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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION. VOL. AP-33, NO. 2. FEBRUARY 1985 131

Antennas Since Hertz and Marconi

JOHN D. KRAUS, ufe fellow, ieee

MY TAIX HAS Uwee paits: first a bit of history, ihcn some things persona!, and finally a pcck into the futurę.

It was ihree centurics ago that Isaac Newton formulated his famous Law of Univcrsa] Gravitation. Because his law violated thc acccpted principlc that action-at-adistance is impossible, Newton himself was reluctant to announce it and be subjected to attack. Edmund Halley, who discovered the comet which bears Im namc. was a fricnd of Newton'* and he pcrsuadcd Newton to let lum present the law before the Royal Society. This Halley did for Newton in London in 1685 and, as Newton had anticipated. hc and liis law were attacked. When Halley’s comet comes around next year. remember what Halley did for Newton.

But by 1839, when Michad Faraday presented thc rcsults of his **Experimental Researches,” with curved lines of forcc extending tluough empty space, the world was at last rcady to embrace action-at-a-distancc.

Based on Faraday’s work, James Clerk Maxwcll umfied the theories of electricity and magnetism in a profound and elegant manner in his ‘Treatise" publislied in 1873. He postulated that light was electromagnetic in naturę and that electromagnetic wavcs of oilicr lengths were possiblc. But in thc ycars that fol-lowcd, many were skcptical of his ideas because. among other things. łus theory gavc a rclativc pcrmittivity of 81 for wuler wheieas the acccpted valuc was less Ihan two.

Tłie American Institute of Electrical Engineers (AIEE) was orgamzed 100 ycars ago, but radio was unknown and there were no antennas. X rays had not bccn discovcrcd. relativity had not bccn proposed. ncither had ąuantum theory'. Cosmic rays were unknown. therc were no airplancs and blood letting with lceches was a standard medical cuie-all. Allhough the elcctric telegraph was king. bdison*s incandescent light was making painfully slow headway against thc entrenched gas iliuminauon industry. In the United States, controvcrsy raged ovcr whether thc electiic Street car or thc horse-drawn car was better, and in England, the Red Flag Act requircd that any sclf propelled highway vchicle be prcccdcd by a inan carrying a red flag by day and a red lantcrn by night. So it was in 1884.

A few ycars earlicr thc Berlin Academy of Science had offered a prize for research on thc relation between electromagnetic forces and dielectric polanzation. Heinrich Rudolph Hertz con-sidered whether thc problem could bc solvcd with oscillations using Lcyden jars or open induction coils. Allhough hc did not pursue this problem, his interest in oscillations had been kindled, and in 1886 as professor at the Techmcal Institute in Karbruhe hc assembled apparatus we would now describe as a complete radio system with an end-loaded haif-wave dipole as transmitting antenna and i resonant square loop antenna as receiver. When

Maaułcript rcceivod Scprembcr 10. 1984.

The author ii with thc Radio Obicrvatory. 2015 Neil Aiwim, The Ohio State Uniremty. Columbus. OH 43210.

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Fig. I. Hcmnch Hcrtz^#s compłcte radio system of 1886 with eod Icoded 1/2-wavclength dipole traasmitting antcoiu (CC') and resonant loop rcceiving antenna (abed). With ioduciion coi! (A) turncd on. sparks at gap B induccd sparks at gap \f ia the rtceiving antenna. (Froin Heinrich Hertza book Electric Waves. MacMiUian. 1893.)

Fig. 2. Display of Hcrtz’s radio apparatus. Spherc loaded l/2-wavclcngth dipole and spark gap for 4 m is m foreground. Cylindrkal parabolic reflcctor with trammittmg dipole for 30 cm i% at Icft (dipole with spark gap is vcrtical on parabola focal axis). Resonant reccivu*g loop on wooden framc U rciting in&idc parabola (at right) (Photo by E C. Jordan )

sparks wcrc pioduccd at a gap at the center of the dipole, spark-ing .ilso occurred at a gap in the nearby loop. During the next two ycars, Hertz cxtendcd his experimcnts and dcmonstratcd reflcction. refraction and polarization, showing that except foi their much greater length, radio waves were one wilii liglit. Hertz turned the tide against Maxwell around. Hertz became the father of radio.

Hertz’s initial expcriments were conducted at wavelengths of about 4 m while his later work was at shorter wavclengths around 30 cm. 1 have consiructed and display herc a working icplica of Hertz's carliest 4 m system but I’m not going to firc it up because it would knock out a lot of radios and TV*s.

If a William Ptoxmirc had bccn around in Hertzb time, Hcrtz’s radio appratus might have receivcd a Goklen Fleece Awaid as a complete waste of moncy and effort a toy of absolutcly no practical value. Ycł from this simplc, fundamenta! beginning

0018-926X/85/0200-0131 $01.00 © 1985 IEEE