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

Received Date: 2026-03-23
Accepted Date: 2026-09-15
Rev Recd Date: 2026-09-08

Available Online: 2026-09-20

Abstract

Abstract

Objective Radio Frequency (RF) switches are critical front-end components in communication and radar systems, especially in active phased array Transmit/Receive (T/R) modules, where their insertion loss, isolation, and power-handling capability directly affect system performance. 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 suffer from considerable parasitic effects at X-band frequencies. The junction capacitance, package inductance, and grounding-via inductance introduce deviations from ideal short- or open-circuit conditions in shunt branches, resulting in increased signal leakage, degraded isolation, and higher insertion loss. Therefore, this paper proposes a low-cost high-isolation X-band Single-Pole Double-Throw (SPDT) RF switch design method based on parasitic-parameter compensation to improve the high-frequency performance of low-cost PIN diode switches. Methods A step-wise synergistic matching strategy, termed “OFF-state prioritized determination and ON-state structural compensation”, is proposed. OFF-state isolation and ON-state transmission conditions are treated separately to reduce coupling between isolation and transmission objectives. First, the OFF-state isolation condition is determined by combining the diode parasitic parameters, compensation stub, and grounding-via inductance to construct a series-resonant network. By compensating the parasitic reactance of the isolation branch, the required impedance condition is satisfied, thereby suppressing signal leakage through the isolated path. After determining the compensation-stub parameters, ON-state structural compensation is further implemented by introducing equivalent capacitance through T-junction edge effects and a stepped-impedance main line. The introduced structural capacitance compensates for the equivalent inductance of the shunt branch and forms a parallel-resonant network, allowing the branch impedance to approach an open-circuit condition at the operating frequency. Thus, signal shunting is reduced and low-insertion-loss transmission is achieved without introducing additional lumped compensation components. Results and Discussions The proposed switch topology is established, and a full-wave simulation model is developed (Fig. 3, Fig. 4(a)). Simulation results demonstrate that the designed switch achieves a return loss better than 20 dB, an isolation higher than 20 dB, and an insertion loss of approximately 0.2 dB within 8.57～9.34 GHz (Fig. 4(b)). A prototype is fabricated and experimentally characterized (Fig. 5). Measurement results indicate that, within 9.5～10.4 GHz, the return loss is better than 10 dB, the insertion loss is lower than 2 dB, and the isolation exceeds 20 dB (Fig. 6). Although the measured operating band shifts upward by approximately 1 GHz compared with the initial simulation results, the measured variation trends agree well with the theoretical analysis. To investigate the frequency shift, the effects of OFF-state junction capacitance and ON-state parasitic inductance are further analyzed. When the OFF-state junction capacitance decreases from 0.24 pF to 0.195 pF, the high-isolation frequency band shifts toward higher frequencies (Fig. 7(a)). With the OFF-state capacitance fixed at 0.195 pF, reducing the ON-state parasitic inductance from 0.7 nH to 0.2 nH also shifts the return-loss response toward higher frequencies (Fig. 7(b)). After correcting the parasitic parameters, the simulated return loss, insertion loss, and isolation show improved agreement with the measured results (Fig. 6). Compared with existing SPDT RF switch designs, the proposed design employs low-cost plastic-packaged PIN diodes and a simple microstrip compensation structure, eliminates the need for additional lumped compensation components, reduces dependence on the intrinsic high OFF-state impedance of PIN diodes, and provides an effective trade-off between manufacturing 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 proposed and experimentally verified. The proposed design combines OFF-state series resonance with ON-state structural capacitance compensation to simultaneously achieve high isolation and low insertion loss. The fabricated switch achieves an isolation higher than 20 dB and an insertion loss lower than 2 dB over 9.5～10.4 GHz. Owing to its simple structure, low cost, and ease of integration, the proposed switch provides a practical solution for low-cost high-isolation RF switches for T/R modules in active phased array systems.

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References(21)

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