GB2152333A

GB2152333A - Full-duplex, electrically switched microwave transceiver

Info

Publication number: GB2152333A
Application number: GB08431272A
Authority: GB
Inventors: Salvatore Amoroso
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1983-12-27
Filing date: 1984-12-12
Publication date: 1985-07-31
Also published as: GB8431272D0; GB2152333B; FR2557403B1; JPS60223234A; DE3447716A1; FR2557403A1

Abstract

A full-duplex microwave transceiver utilizes two narrowband electronically tunable solid-state sources that are operator switchable from transmitter to local oscillator functions. This allows all transceivers to be identical and interchangeable, yet able to be set up as a full-duplex communications link by operator mode selection. A microwave transfer switching device is used to connect the RF sources alternatively to the antenna and receiver.

Description

SPECIFICATION Full-duplex, electrically switched microwave transceiver Technical Field This invention relates to microwave transceivers, and more particularly, to full-duplex microwave transceivers containing separate transmitter and local oscillator RF sources that can be electrically switched between two channels.

Background Art Transceivers are generally known and include transmitter and receiver functions which allow twoway and simultaneous (full-duplex) transmission of information between points. Microwave transceivers utilize a broad range of carrier frequencies, recently into the millimeter wave bands. Transceivers that operate in this wave band are particularly useful where relatively secured transmission is needed as well as in crowded areas such as building-to-building communications where it is necessary to minimize interference with adjacent communication systems. In addition, as the lower microwave bands become increasingly congested, use of the millimeter wave band becomes increasingly more important.

A present problem associated with the manufacture of transceivers in the millimeter wave band is the limited availability and relatively high cost of RF components.

Narrow band, electronically tunable, solid-state oscillators are becoming available and cost-effective in the millimeter wave band. The basic frequency stability of these devices as a function of temperature variation and aging effects is generally not adequate for transceiver application. Means for stabilizing the frequency include techniques such as temperature regulation and/or slaving to a stable reference such as a cavity.

Of general interest for their teachings of transceivers that operate in millimeter wave bands are U.S. Patent No.3,916,412 issued October 28, 1975 to S. Amoroso, Jr. for "Frequency Stabilized Single Oscillator Transceivers", U.S. Patent No.

3,925,729 issued December 9, 1975 to S. Amoroso, Jr. for "Skirt-Tuned Single Oscillator Transceiver, U.S. Patent No.3,939,533 issued January 1976 to S. Amoroso, Jr. for "Single Oscillator Microwave Transceiver", U.S. Patent No, 3,931,575 issued January 6, 1976 to S. Amoroso, J r. for "Filter Stabilized Single Oscillator Transceiver", and U.S.

Patent No.4,411,018 issued October 1983 to S.

Amoroso, Jr. for "Rapidly Stabilized Gunn Oscillator Transceiver", all of which are assigned to the same assignee as the present invention. The transceivers described in these patents are capable of operating in the millimeter range. A particular problem with many prior art microwave transceivers operating in this frequency range is that with a conventional varactor-tuned Gunn oscillator, the resonant cavity associated therewith must be mechanically retuned to change channels. This means that the transceiver cannot be quickly switched to a second channel.

Disclosure of Invention An object of the present invention is to produce a full-duplex microwave transceiver utilizing narrowband tunable solid-state sources.

A particularly feature of the present invention is that all transceivers are identical and interchangeable by virtue of a microwave switching function which interchanges the transmitter and local oscillator RF signals based on the selected channel. This feature simplifies the maintenance and logistic functions for the overall communication system. An additional feature of the switched oscillator configuration is that in the event of a failure of any single RF source, a half-duplex (twoway, not simultaneous) mode of operation is still available. Both features are particularly useful for military applications.

According to the present invention, a pair of microwave transceivers are capable of providing full-duplex operation, and can be electrically switched between two channels. Each transceiver includes a first microwave oscillator circuit and a second microwave circuit. A first resonant cavity, supporting resonance at a first frequency F1, is positioned in a feedback loop of the first microwave oscillator circuit while a second resonant cavity, supporting resonance at a second frequency F2, is positioned in a feedback loop of the second microwave circuit. Each oscillator circuit can be locked to either skirt of the cavity resonance frequency. A transfer switch couples either the first microwave oscillator to the transmitter and the second microwave oscillator to the receiver, or vice versa.

The foregoing and other objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments and accompanying drawings.

Brief Description of Drawings Fig. 1 is a block diagram depicting one embodiment of the full-duplex, electrically switched microwave transceiver according to the present invention; Fig. 2 depicts a frequency plan for a pair of transceivers according to the present invention, operating in a full-duplex mode; and Fig. 3 is a graph showing the relationship between each resonant cavity frequency and the channel frequencies.

Best Mode for Carrying Out the Invention Referring initially to Fig. 1,there is seen one embodiment of a full-duplex, electrically switched microwave transceiver 10 according to the present invention. A particularly important feature of the present invention involves the ability of the microwave transceiver 10 to electrically transition from operation on one channel, i.e., transmitting and receiving on a first set of frequencies, to qperation on a second channel, i.e., transmitting and receiving on a second set of frequencies. In the illustrated embodiment this is accomplished by the presentation of a suitable channel control signal on the line 12 which simultaneously changes the DC voltage output level of the automatic frequency control circuit (explained hereinafter) and also transitions both an input switch 14 and a waveguide switch 16 to its second position.

In the channel A position, as shown in Fig. 1, the input signals, such as voice, data or video, are presented buy a line 13 to the input switch 14 and then by a line 15 to a first oscillator circuit. The first oscillator circuit includes a summer 18 which combines the input signals presented with a feedback signal from a line 17. The output from the summer is presented by a line 20 to the input of a solid-state Gunn oscillator 22. The output of Gunn oscillator 22 is coupled by a suitable transmission line to a coupler 24 where the majority of the micro wave energy is directed through a waveguide 26 to a port 28 of the transfer switch 16. A small amount of microwave energy is inputted into a feedback loop by the coupler 24 to a cavity 30.The cavity 30 is a high Q cavity that is resonant at a particular frequency F1,this resonant frequency F, being set by the inherent characteristics of the cavity 30. A portion of the energy resonating in the cavity 30 is coupled to a detector 32 which provides at its output a DC signal whose level is related to the resonant frequency F, in the cavity 30. The output from the detector is presented to an AFC (automatic frequency control) circuit 34. The AFC circuit 34 uses the DC signal related to the resonant frequency F2 in the cavity and the channel control signal from the line 12, and directs the control signal along the line 17 to one input of the summer 18 closing the feedback loop. The feedback loop locks the Gunn oscillator to a frequency derived from the cavity 30, as offset by the AFC circuit 34.

The full-duplex, electrically switched microwave transceiver of the present invention also includes a second oscillator circuit which has a summer 40, one input of which is connected to one terminal of the input switch 14. The output from the summer 40 is presented along the line 44 to the input of a second solid-state Gunn oscillator 46. The output of the Gunn oscillator 46 is presented by a suitable transmission line to a coupler 48 where the majority of the energy is directed to a port 50 of the transfer switch 16.A smaller portion of the microwave energy is directed by the coupler 48 through a feedback loop to a second cavity 52, also a high Q cavity. A portion of the resonating microwave energy in the cavity 52 is coupled to a second detector 54 which provides at its output a DC signal which is related to the resonant frequency F2 in the second microwave cavity 52. The output from the detector 54 is presented to a second AFC circuit 56 where it is used with the channel control signal on the line 12. The output from the AFC circuit 52 is a control signal which is presented by a line 55 to one input of the summer 40 to close the feedback loop.

In a like manner, this feedback loop locks the Gunn oscillator to a frequency derived from the cavity 52, as offset by the AFC circuit 56.

A duplexer 60, a conventional three-port coupling device, is provided and one input port is coupled by a line 62 to one port 64 of the transfer switch 16.

Microwave energy for transmission is received on this waveguide and is coupled to an antenna 66 which acts as a transmit/receive aperture.

Microwave signals received from the distance station by the antenna 66 is coupled by the duplexer 60 to a waveguide 68 and a conventional mixer 70. A demodulating, or local oscillator signal, is presented to the mixer 70 along the waveguide 72 through an attenuator 74, a port 76 of the transfer switch 16 from the first oscillator circuit. The mixer 70 combines the two microwave signals to form IF frequency signals which are presented to a conventional FM receiver 78.

A particular feature of the full-duplex, electronically switched microwave transceiver according to the present invention is that the first and second microwave oscillator loops can be electrically interchanged as a source for the transmission frequency and as a source of local oscillator frequency for demodulation, without the need to mechanically retune either the Gunn oscillators or the resonating cavities. This might be better appreciated by reference to Fig. 2 which shows a frequency plan for full-duplex operation on two channels; and in addition to Fig. 3 which illustrates the reference cavity frequencies. The microwave transceiver in the present invention is capable of generating the four required frequencies for full-duplex operation on two channels, i.e., frequency Fia, F2a, F2b and Fib.In operation, a channel switch signal presented to line 12 would cause transition of the input signal switch 14, a shift in the signal fed from the AFC circuits to each Gunn oscillator changing the lock points to the opposite skirt (Fig. 3), and a transition of the transfer switch 16 causing the local oscillator source and a transmit frequency source to switch from one oscillator circuit to the other oscillator circuit. Because the intermediate frequency presented to the FM receiver 78 is typically 70 megahertz (Fig. 3) and the separation between transmitter and local oscillator frequency is several times the intermediate frequency (e.g., 300 megahertz), cross-taik from transmitter to receiver is minimized.

Although this invention has been shown and described with respect to a preferred embodiment, it will be understood by those skilled in this art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.

Claims

1. A microwave transceiver capable of being electrically switched between two channels, and providing full-duplex operation on each channel, comprising: a first microwave oscillator means including a first resonant cavity positioned in a feedback loop, said first resonant cavity supporting resonance at a first frequency; a second microwave oscillator means including a second resonant cavity means positioned in a feedback loop, said second resonant cavity means supporting resonance at a second frequency; transmitter means for transmitting a microwave signal at the frequencies generated by either said first microwave oscillator means or by said second microwave oscillator means; receiver means for demodulating a receive microwave signal by combining the same with a signal from either said first microwave oscillator means of said second microwave oscillator means; and a transfer switch means electrically transitionable between a first position, in which said first microwave oscillator means is coupled to said transmitter means while said second microwave oscillator means is coupled to said receiver means, and a second position in which said first microwave oscillator means is coupled to said receiver means while said second microwave oscillator means is coupled to said transmitter means.

2. A microwave transceiver according to claim 1, wherein said microwave transceiver is electrically transitioned between two channels by a channel control signal, and wherein said channel control signal transitions said transfer switch means between its first position and its second position.

3. A microwave transceiver according to claim 2, further including an input switch having a first position for presenting input signals to said first microwave oscillator means and a second position for presenting input signals to said second microwave oscillator means, and wherein said switch is trangitioned between its first and second position by said channel control signal.

4. A microwave transceiver according to claim 1, further including an automatic frequency control means positioned in said feedback loop of both said first microwave oscillator means and said second microwave oscillator means, and wherein said feedback loop of said first microwave oscillator means and said second microwave oscillator means are locked to a skirt frequency associated with said first frequency and said second frequency, respectively, and wherein said automatic frequency control means of said first microwave oscillator means and said second microwave oscillator means, in response to said channel control signal, locks to the other skirt of said first frequency and said second frequency.