Design of a Low-Cost High-Isolation RF Switch for X-Band Active Phased Array T/R Modules

LI Pan; DUAN Chuangwei; ZHU Wenbo; YANG Lixia; LIAO Guisheng

doi:10.11999/JEIT260326

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LI Pan, DUAN Chuangwei, ZHU Wenbo, YANG Lixia, LIAO Guisheng. Design of a Low-Cost High-Isolation RF Switch for X-Band Active Phased Array T/R Modules[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT260326

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LI Pan, DUAN Chuangwei, ZHU Wenbo, YANG Lixia, LIAO Guisheng. Design of a Low-Cost High-Isolation RF Switch for X-Band Active Phased Array T/R Modules[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT260326

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Design of a Low-Cost High-Isolation RF Switch for X-Band Active Phased Array T/R Modules

doi: 10.11999/JEIT260326 cstr: 32379.14.JEIT260326

National Key Laboratory of Photoelectric Information Acquisition and Protection Technology, Anhui University, Hefei 230601, China

Funds: National Natural Science Foundation of China (62501001), Supported by the Project of the National Key R&D Program of China (2024YFB3908202), Anhui Provincial Natural Science Foundation (2508085QF236), General Program of the China Postdoctoral Science Foundation (2025M780492), Anhui Postdoctoral Scientific Research Program Foundation (2026A1274)

Received Date: 2026-03-26
Accepted Date: 2026-09-15
Rev Recd Date: 2026-09-15

Available Online: 2026-09-20

Abstract

Abstract

Objective Radio frequency (RF) switches are key front-end components in communication and radar systems, especially in active phased array transmit/receive (T/R) modules. Positive-intrinsic-negative (PIN) diodes are widely used in high-power microwave switches because of their high power-handling capability, good linearity, and mature fabrication process. However, low-cost plastic-packaged PIN diodes exhibit significant parasitic effects at X-band frequencies. Junction capacitance, package inductance, and grounding-via inductance cause shunt branches to deviate from ideal short- or open-circuit conditions, resulting in degraded isolation and increased insertion loss. To address this problem, a low-cost high-isolation X-band single-pole double-throw (SPDT) RF switch design method based on parasitic-parameter compensation is proposed. Methods A step-wise synergistic matching strategy, termed “OFF-state prioritized determination and ON-state structural compensation”, is developed. OFF-state isolation and ON-state transmission conditions are treated separately to reduce coupling between isolation and transmission objectives. For the isolation branch, OFF-state diode parasitic parameters, a compensation stub, and grounding-via inductance are combined to form a series-resonant network. By compensating parasitic reactance, the branch satisfies the required impedance condition and suppresses signal leakage. After the compensation-stub parameters are determined, ON-state compensation is realized by introducing equivalent structural capacitance through T-junction edge effects and a stepped-impedance main line. This capacitance, together with the total equivalent inductance of the shunt branch, forms a parallel-resonant network, making the branch approach an open-circuit condition at the operating frequency. Thus, signal shunting is reduced and low-insertion-loss transmission is achieved without additional lumped compensation components. Results and Discussions The proposed switch topology is presented, and a full-wave simulation model is established (Fig. 3, Fig. 4(a)). Simulation results show that return loss is better than 20 dB, isolation is higher than 20 dB, and insertion loss remains around 0.2 dB over 8.57–9.34 GHz (Fig. 4(b)). A prototype is fabricated and measured (Fig. 5). Measurement results show that, over 9.5–10.4 GHz, return loss is better than 10 dB, insertion loss is lower than 2 dB, and isolation is higher than 20 dB (Fig. 6). Although the measured operating band shifts upward by about 1 GHz relative to initial simulation results, measured trends remain consistent with theoretical analysis. To explain this frequency shift, OFF-state junction capacitance and ON-state parasitic inductance are further analyzed. As OFF-state junction capacitance decreases from 0.24 pF to 0.195 pF, the high-isolation band shifts to higher frequencies (Fig. 7(a)). With OFF-state capacitance fixed at 0.195 pF, reducing ON-state parasitic inductance from 0.7 nH to 0.2 nH shifts the return-loss response to higher frequencies (Fig. 7(b)). After parameter correction, simulated return loss, insertion loss, and isolation agree more closely with measured results (Fig. 6). Compared with existing SPDT RF switch designs, the proposed design uses low-cost plastic-packaged PIN diodes and a simple microstrip compensation structure, requires no additional lumped compensation components, reduces dependence on the high intrinsic OFF-state impedance of PIN diodes, and achieves a good balance between cost and high-frequency switch performance (Table 1). Conclusions A low-cost high-isolation X-band SPDT RF switch based on parasitic-parameter compensation is presented. By using OFF-state series resonance and ON-state structural capacitance compensation, high isolation and low insertion loss are realized simultaneously. The fabricated switch achieves isolation higher than 20 dB and insertion loss lower than 2 dB over 9.5-10.4 GHz. The switch features a simple structure, ease of integration, and low cost, and provides a practical reference for low-cost high-isolation T/R module RF switches in active phased array systems.
- Active phased array,
- T/R modules,
- High-isolation RF switch circuit,
- Parasitic parameter compensation

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References(21)

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