This thesis presents a dual bandpass filter structure, which consists of a wideband pass filter and a bandstop filter in a cascaded connection. In particular, the bandwidth of each passband in the dual-band filter and the center frequency of the operating band can be controlled by adjusting the characteristic impedance of both the wideband pass filter and the bandstop filter. A dual-band pass filter designed according to the method proposed in this thesis has been fabricated and measured.
최근에는 초고주파 무선 통신 제품에 이중 대역 필터가 사용되었습니다. 본 논문은 BPF와 BSF를 직렬로 구성한 듀얼 밴드이다. 본 논문에서 제안한 방법을 이용하여 이중대역 통과필터를 생성하였다.
따라서 이 기사에서는 2대역 통과 필터의 새로운 설계를 제시합니다.
Introduction
Background and Purpose
Current microwave filter research is very active due to the constant demands of high-performance circuits from modern communication and electronic systems. Most of the work to date has focused primarily on single-frequency band filters, and multi-frequency band filters have been largely ignored. In recent years, dual-band filters have become important components for wireless communication products at microwave frequencies.
Therefore, dual-band RF components such as dual-band filters, antenna and amplifier are essential for the development of mobile communications to design more effective and backward-compatible RF devices. In this thesis, a new configuration of a dual-band pass filter is proposed that can cover the two ISM bands 2.4 GHz and 5 GHz. The dual-band pass filter consists of a broadband pass filter and a band stop filter in a cascade connection.
Research Contents
The theoretical analysis, circuit design and simulated results by ADS (Advanced Design System) are presented in this chapter. And the evaluation of this design proposed in this thesis is shown in this chapter.
Wide-band Pass Filter
- Introduction
- Theoretical Analysis
- Even-mode Analysis
- Odd-mode Analysis
- S-parameter Extraction from Even-odd Mode
- Analysis of 3-Stage Ring Resonators Circuit
- A design of 5-5.05 GHz Band Pass Filter
- Simulation Results
The cutoff frequencies, fc1 and fc2, are the frequencies at which the output signal power drops to half its level at f0, the center frequency of the filter. There are many types of BPFs (bandpass filters), such as half-wavelength resonator filters, parallel-coupled, half-wavelength resonator filters, hairline filters, and interdigital bandpass filters, etc. thesis, we decide to design a broadband BPF using cascaded ring resonators.
One reason is that we need a wideband pass filter of 2.35GHz-5.05GHz, but only the parallel-connected, half-wavelength resonator, series-shunted transmission line structure, and ring resonator can achieve the bandwidth we need. Nevertheless, if we implement the wideband pass filter with the bandwidth we need by using series-shunted transmission line structure, the wideband BPF size should be larger than by using the ring resonator structure [2], and furthermore, the ring - filter is easier to manufacture than the coupled line structure BPF. It is more important only that the BPF with ring resonator has more high performance.
2.2, the total length of the ring is chosen to be equal to one wavelength at the center frequency. 2.2, we can find that the each individual ring resonator circuit is symmetrical and reciprocal along the AA' axis, and therefore we can analyze this circuit by the even-odd mode method. The even mode excitation is obtained by applying equal waves to two ports of the network, while the odd mode excitation is obtained by applying out-of-phase waves to ports 1 and 2.
Since ZL1 is the input impedance with an open stub, it is expressed below as equation (2.1). The input impedance of the open-stub used in the ring resonator circuit is calculated as equation (2.3). The scattering parameters of each ring resonator circuit are extracted by the above even-odd mode analysis results.
For the purpose of this work, we need to design a wideband pass filter whose bandwidth is from 2.35 GHz to 5.05 GHz. The purpose of the program described here is to optimize a function consisting of at most 10 independent variables by finding its minimum value. A search cycle of this method starts with the parameters of the conventional ring resonator circuit shown in [10], and the optimal results obtained are shown in Table 1 below.
The physical dimensions of this wideband pass filter proposed in this thesis are shown in Table 2 below.
Band Stop Filter
- Introduction
- Theoretical Analysis
- Theory Background
- Optimum Formulas
- A design of 2.45~4.95 GHz Band Stop Filter
- Simulation
However, the general difficulties in realizing distributed structures are exacerbated by the specific problems associated with the band-stop structure. The filtering properties of the filter then depend entirely on the design of the characteristic impedances Zi for the open circuit fittings and the characteristic impedances Zi,i+1 for the unit elements and the two termination impedances ZA and ZB. These distributed bandpass structures can theoretically be transformed directly from a conventional L-C gate filter.
An edge-coupled bandstop filter is also available, but is only feasible for very narrow bandwidths. Therefore, we propose a bandstop filter using the serial-ordered structure, because we need to have a bandwidth of 2.45 GHz ~ 4.95 GHz. It should be noted that band stop filters of this type have spurious stop bands that are periodically centered on frequencies that are odd multiples of f0.
At these frequencies the open shunts in the filters are odd multiples of λg0 4 long, with. In this case, there is no need to worry at this point, because the spurious frequencies are not in the spectral band we need. Therefore, under the mapping of equation (3.3), the shunt (capacitive) elements of the low-pass prototype become shunt (open circuit) stubs of the assigned bandstop filter, while the series (inductive) elements become series (shorted) stubs.
The series of shorted stubs are then removed using Kuroda's identities shown in Figure. With the design procedure in the previous section, the unit elements of the bandstop filter are redundant and their filter properties are not utilized, so in this sense the resulting bandstop filter is not optimal. To realize a dual-band pass filter we need a bandstop filter with a bandwidth of GHz.
And that we want to keep the circuit as small as possible, that's why structures with three open shunted plugs are used in the thesis. 3.2, for the design of optimal bandpass filters with three open shunted plugs and a return loss level in the passband of -20 dB, are shown in Table 3.1 for bandwidths between 30% and 150%. In this thesis, we design an optimal microstrip bandpass filter with three apertures (n=3) and partial bandwidth FBW.
In this case, we used the same PCB as the one used to design the wideband pass filter in the previous chapter.
Dual-Band Pass Filter
Theoretical Analysis
As a result, a dual-band filter can be obtained by cascading a wide-pass filter and a band-stop filter, and its transfer function can be approximated as the product of the pass coefficients of the two filters, S21BPF and S21BSF.
A design of the Dual-Band Pass Filter and Simulation Results
Excluding the reflection coefficient S11 and transmission coefficient S21, there is other important coefficient called as group retardation. This is one of the main factors that can affect the performance of the filters.
Fabrication and Measurement
There is a little difference with the simulation results due to some losses and dissipation by transmission lines and. In addition to the transmission and reflection coefficients, there is another important coefficient, namely group delay. They are very similar to the 1.2 ns and 1.3 ns simulation results shown in Figure 4.4, and there are relatively flatter characteristics within two passbands.
Conclusions
1] Ian Hunter, Theory and Design of Microwave Filters, Institution of Electrical Engineers, United Kingdom, 2001. 3] IEEE STD 802.11b, IEEE Standard for LAN Medium Access Control (MAC) and Physical Layer Specification ( PHY), 1999. 5] IEEE STD 802.11g, IEEE Standard for Wireless LAN Media Control (MAC) and Physical Layer (PHY) Specification, 1999.
6] IEEE STD 802.11a, IEEE Standard for Wireless LAN Medium Access Control (MAC) og Phisical Layer (PHY) specifikation, 1999. 7] Lin-Chuan Tsai og Ching-Wen Hsue, “Dual-Band Bandpass Filters Using Equal length Coupled -Serial-Shunted Lines and Z- Transform Technique," IEEE Transactions on microwave theory and techniques, Vol. 10] Hitoshi Ishida og Kiyomichi Araki, "Design og analyse af båndpasfilter med ringresonator," Asia-Pacific Microwave Conference, s.
12] ArunChandra Kundu, Ikuo Awai, “Control of attenuation pole frequency of dual-mode microstrip ring resonator bandpass filter,” IEEE MTT., Vol. Horton and R.J.Menzel, "General theory and design of optimum quarter-wave TEM filters," IEEE Trans., MTT-13, pp. I would like to thank many people who helped me during the last two years.
I am also grateful to other professors in our department for their support and guidance in this work, which are Professor Hyung Rae Cho, Professor Kyeong-Sik Min, Professor In-ho Kang, Professor Ki Man Kim, Professor Ji Won Jung, Professor Young Yun and Young -Su Weon, who is the director of Pusan Broadcasting (PSB). I would like to thank Ms. Min Jee Kim, who is an assistant professor in our department, for her great help in my two years of graduate studies. I certainly cannot thank our labs enough for their timely and selfless assistance.
