Difference between waveguide isolator and microstrip isolator

Waveguide isolators and microwave isolators are critical for preventing signal reflection in RF systems. This guide compares their designs, working principles and applications to derive differences between them.

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.


Waveguide Isolator

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.

waveguide isolator

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.

Microstrip Isolator

A microstrip isolator is a non-reciprocal RF component used in microstrip circuits to allow signal flow in one direction while preventing reverse signal propagation. It protects sensitive components like amplifiers and oscillators from reflected power.

Working principle : Based on the Faraday Effect, where the ferrite material causes signal rotation in one direction, preventing reverse flow. In conjunction with a permanent magnet, the isolator creates a magnetic field that enforces non-reciprocity.

Difference between waveguide and microstrip isolator

Feature Waveguide Isolator Microstrip Isolator
Physical Structure Bulky and rigid; designed for waveguide systems. Compact and planar; designed for microstrip circuits.
Frequency Range Operates at high frequencies, typically in the microwave range. Operates in a broader frequency range, from RF to microwave.
Construction Uses ferrite material enclosed within a metallic waveguide. Combines ferrite materials with planar microstrip technology.
Insertion Loss Generally lower due to efficient waveguide design. Slightly higher due to additional losses in microstrip lines.
Power Handling High power handling capability. Lower power handling capability compared to waveguides.
Size and Weight Large and heavy; not suitable for portable devices. Lightweight and compact; ideal for compact circuits.
Integration Challenging to integrate with planar circuits. Easily integrated with PCB-based designs.
Cost Relatively expensive due to complex manufacturing. Cost effective for mass production.
Performance High performance with minimal loss in specific frequency bands. Adequate performance for low to moderate power applications.
Applications Radar, satellite communication, and high power RF systems. Mobile devices, IoT applications, and low-power RF systems.

Conclusion

Understanding the differences between waveguide and microwave isolators ensures effective selection and integration, enhancing system reliability and performance.

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