RESONANT CAVITY FILTER

Resonant Cavity resonators is a cavity that consists of interior surfaces, reflecting one type of wave. The conducting walls can contain oscillating electromagnetic fields and also have resonant properties. Intensity is caused when the wave is resonant with the filter, allowing the wave to bounce back and forth within the cavity. Low loss occurs from this process. (1) In usual electronic equipment, resonant cavities are made up of a coil and a capacitor which can be either connected in series or parallel. By reducing the capacitance, inductance, or both, the resonant frequency of the circuit may be increased. Highest frequency is obtained when the inductance and capacitance can no longer be adjusted. The coils of the resonant cavity may be adjusted as well. However, tuning a one-half turn coil is very difficult and may not yield desired capacitance. Adjusting the coils may also the circuit to handle only small amounts of current. (2)

Resonant cavities can have a variety of shapes and give the same results. For high-frequency resonators, cavity devices are mostly built rectangular. Other types of filters can be built as cylindrical, or quarter-wave lines joined. (2)

Rectangular waveguide cavity resonator	Quarter-wave Joined
Cylindrical Resonant Cavity being formed from quarter-wave sections	Cylindrical Resonant Cavity

The following are two fitures of a single dielectric resonator. The figure to the left shows the results of the electric conductor. On the right is the response of a 5-pole HFSS filter. (3)

Optimized 5-pole filter in HFSS and Designer

Examples of Filters

· IRIS COUPLED WINDOW FILTERS 35 - 1540 MHz

(courtesy of Polar Electronic Industries Pty. Ltd. )

Figure 1 Design of Iris Coupled Fitlers

Model	5CI1-3	3CI2-3	5CI3-3	5CI8-3	6CI3-1	6CI8-1
Center Frequency	78 MHz	150 MHz	417 MHz	876 MHz	401 MHz	850 MHz
Pass band	0.7 MHz	0.25 MHz	2 MHz	6 MHz	3 MHz	6 MHz
Insertion loss	2.0 dB max	2.0 dB max	2.0 dB max	2.0 dB max	3.0 dB max	2.0 dB max
Number of sections	5	3	5	5	6	6
Weight	18.5 Kg	6.25 Kg	6 Kg	4 Kg	1.3 Kg	0.7 Kg
Length	106 mm	106 mm	330 mm	240 mm	210 mm	140 mm
Width	483 mm	483 mm	483 mm	483 mm	175 mm	175 mm
Height	1580 mm	700 mm	133 mm	133 mm	32 mm	32 mm

Table 1 Specific details of ICF

	FREQUENCY MHz

	FREQUENCY MHz

	FREQUENCY MHz

	FREQUENCY MHz

	FREQUENCY MHz

	FREQUENCY MHz

Figure 2 Frequency Plots of ICF

Loaded waveguide mode - Resonator Cavity	Duplexers
Bandstop Triple cavity	TEM mode, ^1/4 Wave bandpass cavity
Bandpass with Notch - Single cavity

Figure 3 Diagram of Actual ICFs

REFERENCES

1. http://encyclopedia.thefreedictionary.com/resonant%20cavity

2. http://www.fnrf.science.cmu.ac.th/theory/waveguide/Waveguide%20theory%2014.html

3. http://www.ansoft.com/deliveringperformance/cavityfilters.pdf