Terminator3
Advanced Member level 3
Cheap X-band motion sensors such as door openers use separate patch antennas for TX and RX path. It is usually justified by the need of high sensivity, which is obtained by decreasing LO leakage. But as we know such sensors are pretty narrowband, and use only a little bandwidth of few KHz.
Please comment on this idea:
what if we use microstrip T power divider to achieve transciever behaviour?
Microstrip T-power divider have 3 ports:
Port 1 can be connected to Oscillator output (50 Ohm)
So the input from Port 1 will be equally divided between two microstrip lines (100 Ohm each)
Port 2 will be connected to antenna (simultaneous TX/RX transceiver patch antenna)
Port 3 will be connected to single diode mixer
Someone can say that antenna's S11 is not perfect, something around -12dB, and we will have reflected signal, with the same leakage effect as before.
To overcome this problem, I propose to tune microstrip line length between Port 2 and the antenna in a such a way, that reflected LO signal would be in-phase with oscillator signal.
The only drawback of such method i see is that part of received RF power will go back to the Port 1 from Port 2. And only portion of it will continue from Port 2 to Port 3.
But, single diode mixer at Port 3 requires less LO power than single balanced mixer, so it compensates a little received power loss. Also some other power dividing configuration can be used, not equal power divider.
I think this method is better than using Hybrid coupler for isolation.
With Hybrid coupler, not only half of received RF power is lost, also half of LO is lost. As we know, in case of hybrid couplers used for single patch antenna there are 50-ohm resistor on one port. Half of LO power goes to that resistor. Half of received power goes back to oscillator also (50-ohm resistor port is isolated for RX). In case of T-divider we can double available LO power.
Please comment on this idea:
what if we use microstrip T power divider to achieve transciever behaviour?
Microstrip T-power divider have 3 ports:
Port 1 can be connected to Oscillator output (50 Ohm)
So the input from Port 1 will be equally divided between two microstrip lines (100 Ohm each)
Port 2 will be connected to antenna (simultaneous TX/RX transceiver patch antenna)
Port 3 will be connected to single diode mixer
Someone can say that antenna's S11 is not perfect, something around -12dB, and we will have reflected signal, with the same leakage effect as before.
To overcome this problem, I propose to tune microstrip line length between Port 2 and the antenna in a such a way, that reflected LO signal would be in-phase with oscillator signal.
The only drawback of such method i see is that part of received RF power will go back to the Port 1 from Port 2. And only portion of it will continue from Port 2 to Port 3.
But, single diode mixer at Port 3 requires less LO power than single balanced mixer, so it compensates a little received power loss. Also some other power dividing configuration can be used, not equal power divider.
I think this method is better than using Hybrid coupler for isolation.
With Hybrid coupler, not only half of received RF power is lost, also half of LO is lost. As we know, in case of hybrid couplers used for single patch antenna there are 50-ohm resistor on one port. Half of LO power goes to that resistor. Half of received power goes back to oscillator also (50-ohm resistor port is isolated for RX). In case of T-divider we can double available LO power.
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