ELEC 411/EECE 571A Fall 2024 Antenna Lab Solutions PDF

THE UNIVERSITY OF BRITISH COLUMBIA Department of Electrical & Computer Engineering ELEC 411 – Antennas and Propagation | EECE 571A – Antennas and Propagation II Fall 2024 Lab Fundamenta...

THE UNIVERSITY OF BRITISH COLUMBIA Department of Electrical & Computer Engineering ELEC 411 – Antennas and Propagation | EECE 571A – Antennas and Propagation II Fall 2024 Lab Fundamentals – Antenna Arrays What you need to know! A compilation of course performance objectives with detailed enabling objectives. ELEC 411 and EECE 571A students completed two sets of lab assignments from Keysight Technologies and TMY Technologies (TMYTEK) during the term. The set from Keysight Technologies focused on RF/microwave measurement technologies while the set from TMYTEK focused on 5G mmWave phased arrays. The Lab Memos that will be prepared and submitted by each group provide evidence that the teams conducted the labs and obtained useful results. The Lab Quiz to be conducted in class provide evidence that individual students acquired specific knowledge that is expected of them. The Question Bank below provides the list of questions that are relevant to the TMYTEK Labs. Lab T1 – What is the Link Budget? Objectives: T1.1. Become familiar with the practical aspects of measuring the gains or losses of the factors that contribute to the system link budget. T1.2. Conduct experiments to characterize the gains or losses of various components of the TMYTEK 5G mmWave Developer Kit: a. PLO + Attenuator b. Cable#1 c. Cable#2 1  d. Cable#3 e. Cable#4 f. Power splitter, Right side g. Power splitter, Left side h. Power combiner, Right side i. Power combiner, Left side Question Bank: T2.1. What is the purpose of a link budget? Ans. A link budget accounts for all sources of gain or loss between a transmitter or receiver. It allows the designer to predict how received power will change if any of these sources of gain or loss are changed for whatever reason, e.g., component failure, replacement of one component with another type, or trade-off between gains and losses in various parts of the system. T2.2. Why is it good practice to measure the losses or gains associated with each component of a wireless communications system? Ans. It is good practice to measure the losses or gains associated with each component of a wireless communications system because: 1) Such measurements help to confirm that the component is functioning correctly, 2) The values reported in the component’s data sheet might not be accurate, 3) The loss or gain values associated with a component may change with time, and 4) Inaccurate loss or gain values will lead to poor predictions of received power. T2.3. Give the typical losses or gains associated with an RF connector or short piece of coaxial cable at 28 GHz. Ans. In the TMYTEK lab, the typical loss introduced by an RF adapter or connector is between 0.25 and 0.5 dB while the typical loss introduced by a short piece of coaxial cable is between 4.5 and 5.0 dB. Lab T2 – What is the Channel Gain? Objectives: T2.1. Become familiar with the techniques for adjusting and measuring the gain of each of the four Bboard RF channels, and determining the difference in the gain between each pair of channels. T2.2. Conduct experiments to determining the difference in the gain between each pair of channels. Question Bank: T2.1. What is EIRP? Ans. EIRP is Effective Isotropic Radiated Power. It is the product of the transmit power and the antenna gain. It can be regarded as the transmit power that would be required to realize the same power density if the transmitting antenna was an isotropic radiator. T2.2. What is the link margin? Ans. The link margin is the difference between the actual received power and the minimum received power required to achieve a specified or required level of performance. Link margin, also known as fade margin, indicates the amount that the signal can fade before performance is no longer acceptable. T2.3. What is receiver sensitivity? Ans. Receiver sensitivity refers to the minimum received power required to achieve a specified or required level of performance. For analog signals, the level of performance might refer to the signal to noise ratio at the output of the receiver. For digital signals, the level of performance might refer to the bit error rate at the output of the receiver. 2  Lab T3 – What is Constructive/Destructive Interference in Conduction? Objectives: T3.1. Become familiar with how to: a. adjust and measure each RF channel phase, and, b. determine the signal cancellation between different channel pairs when the transmitter and receiver are connected by cables. T3.2. Conduct experiments to compare the expected phase step and measured power on each channel, and plot the results. Question Bank: T3.1. What are two methods for changing the phase difference between two signals that otherwise have the same amplitude and phase? Ans. Three methods for changing the phase difference between two signals that otherwise have the same amplitude and phase include: 1) inserting a transmission line of specified physical length Δℓ in order to introduce a delay in the signal where Δ𝜙 = 𝛽 Δℓ, 2) inserting a digital phase shifter that provides discrete phase shifts in response to digital control signals, 3) inserting an analog phase shifter that provides continuous phase variation over a specified range in response to either a manual input or control voltage. T3.2. What is the purpose of the “phase calibration” in this lab? Ans. In this lab, the purpose of phase calibration is to establish the digital control inputs (steps) required to achieve constructive or destructive interference (or in-phase or out-of-phase) between two signals. Lab T4 – What is Constructive/Destructive Interference in Radiation? Objective: T4.1. Redo Lab T3 using an OTA (over-the-air) link rather than cables Question Bank: T4.1. What are the main differences between the results obtained when the tests are conducted over the air (in radiation) rather than on the bench (in conduction)? Ans. Tests conducted on the bench (in conduction) are more reliable and reproducible than tests conducted over the air (in radiation) because over the air tests are subject to distortion by random signal reflections from objects in the surrounding environment. T4.2. Why are most wireless communications systems tests are conducted on the bench (in conduction) rather than over the air (in radiation)? Ans. Tests conducted on the bench (in conduction) are more reliable and reproducible than tests conducted over the air (in radiation). Lab T5 – How is the Beam Steered? Objectives: T5.1. Become familiar with TMYTEK antenna test fixture that integrates a swing arm, ruler, and protractor and the software used to set the phase step of adjacent channels. T5.2. Devise settings to steer the beam of the mmWave antenna array in particular directions. 3 Question Bank: T5.1. Why is beamforming necessary for operation is millimetre-wave bands? 𝜆2 Ans. Because 𝐴𝑒𝑓𝑓 = 4𝜋 𝐺 and 𝜆 is very small in millimetre-wave bands, we must use antennas with relatively high gains in order to achieve an acceptable received signal level. High gains imply small beamwidths. In mobile or portable communications scenarios, the narrow beams of such high gain antennas must be automatically steered to the appropriate direction in order to close the link. While this could be done mechanically, the size, cost and power requirements of mechanical positioners are usually excessive. Electronic beamforming based upon electronic amplitude and phase shifting is a much more compact and less expensive alternative. T5.2. What principle do phased arrays exploit to synthesize different antenna patterns? Ans. Phased arrays exploit constructive and destructive interference between signals emitted by different array elements to synthesise antenna patterns with peaks and nulls in desired directions. By employing an array of identical elements with identical orientation, uniform spacing, and given amplitude and phase shift, the peaks and nulls can be pointed in desired directions. Lab T6 – How is the Beam Pattern Measured? Objectives: T6.1. Become familiar with TMYTEK antenna test fixture that integrates a swing arm, ruler, and protractor, and the software used to set the phase step of adjacent channels. T6.2. Conduct experiments to measure the pattern of the mmWave antenna array. Question Bank: T6.1. What are the disadvantages of measuring an antenna pattern at regular angular intervals, e.g., 5 degrees? Ans. If one measures an antenna pattern at regular angular intervals, one has to collect measurement data at very small intervals in order not to miss the precise location of the peaks and nulls in the pattern. If one attempts to speed up process by collecting measurement data at wider intervals, one will almost certainly miss the precise location of the peaks and nulls and the resulting pattern will be distorted and inaccurate. T6.2. What is a potentially better alternative to measuring the antenna pattern at regular angular intervals? Ans. A potentially better approach is to employ adaptive sampling and scan the antenna until either: a) the signal strength increases or decreases by a certain amount or b) local maxima and minima are encountered, and record the relevant received signal strength and angular data at each point. : 4