Difference between waveguide isolator vs microstrip isolator
An Isolator is basically a two port and non-reciprocal device which produces a minimum attenuation to E-M waves in one direction and maximum attenuation to the waves in the other direction. Hence it is placed between source and the load so that all the power is transmitted from source to the load and no reflection is fed back to the other direction (i.e. from load to the source). We will see difference between waveguide isolator and microstrip isolator below.
The waveguide isolator can be constructed using rectangular waveguide operating in dominant mode. This is constructed by placing ferrite slab in the waveguide parallel to the narrow wall. These are places where magnetic field exhibits circular polarization which occurs usually at a/4 or 3a/4.
As we know attenuation in ferrite for negative or clockwise circular polarization is very small. It is large for positive or counter clockwise circular polarisation. This happens at resonance frequency. Due to this fact, ferrite slab is placed in such a way so that during transmission it will encounter negative circular polarisation in the reverse direction.
With this waveguide isolator, isolation of about 20 to 30 dB in the reverse direction and insertion loss of about 0.5dB in the forward direction is achieved. VSWR of about 1.1 can be obtained.
Maximum power handling capabilities of the waveguide isolator is limited as reverse power is absorbed in the ferrite due to heat dissipation. To achieve higher dissipation two ferrite slabs having smaller heights need to be used instead of one with larger height.
This isolator requires very high steady magnetic field to operate at higher frequencies. This is the major drawback of waveguide isolator.
Figure-1 depicts waveguide isolator to be used for WG-16 dimension waveguide. It is suitable to be interfaced with UBR100 compliant flanges. It is non-reciprocal device which passes power in only one direction. It is composed of two ferrite strips installed on edge of walls. These strips are biased using a horseshoe permanent magnet which is external to the waveguide. The ferrite strips absorb TE-10 electro-magnetic wave which enters from far end.
The microstrip isolator can be constructed by match terminating one port of 3 port circulator. There are various terminating methods to do so. The same microstrip etching concept on the PCB is used for this purpose.
WAVEGUIDE RELATED LINKS
RF Switch basics and applications along with manufacturers of RF switch refer following link:
For types of waveguide viz. rectangular & circular, waveguide propagation modes, impedance matching of waveguide read following waveguide tutorial.
waveguide basics tutorial
Manufacturers of waveguide components such as waveguide to coaxial adapter, coupler, flanges, gasket, tees, termination, shorts, isolator, circulator, horn antenna, attenuator, feed-thrus, bends, loads, twists, straights, pressure windows, transformers, sliding short circuits, fixed short circuits, sliding mismatches etc. visit following link.
Waveguide components manufacturer
Rectangular waveguide dimensions as per USA standard including frequency, broad dimension and narrow dimensions, visit following link.
Waveguide dimensions table
This article describes microstrip line basics and mention types of microstrip lines and their advantages. READ MORE.
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