W-Band Switch Research

Millimeter-wave switch is extensively applied in the fields of radar, navigation,surveying, communications and electronic countermeasure. PIN switch has manyadvantages, such as simple structure, small size, high performance, low cost and so on, so itoccupies an extremely important role in the millimeter-wave switch. And it’s quitemeaningful to study PIN diode switch.The theoretical and experimental researches on the W-band single-pole single-throw(SPST) switch and single-pole double-throw (SPDT) switch have been finished. Fin linethat has lower loss in the millimeter waveband is chosen as the transmission line, and abeam lead PIN diode is connected in parallel to design W band switch. In this design, thediode’s impedance is matched to reduce insertion loss, and isolation also meets the index.At the same time, theoretical analysis and experimental study on the power capacity of theW-band PIN switch have been done in this thesis. A series of research work was completedfor this purpose.The package structure of diode has significant influences for performance of thecircuit. Firstly, the thesis analyzed PIN diode theoretically and then established a coarsethree-dimensional model in field simulation software Ansoft HFSS according to diode’stheory and structure drawing. The influence on the electric field of diode’s package can besimulated by this model. Then circuit is designed and processed to obtain test results,which are used to extract the parameters of the impedance of the diode on forward-biasedand reverse biased state.Based on this, W-band SPST switch is designed in this thesis. In order to minimize theinsertion loss, only one PIN diode is employed, and the diode’s impedance is matched toreduce unwanted reflections loss. Simulation results show that the switch not only haslower insertion loss, but also obtains high isolation with only one diode. Two switcheswere processed and measured, and the measurement results of insertion loss, isolation,switching time and power capacity were given in chapter3. It can be seen from themeasurement results that the two switches’ insertion loss are all less than1.7dB, and theisolation are all greater than28dB near the center frequency (94.5GHz). Insertion loss of less than2dB and isolation of greater than20dB are obtained over10GHz bandwidth.Switch’s rise time and fall time are all less than2ns. On the "off" state, the power capacityof the duty cycle of1%is greater than150W. Two switches have no significant differencein the performance curve, and the measurement results of two switches are all consistentwith the simulation results.By summing up the experience of the SPST switch, a SPDT switch with the samematching method is designed It can be seen from the measured results that the lowestinsertion loss is2dB, and the highest isolation is40dB at the W-band. Insertion loss of lessthan3dB and isolation of greater than20dB are obtained over5GHz bandwidth, Switch’srise time is less than2.5ns and fall time is less than2ns.