Page 368 - Maxwell House

348 Chapter 6

1. Y-circulator in radar systems allows sharing the same antenna by their transmitter and
receiver as Figure 6.8.7b demonstrates. The transmitter (Tx) generates its pulse signals for
some short time interval. Then Y-circulator directs this powerful signal straight to the
antenna port and isolates the receiver port. If so, Y-circulator with high protection > (20 –
30) dB is typically required. As soon as the radar keeps silence, the signals coming back
from targets are guided to the receiver (Rx) port with low loss (typically, < (0.2 – 0.5) dB).
2. Cascade of two or more Y-circulators forms a 4- or more port circulator. The dual Y-
circulator shown in Figure 6.8.7c is often used to protect highly sensitive negative-
resistance preamplifier (NRPA) such as parametric amplifier or maser against reflections.
The latter might cause the amplifier self-oscillation. As the drawing demonstrates, the
reflected wave is double absorbed by two dummy loads before coming back to the
amplifier.
3. The circulation of power direction reverses (dotted arrow in Figure 6.8.7a) as the bias
changes on opposite that transforms Y-circulator into an electronically controlled switch.
4. The connection of a dummy load to one of the ports converts Y-circulator into an efficient
and lightweight isolator as Figure 6.8.7d illustrates. The forward wave passes freely
straight from input to output port. The return wave due to the possible reflection from the
load connected to the output port follows to a dummy load and disappears there.
5. Combination Y-circulator with filter creates a frequency diplexer combining two and more
signals of different frequencies into one channel or separating them from the common
channel like shown in Figure 6.8.7e. Such wideband signal formation or decomposition are
often utilized in cellular base stations, tactical communications systems called gateways,
and satellite communications hubs, where dozens or even hundreds of simultaneous carrier
channels may be active at any one time. Wideband architectures are also useful in some
applications for military and civil defense, including signals intelligence and electronic
warfare.
Modern Y-circulators have reached a high degree of perfection: frequency band from 30 MHz
to 120 GHz, operation bandpass is up to octave (bandwidth is equal to the lower frequency),
insertion loss in the range of 0.2 – 0.5 dB, isolation between ports around (20 – 30) dB, power
rating from several Watts up to 100 kW (WR design with water cooling). There are some
publications about optical Y-circulator for frequencies around 100 - 200 THz [15, 16].
Unfortunately, the limited size of the book does not allow us to continue. Therefore, we stop
here referring the reader to the specialized literature [17].

REFERENCES

[1] P. V. Nikitin, D. D. Stancil, E. A. Erosheva, Estimating the Number of Modes in
Multimode Waveguide Propagation Environment,
http://www.ee.washington.edu/faculty/nikitin_pavel/papers/APS_2011_modes.pdf
[2] IPC-2141A, Design Guide for High-Speed Controlled Impedance Circuit Boards,
March 2004, http://www.ipc.org/TOC/IPC-2141A.pdf
[3] L. G. Maloratsky, Reviewing The Basics Of Microstrip Lines, Microwaves & RF,
March 2000.
[4] Microwave Encyclopedia, http://www.microwaves101.com