure suitable for use in a mobile device wherein each antenna element is less than 12×12 mm2. In particular embodiments, radiation patterns of the antenna elements are configured to support an envelope correlation coefficient of less than 0.5. In some embodiments, the inner and outer concentric slots are placed on an outer edge of a ground plane with radii of 8-10 mm and 10-12 mm, respectively.
In certain embodiments, the antenna apparatus is configured to support a radiation pattern with efficiency of 90 percent at 3.6 GHz. In particular embodiments, the antenna is configured to support a radiation pattern of an antenna elements with a peak gain of 4.3 decibels-isotropic (dBi) achieved at 3.6 GHz. In other embodiments, the antenna is configured to support a peak gain of 2.98 dBi, which is achieved at 2.52 GHz.
In another exemplary embodiment, a method of transmitting and receiving a signal at varying frequencies from either of two dual-band planar annular concentric slot MIMO antenna elements is provided. An input impedance is varied by selecting a first location on a first antenna element of a first varactor diode. A second location on a second antenna element of a second varactor diode is selected. A signal frequency is tuned by varying either a capacitance of the first varactor diode or a voltage on a second varactor diode.
In some embodiments, the concentric slots are placed on an outer edge of a ground plane. In certain embodiments, tuning the frequency of each antenna element includes applying a voltage between 0 and 10 V to obtain a frequency range between either 1.7 GHz and 2.4 GHz or between 2.4 and 3.8 GHz. In certain embodiments, the antenna is configured to support a radiation pattern with efficiency of 90 percent. In particular embodiments, the antenna is configured to have an efficiency of 90 percent at 3.6 GHz.
In some embodiments, the varactor location is determined by solving the following equation: tan βL1+tan β(L−L1)−ωCZ0 tan βL1 tan β(L−L1)=0, where, L1 is a varactor location, Cv is a reverse-biased varactor capacitance, Z0 is an impedance of a slot antenna element, ω is the angular frequency of operation, and β is the propagation constant, which depends on ω and Cy.
In another exemplary embodiment, a planar MIMO antenna system that is frequency reconfigurable between 1.7 and 3.8 GHz includes the reconfigurable dual-band MIMO antenna apparatus, respective RF chokes for the first and second elements, and respective current limiting resistors for the first and second elements.
In some embodiments, the varactor diodes of the antenna system are configured to change in capacitance from 0.46 pF to 2.4 pF due to a voltage between 10 V and 0 V being applied to either of the varactor diodes, which results in an antenna signal frequency range between 1.7 GHz and 3.8 GHz.
The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure, and are not restrictive.
A more complete appreciation of this 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:
In the drawings, like reference numerals designate identical or corresponding parts throughout the several views. Further, as used herein, the words “a,” “an” and the like generally carry a meaning of “one or more,” unless stated otherwise.
Furthermore, the terms “approximately,” “approximate,” “about,” and similar terms generally refer to ranges that include the identified value within a margin of 20%, 10%, or preferably 5%, and any values therebetween.
Aspects of this disclosure are directed to an antenna apparatus having a compact overall footprint, while at the same time enabling dual-band operation with independent and concurrent tuning capabilities. The described embodiments are suitable for existing fourth generation (4G) standards, as well as for the transition that has begun to fifth generation (5G) radio access networks (RANs). Antenna diversity features, such as those described above and below, help enable the simultaneous integration of mobile devices that use those antennas into 4G and 5G networks. In addition, the proposed 5G radio access technology enabled by the antenna apparatus of the present disclosure is suitable for multiple, concurrent connections using cognitive radio (CR) techniques.
A dual-band, concentric annular slots antenna design is presented in the instant disclosure with flexibility to control both bands. Features include independent and concurrent tuning capability across the dual-band operation, using a simple biasing network. Thus, dual-band operation can be guaranteed over a frequency range from 1.7-3.8 GHz with a compact size, using coverage bands from 1.7-2.4 GHz and 2.4-3.8 GHz. Moreover, independent tuning capabilities with narrow-band (NB) operation enables better power management in 5G communication, along with stable antenna operation. The described antenna design can be fabricated on a board having a volume of 60×120×0.76 mm3, with a single element footprint of just 11×11 mm2.
In order to cover the widest frequency bands of 4G and 5G wireless technologies possible, the width of each annular antenna structure, or slot, and the distances between each slot are optimized for tuning the overall antenna. Another aspect of the described apparatus is the use of two varactor diodes per pair of slots (also referred to as antenna elements) to lower the frequencies of resonating bands, as well as to obtain a continuous sweep of frequencies. The location and placement of the varactor diodes are precisely determined to define the exact resonating bands, to improve input impedance (Zin) matching, and to allow a frequency sweep across wideband spectrum. Parametric analyses were performed to optimize the placement of the varactor diodes on the slot structure, in turn obtaining enhanced Zin matching. The dimensions and diode placements of the described embodiments result in a continuous frequency sweep from 1.7-3.8 GHz, thereby covering several newly used wireless bands found in 5G sub-6 GHz RANs.
The antenna apparatus 100 includes two concentric, annular, slot-based elements, shown in
The distance between the first microstrip feed line 126 and the second microstrip feed line 136 is referenced as “Wi” in
The first outer ring 124 and the second outer ring 134 have a size or diameter, denoted as “SOR” in
In some embodiments, the first inner ring 122, the first outer ring 124, the second inner ring 132 and the second outer ring 134 are approximately 0.5 mm in width. Both the first element 120 and the second element 130 can be placed on the outer edges of the GND plane 140. The second element 130 is separated on the GND plane 140 and the dielectric planar substrate 110 from the first element 120, but is coplanar with the first element 120.
The antenna apparatus 100 also includes varactor diodes 140, 142, 144, and 146, as shown in
As depicted in
The antenna apparatus 100 further includes a defected ground structure (DGS) 150 on the GND plane 140 as shown in
Shorting posts, denoted as “sp” in the
As shown in
As illustrated, the antenna apparatus 100 has a compact planar structure suitable for use in a mobile device, such as a smart phone, a tablet, or a laptop. For example, each of the antenna elements 120 and 130 can be less than 12×12 mm2, as the value of SOR can be less than 11.5 mm. In certain embodiments, the first and second elements 120 and 130 are placed on an outer edge of the ground plane 140, with inner rings 122 and 132 having radii of 8-10 mm and outer rings 124 and 134 having radii of 10-12 mm.
Turning to
The inner rings 122 and 132 and the outer rings 124 and 134 as shown in
The top layer 100C of the fabricated board shown in
Both of the elements 120 and 130 can be reactively loaded using varactor diodes (such as varactor diodes 140-146). In doing so, the capacitance values increase resulting in lowering the fundamental resonance frequency, in addition to reducing with higher-order resonance frequencies to lower bands. As an example, SMV 1231 Series hyperabrupt junction tuning varactors (available from Skyworks Solutions, Inc. of Irvine, Calif.) can be used as the varactor diodes 140-146.
The antenna elements 120 and 130 with short-circuited structures at both ends can be modeled as a half transmission line, corresponding to their respective fundamental resonance frequencies. The fundamental resonance frequency of the antenna element can be represented by the following.
where c is the speed of light, εr is the relative permittivity of the substrate 110, and fr is the fundamental resonance frequency of the antenna element. The radii of the inner rings 122 and 132 and the outer rings 124 and 134 are represented by r1 and r2, respectively. The term 0.5π(r2+r1) represents the mean circumference of combined annular structure (i.e., element 120 or element 130).
Both of the elements 120 and 130 can be reactively loaded using varactor diodes (such as varactor diodes 140-146) to increase capacitance values. In doing so, the capacitance increase results in lowering the fundamental resonance frequency, in addition to reducing with higher-order resonance frequencies to lower bands. The reactive loading is a non-uniform operation that can be determined by using the location (L1) of the varactor diodes 140-146, the capacitance value C of the varactor diodes 140-146, and impedance (Zo) of the slot-line structure 150. The transmission line equivalent circuit model of the antenna apparatus (discussed in further detail below) can be utilized to calculate the resonance frequency. The resonance frequency of the reactively loaded antenna element can be determined numerically solving the below equation:
tan βL1+tan β(L−L1)−ωCZ0 tan βL1 tan β(L−L1)=0 (Eq. 2)
In the above equation, β is the propagation constant and depends on the frequency of operation. The reverse biased varactor capacitance is represented by C, and ω is the angular frequency of operation.
Turning to
In
The antenna apparatus 100, the first element 120, the first connection port 128, the second element 130, the second connection port 138, and the DGS 150 are all substantially similar to those elements as described above. In addition, there is a signal connection 170 connected to the first connection port 128, and a 50-Ω load 172 connected to the second connection port 138. Using configuration 300, a number of MIMO parameters can be collected as shown in the below figures and in Table I found below.
The peak gain and efficiency (% η) values can be evaluated for the antenna apparatus 100 at different frequency bands. For each measurement, a single antenna element (i.e., antenna element 120 or 130) can be observed, while an opposite port can be terminated with 50-Ω load (i.e., either of first port 128 or second port 138).
The envelop correlation coefficient (ECC), peak gain (PG) and % η values were also computed as shown in Table I. ECC values of less than 0.5 were measured over entire bands of operation of the antenna apparatus 100, indicating suitable MIMO characteristics of the apparatus while in operation.
When determining the suitability of the antenna apparatus 100 for 4G and 5G use, the antenna apparatus 100 can be examined in the context of MIMO performance metrics. One important parameter to consider is the ECC (or alternatively denoted as ρe). ECC is a measure of the field coupling between various correlated channels using radiation patterns. Values of ρe less than 0.5 are often sought for suitable MIMO operation. For the design of the antenna apparatus 100, ρe is computed for both simulated and measured patterns. Various values with corresponding frequencies are given above in Table I.
Despite the small footprint and close proximity of the antenna elements 120 and 130, the antenna apparatus 100 supports an envelope correlation coefficient of less than 0.5 with radiation patterns exhibited by the antenna elements (as described in further detail below along with other parameters of the antenna apparatus). As seen in Table I above, the antenna apparatus 100 can be configured to support a radiation pattern of antenna elements with a peak gain of 4.3 decibels-isotropic (dBi) at 3.6 GHz. The antenna apparatus 100 can also be configured to support a peak gain of 2.98 dBi at 2.52 GHz. Moreover, the antenna apparatus 100 can be configured to support a radiation pattern with efficiency of 90 percent at 3.6 GHz. In fact, as seen in the table, all of the ρe values over the entire frequency band validate the suitability of antenna apparatus 100 for MIMO operation.
In certain embodiments, the varactor location is determined by solving Equation 2 as shown above and below where, L1 is a varactor location, Cv is a varactor capacitance, Z0 is an impedance of a slot antenna element. In the below equation, β is the propagation constant and depends on the frequency of operation. The reverse biased varactor capacitance is represented by C, and ω is the angular frequency of operation.
tan βL1+tan β(L−L1)−ωCZ0 tan βL1 tan β(L−L1)=0 (Eq. 2)
At a step 530, a signal frequency is tuned by varying a capacitance of the first varactor diode by applying variable voltage across the varactor diode. According to some embodiments, tuning the frequency includes applying a voltage between 0 and 10 V to obtain a frequency range between either 1.7 GHz and 2.4 GHz or between 2.4 and 3.8 GHz. In instances involving the latter frequency range, the antenna can be configured to have an efficiency of 90 percent at 3.6 GHz. In certain embodiments, the antenna is configured to support a radiation pattern with efficiency of 90 percent.
A total active reflection coefficient (TARC) is another parameter which can be used to characterize the performance of MIMO components, providing a measure of the effective bandwidth of antenna designs.
From the TARC curves shown in
Using this phenomenon, the length of the antenna elements can be mapped to determine the effective electrical length of the resonating bands as well as the mutual coupling between the antenna elements 120 and 130.
As shown in the above embodiments and measured characteristics, each band of the antenna apparatus 100 can be independently and concurrent tuned over a wide frequency range from 1.7 GHz to 3.8 GHz. The antenna apparatus 100 has a low profile and compact planar structure with dual bands of operation. The antenna apparatus 100 can be utilized in existing 4G wireless standards, as well as within with sub-6 GHz bands of 5G operation for new RANs using cognitive radio (CR) techniques.
Obviously, numerous modifications and variations of the present disclosure 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.
