An ultra-wideband, low profile antenna is provided. The antenna includes a ground plane substrate, a feed conductor, a top hat conductor, a shorting arm, and a ring slot. The feed conductor includes a first end and a second end. The first end is configured for electrical coupling to a feed network through a feed element extending from the ground plane substrate. The top hat conductor includes a generally planar sheet mounted to the second end of the feed conductor in a first plane approximately parallel to a second plane defined by the ground plane substrate. The shorting arm includes a third end and a fourth end. The third end is mounted to the top hat conductor, and the fourth end is mounted to the ground plane substrate. The ring slot is formed in the ground plane substrate around the feed element.

BACKGROUND

A classical monopole antenna is a type of radio antenna that consists of a straight rod-shaped conductor that is typically mounted perpendicularly over some type of conductive surface, called a ground plane. In some cases, the ground plane is the earth's surface, while in other cases, the ground plane is formed of a conductive material. The classical monopole antenna has an omnidirectional radiation pattern meaning that it radiates equal power in all azimuthal directions perpendicular to the antenna resulting in a donut shaped radiation pattern. The height of monopole antennas is inversely related to the transmission frequency because operation at low frequencies results in a very large electromagnetic wavelength. As a result, a traditional monopole antenna operating at low frequencies is also physically very large. The physically large size makes the monopole antenna challenging to use in low-profile applications at low frequencies.

SUMMARY

In an illustrative embodiment, an ultra-wideband, low profile antenna is provided. The antenna includes, but is not limited to, a ground plane substrate, a feed conductor, a top hat conductor, a shorting arm, and a ring slot. The feed conductor includes, but is not limited to, a first end and a second end. The first end is configured for electrical coupling to a feed network through a feed element extending from the ground plane substrate. The top hat conductor includes, but is not limited to, a generally planar sheet mounted to the second end of the feed conductor in a first plane approximately parallel to a second plane defined by the ground plane substrate. The shorting arm includes, but is not limited to, a third end and a fourth end. The third end is mounted to the top hat conductor, and the fourth end is mounted to the ground plane substrate. The ring slot is formed in the ground plane substrate around the feed element.

In another illustrative embodiment, a transmitter is provided. The transmitter includes, but is not limited to, a matching network circuit and an antenna. The matching network circuit is coupled to receive a signal through a port and to form a matched signal output through a feed element. The antenna includes, but is not limited to, a ground plane substrate, a feed conductor, a top hat conductor, a shorting arm, and a ring slot. The feed conductor includes, but is not limited to, a first end and a second end. The first end is configured for electrical coupling to the matching network circuit through the feed element to receive the matched signal. The top hat conductor includes, but is not limited to, a generally planar sheet mounted to the second end of the feed conductor in a first plane approximately parallel to a second plane defined by the ground plane substrate. The shorting arm includes, but is not limited to, a third end and a fourth end. The third end is mounted to the top hat conductor, and the fourth end is mounted to the ground plane substrate. The ring slot is formed in the ground plane substrate around the feed element. The matching network circuit is configured to impedance match the antenna.

DETAILED DESCRIPTION

With reference toFIG. 1a, a perspective view of an antenna100is shown in accordance with an illustrative embodiment. Antenna100may include a ground plane substrate102, a top hat conductor104, a feed conductor106, and a feed element108. Ground plane substrate102is electrically grounded and may be formed of any material suitable for forming an electrical ground for antenna100. For example, ground plane substrate102may be formed of a metal sheet alone or with a dielectric or magnetic material or a magneto-dielectric material on a top surface of the metal sheet. Ground plane substrate102is generally planar and defines a first plane. To describe the orientation of the components of antenna100, a coordinate reference system x-y-z is included inFIG. 1a. Based on the defined coordinate reference system x-y-z, the first plane is the x-y plane.

Though the assumption is made that ground plane substrate102is an infinite ground plane, in general, if ground plane substrate102is just slightly larger than top hat conductor104, antenna100is still effective as a radiator. For example, ground plane substrate102larger by a factor of 1.5 times than top hat conductor104is still effective as a radiator. In illustrative embodiment, ground plane substrate102is a metal sheet.

With reference toFIG. 1b, a top view of antenna100is shown in accordance with an illustrative embodiment. In an illustrative embodiment, top hat conductor104is generally planar and oriented in a second plane that is approximately parallel to the first plane defined by ground plane substrate102. Thus, top hat conductor104is oriented parallel to the x-y plane at a height118above ground plane substrate102. Top hat conductor104may be formed of any conducting material suitable for forming a radiator of antenna100.

In an illustrative embodiment, height118is approximately 100 millimeters (mm). In the illustrative embodiment, top hat conductor104has a rectangular shape when projected into the x-y plane. In alternative embodiments, top hat conductor104may form other polygonal, circular, or elliptical shapes when projected into the x-y plane. In the illustrative embodiment, top hat conductor104has a length112in the y-direction and a width114in the x-direction. Length112and width114define a diagonal116. In an illustrative embodiment, length112and width114define are approximately 200 mm though other dimensions may be used depending on the application environment for antenna100.

With reference toFIG. 1c, a side view of feed conductor106is shown in accordance with an illustrative embodiment. Feed conductor106is electrically connected to feed element108. Feed element108is positioned approximately at a center of ground plane substrate102as shown with reference toFIG. 1b. In an illustrative embodiment, feed element108is a short length of coaxial cable including an inner connector109electrically coupled to a point on feed conductor106and an outer conductor110electrically coupled to ground plane substrate102.

In the illustrative embodiment ofFIG. 1c, feed conductor106is generally planar and oriented in a third plane that is approximately perpendicular to the first plane defined by ground plane substrate102. Feed conductor106may be formed of any conducting material suitable for forming a radiator of antenna100.

Feed conductor106includes a top edge120, a first side edge122, a second side edge124, a third side edge126, a fourth side edge128, and a bottom edge130. Top edge120of feed conductor106is electrically coupled to top hat conductor104along diagonal116of top hat conductor104as shown with reference toFIGS. 1aand 1b. In an illustrative embodiment, top edge120of feed conductor106is shorter than diagonal116of top hat conductor104though the difference is not readily visible inFIG. 1b. As a result, feed conductor106is positioned between ground plane substrate102and top hat conductor104.

Top edge120and bottom edge130are generally parallel. First side edge122extends generally perpendicularly from a first end of top edge120. Second side edge124extends between first side edge122and a first end of bottom edge130. Third side edge126extends generally perpendicularly from a second end of top edge120. Fourth side edge128extends between third side edge126and a second end of bottom edge130. Thus, first side edge122and second side edge124form a first side of feed conductor106, and third side edge126and fourth side edge128form a second side of feed conductor106. In the illustrative embodiment, feed conductor106is primarily cone shaped. In alternative embodiment, feed conductor106may not include first side edge122or third side edge126and/or bottom edge130resulting in a triangular shape. In an illustrative embodiment, feed conductor106forms essentially a monopole antenna and can be used to tune and adjust the resonances that result from the monopole structure. These resonances can be optimized such that they merge with the other resonances to form an ultra-wideband antenna. Thus, the shape of feed conductor106can be optimized to increase the bandwidth of antenna100.

With reference toFIG. 2a, a graph is provided that shows a voltage standing wave ratio (VSWR) at feed element108determined by simulating the performance of the antenna ofFIG. 1awith different dimensions for top edge120of feed conductor106. A first VSWR curve200shows a VSWR as a function of transmit frequency that results for top edge120having a value equal to 55 mm. A second VSWR curve202shows a VSWR as a function of transmit frequency that results top edge120having a value equal to 140 mm. A third VSWR curve204shows a VSWR as a function of transmit frequency that results for top edge120having a value equal to 255 mm.

With reference toFIG. 2b, a graph is provided that shows an input resistance (real part of the impedance) determined by simulating the performance of the antenna ofFIG. 1awith different dimensions for top edge120of feed conductor106. A first resistance curve210shows a resistance as a function of transmit frequency that results for top edge120having a value equal to 55 mm. A second resistance curve212shows a resistance as a function of transmit frequency that results for top edge120having a value equal to 140 mm. A third resistance curve214shows a resistance as a function of transmit frequency that results for top edge120having a value equal to 255 mm.

With reference toFIG. 2c, a graph is provided that shows an input reactance (imaginary part of the impedance) determined by simulating the performance of the antenna ofFIG. 1awith different dimensions for top edge120of feed conductor106. A first reactance curve220shows a reactance as a function of transmit frequency that results for top edge120having a value equal to 55 mm. A second reactance curve222shows a reactance as a function of transmit frequency that results for top edge120having a value equal to 140 mm. A third reactance curve224shows a reactance as a function of transmit frequency that results for top edge120having a value equal to 255 mm.

Antenna100is a potentially broadband antenna that is primarily a capacitive antenna in which the parallel capacitance between top hat conductor104and ground plane substrate102is the dominant factor. The magnitude of the parallel capacitance is directly related to the area of top hat conductor104. To achieve a low frequency of operation, the dimensions of top hat conductor104are maximized in view of the dimensional constraints that result based on the application environment for antenna100. The performance of antenna100is examined using full-wave electromagnetic wave (EM) simulations, and the side dimensions of feed conductor106are optimized to achieve the lowest VSWR possible over as wide a frequency band as possible.

With reference toFIG. 3a, a perspective view of a second antenna300is shown in accordance with an illustrative embodiment. Second antenna300may include ground plane substrate102, top hat conductor104, feed conductor106, feed element108, a first shorting arm302, and a second shorting arm304. A greater or a fewer number of shorting arms may be included in alternative embodiments. In the illustrative embodiment, first shorting arm302and second shorting arm304are generally planar sheets and rectangular in shape when projected into the x-y, y-z, or x-z planes though other shapes may be used. For example, first shorting arm302and second shorting arm304may form other polygonal, circular, or elliptical shapes when projected into the x-y, y-z, or x-z planes. First shorting arm302and second shorting arm304further need not be formed of generally planar sheets.

First shorting arm302is electrically coupled to top hat conductor104and to ground plane substrate102as shown with reference toFIG. 3b. Second shorting arm304is also electrically coupled to top hat conductor104and to ground plane substrate102as shown with reference toFIG. 3b. First shorting arm302and second shorting arm304may be formed of any conducting material suitable for forming a radiator of antenna100. The material used to form first shorting arm302and second shorting arm304may be the same or different from each other. The material used to form first shorting arm302and second shorting arm304may be the same or different from that used to form top hat conductor104and/or feed conductor106. The material used to form top hat conductor104and feed conductor106may be the same or different from each other. In an illustrative embodiment, first shorting arm302and second shorting arm304may carry relatively strong current densities. To avoid ohmic losses that could adversely impact the performance of antenna100, good conductors may be used to form first shorting arm302and second shorting arm304.

First shorting arm302includes a top edge306, a first side edge308, a second side edge310, and a bottom edge312. First shorting arm302is electrically coupled to top hat conductor104along top edge306. Top edge306is positioned in a first corner of top hat conductor104. First shorting arm302is electrically coupled to ground plane substrate102along bottom edge312. Top edge306and bottom edge312of first shorting arm302are generally parallel.

Second shorting arm304includes a top edge316, a first side edge318, a second side edge320, and a bottom edge322. Second shorting arm304is electrically coupled to top hat conductor104along top edge316. Top edge316of second shorting arm304is positioned in a second corner of top hat conductor104. Second shorting arm304is electrically coupled to ground plane substrate102along bottom edge322of second shorting arm304. Top edge316and bottom edge322of second shorting arm304are generally parallel. Feed conductor106extends between the remaining corners of top hat conductor104. Thus, first shorting arm302and second shorting arm304are positioned in opposite corners of top hat conductor104on either side of feed conductor106.

One drawback of adding first shorting arm302and second shorting arm304to antenna100to form second antenna300is that the shorting arms are solely responsible for the radiation characteristics at low frequencies, while at higher frequencies they act as an array antenna and can produce undesirable nulls in the radiation patterns. To ensure the antenna maintains consistent omnidirectional radiation patterns across its entire frequency band, the shorting arms are positioned so that the shorting arms are rotationally symmetric. Thus, first shorting arm302and second shorting arm304extend from top hat conductor104and from ground plane substrate102at an angle324and are positioned to be rotationally symmetric. In an illustrative embodiment, angle324is between 10 and 90 degrees. In an alternative embodiment, angle324may be approximately zero if first shorting arm302and second shorting arm304are curved. Considering the currents on shorting arm302and second shorting arm304, this method distributes the currents more symmetrically around antenna100and improves the omindirectionality at higher frequencies.

Top edge306and bottom edge312of first shorting arm302and top edge316and bottom edge322of second shorting arm304have a width326. First side edge308and second side edge310of first shorting arm302and first side edge318and second side edge320of second shorting arm304have a length328. As a result, first shorting arm302and second shorting arm304have a projected length330when projected into the x-y plane as shown with reference toFIGS. 3band 3c. Of course, first shorting arm302and second shorting arm304may be oriented in other directions. For example, bottom edge312of first shorting arm302and bottom edge322of second shorting arm304may be rotated from zero to 90 degrees in the x-y plane. In an illustrative embodiment, width326is approximately 30 mm and length328is approximately 122 mm though other dimensions may be used depending on the application environment for antenna100.

With reference toFIG. 4a, a graph is provided that shows a VSWR at feed element108determined by simulating the performance of the antenna ofFIG. 3a. A fourth VSWR curve400shows a VSWR as a function of transmit frequency that results by including first shorting arm302and second shorting arm304with the illustrative dimensions and with top edge120having a value equal to 255 mm. Third VSWR curve204is included in the graph for comparison.

With reference toFIG. 4b, a graph is provided that shows an input resistance determined by simulating the performance of the antenna ofFIG. 3a. A fourth resistance curve410shows a resistance as a function of transmit frequency that results by including first shorting arm302and second shorting arm304with the illustrative dimensions and with top edge120having a value equal to 255 mm. Third resistance curve214is included in the graph for comparison.

With reference toFIG. 4c, a graph is provided that shows an input reactance determined by simulating the performance of the antenna ofFIG. 3a. A fourth reactance curve420shows a reactance as a function of transmit frequency that results by including first shorting arm302and second shorting arm304with the illustrative dimensions and with top edge120having a value equal to 255 mm. Third reactance curve224is included in the graph for comparison.

The addition of one or more shorting arms results in addition of a parallel inductance. The value of the parallel inductance increases by increasing length328or decreasing width326of first shorting arm302and second shorting arm304. The parallel inductance due to first shorting arm302and second shorting arm304and the parallel capacitance due to top hat conductor104and ground plane substrate102provide a potential parallel resonance below the minimum frequency of operation of antenna100. The placement, the size, and the shape of the shorting arms have a significant effect on the antenna impedance (resistance and reactance). The shorting arms are designed and optimized such that the introduced additional resonance is close to the minimum desired operating frequency of antenna100, so they can merge together to achieve an ultra-wideband (UWB) structure.

With reference toFIG. 5a, a perspective view of a third antenna500is shown in accordance with an illustrative embodiment. Third antenna500may include ground plane substrate102, top hat conductor104, feed conductor106, feed element108, first shorting arm302, second shorting arm304, and a ring slot502. In the illustrative embodiment, ring slot502is a rectangular slot formed in ground plane substrate102. For example, ring slot502may be etched or milled into ground plane substrate102. Ring slot502is symmetrically positioned to surround feed element108. In alternative embodiments, ring slot502may be positioned asymmetrically relative to feed element108. Ring slot502may form other polygonal, circular, or elliptical shapes in the x-y plane.

For simplicity in fabrication, a dielectric material with a top surface formed of a metal sheet is used as ground plane substrate102, and ring slot502is formed by etching of ground plane substrate102. The dielectric constant of ground plane substrate102can change the value of capacitance formed by ring slot502. To minimize the effect of the material, a low dielectric material can be used as ground plane substrate102.

In an illustrative embodiment, ring slot502has a slot width504, a width506in the x-direction, and a length508in the y-direction. In an illustrative embodiment, slot width504is approximately 7 mm, width506is approximately 203 mm, and length508is approximately 203 mm though other dimensions may be used depending on the application of antenna100, and of course, the other dimensions of the components of third antenna500. Ring slot502does not radiate in the band of interest; instead, ring slot502acts as a series capacitance. The value of the series capacitance increases by decreasing width506of ring slot502or by decreasing slot width504of ring slot502. The values for slot width504and width506may be chosen by examining the effect of these two parameters on VSWR, input impedance, and input reactance of antenna100to reduce the quality factor of the additional resonance and achieve an impedance match across the entire band.

With reference toFIG. 6, the effect of top hat conductor104is modeled as a parallel capacitance600, the effect of first shorting arm302and second shorting arm304is modeled as a parallel inductance602, and the effect of ring slot502is modeled as a series capacitance604. Third antenna500can be designed using the equivalent circuit model illustrated inFIG. 6and full wave EM simulation. The placement, mounting angle, and shape of first shorting arm302and second shorting arm304and the placement and shape of ring slot502have a significant effect on the impedance of third antenna500. These characteristics are designed and optimized using full wave EM simulation such that the impedance is well-matched and centered on the Smith chart used for analysis of impedance matching.

With reference toFIG. 7a, a graph is provided that shows a VSWR at feed element108determined by simulating the performance of the antenna ofFIG. 5a. A fifth VSWR curve700shows a VSWR as a function of transmit frequency that results by including ring slot502with the illustrative dimensions and with top edge120having a value equal to 255 mm. Fourth VSWR curve400is included in the graph for comparison.

With reference toFIG. 7b, a graph is provided that shows an input resistance determined by simulating the performance of the antenna ofFIG. 5a. A fifth resistance curve710shows a resistance as a function of transmit frequency that results by including ring slot502with the illustrative dimensions and with top edge120having a value equal to 255 mm. Fourth resistance curve410is included in the graph for comparison.

With reference toFIG. 7c, a graph is provided that shows an input reactance determined by simulating the performance of the antenna ofFIG. 5a. A fifth reactance curve720shows a reactance as a function of transmit frequency that results by including ring slot502with the illustrative dimensions and with top edge120having a value equal to 255 mm. Fourth reactance curve420is included in the graph for comparison.

As shown inFIGS. 7a-7c, series capacitance604helps to decrease the quality factor of the additional resonance, which results in achieving an impedance match across the entire band. The placement and the width of the slot have a significant effect on the capacitance value. The value of the series capacitance increases by decreasing the radius or width506of ring slot502or by decreasing the radius or slot width504of ring slot502.

To obtain the maximum bandwidth available, the transmission and reflection coefficients of third antenna500should be unity inside and outside of the band of interest, respectively. With reference toFIG. 8, a feed network812is shown in accordance with an illustrative embodiment. Feed network812may include a first inductor802, a first capacitor804, a second inductor806, and a second capacitor808. First inductor802and first capacitor804are mounted in series between a port800and ground plane substrate102. Second inductor806and second capacitor808are mounted in series between first inductor802and ground plane substrate102. Feed element108is electrically coupled between second inductor806and second capacitor808.

Feed network812forms a lumped matching network circuit designed to match the transmission and reflection coefficients of third antenna500. The values of first inductor802, first capacitor804, second inductor806, and second capacitor808are designed and optimized to achieve an impedance match to third antenna500across the entire frequency range. Thus, feed network812is coupled to receive a radio frequency (RF) alternating current (AC) signal and to form an impedance matched signal output on feed element108for radiation from third antenna500.

With reference toFIG. 8, a transmitter and/or receiver or transceiver810includes port800, feed network812, and third antenna500in accordance with an illustrative embodiment. The RF AC signal is provided to port800from a signal processor (not shown). Feed network812is coupled to port800to receive the RF AC signal and to form a matched signal output through feed element108for radiation from third antenna500. Feed network812is coupled to feed element108to receive a second RF AC signal received by third antenna500and to form a matched signal output through port800to the signal processor.

With reference toFIG. 9a, a graph is provided that shows a VSWR at feed element108determined by simulating the performance of third antenna500with the illustrative dimensions (top edge120having a value equal to 255 mm) and using feed network812. In the illustrative embodiment, an inductance value for first inductor802was 5.25 nanoHenry (nH), a capacitance value for first capacitor804was 2.2 picoFarads (pF), an inductance value for second inductor806was 4.4 nH, and a capacitance value for second capacitor808was 1.6 pF. A sixth VSWR curve900shows a resulting VSWR as a function of transmit frequency.

With reference toFIG. 9b, a graph is provided that shows a realized gain of third antenna500determined by simulating the performance of third antenna500with the illustrative dimensions (top edge120having a value equal to 255 mm). A gain curve902shows a resulting realized gain as a function of transmit frequency.

With reference toFIG. 9c, a graph is provided that shows an efficiency of third antenna500determined by simulating the performance of third antenna500with the illustrative dimensions (top edge120having a value equal to 255 mm). A first efficiency curve904shows a radiation efficiency as a function of transmit frequency using feed network812. A second efficiency curve906shows a total efficiency as a function of transmit frequency. As shown, third antenna500achieves a 3.8 dBi realized gain at the lowest frequency of operation and 5 dBi over most of the operating band. Over most of the operating band, the total efficiency remains above 90% though the total efficiency is approximately 65% at lower frequencies.

With reference toFIGS. 10aand 10b, graphs are provided that show directional radiation patterns in the x-y (azimuth) plane in the frequency range of 0.2-1.4 gigahertz (GHz). The results were obtained by simulating the performance of third antenna500. A first curve1000shows the representative response at a frequency of 0.2 GHz; a second curve1002shows the representative response at a frequency of 0.4 GHz; a third curve1004shows the representative response at a frequency of 0.6 GHz; a fourth curve1006shows the representative response at a frequency of 0.8 GHz; a fifth curve1008shows the representative response at a frequency of 1.0 GHz; a sixth curve1010shows the representative response at a frequency of 1.2 GHz; and a seventh curve1012shows the representative response at a frequency of 1.4 GHz.

With reference toFIGS. 11aand 11b, graphs are provided that show directional radiation patterns showing directional radiation patterns in the x-z elevation plane in the frequency range of 0.2-1.4 gigahertz (GHz). A first curve1100shows the representative response at a frequency of 0.2 GHz; a second curve1102shows the representative response at a frequency of 0.4 GHz; a third curve1104shows the representative response at a frequency of 0.6 GHz; a fourth curve1106shows the representative response at a frequency of 0.8 GHz; a fifth curve1108shows the representative response at a frequency of 1.0 GHz; a sixth curve1110shows the representative response at a frequency of 1.2 GHz; and a seventh curve1112shows the representative response at a frequency of 1.4 GHz.

With reference toFIGS. 12aand 12b, graphs are provided that show directional radiation patterns showing directional radiation patterns in the y-z elevation plane in the frequency range of 0.2-1.4 gigahertz (GHz). A first curve1200shows the representative response at a frequency of 0.2 GHz; a second curve1202shows the representative response at a frequency of 0.4 GHz; a third curve1204shows the representative response at a frequency of 0.6 GHz; a fourth curve1206shows the representative response at a frequency of 0.8 GHz; a fifth curve1208shows the representative response at a frequency of 1.0 GHz; a sixth curve1210shows the representative response at a frequency of 1.2 GHz; and a seventh curve1212shows the representative response at a frequency of 1.4 GHz.

The simulated results demonstrate that third antenna500provides monopole-like omnidirectional radiation patterns over the entire frequency band of interest. Additionally, third antenna500using feed network812ofFIG. 8achieves a VSWR lower than 2:1 over a 7.5:1 bandwidth. For third antenna500, the value of the comparison factor is 27.6, which is more than twice that of the Goubau antenna as a standard small wideband antenna. As a result, third antenna500provides a better design in terms of the bandwidth-to-size ratio. At the lowest frequency of operation, third antenna500using feed network812ofFIG. 8has electrical dimensions of 0.065λmin×0.13λmin×0.13λmin, where λminis the free space wavelength at the lowest frequency of operation ˜0.2 GHz.

With reference toFIG. 13, a perspective view of a fourth antenna1300is shown in accordance with an illustrative embodiment. Fourth antenna1300may include ground plane substrate102, top hat conductor104, feed conductor106, feed element108, first shorting arm302, second shorting arm304, and a second ring slot1302. In the illustrative embodiment, second ring slot1302is a circular slot formed in ground plane substrate102. Second ring slot1302is symmetrically positioned to surround feed element108. In an illustrative embodiment, second ring slot1302has slot width504. In an illustrative embodiment, slot width504is approximately 7 mm and a diameter of second ring slot1302is approximately 203 mm though other dimensions may be used depending on the application of antenna100, and of course, the other dimensions of the components of third antenna500.

With reference toFIG. 14, a graph is provided that shows a VSWR at feed element108determined by simulating the performance of fourth antenna1300with the illustrative dimensions. A sixth VSWR curve1400shows a VSWR as a function of transmit frequency that results by including ring slot1302with top edge120having a value equal to 255 mm. Fourth VSWR curve400is included in the graph for comparison.

A prototype of third antenna500was fabricated. The prototype was scaled down by a factor of three for simplicity. Thus, the operating frequencies of the antenna scale up by the same factor of three. Feed network812was not considered. With reference toFIG. 15, a graph is provided that shows a VSWR at feed element108generated by the prototype. A seventh VSWR curve1500shows a VSWR as a function of transmit frequency generated by the prototype. An eighth VSWR curve1502shows a VSWR as a function of transmit frequency determined by simulating the scaled version of the antenna. Eighth VSWR curve1502is included in the graph for comparison. The prototype results compare favorably with the simulated results. In the fabricated prototype, Rogers 5880 material with a dielectric constant of 2.2 was used to form ground plane substrate102.

With reference toFIG. 16a, a perspective view of a fifth antenna1600is shown in accordance with an illustrative embodiment. Fifth antenna1600may include ground plane substrate102, top hat conductor104, a feed conductor106, a second feed conductor1602, feed element108, first shorting arm302, second shorting arm304, a third shorting arm1604, a fourth shorting arm1606, and ring slot502. In the illustrative embodiment, second feed conductor1604has the same shape as feed conductor106. In the illustrative embodiment ofFIG. 16a, first feed conductor106is positioned along a center of top hat conductor104parallel to the y-z plane, and second feed conductor1602is positioned along a center of top hat conductor104parallel to the x-z plane.

With reference to the illustrative embodiment ofFIGS. 16aand 16b, first shorting arm302extends from top hat conductor104adjacent a first end1608of feed conductor106, second shorting arm304extends from top hat conductor104adjacent a second end1610of feed conductor106, third shorting arm1604extends from top hat conductor104adjacent a first end1612of second feed conductor1602, and fourth shorting arm1606extends from top hat conductor104adjacent a second end1614of second feed conductor1602.

Using fifth antenna1600additional omnidirectionality can be achieved. However, a drawback of adding more feed conductors and shorting arms is an increase in the corresponding parallel inductance and, as a result, an increase in the minimum frequency of operation. Thus, fifth antenna1600can be used in applications in which omnidirectionality is a higher priority than lowest frequency of operation.

The word “illustrative” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “illustrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, “a” or “an” means “one or more”. Still further, the use of “and” or “or” is intended to include “and/or” unless specifically indicated otherwise.