# Design of Broadband High-Frequency Multi-Throw RF-MEMS Switches
## 3 Results and Discussion
### Key Factors Affecting RF Performance  
In RF MEMS switch applications, isolation is a paramount parameter for assessing switch performance. When the operational frequency of the switch reaches certain thresholds, isolation may decline significantly, jeopardizing adequate signal segregation. In addressing this challenge, our study introduces a novel upper electrode structure, informed by an analysis via Equation (1). The strategy predominantly entails narrowing the width of the upper electrode's tip, consequently reducing its coupling area with the signal line, thereby augmenting the impedance during the switch's off state. This approach enables our design to dramatically mitigate RF signal coupling from input to output, leading to superior isolation performance. Additionally, our switch design incorporates a graded structure to curtail RF performance degradation. This design aims to maintain high isolation levels while diminishing signal loss during transmission, thereby optimizing the switch's overall RF performance. Isolation levels between the conventional straight electrode and our innovative upper electrode design are compared in Figure 5. The results highlight that our upper electrode design offers superior isolation under high-frequency conditions. By contrasting various electrode designs, this research offers potent design and theoretical foundations for optimizing isolation in high-frequency applications of RF MEMS switches.  
The air gap, denoted as \(g\), is a critical determinant of the switch's RF and mechanical properties. The off-state capacitance is a pivotal metric for ohmic-contact RF MEMS switches in gauging a switch's signal isolation capability. It is discerned that \(g\) is the predominant factor prompting variance in off-state capacitance under uniform switch parameters and material conditions. The influence of air gaps on isolation and return losses is depicted in Figure 6. For our study, considering that the trade-off of enlarging the gap is the increase in pull-in voltage, we opted for a \(g\) value of 0.5 \(\upmu\)m.  
Power dividers are crucial in multi-throw switches, where an adept design can maximize signal conservation. In a specific study, RF MEMS switches based on symmetrical circular topology, notably SP7T and SP11T, have been proposed. These switches, with compact dimensions of merely 0.61 mm \(\times\) 0.61 mm, are significantly smaller than conventional CMOS Si-on-insulator switches. Another study presented a radiating MEMS power divider/combiner design that enables equidistant current distribution across multiple switches, offering the merits of bandwidth, low loss, and compactness [30]. Lastly, research has showcased a generic methodology to assess multi-port centric feed circular microstrip disk power divider/combiner circuits, grounded in planar circuit techniques,  
Figure 5: Comparison curve of the isolation of the flat plate and the electrode proposed in this research.  
deploying two-dimensional Green's functions of circular sections [31]. In our work, we adopt a circular topology for the power divider to diminish insertion loss and condense switch size, followed by size optimization. The insertion loss curve of Figure 7 establishes the final dimensions: \(D1\) at \(6\) \(\upmu\)m and \(D2\) at \(10\) \(\upmu\)m. Such optimization further trims insertion loss while preserving switch compactness, enhancing the performance and efficiency of multi-throw switches.