Umair Naeem

Mutual Coupling Reduction for High-Performance Densely Packed Patch Antenna Arrays on Finite Substrate

This paper reports on an effective mutual coupling suppression technique in which a metamaterial superstrate is placed in between the elements of densely packed microstrip phased array. Modified complementary split ring resonators are printed on the decoupling superstrate slab which caters for both surface and space wave effects. A detailed analysis of this proposed scheme is carried out on a low as well as on a high-permittivity substrate. Coupling suppression of 27 and 11 dB is achieved experimentally on the low- and high-permittivity substrates, respectively, with an element separation of λo/8. The design is compact and easy to realize and it removes drawback of poor front-to-back ratio previously reported in other decoupling techniques. In addition to high-coupling suppression, the decoupling slab can be added or removed in real time which makes this technique versatile for various applications having stringent performance requirements.

A Dual-Band Bandpass Filter With Widely Separated Passbands

A novel and compact design of a dual-band filter with widely separated passbands is proposed. Applications of such a device can be found in systems where a single device is responsible for both transmission and reception. The proposed filter is composed of resonators working on two distinct modes. The proposed dual-mode structure offers a good rejection of unwanted resonances, producing a widely separated dual-band response. The idea is demonstrated with the design of a four-pole filter comprising two dual-mode structures and the concept is verified experimentally by the measurement of a fabricated prototype. Finally, a six-pole filter is proposed, showing the possibility of designing higher order filters.

Multifeed EBG dual Band Antenna for Spatial Mission

We present the design of a multibeam reflector antenna fed by a multifeed dual-band electromagnetic band gap (EBG) antenna to achieve a high-gain multispot coverage for space applications. First, we design a dual-band EBG antenna in monofeed configuration. This antenna is composed of double-layer frequency selective surfaces (FSSs) arranged in the longitudinal direction and a square horn as a feed. Then, the same antenna in multifeed configuration is studied, and the results are compared to those obtained in monofeed configuration in order to emphasize the problem of coupling, generally encountered in multifeed configuration. Consequently, filters are used in order to reduce the parasitic interferences and obtain good radiation characteristics. As shown in this paper, the same EBG phase center is obtained in both frequency bands. Finally, we have studied the whole system composed of the offset reflector and the multifeed EBG dual-band antenna. An edge of coverage (EOC) gain higher than 42 dBi and sidelobes levels lower than −18 dBi are obtained over all spots.

Miniaturization of SIW Cavity Filters Through Stub Loading

This article reports on a simple yet efficient miniaturization technique of substrate integrated waveguide cavity resonators through stub loading. The stubs are attached to the cavity side edges and they are coupled with the magnetic fields of the cavity. This setup allows the stub loaded cavity to operate below its fundamental resonant frequency. This miniaturization technique is demonstrated by developing a two pole filter in horizontally and vertically coupled configurations. The potential to incorporate electronic tuning and various possible applications of these miniaturized cavities in low frequency system-in-package designs make them an excellent choice as compared to their conventional counterparts.

A dual-mode dual-band bandpass cavity filter with widely separated passbands

A compact dual-mode dual-band filter with widely separated passbands is proposed for possible integration in a TX/RX front-end. The basic structure is a cavity working on two distinct dual-modes. The design of this cavity realizing a 4-pole dual-band filtering function is detailed. A prototype is fabricated and measured for validating the concept.

Efficient Design Methodology for a Complex DRA-SIW Filter-Antenna Subsystem

This work reports on an efficient design methodology for realizing hybrid filter-antenna subsystems. Designing a filter-antenna subsystem in the case of complex multimode filter is not straightforward. The coupling of the antenna with a multimode filter depends upon several uncorrelated parameters. An efficient design methodology is proposed which can address these complex problems. The work focuses on the characterization of radiating and filtering elements and then proposes a reliable model, which is derived mathematically as well as from rigorous statistical analyses, which can then be used for designing hybrid filter-antenna structures such as a hybrid DRA codesigned with a SIW based multimode filter. A highly compact filter-antenna subsystem has been designed employing the proposed methodology, and the measured results validate the proposed design technique.

Lossy resonators as decoupling elements in densely packed arrays

This article reports on a simple yet efficient technique of magnetic coupling suppression among densely packed E coupled patch antenna arrays. As compared to the traditional techniques to reduce mutual coupling such as inserting a metamaterial structure between the two adjacent elements, the presented technique can achieve a lesser physical gap between the two radiating elements. Two element antenna array is used in this work where edge-to-edge separation of the antenna elements are kept at λ0/3 and isolation of 45 dB has been achieved at 6 GHz.

10W power-amplifier design based on passive load-pull

The general unavailability of highly accurate non-linear simulation models for power amplifier (PA) necessitate the use of expensive active load-pull setups for achieving optimum conditions for efficiency and power. In this paper, a low cost alternative and a first time right design method is presented for PA design based on passive load-pull. A 10 W class-AB PA was designed and fabricated at 2.25 GHz frequency. High attention was paid to make the amplifier much linear in order to meet the challenges of modern-day wireless communications and to support complex modulation formats. The levels of different inter-modulation distortion (IMD) products were measured and also the third order intercept point (IP3) was calculated as Fig. of merit.