Filter Design Basics

1. Center Frequency, Fo
2. Stopband Cutoff Frequency, Fs
3. Selectivity Factor, Q
4. Shape Factor, SF
5. Insertion Loss
6. VSWR and Return Loss
7. Phase Linearity and Group Delay
8. Filter Impedance

 Types of Filters

The two classical approaches in the design of filters are

• Image-parameter
• Network method

Image-parameter method 

        - treats the filter as a transmission line and uses lumped components.

• Constant k filter
• m-derived filter - is a modification of the constant k filter in order to vary the impedance (constant) and the shape factor (steeper).

Network method

     - based on frequency response curve or transfer function.

Other common filter design methods are

• Top-coupled resonator
• Varactor-tuned BPF (Band Pass Filter)

RF Basics

Frequency

Frequency ဆိုတာ RF(Radio Frequency) တစ္ခုလံုးရဲ႕ အေျခခံအက်ဆံုး အစိတ္အပိုင္းျဖစ္တယ္။ Microwave Theory ပိုင္းမွာလည္း Frequency တန္းဖိုးက အေရၾကီးျပီး ရွဳပ္ေထြးလြန္းတဲ့ တြက္ခ်က္မွဳေတြမွာ အျမဲေနရာယူေနတာပါ။ Frequency ဆိုတာနဲ႕ sin wave နဲ႕ cosine wave ေတြကို သတိရၾကမယ္ထင္ပါတယ္။

Electromagnetic (EM) Wave

Electronic Wave အေၾကာင္းေျပာၿပီးဆို Magnetic Wave က ေနာက္က ဆက္ပါလာတာပါ။ Electronic wave သည္ Magnetic wave ႏွင့္ ေထာ့င္မွန္က် သည္။ ေအာက္ကပံုကေတာ့ sine wave ကို EM wave အေနနဲ႕ ျပထားတာပါ။

Radiation Pattern

Radiation Pattern ဆိုတာ Antenna ကေန ထုတ္လြတ္လိုက္တဲ့ Power ကို ေဖာ္ျပသည္လို႕ အဓိပၸါယ္ မွတ္ယူႏိုင္သည္။ Radiation Pattern ရဲ႕ ပံုက ပန္းသီးတစ္လံုးရဲ႕ပံုနဲ႕ တူတယ္။ အလယ္ဝင္ရိုးကို EM Wave လံုးဝမလြတ္ထုတ္ႏိုင္တဲ့ Null Location လို႕ေခၚျပီး အဲဒီ Null မ်ဥ္းေပၚမွာရွိတဲ့ ဘယ္ Receiver မဆို Transmitter က လြတ္တဲ့ သတင္းအခ်က္အလက္ေတြကို ရရွိမည္မဟုတ္။

Field Regions

Field Regions ၃ ခုရွိတယ္။

1. Far Field (Fraunhofer) Region
2. Reactive Near Field Region
3. Radiating Near Field (Fresnel) Region

Far Field (Fraunhofer) Region

Far Field Region က အေရးအၾကီးဆံုးျဖစ္သည္။ Antenna ရဲ႕ Radiation Pattern ကို Far Field Region နဲ႕ပဲ အဓိပၸါယ္ဖြင့္ဆိုသည္။ Antenna အလုပ္လုပ္တဲ့ Region လို႕ သတ္မွတ္လို႕ရပါသည္။ Far Field Region ျဖစ္ဖို႕ အခ်က္ ၃ ခ်က္နဲ႕ ျပည့္စံုရပါမယ္။

where; R = Far Field Region, D = Dimension of antenna

">>" ဆိုတာ အရမ္းၾကီးရမယ္လို႕ အဓိပၸါယ္ရတယ္။ အနည္းဆံုး ၁ဝ ဆၾကီးရပါမယ္။

Reactive Near Field Region 

Reactive Near Field Region ဆိုတာက Antenna ပါတ္ဝန္းက်င္က ေနရာေတြကို ဆိုလိုသည္။ Near Field Region ကို ေအာက္ပါအတိုင္းတြက္ခ်က္ႏိုင္သည္။

Radiating Near Field (Fresnel) Region

Radiation Near Field Region ကေတာ့ Far Field (Fraunhofer) Region နဲ႕ Reactive Near Field Region ၾကားမွာ ရွိပါသည္။ Radiation Near Field Region ကို ေအာက္ပါအတိုင္းတြက္ခ်က္ႏိုင္သည္။

Explain how the length of the antennas, the transmit power and receiver sensitivity can have an impact on your CPE wireless coverage?

Antenna

The length of antenna is defined by the wavelength of the frequency. The longer length of antenna, the higher the gain of the antenna in dBi and the better coverage of CPE.

Transmit Power

Transmit Power is an important parameter of wireless design.

The higher transmit power at lower EVM can give a better performance and longer range of wireless coverage.

Sensitivity

Received Sensitivity is to measure the minimum received signal level of CPE.

Greater sensitivity = longer range

As the signal propagates away from the transmitter, the power density of the signal decreases, making it more difficult for a receiver to detect the signal as the distance increases. Improving the sensitivity on the receiver (making it more negative) will allow the radio to detect weaker signals, and can dramatically increase the transmission range.

Sensitivity, 1dB Compression Point and Dynamic Range

Sensitivity

• The smallest RF Signal that can produce a useful baseband signal at the receiver output.
• Determine how far the receiver can be from the transmitter and still receive an understandable message.

1dB Compression Point

• The point at which the output power differs from the ideal transfer function by 1dB as the input power increases.

Dynamic Range

• The input power range over which the receiver provides a useful output. The low power limit is the sensitivity specification and upper limit is the input power at 1dB compression point.

Dynamic Range = Input 1dB Compression Point - Sensitivity Level

WIRELESS LAN THROUGHPUT TESTING

Recommended Softwares:

1. JPerf 2.0.2
2. NetStress Benchmarking Tool for Wired and Wireless Networks 
3. TamoSoftware Throughput Test Tool

EIRP Calculator

EIRP Calculator

Peak Transmit Power:	dBm
No. of Antenna:
Antenna Gain:	dBi
EIRP Value:	dBm

IEEE802.11 WLAN Standard

802.11 Standard

Standard	Year	Band	Bandwidth	Modulation	Antenna Technology	Data Rate
802.11b	1999	2.4GHz	20MHz	CCK	---	11Mbps
802.11a	1999	5GHz	20MHz	OFDM		54Mbps
802.11g	2003	2.4GHz	20MHz	CCK, OFDM		54Mbps
802.11n	2009	2.4GHz, 5GHz	20MHz, 40MHz	OFDM (Upto 64-QAM)	MIMO with up to Four spatial streams, beamforming	600Mbps
802.11ac		5GHz	40MHz, 80MHz, 160MHz	OFDM (Upto 256-QAM)	MIMO, MU-MIMO with up to eight spatial streams, beamforming	6.93Gbps
802.11ad		2.4GHz, 5GHz, 60GHz	2.16GHz	SC/OFDM	Beamforming	6.76Gbps

Please download 802.11 WLAN Standard for more details.

dBm-mW Conversion Calculator

	mW - dBm Power Conversion Transmit Power in MilliWatts : Total: dBm - mW Power Conversion Enter Power of Card in dBm : Total: