Patent Application
20050253665
1. Field of the Invention
This invention relates in general to RF signal transmission and more particularly, to a device for automatically selecting and creating low-loss RF signal paths.
2. Description of the Related Art
In a multi-band communication system operating throughout the VHF and UHF frequencies (30-1000 MHz), transceivers are able to communicate over multiple frequency bands at various distances by using line-of-sight or beyond line-of-sight RF signal propagation modes. Each mode can have differing power levels and signaling requirements. In line-of-sight mode, transceivers can communicate using low power signals similar to cellular communications and AM/FM radio as long as the transceivers are within line-of-sight distance of each other, roughly 60 miles depending on antenna height. When communicating beyond the line-of-sight to transceivers over 60 miles away, generally ground wave or satellite communications are used requiring very high RF power levels to complete a communication link. In systems operating across multiple frequency bands, proper component matching and signal filtering (isolation) are needed to assure efficient voice and data throughput within the communication system.
To maximize efficiency (reduce RF signal losses) throughout a multi-band communication system, frequency-band specific circuits are typically designed into the path of the transmitted RF signal in order to properly match the RF signal's complex impedances. Complex RF signal impedances must be matched across the operating frequency bands to reduce insertion loss and maintain an efficient system over every frequency of operation. Designs using power splitters, transistor switching, active filtering, matching networks, and diplexing allow for multiple RF signals to share the same components and antennas directly in the RF path, but compensating circuits must also be included in the RF signal path to make up for losses due to these components. These approaches lead to a relatively large number of impedance matching circuits in the RF signal path unnecessarily increasing signal power loss, system complexity, and cost.
Prior art design approaches are limited in application and frequency and cannot work over very large bandwidths for a number of reasons. First some solutions incorporate complex signal path routing, matching and amplification inside low powered semiconductor-based ICs. Secondly, when routing the RF signal through multiple active and passive components, the RF signal's complex impedances vary dramatically from one frequency to the next creating insertion losses and impedance mismatches between the RF signal and components inline with the RF. These losses may cause large mismatches in the Voltage Standing Wave Ratio (VSWR), which degrade RF signal performance and can add unwanted heat in the system. Thirdly, sharing active and passive matching and amplification circuitry with the RF signal path can lead to poor isolation between frequency bands because of the large differences in filtering circuitry required within the multi-band system. Signaling and filter designs are dependant on frequency wavelength and a number of impedance matching circuits are needed to effectively tune the signal path over the entire bandwidth, adding to cost and complexity.
Impedance matching, amplification, and filtering networks are relatively easy to design into a multi-band system as long as the wavelengths within the systems are small, (i.e., the frequency is relatively high) and close to each other as in PCS, GSM and GPS systems in the 800-1900 MHz frequency range. The same design approach used in 800-1900 MHz systems are often not practical and are difficult to implement in a communications system operating throughout the 30-1000 MHz range. This is due to the extreme difference in frequency wavelength and impedance characteristics of radio frequency waves at low frequencies. More exactly, prior art solutions designed into multi-band systems operating close to 1000 MHz will not work for multi-band systems operating close to 30 MHz.
Irons (U.S. Pat. No. 4,165,497) discloses an N×M wideband switching matrix constructed from modules, which are interconnected by a simple series path. Each matrix contains a plurality of input connectors and output connectors that create an RF signal path via a directional coupler. The RF signals will incur a loss of 3 dB when passing through a power divider that leads to the directional coupler. Power dividing devices are always frequency limited, reducing this application to a narrow band of frequencies. Additionally, this RF switching matrix is not “controllable” for particular frequencies, and signal output matching are necessary at each output port. The inventor claims that the intent of this invention is to provide a switching matrix in which package is simplified by the elimination of complicated cross-connections, not to control the RF signal paths in a communication system.
Freeston et al. (U.S. Pat. Pub. No. 20020063475) discloses a device for RF signal switching in a matrix configuration embedded within an Integrated Circuit. At the heart of this invention are a number of switching Single Throw N Pole (STNP) switches, a control unit and a matching/amplification network that will compensate for the losses incurred when the RF signals are routed through the design. Because of the matching/amplification network embedded in the IC, Freeston notes high isolation and low insertion loss, but this is only attainable because of the compensating network. This invention is not applicable to RF signal controlling in a multi-band communication systems because of the high RF power requirements needed in various modes of communication and the inability to immediately provide impedance matching over wide bandwidths at frequencies covering the VHF/UHF communication spectrum.
Clifton (U.S. Patent Pub. No. 20030001787) discloses an antenna switch, and a method of providing an RF signal to an antenna switch. Clifton's design uses small signal transistors and is clearly limited in function for a number of reasons. First, he details the use of a frequency matching circuit in the RF signal path for impedance matching limiting the device and method for a particular antenna and narrow frequency band of operation. Second, transistors are used in the RF signal path to accomplish signal switching. These transistors also serve as small signal amplifiers, limiting the use in high power RF applications. Lastly, Clifton limits the operation of the antenna switch to the GSM 900 and GSM 1800 frequency bands.
Sutton et al. (U.S. Pat. Pub. No. 20020142796) discloses an antenna switch assembly. The antenna switch is embodied as an active device MMIC, and uses a number of supporting active devices directly in line with the signal path. Sutton also claims that a transmit transistor is arranged to provide amplification to the RF signal, to compensate for losses associated with the above-mentioned switching unit. Notably, the device operates only within two frequency bands, 800 and 1900 MHz. The control unit can only be used for distinguishing between these two frequencies. Lastly, a matching circuit is claimed to provide impedance matching between the signal path and the antenna connection limiting this devices operation to these particular frequency bands.
In all prior art devices, RF signal losses are incurred because the active and passive components are in the RF signal path, and designs for low frequency, high power impedance matching, amplification and filtering circuitry are not practical throughout a VHF/UHF multi-band communication system. Additionally, solutions using semiconductors (Silicon, Germanium, Gallium etc.) for signal switching are not practical in high power RF applications. In conclusion, insofar as I am aware, there has not been a device or method developed that automatically detects, identifies, and controls an RF signal path in any multi-band communication system, maintaining low RF system losses under various power condition.
Accordingly, a need exists for a device that will automatically determine the frequency band of an input signal and route the input signal to a low-loss port that will serve as the transmit/receive path until a new frequency is detected.
The present invention concerns a software-based Automatic Radio Frequency (RF) Signal Controller device that works in conjunction with a multi-band transceiver to establish a number of frequency-dependent low-loss RF signal paths. At the time of transmission, the Automatic RF Signal Controller determines the operating frequencies of the input signal and establishes a low-loss RF signal path to one of a number of frequency-band-specific ports. These ports remain active for transmission and reception until the device detects a new frequency. The device and method detail an advancement in the art, enabling multi-band communication systems the flexibility to operate over extremely wide bandwidths and power levels without the need for impedance matching networks, or associated active and passive components, increasing communication efficiency by reducing the RF signal losses directly in RF signal path and reducing the complexity and cost of a multi-band communication system.
The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.
a is a schematic circuit diagram of the inventive automatic RF signal controller;
b is a chart showing exemplary relay combinations;
While the specification concludes with claims defining the features of the invention that are regarded as novel, it is believed that the invention will be better understood from a consideration of the following description in conjunction with the drawing figures, in which like reference numerals are carried forward.
Referring now to
In order to properly route the RF signal to its final output port, a control processor 230 must determine at what frequency the transceiver 100 is operating. This is accomplished by sampling the transmitted RF signal, determining what frequency is in operation, and engaging the appropriate RF relay matrix to allow the RF signal flow to that output port. In order to sample the RF signal without creating RF signal mismatch (loss) or high VSWR, an inductive directional coupler 231 is used. Directional couplers are well known in the art, and operate without being in physical contact with the conductor carrying the RF input signal.
Referring now to
The sampled low voltage RF signal is then carried along the center conductor 305 of coaxial cable 301, through diode 304 to an output 303 of the coupler 231 into a micro-controller 230. Diode 304 allows current in only one direction and therefore, adds the directional characteristic to the coupler 231, preventing the coupler from affecting the input signal. The microprocessor identifies the operating frequency of the signal and compares this signal against a database of possible RF path solutions programmed via software into the microprocessor. The microprocessor unit 230 outputs a voltage signal and/or binary digits that are interpreted by a relay control unit 232. The relay control unit 232 then sets the state of the state of each relay 201, 205, 206, 207, 208, 209, and 210 in accordance with the software instructions.
While the preferred embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions and equivalents will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims.
