# Reconfigurable Diplexer-Based Filtenna for Tx/Rx Operation in Mobile Satellite Terminals
The communications are made at high frequencies (Ka band), using different bands for the uplink (27.5-30 GHz) and downlink (19.7-21.2 GHz). It is essential that mobile devices maintain their simplicity, compactness, efficiency, and low cost, but with the ability to operate in the two different frequency bands. Antennas are an essential component of any wireless communication system. Its development needs to be constant to keep up with new technological challenges and to accommodate different properties in terms of communication. In case of mobile devices using satellite communications, their antennas must be able to operate in the different satellite bands (for Tx and Rx). In addition, more compact devices, more powerful and with a wider range of communications are increasingly in demand; however, the space available is growing increasingly smaller. An antenna that is capable of operating in two different bands, replacing the need for two antennas, saving space, is an important benefit for modern systems. These antennas with the ability to adapt one or more of their operating parameters are referred to as reconfigurable antennas. Reconfigurable antennas can change their properties, such as resonating frequency, gain, radiation pattern, or polarization, according to the communication requirements. A single element can do the same work that would be achieved using multiple elements. To accomplish this adjustment, the physical structure of the antenna can be modified, such as the feeding network or the radiating element, leading to a changing in the current distribution. The reconfigurability can be obtained using some techniques, being popular those using varactors, as tuning elements, or RF-MEMS (Radio Frequency-Micro Electro Mechanical System) and PIN diodes which can act as ON/OFF switches, changing the physical structure of the antenna. In [2], a microstrip patch is presented with the ability to operate at three different bands: 2.3-2.51 GHz, 3.35-3.75 GHz, and 4.95-5.53 GHz. To achieve the reconfigurability, PIN diodes were inserted in the ground plane, which can connect or disconnect different metal structures that allow the adjustment of the operating frequency. A reconfigurable antenna that is capable of changing its radiation pattern and resonating frequency is shown in [3]; this antenna is composed by a circular slot with a PIN diode in the top side of the substrate, allowing the change of the radiation pattern. In the opposite side of the substrate, there is the feed line with a stub, which can be connected to the main line by PIN diodes. So, controlling the state of the switches, it is possible to define if the stubs are or are not connected to the central line, controlling the matching of the antenna and the resonating frequency. A polarization reconfigurable antenna can be seen in [4], where a circular slot was integrated in a circular microstrip patch; two PIN diodes were inserted between the slot and one  
Figure 1: Smart city/Internet of Things (IoT) scenario and satellite communications. of the antennas edges, and if they are connected, it is possible to select the polarization of the antenna. Another technique using RF-MEMS can be seen in [5], where an antenna that can change its radiation pattern is presented, operating at 6.85 GHz. Analyzing the reported works, it is possible to conclude that the presented antennas cannot be integrated into mobile terminals to communicate with satellites constellations. In general, they operate at low frequencies, the bandwidth is narrow, the range of frequencies is small, they need coaxial cables for power supply, and they use capacitors that do not work properly when the frequency increases. In addition, besides the low frequency, in some examples, the complexity is high. In [6], an array of some slots in a \"T\" shape is shown. The slots allow the antenna to operate at two high frequencies: 28 GHz and 38 GHz. PIN diodes were inserted in both arms of each slot in order to achieve the reconfigurability.