This letter presents two high-gain, multidirector Yagi-Uda antennas for use within the 24.5-GHz ISM band, realized through a multilayer, purely additive inkjet printing fabrication process on a flexible substrate. Multilayer material deposition is used to realize these 3-D antenna structures, including a fully printed 120- μm-thick dielectric substrate for microstrip-to-slotline feeding conversion. The antennas are fabricated, measured, and compared to simulated results showing good agreement and highlighting the reliable predictability of the printing process. An endfire realized gain of 8 dBi is achieved within the 24.5-GHz ISM band, presenting the highest-gain inkjet-printed antenna at this end of the millimeter-wave regime. The results of this work further demonstrate the feasibility of utilizing inkjet printing for low-cost, vertically integrated antenna structures for on-chip and on-package integration throughout the emerging field of high-frequency wireless electronics.

Inkjet Printing of Multilayer Millimeter-Wave Yagi-Uda Antennas on Flexible Substrates

This letter presents the design, fabrication, and performance evaluation of a flexible millimeter-wave (mm-wave) antenna array for the fifth generation (5G) wireless networks operating at Ka -band (26.5–40 GHz). The single element antenna is comprised of a coplanar-waveguide-fed rectangular patch tapered at its sides with two vertically oriented slots. The ground is designed with L-shaped stubs to converge the dispersed radiation pattern for improving the directivity and gain. The antenna fabrication is accomplished by two advanced methods of laser-milling and inkjet printing on a thin film of flexible liquid crystal polymer. A novel and time-efficient method for postprinting sintering is also proposed in this letter. The design is extended in a two-element array for the gain enhancement. Measurements have validated that the proposed antenna array exhibits a bandwidth of 26–40 GHz with a peak gain of 11.35 dBi at 35 GHz, and consistent high gain profile of above 9 dBi in the complete Ka -band. These features recommend the proposed antenna array as an efficient solution for integration in future flexible 5G front ends and mm-wave wearable devices.

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Millimeter-Wave Liquid Crystal Polymer Based Conformal Antenna Array for 5G Applications

The emerging applications for wearable electronics have experienced enormous growth over the last decade. Antennas, being one of the critical components in modern wireless devices, thus need to be specifically designed to function while being worn and bent. In this paper, we present a systematic investigation of the effects of bending applied on wearable patch antennas over cylindrical surfaces. The resonant frequency variations and radiation pattern variations have been studied by simulating and measuring patch antennas that are bent by different angles. A frequency shift plot with respect to bending radius has been generated to target antennas for various wearable applications. An analytical approach has been presented to study the effect of resonant frequency shifting for both E- and H-planes bending. A lumped element circuit model is used to interpret the E-plane bending from different perspectives. One of the main objectives of this paper is to develop useful design-oriented charts and provide a better understanding of the effects of antenna bending to assist wearable antenna designers.

A Systematic Investigation of Rectangular Patch Antenna Bending Effects for Wearable Applications

This brief presents a filter-integrated high-efficiency class-F power amplifier (PA). The hybrid cavity–microstrip filtering circuit is employed not only to realize output impedance matching and the third-harmonic manipulation but also to provide high-selectivity bandpass responses. To fulfill the requirements of high-efficiency class-F PAs, cavity resonators and microstrip feeding structures are involved, and their benefits are fully exploited. The metal cavity resonator features a high $Q$ value and, thus, low loss in the passband, resulting in high efficiency. Moreover, metal walls of cavities act as heat sink for the transistor. The microstrip feeding structures are used to improve the skirt selectivity and manipulate the third harmonic. Moreover, it features easy integration with the transistor, and thus, the transition between cavity and microstrip lines is eliminated. The hybrid filter is characterized based on filter synthesis theory. Complex impedance conversion analysis is carried out to guide the impedance transformation from 50 $\Omega$ to a complex one desired by the transistor. For demonstration, a filtering PA operating at 2.4 GHz is designed and measured. It exhibits both high-selectivity bandpass responses and good PA performance with maximum power-added efficiency of 70.9% at 40.8-dBm output power.

Bandpass Class-F Power Amplifier Based on Multifunction Hybrid Cavity–Microstrip Filter

This paper presents a low-profile planar dipole antenna with omnidirectional radiation pattern and filtering response. The proposed antenna consists of a microstrip-to-slotline transition structure as the feeding network and a planar dipole as the radiator. Filtering response is obtained by adding nonradiative elements, including a coupled U-shaped microstrip line and two I-shaped slots, to the feeding network. Within the operating passband, the added nonradiative elements do not work, and thus the in-band radiation performance of the dipole antenna is nearly not affected. However, at the side stopbands, the added elements resonate and prevent the signal passing through the feeding network to the dipole antenna, suppressing the out-of-band radiation significantly. As a result, both satisfactory filtering and radiation performances are obtained. For demonstration, an omnidirectional filtering dipole antenna is implemented. Single-band bandpass filtering responses in both the reflection coefficient and realized gain are obtained. The measured in-band gain is ~2.5 dBi, whereas the out-of-band radiation suppression is more than 15 dB.

Low-Profile Planar Filtering Dipole Antenna With Omnidirectional Radiation Pattern

This paper presents a novel compact low-temperature cofired ceramic (LTCC) bandpass filter (BPF) with wide stopband and high selectivity. The proposed circuit consists of two coupled λg/4 transmission-line resonators. A special coupling region is selected to realize a novel discriminating coupling scheme for generating a transmission zero (TZ) at the third harmonic frequency. The mechanism is analyzed and the design guideline is described. The source-load coupling is introduced to generate two TZs near the passband and one in the stopband. Thus, wide stopband can be obtained without extra circuits. Due to the LTCC multilayer structures, the filter size is 0.058 λg×0.058 λg×0.011 λg, or 2.63 mm × 2.61 mm × 0.5 mm. The simulated and measured results of the demonstrated LTCC BPF are presented to validate the proposed design.

Compact LTCC Bandpass Filter With Wide Stopband Using Discriminating Coupling

This paper presents a new method of using electric and magnetic coupling cancellation to extend the stopband of bandpass filters (BPFs). The mechanism is theoretically analyzed based on the lumped-element equivalent circuit. Due to the cancellation of electric and magnetic coupling between two resonators, three transmission zeros (TZs) can be generated and controlled by manipulating the coupling strength. Using the proposed method together with source-load coupling, a low temperature cofire ceramic (LTCC) BPF is designed with four TZs at the passband edges and within the stopband, resulting in high skirt selectivity and harmonic suppression. Due to the LTCC multilayer structure, the filter size is 0.054 λ
 g
*0.045λ
 g
*0.013λ
 g
, or 2.48 mm ×2.02 mm ×0.6 mm. The theoretical, simulated and measured results of the LTCC BPF are presented to validate the proposed design.

LTCC Bandpass Filter With Wide Stopband Based on Electric and Magnetic Coupling Cancellation

This paper presents a series-fed two-dipole antenna, fabricated on a liquid crystal polymer (LCP) substrate using inkjet-printing technology. The radio frequency characteristics of inkjet-printing silver film onto an LCP substrate are studied using the microstrip line. The proposed antenna consists of two modified dipole elements of distinct lengths: a modified ground plane and a balun filter yielding a wide bandwidth with bandpass responses. The proposed antenna can be used at frequency band of 26-33 GHz. The bending behaviors of the microstrip line and antenna are also measured. Inkjet printing on LCP substrates provides a low-cost, compact, and flexible packaging solution that can be used in future communication technology.

Inkjet Printed Series-Fed Two-Dipole Antenna Comprising a Balun Filter on Liquid Crystal Polymer Substrate

This letter presents a series-fed two-dipole antenna fabricated on a flexible liquid crystal polymer (LCP) substrate by using inkjet printing technology. The proposed antenna consists of two modified dipole elements of distinct lengths, a director element, a modified ground plane, and a balun filter, yielding a wide bandwidth with bandpass responses. The proposed antenna can be used at a frequency band of 26-32 GHz. The bending behaviors of the antennas with and without director elements were analyzed. The bending effect of the antenna should be considered when calculating the gain loss and bandwidth reduction. Inkjet printing on LCP substrates provides a low-cost, compact, and flexible packaging application that can be used in probable and flexible communication technology.

Bending Effect of an Inkjet-Printed Series-Fed Two-Dipole Antenna on a Liquid Crystal Polymer Substrate

This paper presents an S-band low noise amplifier that uses a two-stage configuration. The first stage has a cascode topology and the second stage has a RC feedback topology. The S-band LNA uses a 0.35 μm AlGaN/GaN HEMT on a Si-substrate. The results show a maximum gain of 17.2 dB, a minimum noise figure of 2.9 dB and an input/output return loss greater than 9.2/10 dB. The input IIP3 at 2.8 GHz is 2.5 dBm and the unit consumes 230 mW of power.

Bai-Hong Wei

Papers

Compact LTCC Bandpass Filter With Wide Stopband Using Discriminating Coupling

LTCC Bandpass Filter With Wide Stopband Based on Electric and Magnetic Coupling Cancellation

Inkjet Printed Series-Fed Two-Dipole Antenna Comprising a Balun Filter on Liquid Crystal Polymer Substrate

Bending Effect of an Inkjet-Printed Series-Fed Two-Dipole Antenna on a Liquid Crystal Polymer Substrate

Design of an S-band 0.35 µm AlGaN/GaN LNA using cascode topology