Showing papers on "Ka band published in 2018"

Dual-Band Dual-Linear-to-Circular Polarization Converter in Transmission Mode Application to $K/Ka$ -Band Satellite Communications

Abstract: Many wireless communication applications such as satellite communications use circularly polarized (CP) signals, with the requirement for easy switching of the polarization sense between uplink and downlink. Specifically, in satellite communications, the trend is also to move to higher frequencies and integrate the receiving and transmitting antennas in one dual-band terminal. However, these simultaneous demands make the design and fabrication of the composing parts very challenging. We propose, here, a dual-band dual-linear polarization (LP)-to-CP converter that works in the transmission mode. The working principle of this polarizer is explained through an example for Ka-band satellite communications at 19.7–20.2 and 29.5–30 GHz. The LP-to-CP converter is a single panel composed of identical unit cells with a thickness of only 1.05 mm and a size of 5.3 mm $\times5.3$ mm. Due to its operation in the transmission mode, the polarizer can be combined with a simple dual-band dual-LP antenna to obtain the desired dual-band dual-CP single antenna. However, the unique property of this polarizer is yet the fact that it converts a given LP wave, e.g., x-polarization, to orthogonal CP waves at the two nonadjacent frequency bands, e.g., left-handed CP at lower band and right-handed CP at higher band. The polarizer is tested both with 20 and 30 GHz LP rectangular horns to illuminate a dual-band transmit array (TA) to obtain wide-angle steering of CP beams. The performance of the polarizer and its association with the TA is evaluated through simulation and measurements. We also present design guidelines for this type of polarizer.

Single-Layer Circularly-Polarized $Ka$ -Band Antenna Using Gap Waveguide Technology

Abstract: A single-layer circularly polarized array antenna is proposed in the context of the so-called gap waveguide (GW) technology. This ultracompact antenna combines the corporate-feeding network and the radiating apertures over one single layer, standing out among other solutions proposed so far in this technology. Apertures are backed by chamfered cylindrical cavities and are fed through a corporate feeding network, which combines both groove and ridge GWs. Cavities are naturally integrated within the bed of nails hosting grooves and ridges, leading to a very low-profile $4\times 4$ array. Experimental results are presented to confirm the good radiation performance obtained by simulations. The proposed array architecture may be seamlessly enlarged to any size thanks to the scalability of the gap-based corporate feeding network, making this solution very attractive for medium to high-gain applications.

An Integrated Ka-Band Diplexer-Antenna Array Module Based on Gap Waveguide Technology With Simple Mechanical Assembly and No Electrical Contact Requirements

Abstract: This paper presents the integration of a diplexer with a corporate feed network of a high gain slot array antenna at the Ka-band. A hybrid diplexer-splitter with a novel architecture is proposed to have compatibility for its direct integration with the feed network of the array antenna. A seventh-order hybrid diplexer-splitter is successfully integrated into a corporate feed network of a $16\times 16$ slot array antenna. The proposed integrated diplexer-antenna module consists of three distinct metal layers without the need of electrical contacts between the different layers based on the recently introduced gap waveguide technology. The designed module has two channels of 650-MHz bandwidths each with center frequencies 28.21 and 29.21 GHz. The fabricated prototype provides good radiation and input impedance characteristics. The measured input reflection coefficients for both Tx/Rx ports are better than −13 dB with the measured antenna efficiency better than 60% in the designed passband, which includes the losses in the diplexer.

Toward Ka Band Acoustics: Lithium Niobate Asymmetrical Mode Piezoelectric MEMS Resonators

Abstract: This work presents a new class of micro-electro-mechanical system (MEMS) resonators toward Ka band (26.5-40 GHz) for fifth-generation (5G) wireless communication. Resonant frequencies of 21.4 and 29.9 GHz have been achieved using the fifth and seventh order asymmetric (A5 and A7) Lamb-wave modes in a suspended Z-cut lithium niobate (LiNbO 3 ) thin film. The fabricated device has demonstrated an electromechanical coupling $(k_{t}^{2})$ of 1.5% and 0.94% and extracted mechanical $Qs$ of 406 and 474 for A5 and A7 respectively. The quality factors are the highest reported for piezoelectric MEMS resonators operating at this frequency range. The demonstrated performance has shown the strong potential of LiNbO 3 asymmetric mode devices to meet the front-end filtering requirements of 5G.

A Ka-band CMOS Digital-Controlled Phase-Invariant Variable Gain Amplifier with 4-bit Tuning Range and 0.5-dB Resolution

Abstract: This paper presents a broadband digital-controlled variable gain amplifier (VGA) in 65-nm CMOS. The phase-invariant technique is proposed to minimize the phase variation under different gain modes. The proposed differential VGA achieves a measured gain tuning range of 7.5 dB and gain resolution of 0.5 dB with 1dB , P 3dB and PAE MAX are 2.5 dBm, 5.5 dBm and 18.3%, respectively.

Broadband and Broad-Angle Multilayer Polarizer Based on Hybrid Optimization Algorithm for Low-Cost Ka-Band Applications

Abstract: We present a method to design planar broadband and broad-angle multilayer polarizers. The proposed procedure is based on a hybrid method that combines the analytical transmission line model and the full-wave Floquet analysis in the frequency domain. The unit-cell analysis allows to create a database that relates the geometry with the metasurface impedances. Thus, any kind of geometries (especially those that do not have an equivalent model) can be used. As the database is created for a single-layer structure, the computation time needed for the design process is reduced (compared with the full-stacked unit-cell). As an example, a polarizer is designed as an add-on device that could be integrated to any linearly polarized antenna (without affecting its behavior) to create circular polarization. Experimental results for a five-metasurface-layer design are given, demonstrating insertion loss lower than 0.5 dB and an axial ratio less than 3 dB over the entire band ranging from 24.84 to 30.24 GHz, which corresponds to a fractional bandwidth of 19.6% for an incidence of 0°–50°.

Additive Manufacturing of Ka-Band Dual-Polarization Waveguide Components

Abstract: Additive manufacturing (AM) is emerging as a key technology for the minimization and integration of microwave antenna systems. Among the several AM processes, selective laser melting (SLM) is rather convenient for waveguide components, since it allows for all-metal parts with a mechanical accuracy within 30–60 $\mu \text{m}$ and an equivalent surface electrical resistivity in the range of 10–20 $\mu \Omega \text {cm}$ . This paper reports on the assessment of the SLM applicability to the manufacturing of dual-polarization waveguide components operating in Ka-band, namely, a septum polarizer, a smooth-wall feed horn integrated with the septum polarizer, and an orthomode transducer (OMT). In order to achieve high electromagnetic performance in the Ka-band, the architectures have been optimized for the manufacturing process, above all in terms of orientation on the building platform and minimization of supporting structures. As a consequence, the corresponding prototypes exhibit measured performances in significant agreement with the predicted values. As an example, the return loss of all the components has been measured to be as high as 25 dB, while the measured isolation between the rectangular waveguide ports of the OMT is better than 47 dB.

A Compact Ka-Band Monopulse Cassegrain Antenna Based on Reflectarray Elements

Abstract: A compact Ka-band monopulse Cassegrain antenna based on the reflectarray elements is presented in this letter. The proposed antenna consists of a main-reflectarray, a subreflectarray, a substrate integrated waveguide comparator, and a monopulse feed to achieve good sum–difference characteristics. Compared with traditional monopulse Cassegrain antenna, the total length of the proposed antenna is shrunken to 67.85%. The results of measurement agree with that of simulation very well. The measured SUM beam gain of the proposed antenna is 29.4 dBi by eliminating the loss of Ka-band comparator, the 3 dB beamwidth is 3.85°, the first sidelobe level is under −12 dB, the cross-polarization level is better than −20 dB, and the gain ratios between the SUM and DIFF are about 3 and 5 dB in azimuth and elevation plane, respectively. The measured results show that the proposed antenna is a good candidate for the low-cost multimode tracking system with limited space, especially for that working at high frequency.

An Ultrathin and Polarization-Insensitive Frequency Selective Surface at Ka-Band

Abstract: In this letter, an ultrathin frequency selective surface is developed with a square unit cell loaded with three ring slot pairs. The outer ring slot pair is loaded with metal shorts. It achieves one polarization-insensitive passband with sharp transition at Ka-band. The design is verified with full-wave simulated results, as well as the measured results. The fabricated FSS has a flat passband, and its measured 3 dB bandwidth is from 33 to 37.5 GHz. A complete angular stability study of the FSS has been conducted. Meanwhile, it can directly attach to the aperture of the horn antenna to lower the whole profile of FSS-antenna configuration. Working as a radome, this FSS can be a good candidate for radar communications and radar-cross-section reduction in radar stealth research area at Ka-band.

Two-Wave Ka-Band Nanosecond Relativistic Cherenkov Oscillator

Abstract: This paper presents the results of numerical and experimental study of a Ka-band relativistic Cherenkov oscillator with average diameter of the slow-wave structure ${D} \approx \text {2.6}\lambda $ . ( $\lambda $ is a wavelength). The combined mode selection including the diffraction loss in the electron diode was applied. The high-current accelerator SINUS-200 provided the thin-walled annular electron beam in the range of voltages 350–420 kV and currents of 2.9–3.8 kA at pulsewidth of 10 ns. The generation of 2.5–3-ns pulses at the central frequency 36.4–36.8-GHz and 400–600-MW output microwave peak power was realized. The corresponding efficiency of 42% ± 5% in power conversion has been obtained.

A $K\text{-}/Ka$ -Band Concurrent Dual-Band Single-Ended Input to Differential Output Low-Noise Amplifier Employing a Novel Transformer Feedback Dual-Band Load

Abstract: A concurrent dual-band single-ended input to differential output (single-ended-to-differential) low-noise amplifier (LNA) employing a novel transformer feedback single-ended-to-differential dual-band load is proposed. The developed LNA topology is flexible in controlling the stopband notch frequency by optimizing the transformer’s self-inductance and coupling coefficient. It also has a unique advantage in controlling both the stopband rejection and passband gain balance, simultaneously. The LNA is designed using a 0.18- $\mu \text{m}$ BiCMOS process and exhibits the same single-ended-to-differential peak gains of 19.2 dB at 21.5 and 36 GHz in the low- and high-passband, respectively, with the stopband rejection ratio of 37.1 dB. In the single-ended input to single-ended output (single-ended) mode operation, the designed LNA exhibits the measured peak gains of 15.7/16.6 dB at 21.5 GHz and 15.7/16.7 dB at 36 GHz for the two signal paths. It achieves the best measured single-ended noise figures of 4.3/4.0 and 4.3/4.2 dB for the two signal paths in the respective low and high passbands. The LNA also attains the measured differential gain and phase imbalances of 0.9/1.0 dB and 0.5/10.4 degree in the low/high passband, respectively. This LNA is the first concurrent dual-band single-ended-to-differential LNA integrated on-chip operating in ${K}$ - and Ka -band.

0.25- $\mu \text{m}$ BiCMOS System-on-Chip for K-/Ka-Band Satellite Communication Transmit–Receive Active Phased Arrays

Abstract: The first millimeter-wave system-on-chip for dual-band phased array applications is presented as a proof of concept for K-/Ka-band (20/30 GHz) satellite communication on-the-move applications. Each chip includes four transmit (Tx) and two receive (Rx) channels working at Ka- and K-band, respectively. The proposed architecture enables a half-duplex operating mode in two different bands. Its development was driven taking into account the integration into a realistic Tx/Rx shared aperture phased array architecture. Full amplitude and phase control are provided for each channel with high granularity (65 536 states). The measured results demonstrate the validity of the proposed chip architecture, even though the channel output power and the noise figure (NF) are not in full agreement with the simulations. In Tx mode, the channel provides 9.47 dB of gain with 4.19-dBm output power at 1-dB compression. In Rx mode, the channel gain is 21.6 dB with an NF of 5 dB. In a scenario with 5.265° phase steps and 8-dB amplitude tapering capability, the amplitude and phase root-mean-square (RMS) errors within the Tx bandwidth (29.5–30.8 GHz) are equal to 0.52 dB and 3.74°, respectively. The amplitude and phase RMS errors in the Rx bandwidth (19.7–21 GHz) are equal to 2.05 dB and 12.11°, respectively. The chip consumes 340 mW in Tx and 242 mW in Rx mode and occupies $3.3 \times 3.5$ mm2.

Vanadium Oxide Bandstop Tunable Filter for Ka Frequency Bands Based on a Novel Reconfigurable Spiral Shape Defected Ground Plane CPW

Abstract: This paper proposes and validates a new principle in coplanar waveguide (CPW) bandstop filter tuning by shortcutting defected ground plane (DGS) inductor shaped spirals to modify the resonant frequency The tunable filter is fabricated on a high-resistivity silicon substrate based on a CMOS compatible technology using a $1\,\,\mu \text {m}\times 10\,\,\mu \text {m}$ long and 300 nm thick vanadium oxide (VO2) switch by exploiting its insulator to metal transition The filter is designed to work in Ka band with tunable central frequencies ranging from 282 GHz to 35 GHz The measured results show a tuning range of more than 19 %, a low insertion loss in the neighboring frequency bands (below 2 dB at 20 GHz and 40 GHz in on/off-states) while a maximum rejection level close to 18 dB in off-state, limited by the no RF-ideal CMOS compatible substrate The filter has a footprint of only $0084\cdot \lambda _{0} \times 0037\cdot \lambda _{0}$ (where $\lambda _{0}$ represents the free space wavelength at the highest resonance frequency) thus making it the most compact configuration using CPW DGS structures for the Ka frequency band In addition, a more compact filter concept based on the Peano space filling curve is introduced to increase the tuning range while minimizing the DGS area

On-Wafer Microstrip Meander-Line Slow-Wave Structure at Ka-Band

Abstract: A novel configuration for a Ka-band V-shaped microstrip meander-line slow-wave structure (SWS) is reported. The SWS is designed to work at a voltage less than 4 kV and provide a wide bandwidth. Coplanar waveguide (CPW) input–output feed lines and a shielding structure are incorporated to enable fast on-wafer cold test measurements on a CPW probe station without requiring dicing or a metal enclosure. Simulated dispersion characteristics and coupling impedance for the optimized design are presented. The simulated S11 of the entire structure is better than −15 dB over 25–36 GHz. The proposed configuration is fabricated using $4^{\prime \prime }$ Si wafers and standard microfabrication processes. The measured S11 of the entire structure is better than −10 dB over 20–40 GHz. The observed high insertion loss has been explained in detail, and alternative approaches that can reduce the loss have been proposed. The PIC simulation results show that for a 3.6-kV, 50-mA sheet beam, the output power can potentially reach 14.5 W at 34 GHz with a gain of 21.6 dB. A 3-dB bandwidth of about 25% centered at 32 GHz is also indicated.

A Ka-Band High-Efficiency Transparent Reflectarray Antenna Integrated With Solar Cells

Abstract: A transparent reflectarray antenna integrated with solar cells is presented for satellite communications in the paper. The electromagnetic characteristics of solar cells at Ka -band are investigated, and a sub-wavelength X-shaped dipole element is designed to augment the reflectarray’s performance. A prototype with an aperture of $160\times150$ mm2 is then analyzed, fabricated, and tested to validate the proposed design. The simulation and measurement results show good radiation characteristics, and the measured gain at 20 GHz is 27.3 dBi with an aperture efficiency of 40.0%. Low side-lobe and cross polarization levels are obtained. Furthermore, the solar energy efficiency of the proposed transparent reflectarray antenna is studied through an optical blockage experiment. The optical blockage ratio is less than 9.9% and at least 81% of light transmittance has been achieved. This work continues to propel the research on reflectarray antennas integrated with solar cells, making it more promising for practical applications in space satellite communications.

Ka-Band Dual-Frequency Single-Slot Antenna Based on Substrate Integrated Waveguide

Abstract: This letter presents a novel dual-frequency single-slot antenna in Ka-band based on a substrate integrated waveguide (SIW). From the view of an SIW resonator, the single-slot cuts currents of the TE101 and TE102 mode in two frequencies, respectively, which leads to a dual-frequency performance. In addition, the difference between two resonance frequencies may be tuned by varying the length of the SIW, which changes the resonant frequencies of the two modes. Three antennas operating from 25.3 to 30.7 GHz with gain greater than 6 dBi are designed and fabricated. Simulated and measured results of the antennas are presented as well. The results show that the proposed antennas achieve stable tunable dual-frequency performance, which may be applied to a Ka-band communication system.

Coexistence Downlink Interference Analysis Between LEO System and GEO System in Ka Band

Abstract: With the development of satellite communication techniques, various types of new service have been emerging, which leads to more spectrum resource requirements. However, traditional L(1–2GHz)/S(2–4GHz) bands which are allocated to satellite communications are limited, and these bands cannot meet the increasing bandwidth demands. Therefore, the Ka(27–40GHz) band has attracted the attention of many satellite communication institutes due to the large bandwidth. With the implementation of many Geostationary Earth Orbit (GEO) and Low Earth Orbit (LEO) constellation plans in Ka band, the coexistence interference analysis between LEO and GEO system is important. In this paper, the coexistence downlink interference between LEO system and GEO system is analyzed, and the impact of the exclusive angel strategy on the inference is evaluated. Simulation results show that the exclusive angel strategy can reduce the in-line downlink interference from LEO to GEO. However, it decreases the coverage of LEO. In addition, Simulation results show that there is little downlink interference from the GEO to LEO.

High-gain GaN doherty power amplifier for Ka-band satellite communications

Abstract: A Doherty power amplifier (DPA) implemented in 100 nm GaN process is presented. It features a peak Power Added Efficiency (PAE) of 37%, an output power of 35 dBm and 25 dB gain. For a noise-to-power ratio (NPR) of 15 dB, an output power of 33 dBm is achieved.

40 W Ka-Band Single and Dual Output GaN MMIC Power Amplifiers on SiC

Abstract: This paper presents single and dual output 40 W Ka-Band GaN MMIC PAs fabricated on $\mathbf{50} \ \mu \text{m}$ SiC using Qorvo's QGaN15 released process. The single output PA produces approximately 40 W of output power over the 27.5 - 29.5 GHz band and greater than 30W over the 26.5 - 31 GHz band with greater than 20 % PAE. A balanced PA architecture is selected resulting in return losses greater than 15 dB in fixture. The PA exhibits less than 0.3 dB power droop over a 5 ms pulse width. Design choices minimizing the performance degradation due to process variation are discussed. A dual output PA integrated with an input SPDT switch and output isolation circuitry is also detailed. This variant allowing the output signal to be routed to one of two selectable outputs without requiring large output switch devices is presented with preliminary measured results.

Industrial 0.15-μm AlGaN/GaN on SiC Technology for Applications up to Ka Band

Abstract: This paper describes the main characteristics of the new GaN-on-SiC technology in development at UMS. This technology is based on a $0.15 - \mu \mathrm{m}$ gate-length and it is in the phase of industrial qualification for a target release by the end of the year. The results of two out of four demonstrators already successfully designed on the new technology are also reported: a 29.5–36 Ghz 9W HPA and a 15.5–18.5 GHz 20W HPA.

Dual-Stub Ka-Band Vivaldi Antenna with Integrated Bandpass Filter

Abstract: A dual-stub co-planar Vivaldi antenna with a parasitic element is presented. The dual stub is coupled between the parasitic element and two tapered slots. The parasitic element shape and size is optimised. The use of slits on the outer edge of the ground plane is shown to provide control of beamwidth and maximum gain. A bandpass filter is used for performance control and sub-harmonic suppression.

A Ka -Band Transformer-Based Doherty Power Amplifier for Multi-Gb/s Application in 90-nm CMOS

Abstract: A Ka -band transformer (TF)-based Doherty power amplifier (DPA) is designed and fabricated in 90-nm CMOS process. Symmetrical Doherty structure is used to improve the 6-dB power backoff efficiency. The high turn ratio ( $N = 2$ ) current-type TF is adopted for the load modulation in a DPA to avoid from leakage power. The measured small signal gain is 19.8 dB with 3-dB bandwidth from 28.7 to 41.9 GHz. The proposed PA achieves 20.7-dBm saturated output power with above 32% power added efficiency (PAE) at 34 GHz. In the 6-dB power backoff region, the PAE of the proposed PA is about $1.7\times $ of that in a class-A PA.

Ka-Band Antenna With High Circular Polarization Purity and Wide AR Beamwidth

Abstract: This letter presents the design of a wideband circularly polarized antenna, operating at Ka band. The proposed antenna comprises a circular microstrip patch antenna that is coupled to a microstrip feedline through a modified L-shaped aperture slot. The antenna radiates a wideband right-hand circularly polarized wave with high polarization purity and a wide axial ratio (AR) angular beamwidth. A 4 $\times$ 4 antenna subarray has been designed, fabricated, and measured to validate the proposed concept. The array exhibits a reflection coefficient $S_{11}\, −10 dB over the frequency band 27–31 GHz. Moreover, the 4 $\times$ 4 antenna subarray yields a high level of polarization purity, as well as a flat measured AR $\leqslant$ 1.15 dB over the frequency range 27.55–30.45 GHz (10 $\%$ bandwidth).

A Large Antenna Array for Ka-Band Satcom-on-the-Move Applications—Accurate Modeling and Experimental Characterization

Abstract: We present the accurate modeling and analysis, followed by experimental validation, of a 1024-element (64-by-16) antenna array. This fixed-beam array radiates linear polarization in Ka-band (19.7–20.2 GHz). It acts as a first step in the design and modeling of future antenna arrays for satcom-on-the-move applications. Accurate prediction of the behavior of such a large array is a challenging task since full-wave simulation of the entire structure cannot be considered. By taking advantage of existing formalisms on periodic arrays and by using appropriate methods to efficiently exploit such formulations, it is possible to accurately define the performances of all building blocks, from the feeding circuits to the radiating elements, over a frequency range. Such a detailed design also allows an accurate physical analysis. It has been successfully used to guarantee the measured performances. This paper is intended to detail different steps to antenna designers.

Toward Ka Band Acoustics: Lithium Niobate Asymmetrical Mode Piezoelectric MEMS Resonators.

Abstract: This work presents a new class of micro-electro-mechanical system (MEMS) resonators toward Ka band (26.5-40GHz) for fifth-generation (5G) wireless communication. Resonant frequencies of 21.4 and 29.9 GHz have been achieved using the fifth and seventh order asymmetric (A5 and A7) Lamb-wave modes in a suspended Z-cut lithium niobate (LiNbO3) thin film. The fabricated device has demonstrated an electromechanical coupling (kt2) of 1.5% and 0.94% and extracted mechanical Qs of 406 and 474 for A5 and A7 respectively. The quality factors are the highest reported for piezoelectric MEMS resonators operating at this frequency range. The demonstrated performance has shown the strong potential of LiNbO3 asymmetric mode devices to meet the front-end filtering requirements of 5G.

A Ka-Band Substrate Integrated Suspended Line to Rectangular Waveguide Transition

Abstract: In this letter, a novel Ka -band transition from substrate integrated suspended line (SISL) to rectangular waveguide (RWG) is proposed. In order to broaden the bandwidth, a T-shaped patch is adopted. A back-to-back transition prototype has been designed and fabricated. From 24.6 to 38.5 GHz, i.e., a fractional bandwidth of 44%, the measured return loss is better than 12 dB and the insertion loss is less than 0.34 dB with a minimum of 0.11 dB. Fabricated by using a standard printed circuit board process, the proposed SISL-to-RWG transition has advantages of low manufacturing cost, compact size, lightweight, and self-packaging.

Low-Cost Ka-band Switchable RHCP/LHCP Antenna Array for Mobile SATCOM Terminal

Abstract: Achieving a functional antenna for mobile satellite communications terminals in Ka-band is probably one of the most challenging tasks in current antenna engineering, particularly bearing in mind they need to be low profile and “affordable.” This quest is involving many companies in the field. Our contribution represents one of such efforts. The antenna is based on a slotted waveguide array technology to maximize efficiency and it features a number of novel solutions, going from its robust polarization switching mechanism, to the use of a thin wideband polarizer and the utilization of groove gap waveguides. This communication reports the measured data of a fully functional prototype to validate its novel contributions.

Experimental research on Ka-band coaxial transit-time oscillator

Abstract: In this paper, the simulation and experiment research on a Ka-band coaxial transit-time oscillator is conducted. The asymmetric-mode-competition phenomenon was observed in the experiment, and TE1 1 and TE29 1 modes exist in the output microwaves. Based on the analysis of the mechanism of the asymmetric modes, support posts need to be improved to suppress the asymmetric modes. By using the improved support posts, the effective TEM mode transmission, the small reflection of the TE1 1 mode, and the small excitation of the high order asymmetric modes are expected. In the improved experiment, the output microwaves with the power of 650 MW at the frequency of 26.5 GHz can be obtained with the diode voltage of 450 kV and the beam current of 9.1 kA. The asymmetric modes are effectively suppressed. It should be noted that the power loss caused by the material cannot be ignored in the Ka-band. The corresponding power loss of stainless steel is above 30% compared with the perfect conductor.

A Planar All-Silicon 256-Element Ka-band Phased Array for High-Altitude Platforms (HAPs) Application

Abstract: We describe the design of an active electronically steerable antenna array (AESA) enabling broadband line-of-sight communication from a high-altitude platforms (HAPs). The array is constructed using a multitude of single chip multi-channel beamforming modules capable of switched bi-directional amplitude and phase conditioning at Ka-band enabling a sharing of aperture between transmitting and receiving functions. Use of an open-ended substrate-integrated square waveguide enables wide field of regard. Measured performance of a 256-element AESA using a spherical near-field measurement technique allows for indirect characterization of both far-field gain and excitation uniformity.

A Shared Aperture S/Ka-Band Antenna for Polarization Diversity

Abstract: A dual-band dual configuration reflector antenna is presented for S- and Ka-band communications. It operates in cassegrain configuration at Ka-band and in prime focus configuration at S-band using the same parabolic reflector. It is dual linearly polarized (LP) at S-band and dual circularly polarized (CP) at Ka-band. It reduces space, weight, cost, and RCS. Realized impedance bandwidths ( $\boldsymbol{S}_{11} \leq-10\mathbf{dB}$ ) are larger than 7% at the Ka-band and 10% the at S-band ports. 3dB axial-ratio (AR) bandwidth ≥7% is observed at Ka-band.