The module (WLAN + Bluetooth) is connected to 2.4 GHz antenna (on the other board) via the connector through the 50 ohm (impedance) RF trace.
Should i add some impedance matching circuit to maintain 50 ohm impedance along the RF trace which connects the module, the connector and 2.4 GHz antenna? If so, what is the circuit?
Using the VNA measure the impedance of the antenna itself.
Replace the antenna with a 50 ohms load (or a small 50 ohms resistor) and using the VNA measure the impedance of the RF trace connected to the antenna.
In this way you can find if you need (and where) impedance matching.
The module (WLAN + Bluetooth) is connected to 2.4 GHz antenna (on the other board) via the connector through the 50 ohm (impedance) RF trace.
Should i add some impedance matching circuit to maintain 50 ohm impedance along the RF trace which connects the module, the connector and 2.4 GHz antenna? If so, what is the circuit?
If both the impedance of RF trace and impedance of antenna is 50 ohm, you do not need impedance matching. What you need may be is a capacitor to avoid DC leak to antenna
RF connectors have a designed impedance, they intend to keep this impedance along the transmission line through the connector exactly. Of course, they can't be perfect. The error introduced by a connector is specified by a VSWR (voltage standing wave ratio) value. The largest contribution can be expected from the microstrip to (coaxial) connector transition. The transition can be improved by adjusting the microstrip shape near the connector for minimum VSWR. For a small band application, e.g. 2.4 GHz, the connector effect can be expected to be hidden by the antenna and transceiver impedance mismatch anyway. Simply follow the microstrip layout suggestions from the connector vendor.
In my project, no RF connector (50 ohm) is used. But an ordinary connector (through hole) is used for soldering both module board and other board. Please suggest on this.
The impedance of the antenna on the other board is 50 ohm. I think that the non RF connector would introduce a change in impedance. How to set this connector to 50 ohm?
Very possible. For controlled impedance, you would have a well defined ratio of series L and shunt C. If your connector is too inductive, you can compensate that by adding shunt C. This has two effects: it creates some low pass behaviour, and improves the matching within the pass band (compared to the series inductor without shunt C). But compensation requires that we know the connector properties. The easiest way would be to go to the lab, build a test fixture for the connector and measure it with a VNA (vector network analyzer).
This is how it can be done, if really needed. But most antenna stuff is robust and some small mismatch will not kill your circuit function. If your connector is electrically small compared to the wavelength, then you are lucky because the mismatch created by the connector is small.
I want to know whether i can place impedance matching ckt on the module board before the non RF connector OR on the other board before the antenna. Which one is a must?
depending on the board space, try to have T and TT together so you have more options when you are doing tuning.
I faced some problems when the TT matching circuit is not sufficient to tune the antenna. Have either one of them
close the connector and the other one near the antenna, just on the safe side