A 2.45GHz Power Divider and Patch Antenna

Abstract—This paper consists of two parts; a power divider and a patch antenna. In the first phase a Wilkinson power divider is described with Flexibility and size reduction are achieved simultaneously thanks to both an open-stub loading the input port and additional transmission lines connecting the output ports to the isolation resistance. A power divider working at 2.45 GHz were fabricated and measured. In second phase a rectangular patch antenna is designed feed with microstrip line. To obtain good matching and transmission patch antenna length and width could be adjusted for change in frequency and impedance by tuning. Both the power divider and the antenna have been developed and manufactured using a traditional substrate known FR-4 in order to guarantee their compatibility with the innovative communication systems. Both power divider and patch antenna are designed using ADS and layout is visualized in EM simulation supported within ADS.

Keywords--—Power Divider, Wilkinson Power Divider, Coupler, Patch Antenna, TLines, ADS, EM Simulation, 3-port device, Passive Circuits

INTRODUCTION

POWER divider are key devices in communication systems for differential power amplification or antenna arrays feeding purposes. Wilkinson power dividers constitute efficient components thanks to high isolation between the output ports, and easy design when dealing with planar structures. However, they suffer from a lack of flexibility when connecting the resistance necessary for isolation between the output ports, and in the choice of the characteristic impedance of the quarter-wave length arms. They also suffer from a large surface area, with two quarterwave length transmission lines (TLines). Extra TLines for connecting the isolation resistance. This avoids parasitic coupling between the two out ports, which constitutes a real drawback when dealing with millimeter-wave frequencies. More recently, a general model was developed in order to give design rules for the synthesis of these additional TLines. A large variety of characteristic impedances can be chosen in such a way that various power ratios between the out ports can be reached. The quarter-wave length arms of the conventional impedance transformer were miniaturized thanks to the use of open stubs and/or step impedances. This also enhanced flexibility in the choice of the TLines characteristic impedance. In counterpart, this topology leads to a complex impedance transformation instead of the classical real one[1]. Hence, a capacitance must be added in series with the resistance of the isolation branch so as to compensate the imaginary part. Patch Antennas are widely used in portable wireless devices because of the ease of fabricating them on printed circuit boards. Multiple patch antennas on the same substrate called microstrip antennas, can be used to make high gain array antennas, and phased arrays in which the beam can be electronically steered. At the same time, its flat profile and reduced weight, compared to parabolic reflectors and other antenna options, made it attractive for airborne and spacecraft applications. More recently, those same properties, with additional size reduction using high dielectric constant materials, have made patch antennas common in hand sets, GPS receivers. The paper describes the design and measurements of power divider and patch antenna in different sections. The goal of this experiment to design the 1:2 power divide and connect it with patch antenna to extract Sparameters. After fabrication is done, measurements are taken in in Vector Network Analyzer (VNA).

MODIFIED WILKINSON POWER DIVIDER

According to the proposed Wilkinson power divider scheme, we designed a 1:2 power divider of length λ/4. As it is 3-port power divider (1-input and 2-output), our input characteristic impedance (Zc) is 50 Ω, while the characteristics impedance for other two transmission lines is set at 70 Ω in order to achieve a balanced split between the ports 2 and 3. After analyzing the results at this point, a non-ideal isolation between output ports is found and we incorporated a 100 Ω resistor in order to maintain the level of isolation between port 2 and 3 i.e. S23. Additionally, a 1mm gap was introduced in parallel to the resistor to account for the imaginary component of the impedance. The results were once again examined with the inclusion of the resistor. In the final stage, supplementary transmission lines were connected to establish the connection between the isolation resistor and the outports of the power divider, thereby avoiding any coupling. Following the adjustment of the lengths and widths of the transmission lines, the S-parameters were observed. Through simulation, the transmission between port 1 and the two outports (S21) was measured at -13.88 dB, while the isolation between the two outports, 2 and 3 (S23), reached -8 dB at 2.45GHz. The reflection of outport 3 (S33) was around -12 dB, and for the input port (S11), it was -3.7 dB. The corresponding Sparameters are shown in figure 1. While the results are not so satisfactory at this point but we will look further how we improved our results while fabrication in section Ⅲ. Figure 1 displays the measured S-parameters of the designed power divider in relation to the selected frequency of 2.45GHz.

Fig 1: S11 Parameter

Fig 2: S23 Parameter

Fig 3: S21 Parameter

Fig 4: Fabricated Power Divider

Fig 5: Measurements Taken from VNA

A table showing the measured values below to be clearer and more precise.

TABLE 1. S-PARAMETERS MEASURED FROM FABRICATED POWER DIVIDER.

S-parameters	Values (dB)
S11	-27.719
S22	-11.5665
S33	-11.0969
S31	-3.75
S21	-3.400
S23 -11.3461

The values measured from VNA shows much what we wanted our S-parameters to be, apart from the spike in figure 3 because of more soldering as there is more metallization over Transmission lines.

PATCH ANTENNA

A patch antenna feed with microstrip line is described in this section. Antenna is designed using the same substrate within ADS. By simulation we are able to change fc by Lpatch and the impedance by Wpatch using predefined equation

The geometry of the antenna is subsequently adjusted in order to attain the most favorable measurements. In this context, the momentum simulation is favored as it affords a more precise analysis of the antenna's behavior. The outcomes of the momentum simulation for the planned antenna are illustrated in Fig. 4. Based on the simulation outcomes, the reflection of the input port is -5.2 dB under the most optimal circumstances. In general, for antennas, a reflection parameter S of 10 dB corresponds to an acceptable level of performance. The frequency experiences a slight forward shift due to the constraints imposed by the design and the patch's length being marginally lower than the calculated value.

Fig 6: S11 Parameters of the Patch Antenna

Fig 7: Input Impedance of Patch Antenna

The arrangement of our designed antenna is subsequently fabricated for utilization in production. Two identical antennas are manufactured based on this singular design to be utilized as both transmitting and receiving antennas with equivalent amplifications. These two antennas are situated at a distance of 1 meter from one another and are connected to the ports of the VNA to extract the S-parameters.

Fig 8: Results of Tx and Rx when placed at 1m to each other

As is evident from the figure 6, the S21, which is associated with the insertion loss between the two antennas, is recorded as -42.92 dB, a value in close proximity to the theoretical value of -40 dB. The reflection of port 1, which is associated with the transmitter (S11), and port 2, relevant to the receiver (S22), are recorded as -11.7 dB and -8.6 dB, respectively. In an ideal scenario, S11 would be equivalent to S22. However, due to the presence of losses, these two values differ to a moderate extent. Furthermore, since we do not possess a perfect match, S11 is not equal to zero. Consequently, it is inevitable that we will have a smaller S21 and antenna amplification

CONCLUSION

In this article, we have proposed a modified version of the Wilkinson power divider that uses additional transmission lines and corners, thereby operating at a frequency of 2.45 GHz. The optimization of the lengths and widths of these lines has resulted in a reduction in the coupling between the output ports. To validate the efficacy of the proposed structure, a modified Wilkinson power divider was fabricated using a FR4 substrate. Through measurement, this fabricated device demonstrated a commendable performance in terms of insertion loss, return loss, and isolation, which closely aligned with the simulation results. Furthermore, a patch antenna operating at the same frequency was designed and its performance was evaluated. Subsequently, two identical antennas were fabricated for use as transmitter and receiver, and their S-parameters were monitored. The observed results were found to be consistent with the theoretical calculations. The utilization of the modified power divider in conjunction with the antenna holds great promise for a variety of wireless communication applications. Due to its dual functionality as a power splitter and combiner, it has the potential to significantly enhance the performance of antenna systems, depending on the specific functional requirements.

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A 2.45GHz Power Divider and Patch Antenna