Tri Band Transceiver
1. Introduction
Wireless Testbeds provide the experimental facility to test the validity of algorithms and also to test any wireless setup. The Electrical and Computer engineering department at Stevens Institute of Technology currently has a high speed radio testbed which is capable of transmitting and receiving at 2.4 GHz. 2.4GHz ISM band is free to all, so many applications now are using this band. These applications include digital cordless phone, WLAN (802.11b), HomeRF, RFID, microwave oven and many other proprietary technologies. The large amount of units using the same band has raised the issues of possible interference. This has caused WLAN to migrate to 5.7 GHz ISM band. This has raised the need for a testbed which is capable of transmitting and receiving at 5.7GHz in order to analyze the latest in wireless technology. The objective of this project is to design, build and test a portable wireless Transceiver board capable of operating at the following three ISM bands, 915MHz, 2.4GHz and 5.7GHz.
2. Existing 2.4 GHz Transceiver Board
The current RF transceiver board used in the Wireless Research Lab of Stevens Institute of Technology is capable of transmitting and receiving frequencies in the range of 2.4GHz. The initial approach to our project was to understand the functionality of this design so as to come up with a design capable of handling three different frequencies.
2.1 Transmitter End
The basic components of the transmitter end of the transceiver are the Modulator, Bandpass Filter, Mixer, LO source and Amplifier. This design also uses low pass filters at the IQ end to remove noise from the data acquisition card. The data from the DAQ cards are modulated at 70 MHz with the use of a ZMIQ-70ML modulator. The 70 MHz needed for the modulation is provided by a frequency synthesizer. The modulated signal is passed through a band pass filter with centre frequency of 70 MHz. This removes noise from the modulated signal. The filtered signal is then fed into a mixer, ZAM-42, which accepts the signal at the IF end and a frequency of 2.33 GHz by the frequency source at the Local Oscillator input and produces a carrier signal at 2.4 GHz. This signal is amplified before being transmitted.
2.2 Receiver End
The receiver end of the board reverses the operation of the transmitter end. The received signal is first sent through a low pass filter to remove most of the noise. This signal is then fed into an amplifier before being sent into a mixer which receives a frequency of 2.33 GHz from the LO and subtracts this from the 2.4 GHz signal input to have a signal of 70 MHz generated at the output. A band pass filter is used to filter this signal out and send the signal to the demodulator. The demodulator takes a 70 MHz input from the Local Oscillator to demodulate the signal to have the original data recovered.
2.3 Noise Figure calculations for 2.4 GHz design
Component / NF(dB) / Gain (dB) / NFn / GAINn1 / SLP 2950 / -1 / 0.794328
2 / ZKL 2R5 / 5 / 30 / 3.162278 / 1000
3 / ZAM 42 / -8.5 / 0.141254
4 / SBP 70 / -1.5 / 0.707946
5 / ZKL 1R5 / 3 / 40 / 1.995262 / 10000
59
Nftot = / 2.722148
NF / 4.3491
Gain / 59 dB
2.4 GHz Wireless Testbed Setup
3. Alternate Designs
Based on the existing 2.4 GHz, several different designs were considered for the tri band receiver.
3.1 Double Mixer Design
The modulation of the signal is performed the same as that of the existing 2.4 GHz design. (Refer to section 2.1) The modulated signal is then passed to the mixer. Depending on which frequency you which to transmit the modulated signal at, you pick the mixer. For 900 MHz and 2.33 GHz, only one mixer is used. In the case of the 5.7 GHz section, the signal is first converted to 2.815 GHz using a mixer and this signal is then filtered and passed to a second mixer where it is converted to 5.7GHz. The reason for using two mixers is to avoid the need of an extra frequency source to provide frequency above 5 GHz. This brings the overall cost of the design down by a lot. The downfall of this design is the extra mixer needed which could reduce overall quality of the transmitted signal. The extra mixer and filter also means more board space required.
3.2 Single Stage Conversion Design
This is an expansion of the current 2.4 GHz design where two extra mixers are used working at 915 MHz and 5.7GHz. The major draw back of this design is that we will require LO supplies which are operational at the three different frequencies. This will be both expensive and difficult to obtain. One alternate was to use Voltage Controlled Oscillators as our LO supply. Upon further research on VCOs we came to the conclusion that VCOs will not provide the stability that our system requires. On the receiver end, the same three mixers will be used to down convert the signal. The modulation and demodulation stage are the same as mentioned before.
3.3 900 MHz Modulation
3.4 Tripler Design
3.5 Three Stage Conversion Design
The modulation for this design is carried out at 70 MHz as in the case of the existing design. This is then scaled up to 900 MHz using a mixer. If a 900 MHz signal is required this signal is transmitted. If a 2.4 GHz or 5.7 GHz signal is required then the signal is passed onto the respective mixer. And then amplifier is used to amplifier the signal before transmission.
4. Final Design
The final design chosen for the transceiver was based on the Tripler design. This design was picked since it required the least number of components as well as the smallest range of frequency source.
4.1 Transmitter End
The analog signals from the DAC are first passed through a low pass filter to remove noise. These are then modulated at 70 MHz using a ZFMIQ-70ML modulator. This accepts an input of 70 MHz at the LO end and provides a modulated signal of 70 MHz at the RF end. The 70 MHz at the LO end will be provided by the secondary output of a dual output LO Synthesizer from Praxsym Eng. A splitter is used to split the 70 MHz signal for the transmitter and receiver end. The modulated signal is then filtered using a 70 MHz band pass filter. Depending on what frequency is needed, the 70 MHz modulated signal is input into the respective filter.
900 MHz: The 70MHz filtered signal is passed into the IF input of the ZX05-25MH mixer. A frequency of 845 MHz, provided by the primary out of the dual output LO synthesizer is provided at the LO input of the mixer. The frequency from the LO synthesizer is first split into two using a splitter, which one of the signals sent to The output signal at the RF end will be comprised of various signals at different frequencies. One of these is the summation of the two frequencies which is 915 MHz.
2.4 GHz: The 70MHz filtered signal is passed into the same mixer, ZX05-25MH as before. A frequency of 2.33 GHz is supplied to the LO input by the NovaSource G2. The mixer will add the two frequencies together to obtain a signal at 2.4 GHz.
5.7 GHz: The 70 MHz filtered signal is passed into the ZX05-C60 mixer. A frequency of 1.88 GHz from the NovaSource is passed through a Tripler, ATA 1424. This Tripler has a built in amplifier at the front and back end so the signal is amplified twice to minimize power loss. The tripled signal at 5.63 GHz is then input in to the LO end of the mixer where it is added together with the 70 MHz signal to produce a signal of 5.7 GHz at the RF end.
The signal from the RF end of the mixer is amplified using a ZKL-2R5 amplifier before it is transmitted.
39
Tri Band Transceiver
39
Tri Band Transceiver
4.2 Receiver End
An antennae is used to receive the signal and the signal is transmitted to the respective filter depending on which frequency the transceiver needs to be operated at.
915 MHz: The received signal is passed through a low pass filter with a cut off frequency of 1000 MHz. This will ensure no frequencies above 1000 MHz get passed through to the rest of the receiver. The filtered signal is then passed to an amplifier before being fed into the RF input of the mixer. A frequency of 845 MHz from the LO synthesizer is fed into the LO input. The difference of these frequencies, 70 MHz is obtained at the IF end.
2.4 GHz: The received signal is passed through a low pass filter with a cut off frequency of 2.9 GHz. The filtered signal is then passed to an amplifier before being fed into the RF input of the mixer. A frequency of 2.33 GHz from the NovaSource G6 is fed into the LO input. The difference of these frequencies, 70 MHz is obtained at the IF end.
5.7 GHz: A low pass filter with a cut off frequency of 6.5 GHz is used after the antennae. The filtered signal is then passed to an amplifier before being fed into the RF input of the mixer. A frequency of 5.63 GHz, which is obtained after tripling the input from the NovaSource G6 is fed into the LO input. The difference of these frequencies, 70 MHz is obtained at the IF end.
The signal obtained at the IF end of mixer is fed into a Band pass filter. This is to filter out the 70 MHz signal and reduce as much noise into the demodulator as possible. The filtered signal is amplifier and passed to the demodulator. A frequency of 70 MHz from the dual output synthesizer is used by the demodulator to separate the signal into the Q and I phase.
39
Tri Band Transceiver
39
Tri Band Transceiver
4.3 Calculation of System Specifications
Noise Figure Calculations
Transmitter EndComponent / NF(dB) / Gain (dB) / NFn / GAINn / Cummulative NFn
1 / ZFMIQ-70M / 7.2 / -6.2 / 5.248075 / 0.239883 / 7.20000
2 / SBP 70 / -1.5 / 1 / 0.707946 / 7.20000
3 / ZX05-C60 / -6.9 / 1 / 0.204174 / 5.24807
4 / ZKL 2R5 / 5 / 30 / 3.162278 / 1000 / 18.30004
15.4
Nftot = / 67.60884
NF / 18.3000 / dB
Gain / 15.4 / dB
Receiver End
Component / NF(dB) / Gain (dB) / NFn / GAINn / Cummulative NFn
1 / LPS50006 / n/a / -1 / 0 / 0.794328 / #NUM!
2 / ZKL 2R5 / 5 / 30 / 3.162278 / 1000 / 4.3491
3 / ZX05-C60 / n/a / -6.9 / 1 / 0.204174 / 2.7221
4 / SBP 70 / n/a / -1.5 / 1 / 0.707946 / 4.3491
5 / ZKL 1R5 / 3 / 40 / 1.995262 / 10000 / 4.3629
6 / ZFMIQ-70D / 7.2 / -6.2 / 5.248075 / 0.239883 / 4.3629
54.4
Nftot = / 2.73082
NF / 4.3629 / dB
Gain / 54.4 / dB
The mixers used for all three frequencies had the same noise figures and gain. Also the three different low pass filters used had the same noise figures and gain therefore, the overall NF and Gain of the transceiver operating at either of the three frequencies were the same. Noise figures and gains weren’t available for all the components hence we could not accurately calculate the values.
Calculations for 915 MHz and 2.4 GHz design
Since the 915MHz and 2.4 GHz design use the same components, the calculations for both are identical.
Stage / Part / Gain (dB) / Gain / IP3 (dBm) / IP3 (Watts)1 / ZKL-2R5 / 30 / 1000 / 31 / 1.258
2 / ZK05-25MH / -9.8 / .1047 / 18 / .06309
3 / ZKL-1R5 / 40 / 10000 / 31 / 1.258
Formula used to convert Gain (dB) to the ratio of powers.
10*Log= Gain(dB)
Formula used to convert IP3 (dBm) to IP3(Watts) :
10*Log=IP3(dBm) IP3(Watts)
Calculation for Minimum Detectable Signal (MDS):
MDS=[-174+NF(system) +10Log(BW(system))] dBm
=[-174 + 4.3491 +10Log(24000000)]
=-95.84 dBm
Calculation of net IIP3 for the receiver system:
=+
which gives IIP3 = 6.27604*(10^-5) Watts
IIP3 (dBm)= 10*log(6.27604*(10^-5))
= -42.03 dBm
Calculation of the Dynamic Range:
DR = [2 (IPs - MDS)/3] dB
= [2(-42.03-(-95.84))/3]
= 35.14 dB
Calculations for the 5.7 GHz system:
Stage / Part / Gain (dB) / Gain / IP3 (dBm) / IP3 (Watts)1 / ZKL-2R5 / 30 / 1000 / 31 / 1.258
2 / ZK05-C60 / -8.5 / .1412 / 11 / .012589
3 / ZKL-1R5 / 40 / 10000 / 31 / 1.258
Calculation of IIP3, using above formula:
= -49 dBm
4.4 Component List
Part Description / Part Number / Price / Qty / Company / Tel / Total Price1 / Low Pass Filter / SLP 15 / $ 34.95 / 4 / Minicircuits / 1 800 654 7949 / $ 139.80
2 / Modulator / ZF MIQ 70ML / $ 89.95 / 1 / Minicircuits / 1 800 654 7949 / $ 89.95
3 / Band Pass Filter / SBP 70 / $ 18.95 / 2 / Minicircuits / 1 800 654 7949 / $ 37.90
4 / Mixer / ZX05-25MH / $ 39.95 / 2 / Minicircuits / 1 800 654 7949 / $ 79.90
5 / Mixer / ZX05-C60 / $ 39.95 / 2 / Minicircuits / 1 800 654 7949 / $ 79.90
6 / Amplifier / ZKL-2R5 / $ 149.95 / 3 / Minicircuits / 1 800 654 7949 / $ 449.85
7 / Low Pass Filter / SLP 2950 / $ 34.95 / 1 / Minicircuits / 1 800 654 7949 / $ 34.95
8 / Low Pass Filter / SLP-1200 / $ 34.95 / 1 / Minicircuits / 1 800 654 7949 / $ 34.95
9 / Low Pass Filter / L0065001 / $ 385.00 / 1 / Microwave Circuits / 1 800 642 2587 / $ 385.00
10 / Amplifier / ZKL-1R5 / $ 149.95 / 1 / Minicircuits / 1 800 654 7949 / $ 149.95
11 / Demodulator / ZF MIQ 70D / $ 89.95 / 1 / Minicircuits / 1 800 654 7949 / $ 89.95
12 / NovaSource G6 / NS3-1700102 / $ 750.00 / 1 / Nova Engineering / 1 800 341 6682 / $ 750.00
13 / Tripler / ATA-1424 / $ 324.00 / 1 / Marki Microwave / 408 778 4200 / $ 324.00
14 / Splitter / ZX10-2-25 / $ 34.95 / 1 / Minicircuits / 1 800 654 7949 / $ 34.95
15 / Splitter / ZX10-2-12 / $ 24.95 / 2 / Minicircuits / 1 800 654 7949 / $ 49.90
16 / Splitter / ZX10-2-98 / $ 39.95 / 1 / Minicircuits / 1 800 654 7949 / $ 39.95
17 / SMA Male Connectors / PE-4112 / $ 4.30 / 75 / Pasternack Entp / 949 261 1920 / $ 322.50
18 / SMA Male Right Angle / PE-4083 / $ 15.95 / 20 / Pasternack Entp / 949 261 1920 / $ 319.00
19 / LO Synthesizer / 310-010058-001 / $ 885.00 / 1 / Praxsyms / 217 897 1744 / $ 885.00
20 / Internal Chassis Board / $ 35.00 / 1 / Staffol Brothers / 201 653 6479 / $ 35.00
$ 4,332.40
4.5 Final Layout