Appeal from the District Court of the United States for the Eastern District of New York.
Before MANTON, L. HAND, and SWAN, Circuit Judges.
This appeal involves the validity and infringement of the Lindenblad patent, No. 1,927,522, granted September 19, 1933, on an application filed December 24, 1928, and the Carter patent, No. 1,974,387, granted September 18, 1934, on an application filed June 11, 1930. Both are for short wave directional antennas composed of a pair or pairs of long wires, the two wires of each pair being placed at an angle to each other to form a V. Claims 9, 10, 19, and 23 of the Lindenblad patent and claims 15 and 16 of the Carter patent are in issue.
Directive radio transmission is of commercial importance where communication is regularly carried on between two or more fixed stations. The advantage of highly directive systems for point to point communication is that interference with other systems is reduced and, for a given amount of energy sent out by the transmitting station, a stronger or more reliable signal is heard at the desired receiving point. When radio waves are directed or concentrated upon a given receiver, freedom from interference follows. If the transmitter in New York concentrates its radio waves upon a receiver in a city in Central Europe, no waves or only feeble waves will travel in other directions and, as a result, other receiving stations to the north, west, or south points will not be subjected to interference. If the New York station transmits using a highly directive antenna (as Carter) which concentrates most of the 360 kilowatts of power into a bundle of rays confined within an angle of 20 degrees or less, there would be substantially the same total power concentrated within one-eighteenth of the full compass circle or nearly 18 kilowatts compressed into each one degree sector instead of only one kilowatt. Thus, much of the power that would be wasted if the waves were broadcast in all directions may be brought to bear upon a particular receiving station and the intensity of the receiving signal multiplied.
The best antenna to serve these purposes appeared in 1926 as the Marconi beam antenna. It was made up of a complex network composed of a large number of short wires. It was highly directive and expensive, costing about $100,000 to produce. It was difficult to adjust and keep in repair.
Appellant's models B and C were built in 1929. They were built of pairs of long parallel, simple wires which co-operated to give highly directional effects. They were built at a cost of $30,000 and $48,000 and were made under prior Lindenblad patents.
No successful use of any other directional wireless is referred to until antennas made under the patents here to be considered were built. The first step in the directive antenna (made as model D) under these patents was developed in the invention of Lindenblad. The primary units (like models B and C) were made of long simple wires and the antenna consisted of two such wires placed at an angle with each other to form a V. Although the Vantenna described by Lindenblad had utility, it was not adapted for commercial use until Carter's improvement had been applied for. This antenna consists of one or more pair of long, straight, unmodified wires placed at a preferred angle; when a simple V is used the antenna is bi-directional. The predominant radiation of radio waves from the antenna is in two directions, the direction determined by the line bisecting the angle between the wires. By the use of two V's properly spaced with respect to each other and fed with current in proper phase relation, unidirectional action is secured. The predominant radiation is in one direction only. The direction of the bisector of the angle between the wires is either forward or backward according to the connection used. This is the Carter patent. It was an improvement over the directive antennas which had preceded it. Its cost was $5,000 as against $30,000 for the cheapest previous types. Its directivity was equal to the Marconi beam.
Although the theory of operation of a single wire had been previously developed prior to Lindenblad and Carter, no one had found how the theory could be utilized in the solution of the problem of constructing a highly directive antenna. One of the steps in the development of Carter's patented antenna is set forth in the Lindenblad patent. A long wire V antenna is shown in fig. 2. In the antennas of each of the patents energy is fed into the antenna by transmission line through an impedance matching device, in such a manner that the energy fed to one antenna wire is of opposite fed to one antenna wire is of opposite phase to that fed to the other wire, that is, when the potential at any point on one wire is positive, that of the corresponding point on the other is negative and vice versa.
Lindenblad says that the current on the antenna wires may be in the form of standing waves, or "as a refinement" and "a further object of my invention" is in the form of traveling waves. He says that with traveling wave the sideways radiation is less than with standing waves, but the reduction of radiation in undesired directions may be obtained by other means.
Lindenblad stated nothing as to the advantages of any specific angle between the wires of his V-Antenna and as to any relation between preferred angle, wire length, and wave length. He said that the spacing between the ends of the wires, "while variable" over a long range, should be in the neighborhood of a fifth of the length which, regardless of wave lengths and wire lengths, means an angle under 12 degrees between the wires. The wire length suggested is of the order of five or ten waves long. Carter taught 12 degrees is not the most desirable angle for a V-antenna having wires of these lengths. He developed the theory of long wire V-antennas and taught how to construct them so as to secure maximum directivity by coordinating the angle wire length and wave length. He found that the use of a preferred angle for any given wire length and wave length gave an antenna which was equal or superior in directivity to any known antenna and far less costly to erect. Carter described multiple V-antennas both for preventing undesired high angle radiation, for securing further concentration in the horizontal or compass direction, and for securing unidirectivity.
Claim 10 of the Lindenblad patent is typical and will be selected in determining the question of infringement. It reads: "In combination, a transmission line, and an antenna extending longitudinally in the direction of desired radiant action connected thereto comprising a pair of open ended conductors of the order of magnitude of a number of wave lengths long which are widely spaced at the ends remote from the transmission line and energized with energy or opposite polarity, and spaced at the spacing of the transmission line at their junction therewith."
The inventor intended to get rid of standing waves and he was to accomplish it by lengthening his antenna which eliminated reflection in the antenna. It, however, made the space between the conductors too long to be practicable. His figs. 3 and 4 show the conductors bend back and forth across each other and these figures were for traveling waves only. Fig. 2 was a standing wave antenna and would need an impedance matching device unless the transmission line was very short. He expected some standing waves and thought to improve on the dipole.
Carter's claim 15 reads: "An antenna comprising a pair of relatively long conductors disposed with respect to each other at an angle substantially equal to twice 50.9 (1Claim 16 differs from claim 15 primarily in calling for "a similar parallel pair of conductors spaced at odd number of quarter wave lengths away ...