HK1019834A - Coupled multi-segment helical antenna - Google Patents

Description

Coupled multi-segment helical antenna

Technical Field

The present invention relates to helical antennas, and more particularly to helical antennas having coupled multi-segment radiators.

Background

Modern personal communication devices are widely used in a variety of mobile and portable devices. For conventional mobile devices, it is desirable to minimize the size of a communication device, such as a mobile phone, to a moderate level. However, the demand for small, yet small devices has increased dramatically due to the proliferation of portable, hand-held devices. Recent developments in processor technology, battery technology, and communication technology have made it possible in recent years to drastically reduce the size and weight of portable devices.

One aspect in which size reduction is desirable is the antenna of the device. The size and weight of the antenna play an important role in reducing the size of the communication device. The overall size of the antenna may affect the size of the device body. The smaller the diameter and the shorter the length of the antenna, the smaller the size of the device and the smaller the size of the device body.

The size of the device is not the only factor to consider when designing an antenna for a portable device. Another factor to consider in designing an antenna is the attenuation and/or blocking effect caused by the proximity of the user's head to the antenna during normal operation. Yet another factor is the characteristics of the communication link, such as the desired radiation pattern and operating frequency.

A widely used antenna in satellite communication systems is a helical antenna. One reason helical antennas are widely used in satellite communication systems is because they are capable of generating and receiving circularly polarized radiation used in such systems. Furthermore, helical antennas are particularly useful for devices in mobile satellite communications systems and satellite navigation systems because they can produce radiation patterns that are close to hemispherical.

A conventional helical antenna is manufactured by twisting a radiator of the antenna into a helical structure. A common helical antenna is a quadrifilar helical antenna, which is four radiators equally spaced around a core and excited with a 90 ° phase difference (i.e., the radiators are excited by signals that are one-quarter of a period or 90 ° out of phase). The length of the radiator is typically an integer multiple of a quarter wavelength of the operating frequency of the communication device. Generally, the radiation pattern is adjusted by changing the pitch of the radiators, the length of the radiators (an integral multiple of a quarter wavelength), and the diameter of the core.

Conventional helical antennas may be fabricated using either a wire or strip (strip) process. The radiator of the antenna can be etched or deposited on a thin flexible substrate using a strip line process. The radiators are positioned so that they are parallel to each other, but they make an obtuse angle with one or more edges of the substrate. The substrate is then formed or rolled into a cylindrical, conical, or other suitable shape to form the strip radiator into a spiral.

However, conventional helical antennas have the property that the radiator length is an integer multiple of a quarter wavelength of the desired resonant frequency, resulting in an overall antenna length that is longer than required for some portable or mobile devices.

Disclosure of Invention

The present invention is directed to a helical antenna having one or more helically wound radiators. The radiators are wound so that the antenna is cylindrical, conical or other suitable shape to optimize the radiation pattern. According to the invention, each radiator comprises a set of two or more radiator segments. Each section in the set, while actually isolated from the other sections in the set, is electromagnetically coupled to them. The lengths of the segments in a group are chosen such that the group (i.e. the radiator) resonates at a particular frequency. Since the segments in a group, while essentially isolated from each other, are still electromagnetically coupled to each other, the length of the radiator that resonates at a given frequency can be made shorter than that of a conventional helical antenna.

It is therefore an advantage of the present invention that the coupled radiator portion of a multi-section helical antenna can be made to resonate at a shorter overall radiator length and/or with a smaller volume for a given operating frequency than a conventional helical antenna having the same effective resonant length.

Another advantage of coupled multi-section helical antennas is that the antenna can be easily tuned to a given frequency by adjusting or fine-tuning the length of the radiator sections. Since the radiator is not a single contiguous length but is made up of a set of two or more overlapping segments, the lengths of the segments can be easily changed by fine tuning the radiator after the antenna is manufactured, thereby tuning the antenna frequency appropriately. Furthermore, tuning does not substantially change the overall radiation pattern of the antenna, since the fine tuning does not change the overall actual length of the radiator portion of the antenna.

It is a further advantage of the present invention that the directional characteristics of the antenna can be adjusted to maximize the signal strength in a preferred direction, such as along the axis of the antenna. Thus, for certain applications, such as satellite communications, the directional characteristics of the antenna may be optimized so that the signal strength in the upward direction from the ground may be maximized.

Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings.

Brief description of the drawings

The features, objects, and advantages of the present invention will become apparent from the detailed description set forth below when taken in conjunction with the drawings in which the left-most digit(s) of a reference number is equivalent to the first-appearing digit(s) of the reference number, and in which like reference numbers bear the same letters, and in which:

fig. 1A is a diagram showing a conventional linear quadrifilar helix antenna;

fig. 1B is a diagram showing a conventional strip-line quadrifilar helix antenna;

fig. 2A is a schematic plan view of a quadrifilar helix antenna showing an open termination;

FIG. 2B is a schematic plan view of a quadrifilar helix antenna showing a short termination;

fig. 3 is a diagram showing the current distribution on the radiator of a short-circuited quadrifilar helix antenna;

FIG. 4 is a diagram showing the far surface of an etched substrate with a wire spiral antenna;

FIG. 5 is a diagram showing a near-surface of an etched substrate with a wire spiral antenna;

FIG. 6 is a perspective view showing an etched substrate with a wire spiral antenna;

fig. 7A is a diagram illustrating an open-circuited coupled multi-segment radiator having five coupled segments in accordance with one embodiment of the present invention;

fig. 7B is a diagram illustrating a pair of shorted coupled multi-section radiators according to one embodiment of the invention;

FIG. 8A is a schematic plan view illustrating a short-circuited coupled multi-section quadrifilar helix antenna according to one embodiment of the invention;

FIG. 8B is a diagram illustrating a coupled multi-section quadrifilar helical antenna, which forms a cylindrical shape, according to one embodiment of the present invention;

FIG. 9A is a graph illustrating the degree of overlap δ and spacing s of radiator segments according to one embodiment of the present invention;

FIG. 9B is a graph showing the current distribution on the radiator segments of a coupled multi-segment helical antenna;

FIG. 10A is a diagram showing two point sources with radiation signals 90 out of phase;

FIG. 10B is a diagram illustrating a field pattern due to the point source shown in FIG. 10A;

FIG. 11 is a diagram showing an embodiment in which each section is equidistant from sections on both sides;

FIG. 12 is an exemplary diagram illustrating coupling of a multi-section antenna in accordance with one embodiment of the present invention;

fig. 13 is a diagram showing a comparison between a conventional quadrifilar helix antenna and the radiator portion of a coupled multi-section quadrifilar helix antenna;

fig. 14A is a radiation pattern illustrating one example of a coupled multi-section quadrifilar helical antenna operating in the L-band; and

fig. 14B is a radiation pattern illustrating one example of a coupled multi-section quadrifilar helical antenna operating in the S-band.

Preferred embodiments of the invention

1. Summary and discussion of the invention

The present invention is directed to a helical antenna having coupled multi-segment radiators that can reduce the length of the radiator at a given resonant frequency, thereby reducing the overall antenna length. The implementation of which will be described in detail below in terms of several embodiments.

2. Example Environment

In a broad sense, the present invention may be implemented in any system that utilizes helical antenna technology. An example of such an environment is a communications system in which a user having a fixed, mobile and/or portable telephone may communicate with other personnel via a satellite communications link. In this example environment, the phone must have an antenna tuned to the frequency of the satellite communications network.

The present invention is described in terms of this example environment. The description in these respects is for convenience only. The present invention is not limited to application in this example environment. Indeed, after reading the following description, it will become apparent to one skilled in the relevant art how to implement the invention in other environments.

3. Conventional helical antenna

Before describing the present invention in detail, it is necessary to describe the radiator portion of some conventional helical antennas. In particular, this section of the article will describe the radiator portion of some conventional quadrifilar helix antennas. Fig. 1A and 1B are diagrams illustrating a radiator portion 100 of a conventional four-stranded helical antenna in a line shape and a strip line shape, respectively. The radiator portion 100 shown in fig. 1A and 1B is a quadrifilar helical antenna, i.e., it has four radiators 104 operating with a phase difference of 90 °. As shown in fig. 1A and 1B, the radiators are wound together to form circular polarization.

Fig. 2A and 2B are planar representations showing a radiator portion of a conventional quadrifilar helical antenna. In other words, fig. 2A and 2B show the radiator as if the antenna cylinder were "unrolled" on a flat surface. Fig. 2A is a diagram showing a quadrifilar helix antenna with open-circuited or unconnected together radiators at the distal end. For this configuration, the resonant length 1 of the radiator 208 is an odd multiple of one quarter wavelength of the desired resonant frequency.

Fig. 2B shows a quadrifilar helix antenna with radiators shorted, interconnected, or connected together at the distal end. In this case, the resonant length 1 of the radiator 208 is an even multiple of one quarter wavelength of the desired resonant frequency. Note that in both cases the resonance length 1 is approximate, since small adjustments are usually required to compensate for the non-ideal short and open terminations.

Fig. 3 is a plan representation showing the radiator of a quadrifilar helix antenna 300 comprising a radiator 208 of length l = λ/2, where λ is the wavelength of the desired resonant frequency of the antenna. The curve 304 represents the relative amplitude of the current of the signal on the radiator 208 resonating at a frequency f = v/λ, where v is the velocity of the signal in the radiator medium.

Examples of a quadrifilar helix antenna (strip antenna) implemented using a printed circuit board will be described in more detail with reference to fig. 4-6. The strip quad helix antenna includes a strip radiator 104 etched on a dielectric substrate 406. The substrate is a thin flexible material that can be rolled into a cylindrical shape so that the radiator 104 can be spirally wound around the central axis of the cylinder.

Fig. 4-6 illustrate elements used to fabricate a quadrifilar helix antenna 100. Figures 4 and 5 show views of the distal surface 400 and the proximal surface 500, respectively, of the substrate 406. Antenna 100 includes a radiating portion 404 and a feed portion 408.

In the embodiments described and illustrated herein, the antenna is fabricated by forming the substrate into a cylindrical shape with the near surface on the outer surface of the formed cylinder. In another embodiment, the substrate forms a cylinder shape and the near surface is located on the outer surface of the cylinder.

In one embodiment, the dielectric substrate 100 is a thin, flexible layer of Polytetrafluoroethylene (PTFE), PTFE/glass mixture, or other dielectric material. Although other thicknesses may be selected, in one embodiment, the substrate 406 is on the order of 0.005 inches or 0.13 millimeters thick. Copper is used to provide the signal trace and the ground trace. In another embodiment, other conductive materials may be selected to replace copper based on cost, environmental considerations, and other factors.

In the embodiment shown in fig. 5, the feed network 508 is etched on the feed portion 408 to give the signals provided to the radiators 104(104A-D) that are in phase quadrature (i.e., 0 °, 90 °, 180 °, and 270 ° signals). The feeding portion 408 of the distal surface 400 provides a ground plane 412 for a feeding circuit 508. A signal trace for the feed circuit 508 is etched on the near surface 500 of the feed portion 408.

For purposes of discussion, the radiator portion 404 has a first end 432 and a second end 434 proximate to the feed portion 408 (on the other end of the radiator portion 404). Depending on the antenna embodiment being implemented, the radiator 104 may be etched into the distal surface 400 of the radiator portion 404. The radiator 104 extends from the first end 432 to the second end 434 a length approximately an integer multiple of a quarter wavelength of the desired resonant frequency.

In embodiments where the length of the radiators 104 is an integer multiple of λ/2, the radiators 104 are electrically connected (i.e., shorted) to each other at the second end 434. This connection may be made by a conductor at the second end 434 that forms a loop 604 around the antenna when the substrate forms a cylinder. Fig. 6 is a perspective view of an etched substrate showing a ribbon spiral antenna having a shorting ring 604 at the second end 434.

A conventional quadrifilar helix antenna is disclosed in U.S. patent No. 5,198,831 to Burrell et al (the' 831 patent), which is incorporated herein by reference. The antenna described in the' 831 patent is a printed circuit board antenna having an antenna radiator etched or deposited on a dielectric substrate. The substrate forms a cylinder resulting in a spiral structure of the radiator.

Another conventional quadrifilar helical antenna is disclosed in U.S. patent No. 5,255,005 to Terret et al (the' 005 patent), which is incorporated herein by reference. The antenna described in the' 005 patent is a quadrifilar helix antenna formed from two bifilar helices placed orthogonally and excited with a 90 ° phase difference. The disclosed antenna also has a second quadrifilar helix coaxial with and electromagnetically coupled to the first helix to increase the passband of the antenna.

Yet another conventional quadrifilar helical antenna is disclosed in U.S. patent No. 5,349,365 to Ow et al (the' 365 patent), which is incorporated herein by reference. The' 365 patent is a quadrifilar helix antenna designed in accordance with the linear shape described above with reference to figure 1A.

4. Coupled multi-segment helical antenna embodiments

Having briefly described various forms of conventional helical antennas, coupled multi-section helical antennas in accordance with the present invention will now be described in terms of several embodiments. To reduce the length of the antenna radiator portion 100, the present invention utilizes a coupled multi-segment radiator so that the present invention can resonate at a given frequency with a shorter length than is required for a conventional helical antenna having an equal resonant length.

Fig. 7A and 7B are plan representations illustrating example embodiments of coupling multi-segment helical antennas. Fig. 7A shows a coupled multi-segment radiator 706 terminated in an open circuit (not shorted together) according to a single strand embodiment. Such antennas with open terminations may be used for single-strand, double-strand, four-strand, or other x-strand examples.

The embodiment shown in fig. 7A includes a single radiator 706. The radiator 706 comprises a set of radiator segments. The set comprises two end sections 708, 710 and p intermediate sections 712, where p =0,1,2,3 … (p =3 is shown). The intermediate link is arbitrary (i.e., p may equal zero). The end sections 708, 710, while effectively isolated from each other, are electromagnetically coupled to each other. An intermediate link 712 is located between the end links 708, 710 and provides electromagnetic coupling between the end links 708, 710.

In the open-ended embodiment, the length ls1 of the segments 708 is an odd multiple of one-quarter wavelength at the desired resonant frequency. The length ls2 of the section 710 is an integer multiple of one-half wavelength of the desired resonant frequency. The length lp of each of the p intermediate links 712 is an integer multiple of one-half wavelength of the desired resonant frequency. In the illustrated embodiment, there are three intermediate links 712 (i.e., p = 3).

Fig. 7B shows the radiator 706 of the spiral antenna terminated with a short or connector 722. This short circuit example is not applicable to a single-strand antenna, but it can also be used for a dual, four or other x-strand antenna. As with the open termination embodiment, the radiator 706 includes a set of radiator segments. The set comprises two end sections 708, 710 and p intermediate sections 712, where p =0,1,2,3 … (p =3 is shown). The intermediate link is arbitrary (i.e., p may equal zero). The end sections 708, 710, while effectively isolated from each other, are electromagnetically coupled to each other. An intermediate link 712 is located between the end links 708, 710 and provides electromagnetic coupling between the end links 708, 710.

In the short-circuited embodiment, the length l of the segments 708_s1Is an odd multiple of one quarter wavelength of the desired resonant frequency. Length l of segment 710_s2Is an integer multiple of a quarter wavelength of the desired resonant frequency. Length l of each of p intermediate links 712_pAn integer multiple of one-half wavelength of the desired resonant frequency. In the illustrated embodiment, there are three intermediate links 712 (i.e., p = 3).

Fig. 8A and 8B illustrate coupling multiple sections of a quadrifilar helix antenna radiator portion 800 according to one embodiment of the invention. Fig. 8A and 8B illustrate an example of the antenna shown in fig. 7B, where p = zero (i.e., no intermediate link 712) and the lengths of the links 708, 710 are quarter wavelengths.

The radiator portion 800 shown in fig. 8A is a planar representation of a four-stranded helical antenna having four coupled radiators 804. Each coupled radiator 804 in the coupled antenna actually includes two radiator segments 708, 710 that are close together so that energy in the radiator segment 708 is coupled to another radiator segment 710.

Specifically, according to one embodiment, the radiator portion 800 may be described by two segments 820, 824. The segment 820 includes a plurality of radiator segments 708 extending from a first end 832 of the radiator portion 800 to a second end 834 of the radiator portion 800. Segment 824 includes a plurality of second radiator segments 710 extending from second end 834 to first end 832 of radiator portion 800. Towards the central region of the radiator portion 800, a portion of each segment 708 is adjacent to an adjacent segment 710, so that the energy of one segment is coupled to the adjacent segment in the adjacent region. This relative proximity is referred to herein as overlap.

In a preferred embodiment, each segment 708, 710 is approximately l in length₁=l₂And (= λ/4). The total length of the single radiator comprising the two segments 708, 710 is defined as l_tot’. The amount by which one section 708 overlaps another section 710 is defined as δ = l₁+l₂-l_tot。

For a resonance frequency f = v/λ, the total length of the radiator l_totA length lambda/2 of less than half a wavelength. In other words, the coupling of the radiator comprising a pair of coupling nodes 708, 710 results in that the radiator can resonate at a frequency f = ν/λ even if its total length is smaller than λ/2. Thus, for a given frequency f, the radiator portion 800 of a half-wavelength coupled multi-section quadrifilar helix antenna is shorter than the radiator portion of a conventional half-wavelength quadrifilar helix antenna 800.

To more clearly illustrate the size reduction obtained using the coupling structure, the structure is modified byThe radiator portion 800 shown in fig. 8 is compared with the radiator portion shown in fig. 3. For a given frequency f = v/λ, the length l of the conventional antenna radiator portion 300 is λ/2, while the length l of the coupled radiator segment antenna radiator portion 800 is_tot＜λ/2。

As described above, in one embodiment, the lengths of the segments 708, 710 are l₁=l₂And (= λ/4). The length of each segment can be varied in such a way that₁Is not necessarily equal to l₂They are not equal to lambda/4. The actual resonant frequency of each radiator is a function of the length of the radiator segments 708, 710, the separation distance s between the radiator segments 708, 710, and the amount by which the segments 708, 710 overlap one another.

Note that the bandwidth of the antenna can be adjusted by changing the length of one section 708 relative to the other section 710. For example, lengthen l₁Making it slightly larger than lambda/4 and shortened by l₂Making it slightly less than λ/4 increases the bandwidth of the antenna.

Fig. 8B shows a practical antenna structure for coupling a multi-section quadrifilar helix antenna in accordance with one embodiment of the present invention. It shows how each radiator comprises two segments 708, 710 in one embodiment. The segments 708 extend in a spiral fashion from a first end 832 of the radiator portion to a second end 834 of the radiator portion. The segments 710 extend in a spiral fashion from the second end 834 of the radiator portion to the first end 832 of the radiator portion. Fig. 8B also shows that a portion of the segments 708, 710 overlap such that they are electromagnetically coupled to each other.

Fig. 9A is a diagram showing the spacing s and overlap δ between radiator segments 708, 710. The spacing s is selected so that sufficient energy is coupled between the radiator segments 708, 710 so that they function as a single radiator having an effective electrical length of approximately λ/2 and integer multiples thereof.

Spacing of the radiator segments 708, 710 less than this optimal spacing results in greater coupling between the segments 708, 710. As a result, for a given frequency f, the length of the segments 708, 710 must be increased so as to be resonant at the same frequency f. This can be illustrated by the extreme case where the sections 708, 710 are actually connected (i.e., s = 0). In this extreme case, the total length of the segments 708, 710 must be equal to λ/2 in order for the antenna to resonate. Note that in this extreme case, the antennas are in fact no longer coupled, depending on the use in this description, and the resulting structure is in fact a conventional spiral antenna such as that shown in fig. 3.

Likewise, increasing the amount of overlap δ of the sections 708, 710 will increase coupling. Thus, as the degree of overlap δ increases, the length of the segments 708, 710 also increases.

To quantitatively understand the optimal overlap and spacing of the segments 708, 710, we refer to FIG. 9B. Fig. 9B shows the magnitude of the current on each node 708, 710. The current intensity indicator values 911, 928 show that ideally each segment resonates at λ/4, with the signal intensity at the outer end being the greatest and the signal intensity at the inner end being the least.

In order to optimize the structure of the coupled radiator section antenna, the inventors determined the correct section length l from other parameters using simulation software₁、l₂Overlap δ and spacing. One such software package is an Antenna Optimizer (AO) software package. AO is based on a method of magnetic moment electromagnetic simulation algorithm. AO antenna optimizer version 6.35 (copyright 1994) was written by Brian Beezley, san diego, california.

Note that certain advantages may be obtained by using the structure described above with reference to fig. 8A and 8B. With conventional antennas and coupled radiator segment antennas, the current can be concentrated at both ends of the radiator. This is an advantage in certain applications for coupling radiator segment antennas, in accordance with the array factor principle.

For purposes of illustration, FIG. 10A is a graph showing two point sources A, B, where source A radiates a signal having the same amplitude as source B but with a phase lag of 90 (assuming e is^jωtThe convention of (d). Where sources a and B are separated by a distance of λ/4, the signals are superimposed in an in-phase manner in the direction of propagation from a to B, and in an anti-phase manner in the direction of propagation from B to a. As a result, very little radiation is emitted in the direction B to a. Exemplary field pattern illustrations shown in FIG. 10BThis is done.

Thus, the antenna may be optimally used for most applications when the sources a and B are oriented such that the direction from a to B indicates upward from the ground and the direction from B to a indicates toward the ground. This is because there are few antennas for which the user wants to direct the signal strength towards the ground. This architecture is particularly useful in satellite communications where it is desirable to have most of the signal strength radiate upwards from the ground.

The point source antenna simulated in fig. 10 is not easily implemented using a conventional half-wavelength helical antenna. Consider the antenna radiator portion shown in fig. 3. The concentration of current intensity at both ends of the radiator 208 approximately approximates a point source. When the radiator is rolled into a spiral configuration, one end of the 90 ° radiator is positioned in line with the other end of the 0 ° radiator. This then approximates two point sources on the same line. However, in contrast to the required configuration shown in FIG. 10A, these approximate point sources are separated by approximately λ/2.

Note, however, that the coupled radiator section antenna according to the present invention provides an example in which the approximately spaced distance is closer to λ/4. Thus, the coupled radiator section antenna allows a user to utilize the directivity of the antenna shown in fig. 10A.

The segments 708, 710 of the radiator shown in figure 8 show that the segments 708 are very close to their respective joint 710, and that each pair of segments 708, 710 is relatively far from the adjacent pair of segments. In another embodiment, each segment 710 is equidistant from both segments 708. This embodiment is shown in fig. 11.

Referring now to fig. 11, each section is substantially equidistant from each pair of adjacent sections. For example, the segment 708B is equidistant from the segments 710A, 710B. Namely S₁=S₂. Likewise, segment 710A is equidistant from segments 708A, 708B.

A counterintuitive aspect of this embodiment is that it appears as if there is unwanted coupling. In other words, a segment corresponding to one phase will couple not only with the appropriate segment of the same phase, but also with an adjacent segment that is phase-shifted. For example, 90 ° section 708B would be coupled with section 710A (0 ° section) and section 710B (90 ° section). This coupling is not a problem because the radiation from the upper section 810 can be viewed as two separate modes. One mode comes from the coupling of the adjacent section to the left and the other from the coupling of the adjacent section to the right. However, the phases of both modes are adjusted to provide radiation in the same direction. Thus, such double coupling is not detrimental to the presence of the coupled multi-section antenna.

5. Examples of the invention

Figure 12 is an example of a coupled radiator segment antenna in accordance with one embodiment of the present invention. Referring now to fig. 12, the antenna includes a radiator portion 1202 and a feed portion 1206. The radiator portion includes segments 708, 710. The dimensions provided in fig. 12 illustrate the effect of the segments 708, 710 and the amount of overlap δ of the overall length of the radiator portion 1202.

The length of the segment in a direction parallel to the axis of the cylinder is shown as l of segment 708₁sin α and l of node 710₂sin α, where α is the interior angle of the segments 708, 710.

The degree of overlap of the sections shown in figures 8A and 9A above is shown by the reference character delta. The amount of overlap in the direction parallel to the antenna axis is given by δ sin α as shown in fig. 12.

The segments 708, 710 are separated by an interval s, which may vary as described above. The distances between the ends of the nodes 708, 710 and the end of the radiator portion 1202 are respectively defined by the reference character γ₁、γ₂The intervals shown. Interval gamma₁、γ₂May be equal, but not necessarily. Further, as described above, the length of the segments 708 may vary with respect to the length of the segments 710.

By reference character omega₀The offset is shown taken from one end of the section 710 to the other. From omega_sTo indicate the degree of isolation between adjacent segments 710, which is determined by the diameter of the helix.

Feed portion 1206 includes an appropriate feed network that provides phase quadrature signals to radiator segment 708. The feed network is well known to those of ordinary skill in the art and will not be described in detail herein.

In the embodiment shown in fig. 12, the node 708 is fed at a feed point selected at some distance from the feed network along the node 708 to optimize impedance matching. In the embodiment shown in FIG. 12, this distance is indicated by the reference character δ_{Feeding electricity}Shown.

Note that continuous line 1224 represents the boundary of the ground portion on the far surface of the substrate. The ground portion opposite the node 708 on the distal surface extends to the feed point. The thin portion of the link 708 is located on the proximal surface. At the feed point, the thickness of the near-surface upper segment 708 increases.

An exemplary coupled radiator section quadrifilar helix antenna suitable for operation in the L-band adjacent to 1.6GHz is now provided with dimensions. Note that this is only an example and other dimensions may be used for operation in the L-band. In addition, other dimensions may be used for operation in other frequency bands.

The overall length of radiator portion 1202 in the exemplary L-band embodiment is 2.30 inches (58.4 mm). In this embodiment, the inclination angle α is 73 degrees. From this angle of inclination α, the length l of the segment 708 in this embodiment₁sin α is 1.73 inches (43.9 mm). In the illustrated embodiment, the length of section 710 is equal to the length of section 708.

In an example embodiment, the segments 710 are substantially equidistant from their adjacent segment pairs 708. In one example of this embodiment, the interval s₁=s₂=0.86 inch. Other spacings may also be included, such as 0.070 inches (1.8mm) spacing of a segment 710 from an adjacent segment 708.

In this embodiment, the width τ of the segments 708, 710 is 0.11 inches (2.8 mm). Other widths are also possible.

Exemplary L band embodiments are at γ₁=γ₂A symmetric spacing of =0.57 inches (14.5mm) is characterized. Here by the spacing gamma₁Symmetrical (i.e., gamma) for both ends of radiator portion 1202₁=γ₂) The radiators 708, 710 have an overlap δ sin α (1.73 inch-. 57) of 1.16 inches (29.5mm)Inches).

Offset of pitch omega₀Is 0.53 inch, node isolation omega_sAnd is 0.393 inches (10.0 mm). The diameter of the antenna is 4 omega_s/π。

In one embodiment, the distance δ from the feed point to the feed network is chosen such that_{Feeding electricity}And thus delta_{Feeding electricity}=1.57 inches (39.9 mm). Other feed points may be selected to optimize impedance matching.

Note that the above example embodiment design was used in conjunction with a 0.032 inch thick polycarbonate radome surrounding the helical antenna and contacting the radiator portion. How a radome or other structure affects the wavelength of the desired frequency will become apparent to those skilled in the art.

Note that in the above-described exemplary embodiment, the total length of the radiator portion of the L-band antenna is reduced compared to a conventional half-wavelength L-band antenna. For a conventional half-wavelength L-band antenna, the length of the radiator portion is approximately 3.3 inches (i.e., λ/2(sin α)), where α is the interior angle of the segments 708, 710 with respect to the horizontal) or (81.3 mm). For the exemplary embodiment described above, the overall length of radiator portion 1202 is 2.3 inches (58.42 mm). This represents a substantial reduction in the size of conventional antennas.

Fig. 13 is a side-by-side comparison showing a half-wavelength L-band coupled multi-section antenna radiator portion 1304 and a conventional L-band quadrifilar helix antenna 1308. As shown in fig. 13, the coupled radiator segment antenna radiator portion 1304 is effectively shorter than a conventional quadrifilar helix antenna 1308.

An example embodiment for the S-band of approximately 2.49GHz is now described. In the S-band embodiment of this example, the total length of the radiator portion 1202 is 1.50 inches (38.1 mm). In this embodiment, the inclination angle α is 65 degrees. The length l of the segments 708 in this embodiment₁sin α is 0.95 inches (24.1mm) and the length of segment 710 is equal to the length of segment 708. The spacing of the preferred embodiment is such that segment 710 is equidistant(s) from its adjacent segment pair 708₁=s₂=0.086 inch). Of segments 708, 710 of radiatorThe width τ is 0.11 inches (2.8 mm). For 50 ohm impedance matching, feed point δ_{Feeding electricity}Is 0.60 inches.

The exemplary S-band embodiment is spaced symmetrically (i.e., γ) at both ends of radiator 1202₁=γ₂=0.55 inch). The radiators 708, 710 have an overlap δ sin α (.95 inches-0.55 inches) of 0.40 inches (10.2 mm).

Offset of pitch omega₀0.44 inch (11.2mm), node separation ω_sAnd is 0.393 inches (10.0 mm). The diameter of the antenna is 4 omega_s/π。

Note that the above example embodiment design incorporates a 0.032 inch thick polycarbonate radome that surrounds the helical antenna (and contacts the radiator portion).

In these embodiments, the total length of the radiator portion of the S-band antenna is reduced over a conventional half-wavelength S-band antenna. For a conventional half-wavelength S-band antenna, the length of the radiator portion is approximately 2.0 inches (i.e., λ/2(sin α)), where α is the interior angle of the segments 708, 710 with respect to the horizontal) or (50.8 mm). In the above embodiment, the total length of the radiator portion 1202 is 1.5 inches.

Fig. 14A is a radiation directivity diagram showing one example of a coupled multi-section quadrifilar helical antenna operating in the L-band. Fig. 14B is a radiation directivity diagram illustrating one example of a coupled multi-section quadrifilar helical antenna operating in the S-band. As these directional characteristics show, the antenna provides good omni-directional characteristics in the upper half-plane and exhibits good circular polarization.

In the stripline embodiment described above, the radiator segments 708, 710, 712 are depicted as being disposed on the same surface of the substrate. In another embodiment, the segments need not be located on the same surface of the substrate. For example, in one embodiment, the first end segments (i.e., segments 708) are located on one surface of the substrate and the second end segments (i.e., segments 710) are located on the opposite surface. This and other embodiments are possible without the need for all of the sections 708, 710, 712 to be on the same surface, because it is not necessary to align the edges of the sections for coupling electromagnetic energy. Small deviations in the order of the thickness of the substrate do not have an adverse effect on the coupling. These embodiments, which may allow for selective placement of the segments 708, 710, 712, may be used to provide certain elements or segments on the outside of the antenna at the same time as providing other elements inside the antenna, allowing for access to these elements for certain purposes during tuning, or connection to these elements.

In some applications, an antenna operating at two frequencies is desired. An example of such an application is a communication system operating at one frequency for transmission and at a second frequency for reception. One conventional technique for achieving dual-band performance is to stack the ends of two single-band quadrifilar helical antennas to form a single long cylinder. For example, a system designer may stack an L-band and an S-band antenna together to achieve the characteristics of operation in both the L-and S-bands. However, such stacking increases the overall length of the antenna. The reduction in size achieved by using coupled radiator-section antennas can drastically reduce the overall length of the stacked dual-band antenna.

An additional advantage of a helical antenna with a tuned radiator is that the antenna can be easily tuned after manufacture. The antenna can be tuned simply by fine tuning the sections 708, 710. Note that the tuning can be done without changing the overall length of the antenna, if desired.

Note that the above-described embodiments of coupled radiator-segment antennas are presented in terms of a half-wavelength antenna that resonates at a wavelength equal to an integer multiple of λ/2. It will become apparent to one of ordinary skill in the art after reading this disclosure how to implement the present invention using an antenna that resonates at a wavelength equal to an odd multiple of λ/4 by removing the shorting ring at the distal end of the radiator.

3. Conclusion

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (26)

1. A helical antenna comprising a radiator portion having one or more helically wound radiators extending from a first end of the radiator portion to a second end of the radiator portion, the one or more radiators comprising:

a first radiator segment extending in a spiral manner from a first end of the radiator portion to a second end of the radiator portion; and

a second radiator segment extending in a spiral fashion from the second end of the radiator portion to the first end of the radiator portion;

wherein the first radiator segment is proximate to the second radiator segment such that the first and second radiator segments are electromagnetically coupled to each other.

2. The helical antenna of claim 1, wherein said first and second radiator segments comprise strip segments deposited on a dielectric substrate, said dielectric substrate being shaped such that the radiators are wound in a helical manner.

3. The helical antenna of claim 2, wherein said dielectric substrate is formed in a cylindrical shape or a conical shape.

4. The helical antenna of claim 1, wherein said first and second radiator segments are wire segments.

5. The helical antenna of claim 1, wherein said first radiator segment has a length equal to a length of said second radiator segment.

6. The helical antenna of claim 1, wherein said first and second segments have a length λ/4, where λ is the wavelength of the resonant frequency of the antenna.

7. The helical antenna of claim 1, comprising four radiators, and further comprising a feed network for providing phase quadrature signals to said four radiators.

8. The helical antenna of claim 1, further comprising a feed point for each of said radiators, said feed point being located at a distance from said first end along said first segment, said distance being selected to match the impedance of the radiators to a feed network.

9. The helical antenna of claim 1, wherein said radiator further comprises one or more intermediate radiator segments positioned between said first and second radiator segments.

10. The helical antenna of claim 1, wherein a portion of said first radiator segment is adjacent a portion of said second radiator segment.

11. The helical antenna of claim 1, further comprising a second radiator portion having a plurality of helically wound second radiators extending from a first end of the second radiator portion to a second end of the second radiator portion, each of said second radiators comprising:

a first radiator segment extending in a spiral manner from a first end of the radiator portion to a second end of the radiator portion; and

a second radiator segment extending in a spiral fashion from the second end of the radiator portion to the first end of the radiator portion;

wherein a portion of said first radiator segment is adjacent to a portion of said second radiator segment such that said first and second radiator segments are electromagnetically coupled to one another; and

the second radiator portion operates at a frequency different from a resonant frequency of the first radiator portion, thereby providing dual band operation.

12. The helical antenna of claim 11, wherein said first radiator portion and said second radiator portion are stacked coaxially.

13. The helical antenna of claim 1, wherein said radiators are connected to a feed network at said first end and are connected together at said second end.

14. The helical antenna of claim 1, wherein said radiator is connected to a feed network at said first end and has an open termination at said second end.

15. A helical antenna comprising a radiator portion having a plurality of helically wound multi-segment radiators extending from a first end of the radiator portion to a second end of the radiator portion, each of said multi-segment radiators comprising at least first and second segments, wherein said first segment is substantially isolated from said second segment but electromagnetically coupled thereto.

16. The helical antenna of claim 15, wherein said first and second radiator segments comprise strip segments deposited on a dielectric substrate.

17. The helical antenna of claim 15, wherein said first radiator segment has a length equal to a length of said second radiator segment.

18. The helical antenna of claim 15, wherein said first and second radiator segments are wire segments.

19. The helical antenna of claim 15, wherein said first and second segments have a length λ/4, where λ is the wavelength of the resonant frequency of the antenna.

20. The helical antenna of claim 15, comprising four radiators, and further comprising a feed network for providing phase quadrature signals to said four radiators.

21. The helical antenna of claim 15, further comprising a feed point for each of said radiators, said feed point being located at a distance from said first end along said first segment, said distance being selected to match the impedance of the radiators to a feed network.

22. The helical antenna of claim 15, wherein said radiator further comprises one or more intermediate radiator segments positioned between said first and second radiator segments.

23. The helical antenna of claim 15, wherein a portion of said first radiator segment is adjacent a portion of said second radiator segment.

24. The helical antenna of claim 15, further comprising a second radiator portion having a plurality of helically wound segmented radiators extending from a first end of the radiator portion to a second end of the radiator portion, each of said segmented radiators comprising first and second segments, wherein said first segment is substantially isolated from said second segment as they are electromagnetically coupled to each other.

25. The helical antenna of claim 24, wherein said first radiator portion and said second radiator portion are stacked coaxially.

26. The helical antenna of claim 15, wherein said radiator is spirally wound in a cylindrical or conical shape.