<!doctype html public "-//WebTechs//DTD Mozilla HTML 2.0//EN">  <html> <head> <title>A High Power Hybrid Matrix for Mobile Satellite Communications</title> </head>  <body bgcolor="#ffffff" vlink="#3299cc"> <img align=bottom src="/images/esaf_gr5.gif" alt="European Space Agency"> <br> <hr>  <h2>A High Power Hybrid Matrix for Mobile Satellite Communications.</h2>  <h3>A. Nubla, J.-M. Montero, L. Bustamante</h3> <h4>Rymsa, (E)</h4> <h3>G.A.E. Crone, A.G. Roederer</h3> <h4>Electromagnetics Division, ESTEC </h4> <h3>R. Garcia Prieto</h3> <h4>Mechanical Systems Division, ESTEC</h4> <h3>N. Hill</h3> <h4>Matra Marconi Space, (UK)</h4> <P> <h3>R&#233;sum&#233;</h3> <em> On d&#233;crit une matrice hybride &#224; huit entr&#233;es et huit sorties, avec coupleurs hybrides &#224; 3 dB, d&#233;phaseurs et connecteurs coaxiaux TNC, reli&#233;s les uns aux autres par des lignes de transmission en mode TEM en U. Cette conception est destin&#233;e aux applications &#224; forte puissance o&#249; les produits d'intermodulation passive et les d&#233;charges auto-entretenues sont &#224; proscrire.  Un autre crit&#232;re majeur de la conception est la recherche d'une masse aussi faible que possible. Un mod&#232;le technologique de qualification a &#233;t&#233; fabriqu&#233; et soumis &#224; des essais radio&#233;lectriques, &#224; des essais en environnement et &#224; des essais de tenue en puissance. </em> <P> <strong>Contractors:</strong> <br>Rymsa (E), Matra-Marconi Space (UK) <P> <strong>Funding:</strong> <br> Advanced System Technology Programme No. 4 and the ARTES 5 Project. <br> <p> <h3>Introduction</h3> The market for satellite mobile communications is undergoing significant expansion with future systems being developed for constellations of satellites placed in low Earth-orbits, inclined circular orbits and geostationary orbits. The antenna used for such systems is a key element. Key requirements are contiguous multibeam coverage and power to beam and channel to beam flexibility, to cope with variable traffic demands. The increased primary power available in the new generation of satellites also permits high levels of radio frequency power, placing stringent demands on the high power capability of antennas. <p> One of the most promising candidate antennas for geostationary applications is the semi-active multimatrix fed reflector antenna, which has been patented by ESA [1]. The concept is already flying on the current generation of Inmarsat 3 satellites and will be demonstrated on the land mobile communications payload (LLM) to be flown on ESA's Artemis satellite. <p> Matra Marconi Space, together with Rymsa as subcontractor, have developed this technology beyond Artemis and Inmarsat-3 to meet the challenges of higher power, wider coverage and larger number of beams. <p> The feed system is designed to feed a 5.5 m reflector to give multibeam coverage over Europe using a total of 24 beams formed by three feeds per beam. The system consists of low-level beam-forming network, 24 equally excited high power amplifiers and three eight-by-eight hybrid matrices with eight feeds connected to each output. Each beam is derived from a triplet of feeds, from each matrix, and power is directed to the appropriate feed or output port of the matrix, dependant on the phase at the input. The phases are set up via the low level beam-former (one for each beam). <p> The key element of this system is the high power eight-by-eight hybrid matrix which is the subject of this article. An engineering and qualification prototype of this matrix has been manufactured and has undergone both radio frequency and environmental testing. <p> <h3>Hybrid high power matrix</h3> The matrix is designed around the use of TEM (transverse electromagnetic field mode) bar-lines. These are essentially co-axial lines with square cross-sections in which the inner conductor is suspended inside an outer conductor made of a machined housing. In fact, a U-shaped cross-section is used for the inner conductor (U-line) to save mass. The matrix comprises of twelve 3-dB branch line couplers, four phase equalisers and sixteen transitions from U-line to conventional threaded N-type connectors for cable, all arranged in a planar network of eight-inputs by eight-output ports (Figure 1). <p><a href="images/roedv8n2f1.gif"><img src="images/roedv8n2f1_sm.gif" align=bottom hspace=10 vspace=5 alt="eight-by-eight ort butler high power matric"></a><br clear=all> <em>Figure 1. A eight-by-eight port Butler high power matrix. </em> <p> The outer and inner conductors are made of type 7075-T73 aluminium alloy and have 0.6 mm walls to minimise mass. A set of rexolite and stycast pieces are bonded at branch-line couplers and phase equalisers location. These perform several functions; they support the inner conductors, reduce the length of the couplers and improve the thermal path between inner and outer conductors. Finally, an aluminium lid covers the beam forming network and acts as the fourth wall of the square outer conductor. The mechanical interface allows two matrices to be assembled in back to back configuration, sharing the common lid, thus reducing both mass and volume. <p> To minimise the generation of passive intermodulation products (PIMPs), metal to metal contact (orthogonal to current direction) have been are avoided. The outer and inner conductors and the lid are manufactured as single pieces, and a capacitive contactless design is used for the transitions from U-line to the threaded connector. Aluminium parts are black anodised to achieve an optimum radiative heat transfer to and from the spacecraft. <p> <h3>Electrical design</h3> The electrical design of this equipment has been performed in four main steps: <li>electrical specification of the matrix and its individual elements such as couplers and definition of the global geometry using a planar arrangement as baseline;</li> <li>design and breadboarding of the the most critical elements (3 dB single branch couplers and TNC-U-line transitions);</li> <li>breadboarding and test of other critical components.</li> <li>simulation of the general behaviour of the matrix, importing measured and simulated results into the Touchstone software package.</li> <p> <h3>Manufacture and test</h3> A pair of prototype matrices, assembled back-to-back in a single housing, have been manufactured using approved parts and materials and being fully representative of a flight model in terms of electrical and mechanical performances and mass. The matrices have been tested at radio frequencies under laboratory conditions and have been subjected to vibration and thermal vacuum cycles (qualification level) at Rymsa. Environmental test levels are shown in Table 1. <p> Table 1.Environmental test levels for (a) vibration test and (b) thermal vacuum test. <p> <strong>Table 1(a)</strong><br> <table border cellpadding=10> <tr> <td><strong>Axis</strong></td> <td><strong>Frequency</strong> [Hz]</td> <td><strong>Vibration</strong></td> <td><strong>Duration<strong></td> </tr> <tr> <td valign=top>X, Y, Z - sine</td> <td>&#32;5 - 28<br>28 - 100</td> <td>11 mm - 0 - peak<br>20 <strong>g</strong></td> <td>sweep rate<br> 2 oct/min</td> </tr> <tr> <td>X, Y - random</td> <td>20 - 2000</td> <td>12.4 <strong>g</strong> (rms)</td> <td>120 sec</td> </tr> <tr> <td>Z - random</td> <td>20 - 2000</td> <td>19.5 <strong>g</strong> (rms)</td> <td>120 sec</td> </tr> </table> <p> <strong>Table 1(b)</strong><br> <table border cellpadding=10> <tr> <tr><td>Thermal Vacuum Cycles</td><td>4</td></tr> <tr><td>Hot (Ta)</td><td>106 &#176;C</td></tr> <td>Cold (Ta)</td><td>-35 &#176;C</td></tr> <td>Pressure level</td><td>&#60;1.6 10-5 mbar</td></tr> </table> <p> Comparisons of measured performances versus specifications are shown in Table 2. The mass was measured with stainless steel screws. Table 2 showing also the estimated mass saving if Titanium screws are used. <p> <em>Table 2 - Comparison of measured and specified performance.</em> <p> <table border cellpadding=5> <tr> <td><strong>Parameter</strong></td> <td><strong>Specified</strong></td> <td><strong>Measured</strong></td> </tr> <tr> <td>Maximum RF Power [W]</td><td>220</td><td>220 (by design)</td> </tr> <tr> <td>Interport isolation [dB]</td><td>22</td><td>22</td> <tr> </tr> <td>input and output VSWR</td><td>1.17</td><td>1.2</td> </tr> <tr> <td>Insertion loss (IL) [dB]</td><td>0.5</td><td>0.22</td> </tr> <td>Through-path IL variation [dB]</td><td>+/- 0.2</td><td>+/- 0.12</td> </tr> <tr> <td>PIM (for two 60 W carriers) [dBm]</td><td>-60</td><td>-118</td> </tr> <tr> <td>Multipaction</td><td>single 500 W carrier</td><td>no occurrence</td> </tr> <tr> <td>Connector Type</td><td>TNC</td><td>TNC </td> </tr> <tr> <td>Frequency [Ghz]</td> <td>1.530-1.560</td><td>1.530-1.560</td> </tr> <tr> <td>Measured mass [g]</td><td>3200</td><td>2815</td> </tr> <tr> <td>Estimated mass [g]</td><td>- - -</td><td>2694 (titanium bolts)</td> </tr> <tr> <td>Dimensions [mm]</td><td>- - -</td><td>791 x 807</td> </tr> </table> <p> Insertion phase variation across the band between any input port to any output port was less within &#177;1&#186; with a phase tracking between output ports from a single input port not exceeding half a degree. Radio frequency performance was essentially unaltered after the environmental testing campaign. <p> The PIMP performance of the matrices has been measured at Matra Marconi Space (UK). Four input ports of each matrix have been tested at ambient temperature, and seven order PIMP levels of between -118 dBm and -124 dBm for two 60 W carriers have been measured. Thermal cycling does not affect the generation of passive of intermodulation products by the matrices and there was no evidence of multipaction. <p> <h3>Conclusion</h3> An eight-by-eight port hybrid matrix, for high power applications has been developed. The matrix shows very low insertion loss, no multipactor, low PIMPs and very tight amplitude and phase tracking. This features together with its low mass makes it very suitable for semi-active multi-matrix antennas. Future market opportunities include the Inmarsat Horizons Systems and a number of geostationary missions for hand-held telephony for which the eight-by-eight matrix is an extremely attractive building block. <P> <h4>Reference</h4> [1] Roederer A.G., French patent F-8912584. <p> <hr> <center> <strong> <a href="/publicat/about.htm">About</a> | <a href="/publicat/search.htm">Search</a> | <a href="/publicat/mailpub.htm">Feedback</a> </strong> </center> <hr> <a href="polev8n2.htm"><img align=right src="/images/right.gif" border=0 alt="Right"></a> <a href="andrv8n2.htm"><img align=right src="/images/left.gif" border=0 alt="Left"></a> <a href="/pff/futuv8n2.htm"><img align=right src="/images/up.gif" border=0 alt="Up"></a> <a href="/publicat/publicat.htm"><img align=right src="/images/home.gif" border=0 alt="Home"></a> <a href="/test.html"><img align=right src="/images/ttpbutton.gif" border=0 alt="TTP homepage"></a> <strong>Preparing for the Future Vol. 8 No. 2</strong><br> <em>Published June 1998</em><br> </body> </html> 
