# Analysis and Design of a Diplexing Power Divider for Ku-Band Satellite Applications
## 1 Introduction  
Recent years have seen the development of highly integrated multifunction devices as an effective means of achieving high-performance and low-cost solutions. Incorporating solar panels into electronic devices is a prime example of multifunctionality [1, 2]. This approach is particularly crucial in space communications where sunlight energy harvesting is required [3, 4]. Power dividers and diplexers are pivotal elements in RF systems and instruments. They find extensive application in novel space telecommunications for segregating dual communication pathways. In wireless systems, power dividers are commonly used for power division and power combining with proper isolation and frequency filtering features [5, 6, 7, 8, 9]. Diplexing circuits play a significant role in transceiver front-end wireless systems. They can effectively separate Tx/Rx channels connected to common wideband or dual-band antennas [10, 11, 12, 13]. Therefore, a diplexer technique can be employed to accommodate a system with multiple frequency bands and multiple functionalities. They can be used, for example, in a deep-space probe antenna system, in which the transmit and receive signals are divided to cover a wide communication delay and the space probes are assumed to be far from Earth [14]. Diplexing circuits provide essential filtering characteristics and isolation between Tx and Rx channels in multi-input and multi-output services for a space link. In this scenario, diverse communication links are harnessed to transmit or receive signals from the deep-space probe. This covers extensive distances while minimizing potential interference [15, 16]. Diplexers are often designed using two bandpass filters with coupled resonators or cavities [17; 18; 19; 20]. However, using a combination of low-pass and high-pass filters rather than two bandpass filters is preferable in some cases where the relative bandwidth of the transmit and receive channels is large [21]. Conventional diplexers are usually designed by using a rectangular waveguide, metal cavity junctions, or gap waveguide topologies to achieve desirable filtering performance [22]. However, when implemented in a practical array of probe antennas, these configurations can be cumbersome, heavy, and financially challenging [23], particularly in the context of space explorations in the future. One of the main challenges for modern circuit designers is to design high performance, modular, and integrated microwave components with a compact topology [24; 25; 26]. Several researchers have been focused on designing planar diplexing systems [27; 28]. Certain types among them necessitate the utilization of the low-temperature coferramic (LTCC) fabrication process to attain a more compact (packed) and densely arranged (miniaturized) device. Other types of these components employ microstrips, striplines, planar traces, and coplanar waveguides (CPW). Typically, these components comprise a duo of bandpass filters functioning in distinct frequency bands, interconnected through a distribution network [29; 30; 31]. These combined distribution networks often occupy considerable space and lead to an increase in the overall size of the circuits. Although these planar architectures present good performance at lower frequencies, they strongly suffer from undesired emission and radiation at high frequencies. Substrate integrated waveguide (SIW) is a renowned and currently well-established technological planar platform for RF, microwave, and millimeter-wave communication systems [32; 33; 34]. SIW is the most effective alternative to traditional microstrip or coplanar waveguides at high frequencies with extra performance. They have many features of rectangular waveguides, with the advantage of a low-cost fabrication process based on regular printed circuit board (PCB) technology [35]. SIW technology has found application in the design of various microwave and millimeter-wave components, such as filters, sensors, and reconfigurable electronics [36; 37; 38].