Communications: radio wave antennas – Antennas – Spiral or helical type
Reexamination Certificate
1997-03-27
2001-02-06
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Spiral or helical type
C343S853000
Reexamination Certificate
active
06184844
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to helical antennas. More particularly, the present invention relates to a novel and improved dual-band helical antenna having coupled radiator segments.
II. Description of the Related Art
Contemporary personal communication devices are enjoying widespread use in numerous mobile and portable applications. With traditional mobile applications, the desire to minimize the size of the communication device, such as a mobile telephone for example, led to a moderate level of downsizing. However, as the portable, hand-held applications increase in popularity, the demand for smaller and smaller devices increases dramatically. Recent developments in processor technology, battery technology and communications technology have enabled the size and weight of the portable device to be reduced drastically over the past several years.
One area in which reductions in size are desired is the device's antenna. The size and weight of the antenna play an important role in downsizing the communication device. The overall size of the antenna can impact the size of the device's body. Smaller diameter and shorter length antennas can allow smaller overall device sizes as well as smaller body sizes.
Size of the device is not the only factor that needs to be considered in designing antennas for portable applications. Another factor to be considered in designing antennas is attenuation and/or blockage effects resulting from the proximity of the user's head to the antenna during normal operations. Yet another factor is the characteristics of the communication link, such as, for example, desired radiation patterns and operating frequencies.
An antenna that finds widespread usage in satellite communication systems is the helical antenna. One reason for the helical antenna's popularity in satellite communication systems is its ability to produce and receive circularly-polarized radiation employed in such systems. Additionally, because the helical antenna is capable of producing a radiation pattern that is nearly hemispherical, the helical antenna is particularly well suited to applications in mobile satellite communication systems and in satellite navigational systems.
Conventional helical antennas are made by twisting the radiators of the antenna into a helical structure. A common helical antenna is the quadrifilar helical antenna which utilizes four radiators spaced equally around a core and excited in phase quadrature (i.e., the radiators are excited by signals that differ in phase by one quarter of a period or 90°). The length of the radiators is typically an integer multiple of a quarter wavelength of the operating frequency of the communication device. The radiation patterns are typically adjusted by varying the pitch of the radiator, the length of the radiator (in integer multiples of a quarter-wavelength), and the diameter of the core.
Conventional helical antennas can be made using wire or strip technology. With strip technology, the radiators of the antenna are etched or deposited onto a thin, flexible substrate. The radiators are positioned such that they are parallel to each other, but at an obtuse angle to the sides (or edges) of the substrate. The substrate is then formed, or rolled, into a cylindrical, conical, or other appropriate shape causing the strip radiators to form a helix.
This conventional helical antenna, however, also has the characteristic that the radiator lengths are an integer multiple of one quarter wavelength of the desired resonant frequency, resulting in an overall antenna length that is longer than desired for some portable or mobile applications.
Additionally, in applications where transmit and receive communications occur at different frequencies, dual-band antennas are desirable. However, dual-band antennas are often available only in less than desirable configurations. For example, one way in which a dual band antenna can be made is to stack two single-band quadrifilar helix antennas end-to-end, so that they form a single cylinder. A disadvantage of this solution, however, is that such an antenna is longer than would otherwise be desired for portable, or hand-held applications.
Another technique for providing dual-band performance has been to utilize two separate single band antennas. However, for hand-held units, the two antennas would have to be located in close proximity to one another. Two single band antennas, placed in close proximity on a portable, or hand-held unit would cause coupling between the two antennas, leading to degraded performance as well as unwanted interference.
SUMMARY OF THE INVENTION
The present invention is a novel and improved dual-band helical antenna having two sets of one or more helically wound radiators. The radiators are wound, or wrapped, such that the antenna is in a cylindrical, conical, or other appropriate shape to optimize or otherwise obtain desired radiation patterns. According to the invention, one set of radiators is provided for operation at a first frequency and the second set is provided for operation at a second frequency which preferably is different from the first frequency. Each set of radiators has an associated feed network to provide the signals to drive the radiators. Thus, the dual-band antenna can be described as being comprised of two single-band antennas, each single-band antenna having a radiator portion and a feed portion.
To provide dual-band operation in an integrated antenna package, the two sets of radiators and their associated feed networks (i.e., the two single-band antennas) are stacked, or positioned end-to-end such that they are coaxially aligned with one another.
In one embodiment, the stacked antennas are positioned such that they have the same orientation. That is, their feed portions are oriented toward one end of the dual-band antenna and their radiator portions are oriented toward the other end. Consequently, the portions of the dual-band antenna, from one end of the antenna to the other are: a radiator portion of the first single-band antenna, a feed portion of the first single-band antenna, a radiator portion of the second single-band antenna, and a feed portion of the second single-band antenna.
In one embodiment, each radiator of at least one set of one or more radiators is comprised of two radiator segments. One radiator segment extends in a helical fashion from a first end of the radiator portion of the antenna toward the other end of the radiator portion. A second radiator segment extends in a helical fashion from a central area of the dual-band antenna (i.e., from the other end of the radiator portion of the second single-band antenna) toward the first end of the radiator portion.
In this embodiment, each segment in the set is physically separate from but electromagnetically coupled to the adjacent segment(s) in the set. The length of the segments in the set is chosen such that the set (i.e., the radiator(s)) resonates at a particular frequency. Because the segments in a set are physically separate from but electromagnetically coupled to one another, the length at which the radiator resonates for a given frequency can be made shorter than that of a conventional helical antenna radiator.
As a result of this structure, electromagnetic energy from the first segment of a radiator in the first set is coupled into the second segment of that radiator. The effective electrical length of these combined segments causes the radiator in the first set of one or more radiators to resonate at a given frequency.
An advantage of this coupled multi-segment embodiment is that it can be easily tuned to a given frequency by adjusting or trimming the length of the radiator segments. Because the radiators are not a single contiguous length, but instead are made up of a set of two or more segments, the length of the segments is easily modified after the antenna has been made to properly tune the frequency of the antenna. Additionally, the overall radiation pattern of the antenna is essentially unchanged by th
Filipovic Daniel
Tassoudji Ali
Tidwell Stephen B.
Nguyen Hoang
Ogrod Gregory D.
Qualcomm Incorporated
Wadsworth Phillip R.
Wong Don
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