Multi-feed antenna optimized for non-50 Ohm operation

Abstract

A multi-feed antenna is described where the antenna is optimized for the natural impedance state per frequency band. Multiple feed points are accessed as a function of frequency and use case to provide a feed port that is operating at the natural impedance state for the antenna structure. Impedance transforming circuits can be applied to the feed point to form impedance matching circuits to transform the antenna impedance to a characteristic impedance of the system or circuit interfacing with the antenna. The impedance transforming circuits can be eliminated and the RF circuitry interfacing with the antenna can be configured to operate at the natural frequency of the antenna.

Claims

1. An antenna system optimized for non-50 ohm operation, the antenna system comprising: an antenna comprising a first feed port and a second feed port associated therewith, the antenna having a first frequency band associated with the antenna when excited at the first feed port and a second frequency band associated with the antenna when excited at the second feed port, wherein the second frequency band is distinct from the first frequency band, and the antenna further having a first characteristic impedance associated with the antenna at the first frequency band and the first feed port and a second characteristic impedance associated with the antenna at the second frequency band and the second feed port, wherein the second characteristic impedance is distinct from the first characteristic impedance; a first transmission line having a first end thereof coupled to the first feed port of the antenna, and a second end of the first transmission line being coupled to a first RF circuit, wherein the first transmission line is selected to have an impedance thereof that is equivalent to the first characteristic impedance of the antenna; a second transmission line having a first end thereof coupled to the second feed port of the antenna, and a second end of the second transmission line being coupled to the first RF circuit or a second RF circuit, wherein the second transmission line is selected to have an impedance thereof that is equivalent to the second characteristic impedance of the antenna.

2. The antenna system of claim 1, wherein a matching circuit is coupled between the first RF circuit and the second end of the first transmission line for impedance matching the combination of the antenna and first transmission line with the matching circuit.

3. The antenna system of claim 2, wherein the matching circuit is coupled to the second end of the first transmission line.

4. The antenna system of claim 1, wherein a first matching circuit is coupled between the first RF circuit and the second end of the first transmission line for impedance matching the combination of the antenna and first transmission line with the first matching circuit.

5. The antenna system of claim 4, wherein a second matching circuit is coupled between the second RF circuit and the second end of the second transmission line for impedance matching the combination of the antenna and second transmission line with the second matching circuit.

6. The antenna system of claim 1, wherein each of the second end of the first transmission line and the second end of the second transmission line are coupled to a diplexer or switch, wherein the diplexer or switch is further coupled to the first RF circuit.

7. The antenna system of claim 1, wherein the first RF circuit comprises a first transceiver.

8. The antenna system of claim 1, wherein the second RF circuit comprises a second transceiver.

9. The antenna system of claim 1, wherein the first RF circuit comprises a power amplifier.

10. The antenna system of claim 1, wherein the second RF circuit comprises a receiver circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an antenna connected to a transceiver using a 50 Ohm coaxial cable.

(2) FIG. 2 illustrates an antenna connected to matching circuit which matches the antenna to a 50 Ohm system.

(3) FIG. 3 illustrates an antenna connected to three matching circuits which match the antenna to a 50 Ohm system.

(4) FIG. 4 illustrates an antenna connected to three matching circuits which match the antenna to a 50 Ohm system.

(5) FIG. 5 illustrates an antenna connected to three matching circuits which match the antenna to a 50 Ohm system.

(6) FIG. 6 illustrates a three feed port antenna, with three coaxial cables connected to the antenna, one coaxial cable per feed port.

(7) FIG. 7 illustrates a three feed port antenna, with an impedance transformer connected to each feed port.

(8) FIG. 8 illustrates a three port antenna, with one port tuned to operate at 700 MHz, a second port tuned to operate at 1800 MHz, and a third port tuned to operate at 2500 MHz.

(9) FIG. 9 illustrates an antenna connected to three tunable matching circuits which match the antenna to a 50 Ohm system.

(10) FIG. 10 illustrates an active antenna element connected to three matching circuits which match the antenna to a 50 Ohm system.

(11) FIG. 11 illustrates a two feed port antenna, with two coaxial cables connected to the antenna, one coaxial cable per feed port.

(12) FIG. 12 illustrates a two feed port antenna, with two coaxial cables connected to the antenna, one coaxial cable per feed port.

DETAILED DESCRIPTION OF EMBODIMENTS

(13) This patent describes a method of designing multi-port antennas and connecting these antenna ports to transceivers or other components in an RF system, where the antenna ports are matched to the natural impedance of the antenna at the frequency range that the antenna port is optimized to. Benefits in terms of reduced cost, reduced circuit losses, and a reduction in area required to integrate matching circuits can be had by reducing or eliminating the need to transform impedances as antennas, transmission lines, and circuit components are configured into transceiver systems.

(14) One embodiment of this invention is an antenna containing three feed ports, with port 1 configured for use at low frequency bands, port 2 configured for use at mid-frequency bands, and port 3 configured for use at high frequency bands. The antenna impedance at the three feed ports is the natural frequency of the antenna. A transmission line is attached to each feed port, with the characteristic impedance of each transmission line chosen to equal the impedance of the antenna feed port connected to. The second port of each transmission line is connected to a matching circuit to impedance match the combination of antenna and transmission line to a transceiver circuit. Implementing this configuration allows for the elimination of any matching components at the antenna port, which results in reduced circuit losses, reduced cost, and reduced circuit board area required for antenna and matching circuit. This three feed port configuration also provides the flexibility of choosing different characteristic impedances for the transceiver and matching circuit junction, which can result in the ability to optimize the impedance transformer at the three frequency bands serviced by the antenna.

(15) Another embodiment of the invention is an antenna with multiple feed ports, with each feed port configured for one or multiple frequency bands. The antenna impedance at the various feed ports is the natural frequency of the antenna at the frequency band or bands serviced by the feed port. A transmission line is attached to each feed port, with the characteristic impedance of each transmission line chosen to equal the impedance of the antenna feed port connected to. The second port of each transmission line is connected to a transceiver circuit. The transceiver circuits are designed to have the characteristic impedance of the transmission line that each transceiver is connected to, with this circuit configuration allowing for the elimination of all matching circuits. This configuration allows for reduced circuit losses, reduced cost, and reduced circuit board area required for antenna and matching circuits. This multi-feed port configuration also provides the flexibility of choosing different characteristic impedances for the transceiver, which can result in the ability to optimize the impedance transformer at the three frequency bands serviced by the antenna.

(16) In another embodiment of the invention an antenna with multiple feed ports is configured such that each feed port operates at either transmit or receive frequencies. The antenna impedance at the various feed ports is the natural frequency of the antenna at the frequency band or bands serviced by the feed port. A transmission line is attached to each feed port, with the characteristic impedance of each transmission line chosen to equal the impedance of the antenna feed port connected to. The second port of each transmission line is connected to either a transmit circuit or a receive circuit. The feed ports and transmission lines configured for use with transmit circuits can be design such that a low characteristic impedance is provided at the transmit circuit/transmission line junction. The transmit circuit containing a power amplifier can be designed to have a low characteristic impedance which is typically an inherent trait of power amplifiers. The feed ports and transmission lines configured for use with receive circuits can be design such that a characteristic impedance is provided at the receive circuit/transmission line junction that is optimal for receive circuit designs.

(17) In yet another embodiment of this invention, a tunable matching circuit is positioned at one or multiple feed ports of an antenna that contains multiple feed ports. The tunable matching circuit is configured with a tunable capacitor, switch, PIN diode or other component capable of varying impedance. A transmission line is attached to each feed port, with the characteristic impedance of each transmission line chosen to equal the impedance of the antenna feed port connected to. The tunable matching circuit provides the capability of dynamically altering the impedance of the antenna which can translate into a wider frequency range that the antenna can cover. The second port of each transmission line is connected to a transceiver circuit. The transceiver circuits are designed to have the characteristic impedance of the transmission line that each transceiver is connected to. This configuration provides a method of optimizing the impedance match between the transceiver and the transmission line/antenna. This multi-feed port configuration also provides the flexibility of choosing different characteristic impedances for the transceiver, which can result in the ability to optimize the impedance transformer at the three frequency bands serviced by the antenna.

(18) In yet another embodiment of this invention, an active antenna is configured such that the electrical length or frequency response of the antenna can be dynamically adjusted. The active antenna is formed by coupling a tunable capacitor, switch, PIN diode or other component capable of varying impedance to the radiating element. This active antenna is configured with multiple feed ports and a transmission line is attached to each feed port, with the characteristic impedance of each transmission line chosen to equal the impedance of the antenna feed port connected to. The second port of each transmission line is connected to a transceiver circuit. The transceiver circuits are designed to have the characteristic impedance of the transmission line that each transceiver is connected to. This configuration provides a method of dynamically altering the frequency response of the antenna to allow for the antenna to cover a wider frequency range. This multi-feed port configuration also provides the flexibility of choosing different characteristic impedances for the transceiver, which can result in the ability to optimize the impedance transformer at the three frequency bands serviced by the antenna.

(19) FIG. 1 illustrates an antenna connected to a transceiver using a 50 Ohm coaxial cable. The antenna is matched to a characteristic impedance of 50 Ohms, and the transceiver is matched to a characteristic impedance of 50 Ohms. Also shown is an antenna with characteristic impedance of Za connected to a matching circuit which matches the antenna to a 50 Ohm system. A coaxial cable connects the antenna to a matching circuit which matches a transceiver to the 50 Ohm system.

(20) FIG. 2 illustrates an antenna connected to matching circuit which matches the antenna to a 50 Ohm system. A coaxial cable connects the antenna to a matching circuit which matches a transceiver to the 50 Ohm system. The Smith Chart representation of the antenna impedance, Za, is shown and the three frequency regions of interest, 700 MHz, 1800 MHz and 2500 MHz is shown. The three frequencies have different impedance values.

(21) FIG. 3 illustrates an antenna connected to three matching circuits which match the antenna to a 50 Ohm system. The first matching circuit transforms the antenna impedance Za at 700 MHz to 50 Ohms, the second matching circuit transforms the antenna impedance Za at 1800 MHz to 50 Ohms, and the third matching circuit transforms the antenna impedance Za at 2500 MHz to 50 Ohms. A coaxial cable connects the antenna matching circuits to a matching circuit which matches a transceiver to the 50 Ohm system. The Smith Chart representation of the antenna impedance, Za, is shown and the three frequency regions of interest, 700 MHz, 1800 MHz and 2500 MHz is shown. The three frequencies have been matched to a 50 Ohm system.

(22) FIG. 4 illustrates an antenna connected to three matching circuits which match the antenna to a 50 Ohm system. The first matching circuit transforms the antenna impedance Za at 700 MHz to 50 Ohms, the second matching circuit transforms the antenna impedance Za at 1800 MHz to 50 Ohms, and the third matching circuit transforms the antenna impedance Za at 2500 MHz to 50 Ohms. Each matching circuit is connected to a coaxial cable. The three coaxial cables are in turn connected to a transceiver.

(23) FIG. 5 illustrates an antenna connected to three matching circuits which match the antenna to a 50 Ohm system. The first matching circuit transforms the antenna impedance Za at 700 MHz to 50 Ohms, the second matching circuit transforms the antenna impedance Za at 1800 MHz to 50 Ohms, and the third matching circuit transforms the antenna impedance Za at 2500 MHz to 50 Ohms. Each matching circuit is connected to a coaxial cable. The three coaxial cables are connected to a diplexer or switch, allowing the three coaxial cables to interface to a single transceiver.

(24) FIG. 6 illustrates a three feed port antenna, with three coaxial cables connected to the antenna, one coaxial cable per feed port. The three coaxial cables have different characteristic impedances, with the characteristic impedance of each cable matching the characteristic impedance of the antenna at a frequency band used by the port of the antenna. At the second port of each coaxial cable is a matching circuit which transforms the impedance of the coaxial cable to the characteristic impedance of the transceiver that the coaxial cable is connected to. Also shown is a three feed port antenna, with three coaxial cables connected to the antenna, one coaxial cable per feed port. The three coaxial cables have different characteristic impedances, with the characteristic impedance of each cable matching the characteristic impedance of the antenna at a frequency band used by the port of the antenna. The second port of each coaxial cable is connected to a diplexer or switch which in turn is connected to a single transceiver.

(25) FIG. 7 illustrates a three feed port antenna, with an impedance transformer connected to each feed port. Feed port 1 operates from 600 to 1100 MHz and the impedance transformer transforms the antenna impedance from 20 to 50 Ohms. Feed port 2 operates from 1100 to 1600 MHz and the impedance transformer transforms the antenna impedance from 100 to 50 Ohms. Feed port 3 operates from 1600 to 2700 MHz and the impedance transformer transforms the antenna impedance from 20 to 50 Ohms. The three transformers are connected to three coaxial cables, which in turn are connected to transceivers.

(26) FIG. 8 illustrates a three port antenna, with one port tuned to operate at 700 MHz, a second port tuned to operate at 1800 MHz, and a third port tuned to operate at 2500 MHz. The first and third antenna ports have a characteristic impedance of 20 Ohms, while the second antenna port has a characteristic impedance of 100 Ohms.

(27) FIG. 9 illustrates an antenna connected to three tunable matching circuits which match the antenna to a 50 Ohm system. The first tunable matching circuit transforms the antenna impedance Za at 700 MHz to 50 Ohms, the second tunable matching circuit transforms the antenna impedance Za at 1800 MHz to 50 Ohms, and the third tunable matching circuit transforms the antenna impedance Za at 2500 MHz to 50 Ohms. Each tunable matching circuit is connected to a coaxial cable. The three coaxial cables are in turn connected to a transceiver.

(28) FIG. 10 illustrates an active antenna element connected to three matching circuits which match the antenna to a 50 Ohm system. The active antenna element has one or multiple active components such as switches or tunable capacitors coupled to the radiating element, with these active components independent of the matching circuits at the feed points of the antenna. The first matching circuit transforms the antenna impedance Za at 700 MHz to 50 Ohms, the second matching circuit transforms the antenna impedance Za at 1800 MHz to 50 Ohms, and the third matching circuit transforms the antenna impedance Za at 2500 MHz to 50 Ohms. Each matching circuit is connected to a coaxial cable. The three coaxial cables are in turn connected to a transceiver.

(29) FIG. 11 illustrates a two feed port antenna, with two coaxial cables connected to the antenna, one coaxial cable per feed port. The two coaxial cables have different characteristic impedances, with the characteristic impedance of each cable matching the characteristic impedance of the antenna at a frequency band used by the port of the antenna. At the second port of each coaxial cable is a matching circuit which transforms the impedance of the coaxial cable to the characteristic impedance of the circuit that the coaxial cable is connected to. The second port of the first coaxial cable is connected to a power amplifier which is used for transmitting. The second port of the second coaxial cable is connected to a receiver which is used for receiving signals.

(30) FIG. 12 illustrates a two feed port antenna, with two coaxial cables connected to the antenna, one coaxial cable per feed port. The two coaxial cables have different characteristic impedances, with the characteristic impedance of each cable matching the characteristic impedance of the antenna at a frequency band used by the port of the antenna. The second port of the first coaxial cable is connected to a power amplifier which is used for transmitting. The second port of the second coaxial cable is connected to a receiver which is used for receiving signals. Matching circuits are not required in this circuit configuration due to the antenna being designed such that the characteristic impedance of the two feed ports of the antenna has the same characteristic impedance as the transmission lines connected to the feed ports, and the transmission line characteristic impedance is the same as the characteristic impedance of the power amplifier and the receiver.