Re: PIN switch problem?
I saw your schematic. This is a very common switch design for TDD system. D1 and D2 diodes are always oppositely biased to switch either P2 or P3 to the common port P1 (The control voltages V1 and V2 are always complementary, i.e V1 = High, V2 = 0V or vice versa). Insertion loss is affected by the biasing resistor setting, and the DC blocking resistor. Isolation performance is affected by the RF chokes and the biasing resistor.
I have a few questions about it:
[1] What is your operating frequency ? The BA277 diode is good for VHF band (30 -300MHz) as indicated in the datasheet. But your dc blocking caps in the schematic is 1pF, this maybe too low.
[3] Your biasing resistors are 1 ohm, how is this determined? For a low forward resistance (If=10mA and Vf=1V), assuming you are using a control voltage of 3V, the biasing resistor should be (3-1)/10mA, i.e. 200 ohm. This value will also affect the isolation performance of your switch. Could you try to use 200 ohm fixed biasing resistors, and make your RF chokes (1nH) a optimizable variable (say between 1nH and 15nH)? You can set a goal of say S21= -1.5dB (within your operating frequency) and S31 of say -20dB . Remember to set V1 and V2 correctly during your simulation. The common RF ground return choke is also an important factor.
Lastly, this kind of TDD switch design are widely documented. You can search for Infineon or Philips website for relevant application notes.