AU649325B2 - Low loss, broadband stripline-to-microstrip transition - Google Patents

Description

649325

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): Communications Satellite Corporation ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Low loss, broadband stripline-to-microstrip transition The following statement is a full description of this invention, including the best method of performing it known to me/us:- 9 00 la BACKGROUND OF THE INVENTION The present invention relates to stripline-to-microstrip transitions, and in particular to such a transition incorporated in a printed-circuit antenna which in turn has incorporated therein a low noise amplifier (LNA) block.

Stripline-to-microstrip transitions are known, for example, in USP 4,862,120 and 4,870,375. USP 4,862,120 discloses a wideband stripline-to-microstrip transition in which the transmission mode of energy passes through a plurality of different transitions of transmission mode, from stripline to microstrip. Different interim modes include quasi-coax, a transitional mode, a double slot mode, and coplanar waveguide. This sequence of transitions eventually changes the stripline mode electric field pattern, which extends in two directions from the stripline itself, to a microstrip mode electric field pattern, which extends in a single direction from the microstrip. However, the transition 20 structure" in this patent is somewhat complicated.

USP 4,870,375 discloses a disconnectable microstrip-to- S: stripline transition, in which a phased array antenna contains a plurality of chassis, each including four antenna elements, each element having associated therewith operating electronics which are implemented in a monolithic microwave integrated circuit (MMIC) approach. The transition is-'provided in removable form to enable disconnection of a module between an antenna distribution circuit and a beamformer distribution 30 circuit. In the transition, one low noise amplifier is associated with one antenna element.

In copending, commonly assigned U.S. Patent No.

5,125,109, in which one of the named inventors is also an inventor of the present application, a low noise block down converter (LNB) employing MMICs is provided on a power CjRA< dividing network layer in a printed circuit antenna which may 940316,p:\opcz%&Lommwtk&Utrll -2include a stripline power divider network. The disclosure of that application iu hereby incorporated herein by reference.

It is desirable to have a broadband stripline-tomicrostrip transition between a power dividing network and one or more low-noise amplifier blocks, and to use a mount for the amplifier, if possible, as a connection between the ground plane of the antenna and a radiating element array which constitutes a second ground plane in the antenna.

SUMMARY OF THE INVENTION According to the present invention there is provided a printed-circuit antenna comprising a ground plane, a stripline power divider network disposed over said ground plane, a radiating element array disposed over said stripline power divider network, a low noise amplifier (LNA) block disposed between said ground plane and said radiating element array, and a stripline-to-microstrip transition comprising: 20 a stripline element connected to said power divider network; a microstrip element, connected to said LNA block, and impedance matched with said stripline element; means for connecting said stripline element and said microstrip element electrically; and means for mounting said LNA block vertically between said ground plane and said radiating element array, said mounting means forming a low resistance connection between said ground S plane and said radiating element array, 30 vertical mounting of said LNA block effecting rotation of an electric field generated by said stripline element with respect to an electric field generated by said microstrip element, said mounting means formiVg a termination wall for said electric field generated by said stripline element.

940316,pAopztcommwunkatltr I BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a top view of the inventive microstrip-to-waveguide transition in accordance with one embodiment of the invention; Figure 2 shows a front view of the transition of Figure 1; Figure 3 is a schematic of a vertical mounting of another view of the stripline-to-microstrip transition of the invention, implemented in a printed circuit antenna; Figure 4 shows an end view of the vertical mounting of Figure 3; Figure 5 shows an integrated low noise amplifier schematic; 15 Figure 6 shows a measurement of performance characteristics of a stripline test fixture without a microstrip circuit; Figure 7 shows a measurement of the same fixture, but with microstrip transmission structure incorporated therein; Figure 8 shows return loss and insertion loss without the microstrip mounting block; Figure 9 shows return loss and insertion loss with the mounting block, but without a microstrip line 25 element; and Figure 10 shows return loss of the test fixture with the microstrip line terminated in a 50 ohm chip S. resistor connected to the ground block.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 shows a top view of the inventive microstrip-to-waveguide transition. The stripline center conductor 1 is connected to the low noise amplifier (LNA) circuit 3, which is mounted on an LNA mounting block 2, via a gold ribbon connect 4. The LNA circuit substrate, which is made of alumina, is 10 mils thick.

The stripline center conductor 1 is approximately 212 mils wide in this embodiment, in order to achieve a 0 characteristic impedance, with a ground plane spacing of 160 mils (see Figure An air gap of approximately 5 mils exists between the LNA mounting block 2 and the end of the stripline 1. An air gap of approximately 2 mils exists between the &nd of the alumina substrate and the end of the stripline 1. The gold ribbon 4, which is approximately 5 mils wide, joins the stripline 1 to the microstrip 6 on the LNA circuit 3 (Figure 2) across the small air gap. In so doing, the ribbon 4 rotates through a 900 angle so that it lies flat on both the stripline center conductor 1 and the microstrip 6.

While Figure 1 shows the ribbon 4 lying flat on the 15 stripline center conductor 1, Figure 2 shows the effect of the 900 rotation, and thus shows the ribbon 4 lying flat on the microstrip 6.

In Figure 3, a printed circuit antenna includes a ground plane 10, a power divider network 20 and a radiating element array 30 comprised of a plurality of radiating elements (not shown). Individual elements of the power divider network 20 feed respective ones of the radiating elements. A low noise amplifier circuit 100, which may for example be a two-stage amplifier, is mounted on a metal block 110 which extends between the ground plane 10 and the radiating element array 30 to provide a low resistance connection. The radiating element array 30 constitutes the second ground plane of the antenna; thus, the metal block 110 extends between the two ground planes. An example of such an amplifier is shown in Figure Between the power divider network 20 and the microstrip input 140 is a stripline-to-microstrip transition 130. As seen in Figures 1 and 2, a stripline center conductor 150 is provided on either side of the block 100. The conductor 150 is connected to the amplifier circuit 100 by the stripline-to-microstrip transition 130. The center conductor 150 and the microstrip input 140 and output 145 are separated by approximately mils in the illustrated embodiment, and are connected together by a gold bond wire.

The gold bond is necessary because a DC connection, is required on the RF output for biasing purposes, between the amplifier circuit 100 and the stripline conductor 150. Preferably the bond is a ribbon bond, such as that used in microcircuit assembly, wherein the wire is approximately 5 mils wide and 1-2 mils thick. Tne stripline and microstrip transmission sections are impedance matched. The circuit 100 itself is configured so as to be self-biased, such that a single positive voltage is applied at the output as a bias, and positive and negative voltages are generated from that as necessary. A high electron mobility transistor (HEMT) may be provided at the front end of the circuit to achieve the low noise characteristic.

With the foregoing construction, the vertical metal wall of the carrier block 110 forms a termination of the :stripline transmission mode, in which the electric fields are oriented vertically between the two ground planes comprising the ground plane 10 and the radiating element array 30. In the actual transition region, the electric field of the stripline mode is rotated by 900 to the microstrip mode, since the microstrip circuit itself is oriented vertically. Figure 4 shows the 30 relative 900 orientation between the plane of the stripline center conductor 150 and the microstrip circuit more clearly. The vertical orientation of the amplifier circuit 100 with respect to the power divider network makes it possible to take advantage of the symmetry of the electric field in a stripline transmission mode, and avoids the complicated structure of USP 4,862,120. The vertical orientation of the amplifier circuit "folds" the upper portions of the field down, and also "folds" the lower portions of the field up, to yield the microstrip electric field configuration.

As in copending Application No. 07/210,433, in order to have the LNA block 'ounted on the radiating element array, it is necessary to sacrifice certain ones of the radiating elements which otherwise might be put on the array. Since the elements may be weighted appropriately, the elements to be sacrificed may be selected so as to minimize the effect on performance of the antenna. For example, elements near the center of the antenna may be sacrificed by replacing the power 15 divider elements which would excite them by the INA block.

Figure 5 is a schematic of one example of an integrated LNA circuit. In this particular example, the first and second stage devices are self-biased, and the single bias voltage is brought in through the RF output port.

Figure 6 shows a measurement of the stripline test fixture containing no microstrip circuit. Figure 6 was provided to obtain a baseline measurement to character- 25 ize the return loss and insertion loss of the external RF connectors and a length of stripline between them.

Figure 7 shows the same measurement, but now with S. a 0.260" length of 50 ohm microstrip transmission line on a 10 mil thick alumina substrate inserted on a carrier block in the middle. The extra loss shown in this measurement arises primarily from the length of the microstrip line, and the two stripline-to-microstrip transitions at either end. After taking the inherent microstrip losses into account, it is found that the transition loss itself is less than 0.1 dB. This result is associated with a return loss of approximately 17 dB.

Figures 8-10 show that the energy in the stripline mode is coupled primarily to a microstrip mode by the transition structure.

While the invention has been described in detail with reference to a preferred embodiment, various modifications within the spirit of the invention will be apparent to those of working skill in this technical field. Accordingly, the invention should be considered as limited only by the scope of the appended claims.

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Claims (5)

1. A printed-circuit antenna comprising a ground plane, a stripline power divider network disposed over said ground plane, a radiating element array disposed over said stripline power divider network, a low noise amplifier (LNA) block disposed between said ground plane and said radiating element array, and a stripline-to-microstrip transition comprising: a stripline element connected to said power divider network; a microstrip element, connected to said LNA block, and impedance matched with said stripline element; means for connecting said stripline element and said microstrip element electrically; and means for mounting said LNA block vertically between said ground plane and said radiating element array, said mounting means forming a low resistance connection between said ground plane and said radiating element array, vertical mounting of said LNA block effecting 20 rotation of an electric field generated by said stripline i*I element with respect to an electric field generated by said microstrip element, said mounting means forming a termination wall for said electric field generated by said stripline 6406 element.

2. A printed-circuit antenna as claimed in claim 1, wherein said stripline element comprises a stripline center conductor, and wherein said connecting means comprise gold bond wire. 30 3. A printed-circuit antenna as claimed in claim 1, wherein said gold bond wire comprises ribbon wire substantially 5 mils •wide and 1-2 mils thick.

4. A printed-circuit antenna as claimed in claim 2, wherein said stripline center conductor and said microstrip element are separated by approximately 10 mils. 940315,p\pckatommuricAtWtr8 -9- A printed-circuit antenna as claimed in claim 1, wherein said radiating element array comprises a plurality of radiating elements, and said power divider network comprises a plurality of power divider network elements for feeding respective ones of said radiating elements individually.

6. A printed-circuit antenna as claimed in claim 5, wherein said LNA block is placed on said power divider network so as to replace selected ones of said power divider network elements, so that radiating elements otherwise corresponding to said selected ones of said power divider network elements are not excited.

7. A printed-circuit antenna substantially as hereinbefore described with reference to the accompanying drawings. Dated this 15th day of March, 1994 20 COMMUNICATIONS SATELLITE CORPORATION By its Patent Attorneys DAVIES COLLISON CAVE a 4 *00: a 4.44 4444 4* 4 4 44 4 .7 936piwzuliu, 4W;q, 94316p.\opegkamomwtkrtUW ABSTRACT OF THE DISCLOSURE In a flat antenna incorporating one or more low- noise amplifier circuits onto a power divider network, a stripline-to-microstrip transition is provided. The amplifier circuit is mounted vertically on a block between a ground plane and the radiator level, so that, in the transition, the electric field of the stripline power divider is rotated 900 to the microstrip mod. A block on which the circuit is mounted forms a connection between the ground plane and the layer of radiating elements which constitutes the other ground plane for the antenna. e 0 o *000