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  • mbenkerumass 10:33 pm on November 14, 2019 Permalink | Reply
    Tags: Microwave/RF Engineering   

    IP3 Distortion and Linearity 

    RF/Photonics Lab
    November 2019
    Michael Benker

     

    IP3 Distortion & Linearity

     

    Linearity is the measure of a system’s performance as an output signal being proportional to the input signal level as characterized by Ohm’s Law, V = I*R. Not every system can be expected to perform ideally and thus linearly. Devices such as diodes and transistors are examples of non-linear systems.

    222

    The intercept point of the third order, IP3 is a measure of the linearity of a system. IP3 is the third order of a Taylor series expansion of the input signal’s presence in the frequency domain. Being third order, this term in a Taylor series expansion is understood as distortion since it is different from the sought output signal. In contrast to the second order harmonics, which fall outside of the frequency band of the first order signal, the third order is found in the same frequency band as the original or first order signal. Similarly, consecutive even orders (4, 6, 8, etc) are found outside of the frequency band of the first order signal. Consecutive odd orders beyond the third order such as IP5 and IP7 also cause distortion but are not of primary focus since the amplitude of these order signals are weaker after consequent exponentiation.

    The meaning of an intercept point of an nth order (IPn) on a dBm-dBm axis is the point at which the first-order and nth-order powers would be equal for a given input power. In the case of IP3, this indicates the power level needed for a third-order power to potentially drown out the first-order signal with distortion. The 1 dB compression point defines the range of linear operation for a system.

    55

     

     
  • mbenkerumass 5:53 pm on November 13, 2019 Permalink | Reply
    Tags: Microwave/RF Engineering   

    Scattering Parameters 

    RF/Photonics Lab
    Jared Alves
    November 2019

    Scattering Parameters

    After the mid-1900s, high frequency networks became increasingly prevalent. When analyzing low frequency circuits parameters such as voltages and currents are easily realized. From these signals, Y and Z (admittance and impedance) parameters can be used to describe a network. For the Radio Frequency and Microwave range, S parameters are much more applicable when studying a network of a single port or multiple ports. Each S parameter can be placed in an NxN square matrix where N is the number of ports. For a single port network, only the parameter S11 (also known as ᴦ (gamma or voltage reflection coefficient)) can be realized. The S parameters are unitless because they are ratios of voltages. The parameters can be viewed as both reflection and transmission coefficients for multi-port networks. S parameters with subscripts of the same number are reflection coefficients, as they describe the ratio of voltage waves at a single port (reflected to incident).

    For a two-port network, only parameters S11, S12, S21, S22 exist. For a simple network like this, S11 represents return loss or reflection at port 1. S22 is the output reflection coefficient.  S12 and S21 are transmission coefficients where the first subscript is the responding port and the second the incident port. For example, S21 would be the “forward gain” at port 2 incident from port 1. The following diagram shows an abstracted view of a two-port network, where each “a” and “b” are normalized by the system’s characteristic impedance. Each S parameter can be calculated by terminating a port with a matched load equal to the characteristic impedance. For example, when calculated return loss for a two-port network, port 2 should be terminated by a matched load reducing a2 to zero.  For calculating S1,2 or S2,2 port 1 would be terminated with a matching load to reduce a1 to zero. Each “a” is an incident wave and “b” a reflected wave. Having a matched load at a port results none of the incident wave being reflected due to impedance mismatching.610

    This leads to the following voltage ratios:

    611

    An amplitude with a negative superscript indicates a reflected wave, and an amplitude with a positive superscript indicates a forward propagating wave.

    SParameters

     

     
  • mbenkerumass 5:29 pm on November 12, 2019 Permalink | Reply
    Tags: Microwave/RF Engineering   

    Smith Chart 

    RF/Photonics Lab
    Jared Alves
    November 2019

    Smith Chart

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    The Smith Chart, named after laboratories engineer Phillip Smith, is a graphical tool for solving RF transmission line problems. There are many specific uses for a Smith Chart, but it is most commonly used to visually represent impedance matching problems. Although paper Smith Charts are outdated, RF equipment such as Network Analyzers display information using the chart as well.

    The Smith Chart is a unit circle (radius of one) plotted on the complex plane of the voltage reflection coefficient (ᴦ – gamma). As with any complex plane, the vertical axis is the imaginary and the horizontal axis the real. The Smith Chart can be used as an admittance or impedance chart or both. For a load impedance to be plotted on the chart, it must be normalized (divided by) the characteristic impedance of the system (Zo) which is the center of the chart. With this information in mind, it is apparent that a matched load condition would result in traveling to the center of the chart (where ZL=Zo). Along the circumference of the chart, there are two scales: wavelength and degrees. The degrees scale can be used to find the angle of the complex reflection coefficient. Since the plot is the polar representation of the reflection coefficient, if a line is drawn from the load impedance point to the center of the chart this would be considered the magnitude of the reflection coefficient. By extending the line to the circumference of the circle, the angle (in degrees) can be found. The wavelength scale shows distance across a transmission line in meters. A clockwise rotation represents moving towards the generator whereas a counter-clockwise rotation represents moving towards the load side.

    It is important to note that a Smith Chart can only be used at one specific frequency and one moment in time. This is because waves are functions of both space and time as shown by the equations:

    662

    VF is the forward propagating voltage wave and VR is the reverse propagating voltage wave. If a transmission line system is not impedance matched, a reflected wave will exist on the line which will cause partial or fully standing waves to occur on the line (the reflected wave will add to the incident wave). For the matched condition the reflected wave is zero. Because the Smith Chart can only be used at a specific instant in time and at one frequency the first exponential term in each equation drops out. Because the reflection coefficient is the ratio of the reflected wave to the forward propagating wave, the reflection coefficient becomes:

    663

    Where C is the ratio of the amplitudes of both waves. For a passive load, the reflection coefficient must be equal to one or less because the reflected wave cannot be greater in amplitude than the incident wave.

    Many transmission lines can be approximated as lossless and therefore have zero attenuation. This leads to:

    664

    The propagation constant is a complex number that describes how a wave changes as it propagates down a transmission line. The real part is attenuation constant (Nepers/meter) and the imaginary part is the phase constant or wave number (radians/meter).

    665

    For the lossless condition the attenuation is zero, as stated previously.

    On the Smith Chart, the wavelength λ = 720. This is because the reflected wave must travel the roundtrip distance moved (it must propagate forward and then back again). Using the piece of information, a half wavelength distance is one complete revolution on the chart. This leads to the conclusion that a transmission line that is a half wavelength long does not transform impedance.

     

    The following image shows common points on the Smith Chart.

    661

    The left-hand side of the chart (lying on the real axis) represents a short circuit load. This makes intuitive sense because the reflection coefficient must be real and negative for a short circuit. This is because short circuits have a voltage drop of zero across them which would require a same-amplitude wave with a 180-degree phase shift to cancel the forward propagating wave. The right-hand part of the real axis represents the open circuit load, where the reflection coefficient is purely real but has no phase shift. For an open circuit, the current wave would have to be phase shifted by 180-degrees, but since the reflection coefficient is a voltage reflection coefficient it is not necessary for it to be phase shifted. As shown in the image, the upper half plane is inductive (positive reactance) and the lower half is capacitive (negative reactance).

     

    Smith Chart

     

     
  • mbenkerumass 7:21 pm on November 7, 2019 Permalink | Reply
    Tags: , Microwave/RF Engineering   

    Rat Race Coupler: ADS 

    ECE435 – RF/Microwave Engineering, Professor Dr. Yifei Li
    November 2019
    Michael Benker
    Rat Race Coupler ADS Simulation

     

    1234

     

    project7

     
  • mbenkerumass 4:17 pm on October 30, 2019 Permalink | Reply
    Tags: , Microwave/RF Engineering   

    Directional Coupler ADS Simulation 

    ECE435 – RF/Microwave Engineering, Professor Dr. Yifei Li
    October 2019
    Michael Benker
    Directional Coupler ADS Simulation

     

    Capture

    Project6(Fixed)(1)

     
  • mbenkerumass 7:11 am on October 18, 2019 Permalink | Reply
    Tags: , Microwave/RF Engineering   

    ADS Coupler Momentum Simulation 

    ECE435 – RF/Microwave Engineering, Professor Dr. Yifei Li
    October 2019
    Michael Benker
    ADS Coupler Momentum Simulation

    Build the ADS circuit.

    20191017.3

    Run the momentum simulation and set parameters such as substrate.

    20191017.1

    This is a momentum simulation. Let’s see if we can optimize this.

    20191017.2

    Export the part to be used as a component in the workspace library in ADS.

    20191017.4

    Now run an ADS simulation using the exported component, which uses a database of simulated results.

    20191017.5

    If you step into the component, you will see component features.

    20191017.6

    Now, tune the parameters to begin optimization.

    20191017.7

     
  • mbenkerumass 8:43 pm on October 12, 2019 Permalink | Reply
    Tags: Microwave/RF Engineering   

    NanoVNA – Handheld Vector Network Analyzer 50kHz-900MHz 

    A Network Analyzer for $60 on Amazon. Looking forward to owning my own and spending more time with Network Analyzers, like the one’s in the RF/Photonics Lab.

    nanoVNA

     
  • mbenkerumass 6:19 pm on October 11, 2019 Permalink | Reply
    Tags: , Microwave/RF Engineering, , Research,   

    RCS/ISAR Data Acquisition (testing Demodulator) 

    RF/Photonics Lab at UMASS Dartmouth, Advisor: Professor Dr. Yifei Li
    October 2019
    Michael Benker
    RCS/ISAR Data Acquisition

    The following MATLAB program utilizes a set of data acquired using an oscilloscope to test a demodulator. This is part of a project being undertaken at the UMASS Dartmouth RF/Photonics Lab. To view a published version of the code: rcs20190925.

    Capture4

     
  • mbenkerumass 10:28 pm on October 10, 2019 Permalink | Reply
    Tags: , Microwave/RF Engineering   

    Branchline Coupler – EM Simulation 

    ECE435 – RF/Microwave Engineering, Professor Dr. Yifei Li
    October 2019
    Michael Benker
    ADS Momentum Simulation

    Capture2

    CaptureCapture1Capture3

     
  • mbenkerumass 10:19 pm on October 8, 2019 Permalink | Reply
    Tags: , Microwave/RF Engineering   

    ADS Momentum Simulation 

    ECE435 – RF/Microwave Engineering, Professor Dr. Yifei Li
    October 2019
    Michael Benker
    ADS Momentum Simulation

     

    Capture1Capture2Capture3Capture4Capture5Capture6Capture7Capture8

     
  • mbenkerumass 12:41 am on October 4, 2019 Permalink | Reply
    Tags: , Microwave/RF Engineering   

    Quadrature Hybrid Coupler 

    ECE435 – RF/Microwave Engineering, Professor Dr. Yifei Li
    October 2019
    Michael Benker
    Project 4 – Quadrature Hybrid Coupler

    Presentation: Project4_presentation

    p4tuning

    p4results_optimized

     
  • mbenkerumass 1:30 am on September 17, 2019 Permalink | Reply
    Tags: , Microwave/RF Engineering   

    Smith Chart Impedance Matching 

    ECE435 – RF/Microwave Engineering, Professor Dr. Yifei Li
    September 2019
    Michael Benker
    Project 1 – Smith Chart Impedance Matching

    Presentation: proj1_presentationproj1_schematic

    proj1_smithchart

    proj1_simulation

     
  • mbenkerumass 2:40 am on April 30, 2019 Permalink | Reply
    Tags: , Microwave/RF Engineering   

    20 GHz RF Amplifier Design – ADS 

    ECE336 – Electromagnetic Theory II, Professor Dr. Yifei Li
    April 2019
    Michael Benker
    20 GHz RF Amplifier Design – ADS

    This is a 20 GHz amplifier circuit, made using smith chart impedance matching in ADS. This circuit is one of the first times I have used this powerful software. Glad to be putting my emag theory to work to build something real. The report should be helpful for me to jog my memory to do it again. With the notes I have, a similar circuit should be possible.

    For the impedance matching, I considered using an inductor, though using only caps and t-lines, the result seemed to be cleaner.

    20Ghzamplifiercircuit20Ghzamplifiercircuit2

     

    See the following for the full report:

    ece336projBENKER

     
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