How To Test The Values Of Q On Resonator Oscillator & Quartz Crystal

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How to Test the values of Q on Resonator oscillator & Quartz Crystal

Dec 29, 2020

Values of Q test and the relationship between Qo & the size of cavities

For the cavity filter used in the field of modern mobile communication base stations, the insertion loss is one of the essential RF key indicators. We often expect the smaller the loss, the better: if the insertion loss of the filter can be effectively reduced, it will be of great benefit to the realization of other indicators of the filter or to the entire mobile base station system. The development of modern mobile communications, especially 5G micro base stations, requires the size of filters to become smaller and smaller, which will inevitably bring about the reduction of the unloaded Q value of a single cavity. Therefore, how to effectively use the limited cavity volume and allocate the Q value has become the key to the filter insertion loss.

The designers of most filter design companies design a single cavity with almost the same size for each channel. In fact, the reasonable layout of the size of each single cavity can reduce the insertion loss of the filter, increase the insertion loss margin of the product, and even make the product of the customer index that cannot be achieved in the first place, thereby meeting customer requirements.

1. The relationship between Q value and single cavity size

The Q value is a measure of the average energy storage and loss of the resonant tank. Large energy storage and small loss means high Q value.

The Q value is related to the volume and surface area of a single cavity. The larger the volume, the greater the electromagnetic energy stored in the single cavity. The smaller the surface area, the smaller the loss of the single cavity, and the greater the Q value, and vice versa.

Here we share some reference values of filter single cavity (including circular cavity and square cavity) of different sizes and corresponding Q values of each frequency band. For your reference and reference when designing.

	AMPS	AMPS	GSM	GSM
Cavity size（mm)	F0(RX) 836MHz Q0	F0(TX) 881MHz Q0	F0(RX) 902MHz Q0	F0(TX) 948MHz Q0	F0 1530MHz Q0
20	1280	1310	1330	1360	1730
25	1600	1640	1660	1700	2160
30	1910	1970	1990	2040	9590
35	2230	2306	2330	2360	3020
40	2550	2630	2660	2720	3450
45	2870	2950	2990	3060	3880
50	3190	3280	3300	3400	4310
55	3500	3610	3650	3740	4740

	DCS	DCS	PCS	PCS	UMTS
Cavity size（mm)	F0(RX) 1747MHz Q0	F0(TX) 1842MHz Q0	F0(RX) 1880MHz Q0	F0(TX) 1960MHz Q0	F0 2140MHz Q0
20	1850	1900	1920	1960	2040
25	2310	2370	2390	2440	2550
30	2770	2840	2870	2930	3060
35	3230	3310	3350	3420	3570
40	3690	3780	3820	3900	4070
45	4140	4250	4200	4380	4580
50	4600	4720	4770	4870	5080
55	5050	5190	5240	5350	5580

	AMPS	AMPS	GSM	GSM
Square cavity size（mm）	F0(RX) 836MHz Q0	F0(TX) 881MHz Q0	F0(RX) 902MHz Q0	F0(TX) 948MHz Q0	F0 1530MHz Q0
20×20	1530	1580	1600	1640	2080
25×25	1910	1970	2000	2040	2600
30×30	2300	2360	2390	2450	3110
35×35	2680	2760	2790	2860	3630
40×40	3060	3150	3190	3270	4140
45×45	3440	3540	3590	3600	4660
50×50	3820	3940	3990	4080	5170
55×55	4200	4330	4380	4490	5680

	DCS	DCS	PCS	PCS	UMTS
Square cavity size(mm)	F0(RX) 1747MHz Q0	F0(TX) 1842MHz Q0	F0(RX) 1880MHz Q0	F0(TX) 1960MHz Q0	F0 2140MHz Q0
20×20	2220	2280	2300	2350	2450
25×25	2770	2850	2870	2930	3060
30×30	3320	3410	3450	3520	3670
35×35	3870	3980	4020	4100	4280
40×40	4420	4540	4590	4680	4890
45×45	4970	5100	5150	5260	5490
50×50	5520	5600	5720	5840	6090
55×55	6070	6220	6290	6420	6700

2. Single cavity Q value test

The performance of the filter resonant circuit is described by the quality factor Q. Various characteristics such as frequency selectivity, bandwidth and damping factor can be derived from it. Its definition is as follows:

value of Q=W (energy storage in average time/energy consumption per second)

Article source WeChat public account: filter

We actually test the Q value of a single cavity:

1. In addition to the resonance frequency to be tested, there can be no other frequency components

2. Don't set the instrument bandwidth too large during testing

3. The external coupling cannot be too large or too small, otherwise the true Q value cannot be measured

So how much external coupling is needed?

When Qe= Qu, Qu= 2QL

QL = f0 / △f3dB

Qu = 0 / △f3dB

Today we shared the "Q value test and the relationship between Qo and single cavity size" through a picture of a physical test case. Hope to help engineers again.

Zhe Jiang A-Crystal electronic technology Co.,Ltd

A-Crystal factory tour: https://www.youtube.com/watch?v=uMqJq6e_8Ew

Web: https://www.acrystals.com/

Email: eva.wang@acrystals.com
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