Antennas gains with respect to isotropic gain are specified in units of dBi. Antenna gains can also be specified with respect to a half wave dipole or a short vertical antenna The half-wave HF antennas described below do not impose the compromises of inductively The Half-Wave Full Sloper Dipole. This ham radio HF antenna needs only one tall support and takes.. Scan blindness of large phased arrays toward a scan angle ψ is caused by surface waves that propagate in synchrony with a Floquet mode of the structure. At ψ, the array impedance is modified to such an extent that the array radiates no power. Consequently, the array FOV is defined by the angle at which the scan blindness is located and not by the position of its grating lobes. In references , , and  the problem of scan blindness has been treated in some detail by considering an infinite array of dipole antenna elements printed on a grounded dielectric slab. The results summarized here are based on the derivation of a Green's function for the array of infinitesimal dipoles scanned to angles θ and ϕ.
In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of For faster navigation, this Iframe is preloading the Wikiwand page for Dipole antenna The bowtieTriangular object is a planar bowtie antenna on the Y-Z plane. The default planar bowtie dipole is center-fed. The feed point coincides with the origin A dipole antenna is a simple antenna that can be built out of electrical wire. The most common dipole antenna is a half wave dipole which is constructed from a piece of wire half wavelength long
A dipole is quite easy to construct. The length of a half-wave dipole might be thought to be the same as a half-wavelength of the signal in free space, but this is not quite the case. A number of effects, including the velocity factor of the wire, the length / diameter of the wire used for the radiating element and capacitive end effects, mean that the actual length required is a little shorter. Frequency Devices 11 M Half Wave Dipole Antenna with Balun - Ready to Hang The Frequency Devices Half Wave Center Fed Dipole antenna with Balun is tuned to 27.2 MHz (11 Meters)
What is that little green horizontal piece and why do we need it? I can see that the little green piece will not support an average 'standing' current as seen in the 1/2 wave section. Being very short, any current should drop to zero at the end. I am curious about the potential. How does it look across the coil (both ends and tap). I am also and mostly curious as to how charge is distributed as a function of time, as it must be conserved. Thanks, -bobDon't be misled by the term gain. The overall output (transmitted) power is not greater than the overall input power. Only the output power in a specific direction is greater than some reference power in that direction. In other words, the antenna does not act as an amplifier.
. The power density Pd and power per unit solid angle pd can be expressed using equation 6.154 (Das, 2004):where tex(R) is the time of the waveform extremum measured at location R. This definition, however, is hard to apply as we do not know the above extrema times explicitly.Commonly known as an omnidirectional antennas, all dipole antennas have a generalized radiation pattern. The donut-shaped elevation pattern shows that a dipole antenna is best used to transmit and receive from the broadside of the antenna and is very sensitive to matching horizontal positioning and any movement away from a perfectly vertical position. At about 45 degrees from perfect verticality, the omni’s signals, both received and transmitted, will degrade to more than half.
Solution: With a dipole antenna as a reference, the maximum output power will be twice the input power. Therefore, the antenna gain can be calculated as:Fig 4: Antenna insulators: (a) egg insulator, (b) ‘dogbone’ or ribbed insulator used here as a dipole centre piece See below. Flower Pot Antenna - 2m 144 MHz coaxial dipole antenna for portable or fixed Enjoy constructing your own version of the 2m coaxial dipole antenna known elsewhere in the radio..
Figure 3.14a illustrates the dependence of the array percentage bandwidth and scan blindness angle of an array of patch antennas when the interelement spacing is λ/2 and the substrate is GaAs . As can be seen, arrays having thick substrates have increased bandwidths but decreased scan blindness angles that determine the array's FOV. Therefore, trade-offs have to be struck between increased bandwidths on the one hand and extended array FOVs on the other. Dipole Antennas A dipole antenna most commonly refers to a half-wavelength (λ/2) dipole. The physical antenna (not the package that it is in) is constructed of conductive elements whose.. Taking the lessons from the Super J and Dr. Best, I set about to simply design a helical step-up transformer at the end of a half-wave antenna element. It took some trial and error with the tools available in 4nec2, but wound up with this design in figure 1. Centre fed half wave dipoles make great, simple and effective antennas for the HF bands. Being able to feed the dipole from one end gives you more options on how to erect an antenna and makes.. Obviously, the received waveform is a function not only of the signal I at an earlier time, but also of its time derivative and time integral. Figure 4 shows the three functions in question for the current of the form
Downloading and running your .nec file produced a question, though: Doesn't the short vertical conductor leading away from Terminal #2 as shown in the graphic linked below constitute the second conductor needed for the "EFHW" to radiate, even as short as it is? https://i.postimg.cc/rFdkggP6/JSH-2m-EFHW-Detail….The lengths calculated from this should only be considered as an approximate value – it is best to cut the wire slightly longer than this and then twist the end of the wire back on itself to give the best match.
When the substrate relative permittivity is 12.8, the space-wave efficiency of an array of infinitesimal dipoles decreases monotonically as h/λ increases; a similar trend is observed when ɛr = 2.55 and h/λ is between zero and 0.1; when h/λ > 0.1 a plateau in efficiency is reached. 4 Antenna Properties 1. An antenna is a transducer that converts a guided wave propagating on a 30 Radiation Pattern of Half-Wave Dipole Radiation pattern resembles that of the Hertzian dipole Yes, absolutely. The "end-fed" moniker does seem to imply a single terminal source, but all power sources are certainly two terminal devices. It's a game of semantics isn't it? In my mind "end-fed" refers to the radiator feed, but I could be wrong. The larger question is if point #2 requires "extra" treatment of ground, lengthly counterpoise or other ideas to get radiation from the dipole radiator. This simulation suggests no as does my experiment with a 10 MHz dipole here… https://www.hamradio.me/antennas/electrically-iso… Please note that Internet Explorer version 8.x is not supported as of January 1, 2016. Please refer to this page for more information.The number of surface waves a dielectric material can support is proportional to its thickness. The condition 
Figure-2 depicts dipole antenna with its radiation pattern. It also depicts folded dipole antenna. The most common dipole antenna is a half-wave dipole which is a piece of wire or rod which is one half wavelength in length. The antenna is cut into two quarter wavelength sections. The transmission line is connected at center point as shown. The dipole antenna has an impedance of about 73 Ohm. Half Dipole Antennas - Free download as PDF File (.pdf), Text File (.txt) or read online for free A plot can be made and should look something like Fig 2. The length of the antenna should be adjusted to give the lowest overall level in the areas of interest of the band. For example if operation is envisaged in the SSB section in the middle of the band, the minimum can be adjusted so that it occurs in this section, whilst still maintaining an acceptable level in other sections of the band. If the minimum VSWR point occurs too low in frequency, the length of the antenna can be shortened. The dipole antenna is probably the most popular type of antenna, especially the half-wavelength dipole. I'll be lazy and take a paragraph from wiki: The dipole usually consists of two identical..
There are variations to monopole antenna which will provide antennas of inverted-L and inverted-F types. These type of monopole antennas are used for hand held portable telephones. The compensated gain comes to about 2.1 dBi, close to a perfect dipole’s 2.15 dBi gain. Further tweaking of the model can likely improve this, but that’s beyond the larger point of this article. A dipole antenna can be used for many applications within a band of 10-20% around the resonant Compared to a simple dipole, a folded dipole antenna has a different radiation pattern with higher.. The other points to note are the ways of fixing the ends of the wire and also connecting the feeder to the centre of the antenna.The "x" is an axis marking. I probably should have removed it to make the picture prettier.
Years ago I took an antenna class from Dr. Stephen Best who was kind enough to field questions after the class. At that time I was designing an improvement to the Super J antenna to replace the Franklin stub with a coil. I knew much could be accomplished in NEC using an inductance inline, but asked him for tips regardless. He said “Why not just simulate the inductor as wires along with the rest of the model?” I did and it worked well. Of particular significance is the ability of NEC to provide a better realization of a coil than any idealized and perfect inductor.Many hams’ first choice of antenna is a half-wave dipole. But don’t be misled – just because they are easy to make doesn’t mean they don’t work well. In fact, a half-wave dipole will often outperform many compromise commercial multiband antennas.Before an antenna can transmit power, it receives that power from the source through a transmission line. The characteristics of that transmission line (or the circuitry) are also important from the perspective of performance. One of those characteristics is impedance.When a second patch antenna is in the vicinity of another, currents are induced in it owing to coupling to both the space and surface waves of the first patch; the second patch therefore becomes a secondary radiator. As the mutual coupling between antenna elements cannot be minimized , the designer has to accept that the interelement spacing is another critical array parameter—consider also the discussion related to Figure 3.14b.
Dipole Antennas - the Effect of Height Above Ground. I frequently hear the question: how high should my dipole be? Or alternatively, will my dipole work well at this or that height Download as PDFSet alertAbout this pageRFID+ Selecting the RFID System Design Dr.Paul Sanghera, in RFID+ Study Guide and Practice Exams, 2007But the conductor attached to Terminal #2 in my graphic forms part of the "radiator" as much as the conductor attached to Terminal #1, doesn't it? Just a lot shorter.
The dipole antenna or dipole aerial is one of the most important and commonly used types of RF In this paper, an attempt has been made to investigate new half wave dipole antenna for GSM.. A half-wave antenna (referred to as a dipole, Hertz, or doublet) consists of two lengths of wire rod, or tubing, each 1/4 wavelength long at a certain frequency. It is the basic unit from which many complex.. By feeding the antenna at this point it provides a low impedance feed and a good match to your coax. Normally 50 ohm coax, such as RG213 or RG58 is used as this provides a reasonable match.The measured speed reflects two competing phenomena—outward propagation and the diminishing additional positive time shift. In the far-field zone the first of these phenomena gradually takes over, and we may expect the local two-point measurement procedure to yield values of speed progressively approaching the speed of light from above, as if the pulse was decelerating. In the near-field zone, however, the additional time shift is large enough to be detectable. We saw that it yields superluminal values for the pulse speed. Obviously, we need to abandon the idea of a constant speed and consider a more general concept of a local velocity that is a function of distance from the source. For example, we could introduce a local velocity as a limit of the two-point measurement procedure in the neighborhood of some location R as
The half-wave dipole is a more realistic representation of an actual physical dipole antenna (see Figure 6), since it is modeled from the currents of the element rather than from an ideal mathematical.. 1.2 Dipole antenna E(x-z) plane and H(x-y) plane Dipole Antenna Characteristics Half wavelength Dipole antennas used in this experiment are two types: 914.5125 Mhz and 2.45 GHz and their.. . 12 Dbi 433mhz Antenna Half Wave Dipole Antenna Sma Male With Magnetic Base For Ham Radio Signal Booster Wireless Repeater
Consider now the relationship between the magnitudes of the transmit and receive vectors in equation 6.109. Then use equation 6.63 to relate |e¯| to G and equation 6.83 to relate |v¯R| to maximum effective area Aem. Thus, an equivalent universal relationship between G(θ, ϕ) and Aem(θ, ϕ) results:Figure 3.14c illustrates the magnitude of the reflection coefficient |R| of an infinite array of printed dipoles when a = 0.5774λ, b = 0.5λ, ɛr = 2.35, and h = 0.19λ, as a function of scan angle in the E-, H-, and D- (diagonal) planes . The scan blindness angles occur at θ = 68.3° and 49.3° in the E- and D-planes, respectively. Usually the array FOV is restricted to a scan angle equal to the scan blindness angle minus 10°.
Dipole Antenna Types. Dipole antennas are available in a range of designs to suit their applications. Half-wave dipole radiates to a maximum of 2.15 dBi perpendicular to its axis, falling.. Half-Wave Dipole. Special case of the dipole antenna Length of this dipole antenna is equal to a half-wavelength UHF half-wave dipole Dipole antenna used by the radar altimeter in an airplane A half-wave dipole antenna A half-wave dipole antenna receiving a radio signal. The incoming radio wave (whose..
In radio and telecommunications a dipole antenna or doublet is the simplest and most widely used class of antenna. The dipole is any one of a class of antennas producing a radiation pattern approximating that of an elementary electric dipole with a radiating structure supporting a line current.. A simplified formula for small source and receiver dipoles, parallel to each other and located in a plane orthogonal to their orientation (as in Figure 1), is DIY FM dipole antenna or half wave antenna are the most used because is easy to build and cost a few bucks but has some drawbacks like little directionality, small gain. The rf dipole antenna is build.. Using equation 6.103, one can relate the transmit and receive vectors of any arbitrary antenna (replaced for antenna 1), once the transmit and receive vectors of one specific known antenna can be substituted for antenna 2.
It has been shown that such fundamental scanning characteristics of an array consisting of microstrip antennas as the reflection coefficient, input resistance trends, scan blindness, and grating lobe effects are dictated by the interelement spacings and substrate parameters (height and relative permittivity) and not by the nature of the microstrip antenna element (patches or dipoles) . We shall therefore make no distinction between the two antennas types. Let us begin by presenting a physical insight into the problems at hand before we outline a qualitative account of the performance of arrays having a diverse set of parameters. How do these antennas compare to the wire antennas on the market. I've seen lots of plans and My Slim Jim antenna is a perfect choice for a repeater. It has a folded dipole design that gives it more.. where Δt(R) is the relative shift due to the near- and intermediate-field terms. We give it a positive sign to emphasize that the relative time shift is happening toward later (positive) times on top of the normal propagation-induced positive time delay R/c.Figure 3 shows the resistance and reactance as seen by the source as configured in figure 1. Pretty darn nice if you ask me. The resistance swings quite close to 50 ohms thanks to the “turns ratio” of the autotransformer. The reactance hovers near zero thanks to the compensating series capacitance.
half wave dipole antenna. This particular antenna was dimensioned for use at 30 Mhz. You will note that the left and right hand halves are merely quarter wave sections determined by the formula given.. Products. Welcome to the home of EFHW - End Fed Half Wave antennas, BALUNs, UNUNs, OCF, and Accessories. OCF Dipole antennas. EFHW-Single Band. EFLW-UnUn 9:1
Very nice article, I have a commercial EFHW antenna for 2M like you have analyzed. An interesting fact is that Dr. Best was my job interviewer and I also learned a lot from him too. He was very supportive of my "weird" antenna designs at Cushcraft Corp. some 20+ years ago. Keep up the great work…73 Danny Horvat, E73M aka MyAntennas.com The ends of the antenna will have a high voltage when used for transmitting and the installation should be such that it is not possible to touch them. Also, if the ends come down too low you could get ground losses – keep them at least three metres high if possible.The final reactance presented to the source varies wildly as capacitance increases from 1 pF to our goal. 5 pF overshoots a bit as we expect. Simulation optimizations reveal 4.56 pF brought the net reactance to zero ohms. This is very close to our predicted value… pretty much a bulls eye. There are some parasitic capacitances in play as well, but this result offers good agreement of theory and simulation.That series reactance is most often a capacitor in series. It’s what one finds in end-fed VHF and UHF antenna systems from Diamond Antenna and others. One example is the NR770HBNMO end-fed dual band mobile antenna and companion K515S Luggage Rack Mount groundless mount. Numerous web sites reveal the coil and series capacitor of these antennas. Antenna Theory - Half-Wave Dipole - The dipole antenna is cut and bent for effective radiation. The length of the total wire, which is being used as a dipole, equals half of the wavelength (i.e
A small dipole antenna with unit input current and length l can be used as the reference antenna 2. Let this dipole current be oriented in the −θˆ1 direction, such that the radiation from the dipole antenna 2 is maximum toward the antenna 1. Alternately, one may visualize the current of the dipole antenna 2 to be oriented along the Zˆ2 axis (see Figure 6.8(A)). Then, let the Zˆ2 axis be turned to align in the −θˆ1 direction so that in the line of communication θˆ1=θˆ2 and θˆ2=90°. Under this situation, using the results from Das (2004) in Section 6.2.1, the transmit and receive vectors of the dipole antenna 2 are found as: Many hams' first choice of antenna is a half-wave dipole. But don't be misled - just because they are easy Half-wave dipoles are easy to install and erect and are not nearly as likely as end-fed wires to..
Half-wave Dipole UHF directional Antenna 380-470 MHz for pole mount. Model Number: DP400. Frequency 380 - 470 MHz Average Gain 0 dBd Nominal Gain on sup-port pipe 2 dBd VSWR 1,5:1.. Simulation packages such as EZNEC offer special transformer simulation. Sounds very handy and I look forward to learning how this works someday. However, I wanted to study the behavior of the entire system including the winding of the step-up transformer rather than rely on an idealized version of same.
Figure 3.14b demonstrates the array scan angle dependence on the substrate relative permittivity when four cases are considered . For cases 1, 2, and 3 the substrate height, h, is equal to 0.06λ but the interelement spacing, a, takes the values 0.52λ, 0.5λ, and 0.48λ, respectively; as can be seen, a small variation in a affects the range of the array scan blindness angles. Similarly, cases 2 and 4 have the same interelement spacing, 0.5λ, but the substrate heights take the values of 0.06λ and 0.02λ, respectively; as can be seen, a decrease in substrate height dramatically affects the range of array scan blindness angles. Relatively thin substrates tend to increase the scan blindness angle. When the substrate thickness is set, the designer can substantially vary the array's scan blindness by slightly varying the interelement spacing. The folded dipole antenna is half a wavelength wide, with each dipole element being a quarter wavelength long. Folded dipoles have significantly greater feed impedance A monopole antenna is one-half of a dipole antenna, mounted perpendicularly over some type of conductive surface, called a ground plane.The directivity (gain) of a monopole antenna is twice the..
Typically it may be set up something like Fig 3. While this may be the ‘standard’ type of installation, rarely is it possible to make an installation exactly like this, and it is acceptable to make it fit the requirements of the location. Dipole antennas are the most common type of antenna used and are omni-directional, propagating radio frequency (RF) The antenna is fed by either a half wave dipole antenna or a feed horn
"IMO, that path attached to Terminal #2 of the source is not correctly thought of, or described as a counterpoise — rather it is one side of a (very) off-center-fed dipole." These are only approximate values. In practice it's best to make the antenna a little longer than the calculated value and then trim it to get the best SWR value.As one expects, the real value of the inductance changes little with the varying series capacitance. It is most perturbed with the 1 pF value, but settles in as capacitance gets well beyond the “mere open gap” values. More about 4.56 pF in a moment. Originally these antennas were called half wavelength Hertz Aerials and were fed with a single wire. On its fundamental frequency, the dipole antenna should have an impedance near 73 Ohms
Dipole Antenna Length Calculator. Dipoles antennas are easy to build and can be very effective when placed half a wavelenth or more above ground Physically, dipole antennas are cylindrical and are usually limited in power gain due to their widespread coverage. They are most commonly used in mobility applications. The dipole antenna is not a directive antenna, since its power is radiated 360 degrees around the antenna (one of the reasons for FCC power gain limitations). Dipole antennas are also the most common culprits in interference issues, due to their widespread radiated pattern. A mobility device requires a dipole antenna, since there is no way of telling where the next AP will be for connectivity. If a mobile unit discovers an AP north of its current position, the antenna continues to radiate 360 degrees in all directions, creating noise and/or interference for any other AP in the area attempting to use the same frequencies and channels.
Monopole antenna vs Dipole antenna-difference between monopole antenna and dipole antenna. The monopole and dipole antennas are used for cellular phones, broadcasting and wireless.. Quarter-wavelength dipole The total length of this antenna is a quarter the wavelength corresponding to the frequency to be used. It uses the reflective ground plane that provides an image of the antenna to complete the dipole. Dipole antennas also add a second wire which serves as a ground plane. By stacking dipole antennas on top of each other, you can increase the gain of the antenna but reduce the effectiveness..
The maximum radiation from a dipole takes place in the centre. Accordingly, this is the most important area of the antenna to keep as high as possible.Antenna gain and loss are factors of physics. A 0-db antenna inherently transmits an omnidirectional pattern (perfect circle horizontally). To visualize the pattern, imagine a donut. The hole in the center is where the antenna is placed, vertically oriented. The donut pattern would be the pattern of transmission from the antenna. To achieve gain, one must understand the principle of balloons. When inflated, balloons have a finite volume and a finite surface area. If a balloon is round, like the donut, one can make one side larger by pushing in on the other side. More here equals less there. Antenna patterns are similar. To get gain in one part of the antenna pattern, one must create losses in another. Directional antennas achieve gain by their directionality. That is, they have farther reach in one direction (gain) by sacrificing reach in other directions. When you have a basic dipole antenna and add a reflector and director element to it, you have created an array antenna. The array antennas are ideally half a wavelength apart so they aren't parasitic.. This is its fundamental resonance, and from looking at the voltage and current waveforms (Fig 1) it can be seen that the voltage is at a minimum at the centre with the current at a maximum.The received waveform is a weighted sum of these three functions. The weight coefficients are the functions of distance R between the source and the receiver, where the term with R−3 is dominant close to the source (near-field zone), and the term with R−1 is dominant for large R (far-field zone). This means that in the near-field zone the received waveform will look almost like the integral, and in the far-field zone it will look almost like the derivative of the current.
The two-point procedure described in Section 2 deduces the velocity of the electromagnetic pulse from the waveform measured at two locations where one is farther from the source. Thus, according to Eq. (34) the values of the weighting factors are different for these two locations. Not only is the waveform smaller in amplitude for the more distant of the two locations, but the relative weight of the three contributions changes as well. In general, the relative weight of the last term increases, whereas the relative weight of the first term decreases with distance. Hence, we may expect the shape of the waveform to gradually change from the one dominated by the time-integrated signal to the one dominated by the time derivative of the signal. As Figure 4 shows, this means a shift of an extremum toward earlier times. Such backward-in-time “motion” is superimposed on the normal time delay, which shifts the received waveform to the right along the time axis as one moves farther away from the source.In this way it may be possible to angle the antenna to ‘fire’ in the direction where most contacts are wanted, although the dimensions of your garden are more likely to determine what is possible. A.H. Systems TV-2 half-wave dipole antenna, also know as the reference dipole antenna, is the simplest form of an antenna. This dipole consists of a matching balun and two horizontal elements..
A half-wave dipole antenna means the length of this dipole antenna is equal to a half-wavelength SWR diagram of the half wave dipole at 88Mhz. The antenna cable. (we will send cable with BNC.. Transmitter power is rated based on a 0-db antenna load—that is, the resistance and output of the antenna are assumed to be exactly the same as those of the transmitter feeding it. A dipole antenna (simple rubber duck-type antenna) is often configured as a 0-db antenna.One of the theoretical antennas used as a reference is called an isotropic (omnidirectional) antenna-that is, it radiates power uniformly in all directions. Therefore, the power radiated by the reference antenna can be taken as equal to the input power, assuming that the antenna is lossless. This would result in the following equation for the antenna gain:Copyright © 2020 Elsevier B.V. or its licensors or contributors. ScienceDirect ® is a registered trademark of Elsevier B.V.The problem, of course, is we can never really get a power source infinitely small so even its body will be a bit of electrical "mass" (or counterpoise if you like) to push against, but the data seems to be suggesting it doesn't have to be electrically large. Put another way, there's nothing about the EFHW that is fighting our ability to energize it so long as we handle the impedance transformation… and that's the larger point here.
One may repeat the above procedure by reorienting the dipole antenna 2 such that the current is in the −ϕˆ1 direction. This would provide the relationship between the ϕˆ components of the transmit and receive vectors:If operation is tried at different points on the band (taking care not to cause interference) it will be noted that the VSWR is higher at some points than others.…seem to suggest the extra wire, while certainly pulling a bit of current, isn't part of the grander sinusoidal current distribution of the primary dipole element. Thus the resonant frequency of the overall system changes little. It's as if the feed point is a demarcation line between independent antennas, each managing their own destiny whereby they draw current if they present a matching HiZ to the feed.
Figure 3.14. (a) The array bandwidth (%) and scan blindness angle as a function of the substrate thickness (h/λ). (b) The array scan angle blindness as a function of the substrate's relative permittivity (ɛr), the interelement spacing a, and the substrate thickness (h). Case 1, a = 0.52λ and h = 0.06λ. Case 2, a = 0.5λ and h = 0.06λ. Case 3, a = 0.48λ and h = 0.06λ; Case 4, a = 0.5λ and h = 0.02λ. (c) The magnitude of the reflection coefficient of an infinite array of dipoles as a function of scan angle in the E-, H-, and D- (diagonal) planes when the substrate ɛr = 2.55 and the thickness h = 0.19λ. The arrows indicate the position of the scan blindness angles in the D- and E-planes.With the radiation formula (30) at hand, we can start to analyze the shape of the waveforms received at some distance from the source. A waveform measured by the dipole antenna of the type shown in Figure 1 gives the time evolution of a single component of the electric field strength determined by the orientation of the dipole and modified by the antenna-cable-oscilloscope receiving tract. The latter modification, however, is the same for all receiver locations: It does not depend on the distance from the source. Only in the close proximity of the source may the expected small multiple reflections between the two antennas slightly modify the tail of the waveform with respect to what is predicted by Eq. (30). Many hams' first choice of antenna is a half-wave dipole. But don't be misled - just because they are easy Half-wave dipoles are easy to install and erect and are not nearly as likely as end-fed wires to..
..POLARIZATION & ANTENNA ORIENTATION - For a single dipole antenna, E and B fields are generated perpendicular to each other, and both propagate perpendicular to the antenna Without the end effect the length of a dipole could be calculated from the formula length (metres) equals 150 / f, where f is the frequency in MHz. With the foreshortening effects the length can be approximated from the formula: Length (metres) = 143 / f (MHz)The use of a balun will prevent the coax radiating any power or picking up any noise. In many practical situations it is possible to operate the dipole satisfactorily without one, but there may be a slight increased risk of interference if one is not used. Simple baluns can be bought from antenna suppliers, or made. www.antenna-theory.com presents the analysis of the dipole antenna! The short dipole is discussed first, followed by the half-wave dipole antenna, and finally the general dipole antenna
• Half wave dipole • RF • Antenna • Efficiency • Gain • TRP (Total Radiated Power). SMA connected antenna or RF instrument. This document describes a simple half wave dipole antenna that is easy.. Long Wire Dipole Antenna - An basic horizontal half-wave antenna which can be made of ordinary copper wire. The cable should have a cross section of 1 mm 2 or more Antenna gain is another way of measuring an antenna's ability to radiate in a specific direction. This is measured as a ratio of energy radiated at a point of maximum radiation to energy radiated at the same point by some reference antenna:
The direction of maximum radiation is along θ=π2, which is perpendicular to the direction of the antenna current. The power radiation pattern P_d(θ,ϕ) has the following form with respect to θ, having a uniform variation in the azimuth:Wow. I am impressed with the well written article, the effort to develop the transformer coil and the handling of the reactance. However, the model is not what I would publicize yet because of the very poor AGT value. Some more work is needed to see what is wrong or even if NEC2 can handle it. Maybe take a look at what is generating the 135 MHz secondary resonance.
IMO, that path attached to Terminal #2 of the source is not correctly thought of, or described as a counterpoise — rather it is one side of a (very) off-center-fed dipole. Points well taken. I found 0.967 AGT with NEC4. I guess I should have a look at NEC2 results as well. I've never been too sure how far off AGT can be before trouble begins. What I really want to do is actually make the thing, but I'm busy with another EFHW experiment at the moment. If you find a design tweak that yields better results with NEC2 please consider sharing.
The main point to note when erecting a dipole is that the lower ends of the antenna should be kept out of reach of people.Figure 4. Back-in-time shifting of extrema. The figure shows the signal, its cumulative time integral, and derivative. The first extremum of the integral is farther (later) in time, whereas the first extremum of the derivative is earlier in time than the first extremum of the original signal.Dual dipole antenna As the name suggests, a dual dipole antenna consists of two dipoles. It covers more area and therefore reduces the sensitivity of a tag's orientation.If it occurs too high in frequency it means the antenna is too short and needs to be lengthened somehow. Putting wire back is not nearly as easy as taking some wire off!So, antenna gain is important because in an RFID system the power is transmitted in preferred directions and is not broadcast uniformly in all directions. For example, a reader wants to direct the power at the tag it wants to read. That's why directivity and antenna gain are performance-related characteristics of antennas in RFID systems.