United States Patent (19) 11 Patent Number: 4,503,404 Racy 45) Date of Patent: Mar
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United States Patent (19) 11 Patent Number: 4,503,404 Racy 45) Date of Patent: Mar. 5, 1985 54 PRIMED MICROWAVE OSCILLATOR cludes a single tank conductor (16) coupled to a cou 75 Inventor: Joseph E. Racy, Hudson, N.H. pling conductor (17) by an interdigitated coupler (26). The coupling conductor (17) is connected to the cath 73 Assignee: Sanders Associates, Inc., Nashua, ode of an IMPATT diode (22) which is triggered by the N.H. application of a back-biasing trigger pulse that biases it 21 Appl. No.: 473,173 into its negative-resistance region. When a keying pulse is applied to the IMPATT diode (22), the diode couples 22 Filed: Mar. 7, 1983 power through the interdigitated coupler (26) to the 51) Int. Cl. .......................... H03B5/00; H03B 7/00 tank circuit (16) to cause oscillations that are initially in 52 U.S. Cl. ............................... 331/96; 331/107 SL; phase with any incoming signals, but the frequency of 331/107 G; 330/287 the oscillations is determined by the configuration of 58 Field of Search ................. 331/55, 56, 96, 107 G, the tank circuit (16), not by the frequency of the incom 331/107 DP, 107 SL, 173; 330/286, 287 ing signal. If the incoming signal is near enough to the 56) References Cited resonant frequency, and if the duration of the keying pulses is short enough, the output of the primed oscilla U.S. PATENT DOCUMENTS tor appears to a band-limited receiver to be an amplified 4,056,784 11/1977 Cohn ................................... 330/287 version of the input signal. In another version, the am 4,259,647 3/1981 Chang et al. ............. 331/107 SL X plifying element is a GaAs FET (66) with a tank con Primary Examiner-Eugene R. LaRoche ductor (70) connected to its gate. The tank conductor is Assistant Examiner-Robert J. Pascal in turn coupled to a coupling conductor (62) for posi Attorney, Agent, or Firm-Louis Etlinger; Richard I. tive feedback at the resonant frequency of the tank (70). Seligman 57 ABSTRACT A primed oscillator for microwave amplification in 11 Claims, 4 Drawing Figures U.S. Patent Mar. 5, 1985 Sheet 1 of 2 4,503,404 2 - 777-77 77 . O - lyr a Nt I-V4)4-4444 4. FG. TO HD ANTENNA FG, 4. U.S. Patent Mar. 5, 1985 Sheet 2 of 2 4,503.404 4,503,404 1. 2 By virtue of the coupling from the matching circuit PRIMED MICROWAVE OSCILLATOR to the tank circuit, the amplified signal from the drain terminal is fed back to the tank circuit to maintain oscil BACKGROUND OF THE INVENTION lation. In this version, there is only one resonant circuit, The present invention is directed to microwave oscil so tuning is necessary for only one. The transistor lators. It has particular application to primed oscillators power voltage appears on the matching circuit, but it is employing low-impedance active elements. low enough that it can be blocked by an ordinary micro Primed oscillators are often used to provide high wave capacitor. levels of amplification for microwave signals. When the The invention is defined more specifically in the primed oscillator is activated, it will begin oscillation in 10 claims. phase with an incoming signal if the amplitude of the BRIEF DESCRIPTION OF THE DRAWINGS signal is sufficient and the coupling to the amplifying These and further features and advantages of the device is great enough. One of the difficulties encoun present invention are described by reference to the tered in the use of primed oscillators is that the impe 15 accompanying drawings, in which: dance of the amplifying element typically differs greatly FIG. 1 is a side elevational view, partly in section, of from the impedance of the antenna, and steps must be a stripline oscillator that follows the teachings of the taken to achieve the requisite coupling. present invention; The matching of impedances has been accomplished FIG. 2 is a plan view of the oscillator of FIG. 1 with by employing separate resonant circuits with different 20 the upper dielectric and ground-plane layers removed impedances. However, this has presented the problem to expose the intermediate conductor layer; that the two circuits have to be tuned in tandem during FIG. 3 is a plan view of another embodiment of the manufacturing. This tuning operation complicates the invention with the upper dielectric and ground-plane manufacturing process. layers removed to expose the intermediate conductor SUMMARY OF THE INVENTION 25 layer; and FIG. 4 is a schematic diagram of the oscillator of According to one version of my invention, a planar FIG. 3. transmission-line conductor is connected at one end to an amplifying element such as an IMPATT diode, DESCRIPTION OF THE PREFERRED which transfers power onto the conductor to cause 30 EMBODEMENTS oscillations at the resonant frequency of the conductor. FIG. 1 is a side view of the oscillator showing its The resonant conductor, which thus acts as the tank stripline construction. The oscillator 10 includes upper circuit for the oscillator, has a characteristic impedance and lower ground-plane conductors 12 and 14, respec that is relatively close to that of the amplifying device tively, between which generally planar conductors 16 for efficient coupling of power into the tank circuit. 35 and 17 are disposed, being separated from the ground To transfer power to a transmission line leading to an planes 12 and 14 by a dielectric layer 18. Signals travel antenna, a second planar transmission-line conductor is ing to and from an antenna (not shown) propagate by coupled to the first conductor. It is a resonant line so way of a coaxial cable connected by a coaxial connector that it can be used as an impedance transformer, and its 20 to ground plane 14 and intermediate conductor 16. characteristic impedance is different from that of the An IMPATT diode 22 is connected between ground oscillator tank conductor, having such a value that the plane 14 and intermediate conductor 17, and triggering second conductor can readily achieve an approximate pulses for the diode 22 are applied to it by way of a match of the characteristic impedance of the antenna conductor 24 and intermediate conductor 17. transmission line to the impedance of the diode. The layout of the intermediate conductors 16 and 17 The coupling of the two resonant conductors is pref. 45 is depicted in FIG. 2. Conductor 16 is elongated and erably produced by both edge coupling and capacitive relatively narrow. Its width ordinarily is chosen to coupling for transfer of power between the antenna and minimize its dissipation, i.e., maximize its Q. This nar the oscillator. The coupling between the two resonant row width, together with its thickness and spacing from circuits is at least critical. As a result, the oscillator can the ground planes 12 and 14, results in a relatively high be tuned during manufacturing by adjusting only one of 50 characteristic impedance. Because of the relatively high the resonant circuits, e.g., by adjusting the length of one impedance, conductor 16 can be tapped reliably to of the conductors. match its input impedance to the characteristic impe A different version of my invention also uses a planar dance of the coaxial feed line from the antenna. On the transmission-line conductor as a tank circuit. The tank other hand, conductor 17 is relatively wide, so it and circuit is coupled to a transistor control terminal, such 55 ground planes 12 and 14 form a transmission line having as the gate terminal of a field-effect transistor in a com a lower characteristic impedance. In the middle of its mon-source configuration. The tank circuit is edge cou negative-resistance region, IMPATT diode 22 has a pled to an impedance-matching circuit, which is also a negative resistance that is lower in magnitude than the planar transmission-line conductor, and which is con characteristic impedance of conductor 17 but closer to nected at one end to the transistor's amplifying ter 60 that impedance than to the characteristic impedance of minal-that is, to the drain terminal in the case of a conductor 16. common-source configuration. The characteristic impe At one end of intermediate conductor 16, which acts dance of the tank matches the input impedance of the also as an input tank circuit, is an interdigitated capaci transistor, while the matching circuit is a quarter-wave tor 26 comprising alternating fingers 28 and 30 on con line whose characteristic impedance matches the output 65 ductors 17 and 16, respectively. The capacitor 26 acts as impedance of the transistor to the characteristic impe a low-impedance coupler to the low impedance of the dance of a transmission line that leads from the match diode 22. A high impedance is presented by the other, ing circuit to the antenna. open end of conductor 16. The length of conductor 16 4,503,404 3 4. is approximately one quarter wavelength at a frequency imity of the arms of conductor 17 to the longitudinal within a range of frequencies to which the primed oscil edges 39 of conductor 16. This coupling widens the lator is intended to respond. Therefore, it acts as a reso bandwidth of the oscillator. Thus, the high degree of nant circuit. coupling, in addition to presenting a significant-ampli The center conductor of a coaxial feed line from the tude signal on conductor 17, increases the sensitivity of antenna is electrically connected to conductor 16 at a the oscillator to frequencies on the outer edge of the connection point 32 at which the impedance presented intended frequency range.