Patent Application
20220216612
Omnidirectional antennas with the best performance in terms of gain and bandwidth are increasingly in demand due to the rapid development of wireless communication and sensing systems. The ideal omnidirectional antenna should be broadband and high-gain with minimum gain variation, high efficiency, low weight, low cost, easy to fabricate, and portable for many applications. In addition, most communication systems may require the vertical-polarization antennas that concentrate the transmitted power at low heights above the ground or water in all horizontal directions, which require a wideband omnidirectional antenna with a fixed beam over the operating frequency range. In other words, the stability of the radiation-pattern peak can be vital. Designing an omnidirectional antenna that satisfies all of the preceding characteristics, however, is a significant challenge.
Embodiments of the present disclosure are related to a wideband high-gain coaxial collinear antenna with a stable radiation pattern.
According one embodiment, among others, a coaxial collinear antenna is provided comprising a first segment and a second segment of a coaxial cable for a coaxial collinear antenna. The first segment comprises a first inner conductor and a first outer conductor. The second segment comprises a second inner conductor and a second outer conductor. The first inner conductor of the first segment is electrically coupled to the second outer conductor of the second segment, and the first outer conductor of the first segment is electrically coupled to the second inner conductor of the second segment. The coaxial collinear antenna can comprise a first wire mesh that is attached to the first outer conductor of the first segment and a second wire mesh that is attached to the second outer conductor of the second segment. Also, the coaxial collinear antenna can include an end-fed port situated at a distal end of the coaxial collinear antenna.
In various embodiments, the coaxial collinear antenna can at least one of the first wire mesh and the second wire mesh comprises a plurality of rods. Also, the various embodiments can further comprise an electrically-conductive cable inserted through the end-fed port and through one segment of the coaxial cable. In some embodiments, the electrically conductive cable can have a smaller diameter than the coaxial cable. Additionally, the electrically conductive cable can be coupled to an impedance matching circuit.
In various embodiments, the coaxial collinear antenna can include an impedance matching circuit that connects to the electrically conductive cable. The impedance matching circuit can be coupled to a respective inner conductor and a respective outer conductor of one segment of the coaxial cable.
In various embodiments, the first wire mesh comprises a first rod that is attached to the first outer conductor of the first segment and a second rod that is attached to the first outer conductor of the first segment. Additionally, the first rod and the second rod are diametrically opposite about the first outer conductor of the first segment. Further, a length of the first rod can be determined based at least in part on half of an operating wavelength of the coaxial collinear antenna.
In various embodiments, the first wire mesh can include a first rod that is attached to the first outer conductor of the first segment and a second rod that is attached to the first outer conductor of the first segment. The first wire mesh can also include a third rod that are attached to the first outer conductor of the first segment and a fourth rod that is attached to the first outer conductor of the first segment.
In various embodiments, the end-fed port is located in a respective segment of the coaxial cable at a distance of a quarter-wavelength from an interconnection with a preceding segment. Also, the coaxial collinear antenna can include an electrically-conductive cable that is inserted through an interior of one segment and routed outside of the preceding segment of the coaxial cable. The preceding segment can have a length of a half-wavelength.
In various embodiments, the distal end represents a first distal end for the end-fed port, and the coaxial collinear antenna further comprises a last segment of the coaxial cable short-circuited at a second distal end of the coaxial collinear antenna.
In various embodiments, the first wire mesh for the first segment comprises a first pair of rods and the second wire mesh of the second segment comprises a second pair of rods, wherein the first pair rods and the second pair of rods are aligned along a longitudinal axis of the coaxial collinear antenna.
According to another embodiment, among others, a coaxial collinear antenna is provided comprises a first segment, a second segment, and other segments of a coaxial collinear antenna. The first segment can comprise a first inner conductor and a first outer conductor. The second segment can comprise a second inner conductor and a second outer conductor. The first inner conductor of the first segment can be electrically coupled to the second outer conductor of the second segment. The first outer conductor of the first segment can be electrically coupled to the second inner conductor of the second segment.
The coaxial collinear antenna can also include a first wire mesh, a second wire mesh, an end-fed port, and an electrically conductive cable. The first wire mesh can be attached to the first outer conductor of the first segment. The first wire mesh can comprise a first plurality of rods. The second wire mesh can be attached to the second outer conductor of the second segment. The second wire mesh can comprise a second plurality of rods. The end-fed port can be situated in the particular segment of the coaxial cable. The particular segment can be located at a distal end of the coaxial cable. Additionally, the electrically conductive cable can be inserted through the end-fed port and into the interior of the third segment.
In various embodiments, the electrically conductive cable is coupled to an impedance matching circuit. At least one of the first plurality of rods or the second plurality of rods can include a bend. Also, the first plurality of rods can be coupled to the first outer conductor of the first segment of the coaxial cable. Additionally, the electrically conductive cable can have a smaller diameter than the coaxial cable.
Other systems, methods, features, and advantages of the present disclosure will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present disclosure, and be protected by the accompanying claims.
In addition, all optional and preferred features and modifications of the described embodiments are usable in all aspects of the disclosure taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another.
Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, with emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
The present disclosure relates to a wideband high-gain coaxial collinear antenna with a stable radiation pattern. Based in part on the fat dipole idea, a configuration of the classical center-fed coaxial collinear antenna can be modified in order to construct various embodiments of a wideband end-fed coaxial collinear antenna, as described herein. For example, the embodiments of the present disclosure can include a wire mesh Coaxial Collinear (CoCo) antenna that increases the bandwidth of the antenna while maintaining a stable gain and radiation pattern over a wide frequency band. In one non-limiting example, a −10 dB impedance bandwidth and the gain bandwidth (1 dB variation of the maximum gain versus frequency) of the wideband CoCo antenna of the embodiments at a center frequency of 470 and 900 MHz was achieved, which is three times more than the corresponding bandwidth of the classical center-fed CoCo, while it maintains 9 dB gain. A prototype antenna at 900 MHz was implemented, and the simulation results were confirmed.
A collinear dipole array with an omnidirectional radiation pattern has been a priority candidate for mobile communications. Based on the concept of the Franklin antenna, the CoCo antenna was introduced in 1956. The CoCo antenna has been developed theoretically and experimentally over the years, as an appropriate choice for a high-gain omnidirectional antenna, particularly in VHF/UHF bands due to its simple mechanism of feeding and its ease of manufacturing. The CoCo antenna has been used as an isolated antenna element and in large arrays, for atmospheric and ionospheric radar as well as for commercial communication purposes. CoCo antennas have the gain of more than 10 dBi. However, as a series-fed antenna array, the basic CoCo antenna suffers from narrow bandwidth and frequency dependent radiation patterns (e.g., beam scan pattern).
In the 1980's, early microstrip versions of the collinear antenna arrays were developed. Later, the omnidirectional planar microstrip antenna was developed in 2004. Over the past decade, the different types of planar collinear antennas have been proposed to increase the gain and bandwidth. However, the typical gain for these implementations has been around 5-6 dBi, with approximately 20% impedance bandwidth. Moreover, they suffer from beam scanning over bandwidth due to serial feeding. In one implementation, a three-element array was developed in which each element comprised two driven planar dipoles and two parasitic dipoles. The antenna could realize omnidirectional radiation patterns over a wide frequency band (56.4% impedance bandwidth) with a gain of around 7 dBi and a gain variation less than 1.5 dB. But, the design was parallel-fed instead of series-fed, had a large longitudinal size, and had a complicated structure.
Besides collinear type antennas, wideband single-element antennas, such as bow-tie or biconical antennas, have relatively low gain. There are few examples of conical arrays capable of broader bandwidth with higher gain. However, previous proposed feed networks have caused distortion of the omnidirectional pattern, suffer from beam scanning, need a complicated fabrication process, or are not applicable to an array with more elements. Also, planar slot arrays can reach a gain of 10 dBi, but the bandwidth is only 4.6%.
In another implementation, a self-sustaining maritime mesh network was designed to provide ocean wireless connectivity. In the first prototype, a sleeve dipole antenna was mounted on a buoy as a proper choice due to its light-weight and simple structure considering the environmental factors. In the next phase, a wideband omnidirectional antenna with a narrower beam (9 dBi gain) can be used to improve the communication range and capacity in the rich multipath channel on the ocean.
A desired antenna may be light-weight, low-cost, and have a simple end-fed structure. These features can able the antenna to be capable of mounting on a buoy, while it has a 9 dBi stable omnidirectional beam over the wide bandwidth. Typically, the quality of the impedance matching can be used to determine the bandwidth of narrowband antennas. However, the stability of radiation patterns can be factored in the bandwidth improvement described. In some embodiments, the wideband antenna design can take into account both the radiation pattern and the impedance match. The planar collinear arrays are not a suitable design for some antenna designs because of low gain or beam scanning due to serial feeding. Although the CoCo antenna provides a narrow omnidirectional beam and its gain increases by increasing the number of elements, which is suitable for 9 dBi gain narrow beam, its impedance bandwidth decreases by increasing its gain, and it has a beamscan radiation patterns that limit its functionality to narrowband applications.
The embodiments of the present disclosure relate to an improved coaxial collinear antenna based on the idea of a fat dipole. The embodiments of the present disclosure significantly increase the bandwidth. At first, a series of center-fed CoCo antennas were designed to prove the concept of increasing bandwidth, while maintaining a stable radiation pattern. Then, an end-feed network was added to the embodiments of the antenna to create a wideband fixed beam end-fed CoCo antenna. In the context of the present disclosure, wideband can refer to a bandwidth significantly exceeding the coherence bandwidth of a classical coaxial collinear antenna.
The embodiments of the antenna can benefit from the favorable features of the classical center-fed CoCo antenna, such as the high-gain omnidirectional beam, low-weight, and ease in fabrication. Additionally, while attempting to improve the bandwidth as much as possible by using the fat dipole concept, the embodiments can be designed using a feeding network to omit beam scanning with minimal complexity, to achieve a reasonable trade-off between all the required characteristics of the antenna.
Turning to the drawings,
There are other versions of CoCo antennas that use a junction box, a coupled connection, or a slotted connection between sections, but all keep the phase of the current distribution constant on radiator sections. Electrically interchanging of the inner and outer conductors at each segment produce identical and opposite phase currents in the inner line conductor and on the inside surface of the outer line conductor, as radiating currents. The source generator can excite two antennas, first the outer line conductor and second the inner line conductor, which are fed 180 degrees out of phase. In this example, the source generator can excite the two antennas through the end-fed point. Therefore, there can be a non-zero total current along the coaxial sections as a radiating current.
As illustrated in
Traditionally, a dipole thickness has been increased as a fat dipole to increase the frequency bandwidth of the dipole. In addition, a wire mesh surrounding a dipole has demonstrated similar properties as a fat dipole. To mimic a fat dipole, a wire mesh cage or structure can be added to the outer cylinder of the coaxial cable, while the length (2 L) of each rod in the wire mesh structure can be around the half-wavelength in order to keep the current similar to the classical CoCo antenna.
The wire mesh structures 106 can comprise a set of rods 109 that are attached to a particular segment of the coaxial cable. The wire mesh structure 106 can be constructed from metal, copper, aluminum, brass, and other suitable materials. For example, as illustrated in
In the illustrated embodiment, the rods 110 have a bend 112 at approximately a middle point of each of the rods 110. In other examples, the bend 112 can be located at a different point along the rod 110.
As shown in
As shown in
Although
In other non-limiting example, a pair of sub-rods may replace the rod 110a. For example, a first sub-rod and a second sub-rod may replace rod 110a. The first sub-rod can be connected to the second sub-rod at a first end and the first sub-rod can be connected to an end of the first segment 103. Thus, instead of having a bend point 112, the pair of sub-rods can have a connection point. In this example, the length of each sub-rod can be length L.
To evaluate the effectiveness of the embodiments of the antenna structure to increase the antenna bandwidth, the characteristics of one embodiment of a wideband CoCo antenna 100 was compared with a classical CoCo antenna (
All classical and wideband models were simulated using ANSYS HFSS®. In the first design scheme, the classical center-fed CoCo antenna,
In the second scheme, a twelve-section classical center-fed antenna with RG8A/U coaxial cable dimensions was designed. Four bended rods were connected to each of the outer conductors for the center-fed CoCo antenna, while D increases to 140 mm and other dimensions are kept as the classical center-fed CoCo made from RG8A/U. By using a RG8A/U coaxial cable, it helped to improve the bandwidth compared with air-filled coaxial cable.
Moving on to
In the lower part of the wideband CoCo antenna 100, the semi-rigid cable replaces the inner conductor of the main coaxial cable. Particularly, the semi-rigid cable is inserted through an end-fed port 125 situated at a distal end of the coaxial cable. Reference number 130 illustrates an enlarged view of the end-fed port 125 at the distal end of the wideband end-fed CoCo antenna 100. The end-fed port 125 can be located at a distance of a quarter-wavelength from an interconnection with a preceding segment, as illustrated in
The semi-rigid cable can help bring the excitation point to the center of the antenna to omit beamscan radiation pattern while minimizing the effect on the omnidirectional pattern and antenna performance compared to the center-fed antenna. Indeed, by viewing the entire semi-rigid as a single conductor, the semi-rigid cable has similar functionality to the inner conductor of the main coaxial cable, and the core of the semi-rigid cable brings the excitation point to the desired position.
Next, reference number 140 illustrates an enlarged view of a middle portion of the wideband end-fed CoCo antenna 100. In some embodiments, the semi-rigid cable can be electrically coupled to an impedance matching circuit 145, which in turn is coupled to an inner conductor and an outer conductor of the following segment 103e of the coaxial cable. In some cases, the impedance matching circuit 145 can comprise a quarter-wavelength coaxial transformer and other suitable transformers.
Further, reference number 155 illustrates an enlarged view of a second distal end of the wideband end-fed CoCo antenna 100, which is opposite to a first distal end that includes the end-fed port 125. Reference number 155 illustrates an enlarged view of a short-circuit 158 at about a quarter wavelength from the end of the segment 103f. In this embodiment, the short-circuit 158 comprises connecting the inner conductor of the segment 103f to the outer conductor of the segment 103f.
Next, a discussion of the executed simulations and results is provided. In order to design an exemplary embodiment of the wideband end-fed CoCo antenna 100 with desired characteristics, the simulation results are presented step by step, and compared to the classical CoCo antenna in order to assess the effectiveness of each step. In these non-limiting examples, all antennas have a gain of about 9 dBi at the center frequency around 470 MHz with a total length of 2.5 m.
First, an eight-section center-fed CoCo antenna was simulated. In the first scheme, an eight-section classical and a wideband center-fed CoCo antennas made of air-filled coaxial cables was simulated. In this simulation, the wideband center-fed was employed as one exemplary embodiment among others. The simulation results show that the input impedance of the eight-section classical center-fed CoCo at its resonant frequency is about 121.8Ω, while the simulated input impedance of the wideband center-fed antenna is approximately 42.7Ω. The input impedance can be reduced by adding a wire mesh structure to the conventional configuration. In order to effectively compare the bandwidth, a 120Ω port has been used in the simulation for the classical center-fed CoCo instead of regular 50Ω port to avoid the circuit matching and this enables a more straightforward comparison.
Note that the impedance bandwidth can be calculated using the appropriate port and normalization for center-fed design procedures, to ideally evaluate the capability of the proposed configuration. While considering the effects of all involved parameters including matching circuits, a practical comparison is made between these ideal center-fed assessments and the embodiments of the end-fed design.
Due to the center-fed design, both antennas have a stable omnidirectional broadside radiation pattern. The computed realized gain of both classical and proposed wideband center-fed CoCo antennas is about 9.1 dBi. However, as shown in
Next, a twelve section center-fed CoCo antenna was simulated. The same technique was used to simulate the twelve-section classical and wideband center-fed CoCo antennas. Polyethylene was used as a dielectric to reduce the guided wavelength and the corresponding dimensions. So, the value of D just increases to 140 mm to keep the length of rods around half-wavelength. The number of segments in the polyethylene-filled coaxial cable CoCo antenna is more than an air-filled one to achieve the same gain, which can be due to the smaller guided wavelength. The computed return loss for classical and proposed center-fed CoCo are shown in
The realized gain of the classical CoCo and the wideband antenna is about 9.2 dBi and 9.1 dBi, respectively. The gain bandwidth of the 12-section wideband antenna is about 59.8 MHz, which is also approximately three times broader than the classical center-fed CoCo. The 3 dB variation of the maximum gain versus frequency of the proposed antenna at broadside is about 87.5 MHz (18.6%). Note that the outside of the gain bandwidth, the gain is still around 9 dB, but it is not completely omnidirectional, and there is about 2 dB variation over the broadside direction (θ=90°, ϕ is variable). Also, the similar radiation pattern at the center frequency (470 MHz) of both antennas and the comparison of radiation patterns at different frequencies indicate that the added wire mesh structure produces a wider antenna without any distortion in the radiation pattern. The calculated HPBW is 13.0° and 13.4° at 470 MHz for the 12-section classical and wideband center-fed CoCo antennas, respectively.
When comparing the eight-section wideband center-fed CoCo antenna with air-filled cable and the twelve-section wideband center-fed CoCo antenna using RG8A/U cable, both antennas have the same length (2.5 m), and same realized gain (around 9.1 dBi), and their bandwidth is approximately three times broader than the corresponding classical Coco antenna. Although for the twelve-section wideband center-fed CoCo, both computed bandwidths (impedance and gain bandwidth) are more than 10% (18.0% and 12.7%, respectively). The gain bandwidth is just more than 10% for the 8-section proposed center-fed CoCo. Due to the effect of guided wavelength, more segments are needed to reach 9 dBi gain by using the regular coaxial. Note that the gain of a CoCo antenna increases by increasing the number of sections (e.g. segments). Its impedance bandwidth decreases by increasing its gain while using coaxial cable with polyethylene dielectric helps to keep the gain and bandwidth of the twelve-section CoCo antenna similar to eight-section CoCo antenna. Since adding the wire mesh structure reduces the input impedance, using air-filled cable only helps to choose the input impedance freely for better matching. In other cases, using commercial coaxial cables is recommended.
Additionally, the simulation shows that using the dimensions of RG-218 coaxial cables instead of RG8A/U coaxial cable does not change the performance of the antenna. Further, the wire mesh structure configuration with eight bounded rods attached to each dipole is simulated to evaluate the effect of the number of rods. As shown in
Next, a twelve section end-fed CoCo antenna was simulated. Although the requirement for the wideband antenna with a narrower beam (9 dBi gain with omnidirectional pattern) is satisfied with the proposed center-fed CoCo antenna, the end-fed CoCo antenna is desired to be mounted on a buoy. Thus, this end-fed CoCo antenna should omit beamscan radiation pattern and have a similar characteristic to the center-fed one. As mentioned in previously, the semi-rigid cable can used to excite (i.e. providing current) the antenna in its center while acting in the lower part of the antenna similar to the inner conductor removed from the main coaxial cable. The simulation for the twelve section center-fed CoCo antenna showed that the simulated input impedance of the wideband antenna is about 17Ω in the center of the antenna. Thus, a matching circuit (e.g. an impedance matching circuit) can be used to connect the 17Ω impedance of the center of the antenna to the 50Ω impedance of the semi-rigid cable. In one embodiment, the impedance matching circuit is a quarter-wavelength coaxial transformer (e.g. an impedance transformer). So, the quarter-wavelength coaxial transformer is added between the center and semi-rigid cable, as shown in
As shown in
Typically, the quality of the impedance matching is used to determine the bandwidth of antennas. However, the stability of radiation patterns can be included in the bandwidth improvement approach, and gain bandwidth can play a role in determining the performance of the antenna. The impedance bandwidth in the wideband center-fed antenna is more than the gain bandwidth, but the realistic functionality of the antenna is the gain bandwidth. After modifying the antenna to include end-fed implementation, these bandwidth values come close to each other, which is similar to the gain bandwidth of the center-fed design. As such, this means the performance of the wideband antenna does not change significantly.
Next, the measurement results are discussed. The embodiments of the wideband end-fed coaxial collinear antenna have been prototyped and measured for 900 MHz based on measurement considerations.
The measured pattern shows that Half Power Beamwidth (HPBW) of the antenna is varied between 14° and 16° over the operating frequency range. Moreover,
Overall, the embodiments include a wideband CoCo antenna 100 that increases the bandwidth of the antenna. The simulation results show that the impedance bandwidth has been improved by 300% while maintaining a stable gain and radiation pattern over a wide frequency band. The prototyped antenna at 900 MHz demonstrates 14.8% impedance bandwidth and gain bandwidth
Disjunctive language such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to present that an item, term, etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y, and/or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to each be present.
It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.
This application claims the benefit of, and priority to, co-pending, PCT Application No. PCT/US2020/041220, entitled “Wideband End-Fed Coaxial Collinear Antenna,” filed on Jul. 8, 2020, which claims the benefit of, and priority to U.S. Provisional Patent Application No. 62/871,560, entitled “Wideband End-Fed Coaxial Collinear Antenna,” filed on Jul. 8, 2019, which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2020/041220 | 7/8/2020 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62871560 | Jul 2019 | US |
