GB2270208A - Signal combiners. - Google Patents

Abstract

A combiner for microwave signals comprises a first input 1, a second input 3, and an output 2, the first input being coupled via a delay line 4 and a parallel coupler 5 to the output to provide a main signal path 6, and the main signal path being coupled via the parallel coupler and a Schiffman type phase shifter 7 to the second input. The delay line 4 may provide a 270{ nominal phase delay whilst the parallel coupler 5 and the Schiffman phase shifter 7 are arranged both to provide a 90{ nominal phase shift whereby cancellation between similar in-phase signals applied to the first and second inputs is facilitated. The combiner may provide spurious signal cancellation in a feed forward microwave power amplifier. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO SIGNAL COMBINERS This invention relates to signal combiners and more especially it relates to signal combiners of the kind which facilitate the cancellation of signals.

In microwave power amplifiers for example, it might be required to effect the broadband cancellation of unwanted intermodulation products by feeding forward a signal sample from a main signal path, which sample is processed and combined with the signal in the main path in such a manner that unwanted inter-modulation products are cancelled.

Known signal combiners or signal couplers for performing this function tend either to present an undesirably high loss in the main signal path, e.g. about 3dB, and/or do not provide the required 1800 phase shift between coupled input ports to facilitate spurious signal cancellation.

It is an object of this invention to provide a signal combiner having a broadband response and having the characteristics of low loss between input and output ports and a 1800 phase shift between coupled ports.

According to . the present invention a signal combiner arrangement comprises first input terminal means, second input terminal means and output terminal means, the first input terminal means being coupled via a delay line and a parallel coupler to the output terminal means thereby to provide a main signal path, the main signal path being coupled via the parallel coupler and a Schiffman type phase shifter to the second terminal means.

The delay line may comprise a nominally 270 meander delay line.

The parallel coupler may be a single section quarter wave parallel coupler.

At a nominal operating frequency, the meander delay line may be arranged to afford a 270" nominal phase delay whilst the single section quarter wave coupler and the Schiffman phase shifter may be arranged both to afford a 90" nominal phase shift whereby cancellation between similar in-phase signals applied between the said first and the said second input terminal means is facilitated.

The delay line, the parallel coupler and the Schiffman phase shifter may be fabricated in strip-line component form and contained in a housing to which input and output terminals defining the said terminal means are attached.

Alternatively, the delay line may be at least partly defined by delay elements which form a part of other apparatus, whereby the signal combiner comprises a part of the said other apparatus.

The said other apparatus may be a feed forward microwave power amplifier wherein spurious signal cancellation is effected in the signal combiner.

One embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which; FIGURE 1 is a somewhat schematic circuit/block diagram of a signal combiner, and in which; FIGURE 2 is a circuit layout drawing of the signal combiner shown in Figure 1, fabricated in strip-line form.

Referring now to Figure 1, a signal combiner comprises an input terminal 1, an output terminal 2 and a further input terminal 3. The input terminal 1 is connected to a meander delay line 4 which affords a 270 phase delay at the nominal operating frequency. The meander delay line is arranged to feed a single section parallel coupler 5, thereby to define a though path 6 which extends between the input terminal 1 and the output terminal 2. The further input terminal 3 is coupled to the through path via a Schiffman type phase shifter 7 and a portion 5a of. the single section parallel coupler 5 whereby the further input terminal 3 is, in effect, capacitively coupled to the path 6.

The circuit shown was designed to achieve phase variations within plus or minus onedegree over the frequency range 1.7-2.0 GHz. In the present example the coupling provided by the single section parallel coupler 5 is about 20dB. As will be appreciated by the cognoscenti, the phase of signals in the coupled path Spa. leads the phase of signals in the through path by about 90". By including the Schiffman type phase shifter 7, a further 90" phase shift is introduced into the coupled path. The meander line 4 serves to correct any linear delay provided by the Schiffman type phase shifter 7 whereby signals applied mutually in phase, at the terminals 1 and 3, are cancelled at the output provided the relative amplitudes are suitably chosen.The circuit shown offers the advantage that the through path between the terminal 1 and the terminal 2 may be very low loss and thus ideal for high power signals since losses are minimised. Since cancellation of in phase signals applied between the terminals 1 and 3 may be achieved, provided a suitable coupling ratio is chosen, the circuit lends itself admirably to applications in feed forward high power microwave amplifiers since distortion comprising inter- modulation products produced by the the nonlinearity of amplifiers may be corrected by cancellation of spurious signals.

Although the circuit shown is particularly suitable for signal cancellation in high powered microwave amplifiers, the circuit may find application in other systems, and it may, for example, be useful in interference cancellation equipment.

As shown in Figure 2 wherein parts corresponding to Figure 1 bear the same numerical designations, the meander line 4, the single section parallel coupler 5 and the Schiffman type phase shifter 7, lend themselves to fabrication in strip-line form supported on a suitable substrate.

Claims (9)

CLAIMS:

1. A signal combiner arrangement comprising first input terminal means, second input terminal means and output terminal means, the first input terminal means being coupled via a delay line and a parallel coupler to the output terminal means thereby to provide a main signal path, the main signal path being coupled via the parallel coupler and a Schiffman type phase shifter to the second terminal means.

2. A signal combiner as claimed in claim 1, wherein the delay line comprises a meander line, cable, or transmission line.

3. A signal combiner as claimed in claim 2, wherein the parallel coupler is a single section quarter wave parallel coupler.

4. A signal combiner as claimed in claim 3, wherein the meander delay line is arranged to afford a 270 nominal phase delay whilst the single section quarter wave coupler and the Schiffman phase shift are arranged both to afford a 90" nominal phase shift whereby cancellation between similar in phase signals applied between the said first and the said second input terminal means is facilitated.

5. A signal combiner as claimed in any preceding claim, wherein the delay line, the parallel coupler and the Schiffman phase shifter are fabricated in strip-line component form and contained in a housing to which input and output terminals defining the said terminal means are attached.

6. A signal combiner..as claimed in any of claims 2 to 4, wherein the delay line is at least partly defined by delay elements which form a part of other apparatus, whereby the signal combiner comprises a part of the said. other apparatus.

7. A signal combiner as claimed in claim 6, wherein the said other apparatus is a feed forward microwave power amplifier wherein spurious signal cancellation is effected in the signal combiner.

8. A signal combiner as claimed in claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.

9. A microwave feed forward power amplifier including a signal combiner as claimed in any preceding claim.