What is difference between resonant and non-resonant antenna?Answer:

Every antenna is at resonance according to length to which it is cut ! They are usually cut

to resonate at a particular band of frequencies, ie, Vhf Television band etc. 

If no resonance then no signal is present and in such a case antenna is merely a random

chunk of metal. 

The magnetic field that an antenna puts out will produce an electric current on any conducting

surface that it strikes, however if that surface has a characteristic length the induced current will

be much stronger on the object. For example, when a Citizens Band signal travels through the

air, it completes a cycle in approximately 36 feet. If the object that the magnetic wave strikes is

18 feet long (1/2 wave length), 9 feet long (1/4 wavelength) or 36 feet long (1 full wavelength),

then the induced current will be much higher than if the signal struck a metal object that was not

some appreciable fraction of the wavelength of the signal. 

A resonant antenna is so much more efficient at converting (receiving or transmitting) current

between the field and the antenna's feed-point than a non-resonant antenna that much effort is

put into configuring resonance. A non-resonant antenna still works as an antenna but simply

requires a more sensitive receiver or more powerful transmitter. 

If you have ever heard people say they want to "tune" their antenna, they usually mean they

mechanically change lengths in relation to the frequency / wavelength they are trying to match. It

is also possible to change electrical properties to match frequency, which is more handy for

matching multiple frequencies with a single antenna.

nverted vee antennaFrom Wikipedia, the free encyclopedia

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2008)

An inverted vee antenna is a type of antenna in which the two side of the dipole are perpendicular to each

other instead of parallel. It is typically used in areas of limited space as it can significantly reduce the

ground foot print of the antenna without significantly impacting performance. Viewed from the side, it looks

like the English letter "V" turned upside down, hence the name. Inverted vee antennas are commonly used

by amateur radio stations, and aboard sailing vessels requiring better HF performance than available with a

short whip antenna. Inverted vee antennas are horizontally polarizedand they are almost omnidirectional as

compared to a traditional dipole in which they have a deep null off the ends.

Typical amateur radio inverted vee installed on roof. This multiband antenna allows transmissions on the 40/20/15/10

meter bands. Center point is held up with masting and ends are secured to roof. Two VHF verticals are also shown.

[edit]Use

Typically, the inverted vee antenna requires only a single, tall support at the center, and the ends can be

insulated and secured to anchors near ground level or near the roof if mounted on a house. This simplified

arrangement has several advantages, including a shorter ground distance between the ends. For example,

a dipole antenna for the 80 meter band requires a ground length of about 140 feet (43 m) from end to end.

An inverted vee with a 40-foot (12 m) apex elevation requires only 115 feet (35 m). For radio

amateurs living on small parcels of property, such savings can make it possible to use the lower frequency

amateur bands.

[edit]Properties

In theory, the gain of an inverted vee is similar to that of a dipole at the same elevation because most of the

radiation is from the high-current portion of the antenna, which is near the center. Since the center of both

antennas are the same height, there is little difference in performance. Antenna modeling software bears

this out for free-space models, predicting maximum gain of 2.15 dBi for the dipole and 1.9 dBi for the

inverted vee.

However, in practice, ground proximity and ground conductivity as well as end effects reduce the efficiency

of the inverted vee considerably compared to the dipole: In the 40-foot example above, considering a

useful take-off angle of 40 degrees above the horizon, the inverted vee produces a maximum gain of 1 dBi

in a circular pattern, whereas the dipole produces an oval pattern ranging from 6 dBi toward the sides down

to 1.2 dBi toward the ends.

Elevating the antennas higher above ground somewhat resolves the disparity, but considering the practical,

legal and financial limits which influence most antenna installations, the inverted vee will be observably

inferior in performance to a dipole by 1 to 2 S-units. However, if space is limited, an inverted vee may

permit operation on frequencies that would not be possible with a full-sized dipole.

[hide]

V

T

E

Antenna types

Isotropic Isotropic radiator

Omnidirectional Biconical antenna

Cage aerial

Choke ring antenna

Coaxial antenna

Crossed field antenna

Dielectric Resonator Antenna

Discone antenna

Folded unipole antenna

Franklin antenna

Ground-plane antenna

Halo antenna

Helical antenna

J-pole antenna

Mast radiator

Monopole antenna

Random wire antenna

Rubber Ducky antenna

T2FD Antenna

T-aerial

Umbrella antenna

Whip antenna

Directional Adcock antenna

AWX antenna

Beverage antenna

Cantenna

Cassegrain antenna

Collinear antenna

Conformal antenna

Dipole antenna

Folded Inverted Conformal Antenna

Fractal antenna

Gizmotchy

Helical antenna

Horizontal curtain

Horn antenna

HRS antenna

Inverted vee antenna

Log-periodic antenna

Loop antenna

Microstrip antenna

Offset dish antenna

Patch antenna

Phased array

Parabolic antenna

Plasma antenna

Quad antenna

Reflective array antenna

Regenerative loop antenna

Rhombic antenna

Sector antenna

Short backfire antenna

Slot antenna

Turnstile antenna

Vivaldi-antenna

WokFi

Yagi-Uda antenna

Application-specific ALLISS

Ground dipole

Evolved antenna

Rectenna

Reference antenna

Wullenweber

Rhombic Antennas, V-beam, and Inverted V

 

  

(also see related page curtain arrays)

The rhombic antenna is often claimed to be an exceptionally good antenna with very high gain. We will look at a few rhombic antenna designs (including an Inverted V) in the article below.

If we look at this link to this  pdf document on rhombic design we find suggested dimensions for rhombic antennas. That page agrees with other data I can find on rhombics, such as the once very popular Radio Handbook by Bill Orr W6SAI.

My modeled data agrees with other independent rhombic antenna

models. For example, if we look at the data on the PA6Z Rhombic antenna     page we will find the following rhombic gain values for a 320-meter total wire length rhombic:

14 MHz   = 15.95 dBi

7 MHz     =  10.79 dBi

While this might initially seem like a great deal of gain, we have to remember it includes ground reflection gain. A dipole at reasonable heights typically has over 8 dBi gain. Translating the dBi gain values above to a more standard dBd we have the following:

14 MHz   = 15.95 dBi or 7.5 to 8 dBd gain for the 320-meter wire length rhombic

7 MHz     =  10.79 dBi or 2.3 to 2.8 dBd gain for the 320-meter wire length rhombic

The argument rhombics are "very high gain antennas" seems to fall apart when we compare rhombic antennas to a standard dipole reference antenna with both antennas at the same height. Rhombics do have advantages, but it seems there is a widespread tendency to exaggerate or misunderstand gain. The purpose of this page is to factually describe and illustrate the advantages and disadvantages of rhombic antennas.

Model of a Rhombic Antenna

Let's look at a 2 WL per leg 40-meter rhombic design 120 feet high over medium conductivity soil using number 8 AWG bare copper wire with an 800 ohm termination.

V angle at each end: 70 degrees

Side length (one of four sides): 252 feet

Overall width: 290 feet

Overall length: 414 feet

At first glance our response might be this is a lot of gain. After all, the gain is a whopping 14.42 dBi for this 414 foot long 290 foot wide rhombic antenna. But to get a good idea of the real gain, we should compare it to a dipole or some other standard antenna at the same height. When we do that, we find this large 40 meter rhombic antenna has about (14.42 dBi - 8.5 dBi) 6 dBd gain.  The efficiency is a fairly low 46.6%

Let's double the size and readjust side angles for optimum gain at the new leg length and see what happens......

We now find the following design specifications for an even larger 4 wavelength-per-leg 40 meter rhombic:

V angle at each end: 47 degrees

Side length: 504.4 feet

Overall width: 687.9 feet

Overall length: 737.9 feet

This antenna would use over 2000 feet of wire, and here is how this monster antenna performs at a height of 200 feet above ground.

From EZnec+ ver. 5.0 we have the following patterns:

 The overall efficiency is 47.2%

This rhombic has 16.64-8.5 = 8.14 dBd gain. This is actually about the gain of a pair of 3-element Yagi antennas stacked. Let's compare the

Rhombic to a pair of three element Yagi antenna for 40 meters. Here is the pattern and gain of my two-antenna high 40 meter stack of three element Yagi antennas:

The gain of this antenna system is 7.73 dBd. My two three-element 40 meter antennas are within 1/2 dB of a rhombic 200 feet high occupying a 700 ft by 750 ft area. More important when we look at patterns, the 40 meter Yagi antennas have a cleaner broader pattern. This means less fading and better coverage in the target area using the much smaller Yagi antenna system!

Let's try comparing the rhombic to my planned distributed feed curtain array:

My planned curtain, at 285 feet high and 340 feet wide, has 21.9 dBi gain. Referencing a dipole over earth this is 21.9 - 8.5 = 13.4 dBd gain.

40-meter Rhombic Performance

Comparison

AntennaPhysical size W x L x H

-3dB Beamwidth

Typical gain over dipole

Typical ERP with 1500 watts applied

Antenna

Efficiency

PA6Z rhombic 2-wave per leg

Not given ? 2.3 dBd2,500 watts

?

optimum 2-ave per leg rhombic at 120 feet

290 x 414 x 120 feet

23.3 degrees

6 dBd6,000 watts

46.6%

stacked 3 el. Yagi 40m Antenna at W8JI

70 x 50 feet x 180

feet63 degrees  7.7 dBd

8,500 watts

98%

optimum 4 wave rhombic at 200 feet

690 x 740 feet x 200

feet

16.3 degrees

 8.6 dBd11,000 watts

47.2%

Curtain at W8JI340 x 35

feet x 280 feet

19.3 degrees

13.4 dB33,000 watts

98%

NOTE: Leg length is the length on each side of the four sides of the elongated rhombus or diamond.

Inverted V antenna

In the 1970's I actually had a true inverted V antenna on an FM broadcast tower in a swampy area with wet rich black loam soil. The apex of the antenna was around 400 feet high with legs going up and coming down several hundred feet long.

The inverted V antenna or vertically polarized half-rhombic is half of a standard rhombic turned on its side. Theoretically the terminated inverted V antenna uses the ground below the antenna to make up the "missing half" of the rhombic.

Here is a model of an optimized inverted V half-rhombic over perfect soil:

This antenna is terminated with a 400 ohm resistor, and is worked against 25 radials 1/4 wavelength long. It also has a single wire connecting the grounds below the antenna. Gain of the inverted V over perfect earth is

15.22 dBi, or about 6.7 dB over a dipole at optimum height.

Changing the above antenna's earth to good soil (15 ms/m) with no other changes we have the following patterns:

Gain is now 7.04 dBi, or -1.5 dBd. The antenna has a slight loss from a dipole at optimum height.

This is with no conductor or antenna changes. The only change is the soil

type, which went from perfect lossless soil to good soil.

This actually agrees with my tests at the broadcast station. While I could get reasonable F/B ratio, I had loss over a dipole in the direction the antenna was pointed. After one season I removed my large inverted V antennas and went with a regular dipole antenna about 330 feet in the air.

V-Beam Antenna

The V-beam antenna is the first part of a rhombic antenna. It omits the closing end of the rhombic. As such, we can model it by removing the outer half of a rhombic. This is a four wavelength-per-leg 40-meter V-beam antenna:

 

Gain is 14.15 dBi, or about 6 dB over a dipole. This gain is approximately equal to a small three element Yagi antenna. The main problems is, like the rhombic, the half-power beamwidth is very narrow for the gain. A low gain-beamwidth product occurs because antenna efficiency, even for unterminated systems, is only around 70%.

Much of the 30% power loss is in earth below the antenna. Efficiency climbs to 92% when this antenna is over perfect earth. In the case of perfect earth, the

remaining 8% loss is due to copper losses in the very long #8 copper antenna conductors.

 

 

 

 

 

 

 

 

 

Unfortunately lossless earth doesn't significantly extend the main lobe. Lossless earth primarily fills the nulls, and widens the main lobe. This is a good thing from the standpoint that signals not directly in the main axis improve at no penalty to signals along the main axis.

 

 

 

 

 

 

 

Long wire arrays are also height sensitive. Reduced height greatly lowers efficiency, and a good goal for minimum height is 1/4 of the antenna's leg length. The 4-wavelength per leg V-beam had 6 dBd gain when just under 1 wavelength high.

Reducing height to just under 1/2 wave reduces gain to about 3 dBd or less. The antenna gave up almost 4 dB

of antenna gain for a 60-foot height change on a 40-meter antenna, moving it into the gain range of a simple small extended double Zepp wire antenna. The extended double Zepp would have a wider main lobe for the same gain, because it has higher efficiency. It would also have deeper nulls in the null area.

 

 

 

 

 

Conclusion

Rhombic and related V antennas are often described as extremely high gain antennas, but that claim seems to be a little exaggerated or inflated.  A 2-wavelength per leg rhombic actually has about the same gain as a single three-element monoband Yagi antenna on the design band. Most of the rhombic's performance limitations come from the high levels of spurious lobes and the very poor efficiency, especially over normal soil.  The rhombic has one of the poorest gain-per-acre rankings of any high gain HF antenna array. On the other hand a rhombic antenna does have the very distinct advantage of working over very wide frequency ranges with good SWR and gain, something a basic monoband Yagi can never do. The rhombic is also a simple antenna, requiring only four supports (three supports for the V beam, and one support for inverted V derivatives).

In a large properly designed rhombic, slightly less than half of applied RF power is lost in the termination system. That power is converted to heat. Right away this puts the rhombic at a ~3 dB disadvantage to other more efficient antennas with a similar overall pattern shape or half-power beamwidth. There are ways to use this power but generally very little appears in rhombic resources.

Efficiency and gain could be improved if we recirculated termination power. Rather than converting the power to heat, we could recombine the termination RF back into the main feeder system. Such recombining or recirculating schemes would be fairly simple, although they would require readjustment if the operating frequency was changed. A recirculating system would be comprised of an impedance matching network or stub and phasing system to bring the termination signal back in phase with the applied power. By recombining power that would otherwise be wasted as heat back into the feed system, system gain would increase 2 to 3 dB.  ( I actually used such a system with an "inverted V antenna", which is

actually a vertically polarized half-rhombic antenna. )

Even though not quite the extremely high gain system we are led to believe, the rhombic is not without major advantages over other antennas. It is easy to construct and somewhat non-critical of dimensions. It offers very wide bandwidth performance, being competitive with large log periodic arrays. If we need an easy-to-install very broadband antenna that can easily handle high power and if we are not particularly worried about gain or efficiency, a rhombic is a worthwhile antenna to consider.  The many spurious lobes, while they do rob significant power from the main lobe, can also fill in other directions while transmitting. This is sometimes a plus for broadcasting, if we can align the side lobes with populated areas. Rhombics are not the extremely high gain antennas we are sometimes led to believe, but they do have very distinct advantages when it comes to bandwidth, power handling, ease of construction, and physical and electrical simplicity. The rhombic is a moderate gain very wide bandwidth antenna capable of handling very high power.

 

Since 11/11/2008  

Ferrite rod antenna- an overview, summary, tutorial about the ferrite rod antenna or aerial, a form of RF antenna that is widely used in RFID and transistor radio applications.

Ferrite rod antenna information includes:    •  Ferrite rod antenna basics    •  Ferrite rod antenna parameters

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 antenna basicsAs the name suggests the antenna consists of a rod made of ferrite, an iron based magnetic

material. A coil is would around the ferrite rod and this is brought to resonance using a variable

tuning capacitor contained within the radio circuitry itself and in this way the antenna can be tuned

to resonance. As the antenna is tuned it usually forms the RF tuning circuit for the receiver,

enabling both functions to be combined within the same components, thereby reducing the

number of components and hence the cost of the set.

Typical ferrite rod antenna assembly used in a portable radio

The ferrite rod antenna operates using the high permeability of the ferrite material and in its basic

form this may be thought of as "concentrating" the magnetic component of the radio waves. This is

brought about by the high permeability μ of the ferrite.

The fact that this RF antenna uses the magnetic component of the radio signals in this way means

that the antenna is directive. It operates best only when the magnetic lines of force fall in line with

the antenna. This occurs when it is at right angles to the direction of the transmitter. This means

that the antenna has a null position where the signal level is at a minimum when the antenna is in

line with the direction of the transmitter.

Operation of a ferrite rod antenna

Ferrite rod antenna performanceThis form of RF antenna design is very convenient for portable applications, but its efficiency is

much less than that of a larger RF antenna. The performance of the ferrite also limits the frequency

response. Normally this type of RF antenna design is only effective on the long and medium wave

bands, but it is sometimes used for lower frequencies in the short wave bands although the

performance is significantly degraded, mainly arising from the losses in the ferrite. This limits their

operation normally to frequencies up to 2 or 3 MHz.

Ferrite rod antennas are normally only used for receiving. They are rarely used for transmitting

anything above low levels of power in view of their poor efficiency. It any reasonable levels of

power were fed into them they would soon become very hot and there would be a high likelihood

that they would be destroyed. Nevertheless they can be used as a very compact form of

transmitting antenna for applications where efficiency is not an issue and where power levels are

very low. As they are very much more compact than other forms of low or medium frequency RF

antenna, this can be an advantage, and as a result they are being used in applications such as

RFID.

Ferrite Rod Antenna Parameters

- notes and overview about some of the key parameters associated with ferrite rod antennas and their performance.

Ferrite rod antenna information includes:    •  Ferrite rod antenna basics    •  Ferrite rod antenna parameters

There are a number of ferrite rod parameters that are of key interest when considering their use in

any application.

The two main parameters are the Q of the tuned circuit, and the radiation resistance. These two

ferrite rod parameters govern the areas in which they can be used. The size of the ferrite rod

antenna means that there are some compromises that need to be made in other areas of their

performance. Accordingly it is necessary to make the right balance between the important

requirements.

Ferrite rod antenna QOne of the requirements for an efficient ferrite rod antenna is that it should have a high Q at the

frequencies over which it operates. At frequencies of a few hundred kilohertz, a medium

permeability material would be used and this would enable a Q of about 1000 to be obtained. With

a Q of this value it will mean that the antenna will need tuning if it is to operate over more than a

single channel or frequency. When used in a portable receiver, the tuning can be linked to the

overall receiver tuning and indeed the ferrite rod antenna normally provides the input tuning for

the set.

Typical ferrite rod antenna assembly used in a portable radio

The Qs of the overall antenna may appear very high, and in fact the ferrite in a rod form has a

much higher Q than the basic material as a result of the fact that the rod forms an open magnetic

circuit.

Radiation resistance of a ferrite rod antennaOne of the advantages of using a ferrite in the antenna is that it brings the radiation resistance of

the overall antenna to a more reasonable level. The ferrite rod antenna can be considered as a

small loop antenna. In view of its size, the loop is much less than a wavelength in length and

without the ferrite it would have a very low radiation resistance. Accordingly the losses due to the

resistance of the wire would be exceedingly high. Placing the ferrite core in the coil has the effect

of raising the radiation resistance by a factor of μ^2, and thereby bring the value into more

acceptable limits.

While the introduction of the ferrite rod raises the radiation resistance of the antenna, and hence

reduce the losses due to the resistance of the wire, it does introduce other losses. The ferrite itself

absorbs power. This arises from the energy required to change the magnetic alignment of the

magnetic domains inside the granular structure of the ferrite. The higher the frequency, the

greater the number of changes and hence the higher the loss.

SummaryThe ferrite rod antenna is a particularly useful form of RF antenna design despite its limitations and

drawbacks in terms of efficiency, top frequency and the need for tuning. Nevertheless ferrite rod

antennas are widely used, being used almost universally as the RF antenna in portable radios for

long and medium waveband reception as well as being used in a number of RFID applications.