Patent Application
20140334361
The present invention relates generally to radio communications, and more specifically to apparatus that optimizes frequency division duplex radio communications.
Frequency division duplexing has been used in radio communication systems for many years to allow the simultaneous transmission and reception of radio signals by a radio transceiver. In such systems, two frequency bands are typically used, one for transmission signals and one for reception signals. The frequency bands are separated but filtering is typically needed to prevent undesirable energy that is generated by internal and external sources and that is within the frequency band of the receiver from combining with desirable energy being intercepted by the receive antenna, thereby degrading the reception of the desirable signal. One filtering configuration that is in common use in frequency division duplex systems uses a three port passive electronic component that has a receive port coupled to a receiver input, a transmit port coupled to a transmitter output, and an antenna port coupled to a single antenna that is used for the simultaneous reception and transmission of radio signals coupled in a first signal path between the antenna and receiver and a second signal path between the antenna and the transmitter amplifier. This three port device is commonly called a duplexer or a diplexer. This filtering configuration is commonly found in portable communication devices operating in cellular systems such as those that use well known air-interface standards such as LTE (Long Term Evolution) and W-CDMA (Wideband Code Division Multiple Access), as well as other FDD communication systems.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments that include the aspects of the claimed invention, and explain various principles and advantages of those embodiments.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
Before describing in detail the following embodiments, it should be observed that the embodiments reside primarily in apparatus related to frequency transceivers or transmitters using antenna(s) and a duplexer. Accordingly, the apparatus components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.
Referring to
Referring to
The transmit-receive antenna 230 also intercepts downlink radio signals and couples them to the matching network 225. The radio signals from the matching network 225 are coupled to the antenna port 221 of the duplexer 220, where they are coupled to both the transmit filter portion 223 and a receive filter portion 224 of the duplexer. The receive filter portion 224 has a passband that accommodates (is approximately the same as) the receive frequency band of the communication system. At the antenna port, the receive filter portion 224 provides significant attenuation (for example, greater than 50 dB) at frequencies within the transmit frequency band, and a high return loss (for example, 15 dB) and little insertion loss (for example, 1.5 dB) for signals within the receive frequency band. At the antenna port the transmit filter portion 223 provides a low return loss (for example, less than 1 dB) to frequencies within the receive frequency band. Therefore, almost all of the radio signal from the matching network 225 is coupled to the receive port (R) 218, with very little undesirable energy included, where it is received by the device 100. The physical configuration of transmit-receive antenna 230 and the electrical matching of the transmit-receive antenna 230 to the matching network 225 optimize the gain of the transmit-receive antenna 230 over both the transmit and receive frequency bands of the communication system.
In certain embodiments, the device 100 may also include an optional diversity receive antenna 250 coupled to a diversity receive matching network 245, the output of which is further coupled to a diversity receive filter 240. In these embodiments, the diversity receive antenna 250 is typically physically configured to be de-correlated with the transmit-receive antenna 230 (either in polarization or spatial aspects, or both), and may have a narrower bandwidth than the transmit-receive antenna 230, because the diversity receive antenna 250 needs to have optimum gain only over the receive frequency band. The antennas 230, 250 form the antenna system 260 of the device 100. Diversity receive antenna 250 intercepts radio signals. Those intercepted radio signals are coupled to the diversity receive filter 240 by the matching network. The diversity receive filter 240 rejects most of the energy of the radio signal outside the receive frequency band of the communication system. The filtered signal 241 is coupled to other portions of the transmitter-receiver of the device 100, which perform a diversity receiving function using the filtered signals 215 and 241. The diversity antenna 250 is described above as providing polarization diversity, but in some devices 100 it may alternatively or additionally provide space diversity that is effective for reducing fading effects. A receive antenna 250 and additional receive antennas may be provided for a multiple input-multiple output (MIMO) receive antenna subsystem. For each such antenna, an optional matching network and a receive filter is provided, such as for diversity receive antenna 250.
Duplexers such as duplexer 220 are very commonly used in prior art devices 100 such as portable cellular communication devices. These duplexers are typically passive devices that are well known to have the return loss characteristics at the antenna port 221 described above, and also provide high isolation between the two filters. For example, the transmit to receive isolation can typically exceed 50 dB. Duplexers are sometimes referred to as diplexers. The receive to transmit isolation is also high, and can typically exceed 45 dB. Thus the duplexer 220 allows for effective separation of the transmit and receive signals for frequency division duplex communication systems. The receive filter portion and transmit filter portion each has a respective passband characteristic; the receive and transmit passband characteristics are non-overlapping, and each falls within (i.e., less than or equal to) a respective receive frequency band and transmit frequency band of a communication system. The transfer characteristics of the receive filter portion between the receive port and antenna port are the same in both directions for passive duplexers. Similarly the transfer characteristics of the transmit filter portion between the transmit port and antenna port are the same in both directions for passive duplexers. This includes such characteristics as gain versus frequency, group delay, and ripple.
In some of the prior art embodiments of the device 100, there is no matching network 225 between the antenna 230 and the duplexer 220 or no diversity receive matching network 245 between the antenna 250 and the diversity receive filter 240 (in those embodiments using a diversity antenna).
Referring to
The antenna system used in the device 300 is a simplex antenna configuration. A first receive antenna 352 intercepts downlink radio signals and couples them to a first receive matching network 335, which is designed to optimize the coupling of the first receive antenna 352 to the first receive filter 330 and, as described with reference to transmit matching filter 325, may be a passive network, a switched passive network, or may not be included. The first receive filter 330 rejects most of the energy of the radio signal outside the receive frequency band of the communication system. Alternatively stated, the first receive filter has a passband accommodates the receive frequency band of the communication system. The filtered signal 331 is coupled to other portions of the transmitter-receiver 120 of the device 300, which perform a receiving function using the filtered signal 331. It will be appreciated that the use of separate transmit and first receive antennas 351, 352 allows their physical configuration to be designed to optimize, respectively, the electrical matching of the transmit antenna 351 to the matching network 325 (or to the transmit port 319 of the duplexer when the matching network 325 is not used) and the electrical matching of the first receive antenna 352 to the first receive matching network 335, and also allows the gains of the transmit antenna 351 and the first receive antenna 352 to be increased in comparison to a prior art transmit-receive antenna of the same size, because both the antenna matching and antenna gains are over narrower frequency ranges than in prior art devices 100 as described above with reference to
An additional benefit provided by the unique coupling of the PA 310 to the antenna port of the duplexer 320 is an increase of the receive antenna efficiency in comparison to a simplex antenna configuration that uses a transmit filter alone instead of the reverse duplexer configuration of these novel embodiments. For either configuration, the receive antenna efficiency of antenna 352 is determined by:
Efficiency (in %)=100*(1−10(−ISO/10)*(1−10(−RL/10))), (1)
wherein ISO is the antenna isolation in dB and RL is the return loss in dB at the coupling of the transmit antenna 351 to the duplexer transmit port 319. It will be appreciated that for a given antenna isolation, a lower return loss increases the efficiency. While this formula includes some idealistic assumptions, it will be appreciated that the general result is still true: a lower return loss increases the efficiency of the receive antenna 352. The transmit port 319 of the duplexer has a very low return loss over the receive frequency band because the transmit filter portion 324 is coupled to the optimally terminated receive filter portion 324. This allows most of the small amount of receive signal energy that passes the transmit filter portion 324 to be absorbed by the matching termination 322. The very low return loss is lower than that typically achieved for a separate transmit filter of comparable design. Therefore the receive antenna efficiency is better than that which would be achievable in a diversity system that uses a comparable transmit filter instead of a reverse coupled duplexer.
Another benefit provided by this novel configuration of the duplexer in FDD cellular systems is that duplexers having the necessary transmit and receive frequency ranges have been in use for some time and are very economical. They are less costly than transmit filters would be that have comparable specifications because of the present very high production quantities and long production history for the duplexer.
Referring to
Efficiency (in %)=100*(1−10(−ISO/10−10(−ISO/10)*(1−10(−RL/10))), (2)
wherein ISO is the antenna isolation in dB and RL is the return loss in dB at the coupling of the transmit antenna 351 to the duplexer transmit port 319. It will be appreciated that for a given antenna isolation, a lower return loss increases the efficiency. While this formula includes some idealistic assumptions, including that the ISO is the same for both receive antennas 352, 453, it will be appreciated that the general result is still true: a lower return loss increases the efficiency of the receive antenna 352 and diversity receive antenna 453. For the same reasons given above with reference to
Referring to
In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.
