The subject matter disclosed herein relates generally to radio frequency antennas. More particularly, the subject matter disclosed herein relates to the design, construction, and operation of tunable antennas.
In the mobile communications market, the number worldwide users and the increasing demand for a wide range of mobile services (e.g., including wireless voice telephony, mobile Internet access, fixed wireless Internet access, video calls, and mobile TV technologies) has driven the development of new generations of cellular standards having new frequency bands and higher data rates. To accommodate users on a variety of networks, one solution can be to particularly design mobile devices to be used with a specific network configuration. This approach can lead to manufacturing inefficiencies, however, as multiple variations of the same product would be needed to accommodate the multiple different mobile telecommunications standards.
As a result, it can be desirable for mobile devices to be compatible with more than one set of mobile telecommunications standards to provide manufacturing efficiency (e.g., 1 SKU for all global production) and device versatility. In particular, it is desirable for a mobile device to be able to operate within frequency bands associated with all of 2G (e.g., GSM/CDMA), 3G (e.g., EVDO/WCDMA), and 4G (e.g., LTE) technologies. In addition, further advancements in mobile technology (e.g., LTE, LTE-A, and 5G) will require additional expansions to the range of frequencies in which a mobile device will be expected to be operable. Furthermore, multiple antenna structures (e.g., MIMO, carrier aggregation) can be desired to provide additional functional advantages.
The ability to operate in such a wide range of frequencies can be limited, however, by the physical size of the wireless antenna. Especially in those systems that use multiple antennas in the mobile device, the amount of physical space required can be quite large. In addition, design constrains imposed by the continually shrinking size of modern mobile devices (e.g., slim, chic, curved, narrow bezel) can present a natural conflict with the volume needed to accommodate a multi-frequency antenna system. As a result, it would be advantageous to have an antenna system for advanced mobile technology that can better achieve a wide bandwidth with a small antenna volume.
In accordance with this disclosure, tunable antenna systems, devices, and methods are provided. In one aspect, a tunable antenna system is provided in which a tunable band-stop circuit is provided in communication between a signal node and an electrically small antenna having a largest dimension that is substantially equal to or less than one-tenth of a length of a wavelength corresponding to a frequency within a communications operating frequency band. The tunable band-stop circuit can be tunable to adjust a band-stop frequency.
In another aspect, a method for tuning an electrically small antenna is provided. The method can comprise tuning a tunable band-stop filter connected to the electrically small antenna to adjust a system resonance for the tunable band-stop filter and the electrically small antenna within a desired low frequency band below a band-stop frequency without changing a system resonance for the tunable band-stop filter and the electrically small antenna within a desired high frequency band above the band-stop frequency.
In yet another aspect, a method for tuning an electrically small antenna can comprise connecting a tunable band-stop circuit between an electrically small antenna and a signal node, the electrically small antenna having a largest dimension that is substantially equal to or less than one-tenth of a length of a wavelength corresponding to frequency within a communications operating frequency band, and tuning the tunable band-stop circuit to adjust a band-stop frequency between the desired low frequency band and a desired high frequency band within the communications operating band.
Although some of the aspects of the subject matter disclosed herein have been stated hereinabove, and which are achieved in whole or in part by the presently disclosed subject matter, other aspects will become evident as the description proceeds when taken in connection with the accompanying drawings as best described hereinbelow.
The features and advantages of the present subject matter will be more readily understood from the following detailed description which should be read in conjunction with the accompanying drawings that are given merely by way of explanatory and non-limiting example, and in which:
The present subject matter provides tunable antenna systems, devices, and methods. In particular, the tunable antenna systems, devices, and methods can tune a low band frequency while also maintaining good performance in a high band resonance. In some embodiments, for example, tunable antenna systems can be sized to be resonant at or about a desired high-band frequency (e.g., about 1.9 GHz). In addition, the systems can further be configured to be tunable to exhibit resonance at or about a desired low-band frequency (e.g., between about 700 MHz to 960 MHz, a range that include UMTS frequency bands B5, B8, B12, B13, and B17).
In one aspect, the present subject matter provides a tunable antenna system that includes an electrically small antenna and a tunable band-stop circuit in series with the antenna. Specifically, as illustrated in
To advantageously make use of this limited component space, tunable antenna system 100 can comprise an electrically small antenna 110 (e.g., a small monopole radiator), which can have a largest dimension x that is substantially equal to or less than one-tenth of a length of a wavelength corresponding to a frequency within a communications operating frequency band. In particular, electrically small antenna 110 can be sized such that largest dimension x is substantially equal to or less than one-tenth of a length of a wavelength corresponding to an operating frequency within a desired low-frequency band. In one particular embodiment, for example, electrically small antenna 110 can be a single feed monopole having a pattern length of about 1 inch and a pattern width that is as wide as possible for the device volume to increase bandwidth.
Despite this small size, electrically small antenna 110 can still be of appropriate dimensions to yield a strongly-radiating resonance at a desired high-frequency band. In some exemplary embodiments, for instance, electrically small antenna 110 can be a monopole radiator that is sized to have a real resonance between about 2.2 GHz and 2.5 GHz, and electrically small antenna 110 can have a real resistance greater than about 200 Ω.
With respect to low-band frequencies, however, an antenna of this length generally is not resonant at the low-band operating frequency upon which its length was determined as discussed above. Accordingly, a resonance control element 130 can be provided between electrically small antenna 110 and a signal node S as shown in
To improve the matching of electrically small antenna 110, tunable antenna system 100 can further include a tunable band-stop circuit, generally designated 120, which can be configured to form a band-stop zone between low and high bands. Specifically, for example, in one embodiment illustrated in
Furthermore, in some embodiments, band-stop inductor 122 can be fixed in value, but when taken in combination with tunable capacitor 121, tunable band-stop circuit 120 can exhibit a range of inductances (e.g., between about 2.7 and 6.8 nH) designed to achieve the desired band-stop effect.
In addition, in some embodiments, a fixed capacitor 123 can further be provided in parallel with tunable capacitor 121 and with band-stop inductor 122 as illustrated in
In another configuration shown in
Regardless of the particular configuration of tunable antenna system 100 generally or of tunable band-stop circuit 120 in particular, the matching topology can be designed to use as few as one tunable element (e.g., tunable capacitor 121) to control antenna impedance simply and clearly. (See, e.g.,
Even with just one tunable capacitor as a part of tunable band-stop circuit 120, however, the band-stop zone can be adjusted up and down (e.g., by tuning tunable capacitor 121). Such shifts in the band-stop frequency can strongly affect a system resonance for tunable band-stop filter 120 and electrically small antenna 110 within a desired low frequency band below a band-stop frequency, but there can be little or no impact to a system resonance within a desired high frequency band above the band-stop frequency. In this regard, for example, band-stop inductor 122 can be configured to resonate with electrically small antenna 110 at low-band frequencies, but tunable capacitor 121 can be configured to tune the effective inductance of tunable band-stop circuit 120, which thereby allows tunable band-stop circuit to tune the low-band response. In contrast, at high-band frequencies, tunable capacitor 121 (and fixed capacitor 122, if present) becomes effectively “transparent,” and electrically small antenna 110 operates as though there were no tuning circuit.
For example, as shown in
In this way, this arrangement of electrically small antenna 110 and tunable band-stop circuit 120 can provide high tunability of the low-band frequencies by shifting the band-stop frequency to help match the antenna impedance in the desired low-band frequency range.
In addition, tunable band-stop circuit 120 can also help to broaden the bandwidth of a high frequency operating band, and it can help to increase antenna efficiency in both low- and high-band operation. As shown in
In addition to the combination of elements discussed above, tunable antenna system 100 can further include one or more elements to improve the operational characteristics of the system. Specifically, for example, to allow further tailoring of the high frequency band at which tunable antenna system 100 is resonant, in some embodiments, a resonance control capacitor 133 can be provided in a shunt arrangement between a first node n1 connected between electrically small antenna 110 and a signal node S and a ground as shown in each of the embodiments of
Furthermore, in some embodiments, a high-band bandwidth control capacitor 131 can further be provided in communication with electrically small antenna 110. In particular, bandwidth control capacitor 131 can be provided in series between electrically small antenna 110 and signal node S (e.g., between electrically small antenna 110 and first node n1). In some embodiments, bandwidth control capacitor 131 can have a capacitance (e.g., about 33 pF) selected to achieve a desired bandwidth of a desired high frequency band. Also, in some embodiments, an electrostatic discharge protection capacitor 111 (e.g., a fixed element having a capacitance of about 33 pF) can be provided in communication with electrically small antenna 110. (See, e.g.,
In summary, compelling tunable performance can be achieved with this concept, consisting of low-band tunability with good efficiency along with a stable high band resonance having high efficiency and wide bandwidth. This is particularly useful for handover monitoring and for low-high and high-high carrier aggregation applications.
The present subject matter can be embodied in other forms without departure from the spirit and essential characteristics thereof. The embodiments described therefore are to be considered in all respects as illustrative and not restrictive. Although the present subject matter has been described in terms of certain preferred embodiments, other embodiments that are apparent to those of ordinary skill in the art are also within the scope of the present subject matter.
The present application claims the benefit of U.S. patent application Ser. No. 61/968,930, filed Mar. 21, 2014, the disclosure of which is incorporated herein by reference in its entirety.
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