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INVENTOR, JIHN L, LAAA/AAIS BY . b. edgeon, (). & A4oclbau, a.u.) eur. At TORNEYS 2,839,683 United States Patent Office Patented June 17, 1958 1 2 about 33 db above that for direction 2, and a detector located at this point would thus sample the dif 2,839,683 ferent amounts of energy for the two directions of propa MCROWAVE OUPLEXER-DETECTOR gation. A small probe, placed 0.24 inch from the wave guide John C. Cacheris, Bethesda, Md., assignor to the United wall, was used to measure the frequency dependence of States of America as represented by the Secretary of the relative field intensities for the two directions of the Army propagation, and the results of the tests are shown in Application October 9, 1956, Serial No. 614,998 Figure 3. O The over-all frequency dependence of a duplexer-de 1 Claim. (CI. 250-31) tector designed for 9300 megacycles is shown in Figure 4. At the crystal detector the received signal (direction 1) (Granted under Title 35, U. S. Code (1952), sec. 266) is approximately independent of frequency, while the leakage signal from the energy transmitted in direction 2 The invention described herein may be manufactured 5 from the source is rather frequency sensitive. and used by or for the Government for governmental At 9300 megacycles the insertion loss of the signal purposes without the payment to me of any royalty transmitted through this device is 0.5 db, while the inser thereon. tion loss of the signal received at the crystal is 2.4 db. This invention is related to means for detecting micro The leakage signal, which is 31 db down from the trans waves, and is particularly related to a du 20 mitted signal entering the device can be used as the plexer detector using ferrites. - signal for a superheterodyne system. The It is an object of this invention to place ferrite slabs amplitude of the leakage signal depends upon the position at a point in a microwave guide to distort the electric of the crystal relative to the null of the field distribu field of the microwave energy passing the point so that tion. a crystal detector placed at the point may selectively 25 In the use of the device, let us assume that a signal is distinguish between energy passing the point in one di being transmitted through the guide from a source of rection as against energy flowing past the point in an energy at microwave frequency and that there is no opposite direction. received signal. The crystal detector is in the distorted The specific nature of the invention as well as other electric field and not quite at the null or weakest part of objects, uses and advantages thereof will clearly appear 30 the field, and a meter connected to the from the following description and from the accompany crystal will indicate the rectified current from the crys ing drawing, in which: tal. Now, if some of this transmitted energy is returned Figure 1 shows a portion of a rectangular wave guide to the guide from a reflector or an , the crystal is in containing ferrite slabs and a crystal detector, and with the strongest part of this returned electric field, and it will parts in plan and parts broken. 3. 5 produce a rectified current which will modulate the first Figure 2 shows a chart to indicate the distortion of the current, and the of the first current by this electric field in the above wave guide when microwave second current can be detected by conventional means. energy of a given intensity is sent through the guide in The frequency of the second current may not be the same opposite directions. as the transmitted or first current when the second cur Figure 3 shows a chart indicating the frequency de 40 rent is modified by Doppler effect. pendence of the relative field intensities for the two direc In the use of the device in the laboratory the receive tions of propagation. current may well be a considerable part of the trans Figure 4 shows a chart showing the over-all frequency mitted signal from the source when it is immediately re dependence of a duplexer-detector in the above wave flected from a reflecting means at the load end of the guide at a frequency of 9300 megacycles and with the fer guide. rite sabs in a transverse magnetic field of 1100 oersteds. The ferrite slabs shown and of the general dimensions In Figure 1, a wave guide 10 is adapted to transmit a shown worked well at the particular frequency used in microwave signal at about 9300 megacycles from a source the tests and with the magnetic field strength indicated (not shown) to an antenna in one direction of energy (but the invention is not limited to ferrite slabs of the flow, and to transmit a returned signal from the antenna 50 shapes and dimensions and to the magnetic field strength in the opposite direction of energy flow. A pair of fer indicated) for illustrative purposes. rite slabs, 11 and 12, are placed in the wave guide in It will be apparent that the embodiments shown are the manner shown, and means (not shown) are provided only exemplary and that various modifications can be to produce a magnetic field through the slabs as is indi inade in construction and arrangement within the scope cated by the letters Ha. A crystal detector 13, is placed 5 5 of the invention as defined in the appended claim. in the wave guide adjacent one of the slabs, and is con I claim: nected to conventional current indicating means (not In a transmitting and receiving system having a source shown). of microwave energy and an antenna for transmitting For the configuration shown in Figure 1, most of the and receiving microwave energy, an improved duplexer energy transmitted in one direction from the source to 60 detector comprising in combination: a section of rec the antenna goes around the crystal, while most of the tangular having a first end and a second end, received energy from the antenna is received by the microwave energy from said source being applied to said crystal. - first end, said antenna being coupled to said second end, The severe distortion of the electric field in the pres a pair of ferrite slabs having tapered ends disposed in ence of the ferrite slabs in a magnetic field of 1100 said rectangular waveguide adjacent and parallel the short oersteds, and at a frequency of 9300 megacycles, is shown in Figure 2. Energy of the same intensity was sides of said waveguide in spaced opposed relation, means sent through the wave guide in both directions, and tests producing a transverse magnetic field through said slabs were obtained by using a small probe. The dimensions for shifting a major portion of the transmitted energy to of the rectangular guide were 0.4 by 0.9 inches I. D. At 70 one side of the waveguide and for shifting a major por 0.24 inch from the side wall of the guide the relative elec tion of the received energy to the opposite side of the tric field intensity for the propagation in direction 1 is waveguide, and a crystal in said waveguide placed ad 2,889,688 3 jacent one of said slabs at a point closer to said opposite OTHER REFERENCES side such that the detected signal at the output of said Fox et al.: "Behavior and Application of Ferrite in crystal indicates a relatively small portion of the micro the Microwave Region,” Bell System Technical Journal, wave energy passing through said waveguide from said vol. 34, No. 1, pp. 5 to 101, January 1955. first end to said second end, and a relatively large por Weisbaum et al.: “A Double-Slab Ferrite Field Dis tion of the microwave energy passing through said wave placement Isolator at 11K mc,” Proceedings of the IRC, guide from said second end to said first end. vol. 44, No. 4, pp. 554-555, April 1, 1956. References Cited in the file of this patent UNITED STATES PATENTS 0. 2,649,544 Zaleski------Aug. 18, 1953