Dich, Mikael

Mortensen, Mette Dahl

The design of a low loss one-to-four power splitter suitable for beam forming networks in antenna arrays is presented. The power splitter is constructed of a shorted waveguide in which five coaxial probes are inserted. Methods for the design of the power splitter are presented together with an experimental verificatio

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Downloaded from orbit.dtu.dk on: Dec 17, 2017Low loss power splitter for antenna beam forming networks using probes in awaveguideDich, Mikael; Mortensen, Mette DahlPublished in:Proceedings of the 24th European Microwave ConferenceLink to article, DOI:10.1109/EUMA.1994.337479Publication date:1994Document VersionPublisher's PDF, also known as Version of recordLink back to DTU OrbitCitation (APA):Dich, M., & Mortensen, M. D. (1994). Low loss power splitter for antenna beam forming networks using probes ina waveguide. In Proceedings of the 24th European Microwave Conference (pp. 1791-1795). IEEE. DOI:10.1109/EUMA.1994.337479Low loss power splitter for antenna beam formingnetworks using probes in a waveguideM. Dich and M. Dahl MortensenElectromagnetics Institute, Technical University of DenmarkBuilding 348, DK-2800 Lyngby, DenmarkTelephone +45 4288 1444Fax +45 4593 16341 ABSTRACTThe design of a low loss one-to-four power splitter suitable for beam forming networksin antenna arrays is presented. The power splitter is constructed of a shorted waveguidein which five coaxial probes are inserted. Methods for the design of the power splitterare presented together with an experimental verification.2 INTRODUCTIONPlanar antennas of microstrip patches are often used for airborne radar applications.Such antennas often consist of several panels of microstrip patches. To feed the individ-ual panels from a single input port, a power splitter is needed. The power splitter couldbe constructed using traditional microstrip components (branch-line couplers, Wilkin-son power splitters etc.) but their losses are relatively high. In this paper a low losspower splitter, construced of a piece of shorted waveguide containing coaxial probes ispresented. To design the power splitter both method of moments models and networkmodels have been developed for the probe-to-waveguide components involved. Usingthese models, a four way power splitter with unequal split has been designed, manufac-tured and measured.3 THE POWER SPLITTERThe designed power splitter, shown in Fig. 1, contains five coaxial probes. The inputport is located in the center of the waveguide. To obtain the electrical characteristicsof this probe, a method of moments (MM) model for a single probe inserted into a1791Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 9, 2010 at 08:30 from IEEE Xplore.  Restrictions apply. Line off7 symmetrySETOP VIEWI Xt0 bIa *Figure 1: The four way power splitter' 3infinite waveguide has been developed. The four output port,s are located in pairs nearthe shorted ends of the waveguide. To obtain the characterist'ics of these probes, aMM model for two closely spaced probes inserted into an semi-infinite waveguide hasbeen developed. In calculating the scattering parameters of the entire power splitter aTE10-mode transmission line circuit as shown in Fig. S2'haA been used.port 2port 3port 4port 5port 1 (.): S-parameters for the three-ports- found using MM models.Figure 2: Model for the power splitter1792Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 9, 2010 at 08:30 from IEEE Xplore.  Restrictions apply. 4 THE METHOD OF MOMENTS M)ODELThe MM models of the probe-to-waveguide components are based on the work of' Jarem[1]. The MM models use sinusodial functions for the expansion of the currents on theprobe surface. Only the y-directed parts- of the probe current is included -in the analysisand is approximated by ten filamentary currents equally spaced on- the surface of thecircular probe. The field- scattered from the probe currents are found using the electricalGreen's functions for a rectangular waveguide. The coaxial source is approximatecd by amagnetic frill current radiating into half space. Finally, the probe currents are found byrequiring', in a Galerkin type of procedure, that- the tangential -electric field is zero in thecenter of the probe. Three different MM models have been programmed: one,model fortwo closely spaced probes in a semi-infinite wavegu'ide and models for a single probe inboth a semi-infinite and an infinite waveguide.5 NETWORK MODELSNetwork models have been developed for the three types of proberto-waveguide com-ponents. The network models -make it more feasible to include the -components in amicrowave CAD program, since only three circuit elements are needed to describe eachprobe. The network model for a single probe in an semi-infinite waveguide is shown inFig. 3. The values for the circuit elements can be found from the scattering parametersusing simple expressions.Figure 3: Network model for a probe in a semi-infinite waveguide1793Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 9, 2010 at 08:30 from IEEE Xplore.  Restrictions apply. 6 EXPERIMENTAL RESULTSTo test the performance of both the MM models and the network models, the four waypower splitter was designed using the transmission line circuit show in Fig. 2. Since thepoweri splitter is intended for a microstrip antenna used in a specific SAR radar system,the power splitter was designed with unequal split. The level of the output of two ofthe output ports (ports 3 and 5) are designed to be 70 % of the level of the output ofthe remaining two ports (ports 2 and 4). The input reflection of the input port (port 1)is designed to be as low as possible in the frequency band of operation: 5.3 GHz ± 50MHz. The power splitter was manufactured from standard C-band waveguide and theprobes are standard SMA-connectors with long center conductors.In Fig. 4 the input reflection coefficients of the input port is shown when all the outputports are matched. The solid curve represents the calculated input reflection coefficientand the dashed curve the measured. In Fig. 5 the transmission coefficients between theISil1 [dB] calculated--------- measured4.00 4.25 4.50 4.75 5.00 5.25 5.50 5.75 6.00Frequency [GHz]Figure 4: Measuredway power splitterand calculated input reflection coefficient for the experimental fourinput port (port 1) and port 2 (top curve) and port 3 (bottom curve) is shown. Sincethe power splitter is symmetrical as indicated on Fig. 1, the, transmission coefficientsbetween port 1 and the ports 4 and 5 are equal to the transmission coefficients betweenport 1 and the ports 2 and 3. The loss of the power splitter has been measured to beless than 0.1 dB in the frequnecy band 5.3 GHz ± 100 MHz.1794Authorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 9, 2010 at 08:30 from IEEE Xplore.  Restrictions apply. ISlil [dB]-4.00r -- calculated--------- measuredITS12-5.00 _-' ---6.00-7.00S13-8.00 . - -- _-9.00-90.00 1 5 0 5 . 5. 5 . 0> S~~ ~~~~.OOS.10 5.20 5.30 5.40 S. iO 5.60iFrequency [GHz7Figure 5: Measured and calculated transmission coefficients for the experimental fourway power splitter7 CONCLUSIONIn conclusion, we have demonstrated that a shorted waveguide, in which probes areinserted, can be used as a low loss power splitter. A Method of Moments (MM) modelhas been developed for the relevant configurations of probes in a perfectly electrically-conducting (PEC) waveguide. The power splitter was designed using results computedfrom the.MM model and was subsequently manufactured and measured. The predictedcharacteristics of the power splitter are in excellent agreement with the measured data4Further, it has been experimentally verified that the designed power splitter possess lowlosses.References[1] J. M. Jarem, "A Multifilament Method-of-Moments Solution for the Input Impedanceof a Probe-Excited Semi-Infinite Waveguide", IEEE Transactions on MicrowaveTheory and Techniques, 35(1), pp. 14-19, January 1987.1795I -IAuthorized licensed use limited to: Danmarks Tekniske Informationscenter. Downloaded on February 9, 2010 at 08:30 from IEEE Xplore.  Restrictions apply. 

Low loss power splitter for antenna beam forming networks using probes in a waveguide

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Low loss power splitter for antenna beam forming networks using probes in a waveguide

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