Plural coupled microwave oscillators providing phase shifted...

Oscillators – Plural oscillators – Synchronized – triggered or pulsed

Reexamination Certificate

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Details

C331S056000, C331S101000, C331S1070DP, C331S1070DP, C331S1070DP, C332S105000, C375S279000, C375S308000

Reexamination Certificate

active

06232843

ABSTRACT:

TECHNICAL FIELD
This invention is related to a high frequency transmitter. More particularly, this invention relates to a high frequency quadrature phase shift keying transmitter implemented in a waveguide.
BACKGROUND OF THE INVENTION
Evolving high frequency communications technologies operating from around 27 GHz to 31 GHz are generally full-duplex in nature and are deployed in terrestrial microcells or configured to directly exchange data with low earth orbit satellites. Service providers typically divide the allocated transmit and receive frequency spectrums so that the transmitter in the satellite or base station operates in a lower, and therefore easier to work with, frequency block of around 27 GHz while the transmitter in the consumer's device operates at the higher frequency, e.g. 31 GHz.
FIG. 1
is a high level diagram of a conventional quadrature phase shift keying (QPSK) transmitter
10
used to transmit at around 31 GHz. The transmitter consists of a channel oscillator
11
operating at an intermediate frequency (IF), e.g., 1 GHz, which feeds a quadrature divider
12
that produces two output signals having a relative phase difference of 90 degrees. These signals are provided to separate bi-phase modulator switches
13
,
14
which output either the original input signal, or the input signal phase shifted by 180 degrees, depending on the value of a respective input data bit
15
,
16
. Thus, the first modulator
13
will produce an output signal with a phase of 0 degrees or 180 degrees and the second modulator
14
will produce a signal with a phase of 90 degrees or 270 degrees, according to the value of the input data bits
15
,
16
. The output signals of the modulator switches are mixed with an in-phase combiner
17
to produce a four vector output signal
18
.
The intermediate frequency QPSK signal
18
is input to a preamplifier
19
via a coaxial cable. The amplified signal is processed by an image filter
20
to reduce noise and then combined with a signal from a local high frequency oscillator
21
operating at the transmit frequency, e.g., 31 GHz, with a mixer
22
. A local trap
23
may also be utilized to clip out emissions outside a particular bandwidth in order to comply with applicable government regulations. The final signal is then input to the transmit amplifier
24
It is very difficult to economically generate enough power at 31 GHz to uplink a signal to a satellite or base station. A conventional solid state 31 GHz transmit amplifier is produced as a thin film integrated circuit using GaAs technology. Devices of this type which are powerful enough to produce a one-watt output signal typically cost several thousand dollars each. The high cost of the amplifier places the total cost of the transceiver unit, which includes a transmitter, a receiver, an antenna, and the equipment housing, well beyond the price range of most interested consumers.
Accordingly, it is an object of the invention to provide a high power transmit block for consumer satellite uplinks which may be inexpensively manufactured.
It is a further object of the invention to provide a high frequency transmitter which eliminates the need to internally generate a modulated signal at an intermediate frequency before producing the high frequency output signal.
Yet another object of the invention is to provide a high frequency QPSK transmitter block in which the signal modulation is implemented in a waveguide.
SUMMARY OF THE INVENTION
According to the invention, two Gunn diode cavity oscillators are employed as a quadrature signal source. The cavity oscillators are configured to operate at the transmit frequency, e.g., 31 GHz. The first oscillator is driven by steering voltage which is generated by a phase locked loop. A feedback path from the first oscillator to the PLL is provided to maintain the oscillation phase. The second cavity oscillator is slaved to the first at a specified phase vector, preferably by magnetically linking the oscillators through integral wall apertures designed to ensure a frequency coherence between the two oscillators while maintaining the specified phase vector over the entire normal frequency bandwidth of the devices. Each cavity oscillator is coupled to a waveguide to produce an output signal. The coupling point is selected so that the output signals, i.e., quadrature vectors, are 90 degrees out of phase with each other.
The quadrature vectors are presented to a mirrored pair of bi-phase, solid-state switches realized in a waveguide. Each switch is preferably comprised of a magnetic reflective coupling structure which can be switched according to the value of an input data bit between a hard-wall wave guide short and a compensated, electrically generated shorting plane, such as a diode placed within the waveguide. The distance between the switchable shorting plane and the hard-wall short is selected to produce a switchable net phase change of 180 degrees. The waveguide output from each bi-phase switch is connected to an in-phase combiner to yield a combined QPSK signal that can be applied directly to an antenna.
Accordingly, the present invention allows the generation and combination of two quadrature signal sources, each independently bi-phased switched, in a waveguide system which accepts input data directly and produces a QPSK output signal at the transmit frequency without needing an intermediate frequency stage. Further, the transmitter of the present invention eliminates the majority of components of a conventional transmitter. In particular, the power for the output signal is supplied directly from the cavity oscillators and coupled to the transmitter output through efficient waveguide structures. Therefore, separate high frequency signal amplifiers are not required.


REFERENCES:
patent: 3691479 (1972-09-01), Malcolm
patent: 4551689 (1985-11-01), Scala et al.
patent: 4573213 (1986-02-01), Dixon, Jr. et al.
patent: 4763085 (1988-08-01), Lamberg
patent: 4896123 (1990-01-01), Taub
patent: 4959654 (1990-09-01), Bjorke et al.
patent: 5748679 (1998-05-01), Finkenbeiner et al.

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