US 3276019 A
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Sept. 27, 1966 J. D. FACKLER 3,276,019
COMBINED SEQUENTIAL BEAM SWITCHER AND DUPLEXER USING MICROWAVE CIRGULATORS Filed Feb. 11, 1964 ANTENNA ANTENNA 14 25 DIODE f DIODE RECEIVER 4: SWITCH SWiTCH 3| [ll 7( TRANS- DIODE MITTER SWITCH ANTENNA I TIMNG E RING 42 45 44 COUNTER LJ E PULSE AND GEN DRIVERS M DIODE ANTENNA [31 [14 13 32 ANTENNA TRANS- MITTER DIODE SWTCH ANTENNA v 1 RECEIVER RING COUNTER PULSE GEN AND DRIVERS I NVENTOR. JOHN D FACKLER BYXW ATTORNEY.
Unite States Patent 3,276,019 COMBINED SEQUENTIAL BEAM SWITCHER AND DUPLEXER USING MICROWAVE CIRCULATORS John D. Fackler, Bedford, N.Y., assignor to General Precision, Inc, a corporation of Delaware Filed Feb. 11, 1964, Ser. No. 344,045 3 Claims. (Cl. 343-475) This invention relates generally to radio equipment employing successively energized antennas each for both transmitting and receiving, and particularly to a novel arrangement for performing the dual functions of duplexing and antenna beam switching.
It is believed that the invention will have its principal application in connection with arerial navigation systems using several successively energized antennas for generating beams pointing in different directions and/ or generating beams having different shapes. In such systems it has been customary to provide a duplexer having three terminals connected respectively to the transmitter, the receiver and the antennas. The antenna terminal has been connected to the various antennas through mechanical or ferrite switches operated in the desired sequence. Such an arrangement, while satisfactory, has certain disadvantages. If mechanical switches are used they are subject to wear, they require a considerable length of time to operate, and also require a substantial amount of power for their operation. If ferrite switches are used it is found that the field strength applied is critical, that large amounts of power are required to perform the switching operation at high frequency, and that the insertion loss is not constant because it is related to the field strength.
It is a general object of the present invention to provide an improved duplexing and beam switching arrangement.
Another object is to provide a switching system which may be operated at high speed with very small amounts of power.
Another object is to provide a duplexer and beam switching arrangement in which the voltage standing wave ratio at the receiver is very low.
Briefly stated, the invention uses a multi-armed microwave circulating device of the kind in which energy entering any arm passes through the device in a predetermined direction and out the next arm. The transmitter is connected to one arm. The various antennas are connected to successive arms next adjacent to the transmitter while the receiver is connected to the last arm. In the path between each antenna and the circulator there is interposed a radio frequency diode switch. Each switch is selectively actuatable to be either conductive or reflective to microwave energy. An energizing circuit controls the switches so as to render one of them conductive at a time in succession while the others are rendered reflective. Thus energy from the transmitter passes through the circulator, that that antenna whose associated switch is conductive to microwave energy, is radiated, reflected, and a portion returned to the same antenna and then through the circulator to the receiver.
For a clearer understanding of the invention reference may be made to the following detailed description and the accompanying drawing, in which:
FIGURE 1 is a block diagram of one embodiment of the invention; and
FIGURE 2 is a block diagram of another embodiment of the invention.
Referring first to FIGURE 1 the invention is shown as applied to a self-contained Doppler radar navigation system comprising a transmitter 11, a receiver 12 and three antennas 13, 14 and 15. In this system it is required that the energy from the transmitter be passed for a predetermined time interval to the antenna 13 which radiates the energy and receives it after reflection. The reflected "ice energy is passed to the receiver 12. During a succeeding interval, energy is transmitted from and reecived by the antenna 14. Finally, the antenna 15 is activated for a similar period of time after which the cycle is repeated. The receiver 12 utilizes the information contained in the reflected echos in a manner not here pertinent to derive information useful in navigation. The present invention is directed to the problem of duplexing, that is, the use of the same antenna for both transmitting and receiving, and to the problem of beam switching, that is, activating the three antennas sequentially. The transmitter 11 is connected to a microwave circulator 16 having three arms 17, 18 and 19, the arm 17 being connected to the transmitter. The circulator 16 is of the kind in which microwave energy entering the circulator by any arm is transmitted through the circulator in a predetermined direction as indicated by the arrow and leaves by the next adjacent arm. The circulator 16 may be any of several commercially available models preferably one operating on the principle of rotation of the plane of polarization by a ferrite element subjected to a magnetic field.
The arm 18 of the circulator 16 which is most remote from the transmitter 11 is connected to the receiver 12. The arm 19 is connected to an arm 21 of a circulator 22 similar to the circulator 16. The circulator 22 is provided with the previously mentioned arm 21 and also with arms 23 and 24. The latter is connected to a radio frequency diode switch 25 which in turn is connected to the antenna 15. The arm 23 is connected to an arm 26 of another similar circulator 27 having in addition to the arm 26 two arms 28 and 29. These arms are connected to antennas 14 and 13 through radio frequency diode switches 31 and 32, respectively. All of the connections so far recited are microwave transmission paths such as coaxial lines or waveguides.
The radio frequency diode switches 25, 31 and 32 may be any of several commercially available models. Each switch preferably comprises a resonant cavity such as a section of rectangular waveguide provided with a tuning post and across which is connected a diode. With the diode biased in the forward direction so as to pass current the switch passes radio frequency energy with very little attenuation. When the diode is reversed biased, radio frequency energy is blocked and the switch reflects nearly all of the incident power. Such switches require very little power for their operation and may be operated at very high speeds.
A timing pulse genera-tor 35 generates a series of narrow timing pulses 36 which are applied to a waveform generating circuit 37 such as a ring counter with suitable drivers. The latter circuit generates three series of rectangular voltage waves 41, 42 and 43 as shown. Each has a positive going portion for one-third of a cycle and a relatively negative portion for the remaining two-thirds of each cycle. The three waveforms are out-of-phase with each other as shown. The waveforms 41, 42 and 43 are applied through conductors 44, 45 and 46 to the diode switches 32, 31 and 25, respectively. Each switch is thereby rendered conductive to microwave energy during the positive portion of its associated waveform and is rendered reflective to microwave energy during the negative portion. Thus each switch is conductive one-third of the time and the various switches are conductive in successive time intervals.
In operation, microwave energy from the transmitter 11 passes through the arm 17 to the circulator 16 in the direction indicated by the arrow and leaves by the arm 19. It then travels successively through the circulator 22 and the circulator 27 to the arm 29 and thence to the diode switch 32. When this switch is forward biased the microwave energy passes through the switch 32 to the antenna 13 and, after reflection, passes back through the antenna 3 13 and the switch 32 to the circulator 27. It next travels to the arm 28 but at this time the diode switch 31 is re flective so that the energy passes back through the circulator 27 and through the arms 26 and 23 to the circulator 22. The diode switch 25 is also reflective at this time so that the energy passes through the arms 21, 19 and 18 to the receiver 12. During the next interval the diode switch 31 is conductive so that the antenna 14 is active and in the final interval the diode switch 25 is conductive and the antenna 15 is active. The cycle is then repeated.
Considering the three circulators 16, 22 and 27 as a unit, it is noted that there are a total of five external connection arms 17, 29, 28, 24 and 18, that is, arms which are connected to external components. Finally, assuming the direction of energy flow as indicated by the arrows, the arm 29 is next adjacent to the transmitter; next in succession are arms 28 and 24-; and finally, arm 18 is the arm most remote from the arm 17. It is also to be noted that additional antennas could be accommodated by providing an additional circulator and diode switch. Referring now to FIGURE 2 there is shown an embodiment of the invention in which the three circulators 16, 22. and 27 have been replaced by a single circulator 51 having five arms 52, 53, 54, 55 and 56. The transmitter 11 is connected to the arm 52 while the various antennas and diode switches are connected to the adjacent arms 53, 54 and 55 respectively. The receiver is connected to the most remote arm 56. The embodiment of FIGURE 2 operates in substantially the same manner as the embodiment of FIGURE 1.
In both of the embodiments illustrated phasing problems of the various switches are minimized. The physical distance of each switch from the circulator is unimportant as far as the switching operation or discontinuities in the transmission path are concerned. It may be preferred in some cases to make the distances from the circulator the same in order that the phase of any leakage power may be the same. It is to be noticed that the transmission loss is the same with respect to all of the antennas because the total path length from the transmitter to each antenna and to the receiver is the same. Additionally, it has been found that the described arrangement provides a very low voltage standing wave ratio in the receiver.
Although two preferred embodiments have been described for illustrative purposes, many modifications will occur to those skilled in the art. It is therefore desired that the protection afforded by Letters Patent be limited only by the true scope of the appended claims.
What is claimed is:
1. A combined duplexer and switching system, compris- 111g,
microwave energy circulating means including a plurality of external connection arms for transmitting microwave energy entering any arm through a portion of said means in a predetermined direction and out by the next succeeding arm,
a source of microwave energy connected to one of said arms,
a plurality of antennas connected to successive arms next adjacent to said one arm,
a receiver connected to that arm most remote from said source,
a plurality of radio frequency diode switches one interposed between each antenna and said circulating means,
said switches each being selectively actuable to be conductive or reflective to incident microwave energy, and
cyclically operating means for rendering each switch in succession conductive and the remainder of said switches reflective.
2. A combined duplexer and switching system, comprising,
first, second and third microwave circulators each having first, second and third arms,
each of said circulators being for transmitting microwave energy entering by any ar-m through a portion of said circulator and out by the next adjacent arm,
the direction of transmission being from said first to said second arms, from said second to said third arms and from said third to said first arms, 7 v
a source of microwave energy connected to said first arm of said first circulator,
a receiver connected to said third arm of said first circulator,
said second arm of said first circulator being connected to said first arm of said second circulator,
said second arm of said second circulator being connected to said first arm of said third circulator,
three radio frequency diode switches connected to said second arm of said third circulator, said third arm of said third circulator and to said third arm of said second circulator,
each of said switches being selectively actuable to be conductive or reflective to incident microwave energy,
three antennas, one connected to each of said switches,
control means for rendering each switch in succession conductive and the remaining two switches reflective to microwave energy.
3. A combined duplexer and switching system, comprising,
a microwave circulator having first, second, third, fourth and fifth arms,
said circulator being for transmitting microwave energy entering by any arm through a portion of said circulator and out by the next adjacent arm,
the direction of transmission being from any arm to the next higher numbered arm and thence to the first,
a source of microwave energy connected to said first arm,
a receiver connected to said fifth arm,
three radio frequency diode switches, one connected to each of said second, third and fourth arms,
each of said switches being selectively actuable to be either conductive or reflective -to incident micro-wave energy,
three antennas, one connected to each of said diode switches, and
cyclically operating means for rendering said switches conductive to microwave energy one at a time in succession and for simultaneously rendering the other two switches reflective.
References Cited by the Examiner UNITED STATES PATENTS 9/1959 Heidester 343876 X 5/1962 Ring 3331.1