Empirical Results on EH Antennas
Updated 20170930
My main interest in ham radio is small antennas. It’s easy to make large antennas work, just a matter of bucks, trucks and real estate. Small antennas are an area wide open for experimentation, especially at HF frequencies. This page presents concise conclusions on EH Antennas. To keep it concise I must assume the reader has a basic knowledge of radio and electronics, to the level of amateur radio exams. Many years of experience is recorded here.

Background
Those familiar with EH Antennas should scroll down to the next green heading, as this section gives background information unrelated to my own measurements. Search for “EH antenna” and you will find a lot of information on the Internet. A picture of an EH antenna follows.
Pasted Graphic

Its two copper or aluminium cylinders wrapped around a plastic pipe. The cylinders are driven from a coil, which is connected to a coaxial cable by a tap. As the tap position is moved, a low VSWR dip appears. So it can accept RF power from a transmitter.

What makes this antenna remarkable is the small size. A 20m band (14MHz) EH antenna can be 0.5m long, compared to a half wave dipole at 10m long. The antenna is on the face of it a large breakthrough in technology. Antennas scale directly with frequency, so for mobile comms just tens of millimetres long, or going the other way a top-band (1.9MHz) would be a few metres long.

The size of antennas is a major barrier to reducing the size of all electronic products using radio. Especially, ham radio operators need small antennas because they have to transmit at low frequencies. Conventional antennas can be hundreds of metres long at low frequency. So why is this apparent breakthrough not a mainstream technology? The answer is a long political and technical story, the technical side I will present briefly as possible on this page.

Signal Measurements
Making EH antennas is quite easy, and I encourage anyone with an interest to do so. The materials are cheap, and I never made one yet that failed to give a low SWR reading. I would ignore reactionaries who claim EH antennas only give a good match on Halloween or after sacrificing a chicken! Construction details are found on various websites, but the best and most up to date are in
this book. There is much to be learnt about antennas from constructing, and not just reading textbooks.

Where things become interesting is comparing EH antennas with more conventional types. To make the comparison easy, I used a frequency near 28MHz (10m) for testing. Conventional antennas are of manageable size at that frequency. Most others tried comparisons at much lower frequencies, leading to great expense, time spent, and mistakes. I used various modified CB antennas, which are cheap and easy to setup. Antennas scale directly with frequency, so measurements at 28MHz are equally valid as at any frequency.

These are signal readings taken between my father’s house and mine. The distance is about 3 miles, with a small hill between. A KiwiSDR receiver was used in this case, and the receiving antennas are described
elsewhere on this site.

Boomerang signal readings off KiwiSDR:
Horizontal = -86dBm
Tilted = -74dBm
Vertical = -75dBm

EH antenna signal readings off KiwiSDR:
Horizontal = -96dBm (10dB lower)
Tilted = -80dBm (6dB lower)
Vertical = -80dBm (5dB lower)

Its clear the EH antenna performs worse than the Boomerang CB antenna, which itself is a shortened antenna. In brief, my measurements indicate a 7-10dB worse signal than from a full size half-wave vertical antenna. Measurement inaccuracies are discussed elsewhere on this website.

During 2015 I made extensive tests with a Softrock SDR type receiver, and an off centre fed dipole (windom) over the same path. In this list of signal readings, a modified EH antenna was used, the modification is discussed under “Poynting vector synthesis”. Note the dBm readings in the following list are offset from the first list, due to a different receiver being used.

Bilal Isotron, coax connected to alloy pole: -67.3dBm
Bilal Isotron, modified with floating coax: -68.5dBm
EEF (cylinder) 1 with 2.0m coax: -61.5dBm (repeated at later date)
Modified EH antenna (cylinder) 2 with 2.0m coax: -62.5dBm
SRA disc type, coax 2.0m coax: -63.6dBm
Sloping reference half wave dipole: -67.0dBm
"Venom" half wavelength CB antenna: -53.8dBm
Modified EH (cylinder) 1 with 2.5m tail, air core choke: -61.4dBm
Modified EH 1 with 2.0m tail, 4x FT140-61 choke: -61.5dBm (repeat of prior test)
Modified EH 1 with 1.5m tail, 4x FT140-61, top plate added: -61.1dBm
Modified EH 1 with 1.5m tail, 4x FT140-61, top plate added, coax raised: -61.4dBm
Modified EH 1 with 1.5m tail, 4x FT140-61, T106-6 toroid: -61.1dBm
Two grids with no coax tail: -63.2dBm
Sirio Boomerang 27W, helically loaded dipole: -56.9dBm
Balanced Grids, no common mode, close spaced: -62.0dBm


Despite the windom being sloping, and so mixed polarisation, the half wave “Venom” is a clear winner. The Isotron is very poor, and the EH antenna not far behind! The inescapable conclusion is the EH antenna does not match a full size one. It’s worth noting that a dipole arranged at a metre lower down near a roof gave poor results. This shows why some believe the EH antenna can outperform a dipole; dipoles arranged at a low height can give bad performance. I regard the vertical set up “in the clear” to be a much better reference antenna, and a practical performance standard to aim for.

So with this disappointing result, why continue with research? Three reasons -

  1. 7-10dB loss is not a big difference in HF communications. Propagation effects are much larger
  2. The bandwidth of the EH antenna is unexpectedly wide for such a tiny antenna
  3. The length of coax doesn’t have to be very long to give good performance, on which more later

SWR Measurements

Here is a typical VSWR curve for an EH antenna. Some people failed to make them work in terms of getting a good VSWR, and it’s hard to believe they really tried. It’s easy to get a 1:1 match with these antennas. Tuning the resonant frequency can be done by cutting or extending the cylinders.

TLC10m

The 2:1 VSWR bandwidth is limited to 600kHz. The small bandwidth compared to a large conventional antenna is interesting in itself, and is discussed elsewhere on this site. It should be remembered the bandwidth of a small magnetic loop, of similar size to the EH antenna, will have a bandwidth about 5 times narrower. The subject of SWR is not a big issue with these antennas, so I move on quickly.


Poynting Vector Synthesis
Why the EH Antenna works despite its small size, is allegedly by Poynting vector synthesis. A short simplified summary of what this is follows.

Exactly how a wire antenna (e.g., dipole) radiates is complex and open to debate. James Clerk Maxwell unified the forces of electricity and magnetism in the electromagnetic force. His
famous four equations are a cornerstone of physics, yet have been superseded by quantum mechanics. Unfortunately Maxwell died before his theories were proven, and he knew nothing about antennas. To say the only way electromagnetic waves can be made is by a dipole is not a safe statement. Science is about understanding, so any theory can be challenged, or refined.

The simplest explanation of how an antenna radiates is charge acceleration. Electricity doesn’t work by moving electrons, even Wikipedia makes this error; in an a.c. (alternating current) circuit the electrons don’t actually move on average, just jiggle about. It's the charge making up the current in the wires that actually move (quickly). At UHF and above the electrons would have to move faster than the speed of light to get up the feed line and back every time the polarity reverses. It is plain they don’t travel anything like so fast.

An a.c. current flowing in a wire causes
charge, i.e., magnetic and electric fields to move around/through the wire. If it’s a substantial fraction of a wavelength, the fields are large enough to interact, and form electromagnetic radiation.

One of Maxwell’s students was
John Poynting who developed the theory of how an electromagnetic wave moves. The E (electric) and H (magnetic) components at a distance from an antenna manifest as electromagnetic waves. The problem is a conventional antenna must be of a certain size to generate the Poynting vector.

If we look at an antenna from close up, we detect separate E and H fields. Beyond about 2π
/λ range we don’t, because the E and H fields drop off as a cube-law. All we find is the electromagnetic wave. The separate E + H fields are the reason why the antenna must be so big, so why not combine them directly at the antenna, and make a Poynting vector? This is the key point of the EH antenna; by the Poynting vector principle, it can be much smaller than a normal antenna, perhaps more than 10x smaller.

To generate a Poynting vector, the near E and H fields must be aligned as they are in the Poynting vector. Basic inductor and capacitor circuit elements generate phase shifts, so why not use them to generate alignment of the E and H fields? As said above, the EH antenna has a coil (inductor) which when tapped at the right position give a low VSWR reading. So it looks like we just aligned our fields and generated a Poynting vector with a tiny antenna!

The tiny antenna consists of the coil feeding two cylinders. Here is a photo of an EH antenna for 28MHz as a reminder of how small it is and the construction.
EH_2017

If it is working by Poynting vector synthesis, both the cylinders would be equally “active," i.e. changing their length would make a big difference. It is also obvious that both cylinders would be needed to generate the wavefront (“vector”) in the gap between them.

Whist changing the length of either cylinder makes the frequency shift, the upper cylinder has more effect. So to see if the antenna is working by Poynting vector synthesis, we remove the lower cylinder. Disconnecting the lower cylinder made the resonance increase from 28.0 to 31.6MHz. To get back to 28.0MHz some extra turns were added to the coil.

With the lower cylinder in place, we get a field strength result to the inverted-V:
EH to inverted-V 2017-08-10 at 21.46.09

Now to the MMI-dipole vertical.
EH MMI-dipole vertical 2017-08-05 at 16.38.44

With the lower cylinder disconnected, and a few more coil turns to compensate, I tested again. Inverted-V, then vertical dipole.
EH cylinder removed to inv-V 27.801MHz 2017-08-13 at 14.27.55

Pasted Graphic

The antenna without the lower cylinder performs slightly better than with it. The conclusion is
the EH antenna does not work by Poynting vector synthesis. The lower cylinder is nothing more than a placebo, which reduces the resonant frequency by a small amount. The term “modified EH” above refers to one without the lower cylinder.

I did some other tests with coils and plates, adjusting the phase by physically moving the components around. At no time was a peak in radiation noted. This is also good evidence the Poynting vector cannot be formed directly at the antenna.

Despite this disappointing result, there are still the three reasons noted above to continue research. Looking on the bright side, here’s a photo of the antenna on the air on a summer day.

EH 2017-1

Common Mode Current
The EH antenna and its forerunner Crossed-Field antenna are often dogged by accusations the feed-lines radiate, and not the antenna itself. Prof. Maurice Hately (callsign G3HAT, originator of crossed field antenna) went to his grave arguing the point. The EH antenna and more recent Poynting vector antenna also fail to acknowledge common mode effects.

As concluded in the last section, the EH antenna does not work by Poynting vector synthesis. The most likely way it does work is by radiation from the coax between the antenna and transmitter. It’s time to look how this happens; common mode current.

The term “common mode” means a current is flowing through a ground or alternative path, and in this case the outside of a coax cable. So, is the outside of the coax doing the radiating with the EH antenna, not what we see as the antenna? I decided to answer this question once and for all, with some surprising results.

After making several EH antennas and many hours tapping off coils, I never measured a reduction to near zero, of common mode (CM) current. My measurement instrument is a simple transformer current meter. The promotors of the EH antenna claim that common mode current can be minimised by moving the coil tap; I find it cannot.

An EH antenna without the lower cylinder was constructed, and I found a flat plate to give slightly improved performance. It has the same step-up transformer as the EH antenna. To test radiation from the coax, the length of coax was varied. So to allow retuning the test antenna has a changeable plate at the top, and spare turns on the coil.
E-field antenna

A high impedance coaxial choke (balun) is placed a distance down from the top section to stop common mode current at a defined position. The choke stabilises the tuning to allow reliable adjustment and also marks the edge of the radian-sphere as defined in the Chu-Wheeler ESA formulas. In effect, it “cuts” the coax to allow different lengths to be tested easily by shuffling the turns through the ferrites.

One choke used was made of four FT140-61 ferrite rings. Ferrite 61 offers a good combination of inductive and resistive impedance above about 20MHz. The RG58 cable was wound 4 times through a stack of 4 rings. Effectiveness of the choke was confirmed by the VSWR reading on the analyser staying unchanged when the cable below the choke was touched or connected to anything. A simple current-clip meter was also used to check the amount of common mode current

Coax choke

Several tests were made on the length of cable between the top section and choke. It was found for coax lengths approaching 1/4λ between the top section and choke, an air cored choke could be used. But signal results for that arrangement were no better than for much shorter cable lengths. For shorter lengths than 1/4λ high impedance ferrite chokes had to be used because air core didn't have enough impedance to stabilise the tuning.

Feed-line length reduction
It was decided to begin with 1.5m of cable and antenna length of 1.0m. The frequency used for all these tests was near 28.0MHz (λ/4 = 2.7m). So the starting point comparison was for a total length close to a quarter wave. The KiwiSDR S-meter extension was used to obtain a trace, from the inverted-V
Screen Shot 2017-07-01 at 12.20.00

It was found rotation of the paddle and position of the coax on the roof made no difference to the signal. Reducing the cable to 1.0m:
Screen Shot 2017-07-02 at 19.49.41

The first plot omits the -90 cal line but was the same level by inspection. Unfortunately the KiwiSDR S-meter extension doesn’t give a numerical readout or 1dB calibration lines. Then the paddle was moved down to 30cm and the cable reduced to 0.6m.
Screen Shot 2017-07-04 at 21.31.08
The same trace was produced. The total length was now 130cm. To compensate for length reduction the coil tap off positions had to change. Next at 100cm, which is 18% of a dipole length.
Screen Shot 2017-07-05 at 19.04.38
This at last produces a definite reduction in signal strength.

Conclusions on common mode current
There seems to be some kind of threshold point at 0.1λ total length (0.05λ coax length), and when the feed-line is shorter than the antenna itself. The active length of the whole antenna was reduced from 2.5m to 1.5m with no measurable reduction in effectiveness. This is 60%, which should have a large effect according to the conventional theory of cable radiation. Reducing to 0.1λ (0.11m) for the whole antenna did start to reduce effectiveness.

The 60% length reduction of the total antenna is a definitive test. Strong common mode current on the feed line suggests there’s a contribution from it, but reducing from 150cm to 60cm (2.5x) with no effect indicates the opposite. So, I conclude common mode current is not the primary source of radiation, but the coax cable needs to be equal or longer than the antenna itself for efficient operation. It could be that the coil losses become dominant, or the length is reduced to some fundamental limit.

Restating three reasons to continue research.
1 7-10dB loss is not a big difference in HF communications. Propagation effects are larger
2 The bandwidth of the EH antenna is unexpectedly wide for such a tiny antenna
3 The length of coax doesn’t have to be very long to give good performance

Point 3 has now been addressed. Next to a couple of experiments to change the layout of the EH antenna and try to improve performance.


Grid/Mesh Antenna

It was suggested by
this paper that a metal plate spaced about 0.1λ away from a "ground" plate can produce far field radiation. A prototype was constructed to begin testing the idea the EH antenna did not perform well due to dead capacitance.

EEF up2
This is 0.7m high measured from the bottom of the grey coaxial choke box to the top. In terms of Chu-Wheeler radian sphere, the radius is <0.5m. Electrically it's more similar to the EH antenna than appearances may suggest. However, the antenna performed poorly, no better than the cylindrical EH without the lower cylinder. Also the coil construction proved lossy. Another prototype was constructed.

Spacing effects of grids/mesh plates
There are arguments over radiation from "EH antennas" by common mode currents on coaxial cable. A way to greatly reduce this effect is make the antenna balanced. Another experiment was to feed two plates (actually aluminium grids) from a high voltage step up transformer; again a modified EH antenna. The main feature of this design is it’s balanced to minimise common mode current.

This was briefly tested at a field day site, and made a few European contacts under difficult radio and environmental conditions. It was 5% λ in size with minimal common mode current. It was found moving the grids apart improved the performance.

BEEF vertical

Another prototype was made with the grids closed together and in an 'X' pattern. The grid antenna is not a dipole, so feeding at any point on the grids makes no difference to the VSWR. This version had close spacing and performed poorly.

CM current is the enemy of this type of antenna and allowing it doesn’t improve effectiveness. It appears the phase shift across large elements counteracts the desired mode of radiation. So allowing common mode or making the antenna more than about 0.06λ is counter productive. Most importantly, the failure of the close spaced design suggests the theory of dead capacitance is correct.

Conclusions on EH antennas

  1. It does not perform as well as a large conventional antenna
  2. The radiation mostly doesn’t come from the coax cable, but from the high voltage plate
  3. Poynting vector synthesis doesn’t work

The EH antenna is a form of radiating tuned circuit. The combination of high electric field between the top grid/plate and a fairly short length of coax cable seems to be how the antenna is operating. The necessary magnetic field for the E x H vector probably comes from the high voltage plate also. More work on how the antenna radiates is elsewhere on this site.


These findings are controversial because of the doctrine antennas can only radiate by charge acceleration caused by RF current in wires. Evidence suggests there’s a useful effect in the EH antenna, but NOT vector synthesis. This grain of truth is buried under lots of prejudice and politics. Dispensing with the terms “EH antenna” and “crossed-field” is a good idea, I do so on my next web page.


Comparing the size of one of the test antennas (left) and half-wave vertical. Is the big one worth the extra 7-10dB signal?

EEF comparison

Having refuted the common mode current theory, there are two points left to investigate; >7dB loss is happening somewhere; The bandwidth is unexpectedly wide for such a tiny antenna. Those points are left to another web page, look down the menu on this site to find it.

To round off this page, a look at the latest work of the proponents of the EH antenna. It is now renamed the “Poynting vector antenna” PVA.


Poynting Vector Antenna (PVA)

I constructed a PVA for the 20m band (14MHz).
PVA1

This antenna whatever I did to it performed poorly, very “dead” and lacking in background noise. I didn’t try it on the roof, but in the loft it was 2 or more ’S’ points below the external wire antennas. The one with bottles covered in copper is very similar to those shown on
the site of SM6DCO (Conny).

It was found the loading coil (just visible in the photo) and balun (in the transparent topped box) got warm with only 10W power. Also, connecting the top “bottle” at the end produced the same SWR, and the same background noise. This experiment proves these antennas are little more than radiating tuned circuits, as was found with the original form of EH antenna.

So again the Poynting vector synthesis is disproved. However, not everything is lost, as there is still much research to be done in small antennas…