Ferrite crystal resonator coupling structure

Details Ferrite crystal resonator coupling structure Ferrite crystal resonator coupling structure

2001-11-29

2004-04-27

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Automatically controlled systems

C333S219000, C333S219200

Reexamination Certificate

active

06727775

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to high frequency resonators, and more particularly to ferrite crystal resonators useful in high frequency oscillator, filter and other applications.
BACKGROUND OF THE INVENTION
Ferrite materials such as pure or doped yttrium-iron-garnet (YIG) have been used as resonating elements, typically in the form of a spherical crystal or thin layer, to construct high frequency capable resonators. In addition to YIG, other ferromagnetic material such as, for example, NiZn, MgMn, LiZn, may be used as resonating elements. Ferrite resonators have several applications, including high frequency filters and local oscillators for use in high frequency transceiver systems, such as those that operate in the microwave and millimeter wave frequency bands from approximately 1 GHz to 40 GHz.
The increase in the number of applications for Ku and Ka band transceivers has created a need for up-converter and down-converter designs that are capable of addressing multiple frequency ranges of 1 GHz bandwidth or more over the 1 GHz to 40 GHz frequency ranges. The market for these devices depends upon a combination of low cost and high performance, and the ability to address multiple frequency ranges with the same design.
There are several modes in which such high frequency transceiver systems are designed to operate, including the Frequency Division Multiple Access (FDMA) mode and the Time Domain Duplex (TDD) mode. In the FDMA mode, the transceiver both receives and transmits data simultaneously on separate receive and transmit frequencies. In the TDD mode, the transceiver operates at a single frequency at a time and either transmits or receives but not both. Regardless of whether the transceiver is designed to operate in the FDMA mode or TDD mode, the ideal transceiver system is able to have its frequency of operation set remotely and changed at will according to traffic needs. However, until now, such systems have generally been quite expensive or unable to provide the performance levels required.
FIG. 1
shows a block diagram of a typical Ku/Ka band transceiver
10
which operates in the FDMA mode and includes an upconverter/downconverter unit
12
. The received signal
14
from the antenna
16
is directed via a diplexer
18
to a low noise amplifier
20
. The received signal
14
is down-converted by a receive mixer
22
which mixes the received signal
14
with a down-conversion signal
24
to obtain a received intermediate frequency (IF) signal
26
. The received IF signal
26
is amplified by an IF amplifier
28
and transmitted to other equipment for further processing. The down-conversion signal
24
is supplied by a receive local oscillator subsystem
30
through a receive band-pass filter
34
to the receive mixer
22
. The down-conversion signal
24
may, for example, be approximately 18 GHz, in which case the receive band-pass filter is an 18 Ghz band-pass filter. On the transmit side, a transmit IF signal
36
is received from other equipment and directed through a transmit IF amplifier
38
to a transmit mixer
40
. The transmit mixer
40
up-converts the transmit IF signal
36
by mixing it with an up-conversion signal
42
supplied to the transmit mixer
40
by a transmit local oscillator subsystem
32
through a transmit band-pass filter
44
. The up-conversion signal
42
may, for example, be approximately 27 GHz, in which case the transmit band-pass
44
filter is a 27 Ghz band-pass filter. The up-converted transmit signal
46
is amplified by a transmit power amplifier
48
to the appropriate transmit power level and sent to diplexer
18
to be transmitted by the antenna
16
. As may be appreciated, the receive and transmit local oscillator subsystems
30
,
32
are the heart of the upconverter/downconverter
12
in the transceiver
10
of FIG.
1
. The other circuit elements of the transceiver
10
are available from a number of sources and, with the exception of the transmit power amplifier
48
, can be made reasonably broadband.
In general, three different types of local oscillators have been used in high frequency transceivers: varactor tuned oscillators (VCOs), dielectric resonator oscillators (DROs), and YIG tuned oscillators (YTOs). In all three cases the desired frequency of operation is achieved by phase locking the signal source to a low noise crystal reference oscillator using a phase lock loop, and in the case of tunable systems by synthesis techniques.
VCO synthesizers typically have poor phase noise qualities and limited tuning bandwidth. These inherent limitations result because most high performance varactors have an effective unloaded quality factor, “Q”, of less than 100 at 5 GHz, and less than 50 at 10 GHz. The operational, or “loaded” circuit Q is a fraction of this value. This low Q limits both the phase noise and tuneability, since wider tuning range demands more coupling or lower Q, and results in worse phase noise. As the frequency of operation gets higher this gets worse. Also, varactors have severe thermal drift that must be compensated for in system applications. These factors limit applicability of varactors in high frequency applications such as local multipoint distribution system (LMDS) and satellite data communications, as well as in high data rate applications where phase noise is critical.
DRO's are single frequency devices. Their frequency tuneability is minimal, typically sufficient only for phase locking. Therefore they are used in phase locked oscillators. Dielectric resonators have Q's on the order of 1000 at 10 GHz, but this too declines with frequency. They are used in applications that need low phase noise and low cost, at a sacrifice of tuneability.
YTOs have the advantage of very low phase noise and wideband tuneability. The intrinsic Q of a YIG sphere is typically 1000 at 2 GHz and increases with frequency. YIGs are also magnetically tunable over multiple octaves in the microwave frequency range. However, YTOs are typically much costlier than VCOs or DROs because of the magnetic circuit drivers and magnet design involved, the complexity and associated labor cost of mounting and aligning the YIG sphere in the circuit for proper coupling, and because the coupling structure typically precludes the use of packaged transistors for wideband applications. However, in high data rate frequency agile applications, YTOs are practically the only way to go in spite of the much higher cost of YTO synthesizers.
FIG. 2
shows a schematic diagram of a typical YTO circuit
50
. A YIG sphere
52
is positioned within a direct current (DC) magnetic field (represented by arrow H
dc
). The DC magnetic field H
dc
is applied to the YIG sphere
52
by a magnet having a pole tip
54
positioned proximate to the YIG sphere
52
. The YIG sphere
52
is coupled with a coupling line
56
positioned between the magnet pole tip
54
and the YIG sphere
52
. An active device
58
capable of amplification or intrinsic or induced negative resistance and having two or more terminals, e.g., a Si bipolar transistor or a GaAs MOSFET, is connected at an input port
58
A thereof, e.g., the emitter terminal or the source, drain, or gate terminal, to a first end
56
A of the coupling line
56
. A second end
56
B of the coupling line
56
may be connected to a capacitor
60
. An appropriate feedback element or feedback circuitry
62
may be connected to a feedback port
58
B, e.g., the base terminal or the source, drain or gate terminal, of the active device
58
so that the resonance provided by the YIG sphere
52
creates a negative resistance at an output port
58
C, e.g., the collector terminal or the source, drain or gate terminal, of the active device
58
. The quality factor Q of this negative resistance and the inherent 1/f noise characteristics of the YTO circuit
50
determine the phase noise of the output oscillations. If required, an output matching circuit
64
may be connected to the output port
58
C of the active device
58
.
The applied DC magnetic field H
dc
sets up resonance in the YIG sphere
52
in

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