Microwave multiband filter

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  • Unlted States Patent [19] [11] Patent Number: 4,763,089 Pon [45] Date of Patent: Aug. 9, 1988

    [54] MICROWAVE MULTIBAND FILTER Primary Examiner-Marvin L. Nussbaum . Attarne , A ent, 0r FirmFlehr, Hohbach, Test, [75] Inventor: Chuck Y. Pon, Belmont, Calif. Albrittgn 8? H erb en

    [73] Assignee: Dalmo Victor, Inc., Belmont, Calif. [57] ABSTRACT

    [21] APP]- NO-I 105,899 A multiband microwave ?lter that can selectively trans - _ mit a broadband signal or any discret or combination of

    [22] Flled' oct' 8 1987 prede?ned frequency bands. The ?lter has two trans [5l] Int. Cl.4 ..................... .. H01P 1/213; HOlP l/203 mission lines, with an output port at one end of a ?rst [52] US. Cl. .................................. .. 333/202; 333/103; one of the transmission lines. A switch selectively trans

    333/ 134; 333/205 mits an input signal to one of the transmission lines. The [58] Field of Search .............................. .. 333/202-208, ?lter also has a plurality of narrowband directional

    333/1, 103-105, 110, 174, 177, 219, 221, 235, ?lters, each of which is used to transmit signals in a 246, 262, 263, 109, 126-128, 132, 134-136, 101, corresonding frequency band from one of the transmis

    175, 245, 106-108 sion lines to the other. Each directional ?lter includes at [56] References Cited least one diode for enabling and disabling the operation

    U.S. PATENT DOCUMENTS of the direction ?lter in accordance with a bias voltage applied to the diodes. By controlling the switch and

    3,503,014 3/1970 Hall et al. ........... .. .. 333/207 x applying appropriate bias "wages 1 each Ofthe diodes 4,349,799 9/1982 Blocksome et a1, _, 333/105 X the microwave ?lter can selectively transmit a broad 4,584,543 4/1986 Taylor, Jr. et al. ............... .. 333/103 band signal or any discret or combination of the fre

    quency bands transmitted by the directional ?lters. FOREIGN PATENT DOCUMENTS

    0051312 3/1985 Japan .................................. .. 333/103 4 Claims, 7 Drawing Sheets

    CONTROL LOGIC 35 I10

    POFiTi 26\\ l____________lpoF3-|-2 SPDT I I j

    N H SWITCH _ : : 30

    2o \22 1 i l l\

    PORN T : f T : f 2 f' 4 \_ o 1 o 2 | o n |

    | |

    24 I I | 1 1 | | I 1 1. _ _ _ _ _ _ _ __ _|

    POFiT 3

  • U.S. Patentv Aug. 9, 1988 Sheet 1 of 7 4,7 63,089

    CONTROL LOGIC 35 J10

    PORTI 26\ l____________|POBT2 SPDT I I 7 IN '> SWITCH _ : : 30

    2o \22 5 i a i I I _ o _ 0 I T ' l\ PORK : f1 : f2 '1' : in I

    I |

    241 I I L ______ _ _ J

    PORT 3

    FIGURE 1

    >50 60 k 49 J 59

    [1 58 [1 \ 46\ 48/47

    I: ha _ \56 1 57} _ T 54

    40 //

    44b

    52f 146 f 1

    FIGURE 2A FIGURE 25 SERIES DIODES SHUNT DIODES

  • US. Patent Aug. 9, 1988 Sheet 2 of 7 4,763,089

    PORT 1 20 |' 20 PORT 2

    @ C01 C12

    @ C12 @ C01

    PORT-3 Z0 |-| - Z0 PORT4

    f1 = lower edge of channnel

    f2 = upper edge of channel

    g1 ,92 are lowpass prototype normalized element values

    Qe = g1/m = external Q

    FIGURE 3 THREE RESONATOR DIRECTIONAL FILTER

  • 4,763,089 US. Patent Aug. 9, 1988 Sheet 3 of 7 50 0.003" DIAMETER

    IJ/ KPORTZ PORT 1\

    0

    \PORT 4 PORT 31

    FIGURE 4A

    TRANSMISSION

    S21 / DIODE BIAS OFF

    S24 DIODE BIAS ON

    824 DIODE BIAS OFF

    I

    dB

    20

    17 16 15 14 12 11

    FREQUENCY (GHZ)

    FIGURE 48

  • US. Patent Aug. 9, 1988 Sheet 5 0f 7 4,763,089

    S 21 TRANSMISSION 0

    4 ' BROADBAND MODE

    ALL DIODES BIAS OFF

    dB -

    \ BANDSTOP FILTER DIODES BIAS ON

    -20

    _3O I I I | I I I I I 7 a 9 1o 11 12 13 14 15 1e 17 1a

    FREQUENCY (GHz)

    FIGURE 6

    TRANSMISSION 0

    CH2 CH4 - CH1 CH3

    -1o

    dB

    _2O _

    _30 IIIIIII III I III 7 8 9 IO 11 12 13 14 15 16 17 18

    FREQUENCY (GHZ)

    FIGURE 7

  • US. Patent Aug. 9, 1988 Sheet 7 0f 7 4,763,089

    TRANSMISSION 0

    521 x

    ,W __ CH1 CH 2 CH 3 CH4 CH 5 CH 6 CH 7 CH 8

    1O

    dB

    20 -

    30 5

    FREQUENCY (GHZ)

    FIGURE 9

    TRANSMISSION

    -- CHANNEL 2 CHANNEL 4

    ~10

    dB

    _3O l I l M I II A I e 7 a 9 1 0 11

    FREQUENCY (GHz)

    FIGURE 10

  • 4,763,089 1

    MICROWAVE MULTIBAND FILTER

    The present invention relates generally to microwave circuitry, and particularly to microwave bandpass ?l ters.

    BACKGROUND OF THE INVENTION

    The prior art includes directional microwave ?lter circuits, but does not include multiband microwave ?lters which can selectively transmit any discrete or combination of narrowband signals without resorting to the use of single pole multi-throw switches.

    In a growing number of applications, it is necessary to be able to separate and identify many narrowband sig nals in a high density signal environment. Given the high processing speeds of currently available signal processors, microcomputers and minicomputers, such applications need multiband microwave ?lters which can switch frequency bands easily and quickly. An obvious, but inadequate, design of a multiband

    microwave ?lter is one which connects a set of band pass ?lters with two single pole multithrow switches. However, the maximum number of output ports for a multithrow switch is typically less than eight due to physical constraints, and the insertion loss of each switch is about 3 dB (decibels) at X-band frequencies. Consequently, any system with more than eight chan nels will require more than two multithrow switches which will increase the signal loss accordingly.

    It is therefore a primary object of the present inven tion to provide an multiband microwave ?lter which can selectively transmit any combination of a large number of frequency bands without resorting to the use of single pole multithrow switches. Another object of the present invention is to provide

    a multiband microwave directional ?lter which can also be used as an allpass circuit.

    SUMMARY OF THE INVENTION

    In summary, the present invention is a multiple band microwave ?lter having a plurality of narrow band directional ?lters between two transmission lines. Each of the directional ?lters can be enabled or disabled by a corresponding control signal. Also, a switch directs an incoming signal to one of the two transmission lines. If the incoming signal is coupled to a ?rst one of the trans mission lines, while all of the directional ?lters are off, the circuit acts as an allpass circuit. If the incoming signal is coupled to the other transmission line, only the frequency bands corresponding to the directional ?lters which are enabled are transmitted to an output port on the ?rst transmission line. Thus, by controlling the switch and by selectively enabling the directional ?l ters, the circuit can be used to transmit selectively a broadband signal or any discrete or combination of narrow band signals.

    BRIEF DESCRIPTION OF THE DRAWINGS

    Additional objects and features of the invention will be more readily apparent from the following detailed description and appended claims when taken in con junction with the drawings, in which:

    FIG. 1 is a block diagram of a diode switched ?lter bank incorporating the present invention. FIGS. 2a and 2b depict two microwave directional

    ?lters which can be used in the present invention.

    5

    15

    20

    35

    45

    55

    60

    65

    2 FIG. 3 is a schematic representation of a single three

    resonator directional ?lter. FIG. 4a depicts a single switchable resonator, and

    FIG. 4b shows transmission response measurements made using this resonator. FIG. 5 is depicts a four channel, 8 to 18 GHz switch

    able ?lter bank prototype. FIG. 6 shows the transmission frequency response of

    the ?lter in FIG. 5, in broadband mode, and FIG. 7 shows the transmission response for each channel with the other three channels off. FIG. 8 depicts an eight channel, 6 to 10 GHz switch

    able ?lter bank. FIG. 9 depicts the individual channel transmission

    responses of the ?lter bank in FIG. 8, and FIG. 10 depicts the transmission response with channels 2 and 4 on.

    DESCRIPTION OF THE PREFERRED EMBODIMENT

    Referring to FIG. 1, there is shown a circuit sche matic of a diode switched ?lter bank which can be used to transmit selectively a broadband signal or any dis crete or combination of narrow band signals centered at frequencies fl to fn while maintaining a low input VSWR (voltage standing wave ratio).

    In the preferred embodiment, the ?lter bank 10 com prises an input port 20 which is controllably coupled by a single pole double throw switch 22 to either of two transmission lines 24 and 26. The output port 30 of the device is at the end of transmission line 26. When the switch 22 is set to couple the input port 20 to line 26, the device 10 is an allpass circuit. When switch 22 is set to couple the input port 20 to

    line 24, the device 10 is a multiple band ?lter. Only the frequency bands passed by the directional ?lters 40 will be passed to the output port 30. The directional ?lters 40 used in the preferred embodiment are stipline direc tional ?lters, each directional ?lter 4011 having three resonators 44a44c. As known to those skilled in the art of microwave

    ?lter design, the number of resonators used in a direc tional ?lter is determined by the desired attenuation skirt on the corresponding frequency band. In other words, by using more resonators, once can increase the sharpness of the shape of the frequency band to be passed by the ?lter 10. As will be explained in more detail below, a set of

    control signals from Control Logic 35 (typically a com

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