2 Buried Power Dividers 1:4 in Mulitlayer LTCC
The phased array antenna concept of the project HIFE as part of an ESA ARTES-3 program, motivates the development of a power distribution network in multi-layer LTCC. Applications like satellite communication with broadband multimedia services are requiring solutions of that kind. The innovative antenna concept provides multiple beams with different directions of radiation. The main advantage is the flexible use of bandwidth exclusively in the desired ground zones.
A multiple beam concept implies that every antenna element has to receive the information of all participating beams. In order to maximize miniaturization, a compact distribution network was needed. Within the EASTON project, funded by the German Space Agency, a power distribution module for Ka-band down-link (17-21 GHz) on multi-layer LTCC has been developed, which would fit into the concept of the HIFE project. LTCC has been chosen to stack two distribution networks (each with 1 input and 4 output ports) on top of each other within the multilayer ceramic. Each network consists of 3 Wilkinson dividers with buried screen printed resistors as well as several optimized waveguide transitions. Stripline technology has been utilized, while via chains suppress cross-talk from one part of the circuit to another. The final module demonstrates the benefits LTCC: compact size, low cost and reliable performance. The photograph shows the entire divider module.
The design and development activities within this project have been concentrated upon the optimisation of the buried stripline waveguides, the Wilkinson dividers with buried screen printed resistors as well as the 5 different transitions within the multilayer LTCC and the housing. Green TapeTM multilayer LTCC from DuPont has been selected to develop the buried divider networks. Basic investigations have shown, that the multilayer ceramic is suitable to be used in microwave applications. The lsetup consists of: In total 10 layers with different tape thickness (A2 and AX) have been utilized to realise two buried striplines (SL1 and SL2) for the dividers and a microstrip line (MS) on top of the substrate. All RF-ports are on the same level at SL1 at a height of 1mm. This requires interlayer transitions from MS to SL1 and from SL2 to SL1. Further transitions are from the ports on the LTCC to the GPPO connectors within the DISPAL housing. Some selected results are described in the following sections.
Wilkinson Dividers in LTCC
Each network includes one input and four output ports. A binary tree is formed of three Wilkinson dividers. The resistors thereof are buried components to provide short connections without additional parasitics. Wider strip lines give lower ohmic losses. Thus the inner line impedance of the strip lines was decided to be 30 Ohm. Therefore the resistor value of the Wilkinson divider is 60 Ohm. The optimisation of the divider design was done with the IMST in-house developed 3D FDTD field simulator EMPIRETM. The following figure shows a Wilkinson divider in the software environment with visualised field distribution of the perpendicular electric field for two different field excitations. Via chains around the structure suppress unwanted cross-talk.
In the next step three dividers were combined to a (1 : 4) distribution network. Optimum chamfered bends and interconnecting lines lead to an overall satisfying electrical behaviour. The structure together with the field distribution of the perpendicular electric field is shown above. The field excitation at port 2 gives a good imagination of the increasing isolation between adjacent output ports. The power is reduced by 3 dB at every divider stage. This relationship is illustrated nicely by the fading amplitude of the electric field.
print view
