Copyright © 2011 IEEE.
Design and verification of ARGOS Tx/Rx space segment antenna L. Duchesne*, M. LeGoff*, L. Durand*, J. M. Baracco+, L. J. Foged# *
SATIMO Main Office, 17 Avenue de Norvege, 91140 Villebon-sur-Yette, France,
[email protected] + MARDEL, 2423, Avenue Emile Hugues, 06140 Vence, France,
[email protected] # SATIMO, Via dei Castelli Romani 59, 00040 Pomezia, Italy,
[email protected]
Abstract— An innovative Tx/Rx on-board antenna configuration suitable for ARGOS satellite applications has been studied, manufactured and tested. The antenna operates in right hand circular polarization at two narrow band frequencies centred around 402MHz and 466MHz and has an iso-flux type radiation pattern in the angular range from 0° to 63°. The electrical performance, thermal and mechanical issues and the minimization of the overall mass and envelope have been the design drivers in the study. Several antenna solutions ranging from different helix type antenna implementations to planar and 3D array constellations have been investigated and trade-off in the initial study phase. The final antenna structure selected for further investigation, elegant bread boarding and test is based on an axial dual element array configuration providing the desired iso-flux shaped pattern with minimum mass and overall size. The antenna is shown in Fig. 1 during testing in the SATIMO SG-64 multiprobe spherical range. This paper describes the pertinent phases of the study: Considerations on the antenna design trade-off activity, selection of the candidate antenna technology, manufacturing, tuning and final testing.
I. TRADEOFF STUDY AND SELECTION OF ANTENNA TECHNOLOGY The almost natural choice for the type of gain coverage required for the considered application is a quadrifilar helix. This antenna was selected as the performance benchmark antenna for the study. Several antenna candidates, including planar array antennas, have been evaluated in order to reproduce a similar gain coverage. Some of the investigated antenna configurations are illustrated in Fig. 2. Most of the candidate elements consist of a relatively complex structure and require a larger volume than the helix. Nevertheless, one of the candidate elements, consisting in an axial two elements array, has been selected has a potential challenger to the classic quadrifilar helix. The selected candidate element, which can be seen as an helix decomposed in two elements, has a larger diameter than the equivalent helix with comparable or even smaller height. The larger diameter of the chosen antenna is for a part due to the choice of using metallic radiating elements in order to obtain a fully metallic structure which is appreciable for space applications. Moreover, the choice to avoid dielectric for the elements allows optimising the radiation efficiency of the antenna. The resulting antenna structure is very robust and well suited for space environment.
Fig. 1 Selected ARGOS antenna configuration based on superposed radiating elements
Fig. 2 Different candidate elements considered
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Another, and non negligible, advantage of the selected antenna structure is its capacity of handling dual circular polarisation which is not the case of the quadrifilar helix. This quality combined with the possibility to obtain a good matching on fairly large bandwidths and to handle relatively high power levels could be decisive for certain applications compared to an helix. The axial two elements array was selected for elegant bread boarding and measurement.
configuration in order to obtain the desired gain coverage over the two bands of the ARGOS application. After having selected the preferred distance between elements and their corresponding amplitudes and phases, several mechanical profiles to be placed below the upper element have been studied in order to minimise the blockage created by this element. The hyperbolic profile in upper right position in Fig. 4 offers the best compromise as the impact on axial ratio and back radiation are minimized for this element.
II. SELECTED ANTENNA TECHNOLOGY The selected antenna technology is based on two superposed radiating elements as shown in Fig. 3. One major difficulty with this type of design is to avoid a large blockage due to the presence of the upper element. Consequently, the diameter of the radiating elements has to be reduced as much as possible, maintaining nevertheless a sufficient bandwidth and radiating efficiency.
Fig. 3 Details of the Selected ARGOS antenna configuration based on superposed radiating elements
Two fully metallic radiating elements have been considered. The first one was an annular slot cut in the upper ground plane of a circular cavity, while the second one was a circular patch supported by a central post. With the use of notches cut in the circular patch it has been possible to obtain similar diameter for both structures. Consequently, because of its more robust construction and easier feeding the circular patch has been chosen. In order to obtain a sufficient bandwidth on both bands of the application, capacitive coupling from four vertical probes has been chosen for this element. The feeding by probes also allows to dispose of a large space to integrate the stripline feed network of each element. This feed network generate a sequential rotation with the help of two compact 90° couplers especially designed for this application. The chosen radiating element combined with its feed network provide a circular polarisation of very good quality. After having defined the radiating element structure, the complete array has been designed. A parametrical analysis has been done in order to determine the best distance between elements and the best amplitude and phase distribution between these two elements for each mechanical
Fig. 4 Various profiles that have been studied for upper element
The selection of the most suited profile and the design of a printed power divider generating the required amplitude between the two elements of the antenna and which is integrated inside the central tube of the antenna has completed the design phase. The antenna calculated electrical performance is illustrated in Fig. 5 and Fig. 6.
Fig. 5 Predicted radiated performance F = 402MHz
Copyright © 2011 IEEE.
Measured phase imbalance of the coupling factors 2.00
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Fig. 9 Mesured phase imbalance of the coupling factor
Fig. 6 Predicted radiated performance F = 466MHz
III. ANTENNA TESTING Before to verify the performances of the complete antenna in a SATIMO SG-64 multi-probe spherical near field test range, the performance of various parts of the antenna have been measured separately. The performance of the printed 90° couplers have been verified on a network analyser. The compact coupler prototype is shown in Fig. 7, and the corresponding measured magnitude of the coupling factor is presented in Fig. 8. The experimental phase imbalance is shown in Fig. 9.
Then the radiating performances of a radiating element has been verified in the SATIMO SL18GHz equipment. Finally the complete antenna has been optimised by tuning the distance between elements and the amplitude and phase between them using radiation pattern measurements. For this application the phase difference between elements is adjusted by rotating the element with respect to each other. After having fixed the final antenna configuration which is close to the one predicted by numerical analyses, the printed power divider generating the right amplitude distribution between elements has been designed and its performances have been verified on a network analyser. This power divider is presented in Fig. 10 and the corresponding measured amplitude distribution is plotted in Fig. 11. After having integrated this power divider in the inner tube of the antenna, the final testing of the antenna in the SATIMO SG-64 have been performed. The resulting directivity patterns are shown in Fig. 12 and Fig. 13.
Fig. 7 Compact 3dB 90° coupler realization for RHCP polarization synthesis Fig. 10 Optimized prototype of printed power divider Measured magnitude of the coupling factors
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Fig. 11 Measured amplitude distribution of the printed power divider
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Copyright © 2011 IEEE.
Measured Directivity, f=401 MHz, average of 4 main cuts (0, 45, 90, 135 deg.) 5 4.5 4 3.5 3 2.5 2 1.5
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larger diameter than the equivalent helix with the same height. The element is capable of providing dual circular polarisation which is not the case of the quadrifilar helix. And is a fully metallic structure which is appreciable for space applications. Moreover, the choice to avoid dielectric for the elements allows optimising the radiation efficiency of the antenna. The resulting antenna structure is very robust and well suited for space environment. Good matching and radiation performances responding to the ARGOS application have been obtained. Losses in the feed network between the two elements should be minimised and the radiation efficiency of the elements, in particular in the upper band could be further improved. REFERENCES
Fig. 12 Measured directivity pattern F = 402MHz [1] RHCP F=401 MHz LHCP F=401 MHz RHCP F=403 MHz LHCP F=403 MHz RHCP F=465.9375 MHz LHCP F=465.9375 MHz RHCP F=468.925 MHz LHCP F=468.925 MHz Gain max. Tx Gain min. Tx Gain min. Rx
Measured Directivity, average of 4 main cuts (0, 45, 90, 135 deg.) 10 5 0
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Fig. 13 Measured directivity pattern F = 466MHz
The measured antenna efficiency / losses are illustrated in Fig. 14. The loss budget break down is shown in Fig. 15. f (MHz) 401 403 465.9375 468.925
Dir ET 3.80 3.84 3.98 4.00
Dir RC Polar Losses Gain RC Total Losses efficiency% 3.74 0.06 2.24 1.56 69.75 3.79 0.05 2.10 1.74 66.91 3.90 0.08 1.90 2.08 61.93 3.94 0.06 1.54 2.46 56.67
Fig. 14 Measured antenna efficiency / internal losses f (MHz) 401 403 465.9375 468.925
Cables&Divider Losses 0.54 0.54 0.61 0.62
Return&Load Losses 0.24 0.37 0.16 0.36
Coupler Losses 0.12 0.12 0.13 0.13
Dielectric&Ohmic losses 0.60 0.66 1.10 1.29
Fig. 15 Breakdown of the antenna efficiency / internal losses on different constituents
IV. CONCLUSION An innovative Tx/Rx on-board antenna configuration suitable for ARGOS satellite applications has been studied, manufactured and tested. The antenna operates in right hand circular polarization at two narrow band frequencies centred around 402MHz and 466MHz and has an iso-flux type radiation pattern in the angular range from 0° to 63°. The almost natural choice for the type of gain coverage required for the considered application is a quadrifilar helix. The selected axial two elements array element has a slightly
M. Sabbadini, L. J. Foged, J. M. Baracco, M. Bandinelli, M. Bercigli, “Wideband Medium-Gain Radiating Elements in Multi-Layer Composite Technology, 25th ESA antenna workshop, Noordwijk, The Netherlands. M. Sabbadini, A. Giacomini, M. Bandinelli, M. Bercigli, D. Gabbani, J. M. Baracco, L. J. Foged, “Numerical modelling and experimental validation of multilayer antennas with complex feeding network”, 26th ESA antenna workshop, Noordwijk, The Netherlands. A. Giacomini, L. J. Foged, J. M. Baracco, M. Bandinelli, M. Sabbadini, “Dual polarised multi-layer antenna with complex feeding network”, Eucap 2009, 3rd European Conference on Antennas and Propagation, March 2009, Berlin, Germany.
