Types of Antennas

Types of antennas

1. Folded Dipole

Radiation Pattern: BIDIRECTIONAL

Feed Impedance: 292

A folded dipole is a half-wave dipole with an additional wire connecting its two ends.

If the additional wire has the same diameter and cross-section as the dipole, two nearly

identical radiating currents are generated. The resulting far-field emission pattern is nearly

identical to the one for the single-wire dipole described above; however, at resonance its

input (feedpoint) impedance is four times the radiation resistance of a single-wire dipole.

This is because for a fixed amount of power, the total radiating current is equal to twice the

current in each wire and thus equal to twice the current at the feed point.

The tips of the antenna are folded back until they almost meet at the feedpoint, such

that the antenna comprises one entire wavelength. This arrangement has a greater

bandwidth than a standard half-wave dipole. If the conductor has a constant radius and

cross-section, at resonance the input impedance is four times that of a half-wave dipole.

2. Ground Plane Antenna

Feed Impedance: 37 (if radials are horizontal)

50 (if radials are at 45)

To function as a ground plane, the conducting surface must be at least a quarter of

the wavelength (/4) of the radio waves in size. In lower frequency antennas, such as

the mast radiators used for broadcast antennas, the Earth itself (or a body of water such as

a salt marsh or ocean) is used as a ground plane. The radio waves from an antenna element

that reflect off a ground plane appear to come from a mirror image of the antenna located

on the other side of the ground plane. The ground plane must have good conductivity; any

resistance in the ground plane is in series with the antenna, and serves to dissipate power

from the transmitter.

3. Invisible Antenna

i. Clothesline Antenna

This antenna is utilizing ordinary clothesline by simply insulating the pulleys from

their support points. It uses an conducting type of clothesline; such as a heavy gauge

stranded electrical wire with Teflon or Vinyl insulation.

It works at all the HF bands, and it gets great results. It doesnt need a tuner because

its dead-on resonant on the 160, 80, 40, 20, 15 and 10 meter bands. A tiny tweak will bring in

12 and 17 meters, too.

ii. Invisible Long-wire

An antenna, several wavelengths long, made up of a small-diameter enameled wire.

The smaller the wire, the more invisible the antenna will be. It is also known as long-

conductor antenna.

iii. Rain gutter antenna

A gutter antenna is an inconspicuous antenna utilizing the gutter and downspout

system of a building.

The pattern will depend where you connect the feed wire. If you feed it at one end

then the pattern on 40m will be mostly omnidirectional, but with strongest signals to the

EAST/WEST. On 20m the maximums will tend to be NORTH/SOUTH. On higher bands there

will be multiple lobes and nulls in the pattern. 80m is generally omnidirectional, reasonably

good for local NVIS contacts.

A good set of ground radials will help a lot on 40m and 80m where the

feedpoint impedance will be low (6 to 20 ohms) due to the low height

above ground. Feeding at an end is probably a better choice than at some point in the

middle of the antenna.

iv. Flagpole antenna

A flagpole antenna is a vertical antenna disguise as a flagpole. It is assumed that the

height of the pole correspond to a quarter wavelength for a chosen band.

One advantage of having the tuner at the antenna is that when or if one presses the

vertical into multi band service it is very helpful to eliminate the coaxial cable run located

between the antenna and the tuner this line section can and does see large mismatches

during multi band service and as we all know mismatches on coaxial cable increases the

coaxial loss dramatically. Eliminating that loss as a function of mismatch feeds one up to

consider the tuner settings and the resulting match to be more efficient. There are

anecdotal techniques that are consolations but the best or less loss approach is to eliminate

that run that is not matched by a tuner because it is after the tuner.

4. Indoor Antenna

A type of radio or TV antenna placed indoors, as opposed to being mounted on the

roof. Indoor antennas are usually a simple and cheap solution that may work well when the

receiver is relatively near to the broadcasting transmitter and the building walls do not

shield the radio waves too much.

Being close to other electric or electronic equipment in the building, an indoor

antenna is prone to picking up more electrical noise that may interfere with a clear (analog)

reception. Used for digital broadcast, the noise is less of a factor, which recently makes this

type of antenna a more popular solution.

Its main advantage is that it is free from weathering effects, wind damage and

it is readily available at any weather conditions.

5. Inverted L Antenna

A convenient low-band antenna for amateurs with space limited to one tree or tower

and some other supporting structure.

It is top-loaded vertical which require a fairly good ground radial system for efficient

operation.

Long wires fed against earth which are 5, 7, 9, 11, 13 or 15 electrical quarterwaves long

will have feedpoint impedances somewhere between 150 and 250 Ohms. Consequently we

can feed such antennas with 50 Ohms cable via a 1:4 balun. At the same time the need for

good earth becomes less important. A galvanized iron tube driven into the ground with a

few short radials around.

6. Long-Wire and Traveling Wave Antenna

A traveling wave antenna is an antenna without any standing waves resulting from

audio signals.

I. Long single wire antenna

Radiation Pattern: BIDIRECTIONAL (unterminated end)

UNIDIRECTIONAL (terminated end)

A long single wire antenna is a single wire antenna that has a wavelength or longer at

the operating frequency. In general, the gain achieved with long-wire antennas is not as

great as the gain obtained from the multi element arrays studied in the previous section.

They are widely used as receiving antennas on the long wave, medium wave, and

short wave bands, as well as transmitting antennas on these bands for small outdoor,

temporary or emergency transmitting stations, as well as in situations where more

permanent antennas cannot be installed. The longer the wire, the greater the power gain.

II. V-Beam Antenna

Radiation Pattern: BIDIRECTIONAL (unterminated end)

UNIDIRECTIONAL (terminated end)

Terminating Resistance: 600

Feed Impedance: 300 to 450 (terminated end)

Two long wires combined to form a V with an angle that is twice that of the major

lobes of the wires with the wires excited out of phase.

The radiation along the bisector of the V adds and the radiation in the other

directions tend to cancel.

The longer the wires in terms of the wavelength, the greater the gain and the

sharper the directional pattern.

Since the V beam is a non resonant antenna, It really isn't "cut" for any band but the

relationship between the length of the legs and the apex angle of the V determine the band

on which it will be most "focused". Generally you get useful gain from 1/2 to 2 times the

frequency at which it is "focused". If you design for maximum focus on 14 MHz, it will work

well from 7 MHz to 28 MHz.

III. Beverage Antenna


A long wire receiving antenna mainly used in the high frequency (shortwave)

and medium frequency radio bands. It is used by amateur radio, shortwave listening,

and long wave radio DXers and military applications.

While these antennas provide excellent directivity, a large amount of space is required.

Beverage antennas are highly directional and physically far too large to be practically rotated

so installations often use multiple antennas to provide a choice of azimuthal coverage.

Beverage antennas require the bending of radio waves to work. Lower frequency

radio waves bend around mountains, into valleys, and have deeper earth penetration. Poor

conductivity earth helps provide earth penetration, and the necessary bending. (Often called

tilt angle).

It has been said "A Beverage antenna should be run across a desert with a swamp at

each end" A Beverage will not work well over highly conductive ground or sea water. (The

swamp at each end was for your ground rod.)

IV. Fishbone Antenna


Antenna consisting of a series of coplanar elements arranged in collinear pairs,

loosely coupled to a balanced transmission line. Directional antenna in the form of a plane

array of doublets arranged transversely along both sides of a transmission line.

This antenna provides higher gain per acre than does a rhombic. It is essentially a

wave antenna which evolved from the Beverage antenna.

Fishbone antennas may be used in various arrays, according to the directivity

patterns desired. The one commonly used consists of two fishbones in broadside using

common intermediate supporting structures. The two-bay design unites the transmission

lines symmetrically and the main line to the receiver is then of one-half of the antenna

characteristic impedance.

7. Loop Antennas

A loop antenna is a closed-circuit antenna, that is, one in which a conductor is formed

into one or more turns so its ends are close together.

I. Large Loop

Large loop is a loop in which current is not the same either in amplitude or phase in

every part of the loop.

i. Half-wave loop antenna

Length of each side: /8

F/B Ratio: 4 6 dB

It is more efficient than a 1/4 wavelength monopole, because it is balanced and needs

no ground. It offers more low-angle performance than a horizontal dipole below a half

wavelength. Best of all the half-wavelength is space efficient - a square version for 20m is

only about 8 feet wide, while a monopole would be 16 feet long and a dipole 32 feet

long. As an added bonus, the half-wavelength loop doubles as a full-wavelength loop at

double the frequency. So you can use the 20m loop on 10m, the 30m loop on 15m, the 40m

loop on 20m, the 80m loop on 40m, and the 160m loop on 80m.

The feedpoint impedance of one of these is nowhere close to 50 ohms and that means

coax wont feed one well unless you make a matching device for it. The losses involved in

using a matching device probably outweigh the benefits of using the small loop. The pattern

of this antenna seems to be such that its not very useful for DX. A regular half-wave dipole

worked better and didnt need any special feed system.

ii. Full wave loop antenna

Feed Impedance: 100

Length of each side: /4

F/B Ratio: 2dB

Conductor length:

Gain: 2.1 dBd

Radiation Pattern: OMNIDIRECTIONAL

They are much quieter than a dipole or a vertical, have a broader bandwidth and will usually out perform a dipole antenna.

Its radiation is maximum perpendicular to the plane of the loop and minimum in any direction in the plane containing loop.

II. Small Loops

Conductor length: 0.1 - 0.085

Directional Pattern: BIDIRECTIONAL (vertically polarized)

OMNIDIRECTIONAL (horizontally polarized)

A small loop can be considered to be simply a large coil, and the current distribution

in such a loop is the same as in a coil. That is, the current has the same phase and the same

amplitude in every part of the loop.

It is a closed loop. These antennas have low radiation resistance and high reactance, so that

their impedance is difficult to match to a transmitter. As a result, these antennas are most

often used as receive antennas, where impedance mismatch loss can be tolerated

The small loop is often referred to as the dual of the dipole antenna, because if a

small dipole had a magnetic current flowing (as oppose to electric current as in a regular

dipole), the fields would resemble that of a small loop.

III. Ferrite core loops

Modern AM radios usually use a loop antenna wound around a ferrite rod to increase

its inductance without requiring such a large size. The term loop stick refers to the

underlying loop antenna and the stick shape of the ferrite rod.

As with all small loops, loopstick antennas are most practical at lower frequencies such as

the medium-wave (5201610 kHz) and long-wave (150300 kHz) AM broadcast bands, using

ferrite materials which are not too lossy at these frequencies. A multiband receiver may

contain tap points along the winding in order to tune the loopstick antenna at widely

different frequencies.

As with all small loop antennas, loopstick antennas are largely immune to locally generated

(within the near field) electrical noise, as they are coupled directly to the magnetic field.

Loopstick antennas are also used in radio direction-finding (RDF) applications.

IV. Aperiodic loop Array

F/B Ratio: 10 dB


This antenna is a wideband array of loop antennas. Unlike most of the loops, the loop

elements in an aperiodic array are untuned. This antenna is omnidirectional because it is

purposely unbalanced, and also because the isolating resistor causes the antenna to appear

as two closely-spaced short monopoles.

8. Direction Finding Antennas

I. Ferrite Rod Antenna or Loopstick Antenna

Frequency limits operation up to 2 or 3 MHz

Directional Pattern: BIDIRECTIONAL (vertically polarized)

OMNIDIRECTIONAL (horizontally polarized)

The ferrite rod antenna is a form of RF antenna design that is almost universally used in

portable transistor broadcast receivers as well as many hi-fi tuners where reception on the

long, medium and possibly the short wave bands is required.

Ferrite rod antennas are also being used increasingly in wireless applications in areas

such as RFID. Here the volumes of antennas required can be huge. The antennas also need

to be compact and effective, making ferrite rod antennas an ideal solution.

Ferrite rod antennas are normally only used for receiving.

A loop stick antenna may be made to have a single null if a second element is added.

The element is called a sensing antenna, because it gives an added sense of direction to the

loop pattern.

II. Adcock Antenna

The Adcock antenna is an antenna array consisting of four equidistant vertical

elements which can be used to transmit or receive directional radio waves.

Although originally conceived for receiving Low Frequency (LF) waves, it has also been

used for transmitting, and has since been adapted for use at much higher frequencies, up

to Ultra High Frequency (UHF). The Adcock antenna array has been widely used

commercially, and implemented in vertical antenna heights ranging from over 130 feet (40

meters) in the LFR network, to as small as 5 inches (13 cm) in tactical direction

finding applications (receiving in the UHF band).

III. Snoop Antenna

It is an antenna ideally suited to close-range direction finding. It is made up from a

length of RG-8 coax with the outer shield broken at the top and configured to form a small

loop.

It gives a detectable maximum reading when the grounded end of the loop is pointed

in the direction of the transmitter.

9. Broadband Antennas

I. Cage Dipole Antenna

Typical Spacing: 0.02 or less

Feed Impedance: 50-75

A cage dipole is basically an attempt to achieve a broader SWR bandwidth by using a

thicker radiator. A typical HF cage dipole can exhibit a 2:1 SWR frequency range almost 2

times broader than a single-wire dipole.

The frequency range of a cage dipole is from 2.5 up to 30MHz.

The multiplicity of conductors increases the effective bandwidth of the antenna and

reduces losses caused by the resistance of the wire conductors.

II. Biconical Antenna

Polarization: Vertical

Impedance: 50

Frequency range: 30 300 MHz

It is a balanced broadband antenna that consists of two metal cones arranged so that

they meet at or near the vertices. It is fed at the point where the vertices meet.

It is consist of two half elements in the form of cones joined at the center, the

feedpoint, at the vertex of each cone. In VHF or UHF service, the individual wires or rods

might screw into a hub/feedpoint, allowing for rapid assembly and disassembly at field sites.

It is used for emissions and immunity testing to meet various EMC standards

specified by FCC, CISPR and EN. It is easier to use for vertical site attenuation measurements,

because of the long dipole element lengths at lower frequencies (5 meters at 30 MHz).

The exact feed-point impedance of this antenna depends on the flare angle of the

cones and the separation between their vertices.

III. Conical Monople Antenna


Feed Impedance: 52

A Conical monopole antenna is a form of

biconical antenna in which the lower cone has

been replaced by a ground plane. The upper

cone is usually bent inward at the top.

It is often constructed in the form of a

wire cage and a good ground system must be

furnished for the conical monopole to work

well.

It is widely used both in commercial and military applications needing an omnidirectional

pattern and vertical polarization. It is also useful in observing the electromagnetic spectrum,

and subsequently in jamming activity.

IV. Discone Antenna


Feed Impedance: 52


It is characterized by very wide bandwidth, covering approximately a ten-to-one

frequency range, and an omnidirectional pattern in the horizontal plane. The signal is

vertically polarized and the gain is comparable to that of a dipole.

It is a wideband antenna, representing a biconical antenna wherein a flat, round disk

is used to replace the upper conical section of the antenna. Its lowest operating frequency is

determined by the height of the cone and the radius of the disk.

This antenna is usually oriented so that the disk is horizontal and on top of the cone.

V. Double Bazooka Antenna

Feed Impedance: 72

Double Bazooka antenna is an antenna consisting of a dipole with two quarter-wave

coaxial resonator stubs connected in series. It is sometimes called Coaxial Dipole.

VI. Snyder Antenna

Feed Impedance: 52

Snyder antenna configured like a crossed double bazooka, but this time using a 25-ohm

line as its resonators. It exhibits a W-shaped SWR characteristic.

VII. Bowtie Antenna

Radiation Pattern: BIDIRECTIONAL (without reflecting screen)

UNIDIRECTIONAL (with reflecting screen)

A broadband antenna used at VHF and UHF consisting of two triangular pieces of stiff

wire, or two triangular flat metal plates. The feed point is at the gap between the apexes of

the triangle.

For a unidirectional pattern, a reflecting screen may be provided.

This antenna is a two-dimensional form of a biconical antenna.

10. Multiband Antennas

Multiband antenna is intentionally designed for operation on a number of different

frequencies, any harmonics or spurious frequencies that happen to coincide with one of the

antenna resonant frequencies will be radiated with very little attenuation.

I. Multiple Dipole Antenna

Feed Impedance: 52

Multiple dipole antennas are an antenna system consisting of a group of center-fed

dipoles, which connected in parallel at the point where the transmission line joins them.

The dipole elements are individually cut to be /2 at different frequencies.

II. Open-Sleeve Antenna

This is an antenna consisting of a base-fed central monopole with two parallel closely-

spaced parasites, one on each side of the central element and grounded at each base.

The lengths of the parasites are roughly one-half that of the central monopole.

The amplitude of the current induced in each sleeve element equals that of the current

in the central element but the phases are opposite.

III. Windom Antenna

This antenna is a multiband wire antenna that uses a single-wire feed line. It is a half-

wavelength horizontal antenna, fed slightly off center This antenna will operate

satisfactorily at all of the even harmonics, as well as the fundamental frequency. A parallel-

wire line can be used with off-center feed in an antenna that is sometimes called Windom,

although the antenna is not a true Windom.

IV. Trap Antenna

A type of antenna using tuned circuits of appropriate design that are strategically

placed in a dipole.

Traps must be suitable for outdoor use; it is not useful over 30MHz. If the operating

frequency is below that of a trap resonance, the trap behaves as an inductor. If the

operating frequency is above that of a trap resonance, the trap behaves as a capacitor.

11. Multi Element Arrays

I. Collinear Array

A Collinear array is a type of broadside array using halfwave dipoles. This is called a

collinear array because the axes of the elements are all along the same line. Suppose that

the collinear antenna is used for transmitting, and imagine a receiving antenna placed along

the main axis of the antenna.

A linear array of radiating elements (usually dipoles) with their axes arranged in a

straight line. This array is always operated with the elements in phase. The directivity of this

array, in the plane of the array, increases with length.

When a collinear array is mounted with the elements vertical, the antenna radiates

equally in all directions. When it is mounted horizontally, the directive pattern in the vertical

plane at right angles to the array is the same as the vertical pattern of a simple /2 antenna.

II. Phased Array

This array is a group of antennas, connected to the transmitter or receiver, whose

radiation beam can be, adjust electronically without physically any moved parts.

To produce the desired radiation pattern, the element currents must have the required

magnitude and the required phase relationship.

Phased arrays can be made by connecting together any of the simple antenna types.

Depending on the geometry of the array and the phase and current relationships between

the elements, the array can be either broadside or end-fire.

It is most receptive when the angle of arrival is 90 degrees. In contrast, when the

angle of arrival is 45 or 135 degrees, the antenna array has zero output power, no matter

how much power is in the incident plane wave. In this manner, a directional radiation

pattern is obtained even though the antennas were assumed to be isotropic. Even though

this was shown for receiving antennas, due to reciprocity, the transmitting properties would

be the same.

III. 4-Squared Array

Forward Gain: 5.5 dB

F/B Ratio: 20dB or better

The 4-Squared array is a versatile array having four elements arranged in a square. Its

symmetry allows directional switching in 90 increments. It has four located in the corners of

a square that is one quarter wavelength on a side. With proper phasing, directivity can be

selected along the squares diagonal.

IV. Log Periodic Dipole Array

Forward Gain: 8.2dBi or 6.1dBd

Radiation Pattern: UNIDIRECTIONAL or BIDIRECTIONAL

Bandwidth ratio: 10:1 or greater

Frequency range: 80 MHz to 2 GHz

An array consisting of several dipoles elements of different length and relative phasing,

fed from a two-wire line which is transposed between each adjacent pair of dipoles.

The array is fed from the narrow end, and its maximum radiation is in this direction. It

exhibits essentially constant characteristics over a frequency range: the same radiation

resistance and the same pattern characteristics.

The log-periodic dipole array is the most popular antenna for television reception.

V. Log Periodic V-Array

Forward Gain: 9 to 13 dBd

Radiation Pattern: UNIDIRECTIONAL

Frequency range: 80 MHz to 1 GHz

Polarization: Linear

A modification of the Log Periodic V-Array capable of operating at higher resonance

modes with an increased gain by tilting the elements toward the apex.

A higher resistance mode is defined as a frequency that is an odd multiple of the

fundamental array frequency.

VI. Log Yagi Array

Forward Gain: 11.5 dBd


Beamwidth: 42

The array uses the concept of log periodic dipole as the concept, but with the addition

of the technique of adding parasitic elements. It provides higher gain and greater directivity

than would be realized with either the Log Periodic V-Array or the Yagi array alone.

VII. Quad Array

Forward Gain: 2 dB over a Yagi


Radiation resistance: 120

A Quad array is a popular type parasitic array using rectangular or diamond-shaped full-

wave wire loop elements. It is use in much the same way as dipole elements in the Yagi

antenna. It consists of a driven loop, one wavelength in circumference a reflector loop and a

director loop.

VIII. Sterba Array

Polarization: Horizontal (only a practicable type at

lower frequency)

Impedance: 600

It is a broadside radiator consisting of both

collinear and parallel elements with /2 spacing

between the latter. Its distinctive feature is the

method of closing the ends of the system. For direct

current and low frequency ac, the system forms a

closed loop, which is advantageous in that heating

currents can be sent through the wire to melt the ice

that forms in cold climates.

It is a modest-gain single-band antenna.

It is named after EJ Sterba, who developed a simple

curtain for Bell Labs in the 1930's. It has multiple feed

arrangements.

IX. Bruce Array


It consist simple of a single wire folded so that the vertical sections carry large currents

in phase while the horizontal sections carry small current flowing in opposite directions with

respect to the center of that section.

The array should be two or more wavelengths long to achieved a worthwhile gain.

X. Bobtail Curtain Array

Forward Gain: 5 dB over a single element

Radiation Pattern: BIDIRECTIONAL

The Bobtail is a simple three-element vertical broadside-array with a unique feed

system that produces binomial current distribution. This array uses the principles of co-

phased vertical to produce a broadside bidirectional pattern. It performs as three in phase

top-fed vertical radiator approximately /4 in height and spaced approximately /2.

It is most effective for low-angle signal and makes an excellent long-distance

antenna.

12. Mobile and Maritime Antenna

I. Stubby Antenna

This antenna is a helically wound radiator made up of stiff copper wire enclosed in a

protected covering of a rubber-like material. The inductance of the helical windings provides

electrical loading for the antenna.

II. Coaxial Whip Antenna

This antenna is a half-wave vertical dipole fed through one radiating elements with

coaxial cable. The whip is the top half (quarter wavelength) of the radiating elements.

The skirt is a metal cylinder mounted just below the insulator and which is quarter

wavelength long. This element, plus the whip completes the half wave dipole radiator.

The trap is a portion which effectively insulates the bottom of the skirt from the outer

conductor of the coaxial line permitting the skirt to act as a radiating element. The mast

supports the antenna structure.

III. Mobile- J Antenna

Directional Pattern: OMNIDIRECTIONAL

It is mechanically modified version of the zepp (zeppelin) antenna. This is an antenna

consisting of a half-wavelength radiator fed by a quarter-wave matching stub.

IV. Super-J Antenna

Gain: 6 dB over a /4 whip

3 dB over 5/8-wave antenna


It is an antenna constructed from a basic J-pole antenna with an extra half-wave

section added on top. The radiating section of this antenna is two half-wave that are in

phase.

V. 5/8 Antenna

Gain: 3 dB over a /4 whip


This antenna is often used vertically as either a mobile or base antenna in VHF and

UHF systems. Like the quarter-wave monopole, it has omnidirectional response in the

horizontal plane. However, the radiation is concentrated at a lower angle, resulting in gain in

the horizontal direction, which is often useful. In addition, it has a higher feedpoint

impedance and therefore does not require as good a ground, because the current at the

feedpoint is less.

This antenna is suitable for mobile or fixed-station use because it is small,

omnidirectional, and can be used with radials or a solid-plane ground (such as a car body). If

radials are used, they need to be only /4 vertical.

To reduce the ground effect, 5/8 wavelength antenna should be installed at least 1/2

wavelength above ground to 1.5 wavelength above ground. For best result, adjust the

length of the antenna to get the smallest SWR, or adjust loading coil for the best matching

impedence.

13. Space Communication Antennas

I. Turnstile Antenna

Radiation Pattern: omnidirectional (in the plane of the turnstile)

Radiation Resistance: 37

Gain: - 0.86 dB

Beamwidth: 50 (-3dB)

An antenna consisting of two half- wave dipoles placed at right angles to each other

and fed 90 out of phase with each other.

The configuration results in two dipole patterns combining and producing an almost

circular pattern in the plane of the turnstile.

If it were mounted in the horizontal plane, the antenna would radiate horizontally polarized

waves about equally well in all directions along the ground.

II. Quadrifilar Helix Antenna

This spacecraft antenna embodies a unique configuration and method of feeding

loop elements to produce radiation having a controllable pattern shape.

It comprises of 2 bifilar helical loops oriented in a mutually orthogonal relation on a

common axis.

The terminals of each loop are fed 80 out of phase, and the current in the two loops

are in phase quadrature (90out of phase).

It is especially attractive for certain spacecraft applications because it can provide

omnidirectional radiation in a single hemisphere without requiring a ground plane.

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Types of Antennas