Jim S. Sun

Multilayer Planar Tunable Filter With Very Wide Tuning Bandwidth

In this paper, we propose and develop a partially shielded tunable filter structure using a varactor-loaded split-ring resonator. The novel physical topology of the filter is suitable for vertical stacking of filters and enables a compact multilayer tunable filter for applications requiring a very wide tuning range. The capacitance range and ratio needed to achieve the designated tuning range are presented, and analytical solutions are given for the second and third higher order modes for synthesis in the spurious-free filter operation range. Two prototypes are developed. A partially shielded tunable filter using varactor-loaded split-ring resonators is developed to verify the design method and to demonstrate the wide tuning range of a tunable filter. To further extend the tuning range, a filter bank with three stacked tunable filters at different frequency bands are designed and developed. With slight overlap between neighboring bands, a continuous tuning range of more than 6:1 is achieved.

Frequency-Scanning Phased-Array Feed Network Based on Composite Right/Left-Handed Transmission Lines

This paper presents an all-passive phased-array feed network based on composite right/left handed (CRLH) transmission lines (TLs). A CRLH TL enables systematic engineering of the phase response providing phase advance in addition to phase delay. When utilized in a phased-array feed network, an all-passive 1-D frequency-scanning array can be designed with a large scanning angle range toward both positive and negative elevation angles. This unique feature cannot be realized using conventional delay lines or dispersive lines that do not contain left-handed properties. Also, unlike the previously studied CRLH-based leaky-wave antennas that provide similar 1-D continuous frequency-scanning functionality, the proposed method completely decouples the radiating antenna element from the array factor; thereby providing extra design freedom and enhanced radiation performance. To validate the added advantage, we use the proposed CRLH-based phased-array feed network to demonstrate simultaneous controllability of the radiated polarization and array current amplitude distribution.

Ring-Resonator-Inspired Power Recycling Scheme for Gain-Enhanced Distributed Amplifier-Based CRLH-Transmission Line Leaky Wave Antennas

We propose a novel power recycling scheme for distributed amplifiers (DAs) integrated with composite-right/left handed transmission line leaky wave antennas (LWAs). This new type of power recycling scheme is essentially inspired by a ring-resonator. By forming a closed-loop on the drain side LWA of the DA, we create the ring-resonator that is actively coupled by the DA from the gate line and hence can obtain a substantial gain enhancement compared to the one directly terminated without the loop. Such enhancement fluctuates with respect to the frequency. At the resonant frequencies of the closed-loop ring-resonator, the enhancement reaches a maximum. The phenomenon will be explained and derived theoretically in detail, and then validated through the real implementation.

Optimization and Modeling of Sparse Conformal Retrodirective Array

Conformal scanning arrays are important for scanning ranges beyond ±90 degrees and the retrodirective array (RDA) is known as a promising candidate for this application. We discuss the optimization of a previously realized conformal sparse RDA by means of the genetic algorithm, and the RDA numerical model that is used in this approach. In particular, we improve the numerical model of the RDA by identifying practical factors that previous model failed to account for. The impact of each practical factor on the RDA monostatic pattern is visualized, and the improved model provides much better prediction of the monostatic pattern.

Dual-mode tunable filter with simple bandwidth control scheme

In this paper, we present the realization of a constant bandwidth two pole tunable filter by means of dual mode resonance. The proposed filter has a simple bandwidth control scheme, making numerical optimization of the bandwidth variation across the tuning range possible. A prototype having tuning range of 0.85∼1.4GHz using lumped inductors as input/output coupling elements has been realized. The bandwidth varies between 51∼59MHz across the tuning range and good matching is achieved within the whole tuning range.

An alternative technique in designing a low-profile two-pole bandpass Frequency Selective Surface (FSS) using aperture coupling interlayer

This paper presents an alternative design approach for low-profile, two-pole bandpass Frequency Selective Surface (FSS) using an aperture-coupling interlayer. In addition to this proposed method in providing close spacing between the FSS resonator layer, miniaturized complementary Jerusalem cross shaped FSS is used to further maintain a robust filtering response to oblique-angled plane waves. The proposed technique is not limited to a particular FSS shape and can be applied for arbitrary separation between the FSS layers. To demonstrate the proposed method, a two-pole FSS with the unit-element dimension of much less than λo/2 and total thickness of around λo/30 is designed using the aperture interlayer and measured. Both simulated and measured results show selective two-pole filtering response that is robust for various oblique angle incidences and polarizations.

Novel microstrip diplexer for ultra-wide-band (UWB) and wireless LAN (WLAN) bands

A new microstrip diplexer for ultra-wide-band (UWB) and wireless LAN (WLAN) bands is presented in this paper. The proposed structure integrates a multipole directional filter operating at WLAN band coupled to a UWB filter. The prototype is capable of processing the whole UWB region (from 3.1 to 10.6 GHz) with the WLAN band notch in one channel, and the passband WLAN band in other channel with a good selectivity due to the presence of transmission zeros at both sides of the WLAN band. The proposed diplexer is simple to fabricate, as it is designed using planar microstrip technology, and presents compact dimensions, making use of a low number of elements. Moreover, it presents the capacity of processing a narrow band (WLAN with 8% bandwidth) with a wide band (UWB). Simulated and measured results are presented with good agreement and the diplexer presents a good performance up to 15 GHz.

New approach to multi-stage directional filter based on band-reject filter design

A new structure for realizing multi-stage directional filter is proposed in this paper. Instead of relying on one-stage directional filter as the building block, this approach relies on stand-alone band-reject filters. In this paper we investigate the viability of this idea by developing a three-stage directional filter prototype with elliptic response and 5.5% bandwidth. It is demonstrated that the final directional filter response is very close to the constituting band-reject filter, hence allows us to synthesize the directional filter with various kinds of responses in a more precise way based on the rich legacy from the filter community.

Multistage Directional Filter Based on Band-Reject Filter With Isolation Improvement Using Composite Right-/Left-Handed Transmission Lines

The λ/2 strip-resonator directional filter has good balance between compactness and robustness against manufacturing error. However, there have been difficulties in generalizing the strip-resonator directional filter to realize multipole filtering responses. This paper presents the theory, experiments, and improvement of a new structure of strip-resonator directional filter based on a band-reject filter. This new structure allows the realization of multipole responses and theoretically does not limit the types of filter responses. A three-pole elliptic directional filter prototype is studied thoroughly to show that its performance can be predicted accurately by a conventional filter structure. We also propose a modification of the delay-line part using composite right-/left-handed transmission line to improve the isolation. An isolation level of 30 dB is shown to be achieved consistently.

A sparse conformal retrodirective array for UAV application

Unmanned aerial vehicles (UAVs) are highly mobile units that can be employed as safe and efficient communication relays for various surveillance, reconnaissance, and other tactical missions. However due to their small size, these platforms are extremely payload and power limited and demand system features such as being extremely lightweight and capable of real-time beamforming. Retrodirective arrays can automatically create and maintain high gain communication links with a target without any complex beamforming hardware or processing. This paper develops and presents a conformal sparse retrodirective array. The sparse design combined with the beneficial beamforming properties of a retrodirective array alleviates the amount of circuitry required, leading to a more efficient system and a promising candidate for UAV applications. Measured monostatic and bistatic patterns demonstrate proper operation of the proposed system.