Gain Pattern Research Articles

Trajectory of blood pressure levels and weight gain in pregnant women: A group-based approach

Background and objectivesMorbidities associated with increased blood pressure levels during pregnancy represent one of the main causes of maternal mortality. The objective was to identify patterns of systolic blood pressure (SPB) trajectory in pregnant women undergoing prenatal care at the Unified Health System, and associations with weight gain trajectory, demographic, obstetric, anthropometric data, and health related behaviors. Methods and resultsCohort study with pregnant women using the public health services in Brazil. Data were collected through questionnaires and medical records. Trajectory patterns of SBP and weight gain were identified by a group-based trajectory model. For trajectory analysis, 460 women had SBP information available, totaling 2839 measurements, with an average of 6.2 measurements during pregnancy. Three SBP trajectory patterns were identified and classified as “Group 1” (48.0%), with a mean of 103 mmHg (95% CI 102.5–103.7 mmHg), “Group 2” (42.7%) with a mean of 114 mmHg (95% CI 113.7–114.9 mmHg), and “Group 3” (9.1%) with the highest mean SBP value of 130 mmHg (95% CI 128.8–131.5 mmHg). It was observed that regardless of the weight gain trajectory group, women classified in the group with the highest SBP had the highest SBP levels. The probability of being classified in Group 3 was higher among women with higher education, who started pregnancy presenting obesity, and who were using antihypertensive drugs. ConclusionThe probability of belonging to groups with a greater trajectory of SBP during pregnancy was associated with obesity, education, and hypertension under treatment.

The Effect of Chia Seeds on High-Density Lipoprotein (HDL) Cholesterol.

Chia seeds are touted as a healthy food capable of providing a beneficial effect on high-density lipoprotein (HDL) cholesterol. Similar claims have been made for oats in various forms, claiming that they improve cholesterol or are in some way "heart healthy." This study aims to demonstrate the effect of daily consumption of chia seeds, if any, on HDL cholesterol levels and compare this to the effects of oats on HDL levels. This pilot study is a randomized controlled trial performed at an academic primary care center. Participation was voluntary, and all participants provided written consent prior to enrollment. There were no exclusion criteria other than that participants must be adults and willing to come in to get their cholesterol profiles checked at the beginning and end of the study. The participants consumed their assigned breakfast in a standard serving size for a month with blood draws and weights recorded before and after the diet. The patients' cholesterol profiles were also compared with their weights. To standardize the delivery of chia seeds, the group consuming chia seeds mixed them with oatmeal. The three meal groups consisted of Cheerios (red group), oatmeal (white group), and oatmeal with chia seeds (blue group). Initially, there were a total of 11 subjects, three in the red group, four in the white group, and four in the blue group. Two subjects were lost to follow-up, one each from the red and white groups. Statistical analysis including one-way analysis was done with the means, Wilcoxon/Kruskal-Wallis, and one-way analysis tests. The results showed a similar weight gain pattern between the three groups, with an average of 2.8 lbs gained in the red group, 2.4 lbs gained in the white group, and 2.6 lbs gained in the blue group. The average HDL levels decreased by 1.00 mg/dL in the red group (standard deviation (SD) 2.82843), increased by 2.00 mg/dL in the white group (SD 8.88819), and increased by 5.75 mg/dL in the blue group (SD 8.01561). The HDL:total cholesterol ratios decreased by 0.00748 in the red group (SD 0.002660), an average of 0.04053 in the white group (SD 0.028138), and an average of 0.01614 in the blue group (SD 0.023808). The results suggest that both chia seeds and oatmeal may be good dietary sources to naturally increase HDL cholesterol, more substantially so with the diet including chia seeds, but may or may not improve total cholesterol:HDL ratios. The effect of weight gain is unclear, as all groups gained weight similarly. Hence, further study is warranted.

Numerical simulations of an integrated radio-frequency/wireless coil design for simultaneous acquisition and wireless transfer of magnetic resonance imaging data

Objective. A novel magnetic resonance imaging (MRI) radio-frequency (RF) coil design, termed an integrated RF/wireless (iRFW) coil design, can simultaneously perform MRI signal reception and far-field wireless data transfer with the same coil conductors between the coil in the scanner bore and an access point (AP) on the scanner room wall. The objective of this work is to optimize the design inside the scanner bore to provide a link budget between the coil and the AP for the wireless transmission of MRI data. Approach. Electromagnetic simulations were performed at the Larmor frequency of a 3T scanner and in a WiFi wireless communication band to optimize the radius and position of an iRFW coil located near the head of a human model inside the scanner bore, which were validated by performing both imaging and wireless experiments. Main Results. The simulated iRFW coil with a 40 mm radius positioned near the model forehead provided: a signal-to-noise ratio (SNR) comparable to that of a traditional RF coil with the same radius and position, a power absorbed by the human model within regulatory limits, and a gain pattern in the scanner bore resulting in a link budget of 51.1 dB between the coil and an AP located behind the scanner 3 m from the isocenter, which would be sufficient to wirelessly transfer MRI data acquired with a 16-channel coil array. The SNR, gain pattern, and link budget for initial simulations were validated by experimental measurements in an MRI scanner and anechoic chamber to provide confidence in this methodology. These results show that the iRFW coil design must be optimized within the scanner bore for the wireless transfer of MRI data. Significance. The MRI RF coil array coaxial cable assembly connected to the scanner increases patient setup time, can present a serious burn risk to patients and is an obstacle to the development of the next generation of lightweight, flexible or wearable coil arrays that provide an improved coil sensitivity for imaging. Significantly, the RF coaxial cables and corresponding receive chain electronics can be removed from within the scanner by integrating the iRFW coil design into an array for the wireless transmission of MRI data outside of the bore.

EPH137 Group-Based Trajectory Modeling to Identify Patterns of Antipsychotic-Induced Weight Gain Among Children and Adolescents

Antipsychotic-induced weight gain (AIWG) is the most common side effect associated the use of second-generation antipsychotic (SGA) medications among children and adolescents. Group-based trajectory model (GBTM) can graphically display the longitudinal weight change overtime. The objective of this study was to model the development of AIWG among children and adolescents taking SGAs.

Mutual coupling reduction in a textile ultra-wide band MIMO antenna

This paper presents a mutual coupling reduction technique in a textile ultra-wideband (UWB) multiple-input–multiple-output (MIMO) antenna system implemented on a textile substrate. The compact textile UWB MIMO antenna consists of two patch antennas implemented on a felt textile substrate. The compact size and close placement of the antennas in a MIMO system cause higher mutual coupling which deteriorates the performance of the communication systems. To minimize the mutual coupling, Parasitic Elements and Defected Ground Structures are used in the designed textile UWB MIMO antenna. The MIMO antenna performed very well over almost the whole UWB frequencies ranging from 3.29 GHz to 13.3 GHz. The simulated and the measured parameters showed a good impedance matching with an impedance bandwidth of 133.4%. The results showed an improvement of 20 dB isolation at certain frequencies without impacting the reflection coefficient S11 and the antenna impedance bandwidth. The MIMO antenna has good diversity performance parameters in terms of Envelope Correlation Coefficient (ECC), Diversity Gain, Mean Effective Gain (MEG) and radiation pattern and the results indicate that the textile antenna is suitable for UWB MIMO applications. The overall size of the antenna is 30x60 mm2. Fully embroidered structure provides freedom of movement and comfort, so it is a good fit for Wireless Body Area Network applications.

Design of Millimeter Wave Radar Antenna Array with Flat-top Pattern

In this paper, a planar millimeter wave radar array antenna with flat-top pattern is proposed for wide detection angle. Firstly, the Chebyshev synthesis method is used to design the linear array with high gain and low sidelobe pattern which works in the 24 GHz frequency band. The maximum gain of the linear array is roughly 15 dBi, and the main-sidelobe ratio is close to 20 dB. By setting the excitations and phases distribution of the planar array feeding network, a 5××4 antenna array with a flat-top pattern is obtained. The simulated and measured results show that the radar antenna array has a wide half-power beamwidth of 88 degrees, which can ensure that the automotive radar has a longer detection range and a larger monitoring angle.

A Novel Wide-Band Directional MUSIC Algorithm Using the Strength Proportion.

The directional multiple signal classification (Dir-MUSIC) algorithm based on the antenna gain array manifold has been proposed to find the direction of the partial discharge (PD) source in substations. However, PD signals are wideband signals and the antenna gain pattern functions are always different at different frequencies; therefore, the accuracy can be improved using a wideband Dir-MUSIC algorithm. In this paper, wideband Dir-MUSIC algorithms are discussed and a novel wideband Dir-MUSIC algorithm using the strength proportion (DirSP) is proposed. This algorithm estimates a focusing PD signal at a certain frequency using the strength proportion among different directions, and then the Dir-MUSIC algorithm can process the focusing PD signal at this frequency. In simulations, when the antenna gain functions among different frequency bins are quite different, the Dir-MUSIC algorithm loses accuracy; meanwhile, DirDP performs very well. In the experiments, we deal with six sets of samples, and the mean error and standard deviation are both smaller than 4° better than other methods.

D-Band Integrated and Miniaturized Quasi-Yagi Antenna Array in Glass Interposer

An integrated and miniaturized D-band quasi Yagi antenna in glass interposer is presented. Single element, 1×2 and 1×4 test coupons are fabricated on 100-μm glass substrate with low-loss polymer buildup films and the return loss, gain and radiation pattern of the antennas are characterized. The proposed antenna utilizes a monopole radiator to achieve a higher bandwidth. Advantages of the glass substrate for beyond 5G communications in terms of enabling fine features and compact integration of other active and passive devices through chip embedding is discussed. An analysis of the substrate modes to ensure proper mode propagation in the selected stack-up is presented. Furthermore, the paper discusses the challenges in planar antenna measurements in sub-THz frequencies and it presents two measurement setups to overcome these challenges. The first is a low-cost probe-station-based measurement setup to characterize the return loss and boresight gain, and the second is a diode-detector-based setup to measure the normalized radiation pattern. The proposed antennas achieve high bandwidth covering the frequency range of 110-170 GHz, and 4.78 dBi, 8.41 dBi, and 11.04 dBi gain for the single element, 1×2 and 1×4 array, respectively.

Multiband Compact mmW Antenna for 5G Smart Phones

The design of a millimeter wave (mmW) antenna for the 5G mobile applications is presented in this paper. designed antenna has dimensions of 10×10×0.245 mm3. This includes the copper ground plane. The resonance of the proposed mmW antenna lies within the range of 33 GHz and 43 GHz. These frequency bands are covering the 5G proposed band in terms of the signal speed, data transmission, and high spectral efficiencies. High-frequency structure stimulation (HFSS) software is used to simulate the proposed 5G antenna including the characteristics of S-parameters, gain, and radiation pattern. Simulation results show that the return loss at resonant frequencies goes - 22 dB, which satisfies the requirements of 5G mobile technology.

Investigation of a novel heat dissipation concept with controllable thermal and EM performance for reliable electronics and communication systems

This paper presents a novel efficient heat dissipation concept in electronics with switch controllable thermal and electromagnetic (EM) performance. Besides the traditional implementation of heatsinks on the back of the antenna in communication systems, a passive technique by introducing a reconfigurable heatsink that reuses the air space above the antenna for additional heat dissipation channels is proposed. The non-contact heatsink is lifted with a tiny air gap from the antenna and partially connected with the antenna through physical switches/poles that balance the EM performance and heat dissipation efficiency, which eliminates the negative impact of the heatsink on the antenna EM performance. EM effects of heatsink on the antenna in terms of locations of contacts, states of switches, and various dimensions are thoroughly investigated. To demonstrate the design efficacy for optimized thermal efficiency and EM performance, a properly designed heatsink is implemented on the top of a simple patch antenna. The measured results show that good heat dissipation is achieved without deteriorating the EM performance of the antenna, in respect to return loss, gain, and radiation patterns. When the switches are OFF and ON, the reflection coefficient of the antenna is measured as −20.82 dB and −17.56 dB, respectively. In addition, with a 20 mW heat source at the input port of the antenna to mimic the heat generation from the electronics, the temperature of the antenna surface is reduced with the front-integrated heatsink by 7.4 °C and 13.4 °C when the connection switches are turned OFF and ON. The implementation of the front-integrated heatsink on the antenna fully demonstrates the proposed heat dissipation concept which provides an effective way to solve the tradeoff between thermal inefficiency and EM performance.

Design of Microstrip Antennas Array for Wireless Applications by Using HFSS

The modern wireless communication desires high gain, wide bandwidth and minimal size antennas that are efficient to provide improved performance over a wide range of frequency spectrum. This requirement leads to the design of microstrip patch antenna. This paper presents the design of compact 1X2 microstrip patch antenna array which uses the corporate feed technique for excitation. The proposed antenna is designed on FR-4 substrate with dielectric constant 4.4 and thickness 1.6mm. Dielectric constant and parameters like Return Loss, Gain and Radiation pattern are calculated using high frequency simulation software. The fabricated antennas results are to be compared with Simulation results. The antenna has been designed for the range 2.4 GHz. Keywords: Microstrip antenna, corporate feed, FR-4 substrate, Microstrip antenna array

DESAIN ANTENA MICROSTRIP RECTANGULAR ARRAY 1x4 PADA FREKWENSI 2.2 UNTUK RADAR KAPAL

This study aims to analyze antennas' characteristics at a frequency of 2.2 GHz, including the value of return loss, VSWR, gain, bandwidth, surface current, and radiation pattern. The antenna characteristics have been designed using simulations made with FR-4 substrates with a dielectric constant ε_r= 4.3 and substrate thickness (h) = 1.6 mm and copper patches with a patch thickness of 0.035 mm. Single antennas are made first to get the desired parameters, then continue to make 1x2 and 1x4 antenna arrays. The feeding antenna array is arranged using the Wilkinson power divider technique on the side of the patch. Antenna array planning aims to increase the antenna gain value as well as the antenna directivity value. From the simulation results, successive values were obtained starting from a single antenna, a 1x2 antenna array, and a 1x4 antenna array which included return loss of -22 dB, 25.9 dB, and -15.3 dB. Swr values are 1.1,1.1,1,1.4 each. The gain values are 3.38 dB, 5.52 dB, 7.84 dB, respectively. Antenna bandwidth is obtained by 100 MHz, 400 MHz, and 200MHz. The angular width obtained is 99.40, 92.20, and 80.20.

Miniaturized Four-Port MIMO Implantable Antenna for High-Data-Rate Wireless-Capsule-Endoscopy Applications

This study proposes a miniaturized four-port multiple-input multiple-output (MIMO) implantable antenna for wireless capsule endoscopy (WCE). The proposed MIMO implantable antenna operates in the 2.45 GHz industrial, scientific, and medical (ISM) band, has a compact size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.2\,\, \times 5.2\,\, \times 0.127~\text {mm}^{3}$ </tex-math></inline-formula> , and comprises four meandered resonators sharing a common slotless ground plane with an acceptable bandwidth (14.2%) and low mutual coupling. These features help the antenna achieve high data rates and countering multipath distortions, as confirmed using MIMO channel parameters. The calculated link budget analysis of the proposed antenna suggests that seamless high-rate (78-Mbps) information transmission can be efficiently achieved over a distance of up to 10 m (when placed in the large intestine). The proposed MIMO implantable antenna was optimized by placing it inside a capsule comprising sensors, batteries, and electronic components and was subsequently fabricated. The simulated ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters, gain, and radiation patterns) and measured (in the minced pork) results were in close agreement with a measured bandwidth of 350 MHz and a peak measured gain of −20.1 dBi. To ensure patient safety, the specific absorption rate (SAR) was evaluated for all the four ports in different environments (stomach and small and large intestines), and satisfactory results were obtained. MIMO performance parameters, such as the envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity (CC), were also evaluated and acceptable values were noted. To the best of our knowledge, this is the most compact four-element implantable MIMO antenna designed so far for biomedical applications.

Passive Antenna Characterization Through Impedance Correlations in a Diffuse Field

Ambient noise correlations allow the passive recovery of Green’s functions between two probes. Recently, the same approach has been applied to electromagnetism, but by correlating diffuse fields in mode-stirred chambers. Until now, only the correlation of S-parameters has been studied. However, it has very recently been shown that the result can be difficult to interpret. To overcome this limitation, a new approach is proposed in this article to directly estimate the self- and mutual impedances of two coupled antennas from impedance correlations. The theoretical developments presented are validated experimentally in a reverberation chamber (RC) excited by a single antenna where mechanical and source stirring techniques are combined to generate a sufficiently diffuse field environment. It is shown, with antennas of different properties, that this approach allows reconstructing with good accuracy the complex impedance matrix between two receiving antennas as well as the transmission coefficient between them. The extracted gain pattern, in good agreement with that measured in an anechoic chamber, shows the good sensitivity of the proposed passive characterization technique.

Artificial homeostatic temperature regulation via bio-inspired feedback mechanisms

Homeostasis comprises one of the main features of living organisms that enables their robust functioning by adapting to environmental changes. In particular, thermoregulation, as an instance of homeostatic behavior, allows mammals to maintain stable internal temperature with tightly controlled self-regulation independent of external temperatures. This is made by a proper reaction of the thermoeffectors (like skin blood vessels, brown adipose tissue (BAT), etc.) on a wide range of temperature perturbations that reflect themselves in the thermosensitive neurons’ activity. This activity is being delivered to the respective actuation points and translated into thermoeffectors’ actions, which bring the temperature of the organism to the desired level, called a set-point. However, it is still an open question whether these mechanisms can be implemented in an analog electronic device: both on a system theoretical and a hardware level. In this paper, we transfer this control loop into a real electric circuit by designing an analog electronic device for temperature regulation that works following bio-inspired principles. In particular, we construct a simplified single-effector regulation system and show how spiking trains of thermosensitive artificial neurons can be processed to realize an efficient feedback mechanism for the stabilization of the a priori unknown but system-inherent set-point. We also demonstrate that particular values of the set-point and its stability properties result from the interplay between the feedback control gain and activity patterns of thermosensitive artificial neurons, for which, on the one hand, the neuronal interconnections are generally not necessary. On the other hand, we show that such connections can be beneficial for the set-point regulation and hypothesize that the synaptic plasticity in real thermosensitive neuronal ensembles can play a role of an additional control layer empowering the robustness of thermoregulation. The electronic realization of temperature regulation proposed in this paper might be of interest for neuromorphic circuits which are bioinspired by taking the basal principle of homeostasis on board. In this way, a fundamental building block of life would be transferred to electronics and become a milestone for the future of neuromorphic engineering.

Weight gain patterns among pregnancies with obesity and small- and large-for-gestational-age births.

This case-cohort study estimated associations between gestational weight gain (GWG) and small-for-gestational-age (SGA) and large-for-gestational-age (LGA) births stratified by obesity class (I: 30-34.9kg/m2 ; II: 35-39.9kg/m2 ; III: ≥40 kg/m2 ) (Magee-Womens Hospital, Pittsburgh, Pennsylvania, 1998-2011). First-trimester GWG was categorized as being below (<0.2kg), within (0.2-2.0kg), or above (>2.0kg) the Institute of Medicine recommendations. For second- and third-trimester GWG, four linear trajectorieswerederived: approximating maintenance (slope -0.05 ± 0.03 kg/wk), approximating the recommendations (0.27 ± 0.01 kg/wk; reference), higher than the recommendations (0.54 ± 0.01 kg/wk), and highest among those above the recommendations (0.91 ± 0.02 kg/wk). For classes I, II, and III, respectively, there were 1290, 1247, and 1198 pregnancies in the subcohort; 262, 171, and 123 SGA cases; and 353, 286, and 257 LGA cases. First-trimester GWG was not associated with SGA/LGA births. Second- and third-trimester weight maintenance was associated with potentially lower LGA risk (risk ratio [RR]: 0.80; 95% confidence interval [CI]: 0.55-1.1) but not higher SGA risk (RR: 0.98; 95% CI: 0.64-1.5) for class III. Inaddition,some sensitivity analyses supported no increased SGA risk with second- and third-trimester weight maintenance for classes I and II. Second- and third-trimester weight maintenance may be associated with more optimal birth weight for gestational age. However, how this could be achieved (e.g., through diet and exercise interventions) is unclear, given the observational design of our study.

Patterns of maternal gestational weight gain in association with allergic diseases in offspring: A prospective cohort study.

To evaluate the association between patterns of gestational weight gain (GWG) and allergic diseases in offspring. Prospective cohort study. Prenatal clinics in Wuhan, China. A cohort of 2546 mother and offspring pairs were enrolled before 16 weeks of gestation and followed up to 24 months postpartum. Maternal body weights were measured regularly during pregnancy, and their GWG patterns were estimated using the growth mixture model. Robust Poisson models were used to evaluate relative risk (RR) and 95%CI after multivariable adjustment. Offspring atopic allergy and allergic contact dermatitis were defined according to a physician's diagnosis reported by the mother, and food allergy was reported by the mother. Three GWG patterns were identified: 18.1% (461) of the women were described as pattern1, characterised by rapid GWG earlier in pregnancy; 56.6% (1442) of the women were described as pattern2, with steady GWG throughout pregnancy; and 25.3% (643) of the women was described as pattern3, with rapid GWG later in pregnancy. By the age of 24 months, 360 (14.1%), 109 (4.3%) and 757 (29.7%) offspring had atopic allergy, allergic contact dermatitis or food allergy, respectively. Compared with women in GWG pattern2, the RRs (95%CIs) among women in pattern1 were 0.74 (0.55-0.99) for atopic allergy, 0.64 (0.36-1.15) for allergic contact dermatitis and 0.95 (0.81-1.12) for food allergy. Maternal GWG pattern characterised by rapid GWG earlier in pregnancy was associated with a lower risk of atopic allergy in offspring.

Wide-Band Antenna on Flexible and Thin Substrate for Wireless Systems

This paper presents the design of a flexible monopole antenna for wideband applications. The proposed antenna is printed on flexible substrate material having a dielectric constant of 3 for the design and fabrication of the proposed antenna. The antenna dimensions are 3.8 cm × 4.1 cm × 0.025 cm. The antenna characteristics are investigated not only in flat conditions but also under bending configuration. Both flat and bending configurations are operated at frequency bands from 2.4 GHz up to 10 GHz with S- parameters lower than − 10 dB. The antenna parameters such as gain, efficiency, and radiation patterns are studied for both configurations. A deep study for time-domain response is discussed to validate the performance of the proposed antenna to operate at a wide band with a highly correlated response.

Design of 60 GHz millimeter‐wave SIW antenna for 5G WLAN/WPAN applications

AbstractBroadband millimeter Wave (mmWave) transmission at the 60 GHz band is a great prospect to meet the demanding high data rate requirements of future wireless personal area network (WPAN) and wireless local area network (WLAN) 5G networks. This paper proposes a single layer H‐plane sectoral horn mmWave antenna at 60 GHz using substrate integrated waveguide (SIW) technology for the future high‐speed short range WPAN and WLAN networks. The benefits of the proposed antenna are high gain, low cost, small size, and ease of integration with other planar circuits. The proposed SIW horn is constructed with RT/duroid 5880 substrate, which has a relative permittivity and loss tangent with a thickness of 0.508 mm. The novelty of this work is; a wider bandwidth is achieved by adding striplines at the horn aperture to match the antenna with air and to increase the antenna operating bandwidth. In addition, the antenna gain is improved by adding a dielectric lens with the striplines at the radiating end. During these steps, the antenna parameters are tuned and optimized to achieve the best results as compared to related previous studies. The proposed antenna's performance is analyzed in terms of gain, return loss (S11) and radiation pattern at a frequency of 60 GHz. Simulation results are carried out by using industry standard software, Computer Simulation Technology (CST) microwave studio. The designed antenna achieves a peak gain of 13 dB and impedance bandwidth when , 8.6 GHz (13.688%) for the reflection coefficient of . The results show that the proposed antenna achieves stable tunable 60 GHz frequency performance, which makes it feasible to deploy in WLAN/WPAN operating in mmWave bands.

A noise autocovariance model for SAR altimeter measurements with implications for optimal sampling

Earlier work has empirically demonstrated some advantages of an increased posting rate of Synthetic Aperture Radar (SAR) altimeters beyond the expected ground resolution of about 320 m in Delay-Doppler (unfocused SAR, UFSAR) processing, corresponding to ∼20 Hz sampling. Higher posting rates of 40–80 Hz were shown to prevent spectral aliasing of the signal, enable to measure swell wave related signal distortions and may lead to a reduced root mean square error of 1 Hz estimates of Sea Surface Heights (SSH), radar cross section (sigma0) and Significant Wave Heights (SWH) from current SAR altimeters. These improvements were explained by the narrow noise autocovariance function of the waveform signal’s power speckle noise in along-track direction on one hand, and frequency doubling by power detection (squaring of the signal) on the other. It has not been explained, however, why the power speckle noise decorrelates faster than anticipated by the predicted Doppler resolution, and whether this decorrelation depends on the altimeter and processing configuration. Also, it has not been shown explicitly that the estimates of SSH, SWH and sigma0 decorrelate in the same way. Describing the noise autocovariance function – or equivalently the noise power spectral density via the Wiener-Kintchin theorem – is necessary on two counts: Knowing the noise autocovariance allows to apply optimal filtering strategies that maximize precision on one hand, while the noise power spectral density predicts the frequencies contained in the noise (and signals), which in turn determines the required sampling frequency according to the Nyquist theorem. Using a newly derived analytic noise autocovariance model for UFSAR-processed altimeter data, we show that the swift signal decorrelation is mainly due to the observation geometry. Furthermore, our results demonstrate that the noise autocovariance functions of power speckle, SSH, SWH and sigma0 estimates in along-track direction are different and depend on the sea state. On top of that, the noise autocovariance functions are strongly dependent on the number of Doppler beams used for multilooking, the used retracker, and the processing choices such as antenna gain pattern compensation and windowing within the UFSAR processing (Level-1b). We validated our noise autocovariance model with segments of 42 Sentinel-3B overpasses. Our findings are in accordance to all earlier work, but indicate that the reported precision improvements with respect to 20 Hz may have been too optimistic and that the SSH, SWH and sigma0 generally decorrelate slower than the power speckle noise. We found that the required posting rate is always higher or equal to 40 Hz. Our results will potentially enable improved spectral analysis and optimal filtering of any UFSAR altimetry data. More importantly, our results can be used to trade off different aspects for determining an optimal posting rate in UFSAR altimeter processing in different sea states and with changing processing parameters, which is necessary in view of strict precision requirements of existing and future SAR altimetry missions.