The present invention relates generally to multi-band antennas, and more specifically, to multi-band inverted-L antennas for use in global satellite positioning systems.
Receivers in global navigation satellite systems (GNSS's), such as the Global Positioning System (GPS), use range measurements that are based on line-of-sight signals broadcast by satellites. The receivers measure the time-of-arrival of one or more of the broadcast signals. This time-of-arrival measurement includes a time measurement based upon a coarse acquisition coded portion of a signal, called pseudo-range, and a phase measurement.
In GPS, signals broadcast by the satellites have frequencies that are in one or several frequency bands, including an L1 band (1565 to 1585 MHz), an L2 band (1217 to 1237 MHz), an L5 band (1164 to 1189 MHz) and L-band communications (1520 to 1560 MHz). Other GNSS's broadcast signals in similar frequency bands. In order to receive one or more of the broadcast signals, receivers in GNSS's often have multiple antennas corresponding to the frequency bands of the signals broadcast by the satellites. Multiple antennas, and the related front-end electronics, add to the complexity and expense of receivers in GNSS's. In addition, the use of multiple antennas that are physically displaced with respect to one another may degrade the accuracy of the range measurements, and thus the position fix, determined by the receiver.
There is a need, therefore, for improved antennas for use in receivers in GNSS's to address the problems associated with existing antennas.
Embodiments of a multi-band antenna are described. In some embodiments, the antenna includes a first antenna element and a second antenna element. The first antenna element and the second antenna element are configured to transmit and receive signals in a first band of frequencies and in a second band of frequencies. Frequencies in the second band of frequencies are greater than frequencies in the first band of frequencies. A first pair of delay lines, connected in series, is coupled to the first antenna element and a second pair of delay lines, connected in series, is coupled to the second antenna element. A first delay line in the first pair of delay lines and the second pair of delay lines is configured to phase shift electrical signals coupled to the first antenna element and the second antenna element such that a first impedance of the antenna is approximately equal in the first band of frequencies and the second band of frequencies. A second delay line in the first pair of delay lines and the second pair of delay lines is configured to convert the first impedance to a second impedance.
In an exemplary embodiment, the second impedance is 50 Ω, or approximately 50 Ω.
The antenna may include a first resonance circuit coupled to the first antenna element and a second resonance circuit coupled to the second antenna element. The first resonance circuit and the second resonance circuit are configured to each have an impedance greater than a predetermined value in the second band of frequencies such that electrical signals corresponding to the first band of frequencies are coupled to and from the first antenna element and the second antenna element and electrical signals corresponding to the second band of frequencies are substantially coupled to and from a portion of the first antenna element and a portion of the second antenna element.
A central frequency in the second band of frequencies may be approximately 5/4 times a central frequency in the first band of frequencies. Alternately, a central frequency in the second band of frequencies may be approximately 1.29 times a central frequency in the first band of frequencies.
The second delay line in the first pair of delay lines and the second pair of delay lines may have an impedance that is approximately a geometric mean of the first impedance and the second impedance.
The first antenna element and the second antenna element may be arranged approximately along a first axis of the antenna.
The first antenna element and the second antenna element each may include a monopole situated above a ground plane. The monopole may include a metal layer deposited on a printed circuit board. The printed circuit board may be suitable for microwave applications. The first antenna and the second antenna may each be inverted L-antennas.
In some embodiments, the monopole is in a plane that is approximately parallel to a plane that includes the ground plane. In some embodiments, the monopole is in a plane that is approximately perpendicular to a plane that includes the ground plane.
In some embodiments, the antenna may include a third antenna element and a fourth antenna element. The third antenna element and the fourth antenna element are configured to transmit and receive signals in the first band of frequencies and in the second band of frequencies. A third pair of delay lines is coupled to the third antenna element and a fourth pair of delay lines is coupled to the fourth antenna element. A third delay line in the third pair of delay lines and the fourth pair of delay lines is configured to phase shift electrical signals coupled to the third antenna element and the fourth antenna element such that the first impedance of the antenna is approximately equal in the first band of frequencies and the second band of frequencies. A fourth delay line in the third pair of delay lines and the fourth pair of delay lines is configured to convert the first impedance to the second impedance.
The antenna may include a third resonance circuit coupled to the third antenna element and a fourth resonance circuit coupled to the fourth antenna element. The third resonance circuit and the fourth resonance circuits are each configured to have an impedance greater than the predetermined value in the second band of frequencies such that electrical signals corresponding to the first band of frequencies are coupled to and from the third antenna element and the fourth antenna element and electrical signals corresponding to the second band of frequencies are substantially coupled to and from a portion of the third antenna element and a portion of the fourth antenna element.
The third antenna element and the fourth antenna element may be arranged substantially along a second axis of the antenna. The first axis and the second axis may be rotated by approximately 90° from one another.
In some embodiments, a feed network circuit is coupled to the first, second, third and fourth antenna elements. The feed network circuit is configured to phase shift the electrical signals coupled to and from the antenna elements such that radiation to or from the antenna is circularly polarized. The circularly polarized radiation to or from the antenna may be right hand circularly polarized or left hand circularly polarized. The feed network circuit may be configured to phase shift the electrical signals coupled to neighboring antenna elements in the antenna by approximately 90°.
The embodiments of the multi-band antenna at least partially overcome the previously described problems with existing antennas.
Additional objects and features of the invention will be more readily apparent from the following detailed description and appended claims when taken in conjunction with the drawings.
Like reference numerals refer to corresponding parts throughout the several views of the drawings.
Reference will now be made in detail to embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention.
The multi-band antenna covers a range of frequencies that may be too far apart to be covered using a single existing antenna. In an exemplary embodiment, the multi-band antenna is used to transmit or receive signal in the L1 band (1565 to 1585 MHz), the L2 band (1217 to 1237 MHz), the L5 band (1164 to 1189 MHz) and L-band communications (1520 to 1560 MHz). These four L-bands are treated as two distinct bands of frequencies: a first band of frequencies that ranges from approximately 1164 to 1237 MHz, and a second band of frequencies that ranges from approximately 1520 to 1585 MHz. Approximately center frequencies of these two bands are located at 1200 MHz (f1) and 1552 MHz (f2). These specific frequencies and frequency bands are only exemplary, and other frequencies and frequency bands may be used in other embodiments.
The multi-band antenna is also configured to have substantially constant impedance (sometimes called a common impedance) in the first and the second band of frequencies. These characteristics may allow receivers in GNSS's, such as GPS, to use fewer or even one antenna to receive signals in multiple frequency bands.
While embodiments of a multi-band antenna for GPS are used for as illustrative examples in the discussion that follows, it should be understood that the multi-band antenna may be applied in a variety of applications, including wireless communication, cellular telephony, as well as other GNSS's. While the embodiments of the multi-band antenna take advantage of phase relationships at two frequency bands of interest, the technique describe may be applied broadly to a variety of antenna types and designs for use in different ranges of frequencies.
Attention is now directed towards embodiments of the multi-band antenna.
Each of the inverted-L elements 122 has two segments 126, 127. The first segment 126 (e.g., 126-1 of inverted-L element 112-1), has a length (when projected onto the ground plane 110) of LA+LB, and the second segment 127 has a length (when projected onto the ground plane 110) of LE. The first and second segments 126, 127 of each inverted-L element 122 are electrically separated from each other by a tank circuit 124 (e.g., tank circuit 124-1 for inverted-L element 122-1).
In a first band of frequencies, the tank circuits 124 have low impedance, and therefore allow electrical signals 130 to be coupled to both segments of the inverted-L elements 112. In a second band of frequencies, however, the tank circuits 124 have high impedance and effectively block the electrical signals 130 from reaching the second segments 127 of the inverted-L elements 122. From another viewpoint, for signals in the first band of frequencies the effective length of each antenna element 122-1, 122-2 is LA+LB+LE, while for signals in the second band of frequencies the effective length of each antenna element 122-1, 122-2 is LA+LB.
In an exemplary embodiment, each instance of the tank circuit 124 may be a parallel inductor and capacitor. The tank circuit 124 is sometimes called a resonance circuit. For example, the tank circuit 124 may exhibit resonance at a center frequency f2 in the second band of frequencies. In this way, the tank circuit 124 may be used to act as a trap for electrical signals 130 in the second band of frequencies.
Each of the inverted-L elements 112, such as inverted-L element 112-1, may have a monopole positioned above the ground plane 110. In the antenna 100, the monopole is in a plane that is approximately parallel to a plane that includes the ground plane 110. The monopole may be implemented using a metal layer deposited on a printed circuit board. The monopole, when operated in the second band of frequencies, may have a length LA+LB (114, 116), a thickness 132, a width 134, and may be a length LD 120 above the ground plane 110. As noted above, when operated in the first band of frequencies, the monopole has a length of LA+LB+LE (114, 116, 117). The two inverted-L elements 112 may be separated by a distance LC 118. The inverted-L element 112-1 may have a tilted section that has a length projected along the ground plane 110 of LA 114. This tilted section may alter the radiation pattern of the antenna 100. It does not, however, modify the electrical impedance characteristics of the antenna 100.
In some embodiments, the antenna 100 may include additional components or fewer components. Functions of two or more components may be combined. Positions of one or more components may be modified. For example, the monopoles in the inverted-L elements 112 may have alternate geometries. This is shown in
In some embodiments, the antenna 200 may include additional components or fewer components. For example,
In other embodiments, the antenna 200 or the antenna 100 (
The antenna 300 does not include respective tank circuits, such as the tank circuits 124 (
In some embodiments, the antenna 300 may include additional components or fewer components. Functions of two or more components may be combined. Positions of one or more components may be modified.
As illustrated in
In some embodiments, the feed network circuit 400 may include additional components or fewer components. Functions of two or more components may be combined. Positions of one or more components may be modified.
Attention is now directed towards illustrative embodiments of the multi-band antenna and phase relationships that occur in the at least two frequency bands of interest. While the discussion focuses on the antenna 300 (
Referring to
In embodiments where the inverted L-elements are supported by printed circuit boards, the geometry of the inverted-L elements 112 and/or 212 are a function of the dielectric constant of the printed circuit board or substrate. Using
LB=0.152λ(−0.015756ε+1.053256)
LD=0.08λ(−0.015756ε+1.053256)
and
Width=0.024λ(−0.015756ε+1.053256).
If a substrate with a lower dielectric constant ε is used, the lengths of the inverted-L elements 112 and/or 212 will be larger for a given central frequency f1. Note that LC is approximately independent of ε.
The geometry of the antenna 300 has advantageous properties. This is illustrated in
The length d2 614-2 of the second delay line 612-2 is chosen such that it corresponds to a phase shift of 90° (λ/4) at frequencies proximate to the first and the second band of frequencies. For this reason, the second delay line 612-2 may be called a quarter wave line. In addition, the second delay line 612-2 has a characteristic impedance that is equal to, or approximately equal to the geometric mean of the impedance at the central frequency f1 and the desired final impedance of 50 Ω. In this way, the impedance of the inverted-L element 112-1 is transformed to approximately 50 Ω in the first band of frequencies and the second band of frequencies. Similar impedance transformation networks may be applied to the other inverted-L antenna elements 112 in the antenna 100 (
In an exemplary embodiment, at 1200 MHz a phase shift of 360° corresponds to 0.250 m. At 1552 MHz, a phase shift of 270° corresponds to 0.242 m. These two lengths are within 3% of each other. As a consequence, if the length d1 614-1 is in the range of 0.242-0.250 m the impedance at 1200 MHz remains approximately unchanged (12.5 Ω) and the impedance at 1552 MHz is phase shifted by an additional 180° resulting in an impedance that is approximately the same as that at 1200 MHz. As a compromise, the length d2 614-2 corresponds to 1377 MHz (approximately mid-way between 1200 and 1552 MHz). In one embodiment, the characteristic impedance of the quarter wave delay line 612-2 is approximately 25 Ω. This results in an approximate impedance of 50 Ω at the 1200 and 1552 MHz.
In some embodiments, the embodiment 600 may include additional components or fewer components. Functions of two or more components may be combined. Positions of one or more components may be modified. While the embodiment 600 illustrates an impedance transformation applied to two modes of an antenna, in other embodiments similar impedance transformations may be applied to more than two modes of an antenna.
Attention is now directed towards embodiments of processes of using a multi-band antenna.
In some embodiments, the embodiment 900 may include fewer or additional operations. An order of the operations may be changed. At least two operations may be combined into a single operation.
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. Thus, the foregoing disclosure is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings.
It is intended that the scope of the invention be defined by the following claims and their equivalents.