Jack Ramsay, who has written extensively in this field, discusses in this issue thecontributions of Oliver Lodge in "quasi-optics."

lodge On Quasi-Optics"Sir Oliver Joseph Lodge (1851-1940) was 2. Measurement of Reflection Coefficients their length ... their theory is worked out.

the originator of the adjective "quasi- Using his spark transmitter, coherer More interest attaches to polarization,optical" for those microwave techniques detector and the waveguide antennas double refraction and dispersion experi-which simulate optical phenomena. He s, ot "himself demonstrated quasi-optical experi- Lodge set up various sheets of material ments.ments at his memorial lecture on "The and radiated microwaves at 450 to the 6. Simulation of the Nicol Prism Polarim-Work of Hertz and his Successors" in 1894. sheets. On the receiving galvanometer he eter usi;ig Wire GridsLodge was especially familiar with Hertz' measured the reflection. Numbers werework as he had translated Hertz' papers for obtained for window glass, a drawing The transmitter and receiver waveguidepublication in "Nature," and admired his board, a wet towel, lead foil, tin foil, and antennas were fitted with polarizationquasi-optical experiments. sheet copper. Even a human body was filters made of copper wire grids, and

used as a target too! The reflection co- arranged to be cross-polarized. The inser-We think it worthwhile to give a note onOliver Lodge in view of the recent revival of efficient was second to the lowest-the tion of a third grid, with its wires at 450

O >Qq ~~~~~~~~betweenthe two crossed grids, restoredinterest in "quasi-optics," which is now glass."some of the obliterated effect" due togenerating new trends and techniques. 3. Measuremenzt of Refraction by a Prism t i c

Lodge is peculiarly suited to be the father of the initial cross-polarization. This wastechniques which are partly electrical and The parain prism was about a cubic Hertz' famous analog experiment of thepartly optical, for he made several contribu- foot in volume and had angles of 750, 600 nicol, repeated by Lodge at a shortertions of a fundamental character to the hy- and 450. Refraction was demonstrated. wavelength.brid subject. He devised and named the 4. Focusing by a Leos."coherer," which was a point contact 7. Demonstration of Bi-ewster Atglerectifier. He made the first waveguide In his 1894 lecture Lodge demonstratedradiators by enclosing a spark gap in a with a 9 inch glass lens which he first set Lodge used the largest face of histube with one end open. He was an au- up optically by the light of a taper. The paraffin prism as a dielectric interface,thority on resonance and invented "tuning." increase in output at microwaves due to and using the transmitter, receiver, andHe made resonant cavities with radiating the lens was demonstrated. In 1889, how- grids, showed that "when light is re-irises. He made the first microwave lens ever, he had made a 1-meter square lens flected from the boundary of a trans-using pitch as the material. of pitch weighing 336 pounds. The wave- parent substance at the polarizing angle,

For the quasi-optical experiments Lodge length then used was 101 cm and the re- the electric vibrations of the reflectedalso constructed reflectors of different ma- sults were less successful than at shorter beam are perpendicular to the plane ofterials, made a paraffin prism, an Arago wavelengths. reflection." With the electric vibrationdisc, a diffraction grating, polarization perpendicular to the plane of incidence,grids, and a zone plate. Thus he had the 5. Demonistration of Quasi-Optical Dif- "plenty of radiation" was reflected; withequipment for the quasi-optics-spark fraction the vibration parallel to the plane,generators, point-contact rectifiers and For the "bright spot" experiment an "hardly anything" was reflected.galvanometers, wave-launchers in the form 18-inch circular copper disc was used Many other followers of Hertz were toof waveguide and lens antennas and a successfully. The diffraction grating had make even more striking "quasi-optical"variety of components based on the optical copper strips 2 inches broad and 2 inches exeren Lode made asconvicingdevices. experiments but Lodge made a convincingapart, but results were not satisfactory start.The quasi-optical experiments demon- due to room reflections. The zone plate,

strated by Lodge included the following: of tin foil on glass, did not work verywell either (Lodge's contemporary, Reference

1. Radiation from a spark-excited wave- Chunder Bose, however, could measure Lodge, 0. J., "Signalling Across Spaceguide to a waveguide receiving altenna wavelengths accurately at microwaves Without Wires," published by The Elec-containzing a coherer. using a diffraction grating). trician Printing and Publishing Company,The wavelengths used were 3 inches Lodge's attitude to the classical dif- London, England, 1899.

and 7 inches. The directivity of the wave- fraction is strange today. He said "Reallyguide antennas was shown. Attenuation there is nothing of much interest in dif- A complete bound set of our ninth series ofof the transmitter was demonstrated by fraction effects, except in the demnonstra- articles is available on request. Write tostopping down itS waveguide radiator by toso h ae n h esr f Hrl ehmna l o orstirises. In a polarization experiment the toso h ae n h esr f Hrl ehmna I o orstcoherer was placed axially instead oftransversely and "had the advantage ofdoing away with the polarizing, or rather _analyzing, power of a crossway tube." fLodge had discovered TB and TM waves A i 1 1 - /by accident. Note he also used "inte- /1L.grated antennas" as we now call them. cuTLER-HAMMER ______/OIV/SJO//_________________

IEEE spectrum APRIL 19665