Jun Xu

A Lightweight 3-D Printed

A 3-D printed fourth-order cavity bandpass filter (BPF) centered at 10 GHz and with a 3% fractional bandwidth is presented in this letter. The BPF was designed using two high-Q spherical dual-mode cavity resonators, and was fabricated using a stereolithography-based 3-D printing technique. Compared to dual-mode filters constructed by square or cylindrical resonators, the use of spherical resonator gives a wider spurious-free region. In order to fully exhibit the light weight advantage of additive manufacturing, the redundant material outside of the filter was removed. In addition, rectangular apertures were added through the cavities and waveguide walls without interrupting the surface current distributions, which further yields reduced filter weight as well as easier electroplating. Measured results of the BPF exhibit an excellent agreement with simulations.

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A novel W-band solid-state power divider/combiner network is proposed, using a compact waveguide configuration of magic tee and waveguide-to-microstrip transition. The novel magic tee is improved by using an inverted T added into the double-T junction. The measured isolation of the novel magic tee between two output ports is better than 13.5dB. The measured return loss of divider/combiner network is better than 15dB from 92GHz to 96GHz frequency range.

-Band Bandpass Filter Based on Spherical Dual-Mode Resonators

This paper provides an overview of five 3-D printed microwave passive circuits operating at frequencies ranging from X-band to W-band. These circuits were produced from polymers using stereolithography printing and were coated with copper via electroplating. Such polymer-based circuits exhibit significantly reduced weights compared with those made from metal. In addition, 3-D printing offers great flexibility and allows new designs to be constructed. Examples of these novel designs will be described and measurements of some designs will be presented.

A novel W-band solid-state power divider/combiner network based on waveguide microstrip structure

An ultra-wideband suspended stripline (SSL) structure high-pass filter with multi-stubs is proposed. A quasi-lumped approach is used to design the filter based on a 7th-order Chebyshev high-pass filter. For the designed high-pass filter, from 5.7 to 30 GHz, the insertion loss is less than -0.5 dB and the return loss is better than -11 dB. From 5.7 to 20 GHz, the return loss is greater than -17 dB, while the suppression of filter is better than -57 dB below 5 GHz.

3-D printed lightweight microwave waveguide devices

In order to meet the need of anti-interference in the millimeter wave receiver and radar, fundamental theory of the image rejection sub-harmonic mixer was introduced first, then a design proposal of a X-band image-rejection balanced mixer was proposed. The mixer is made up of two mixer units, RF signal and image signal can be distinguished by the phase relationship of the outputs from two units. The RF outputs of the two units are in-phase and combine, the image output of the two units are 90 phase difference and offset. Passive part simulation and harmonic balance simulation of the mixer were finished by the software HFSS and ADS, respectively. The mixer was finally fabricated and tested. The tested result shows that, when RF and IF are 9.3~9.7GHz and 100MHz respectively, the convention loss is about 8.8dB, the image rejection is larger than 17dB, all the port-to-port isolations are larger than 20dB, the voltage standing wave ratio(VSWR) of the RF port and LO port are less than 1.3 and 2.2 respectively, the input power 1dB compression point is 11.5dBm.

Design of UWB high-pass filter using the suspended stripline

This paper presents an X-band eighth-order quasi-elliptic circular waveguide dual-mode bandpass filter (BPF) that is manufactured using a fast and low-cost stereolithography-based 3-D printing technique. The 3-D printed filter has advantages of a more convenient integration free of either assembly or post fabrication tuning and furthermore a lightweight of 111 g. A ceramic-filled resin with an enhanced thermal handling capability is used as the filters building material, which makes the filter capable of operating under much higher temperatures than the one made from ordinary photosensitive resins. Surface metallization of the filter is realized by a layer of electroless plated copper. In the measured passband 8.01–8.44 GHz, the filter exhibits a return loss over 10 dB and a corresponding insertion loss of 0.32–0.68 dB.

Design of a X-band image rejection balanced mixer

This paper presents a lightweight Ka-band slotted rectangular waveguide bandpass filter that is fabricated using a fast and low-cost stereolithography-based 3-D printing technique. The filter is printed with a low-density ceramic-filled resin that features a much higher mechanical strength and a much better thermal handling capability than these properties of ordinary resin-based 3-D printing materials. The ceramic-resin-based filter exhibits a measured insertion loss of 0.23–0.5 dB in its passband 30.1–33.7 GHz, and a weight around 39% smaller than that of the filter with the same geometry but made from aluminum.

An X-band lightweight 3-D printed slotted circular waveguide dual-mode bandpass filter

An experimental study of leakage current is presented in a semi-insulating (SI) GaAs photoconductive semiconductor switch (PCSS) with voltages up to 5.8 kV (average field is 19.3 kV/cm). The leakage current increases nonlinearly with the bias voltage increasing from 1.2×10 A to 3.6×10 A. Furthermore, the dark resistance, which is characterized as a function of electric field, does not monotonically decrease with the field but displays several distinct regimes. By eliminating the field-dependent drift velocity, the free-electron density n is extracted from the current, and then the critical field for each region of n(E) characteristic of PCSS is obtained. It must be the electric field that provides the free electron with sufficient energy to activate the carrier in the trapped state via multiple physical mechanisms, such as impurity ionization, field-dependent EL2 capture, and impact ionization of donor centers EL10 and EL2. The critical fields calculated from the activation energy of these physical processes accord well with the experimental results. Moreover, agreement between the fitting curve and experimental data of J(E), further confirms that the dark-state characteristics are related to these field-dependent processes. The effects of voltage on SI-GaAs PCSS may give us an insight into its physical mechanism.

Lightweight low-cost Ka-band 3-D printed slotted rectangular waveguide bandpass filters

This paper reports a novel wideband two-way power divider with improved out-of-band rejection based on substrate integrated waveguide (SIW) technology. Periodic radial line slots are etched on the bottom side of SIW to achieve the band-stop characteristic. The band-pass response is achieved by combing the band-stop characteristic of the radial line slots and the high-pass characteristic of SIW. An experimental circuit is fabricated by the traditional printed circuit board technology. The measured results show that the power divider has the advantages of wideband (about 42.8% with center frequency 7GHz for Return Loss > 10 dB) and sharp roll-off skirts (better than 37 dB/GHz).

Roles of voltage in semi-insulating GaAs photoconductive semiconductor switch

This letter presents the measurement of photoconductive semiconductor switch (PCSS) based on semi-insulating (SI) GaAs in its linear mode, through which output voltage saturation and sublinear current-voltage characteristics were obtained. The measurements of its dark-state characteristics were also taken to explore the underlying physical mechanism. Both the resistance and free-carrier concentration of ON-state and dark-state PCSS were extracted and analyzed. Remarkable contrasts between the resistance characteristics and obvious parallels for the features of free-carrier density indicate that the sublinear current-voltage characteristics of PCSS are related to the negative differential mobility and the native defect EL2 levels of SI GaAs. The sublinear current-voltage characteristics and the saturation of output voltage exhibited in terahertz pulse generator based on GaAs PCSS are ascribed to the intrinsic characteristics of PCSS.