Crossed field antenna

A crossed field antenna, or CFA, is a type of antenna for long and mediumwave broadcasting, patented in 1986, which was claimed to have the same efficiency as a conventional antenna but only one-tenth the overall height. The invention was received with incredulity from experts in electromagnetics and antenna technology owing to the deficient theoretical justifications offered and the lack of viable experimental verification.

The physical structure of a crossed-field antenna is:

• A horizontal metal disc (or "D-plate") raised above and insulated from the ground plane;
• A vertical hollow metal cylinder (or "E-plate") of smaller diameter than the disc, which it is mounted concentrically above and insulated from;
• A metal lattice funnel (or "extended conical section") radiating above and outward from and connected to the top of the cylinder.

The antenna's operation is described in its inventor's literature. An independent report by Trainotti and published by the Institute of Electrical and Electronics Engineers (IEEE) suggested that the Crossed Field Antenna was no more efficient than a conventional antenna design of the same height. The data presented in figure 31 of the Trainotti report shows measured field values up to 15 dB lower than from a theoretical 100% efficient monopole (see External links below). The report also states that the presence of the D-plate always has a deleterious effect on the CFA's performance, meaning that removing the D-plate will improve the performance although the resulting antenna is not a CFA.

The Isle of Man International Broadcasting Company (IMIB) planned to begin a long-wave service under the name Musicmann 279 using a Crossed Field Antenna located in Ramsey Bay off the coast of the Isle of Man. The company did extensive studies on the existing Crossed field antennas in Egypt. (See details on the discussion page of this article.)

There are a handful of CFAs operating in Egypt, at powers ranging from 1 kW to 100 kW. These have been operational for over ten years and were developed by the engineering sector of the ERTU the Egyptian state broadcaster for their own use. Many CFA projects in other countries failed including those in Australia, Brazil, China, Germany, Italy and the UK.^[1]

The last commercial CFA was installed in 2003. At the General Assembly of the DRM Consortium in Hangzhou China in April 2004, a Chinese manufacturer Zhongli made a demonstration with assistance from Thales SA and fed their new Crossed Field Antenna with 6 kW of DRM power. (RadioNews Issue15 Spring2004). Results of the test are unavailable.

2009 tests, Silsden, W. Yorkshire, U.K.

In the period August 2008 to September 2009 Communications Dynamics (I.o.M.) Limited (or CDL) and Kabbary Antenna Technology (Egypt) Ltd. (or KAT) co-operated in the construction and testing of various CFA's at Silsden in West Yorkshire, U.K. The testing was carried out by both CDL/KAT and an independent company, Arqiva.

The published results used an 8m high CFA at ground level, and also mounted on a 5m high platform. The frequency used for these tests was 1593 kHz (188.24m); using a 5W carrier wave only, no modulation. The reasons for the platform were to simulate installation of a CFA antenna on the roof of a studio or transmitter building, and, as stated in the report, the CFA would not work on the ground; this also made it easier to adjust the CFA settings to enhance radiation in the ground wave at low elevation angles.

The test results also clearly show that the near electric fields (displacement current) do not extend further from the CFA than its very small elevated ground plane. With the classical tuned monopole the displacement current extends as far away as half a wavelength from the mast independent of its height; this is also the maximum distance covered by the ground surface currents closing the antenna electric circuit.^[2] For this reason the classical tuned monopole needs a much larger high conductive ground plane than is needed for the CFA to maintain a high level of efficiency. This is a clear indication of Maurice C Hately's controversial PVS technology that he developed from his analysis of the near field effects around the classical half wave dipole.^[3]

It was concluded that the CFA worked slightly better than the equivalent 1/4 wave vertical monopole (When situated on the platform).^{[4] [5]}

The CFA used in the Silsden tests — an 8m high CFA — is approximately 1/6 the height needed for the equivalent 1/4 wave monopole (1593 kHz = 188m wavelength, 1/4 wavelength = 47m, CFA height is 8m). This shows that the original claim for the CFA — having an equal performance for 1/10 the height of a conventional 1/4 wave monopole — is not correct; but still an impressive size to performance ratio has been shown.^{[4] [5]}

Even on a 5m platform, the overall height of the antenna system (13m) is only around 25% the height of a 1/4 wave monopole (47m), with slightly better performance. However, the comparison is spurious because simpler medium-wave broadcast antennas than either of these are already in common use and do not require to be placed on a massive structure to work efficiently.

• 

  Typical test CFA in-situ on platform.

References

1. ^ Stone, J.L. (2006). "Whatever Happened to the commercial CFA?". Antennex. http://www.antennex.com/Stones/st0806/ant_prop.html#whatever_happened. Retrieved 2008-02-05. 
2. ^ G.H.Brown, R.F.Lewis, and J.Epstein (1937). "Ground Systems as a Factor in Antenna Efficiency". IRE. http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1686419. Retrieved 2011-01-24. 
3. ^ F.M. Kabbary, M. Khattab, and M.C. Hately (1997). "Extremely small high power MW broadcasting antennas". IEE. http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=IEECPS0019970CP447000421000001&idtype=cvips&gifs=yes. Retrieved 2011-01-24. 
4. ^ ^{a b} CDL/KAT and Arqiva Ltd. (2010). "CDL/KAT and Arqiva Ltd. Full Silsden test reports". CDL/KAT and Arqiva Ltd.. http://www.crossedfieldantenna.com/DocLib/silsden-report.pdf. Retrieved 2011-01-14. 
5. ^ ^{a b} CDL/KAT and Arqiva Ltd. (2009). "CDL/KAT and Arqiva Ltd. test reports". CDL/KAT and Arqiva Ltd.. http://www.crossedfieldantenna.com/DocLib/silsden-short-report.pdf. Retrieved 2010-05-18. 

External links

• PDF document published by KAT & Arqiva of field test results ending 2009 (pdf)
• Kabbary Antenna Technology - KAT Company
• MM279 Planning Inquiry - Written Statement by Brian Stewart, CFA Expert Witness (pdf)
• ‘On the Crossed Field Antenna Performance’ – V Trainotti, L Dorado (pdf)
• Four Egyptian MW Broadcast Crossed-Field-Antennas (NAB99)
• Hately (GB) / Kabbary (EG) - Radio Antennas (Patent 1989)
• Hately (GB) / Kabbary (EG) - Radio Antenna (Patent 1999)
• Hately (GB) - Radio Antennas (Patent 2003)
• Kai Borui (CN) - Cone-shaped crossed field emission antenna assembly (Patent 2004)
• Stone (US) - Editorial August 2006 in international antenna magazine