WO2015150741A1

WO2015150741A1 - Microwave signal splitter with phase reversal of one output

Info

Publication number: WO2015150741A1
Application number: PCT/GB2015/050899
Authority: WO
Inventors: Alan Trevor Wilson; Jimmy Gin-Men YIP
Original assignee: Linwave Technology Ltd
Priority date: 2014-03-31
Filing date: 2015-03-25
Publication date: 2015-10-08
Also published as: GB2525844A; GB2525844B; GB201405787D0

Abstract

A microwave signal splitter and phase inverter comprises a microwave signal input connected to, in sequence, a first microstrip splitter section (1) in which the signal is split into two signal paths (2 and 3) of equal amplitude and in phase, a second section (4) comprising, for each signal path from the first section, a broadband unbalanced to balanced tapered transition (5 and 6) into a balanced signal line having equal top and bottom conductors with a dielectric layer therebetween, and a third section (7) comprising for each balanced line a broadband balanced to unbalanced microstrip tapered transition (8 and 9). The top conductor of one balanced line is connected to a signal line of one microstrip tapered transition and the bottom conductor of the other balanced line is connected to the signal line of the other microstrip transition, whereby the signal phase in one signal path is inverted with respect to the signal in the other signal path.

Description

MICROWAVE SIGNAL SPLITTER WITH PHASE REVERSAL OF ONE

OUTPUT

Field of the Invention

[0001] This invention relates to a microwave signal splitter with phase rever- sal of one output (often referred to as a 180° hybrid splitter).

Background to the Invention

[0002] Microwave signal splitters are employed in many applications, for example to split a signal to feed multiple antennae. Certain applications require phase reversal (180° phase shift) of one output line, for example when feeding differential amplifiers. Several types of 180° splitter are currently in use at microwave frequencies. Rat-race couplers exhibit a natural 180° phase split and various types of quadrature (90°) couplers exist which can be converted to 180° using a 90° offset. Phase reversal can be achieved by the use of an L-C resonant circuit, ferrite transformers or by the use of unequal path lengths. Each of these can be effective in a limited frequency range (typically 20% bandwidth).

[0003] Broadband (multi-octave) 180° splitters are usually based upon either symmetric or asymmetric non-uniform coupled lines.

Summary of the Invention

[0004] According to the present invention, there is provided a microwave signal splitter and phase inverter, comprising a microwave signal input connected to, in sequence, a first microstrip splitter section in which the signal is split into two signal paths of equal amplitude and in phase, a second section comprising, for each signal path from the first section, a broadband unbalanced to balanced tapered transition into a balanced signal line having equal top and bot- torn conductors with a dielectric layer therebetween, and a third section comprising for each balanced line a broadband balanced to unbalanced microstrip tapered transition, and wherein the top conductor of one balanced line is connected to a signal line of one microstrip tapered transition and the bottom conductor of the other balanced line is connected to the signal line of the other mi- crostrip transition, whereby the signal phase in one signal path is inverted with respect to the signal in the other signal path.

[0005] Each microstrip transition may be connected to a respective coaxial connector. The microstrip transition of at least one signal path may be twisted to present the signal line to the output conductor of the coaxial connector. Alternatively, at least one of the microstrip transitions is moved out of the plane of the microstrip to present the signal line to the output conductor of the coaxial connector.

[0006] The present invention has the specific benefits of: 1 . Equalling or improving upon the symmetric or asymmetric non uniform line couplers, when used as a 180° power splitter/combiner;

2. Offering isolation between ouput ports;

3. Being realisable over much broader bandwidth / higher frequency;

4. Being realisable in a smaller size (<20%);

5. Being realisable with lower weight (<20%); and

6. Being available as a connectorised or drop-in / SMT module.

Brief Description of the Drawings

[0007] In the drawings, which illustrate an exemplary embodiment of the invention: Figure 1 is a schematic of the microwave splitter and phase inverter;

Figure 2 is a top plan view of the device represented by Figure 1 , with one balanced line twisted so that both microstrip lines appear on the top surface;

Figure 3 is a graph comparing the magnitude imbalance between the split output signals for the splitter and phase inverter of the present invention with that obtained for a conventional splitter;

Figure 4 is a graph comparing the phase imbalance of the same output signals; and

Figures 5-8 illustrate diagrammatically four different configurations of power splitter which are applicable to the device of the invention. Detailed Description of the Illustrated Embodiment

[0008] Referring to Figures 1 and 2, the first section 1 comprises a broadband splitter which is generally of conventional microstrip or stripline construction and is configured with high impedance outputs 2 and 3 of equal amplitude and phase (to provide line widths compatible with a balanced line, the output impedance being optimised to transform smoothly from unbalanced line to balanced line in the second section 4 via tapered transitions 5 and 6 of the microstrip. The balanced line section in each arm needs to be long enough to allow balanced signals to develop. The third section 7 comprises a balanced to unbalanced transition via a reverse tapered portion returning to microstrip 8 and 9 for the output connections. The tapered transitions 5 and 6 are each formed by tapering the width of the ground plane on the microstrip down to the width of the signal conductor, over as short a distance as possible. The balanced lines are then constituted by the metal strip conductors on opposed faces of a thin strip of the substrate. The balanced to unbalanced transitions 8 and 9 are achieved by widening the substrate and the line on one side of the balanced line to become a ground plane. The top conductor of one balanced line is connected to the signal line of the microstrip taper and the bottom conductor of the other balanced line is connected to the signal line of the microstrip taper in the third section, which is connected to a respective output in order to reverse the phase.

[0009] Figure 2 shows the physical embodiment of the device. The microstrip is fabricated by a printed circuit board process to form metal conductors on an insulating dielectric substrate with a continuous metal layer bonded to the opposite side of the substrate to form a ground plane. The power splitter could be achieved in a number of known ways, such as resistive power splitter, multisection Wilkinson with equal or non-equal length sections. Resistive splitters can be arranged in both a star and delta format, as illustrated in Figures 5 and 6 respectively. They are very broadband and can be extremely small. However they exhibit loss (an equal split has an additional loss of 3dB) and the isolation is only the same as the insertion loss. The basic Wilkinson power splitter has 3 ports: ports^'! , 2 and 3 each matched to 50ohm, as may be seen from Figure 7. It provides an equal split of power from port 1 to both port 2 and 3 with negligible additional loss and offers isolation between port 2 and 3. It has a useful bandwidth of around 20%, this can be increased slightly using transformers. Multi-octave bandwidth can be achieved by having multiple sections /resistors, as shown in Figure 8. Improved performance can be achieved by choosing different lengths for each section. This stops the peaks and troughs of the frequency response occurring at the same point, hence can improve the broadband return loss. [0010] Referring now to Figures 3 and 4, a test was carried out to compare the performance of the 180° hybrid splitter of the present invention with that of a conventional broadband 180° hybrid splitter of the type typically based on either symmetric or symmetric non-uniform coupled lines. Figure 3 shows the magnitude imbalance between the split output signals for the two devices plotted against frequency. It will be seen that the splitter of the present invention maintains a significantly smaller magnitude imbalance between the output signals over a much greater bandwidth than the conventional device. Figure 4 plots phase imbalance between the output signals against frequency, and it will be seen that for the greater part of the bandwidth the splitter according to the pre- sent invention maintains an imbalance significantly less than 5°, while the conventional splitter shows an imbalance of between 5° and 10° over a wide range of frequencies.

[0011] It will be appreciated that, while a two-way splitter has been illustrated and particularly described, the invention is applicable to multi-way splitters with phase inversion, the outputs from the initial splitting stage passing to the inputs of further splitting stages before the unbalanced to balanced and balanced to unbalanced transition stages with phase reversal of one of each pair of outputs.

Claims

1 . A microwave signal splitter and phase inverter, comprising a microwave signal input connected to, in sequence, a first microstrip splitter section in which the signal is split into two signal paths of equal amplitude and in phase, a second section comprising, for each signal path from the first section, a broadband unbalanced to balanced tapered transition into a balanced signal line having equal top and bottom conductors with a dielectric layer therebetween, and a third section comprising for each balanced line a broadband balanced to unbalanced microstrip tapered transition, and wherein the top con- ductor of one balanced line is connected to a signal line of one microstrip tapered transition and the bottom conductor of the other balanced line is connected to the signal line of the other microstrip transition, whereby the signal phase in one signal path is inverted with respect to the signal in the other signal path.

2. A microwave splitter and phase inverter according to Claim 1 , wherein each microstrip transition is connected to a respective coaxial connector.

3. A microwave splitter and phase inverter according to Claim 2, wherein the microstrip transition of at least one signal path is twisted to present the signal line to the output conductor of the coaxial connector.

4. A microwave splitter and phase inverter according to Claim 2, wherein at least one of the microstrip transitions is moved out of the plane of the microstrip to present the signal line to the output conductor of the coaxial connector.