## CFA vs. Conventional Theory

Undoubtedly there is more for everyone to learn about CFAs—including ourselves, the inventors. However, let me outline a few concepts of CFAs in relation to “conventional” theory.

#### The Fields

The D plate of the CFA is a parallel capacitor, which with an AC signal creates a surrounding H field. This is well known and is even used to prove continuity of the fourth Maxwell equation i.e. curl H = J + D’. Feynam’s lectures on physics even evaluates how to calculate the H field surrounding a capacitor. If anyone is not convinced, they can simply measure the existence of the H field around a capacitor and prove that it is 90 degrees phase advanced from the applied voltage and also the E field lines between the plates.

The E plate produces E-lines since it is also a capacitor. There can be no question of this either.

If both the D and E plate structures were fed together with voltage signals which were in phase, then, I’m afraid we would have E and H fields which are 90 degrees out of phase close to the D and E plates. This is similar in some ways to a conventional antenna. There should be little radiation and the behaviour would mimic an extremely short antenna. Radiation would be produced from conventional theory in the very far field and have little power. Indeed some publications have presented this feature—ignoring the phase details of the feeders and also the phase properties of the field distributions surrounding the antenna which actually produce the radiation.

#### Phase Shift

Now phase shift the D plate voltage by 90 degrees. Then we have E and H in time phase close to the structure. However, a point of note which has unfortunately not been communicated by us very well in the past. If the phasing is 90 degrees one way, the Poynting vector S = E x H is inward. No power radiation is possible as the radiation resistance has a high impedance. I believe many people have dismissed the CFA because they have attained the 90 degrees but no or extremely small levels of radiation. When the correct 90 degrees is achieved, i.e. phase shifted the other way, S = E x H is outward and power radiation occurs.

#### Where is the Radiation?

This is the ultimate test of the CFA. Where does the power radiation start? If it is conventional theory, then close to the antenna will be inductive reactive field, which has a well-established relationship with distance from the antenna. If it is power radiation and most of the fields participate in this radiation, then the distribution with distance will be different showing the CFA is a different type of antenna system. In addition, because the fields close to the CFA are “strong” in comparison to fields in the far field which produce radiation in conventional theory, then we may expect strong radiation.

I have not suggested anything which is unusual or breaks any electromagnetic laws. Simply, E and H in time phase produce radiated power—the Poynting theorem. The D and E structures produce E and H fields, easily experimentally proved, and these are simply made to be in time phase.

#### Voltage Levels

A further proof is also the voltage levels on the antenna structures. The CFA appears to have about 1/6 the voltage level of conventional antennas. In conventional theory this should result in much less radiated power than is measured, even for the “worst” CFAs!!

In all of this, one must also get the ratio of E/H to match space impedance for maximum power transfer, so you can appreciate that 90 phase and little power is actually a space impedance matching problem. The voltages on the E and D plates must be altered to change the field strengths for maximum radiation. This has been how Dr. Kabbary has maximised radiation on the Egyptian CFAs.

#### Conventional Theory Does Not Apply

Now, in terms of conventional theory, well the CFA is fundamentally different and standard antenna formulae and techniques cannot be invoked when E and H exist close to the structure in time phase. Conventional theory cannot accommodate this fact and thus should not be applied. I suppose it is obvious from another viewpoint. Conventional monopoles have one signal feed to the antenna structure and an earth. The Groundplane CFA has two signal feeds to two structures and an earth. There is no way conventional theory of monopole structures can be transferred directly without alteration to another type of antenna.

A further thought relates to phasing circuits. One remarkable feature is that the phasing circuit to provide 90 phase shift appears to compensate frequency movements when radiating. The E and D plates go “off frequency” together as they are both capacitive thus introducing “wider” band radiation as E and H are still then in time phase.

#### FCC & CFA

There has been some question about the CFA in regard to the FCC 73.186 et al. Let me mention a few details. The purpose of the National Association of Broadcasters paper scheduled for the April 1999 convention in Las Vegas is to present broadcasting CFAs to the US. For that reason, and because no one has actually built a broadcast CFA in the US, we have not been motivated to satisfy every demand of the FCC yet. Give us time! However, in our paper relative normalised radiation field strength patterns of a broadcast CFA (at reduced power) taken at about 600m (not the 1km for the FCC 73.186) are presented. We have the measurement values and will bring these to the NAB conference. We also hope that prior to NAB, some more information regarding FCC criteria will be available as further measurements are taken in this respect.

One need only take a field strength meter and measure the shear signal strength levels of a CFA. Having done this for the CFAs in Egypt, there is no comparison. The levels are so strong.

In this respect, last year I asked the BBC to make reception checks on a 30kW 1161kHz CFA in Cyprus—a distance of about 500km from the CFA. The BBC reported fair-strong signal strengths during daytime and evening with no fading characteristics. No other distant broadcast programmes using even higher power levels compare. This is reported in the NAB conference.

#### Build, Phase & Believe!

I realise the CFA will still face opposition and still come in for criticism, some perhaps justified, a lot of it not. However, what concerns me is that those who have been most vocal in dismissing it have never actually built one and properly phased it! If I truly felt that they didn’t work, I’d pack it in—since I’d be wasting my time.

Originally posted on the AntennaX Online Magazine by Dr. Brian Stewart, MM1DVD

*Last Updated : 3rd May 2024*