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(11) | EP 0 074 613 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Ridge waveguide-to-microstrip line transition for high frequency amplifier |
| (57) The ridge waveguide-to-microstrip line transition for an amplifier (4) connects a
microstrip circuit (30) with a ridge waveguide (22) having a waveguide body (22')
and a ridge (22H). This transition has a simple construction and comprises bias supply means for supplying
the amplifier with a d.c. bias voltage, and a thin layer (26) of an insulating means
interposed between said waveguide body (22') and the ridge (22") to block the supply
of said d.c. bias voltage to said waveguide body (22'). The ridge (22") may be provided with means (23 to 25) for connecting it with said bias supply means, said connecting means (23 to 25) extending throughout said insulating means (26) to project from said waveguide body (22'). |
[0001] The present invention relates to ridge waveguide-to-microstrip line transitions and, more particularly, to a ridge waveguide-to-microstrip line transition for an amplifier of the type which uses a field effect transistor (FET) or the like.
[0002] Generally, a waveguide to-coaxial line transition or a ridge waveguide-to-microstrip line transition is employed to supply an FET amplifier with a microwave signal coming in through an antenna. Such a transition is required to prevent a d. c. bias voltage to an FET or like amplifier from flowing into the waveguide. This requirement has been met in prior art waveguide-to-coaxial line transitions by the use of a circulator or a chip capacitor, as disclosed in U. S. Patent 4,152,666 issued on May 1, 1979. For a ridge waveguide-to-microstrip line transition, on the other hand, it has been customary to install a chip capacitor in a microstrip line or, as taught by Yatsuka et al. in "Millimeter-wave IC Components using Fine Grained Alumina Substrate" (1980 IEEE MTT-S International Microwave Symposium Digest, pp. 276-278, particularly Figure 6), to use a microstrip line as a coupling line. However, the use of a chip capacitor for blocking a d. c. voltage results in reflection or the like due to electric discontinuity or mismatching which would occur in a position where the capacitor is located. The use of a coupling line is objectionable in that the coupling line must be designed very small in the frequency band of several tens of GHz, making its production difficult. Additionally, these implements commonly require a strip line for the supply of a d. c. bias voltage, apart from the microstrip line for signal transmission. The strip line for the d. c. bias supply would invite mismatching as the chip capacitor.
[0003] It is an object of the present invention to provide a ridge waveguide-to-microstrip line transition for an amplifier, which is simple in construction and has desirable characteristics.
[0004] In accordance with the present invention, there is provided a ridge waveguide-to-microstrip line transition for an amplifier, which connects a microstrip circuit with a ridge waveguide which has a waveguide body and a ridge, comprising a bias supply means for supplying the amplifier with a d.c. bias a thin layer of an insulating means interposed between the waveguide body and the ridge to block the supply of the d. c. bias voltage to the waveguide body.
[0005] The present invention will be described in detail with reference to the accompanying drawings.
[0006]
Figure 1 is a diagram showing an example of prior art connections of a ridge waveguide-to-microstrip line transition and an FET amplifier;
Figure 2 is a diagram showing a ridge waveguide-to-microstrip line transition embodying the present invention;
Figures 3A and 3B show in plan and side elevation, respectively, a practical structure of the transition indicated in Figure 2;
Figure 4 is a diagram showing another embodiment of the present invention;
Figures 5A and 5B show in plan and side elevation, respectively, a practical structure of the transition indicated in Figure 4;
Figures 6A and 6B are graphs representing return loss to frequency characteristics of ridge waveguide-to-microstrip line transitions with and without a spacer, respectively; and
Figures 7A and 7B are graphs representing insertion loss to frequency characteristics of ridge waveguide-to-microstrip line transitions with and without a spacer, respectively.
[0007] Referring to Figure 1, a microwave signal coming in through an antenna (not shown) and having a frequency of several tens of GHz, for example, is coupled to the input of a ridge waveguide-to-microstrip line transition 1. In detail, the microwave signal is fed to the input of a ridge waveguide 2 which is made up of a waveguide body 2' and a ridge 2". Connected between the ridge waveguide 2 and a microstrip circuit 3, the transition 1 serves to convert the input microwave signal from a waveguide transmission mode to a microstrip line transmission mode. The waveguide 2' is directly connected to the ridge 2". The microstrip circuit 3 comprises a strip line 8 for signal transmission, a strip line 8' for the supply of a d. c. bias voltage and an input matching circuit (not shown), all of which are formed on a substrate of alumina or the like. The strip line 8 includes a coupling line 8" adapted to block a d- c. voltage. The strip line 8 is connected at one end with the ridge 2" and at the other end with a terminal 11, that is, the gate of an FET amplifier 4. With this arrangement, the microwave signal processed by the transition 1 is coupled to the gate of the FET amplifier 4 via the strip line 8. The FET amplifier may be replaced by any other type of high frequency amplifier, if desired.
[0008] A gate bias voltage circuit 6 is connected with a terminal 12 of the microstrip circuit 3 so as to supply the gate of the FET amplifier 4 with a d. c. bias voltage via the strip lines 8' and 8. The coupling line 8" prevents this d. c. bias voltage from being grounded through the ridge 2".
[0009] The FET amplifier 4 amplifies the microwave signal and delivers its output to a terminal 13 of a microstrip circuit 5. The microstrip circuit 5 comprises an output matching circuit (not shown), a strip line 16 and a coil 9, all of which are formed on a substrate. The amplified microwave signal is fed through the strip line 16 to a terminal 14 which connects to the following RF signal processing circuit (not shown). A drain bias voltage circuit 7 is connected with a terminal 15 of the microstrip circuit 5 to supply a d. c. voltage to the drain of the FET amplifier 4 via the coil 9 and strip line 16. The source of the FET amplifier 4 is grounded.
[0010] As previously pointed out, such a circuit arrangement is not acceptable in that production of the coupling line 8" is difficult and in that the strip line 8' for d. c. voltage bias brings about mismatching.
[0011] A primer feature of the present invention is, as will become apparent later, that a thin spacer of insulator intervenes between the waveguide and the ridge of a ridge waveguide in order to intercept the gate bias voltage for an FET amplifier. A second feature is that the ridge is supplied with a d. c. bias voltage from the outside of the ridge waveguide to prevent mismatching in a microstrip circuit.
[0012] The ridge waveguide-to-microstrip line transition shown in Figure 2 has both the first and second features stated above. It will be described with reference to Figures 3A and 3B as well.
[0013] In Figure 2, a microwave signal is coupled to an input 10 of a ridge waveguide-to-microstrip line transition 21 which is interposed between the ridge waveguide 22 and a microstrip circuit 30. As best shown in Figures 3A and 3B, the ridge waveguide 22 includes a waveguide body 22', a ridge 22" which includes a bolt 24, a nut 25 and a metallic terminal plate 23, for the supply of a gate bias voltage, a spacer 26 made of an insulating material (e.g. 0.05 mm thick polyester sheet), and a shaped piece of insulating resin .27. The spacer 26 sets up d. c. insulation between the waveguide body 22' and the ridge 22" but allows a microwave signal to pass therethrough. The resin 27 electrically insulates the bolt 24, nut 25 and terminal plate 23 from the waveguide 22'.
[0014] As shown in Figures 3A and 3B, the microstrip circuit 30 comprises a microstrip line 31 for signal transmission, a microstrip line 32 for grounding and an input matching circuit (not shown), all of which are formed on the surfaces of a substrate 30' made of alumina. A ribbon metal line 28 connects the ridge 22" with one end of the microstrip line 31. The other end of the microstrip line 31 is connected to the gate 34 of the FET amplifier 4. The source of the FET amplifier 4 is connected to the waveguide body 22' and, therefore, to the ground, while the drain 35 is connected to the microstrip circuit 5 as in the circuitry shown in Figure 1. As also shown in Figures 3A and 3B, the microstrip circuit 30 is made up of a substrate 5' made of alumina, a strip line 16 for signal transmission, a strip line 17 for grounding and an output matching circuit (not shown}.
[0015] In the converter described above, a microwave signal applied to the input 10 is fed to the FET amplifier 4 by way of the ridge 22', ribbon metal line 28 and microstrip line 31. A d. c. bias voltage from a gate bias voltage circuit 6 is fed to the gate of the FET amplifier 4 through the terminal plate 23, nut 24, ridge 22", ribbon metal line 28 and microstrip line 31 in succession.
[0016] It will thus be seen that the microstrip circuit 30 in the circuitry of Figure 2 does not need the coupling line 8" or the bias strip line 8' as indicated in Figure 1, because the spacer 26 blocks a d. c. voltage while the bias voltage is fed through the ridge 22". This renders the transition readily producible and excellent in electrical characteristic s.
[0017] Referring to Figure 4, there is shown another embodiment of the present invention which is furnished only with the first feature in order to promote far easier production.
[0018] The ridge waveguide-to-microstrip line transition 51 shown in Figure 4 includes, as indicated in Figures 5A and 5B, a waveguide body 52', a ridge 52" and a spacer 53 made of an insulating material. The waveguide body 52', therefore, is insulated from the ridge 52" against a d. c. voltage while the microwave signal is coupled through the spacer 53. As shown in Figures 5A and 5B, a microstrip circuit 60 comprises a substrate 60' made of alumina, a microstrip line 61 for signal transmission, a strip line 62 for connection, a strip line 63 for a d. c. bias terminal, and a grounding strip line 64. The ridge 52" is connected with one end of the microstrip line 61 by a ribbon metal line 54. The other end of the microstrip line 61 is connected with the gate 34 of the FET amplifier 4. The output of the bias voltage circuit 6 is coupled to the strip line 63 and the d. c. voltage is supplied to the gate 34 of the FET amplifier 4 via the strip lines 63, 62 and 61. Yet, the d. c. voltage is prevented by the spacer 53 from reaching the waveguide body 52 and, therefore, to-the ground. The rest of the construction and operation of this circuitry will be apparent from the foregoing description.
[0019] Curves shown in Figures 6A and 6B represent return loss vs. frequency characteristics actually measured with circuitries of the type shown in Figure 2 with and without a 0.05 mm thick polyester sheet. Curves shown in Figures 7A and 7B, on the other hand, indicate insertion loss vs. frequency characteristics measured under the same conditions as the curves in Figures 6A and 6B. It will be clear from these curves that the return loss and insertion loss are quite negligible and, additionally, the presence and absence of the spacer does not cause any appreciable difference in characteristics.
1. A ridge waveguide-to-microstrip line transition (21;51) for an amplifier adapted
to connect a microstrip circuit (30;60) with a ridge waveguide (22;52) having a waveguide
body (22';52') and a ridge (22";52") comprising bias supply means for supplying the
amplifier with a d.c. bias voltage, and a thin layer (26;53) of an insulating means
interposed between said waveguide body (221;52') and said ridge (22"; 52") to block the supply of said d.c. bias voltage to said
waveguide body (22';52').
2. A ridge waveguide-to-microstrip line transition as claimed in Claim 1, in which
said ridge (22") is provided with means (23 to 25) for connecting said ridge with
said bias supply means, said connecting means (23 to 25) extending throughout said
insulating means (26) to project from said waveguide body (22').