Spiral ultra-wideband microstrip quadrature directional coupler

Abstract

The invention relates to the field of microwave engineering, and in particular, to waveguide-type coupling devices consisting of two coupled lines. The invention can be utilized as a hardware component for thin-film integrated high-frequency units (such as splitter/adder circuits), UHF power amplifiers, couplers, radiofrequency multiplexers, phase shifters, filters and other units in wireless devices used for various purposes. The benefit of the invention claimed lies in increase in efficiency of utilization of the usable area of a dielectric substrate and decrease in overall dimensions of the device and widening of the operating frequency band. This benefit is achieved by inclusion of two electromagnetically coupled microstrip transmission lines to the helical ultra-wideband microstrip quadrature directional coupler, which are designed as flat bilifar helices and are arranged on a dielectric substrate, the backside of which is partially or completely metalized or suspended over a metal surface. The couple differs from other analogous devices in its helices which have more than one turns with one helix of the coupler rotated relative to the other around their common center, while clearances between the coupled transmission lines and their cross-sectional dimensions are constant.

Claims

1. A helical ultra-wideband microstrip quadrature directional coupler comprising: two electromagnetically coupled microstrip transmission lines designed as flat bilifar helices arranged on a dielectric substrate with the backside completely metalized or suspended over a metal surface, wherein the helices have more than one turn with one helix of the coupler rotated relative to the other around their common center, while clearances between the coupled transmission lines and their cross-sectional dimensions are constant, and wherein the helices have a planar line bend angle of about 45 degrees at at least one turn.

2. The helical ultra-wideband microstrip quadrature directional coupler of claim 1, wherein the number of turns of the helices is greater than one, and wherein one helix runs in the opposite direction to the other about a common center.

3. A ultra-wideband helical microstrip quadrature directional coupler, comprising; a dielectric substrate defined by a topside and a completely metalized underside; and two electromagnetically coupled microstrip transmission lines configured as flat bilifar helices, wherein the helices having more than one turn with one helix rotated relative to the other helix around their common center with the dielectric clearances between the transmission lines and their cross-sectional dimensions being constant, wherein the space utilization of the dielectric substrate and coupler frequency bandpass versus signal loss are improved, wherein the helices have a planar line bend angle of about 45 degrees at at least one turn, and wherein the coupler is operative at frequencies below fifteen gigahertz.

4. The quadrature coupler of claim 3; wherein the transmission lines are suspended above the dielectric substrate.

5. A helical ultra-wideband microstrip quadrature directional coupler comprising: two electromagnetically coupled microstrip transmission lines designed as flat bilifar helices arranged on a dielectric substrate with the backside completely metalized or suspended over a metal surface, wherein the helices have more than one turn with one helix of the coupler rotated relative to the other around their common center, while clearances between the coupled transmission lines and their cross-sectional dimensions are constant, and wherein the helices have a planar line that are curved at at least one turn.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a microstrip directional coupler known from Maloratskiy L. G., Yavich L. R. “Design and Calculation of UHF Elements Based on Strip Lines” with cross-sectional dimension W of the microstrip lines and clearance g between them. Coupler leads (branches) are hereafter designated as follows: 1— input; 2— coupled output; 3— direct output; and 4—isolated output.

(2) FIG. 2 shows a tandem microstrip directional coupler known from Maloratskiy L. G. “Minituarization of UHF Elements and Devices” with cross-sectional dimension W of the microstrip lines and clearance g between them. Jumpers 5 are used to connect sections of the microstrip lines.

(3) FIG. 3 shows a tandem directional coupler known from Lekhitser A. Y., Fedosov A. N. “Tandem Directional Couplers and Units Based on Them”, in which microstrip transmission lines are formed as a flat single-turn bilifar helix. Jumpers 5 are used to output signals from the center of the helix.

(4) FIG. 4 shows top view of a helical ultra-wideband microstrip quadrature directional coupler with transmission lines formed as a bilifar helix with constant cross-sectional dimensions W of coupled lines and clearances g between them, and with planar line bend angle of 45 degrees. Jumpers 5 are used to output signals from the center of the helix. The figure shows main coupling areas— K1 and K2, where each area has three coupled lines, and K3 and K4, where each area has four coupling lines.

(5) FIG. 5 shows front view of a coupler with transmission lines formed as a bilifar helix with constant cross-sectional dimensions of coupled lines and clearances between them and with planar line bend angle of 45 degrees. The coupled transmission lines are arranged on one side of a dielectric substrate, while the other side of the substrate is metalized.

(6) FIG. 6 shows top view of a coupler with transmission lines formed as a bilifar helix with constant cross-sectional dimensions W of coupled lines and clearances g between them and with planar lines with curved bends. Jumpers 5 are used to output signals from the center of the helix.

(7) The options of formation of coupled lines shown in FIG. 4 to FIG. 6 are not exhaustive. Thus, for instance, the bilifar helix can be formed of planar lines curved along their entire length.

(8) FIG. 7 shows cross-plots of transmission factors against frequency of a tandem coupler and a helical coupler with constant cross-sectional dimensions of coupled transmission lines and clearances between them (with a regular structure), which are loaded to 50 Ohm, in splitting/adding.

(9) FIG. 8 shows a splitting/adding diagram of 3-dB couplers 6 loaded to a matched load.

DETAILED DESCRIPTION OF THE INVENTION

(10) The directional coupler design is based on use of two electromagnetically coupled microstrip lines formed as flat bilifar helices with more than one turns; at the same time, one helix is rotated relative to the other around their common center. As it is shown in FIG. 4 and FIG. 6, jumpers 5 (wire, foil, hybrid-grown or any other jumpers) can be used to output signals from the center of the helix.

(11) In its essence, such coupler is a tandem connection of multiple sections of coupled lines, which is one of well-known ways to widen the operating frequency band of tandem directional couplers (tandem connection of coupled lines is described in Meshchanov V. P., Feldstein A. L. “Automated Design of UHF Directional Couplers”, “Svyaz” Publishing House, Moscow, 1980, p. 96-97). Thus, for instance, FIG. 4 shows four main coupling areas of a coupler with transmission lines made up of linear sections of a bilifar helix with constant cross-sectional dimensions W of coupled lines and clearances g between them, and with planar line bend angle of 45 degrees. Coupling areas K1 and K2 have three coupled lines each, and areas K3 and K4 have four coupled lines each. Cascade connection of the four areas with different coupling levels in such coupler provides for significant widening of its operating frequency band (up to 2.5 octaves) in comparison to conventional tandem couplers with two coupling cascades.

(12) FIG. 7 shows estimated splitting/adding loss probability graphs for three types of 1-6 Hz 3 dB couplers, one branch of which is loaded to a matched load. The diagram of splitting/adding measurement is provided in FIG. 8.

(13) Since the electromagnetically coupled lines are coiled into a helix, the coupler is at least two to three times smaller than its prototype (such decrease in the dimensions is in inverse proportion to the number of turns of the bilifar helix) and, therefore, the efficiency of utilization of the substrate usable area is significantly higher.

(14) Thus, the essential features of this technical solution provide for significant widening of the operating frequency range of the coupler and, therefore, make it smaller and improve efficiency of utilization of the substrate usable area, which ensure the claimed benefits of the invention.