Summary of Teardown and Experiments with a Doppler Microwave Transceiver
This article details the teardown of a Microsemi C900502 10.525 GHz X-band Doppler radar motion sensor. It highlights the module's sturdy metal casing, patch antennas etched on the PCB, and a simple three-wire interface (+5V, ground, IF output). The internal oscillator utilizes a single FET coupled with a dielectric resonator made of barium titanate, which is not physically connected to other components but interacts via electromagnetic fields. The text also notes the presence of distributed element filters, specifically radial stubs, and explains how shielding cavities affect the resonant frequency.
Parts used in the Microsemi C900502 Project:
- Microsemi C900502 10.525 GHz X-band Doppler radar motion sensor
- Metal casing
- PCB with etched patch antennas
- +5V power connection
- Ground connection
- IF output connection
- FET (Field Effect Transistor)
- Dielectric resonator
- Distributed element filters
- Radial stubs
I got a couple of Microsemi’s C900502 10.525 GHz X-band Doppler radar motion sensors a while ago. This batch was made in UK and had “UK patents 2243495 and/or 2253108 apply” printed on the case. I have seen a teardown of an HB100 Doppler radar module before and was wondering if I this one is any different inside.
The C900502 transceiver has a very sturdy metal casing. It is measured at roughly 5cm by 5cm by 1cm. The transmitter and receiver antennas are patch antennas etched directly onto the PCB as you can see from the picture below:
On the back side you can see the patent number stamped onto the casing. There is an adjustment hole underneath the model number sticker. Using a screw driver, you can make fine adjustments of the transmitted frequency. Using this module is simple and only three connections are required: +5V, ground, and IF output.
Here is a closeup of the oscillator portion. The oscillator consists of a single FET. The brown cylindrical component is a dielectric resonator. Note that it is not physically connected to any other components. The coupling is achieved strictly via the electromagnetic fields outside the cylindrical boundary of the dielectric resonator. The resonant frequency (TE01n mode) of the dielectric resonator can be calculated as:
r
aL+3
45
where the relative permittivity of the dielectric material is usually between 30 and 50. Barium titanate(BaTiO3) is a common material used for the dielectric resonator.
You can also see many distributed element filters on the PCB. Here you can see two radial stubs.
Here is another picture of the dielectric resonator oscillator. The cylindrical resonator has a radius of 2.48 mm and is roughly 3 mm in height. The actual resonant frequency is slightly different than what is obtained from the equation mentioned earlier due to the fact that the oscillator is inside a shielding cavity and the cavity affects the surrounding field of the resonator. This changes the boundary condition and causes the resonate frequency to shift. The screw for fine-tuning the oscillate frequency works in a similar fashion.
Read More: Teardown and Experiments with a Doppler Microwave Transceiver
- How many connections are required to use this module?
Only three connections are required: +5V, ground, and IF output. - What material is commonly used for the dielectric resonator?
Barium titanate (BaTiO3) is a common material used for the dielectric resonator. - Can the transmitted frequency be adjusted?
Yes, fine adjustments can be made using a screwdriver through an adjustment hole underneath the model number sticker. - How is coupling achieved in the oscillator portion?
Coupling is achieved strictly via the electromagnetic fields outside the cylindrical boundary of the dielectric resonator. - Are the transmitter and receiver antennas separate components?
No, the antennas are patch antennas etched directly onto the PCB. - Why is the actual resonant frequency different from the calculated value?
The oscillator is inside a shielding cavity that affects the surrounding field of the resonator, changing the boundary condition and shifting the frequency. - What type of filter components are visible on the PCB?
Many distributed element filters are on the PCB, including two radial stubs. - Is the dielectric resonator physically connected to other components?
No, the brown cylindrical component is not physically connected to any other components.
